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Use in an electrical power system with a circuit breaker

1. other circuit that responds to the AC output for gener ating a second electrical signal that increases in magni tude from an initial value to an accumulated value when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz for the relay A reset control signal representative of a reset rate parameter is sup plied for the relay The generating circuit includes cir cuitry responsive to the reset control signal for decreas ing the magnitude of the second electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumulated value if the value of actual volts per Hertz is less than the pickup level of volts per Hertz throughout the reset time interval Other apparatus and method forms of the invention for achieving the above stated and other objects of the invention are also disclosed and claimed herein Other objects and features will be in part apparent and in part pointed out hereinafter BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a block diagram of an electrical power system with equ protected by a volts per Hertz relay of the invention FIG 2 is a functional block diagram of a volts per Hertz relay the invention which also represents various protective relaying methods of the invention having steps corresponding to the functions associated with the blocks 25 30 35 40 45 50 55 60 65 4 FIG 3 is a pictorial diag
2. If half cycle 183 is present a branch is made from step 655 to a step 657 to read a digital electrical signal representa tive of the volts per Hertz pickup value on Alarm Pickup thumbwheels 102 If half cycle 183 is not pres ent operations proceed from step 655 to a step 659 to determine whether half cycle 181 is present If half cycle 181 is present a branch is made from step 659 to a step 661 to read a digital electrical signal representa tive of the volts per Hertz pickup value on Time Trip Pickup thumbwheels 104 If half cycle 181 is not pres ent operations default to step 653 Operations proceed upon the completion of any of steps 653 657 or 661 to go to a step 663 to compensate for filter rolloff It is noted that the same AC peak volt age in the power system will produce different values of AC output peak voltage V from filter 65 depending on the system frequency F 1 2t In general a low pass filter produces lower voltage V at higher frequencies F A filter transfer characteristic T F expresses the ratio of the peak voltage V at each frequency F to the peak voltage V at some reference frequency F The filter transfer characteristic T F is prestored in EPROM 221 for an expected range of frequencies The value of TE corresponding to the first time period t FIG 6 is 4 788 619 21 obtained in step 663 and then used as a multiplying factor to adjust the electrical level PU PU1 or PU2 obtained from the respective e
3. 1 PROTECTIVE RELAYS AND METHODS NOTICE A portion of the disclosure of this patent document contains material to which a claim of copyright protec tion is made The copyright owner has no objection to the facsimile reproduction by anyone of the patent doc ument or the patent disclosure as it appears in the Pa tent and Trademark Office patent file or records but reserves all other rights whatsoever BACKGROUND OF THE INVENTION The present invention relates to protective relay ap 5 10 paratus for electrical power systems and methods of 15 such protection More particularly the present inven tion relates to overexcitation relay apparatus and meth ods of overexcitation protection Overexcitation is excessive magnetic flux density which saturates the magnetic cores of protected equip ment such as generators transformers and iron core reactors When a magnetic core is saturated by an alter nating current AC source any increase in flux density greatly increases the amount of heat generated in the core Modern equipment designs are especially sensitive to overexcitation because they normally operate with high flux densities Automation of substations and gen erating facilities is also increasing the need for overexci tation relaying The magnetic cores of power system equipment typi cally have silicon steel laminations to reduce eddy cur rents However during overexcitation the eddy cur rents in the core become a
4. 6 30 82 Beckwith Electric Co Pride Programmable Overex citation Relay 8 pages Specifications 2 pages Table of Contents and pp 1 59 of text pp 54 56 58 absent 6 1982 Meisinger et al An Overexcitation Relay with In verse Time Characteristics Pennsylvania Elec wb 38 R NN DS ss o I RE AJ x ON 5 w x N 8 s ES 4 788 619 Nov 29 1988 Patent Number Date of Patent 11 45 Assoc Relay Com Mtg Pittsburgh PA pp 1 6 5 25 84 Pettigrew Overexcitation Protection with Micro processor Based Volts Per Hertz Relay Pennsylvania Elec Assoc Relay Com Mtg Allentown PA pp 1 19 1 18 85 Basler Electric Co EDM 200 Exciter Diode Moni tor 4 pages 1 85 Westinghouse Flectric Corp Type MVH Micro processor Volts Per Hertz Relay 17 pages 5 1985 Lakin et al Advanced Overexcitation Protection for Generators and Transformers Pennsylvania Elec Assoc Generator Subcom of Relay Com pp 1 9 9 20 85 Pettigrew et al Operating and Application Experi ence with a Microprocessor Based Volts Per Hertz Relay 40th Annual Conf for Protective Relay Engrs Title Page Abstract Table of Contents pp 1 27 Apr 13 15 1987 Primary Examiner A D Pellinen Assistant Examiner Derck S Jennings Attorney Agent or Firm Senniger Powers Leavitt and Roedel 57 ABSTRACT Protective relay for use in an electrical power syst
5. BINARY 0 00 00000000 1 01 00000001 2 03 00000011 3 07 00000111 4 OF 00001111 5 1F 00011111 6 3F 00111111 7 TF 01111111 8 FF 11111111 9 FF 11111111 10 FF 11111111 LEDs in bargraph are connected to that least signifi cant binary bit is supplied to lowest value LED and most significant binary bit is supplied to 80 value LED Because there are 8 bits in a byte corresponding to the first 8 LEDs and there are 10 LEDs in the array 277 to be controlled additional steps in routine 643 of FIG 18 are needed After step 803 a test step 805 determines whether NR is ten If so a step 807 activates pins P26 and P27 to turn on the LEDs indicative of 90 and 100 accumulated value If in step 805 NR is not ten a test step 809 determines whether NR is nine If so a step 811 activates only pin P26 to turn on the LED indica tive of 90 accumulated value If in step 809 NR is not nine then a step 813 clears the two high order bits for 90 and 100 by bringing pins P26 and P27 low After any oil steps 807 811 or 813 are completed a step 815 is executed to send the logic levels currently in the two high order bits for P26 and P27 and the logic levels in the BAROUT byte from Table 1 to the LEDs in array 277 In this way the Time Progression Display faithfully and advantageously displays the accumulated value in the register TTTIMER After step 815 a RETURN 817 is reached i It is apparent that the volts per Hertz relay 59 can be implemented i
6. First a half period time interval t between zero crossings 171 and 173 of a first negative half cycle 175 of the AC output filter 65 waveform is measured On the very next posi tive half cycle 181 an electrical level PU for timed trip 10 20 25 30 35 45 50 55 65 12 is calculated On the next two consecutive positive half cycles 185 and 183 an instantaneous trip electrical level PU2 and an alarm electrical level PU1 are calcu lated respectively and as a function of the correspond ing V Hz front panel settings for Instantaneous Pickup 106 and Alarm Pickup 102 The microprocessor is pro grammed to compute the electrical levels PU PU1 and PU2 starting with each positive going zero crossing in short time intervals 191 193 and 195 respectively or during the preceding intervals while the waveform is negative and the microcomputer is in effect waiting for the positive half cycles to occur Because the micro processor makes the computations in a very short per iod compared to the width of a half cycle of the AC output voltage sinusoid the computations of the electri cal levels are completed well before the AC output voltage reaches any pickup value In the case of time trip monitoring in half cycle 181 the microprocessor determines whether the pickup electrical level PU was exceeded If so then after the AC output voltage falls below PU again and during a time interval 197 before the next zero crossing the m
7. Output Disable high also extinguishes the Time Status LEDs 277 by forcing latch 271 to high impedance A pull down resistor 311 is provided for the output of Watchdog 301 If the Output Disable is the result of something other than hardware failure it is suitably remedied by manually interrupting operating power and turning it back on A Test Mode switch 313 con nected to microcomputer 201 pin P13 is used to tempo rarily cause microcomputer 201 to turn on all LEDs in sequence thrreby verifying their operation and proper microprocessor operation Input control 303 includes the filter 65 which is fed by potential transformer 63 on input lines A and B of FIG 7 Two testable inputs TO and TI of microcom puter 201 are respectively connected to input control circuit 303 Testable input TO changes state at each zero crossing of the AC output filter waveform of FIG 6 and TO is low when the AC output is negative or zero and otherwise is high Testable input T1 is low either when the AC output is negative or when it is greater than an electrical level PU PU1 or PU2 to which the AC output is compared A 16 bit counter and latch is formed by connecting two 74HC540 counter and latch chips 321 and 323 to gether These counters are connected to a first compar ing means in input control 303 for measuring the time period between zero crossings which comparing means is OR ed with a second comparing means for measuring the time period during which any
8. fuse 75 and the trip coils 41TC and 52TC In this way when either a timed trip or an instantaneous trip occurs the circuit breaker 52 is tripped to isolate the generator 11 and unit trans former 21 from bus 55 and field circuit interrupter 41 is tripped to disconnect the field winding 39 from exciter 37 and to lower the generator voltage as quickly as possible by means of discharge resistor 47 dissipating field current As a result volts per Hertz relay 59 ac complishes its trip functions to remove a dangerously excessive or persistent volts per Hertz condition from an electric power system Relay 59 also includes self monitoring functions and should these indicate that the relay 59 is malfunctioning Relay Fail contacts 89 close to energize a Relay Fail warning device 91 A power supply 93 for the circuitry of relay 59 is connected to fuses 75 and 77 and suitably has a conven tional low burden flyback switching design which de livers a nominal 12 VDC FIG 2 shows a functional block diagram and method diagram of volts per Hertz relay 59 Potential trans former 63 senses a single phase of system voltage An arrangement that senses all three phases and relays on the highest voltage can alternatively be provided This transformer 63 has a maximum saturating V Hz of 5 for example over a voltage range of 10 to 360 VAC and a frequency range of 2 to 72 Hz in the preferred embodi ment The AC signal from the secondary of the input se
9. loss of sensing circuit 501 has three comparators 503 505 and 507 the last two of which have RC charging circuits 509 and 511 which are dis charged repeatediy by normal occurrence of the cycles of the AC output If the AC output is lost comparator 507 output goes low activating the LOS output Also in FIG 11 further circuitry for magnitude loss of sensing is connected to the AC output of filter 65 on line A A protective diode circuit 521 clamps any AC output from filter 65 outside the range 12 volts The AC output is rectified by an operational amplifier and diode circuit 523 The rectified output is supplied to an RC peak detecting circuit 525 which has approximately 1 millisecond charging time and one second discharging time The RC circuit 525 feeds a comparator circuit 527 which compares the AC output peak value with a preset reference level Normally the peaks are above the refer ence level and the output of circuit 527 is high The output of circuit 527 is clamped to that it does not go outside the range 0 to 5 volts set by a clamping circuit 529 Normally this output is high Finally an open col lector comparator 531 compares to a reference level the high or low output of circuit 527 as clamped by circuit 529 and the reference level is about 2 3 of 5 volts The output of comparator 531 is wire ORed to the LOS loss of sensing output line with the output of comparator 507 If the AC output voltage on line A abnormally falls to 2
10. of the electrical levels PU PU1 or PU2 is exceeded Microcomputer 201 is connected to the thumbwheel switches 230 through latch 241 and is also fed by the first comparing means and programmed to produce a digital signal on bus 211 representing the electrical level PU PU1 or PU2 which is a function of both the time period and the pickup 4 788 619 17 value settings on the thumbwheels This digital signal is communicated to a digital to analog converter DAC 331 with a current to voltage output operational ampli fier 333 and its associated components DAC 331 and amplifier 333 convert the digital signal to an analog voltage signal DACREF which also represents the electrical level The analog signal DACREF is con nected to the input control 303 and to the second com paring means therein which also is connected to the AC output filter waveform to detect when the AC output exceeds the analog signal DACREF in magnitude Mi crocomputer 201 is also fed by the second comparing means and programmed to produce an output signal e g P14 P16 for Time Trip Pickup Instantaneous Trip or Alarm depending on the half cycle of the waveform tested when an excess is detected by the second com paring means Since the second comparing means is OR ed with the first comparing means the counters 321 and 323 measure the length of time in each half cycle during which the excess is present Microcomputer 201 also uses this further counter information to comp
11. per Hertz is less than the pickup value of volts per Hertz and producing a display indicative of the magnitude of the second electrical signal as it increases and de creases in magnitude 53 A protective relaying method for use in an electri cal power system with a circuit breaker for connecting and disconnecting first and second electrical conduc tors which are energizable with an AC voltage that has a value of actual volts per Hertz the method compris ing the steps of generating an electrical signal that increases in magni tude from an initial value to an accumulated value when the actual volts per Hertz exceeds a prese lected pickup level of volts per Hertz supplying a reset control signal representative of a reset rate parameter and decreasing the magnitude of the electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accu mulated value if the value of actual volts per Hertz is less than the pickup level of volts per Hertz throughout the reset time interval 54 A protective relay for use with electrical appara tus to be protected that is energizable with an AC volt age having a varying value of actual volts per Hertz and for use with means for sensing the AC voltage to produce an AC output and with a circuit breaker for connecting and in response to an electrical trip discon necting the electrical apparatus the protective relay comprising means re
12. purposes then after a period of time that depends on the subse quent amounts and variation of the actual volts per Hertz normally open Timed Trip contacts 81 of relay 59 close When contacts 81 close a circuit is completed to actuate a visual Trip Target device 83 which is a magnetically latched manually reset indicator Also contacts 81 are connected to parallel connected trip coils 41TC and 52TC for the field circuit interrupter 41 and the circuit breaker 52 respectively The trip coils 41TC and 52TC are respectively interlocked with ser ies connected auxiliary contacts 41a and 52a of inter rupter 41 and circuit breaker 52 respectively Contacts 41a are closed when the interrupter 41 contacts 43 are closed and open when contacts 43 are open Contacts 52a are closed when main contacts internal to breaker 52 are closed and open when those main contacts are open If the actual volts per Hertz exceeds a third pickup value which is set higher than the other two pickup values for instantaneous trip purposes then normally maa 0 par 5 20 35 40 45 60 65 6 open Instantaneous Trip INST TRIP contacts 85 of relay 59 close There is no intentional time delay built into relay 59 for this purpose When contacts 85 close a circuit is completed to actuate another visual Trip Target device 87 which indicates that instantaneous trip has occurred Contacts 85 and Target 87 are connected in series with each other between
13. significant factor in the heat ing of the equipment Leakage or stray flux also enters nonlaminated parts such as structural steel of the gener ators transformers and reactors to produce substantial eddy current losses there also Overheating causes se vere damage and equipment failure by deteriorating electrical insulation in the equipment The voltage across a winding on the magnetic core of protected equipment is according to a basic physical principle known as Lenz s Law proportional to the time derivative of the flux density Consequently the flux density is proportional to the time integral of the voltage across the winding In an AC electric power system in which the voltage is essentially sinusoidal the time integral of the voltage is by elementary calculus proportional to the ratio of the voltage to the frequency in Hertz Consequently an overexcitation relay is also called a volts per Hertz V Hz relay in the art Exces sive flux density can occur due to either an overvoltage condition at normal frequency normal voltage at a reduced frequency underfrequency or in general an excessive value of the ratio of voltage to frequency One important application of V Hz overexcitation relays is to protect directly connected generator unit step up transformers These unit transformers may be subjected to overexcitation during generator startup or shutdown power system islanding overloads and load rejection any of which cond
14. the LED bargraph 123 is executed as more fully discussed in connection with FIG 18 Following step 643 in FIG 12 a step 645 reads in the reset rate parameter from the Reset Dial thumbwheels 122 of FIG 3 Next a testing step 647 determines whether the AC output of FIG 6 has gone positive Until it does operations loop back to step 647 itself and in effect wait until zero crossing 173 of FIG 6 is reached Then operations proceed to a step 649 to read the external counters 321 and 323 which at this time hold a value repesentative of the width of a half cycle of the AC output which for present purposes is a first time period t and also designated LOGFQ The counters now having been read they are reset by send ing a Counter Clear low active pulse from pin P12 to the CCLR pins of the counters 321 and 323 whence point A of FIGS 12 and 14 is reached In FIG 14 operations proceed from point A to a step 651 to determine when the AC output is positive indi cating the beginning of one of the positive half cycles 181 183 and 185 A modulo 3 software counter keeps track of the identity of the positive half cycles If half cycle 185 is present a branch is mae from step 651 to a step 653 to read a digital electrical signal representative of the volts per Hertz pickup value on Instantaneous Pibkup thumbwheels 106 If half cycle 185 is not pres ent operations proceed from step 651 to a step 655 to determine whether half cycle 183 is present
15. the second electrical level repeat edly generating a second electrical signal that varies over time as a function of the interval and second time period repeatedly producing a third electrical signal when the second electrical signal exceeds a threshold magnitude and repeatedly increasing the third electrical signal by amounts depending on the second electrical 4 788 619 25 signal and producing a time trip signal for the relay to cause the circuit breaker to disconnect the conductors when the third electrical signal exceeds a predeter mined level 8 A protective relay as set forth in claim 7 further comprising means for supplying a reset control signal said means for generating including means responsive to the reset control signal and operative upon an occur rence of the time trip signal for progressively decreas ing the third electrical signal in magnitude during a rest time interval dependent upon the reset control signal 9 A protective relay for use in an electrical power system having electrical conductors which are energiz able with an AC voltage the protective relay compris ing means for sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings means for supplying an electrical signal representing a preselected pickup value of volts per Hertz for the relay and means responsive to the AC output and to the electri cal signal for generating an electrical lev
16. time A setting of 00 on thumbwheels 122 enables the reset time to be instantaneous Three Alarm Pickup thumbwheels 102 adjustably establish the pickup point for the alarm output and are adjustable from 1 00 to 3 99 V Hz in 0 01 V Hz incre ments Two Alarm Time Delay thumbwheels 114 estab lish the definite time delay for alarm output and are adjustable from 0 1 to 9 9 seconds in 0 1 second incre ments A setting of 00 signifies an instantaneous alarm output Also on the front panel of FIG 3 a red light emit ting diode LED Alarm Pickup indicator 111 is illumi nated to indicate that the alarm pickup setting has been exceeded and that the Volts per Hertz relay 59 is timing for alarm purposes Another red LED 117 acts as a Time Trip Pickup indicator which illuminates to indi cate that the time trip pickup setting has been exceeded and that the relay 59 is timing for time trip purposes A 20 25 35 40 45 50 65 8 red LED Power indicator 131 lights when the power supply is providing nominal 12 VDC to the internal circuitry of relay 59 Magnetically latching manually rest Trip Target indicators 87 and 83 provide visual indication that the respective Instantaneous or Timed Trip trip output relay has been energized Each Trip Target indicator is manually reset by a target reset lever not shown Each of the output contacts of the Volts per Hertz relay can be manually actuated by insertion of a 4 inch diameter nonco
17. 3 The output of inverter 465 is diode ORed with power sup ply signal PS If either the output of inverter 465 or signal PS goes high an Output Disable signal OD is produced Output C from the Watchdog 301 of FIG 9 clocks a D flip flop 471 of FIG 8 and supplies a Q output low through a buffer 473 to activate the reset input RST of microcomputer 201 because the Watchdog 301 has detected a loss of pulses The input RST is also acti vated for a predetermined initial time period on 5 volt logic supply voltage power up by a detector circuit 475 through a buffer 477 An Alarm Pickup LED 481 in FIG 8 is turned on as appropriate to indicate that the alarm timer is timing by the Q output a flip flop 483 which has its D input connected to pin P20 and is clocked by the ALE line This flip flop 483 is preset on power up with Q output high LED off by the detector circuit 475 In FIG 10 filter 65 is an input voltage divider 489 followed by a set of 4 cascaded 2 pole low pass Cheby shev active filter circuits 491 493 495 and 497 the circuit 491 being shown in schematic detail In FIG 11 a loss of sensing circuit 501 detects when the output of OR gate 409 indicates frequency out of range or insufficient AC output voltage from filter 65 to make effective volts per Hertz sensing possible If loss of sensing occurs an active low LOS output is set low by circuit 501 and sent to pin P10 of microcom puter 201 4 788 619 19 In FIG 11 the
18. 3 volts rms or less and does not recover within about 1 second the output of comparator 531 goes low and brings loss of sensing LOS low at microcomputer 201 pin P10 When loss of sensing occurs microcomputer 201 turns off all of the outputs for LEDs and causes all output contacts to go to their unenergized or deactu ated states Microcomputer 201 continues to monitor pin P10 and waits for more AC output to which it can synchronize its operations In FIG 12 operations of microcomputer 201 com mence with a START 601 and proceed to a subroutine Standard Check STDCHK 603 described in more detail in FIG 13 In FIG 13 operations proceed from a BEGIN 605 to a step 607 in which a pulse is output at pin P25 to toggle the Watchdog circuit 301 Next in a step 609 a test is made to determine whether both a resetting of the accu mulated value for time trip purposes in a register TTTIMER is in progress and whether this register has been decremented to its initial value of zero If so oper ations branch to a step 611 to turn off all LEDs of the bargraph 123 turn off the time trip output clear the register TTTIMER to zero and indicate that reset is complete by setting a flag RESET to zero Upon com pletion of step 611 or if the test of step 609 is not met then operations proceed to a step 613 to determine whether the Alarm timer has timed out indicating an alarm condition If so then operations branch to a step 615 to turn on the Alarm o
19. 788 619 27 22 A protective relay as set forth in claim 9 wherein said means for generating includes comparing means for detecting the zero crossings in the AC output counter means connected to said comparing means for measur ing the time period between zero crossings and a digital computer connected to said means for supplying the electrical signal representing the pickup value and also fed by said comparing means and said counter means and programmed to produce a digital signal represent ing the electrical level which is a function of both the time period between zero crossings and the pickup value 23 A protective relay as set forth in claim 9 wherein said means for generating includes first comparing means for detecting the zero crossings in the AC output counter means connected to said first comparing means for measuring the time period between zero crossings a digital computer connected to said means for supplying the electrical signal representing the pickup value and also fed by said first comparing means and said counter means and programmed to produce a digital signal rep resenting the electrical level which is a function of both the time period between zero crossings and the pickup value a digital to analog converter for converting the digital signal to an analog signal which also represents the electrical level and second comparing means con nected to the AC output and to the analog signal for detecting when the AC outp
20. 93 for output contacts of Instantaneous Trip Alarm and Timed Trip Also an LED 295 is actuated through a buffer 297 from the microcomputer 201 pin P14 Operation of the microcomputer 201 is continuously monitored by a program monitor circuit labelled Watchdog 301 An input control circuit 303 has micro processor resetting circuitry which cooperates with Watchdog 301 in response to output P25 to provide a latched automatic computer reset RST in event of malfunction Reset in this sense holds the microcom puter 201 operations at an initial location in software until the reset is lifted and is not referring to the process of decreasing the magnitude of the digital signal corre sponding to an accumulated value in the integrator timer for volts per Hertz relaying purposes Circuit 303 also includes a circuit for generating an interrupt signal INT when a loss of power to reclosing relay 59 is anticipated Loss of power is determined to be immi nent when a DC power supply output 12 falls below a predetermined level In normal operation the microcomputer 201 ran domly outputs pulses at intervals that have a reasonably predictable arithmetic mean If these pulses are dis rupted the program monitor watchdog circuit 301 dis continues microcomputer 201 operation and provides an Output Disable OD high which actuates Relay Fail output 305 through an inverter 307 with hysteresis fol lowed by an inverter 309 to Relay Fail output 305 The
21. ST TIME PERIOD LOGFO t ZERO COUNTERS US Patent Nov 29 1988 Sheet 10 of 14 4 788 619 G FIGI4 READ WES N INSTANTANEOIS PICKUP THUMEWHEELS READ ALARM PICKUP THUMBWHEELS E COMPENSATE FOR FILTER ROLLOFF COMPUTE ELECTRICAL LEVEL Pu Puh PAZ AS FUNCTION OF TIME PERIOD AND PICKUP OUTPUT DIGITAL SIGNAL FOR Pu Puli OR Pul f DAC 667 8 CET US Patent Nov 29 1988 Sheetllof14 4 788 619 FIG 15 669 yes ELEC TRICAL LEVEL EXCEEDED TWICE gt 675 TURN OFF INSTANTANEOUS OUTPUT OUTPUT RESET ALARM FREQ 8 685 687 KES 77 reg ESTSCL EP TIMUAL US Patent Nov 29 1988 Sheet 12 of 14 4 788 619 PICKUP DEGREMENT Bu GRNT TIMER READ EXT 18 COUNTERS TIMED TRIP TEST 2x TBLKLOGER T TIME OVAL er MAGCAL Mer J EEN OF 2 TIME PERICOS US Patent Nov 29 1988 Sheet 13 of 14 4 788 619 FIG IT TIMING INTERRUPT ROUTINE TT TIMER TIM VAL 757 a7 T TIMEOUT Gr TIMER 00 VES TT TIMERS TT TIMER TIMVBL gt RESET TIMEOUT Z AR TIMER 20 769 US Patent Nov 29 1988 Sheet 14 of 14 4 788 619 20 80 NR 5 INT 10x a Q FIG 18 UPDATE BAR GRAPM ROUTINE E43 TABLE ACCESS CONVERT NG TO 8 LED ACTIVATION BAROUT BYTE 807 TURN ON 90 AND 100 LEDS SEND 2 HIGH ORDER BITS AND BAROUT BYTE ro LEDS RETURN 4 788 619
22. TC power transformer 57 Circuit breaker 52 connects and discon nects the conductors of lines 49 and of bus 55 which are energizable with an AC voltage A primary winding of LTC transformer 57 is connected to remote lines 56 and a secondary winding of transformer 57 supplies three phase distribution lines 58 4 788 619 5 Volts per Hertz protective relay 59 is an apparatus of the invention operating according to methods of the invention to advantageously act as an intelligent ap paratus for detecting excessive volts per Hertz condi tions in the system of generator 11 and unit transformer 21 A sensing circuit 61 includes a potential transformer PT 63 having a primary connected across two or more of the lines 13 to sense an AC voltage thereacross PT 63 is represented in block form as it is suitably a system potential transformer feeding another potential sensing transformer which latter PT is associated with relay 59 A secondary output of the PT 63 is connected to a low pass filter 65 associated with relay 59 that filters the fundamental frequency of the AC voltage and suppres ses its harmonics The filter 65 produces an essentially sinusoidal AC output which has zero crossings and a time period between zero crossings to the rest of the volts per Hertz protective relay 59 Relay 59 operates a set of output relay contacts which are connected ac cording to a typical application as shown in the lower half of FIG 1 It is to
23. TE Al BRM Derseror TIMER OUTPUT ALARM NA VEE DELAY 105 129 INST TRIP LEVEL INST DETECTOR OUTPUT INST PICKUP 06 US Patent Nov 29 1988 Sheet3of14 4 788 619 FIG 3 06 104 Ca gt 122 sat PUSH TO 7 MED ENERGIZE INST TRIP md rr n 47 US Patent Nov 29 1988 Sheet 40014 4 788 619 FOA V Ha PIGS TIME Nov 29 1988 Sheet 50 14 4 788 619 US Patent GCN IIG 1707 FPINSYFW 7 7 ds b6 56 Yi MU Lp 7 143033 Ad SP saidis yd NIE TE ae LEN 900 339 3784 PYNSYTM SLI L6 16 El IL 191 A ei me Ze le Nd EE ERT N u V PANG OFW 4 9 4 788 619 Sheet 6 of 14 Nov 29 1988 U S Patent SHINGO ta N lt Ng Lid P GOE Log O rot iy 10 OE 2 a 7 Kgg elp ny ri u GI SEZ 44O IP2 o im L OBW MZ T7IPFHMEW IHL OFZ EZ N 70 1N02 LON 2 7 Ziy US Patent Nov 29 1988 Sheet 7 0f 14 4 788 619 mere INPUT CONTROL 303 P O OAT REF 7 ee bene E Esas ser al pA EL PS U S Patent Nov 29 1988 Sheet 80f14 4 788 619 FIG 9 WATCHDOG 30 US Patent Nov 29 1988 Sheet 9 of 14 4 788 619 TOGGLE WATCHDOG gene 609 srpcwK TURN OFF BARGRAPA ENT OUTPUT CLEAR TT TIMER KESETEO TURN ON ALARM TURN ON 7 7 OUTPUT ro TRIP BREGKER READ EXT COUNTERS FOR FIR
24. United States Patent p9 Ott et al 54 PROTECTIVE RELAYS AND METHODS 75 Inventors Matthew J Ott Highland Timothy M Wilkerson Madison County both of Ill 73 Assignee Basler Electric Company Highland Il l 21 Appl No 42 436 22 Filed Apr 24 1987 BY int Oasen HO2H 3 20 52 U S e EN ME 361 91 361 62 361 59 361 75 361 89 364 483 340 663 58 Field of Search 361 21 35 59 62 361 65 71 75 86 88 89 91 340 663 364 483 56 References Cited U S PATENT DOCUMENTS 3 590 326 6 1971 Watson sessrsessrersrsessessesese 361 96 3 703 717 11 1972 Kuster w 340 253 Y 4 246 623 1 1981 SUN nennen 361 97 4 272 816 6 1981 Matsumoto mo 364 483 4 420 805 12 1983 Yamaura et al 2 364 184 4 428 022 1 1984 Engel et al 361 96 4 535 409 8 1985 Jindricketal 364 481 4 694 374 9 1987 Verbanets Jr secere 361 91 X 4 701 690 10 1987 Fernandez et al 322 28 OTHER PUBLICATIONS Elmore et al Overexcitation Analysis and Detection with Microprocessor Based Relay in Minnesota Power Systems Conference 12 pp Oct 7 9 1986 ASEA Over Excitation Relay Type RATUA Edi tion 1 2 76 File R Part 1 4 pages MCS 48 TM Family of Single Chip Microcomputers User s Manual Intel Sep 1980 Face Sheet plus pp 1 1 thru 1 15 and 4 1 thru 4 8 ASEA Type RATUB V Hz Overexcitation Relay for Transformers pp 1 3
25. an more precisely and rapidly simulate the actual heating characteristics of protected apparatus to provide improved protective relays and methods which can more precisely and rapidly simulate the actual cooling characteristics of protected appara tus to provide improved protective relays and methods which can avoid unnecessary tripping and consequent loss of use of protected equipment to provide improved protective relays and methods which are more conve nient in adjustment and use and to provide improved protective relays and methods which are more reliable and economical Generally one form of the invention is a protective relay for use in an electrical power system having elec trical conductors which are energizable with an AC voltage The protective relay includes a circuit for sens ing the AC voltage to produce an AC output that has 4 788 619 3 zero crossings and a time period between zero cross ings a circuit for supplying an electrical signal repre senting a preselected pickup value of volts per Hertz for the relay and a circuit responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level In this way the output signal is produced when a volts per Hertz value of the AC voltage exceeds the prese lected pickup value of volts per Hertz
26. asuring the time period between zero crossings dur ing a half cycle of one polarity and means for compar ing the AC output with the electrical level during a half cycle of the opposite polarity 19 A protective relay as set forth in claim 9 wherein the AC output has half cycles further comprising means for supplying a second electrical signal repre senting a second preselected pickup value of volts per Hertz for the relay said means for generating including digital computer means for computing in first and sec ond half cycles of the AC output different values of the electrical level by said function of the time period and pickup value corresponding to the first named prese lected pickup value and the second preselected pickup value respectively and for producing the output signal when the AC output exceeds the value of the electrical level so computed in the first half cycle and for produc ing another relay signal when the AC output exceeds the value of the electrical level so computed in the second half cycle 20 A protective relay as set forth in claim 9 wherein said means for sensing includes a low pass filter 21 A protective relay as set forth in claim 20 wherein said filter has a rolloff characteristic and said means for generating includes a digital computer programmed to generate the electrical level so as to compensate for the rolloff characteristic at a frequency corresponding to the time period between zero crossings 4
27. at said Letters Patent is hereby corrected as shown below In the drawings Sheets 9 14 Figures 12 18 the following notice should appear at the bottom of each sheet BASLER ELECTRIC CO 1987 Signed and Sealed this Fifth Day of December 1989 JEFFREY M SAMUELS Attesting Officer Acting Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 4 788 619 DATED November 29 1988 INVENTOR S Matthew J Ott and Timothy M Wilkerson It is certified that error appears in the above identified patent and that said Letters Patent is hereby corrected as shown below In the drawings Sheets 9 14 Figures 12 18 the following notice should appear at the bottom of each sheet BASLER ELECTRIC CO 1987 Signed and Sealed this Fifth Day of December 1989 Attest JEFFREY M SAMUELS Attesting Officer Acting Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 4 788 619 DATED November 29 1988 INVENTOR S Matthew J Ott and Timothy M Wilkerson It is certified that error appears in the above identified patent and that said Letters Patent is hereby corrected as shown below Column 24 claim 3 lines 26 and 27 period which should read period between zero crossings which lines 28 and 29 period between zero crossings during should read period du
28. ay 59 begins the linear reset process again 4 788 619 9 and reduces the percentage accumulated value 155 in FIG 5 with the same slope parameter FP as the slope parameter of the earlier decreasing percentage value 147 Parameter FP in seconds per percent is the recip rocal of the slope in percentage per second A reset time period 157 is consumed in returning the accumu lated value of 100 to its initial value of 0 Clearly the reset time period 157 is longer than the relatively short reset time period 149 which would have been used to reset from the lower accumulated value at point 144 Advantageously the relay 59 adapts its actual time of reset to the different projected temperatures of the pro tected equipment resulting from the history of actual volts per Hertz in the electric power system Also the relay 59 adapts its actual time T to trip to the relatively accurate simulation of heating and cooling in the pro tected equipment which corresponds to the percentage accumulated value resulting from the history of actual _ volts per Hertz so that unnecessary tripping is pre vented but necessary tripping occurs as soon as it is needed The Volts per Hertz overexcitation relay 59 advanta geously is used to protect generators transformers and iron core reactors from adverse effects of excessive heating as a result of overexcitation The relay advanta geously models the heating and cooling characteristics of the protected equip
29. be understood that while a simple coil and contact electromechanical relay is termed a relay in the electrical art the phrase protective relay cf ANSI Standard C37 90 1978 refers to an electrical device designed to respond to input conditions in a prescribed manner and after specified conditions are met to cause contact operation or similar abrupt change in associated electrical circuits Limit switches and simi lar simple devices are not protective relays in this sense A relay may consist of several relay units or circuits each responsive to a specified input with the combina tion of units providing the desired overall performance characteristic of the relay Pickup occurs in a protec tive relay when a specific condition or conditions that the relay is designed to respond to are met Pickup encompasses the activation initiation or enablement of a protective relay timing or other function whether or not an alarm or trip output occurs Some of the output contacts in FIG 1 of volts per Hertz relay 59 are next described If the actual volts per Hertz exceeds a pickup value for alarm purposes for a definite period of time normally open Alarm ALM contacts 71 of relay 59 close and actuate a visual or audible alarm device 73 connected in series therewith to and supply terminals through two fuses 75 and 77 If the actual volts per Hertz exceeds another larger pickup value that is set for timed trip
30. calculated by any of the eguations 2 and 5 10 and then used to compute the accumulated percentage value according to eguations 1 3 and 4 The pickup levels just mentioned are initially com puted as follows PU VHSX VSx 10 1000x LOGFO R 11 PU1 VHS1x VSF x 10 1000x LOGFQ 12 PU2 VHS2 x VSFx 10 1000 x LOGFQ 13 In words each pickup electrical level PU PU1 or PU2 is computed from its respective Volts per Hertz setting VHS VHSI or VHS2 on thumbwheels 104 102 or 106 The setting is multiplied by a voltage scaling factor VSF and by a front panel thumbwheel multiplication constant of 10 and then divided by the time period LOGFO equals t in milliseconds Scaling factor VSF makes the result compatible with the range of a digital to analog converter DAC used with the microproces sor 201 and is predetermined from an incoming test frequency and front panel setting and a voltage division ratio inherent to the hardware of relay 59 The microprocessor and associated hardware dis cussed hereinbelow in connection with FIG 7 advan tageously performs all detection timing and computa tion operations for the Integrator Timer and other blocks of FIG 2 The microprocessor synchronizes its operation to the input waveform and independently monitors each front panel thumbwheel setting With reference to FIG 6 sensing in one micro processor based preferred embodiment is advanta geously performed on a three cycle basis
31. ck to START in the main loop of FIG 12 to continue with step 603 of FIG 12 In FIG 17 a timing interrupt routine is executed by microcomputer 201 every 10 milliseconds whereby operations in the main loop or any subroutine are inter rupted so that the microcomputer performs the steps of FIG 17 Upon interrupt operations proceed from a BEGIN 740 to a test step 751 to determine whether operations in the main loop are in a time trip pickup state as indicated by testable input TO high testable input T1 low and cycle counter indicating cycle 181 If there is time trip pickup operations branch to a step 753 to increase the value in register TTTIMER by the amount TIMVAL according to equation 4 Next a test step 755 determines whether there is a carry from register TTTIMER meaning that it has reached its maximum value If so then a step 757 sets a timeout bit TTTIMEOUT which signifies that the register TTTIMER has reached a 100 value which will cause a breaker trip when subroutine STDCHK is next exe cuted see steps 617 and 619 of FIG 13 Further in FIG 17 operations go from step 751 to a test step 761 if there is no time trip pickup condition Test step 761 determines whether there is a reset condi tion underway resetting of TTTIMER as indicated by flag RESET 1 If so resetting is indicated and opera tions branch to a step 763 to decrease the value in regis ter TTTIMER by the amount TIMVAL according to equation 17 The
32. ctrical signal that begins at an initial value and changes in value generally representing heating of the apparatus to be protected when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz for the relay and means for supplying a reset control signal said means for generating including means responsive to the reset control signal when the value of actual volts per Hertz becomes less than the pickup level of volts per Hertz for resetting the electrical signal in value over a reset time period that is a direct func tion of the amount of heating which the value of the electrical signal represents when resetting be gins provided the level ff actual volts per Hertz is less than the pickup level of volts per Hertz throughout the reset time period until the initial value of the electrical signal is reached 61 A protective relay as set forth in claim 60 wherein said means for supplying the reset control signal in cludes adjustable means for establishing a rate of change of the electrical signal when resetting in value which rate of change is substantially independent of the value of the electrical signal attained when resetting begins x x UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO 4 788 619 DATED November 29 1988 INVENTOR S Matthew J Ott and Timothy M Wilkerson i lt is certified that error appears in the above identified patent and th
33. e sponse to the output signal to disconnect the conductors when the AC output exceeds the electrical level whereby the circuit breaker is tripped when a volts per Hertz value of the AC voltage exceeds the preselected pickup value of volts per Hertz 51 The method as set forth in claim 49 further com prising the steps of measuring a second time period during which the AC output exceeds the electrical level and generating a second electrical signal as a function of the first named time period and the second time period so that the second electrical signal repre sents a ratio of volts per Hertz of the AC voltage to the pickup value of volts per Hertz 52 A protective relaying method for use in an electri cal power system with a circuit breaker for connecting and disconnecting first and second electrical conduc tors which are energizable with an AC voltage that has a value of actual volts per Hertz and with means for sensing the AC voltage to produce an AC output the method comprising the steps of supplying a first electrical signal representing a prese lected pickup value of volts per Hertz 15 20 25 30 35 45 55 60 65 32 generating a second electrical signal which increases im magnitude during the time when the value of actual volts per Hertz exceeds the pickup value of volts per Hertz for the relay and the second elec trical signal decreases in magnitude during the time when the value of actual volts
34. e Chip Microcomputers Users Manual 1980 Intel Corp Chapter 1 and first 7 pages of Chapter 4 Microcomputer 201 addresses EPROM 221 at a set of address pins A0 A11 by supplying the lower 8 bits of the address from a set of pins DB7 0 to an address latch 225 while enabling it from pin ALE Address Latch Enable The lower 8 bits of the address are then as serted to EPROM 221 by the Q outputs 8Q 1Q of latch 225 and the upper 4 bits of the address are asserted by microcomputer 201 from port P2 pins 0 3 A chip en 4 788 619 15 able CE input of EPROM 221 is actuated by a signal from pin PSEN and an 8 bit output from pins 07 00 of EPROM 221 is fed back to pins DB 7 0 of microcom puter 221 thereby reading EPROM 221 Front panel thumbwheel switches 230 allow the user to program the V Hz relay 59 or various pickup set tings time settings and a reset rate parameter as dis cussed in connection with FIG 3 Each thumbwheel selects an array of diodes leading to four output lines which when energized produce binary coded decimal BCD nibbles depending on thumbwheel setting which are read by the microcomputer 201 To energize the thumbwheel switches 230 microcomputer 201 latches a byte into address latch 225 The byte has 8 bits one of which is a 1 and the rest are 0 Thumbwheel switches 230 have 8 input lines 231 and 8 output lines 235 to an 8 bit latch 241 A single one of the 8 input lines is energized to address two of the thumb
35. e a digital signal having a value which is a function of both the time interval and the pickup level a digital to analog converter for convert ing the digital signal to an analog signal and second comparing means responsive to the AC output and the analog signal for detecting when the AC output exceeds the analog signal in magnitude the digital computer also being fed by the second comparing means and programmed to produce and increase the electrical signal in magnitude when the second comparing means detects that the AC output exceeds the analog signal in magnitude 49 A protective relaying method for use in an electri cal power system with a circuit breaker for connecting and disconnecting first and second electrical conduc tors which are energizable with an AC voltage the method comprising the steps of sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings supplying an electrical signal representing a prese lected pickup value of volts per Hertz generating an electrical level as a function of both the time period and the pickup value and producing an output signal when the AC output ex ceeds the electrical level so that the output signal is produced when a volts per Hertz value of the AC voltage is in excess of the preselected pickup value of volts per Hertz 50 The method as set forth in claim 49 further com prising the step of tripping the circuit breaker in r
36. e actual volts per Hertz 141 for a time Percentage value 143 toward trip accumulates in FIG 5 during the time of excessive volts per Hertz 141 and the LEDs of bargraph 123 are turned on in ascend ing order of accumulated value ET until some of them but not all are on at point 144 Then without any trip having occurred the actual Volts per Hertz 145 sensed falls below the pickup value VHS The Time Trip Out put relay 127 does not close because 100 value has not been reached The LEDs of the TSD are turned off in descending order from right to left yellow to green as resetting proceeds and the percentage value 147 falls with a slope parameter FP in seconds per percent determined by the front panel setting on thumbwheels 122 The Time Status Display thus shows in an impres sively visual way the operations of the Time Trip func tion of the Volts per Hertz relay regardless of whether the relay actually trips If the actual volts per Hertz VH remained below pickup VHS a reset time 149 in FIG 5 would elapse whence 0 value would be reached Before reset time 149 elapses however the actual volts per Hertz 151 exceeds pickup value VHS again Percentage value 153 accumulates this time all the way to 100 at a point 154 whence the relay 59 trips its Time Trip Output relay 127 of FIG 2 and closes contacts 81 of FIG 1 Inter rupter 41 and breaker 52 of FIG 1 are both tripped removing the excessive volts per Hertz condition in FIG 4 Rel
37. e of the second electrical signal includes a series of display means connected to said means for generating the second electrical signal so that the series of display means are activated in a first order as the second electrical signal increases in value and are deac tivated in reverse when the second electrical signal decreases in value 39 A protective relay as set forth in claim 38 wherein said means for generating the second electrical signal also includes means for computing a whole number directly related to the magnitude of the second electri cal signal which number is equal to the number of the display means which are to be activated to represent that magnitude and for supplying a set of activating signals equal in number to the whole number so com puted in order to activate the corresponding number of display means 40 A protective relay as set forth in claim 37 wherein said means for generating the second electrical signal also includes means for doing so by repeatedly produc ing a third electrical signal that varies as a function of both the pickup value and a first time interval between zero crossings over time repeatedly measuring a second time interval during which the AC output exceeds the third electrical signal in magnitude repeatedly generat ing a fourth electrical signal that varies over time as a function of the first and second time intervals repeat edly increasing the second electrical signal by amounts depending
38. easuring a second time period during which the AC output exceeds the second electrical level repeatedly generating a second electri cal signal that varies over time as a function of the interval and second time period repeatedly producing a third electrical signal when the second electrical signal exceeds a threshold magnitude and repeatedly increas ing the third electrical signal by amounts depending on the second electrical signal and producing a time trip signal for the relay when the third electrical signal ex ceeds a predetermined level 15 A protective relay as set forth in claim 14 further comprising means for supplying a reset control signal said means for generating including means responsive to the reset control signal and operative upon an occur 10 15 20 25 30 35 40 45 50 55 60 65 26 rence of the time trip signal for progressively decreas ing the third electrical signal in magnitude during a reset time interval dependent upon the reset control signal 16 A protective relay as set forth in claim 9 wherein the AC voltage has a value of actual volts per Hertz further comprising means for supplying an additional pickup value signal representing a preselected time trip pickup value of volts per Hertz for the relay said gen erating means also including means for generating a further electrical signal which increases in magnitude during the time when the value of actual volts per Hertz exce
39. eds the time trip pickup value and which decreases in magnitude during the time when the value of actual volts per Hertz is less than the time trip pickup value of volts per Hertz the relay also compris ing means for producing a display indicative of the magnitude of the further electrical signal as it increases and decreases in magnitude 17 A protective relay as set forth in claim 9 wherein the AC voltage has a value of actual volts per Hertz further comprising means for supplying a time trip pickup signal representing a preselected time trip pickup value of volts per Hertz for the relay and means for supplying a reset control signal representing a reset rate parameter for the relay said generating means also including means responsive to the AC output for gener ating a second electrical signal that increases in magni tude from an initial value to an accumulated value when the actual volts per Hertz exceeds the time trip pickup value and responsive to the reset control signal for decreasing the magnitude of the second electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumu lated value if the value of actual volts per Hertz is less than the time trip pickup value throughout the reset time interval 18 A protective relay as set forth in claim 9 wherein the AC output has half cycles of two opposite polarities and said means for generating also includes means for me
40. el as a function of both the time period between zero crossings and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level to indicate that a volts per Hertz value of the AC voltage exceeds the preselected pickup value of volts per Hertz for the relay 10 A protective relay as set forth in claim 9 wherein said generating means comprises means for producing the output signal for the relay when the AC output exceeds the electrical level for a predetermined length of time 11 A protective relay as set forth in claim 10 further comprising electrical alarm control contacts operable in response to said output signal 12 A protective relay as set forth in claim 9 wherein said generating means comprises means for producing the output signal for the relay substantially instanta neously when the AC butput exceeds the electrical level 13 A protective relay as set forth in claim 12 further comprising instantaneous trip contacts operable in re sponse to said output signal 14 A protective relay as set forth in claim 9 further comprising means for supplying an additional pickup value signal representing a preselected time trip pickup value of volts per Hertz for the relay and said means for generating includes means for repeatedly producing a second electrical level that varies as a function of the time trip pickup value and an interval between zero crossings over time repeatedly m
41. em having electrical conductors which are energizable with an AC voltage The protective relay includes a circuit for sensing the AC voltage to produce an AC output that has zero crossings and a time period be tween zero crossings a circuit for supplying an electri cal signal representing a preselected pickup value of volts per Hertz for the relay and a circuit responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level In this way the output signal is produced when a volts per Hertz value of the AC voltage exceeds the preselected pickup value of volts per Hertz for the relay Other protective relay apparatus and methods are also disclosed 61 Claims 14 Drawing Sheets BREAKGK 52 raesa7 7 85 CIRCUIT US Patent Nov 29 1988 Sheet 1 of 14 4 788 619 59 VOLTS HERTE RELAY SENS NG LAE 6 EA CONTACTS gt 2 j 55 36 48 sal 7 u Ng A sg a CIRCUIT M Na BREAKER 52 75 37 e er LIAM tangan 1 la P Ta MP Tag e E y 524 59 8 n ba 73 77 US Patent Nov 29 1988 Sheet 2of14 4 788 619 Pie TIME 104 TRIP UM 63 65 ya 127 5 A e FILTER Je 7 IN INTEGRATOR 7 N TIMER OTP UT 2 SENSING 103 LED BAR GRAPH LINEAR 02 RESET HART RESET by 113 US PAT OTS 2EENI
42. et by a Time Dial 120 A linear reset circuit 121 responds to the time trip level detector 103 when the volts per Hertz decreases below pickup and causes the numerical value from integrator timer 119 to decrease in magnitude from its accumulated value to the initial value in a reset 4 788 619 7 time interval which varies directly with the accumu lated value if the value of actual volts per Hertz is less than the time trip pickup level of volts per Hertz throughout the reset time interval A reset slope param eter for reset purposes is set by Reset Dial 122 A LED bar graph circuit 123 is responsive to the integrator timer 119 and to the linear reset circuit 121 to produce a display indicative of the magnitude of the numerical value as it increases and decreases in magnitude If and when the integrator timer 119 accumulates a value which exceeds a predetermined maximum a time trip signal is sent to actuate a Time Trip output relay 127 with contacts 81 of FIG 1 This relay is deactuated and contacts 81 are opened when the linear reset circuit 121 decreases or reduces the accumulated value to its initial value Instantaneous Trip Level Detector 105 actuates In stantaneous Output Relay 129 and closes contacts 85 of FIG 1 when the instantaneous trip pickup level on thumbwheels 106 is exceeded In FIG 3 front panel details of a preferred embodi ment of volts per Hertz relay 59 are shown Three In stantaneous Pickup thumbwheels 106 ad
43. et forth in claim 25 wherein said means for generating includes means operable when the ratio exceeds a predetermined value for re peatedly producing a third electrical signal and increas ing it in magnitude by an amount which is a direct func tion of the excess of the ratio over the predetermined value 27 A protective relay as set forth in claim 26 further comprising means for producing a display indicative of the magnitude of the third electrical signal 0 w 5 40 45 55 60 65 28 28 A protective relay as set forth in claim 25 wherein said means for generating also includes means operable when the ratio exceeds a predetermined value for re peatedly producing a third electrical signal and increas ing it in magnitude by an amount which is a direct func tion of the excess of the ratio over the predetermined value and for producing a time trip signal for the relay to cause the circuit breaker to disconnect the conduc tors when the third electrical signal exceeds a predeter mined level 29 A protective relay as set forth in claim 28 further comprising means for supplying a reset control signal said means for generating including means responsive to the reset control signal and operative upon an occur rence of the time trip signal for progressively decreas ing the third electrical signal in magnitude during a reset time interval dependent upon the reset control signal 30 A protective relay as set for
44. et forth in claim 3 further comprising adjustable means for supplying an addi tional electrical signal representing the predetermined value of volts per Hertz to said means for generating 5 A protective relay as set forth in claim 1 wherein said means for generating includes means for producing a second electrical level as a function of the time period between zero crossings which second electrical level is less than the first electrical level measuring a second time period during which the AC output exceeds the second electrical level generating a second electrical signal as a function of the first and second time periods to represent a ratio of volts per Hertz of the AC voltage to a predetermined value of volts per Hertz and when the ratio exceeds a preestablished amount repeatedly producing a third electrical signal and increasing it in magnitude by an amount which is a direct function of the excess of the ratio over the preestablished amount 6 A protective relay as set forth in claim 5 further comprising means for producing a display indicative of the magnitude of the third electrical signal 7 A protective relay as set forth in claim 1 wherein said means for generating also includes means for re peatedly producing a second electrical level less than the first electrical level and that varies as a function of an interval between zero crossings over time repeat edly measuring a second time period during which the AC output exceeds
45. for the relay In general another form of the invention is a protec tive relay for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts per Hertz and with means for sensing the AC voltage to produce an AC output The protective relay includes a eircuit for supplying a first electrical signal representing a preselected pickup value of volts per Hertz for the relay Another circuit responds to the AC output and to the electrical signal for generating a second electrical signal which increases in magnitude during the time when the value of actual volts per Hertz exceeds the pickup value of volts per Hertz for the relay and the second electrical signal decreases in magnitude during the time when the value of actual volts per Hertz is less than the pickup value of volts per Hertz A further circuit produces a display indicative of the magnitude of the second electrical signal as it increases and decreases in magnitude Generally a further form of the invention is a protec tive relay for use in an electrical power system with a circuit breaker for connecting and disconnecting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts per Hertz The protective relay includes a circuit for sens ing the AC voltage to produce an AC output and an
46. hat the ratio M V PU is related to these readily measurable time periods by a number of trigonometric eguations some of which are listed below and are eguivalent M 1 sin pito t 6 M 1 cos pi 2 t3 t o M 1 sin pi 2X1 13 1 8 4 788 619 11 continued to t1 9 M 2X a X WG 13 where pi is the ratio of the circumferences of a circle to its diameter 3 14159 In the software for a preferred embodiment a lookup table for example is prepared for the appropriate trigo nometric function For example in software for a pre ferred embodiment that computes equation 9 a lookup table called TBL is prepared for the trigonometric ratio function involving to t therein tj is designated LOGFO and t t3 is called MAGCAL for the pres ent purposes Equation 9 for that embodiment is there fore expressed as M22XTBLXLOGFO MAGCAL 10 Compared with approaches that integrate the input waveform with unavoidable ripple and excessive time delays the preferred embodiment measures a time inter val t between zero crossings of the AC output filter waveform fundamental and generates a corresponding freguency dependent reference voltage or electrical level PU PU1 and PU2 depending on the V Hz pickup settings and the time period or interval t1 Then time period t3 during which the AC output waveform ex ceeds the electrical level if at all is measured From the measurements ratio M is readily
47. icroprocessor calculates the ratio value M and com putes the incremental value TIMVAL further mathematical discussion of a reset aspect of some preferred embodiments is provided next If the waveform peak value V in the half cycle 181 of FIG 6 becomes less than the electrical level PU the microprocessor decreases the Integrator Timer accu mulated value at a linear rate ramping down that is based on that accumulated value and a reset rate param eter value from the front panel reset thumbwheels 122 A total delay TDR for reset in seconds is expressed by the formula TDR ET FST x FPX 100 14 where ET is accumulated value toward trip before resetting begins FP is the setting on the front panel Reset Thumbwheels 122 and FST is a 100 level of accumulated value that would be needed for a time trip to occur ET FST is same ratio as the fraction of the LEDs in bargraph 123 which are lighted when resetting begins A digital signal produced by thumbwheels 122 to represent setting FP is regarded as an example of a reset control signal representative of a reset rate param eter for the relay The resetting occurs on an incremental basis so that incremental value TIMVAL during reset is calculated as TIMVAL RSTSCL FP 15 where RSTSCL is a reset scaling factor equal to one hundredth of the full scale trip value FST times the time base DT e g DT 10 msec Substituting the definition of RSTSCL as well as equation 14 into equation 15
48. isconnecting the electrical apparatus which is energizable with an AC voltage that has a value of 4 788 619 33 actual volts per Hertz the method comprising the steps of generating an elecrrical signal in response to the AC voltage so that the electrical signal changes in mag nitude from an initial value to an accumulated value generally representative of heating of the apparatus to be protected when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz producing an electrical trip for the circuit breaker when the accumulated value reaches a predeter mined amount and upon an occurrence of the electrical trip returning the electrical signal from its accumulated value during a reset tire interval related to the thermal time constant of the apparatus to be protected to allow cooling of the apparatus the electrical signal generally representing the cooling during the reset time interval 58 A protective relay for use with electrical appara tus to be protected that is energizable with an AC volt age that has a varying value of actual volts per Hertz and for use with a circuit breaker for connecting and in response to an electrical trip disconnecting the electri cal apparatus and with means for sensing the AC volt age to produce an AC output the protective relay com prising means responsive to the AC output for generating an electrical signal that begins at an initial value and changes i
49. itions can create an under frequency or overvoltage condition and consequent overexcitation For example DC field current is typically applied to a field winding of a generator when the machine is above 90 of its rated speed If the field current is applied early before sufficient generator speed is reached on startup or not removed soon enough after generator speed has fallen substantially during shut 20 25 30 35 40 45 50 55 60 65 2 down the generator AC terminal voltage may be much higher than appropriate for excitation purposes relative to the actual electrical frequency since fre quency is proportional to generator speed Some generators are equipped with automatic volt age regulators which supply varying amounts of DC field current to maintain the generator AC voltage at a preset value at rated frequency The preset value is reduced by the regulator if frequency falls substantially An overexcitation relay advantageously is provided as backup protection for underfrequency relaying and Volts Hertz control functions in the generator voltage regulator In another application load tap changing LTC transformers and line voltage regulators may be sub jected to excessive volts per Hertz during abnormal system frequency conditions due to their constant volt age control function Also the failure of an LTC con troller may result in a runaway condition producing dangerously high voltage and conse
50. justably estab lish a pickup point for the instantaneous trip output A suitable range of adjustment is from 1 00 to 3 99 V Hz in 0 01 V Hz increments Three Time Trip Pickup thumbwheels 104 adjustably establish the pickup point for the time trip output A suitable range of adjustment is also from 1 0 to 3 99 V Hz in 0 01 V Hz increments Two Time Dial thumbwheels 120 adjustably select a particular inverse square characteristic curve for the relay Adjustment is from 0 1 to 10 in increments of 0 1 A setting of 00 is equivalent to a setting of 10 Two Reset Slope thumbwheels 122 adjustably estab lish a linear rate of reset per percent of full scale accu mulated value or equivalently in per unit of accumu lated value in integrator timer 119 to model the cooling rate of protected equipment Adjustment is from 0 1 to 9 9 seconds per percent of accumulated value in 0 1 second increments In other words if the relay 59 inte grator timer 119 accumulates sufficiently 100 to do a time trip then the relay will reset in one hundred 100 times the number of seconds indicated by thumbwheels 122 and deactuate the output relay at that time How ever if the integrator timer 119 accumulated 50 of the amount needed to trip and then the overexcitation ceases then the accumulated value will become fully reset in 50 of 100 times the time shown on thumb wheels 122 LED bar graph 123 shows the accumulated value in the integrator timer 119 at any given
51. ment By accumlating value towards tripping whenever the timed trip volts hertz pickup setting VHS is exceeded the relay simulates heat buildup within the protected equipment Once heated of course the metal in the equipment does not cool instantaneously To model the cooling over time the volts per Hertz relay has a linear reset characteristic which can be adjusted to closely correspond to the cooling rate of the protected equipment In this way as heat builds up and dissipates within the protected equip ment due to overexcitation excursions it is closely pro tected by the relay tripping and reset characteristic An inverse square timed trip characteristic stored in 5 10 20 25 30 35 relay 59 allows relay 59 to be closely coordinated with 40 a damage curve for the protected equipment This close coordination allows optimum utilization of the protected equipment by avoiding unnecessary trips and corresponding loss of utilization of the protected gener ating equipment for example The definite time alarm feature allows even more effective use of equipment by alerting an operator of potentially dangerous condi tions Once alerted the operator can take corrective action to prevent the necessity of a relay trip Alterna tively the definite time alarm output contact is used to initiate automatic corrective action The instantaneous trip feature provides high speed tripping for the most severe conditions To imple
52. ment the inverse square timing and reset for the Time Trip feature an Integrating Trip Timer func tion within a microprocessor circuit of relay 59 is initi ated when preselected pickup value VHS has been exceeded The timer begins timing ramping up in ac cordance with a preestablished inverse square curve until a trip output is produced A total time delay TDL required for time trip at constant ratio M is given by the formula TDL Time Dial Setting M 1 1 where M VH VHS 45 50 60 65 10 and VH is the Actual V Hz and VHS is the V Hz Pickup Setting on thumbwheels 104 In actuality the ratio M varies with time Accord ingly an incremental value TIMVAL is calculated at equal intervals DT for equally spaced times N 1 2 3 where TIMVAL FSTX DT TDL N 3 and FST is a 100 level of accumulated values that would be needed for a time trip to occur The incremen tal values are accumulated as a total in a register TTTIMER by summing them according to the follow ing recursive equation as long as ratio M exceeds unity TITIMER TTTIMER TIMVAL 4 When the total TTTIMER reaches a predetermined value of 100 FST a time trip signal is produced In this way when the ratio M exceeds a preestablished amount e g unity a digital electrical signal corre sponding to TTTIMER is increased in magnitude by an amount which is a direct function of the excess of the ratio over the predetermined value This is becau
53. n a test step 765 determines whether the value in TTTIMER has been reduced to its initial value of zero i e that the register in its function as a reset timer has timed out If so a step 767 then sets a Reset Timeout Bit indicating that TTTIMER is zero for STDCHK purposes In FIG 17a RETURN 769 is reached in the interrupt routine if any of the following occur 1 RESET is not one in step 761 2 there is no TTTIMER carry in step 755 3 the contents of TTTIMER are not zero in step 765 4 step 757 is completed or 5 step 767 is com pleted Upon reaching RETURN 769 the timing inter rupt routine is completed and operations go back to whatever point in the main loop or subroutines of the rest of the software at which the interrupt occurred In FIG 18 a further subroutine to update bargraph 123 corresponding to step 643 of FIG 12 is described in greater detail Operations commence with BEGIN 800 and proceed to compute a whole number NR equal to the first integer less than or equal to ten times the ratio of the value in register TTTIMER to its maximum value FST In other words NR is a whole number between O and 10 representative of an accumulated value in TTTIMER Next in a step 803 a table access 4 788 619 23 according to Table I hereinbelow is made to convert the whole number NR to an activation byte BAROUT for turning on an appropriate number of the 8 LEDs in FIG 7 that are fed by latch 271 TABLE I NR HEX
54. n numerous alternative embodiments en tirely in hardware in hardware with firmware compo nents in a microcomputer with associated input and output outboard hardware as illustrated herein and in a microcomputer with essentially no outboard hardware The exposition of a theory of operation with formulas hereinabove describes some of the preferred embodi ments and does not limit the spirit and scope of the invention In view of the above it will be seen that the several objects of the invention are achieved and other advanta geous results attained As various changes could be made in the above con structions and method steps without departing from the scope of the invention it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustra tive and not in a limiting sense What is claimed is 1 A protective relay for use in an electrical power system with a circuit breaker for connecting and discon necting first and second electrical conductors which are energizable with an AC voltage and means for sensing the AC voltage to produce an AC output that has zero 5 10 15 20 25 30 35 40 45 50 55 60 65 24 crossings and a time period between zero crossings the protective relay comprising means for supplying an electrical signal representing a preselected pickup value of volts per Hertz for the relay and means respon
55. n value generally representing heating of the apparatus to be protected when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz for the relay and for generating a trip output for initiating the electrical trip when the electrical signal reaches a predetermined value and means for supplying a reset control signal said means for generating including means responsive to the reset control signal before a trip output occurs for resetting the electrical signal in value over a first reset time period provided the value of actual 10 20 25 30 35 40 45 50 55 65 34 volts per Hertz becomes and remains less than the pickup level of volts per Hertz until the initial value is reached and responsive to the reset con trol signal upon an occurrence of the trip output for resetting the electrical signal to the initial value over a second reset time period which exceeds the first reset time period in length 59 A protective relay as set forth in claim 58 wherein the first reset time period varies as a function of the value of the electrical signal attained when resetting begins 60 A protective relay for use with electrical appara tus to be protected that is energizable with an AC volt age having a varying value of actual volts per Hertz and with means for sensing the AC voltage to produce an AC output the protective relay comprising means responsive to the AC output for generatig an ele
56. nducting rod as a Push to Energize element through respective access holes 135 137 and 139 in the front panel In a Time Status Display TSD a series of ten LEDs of bar graph circuit 123 are used to indicate accumula tion of numerical value towards trip 100 or decrease thereof toward reset 0 Each LED represents 10 of a total accumulation of 100 A first left set of three LEDs in the TSD are green a second middle set of four LEDs are yellow and a third right hand set of three LEDs are red When a preselected level VHS on the Timed Trip Pickup thumbwheels 104 is exceeded the LEDs of the TSD bargraph circuit 123 are turned on in ascending order from left to right green G to yellow Y to red R as percentage value toward trip is accumulated When all LEDs are illuminated the Time Trip Output relay is energized closing its contacts 81 When the preselected level on the Timed Trip Pickup thumbwheels 104 is no longer exceeded after trip the LEDs of the TSD are turned off in descending order from right to left red to green as a decrease in percentage value toward reset occurs When all LEDs in bargraph 123 are extin guished the Time Trip Output relay 127 of FIG 2 is deenergized opening its contacts 81 In another hypothetical sequence of events shown in FIGS 4 and 5 the Time Trip Pickup value VHS dashed line of FIG 4 is at first greater than the actual volts per Hertz 139 in the power system and then is itself exceeded by th
57. ne and address line Al are low OR gate 343 produces an active low when the RD line and address line AO are low In FIG 8 the circuitry of input control 303 is de tailed Low pass filter 65 produces the AC output on a line 401 The AC output is rectified and supplied to the noninverting input of a first open collector compar ator 405 by a voltage dividing and diode clamp circuit 407 An inverting input of comparator 405 is resis tively connected to ground so that its reference for comparison is zero The output of comparator 405 is connected through an OR gate 409 to testable input TO Comparator 405 thus acts as a zero crossing detector The AC output from filter 65 is also rectified and supplied to the inverting input of a second opencol lector comparator 415 by a voltage dividing and diode clamp circuit 417 A noninverting input of compar ator 415 is resistively connected to the electrical level 20 25 35 40 45 50 55 60 65 18 DACREF which provides a reference for comparison which is PU PU1 or PU2 of FIG 6 depending on which half cycle of the AC output is analyzed The output of comparator 415 is connected through an OR gate 419 to testable input T1 Comparator 415 thus acts as means for holding input T1 low whenever the AC output voltage on line 401 exceeds the electrical level DACREF An O Ring diode 421 is connected be tween the outputs of the comparators 405 and 415 so that c
58. not occurring Operations proceed from step 701 to a test step 705 to determine whether half cycle 183 is occurring If so operations branch to a step 707 to turn on the Alarm LED because the alarm pickup level is exceeded After step 707 a step 709 decrements an alarm timer which was Originally initialized at a value corresponding to the Alarm Time Delay on thumbwheels 114 If half cycle 183 is not occurring operations proceed from step 705 to a test step 711 to determine whether half cycle 181 is occurring If so operations branch to a step 713 to turn 25 40 45 so 60 65 22 on the Time Trip LED 117 of FIG 2 295 in FIG 7 Also in step 713 the RESET flag is set to zero since resetting should not occur when the pickup level PU is exceeded After step 713 a step 715 reads external counters 321 and 323 to obtain a measured time period t3 of FIG 6 also designated MAGCAL herein Next in a step 717 the ratio M is computed as a function of the two time periods t LOGFQ and t3 MAGCAL ac cording to equation 10 Then in a step 719 a time delay length TDL is computed according to the inverse square relationship in M and from the Time Dial setting on thumbwheels 120 according to equation 1 Opera tions then proceed to a step 721 to compute an incre mental value TIMVAL according to equation 3 After any of steps 703 709 or 721 is executed operations go to execute subroutine STDCHK in a step 723 and then loop ba
59. nsing transformer 63 is passed through a low pass third harmonic 180 Hz filter This filter substantially eliminates the peak distorting effect that third harmonic content in the AC signal places on a 60 Hz fundamental waveform Greater sensitivity and accuracy is achieved because the third harmonic filter attenuates third har monic distortion Potential transformer 63 feeds filter 65 which in turn supplies the AC output fundamental fre quency to an Alarm Level Detector 101 with adjustable Alarm Pickup thumbwheels 102 Time Trip Level De tector 103 with adjustable Time Trip Pickup thumb wheels 104 and an Instantaneous Trip Level Detector 105 with adjustable Instantaneous Trip Pickup thumb wheels 106 Alarm Level Detector 101 turns on an Alarm LED 111 to indicate that an alarm pickup value is exceeded and a definite timer 113 with adjustable Alarm Time Delay thumbwheels 114 is activated to determine whether the alarm pickup value is exceeded for at least a predetermined length of time If so an Alarm Output relay 115 is actuated and contacts 71 of FIG 1 close Time Trip Level detector 103 is set to a higher pickup level If this higher level is exceeded a time trip pickup LED 117 is turned on to indicate the occurrence Then an integrator timer 119 starting from an initial value electrically accumulates a numerical value toward pos sible trip An adjustment parameter K for an inverse square characteristic for this integrator timer is s
60. omparator 405 also holds input T1 low whenever the AC output voltage is negative When OR gate 419 output is high it lifts a reset high from a RST pin of a divide by two circuit 431 The clock input of circuit 431 is supplied by the Address Latch Enable line which toggles at a 400 KHz rate The output Q1 from circuit 431 is connected to the counter clock input CCK of counter 323 and to both latch clock inputs RCK of the counters 321 and 323 to operate the counters when needed as indicated by T1 low A power supply output circuit 441 has numerous capacitors for filtering and zener diodes for providing various regulated voltages A voltage regulator chip 443 provides 5 logic level supply voltage from 12 volts input A 9 volt Zener diode 445 provides a 9 volt regulated voltage to a variable resistor 447 con nected by line CAL to DAC 331 A comparator 451 and an inverter 453 are connected to and responsive to the output circuit 441 to provide a low active interrupt INT to microcomputer 201 in the event of power sup ply failure or loss of operating power A high active signal PS is provided in the same event to Watchdog 301 In FIG 9 Watchdog 301 is supplied with recurring pulses from pin P25 of microcomputer 201 These pulses are buffered by circuitry 461 and charge a capaci tor 463 keeping the output of an inverter 465 low If the pulses cease the output of inverter 465 goes high pro viding an output C to clock the input circuit 30
61. on the fourth electrical signal and producing a time trip signal for the relay to cause the circuit 10 20 25 30 35 40 45 50 55 60 65 30 breaker to disconnect the conductors when the second electrical signal exceeds a predetermined level 41 A protective relay as set forth in claim 37 further comprising means for supplying a reset control signal representing a reset rate parameter for the relay said generating means also including means responsive to the reset control signal for decreasing the magnitude of the second electrical signal from a first value that it has reached during the time when the actual volts per Hertz exceeds the pickup value to a second value in a reset time interval which varies directiy with the first value 42 A protective relay as set forth in claim 37 wherein the AC output has half cycles and zero crossings fur ther comprising means for supplying a further signal representing a second pickup value of volts per Hertz for the relay said means for generating including digital computer means for computing in first and second half cycles of the AC output first and second values of an electrical level as a function of a time interval between zero crossings and a pickup value corresponding to the first named and second pick up values respectively and for producing a third electrical signal for increasing the second electrical signal when the AC output exceeds the first value of the elect
62. opposite polarities and said means for generating also includes means for measuring the first time period between a pair of the zero crossings during a half cycle of one polarity and means for comparing the AC output with the electrical level during a half cycle of the opposite polarity 33 A protective relay as set forth in claim 25 wherein the AC output has half cycles further comprising means for supplying a further signal representing a second pickup value of volts per Hertz for the relay said means for generating also including digital com puter means for computing in first and second half cycles of the AC output first and second values of the electrical level by the function of first time period and pickup value corresponding to the first named and sec ond pickup values respectively and for producing the second electrical signal when the AC output exceeds the first value of the electrical level in the first half cycle and for producing another relay signal when the AC output exceeds the second value of the electrical level in the second half cycle 4 788 619 29 34 A protective relay as set forth in claim 25 wherein said means for sensing includes a low pass filter 35 A protective relay as set forth in claim 34 wherein said filter has a rolloff characteristic and said means for generating includes digital computer means pro grammed to generate the electrical level compensating for the rolloff characteristic at a frequency cor
63. or the relay Then the relay produces a nonlinear time to reset TDR value according to the equation 19 using the computed constant C and value of estimated temperature rise TR found from TR TB TR1 TB X ET FST 20 or from whatever formula is found to most precisely relate the accumulated value ET to temperature rise TR The incremental value TIMVAL equation 16 is computed on the basis of the computed value of TDR and TTTIMER is decremented according to equation 17 In still other embodiments equation 18 is recog nized to be a solution of a difference equation ETIN4D EIN __ 1 DT ET C which is then solved and corresponds to the following recursive equation for programming purposes TTTIMER TTTIMER TIMVAL 22 where TIMVAL DTx TITIMER 23 In this way the value in TTTIMER decays exponen tially and thereby accurately simulates the cooling of protected equipment Since a decaying exponential approaches zero only asymptomatically this embodi ment is programmed to deactuate the time trip output upon reaching a value such as 10 of FST In FIG 7 relay 59 uses an 80C39 microcomputer 201 that has a data bus 211 and operates in accordance with a main program and a timing interrupt routine which are stored inan EPROM erasable programmable read only memory 221 The 80C39 microcomputer 201 is one of a family of MCS 48 TM computers from Intel Corporation Santa Clara California See MCS 48 TM Family of Singl
64. oyed for further clarity wherein a slash through a line indicates multiple electrical conductors equal in number to a number indi cated nearby Slashes on either side of resistor 247 indi cate that this component is replicated for each conduc tor in a bus Conductors WR RD ALE P10 P12 P20 P24 P26 P27 A0 A1 A3 and A6 are broken in the drawing for clarity although complete connections are represented thereby Chip pins that are unused held inactive or represent power leads VCC and VSS are omitted for clarity in accordance with conventional drawing practice in the art Microcomputer 201 has a 6 MHz clock crystal 261 connected between input pins X1 and X2 and a capacitor 263 connected from pin X2 to common Microcomputer 201 provides signals on bus 211 to an 8 bit latch 271 which together with two buffers 273 and 275 from pins P26 and P27 respectively actuate a set of ten LEDs 277 for a Time Status display corresponding to bargraph 123 of FIG 2 Latch 271 and LEDs 277 are an example of a means for producing a display indica tive of the magnitude of a digital signal repesenting the TTTIMER accumulated value as it increases and de ta 5 20 25 55 65 16 creases in magnitude Latch 271 is clocked by chip enable OR gates 281 and 283 when Write WR and output P24 and address bit A3 simultaneously are low Microcomputer 201 also provides signals from pins P15 P17 to three buffers that actuate three relay drivers 2
65. perature rise TR is directly related and approxi mately proportional to the accumulated value of the integrator timer in relay 59 when the Time Dial setting is correctly made after temperature measurements on the protected equipment A front panel setting is set for an appropriate parameter of the reset time relationship Since equation 19 can be linearized the parameter selected is a straight line slope reciprocal such as sec onds per percentage front panel setting FP in the preferred embodiment FP is set equal to or greater than the time experimentally determined for the machine to 20 25 30 35 45 55 60 65 14 cool from a maximum tolerable temperature rise TR1 under overexcitation conditions to base temperature TB such as 5 degrees above normal operating temperature rise It is to be understood that in alternative embodiments of the invention other parameters can be input by front panel thumbwheels For example an experimentally determined cool down time can be entered on one set of thumbwheels with a ratio of the maximum tolerable temperature rise TR1 and base temperature TB on an other set of thumbwheels to describe the unit of pro tected apparatus Equation 19 is solved with TR set equal to TR1 to obtain thermal time constant C in an initialization routine on power up Constant C so com puted electronically constitutes another example of a reset control signal representative of a reset rate param eter f
66. quations 11 12 or 13 The adjusted electrical level PU PU1 or PU2 corre sponding to the half cycle 181 183 or 185 respectively is computed in step 665 and then output as a digital signal to DAC 331 whence a point B of FIGS 14 and 15 is reached In FIG 15 operations proceed from point B to a step 669 to determine from repeated checking of testable inputs T1 and TO during a given positive half cycle such as 181 whether the electrical level e g PU is exceeded in two repeated checks If so operations branch to a PICKUP point in the software of FIGS 15 and 16 If not operations proceed to a test step 673 If half cycle 185 is occurring in step 673 operations branch to a step 675 to turn off the instantaneous output relay and open contacts 85 of FIG 1 because the instantaneous pickup level is not exceeded If half cycle 185 is not occurring operations proceed from step 673 to a test step 677 to determine whether half cycle 183 is occurring If so operations branch to a step 679 to turn off the Alarm LED and Alarm output relay and open contacts 71 of FIG 1 because the alarm pickup level is not exceeded If half cycle 183 is not occurring operations proceed from step 677 to a test step 681 to determine whether half cycle 181 is occurring If so operations branch to a step 683 to turn off the Time Trip LED After step 683 a test 685 checks whether the Reset dial 122 of FIG 3 is set to 00 and if so the register TTTIMER is se
67. quent overexcita tion An overexcitation relay associated with an LTC transformer provides overexcitation protection for the transformer while allowing a wide range of voltage control operation In the prior art it has been known to produce an integral of the system voltage and compare it with a preset level to determine when excessive volts per Hertz is present However the process of integrating is time consuming and an overexcitation relay which operates more swiftly is desirable Also it has been known to provide a time trip function in which a condi tion of excessive volts per Hertz causes a timer to even tually trip a circuit breaker During overexcitation heat accumulates in the pro tected equipment When and if the overexcitation ceases the equipment cools It has been known to reset a volts per Hertz relay in a predetermined period of time after an excessive volts per Hertz condition has ceased regardless of the degree of excessive volts per Hertz and the time during which that condition has persisted It would be desirable to provide a volts per Hertz relay that actually and rapidly simulates the real heating and cooling characteristics of protected appara tus SUMMARY OF THE INVENTION Among the objects of the present invention are to provide improved protective relays and methods which can determine the existence of an overexcitation condi tion more swiftly to provide improved protective re lays and methods which c
68. r decreasing the magni tude of the electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumulated value if the value of actual volts per Hertz is less than the pickup level of volts per Hertz throughout the reset time interval 45 A protective relay as set forth in claim 44 wherein said reset control signal supplying means includes ad justable means for establishing a reset slope in seconds per unit of accumulated value of the electrical signal 46 A protective relay as set forth in claim 44 wherein said reset control signal supplying means includes ad justable means for establishing a rate of decrease of magnitude of the electrical signal which is substantially 4 788 619 31 independent of the atcumulated value of the electrical signal 47 A protective relay as set forth in claim 44 wherein said means for generating includes means for resuming an increase in the magnitude of the electrical signal when the actual volts per Hertz exceeds the pickup value and the electrical signal has not been decreased in value to the initial value 48 A protective relay as set forth in claim 44 wherein said means for generating includes first comparing means for detecting zero crossings in the AC output counter means for measuring a time interval between the zero crossings digital computer means fed by the first comparing means and said counter means and pro grammed to produc
69. ram of controls and displays on a panel of a volts per Hertz relay of the invention FIG 4 is a diagram of a varying actual volts per Hertz versus time in an electrical power system FIG 5 is a diagram of an electrical signal versus time produced in a volts per Hertz relay of the invention increasing and decreasing and then increasing again until a 100 value is reached whence a trip signal is provided by the volts per Hertz relay of the invention a set of ten display light emitting diodes LEDS from the panel of FIG 3 being aligned with the vertical axis for illustration FIG 6 is a waveform diagram of operations of a volts per Hertz relay of the invention in various half cycles of an AC output waveform FIG 7 is a block diagram of a microprocessor based circuit of a volts per Hertz relay of the invention FIG 8 is a schematic diagram of an input control circuit in part of FIG 7 FIG 9 is a schematic diagram of a watchdog circuit for FIG 7 FIG 10 is a schematic diagram of a filter circuit in FIG 1 and in the input control circuit of FIG 8 FIG 11 is a schematic diagram of a loss of sensing circuit in FIG 8 and FIGS 12 18 are flowcharts of a main routine inter rupt routine and subroutines in the operations and soft ware of the inventive volts per Hertz relay operating according to methods of the invention Corresponding reference characters indicate corre sponding parts throughout the several views of the dra
70. respond ing to the first time period 36 A protective relay as set forth in claim 25 wherein said means for generating includes a digital computer and the relay further comprises a series of light emitting means connected to said digital computer to indicate an accumulation of a numerial value toward a trip condi tion 37 A protective relay for use in an electrical power system with a circuit breaker for connecting and discon necting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts per Hertz and with means for sensing the AC voltage to produce an AC output the protective relay comprising means for supplying a first electrical signal represent ing a preselected pickup value of volts per Hertz for the relay means responsive to the AC output and to the electri cal signal for generating a second electrical signal which increases in magnitude during the time when the value of actual volts per Hertz exceeds the pickup value of volts per Hertz for the relay and the second electrical signal decreases in magnitude during the time when the value of actual volts per Hertz is less than the pickup value of volts per Hertz and means for producing a display indicative of the mag nitude of the second electrical signal as it increases and decreases in magnitude 38 A protective relay as set forth in claim 37 wherein said means for producing a display indicative of the magnitud
71. rical level in the first half cycle and for producing another relay signal when the AC output exceeds the second value of the electrical level in the second half cycle 43 A protective relay as set forth in claim 37 further comprising means for producing a trip output for the circuit breaker when the magnitude of the second elec trical signal reaches a predetermined value and means for supplying a reset control signal said means for gen erating including means responsive to the reset control signal and operative upon an occurrence of the trip output for progressively decreasing the second electri cal signal in magnitude during a reset time interval dependent upon the reset control signal 44 A protective relay for use in an electrical power system with a circuit breaker for connecting and discon necting first and second electrical conductors which are energizable with an AC voltage that has a value of actual volts per Hertz the protective relay comprising means for sensing the AC voltage to produce an AC output means responsive to the AC output for generating an electrical signal that increases in magnitude from an initial value to an accumulated value when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz for the relay and means for supplying a reset control signal representa tive of a reset rate parameter for the relay said generating means including means responsive to the reset control signal fo
72. ring Column 25 claim 8 line 10 rest should read reset claim 12 line 42 butput should read output Column 33 claim 57 line 15 tire interval should read time interval Column 34 claim 60 line 31 level ff should read level of Signed and Sealed this Fifteenth Day of August 1989 Attest DONALD J QUIGG Altesting Officer Commissioner of Patents and Trademarks
73. se M 1 is in the denominator of equation 1 and there fore TIMVAL from equation 3 equals M 1 2xDT Time Dial Setting TIMV AL is greater as M increases so that there is a direct function relation ship and not an inverse relationship Actual volts per Hertz VH is proportional to the product of the measured peak voltage V and the half period of each cycle 1 2F where F is actual fre quency Volts per Hertz pickup value VHS is propor tional to the product of an electrical level PU for pickup comparison purposes multiplied by the same half period of each cycle Consequently the ratio M of equation 2 that should be measured for use in equations 1 3 and 4 is also given by M V PU 6 Using the relationship of eguation 5 it is further ad vantageously recognized herein that the ratio M can be measured by measuring time periods associated with the AC output waveform from filter 65 Measuring of time periods is readily accomplished by the microprocessor and inexpensive associated hardware For this purpose three time periods are defined as follows A t half period time interval of AC output filter waveform B t3 period of time in a half cycle of the waveform during which the waveform exceeds the electrical level PU calculatedfrom pickup V Hz VHS on dial 104 and from t C to time from zero crossing to instant when wave form first exceeds electrical level PU to t1 t3 2 Inspection of FIG 6 shows t
74. sive to the AC output and to the electri cal signal for generating an electrical level as a function of both the time period between zero crossings and the pickup value and for producing a trip signal for the relay to cause the circuit breaker to disconnect the conductors when the AC output exceeds the electrical level whereby the circuit breaker is tripped when a volts per Hertz value of the AC voltage exceeds the preselected pickup value of volts per Hertz for the relay 2 A protective relay as set forth in claim 1 wherein said means for generating includes means responsive to the AC output and to the electrical signal supplying means for measuring a value of the time period between a pair of the zero crossings and producing the electrical reference level as a direct function of the pickup value divided by the value of the time period between zero crossings 3 A protective relay as set forth in claim 1 wherein said means for generating includes means for producing a second electrical level as a function of the time period which second electrical level is less than the first electri cal level for measuring a second time period between zero crossings during which the AC output exceeds the second electrical level and for generating a second electrical signal as a function of the first and second time periods to represent a ratio of volts per Hertz of the AC voltage to a predetermined value of volts per Hertz 4 A protective relay as s
75. sponsive to the AC output for generating an electrical signal which changes in value generally representing heating of the apparatus to be pro tected when the actual volts per Hertz exceeds a preselected pickup level of volts per Hertz for the relay and for generating a trip output for initiating the electrical trip when the electrical signal reaches a predetermined value and means for supplying a reset control signal said means for generating including means responsive to the reset control signal upon an occurrence of the trip output for resetting the electrical signal in value so that the resetting consumes a reset time period generally corresponding to a length of time for the apparatus to be protected to cool 55 A protective relay as set forth in claim 54 wherein said means for supplying the reset control signal in cludes adjustable means for establishing a reset slope in seconds per unit of value of the electrical signal 56 A protective relay as set forth in claim 54 wherein said means for supplying the reset control signal in cludes adjustable means for establishing a rate of de crease of magnitude of the electrical signal which is substantially independent of the value of the electrical signal 57 A protective relaying method for use in an electri cal power system with electrical apparatus to be pro tected having a thermal time constant and with a cir cuit breaker for connecting and in response to an elec trical trip d
76. t to its initial value of zero in a step 687 If the Reset dial 122 is not set to 00 then operations branch from step 685 to compute an incremental value TIMVAL according to equation 15 in a step 689 After any of steps 675 679 687 or 689 is executed operations loop back to point FREQB of FIGS 15 and 12 and continue with step 639 of FIG 12 If the test of step 681 of FIG 15 is not met operations default to START of FIGS 15 and FIG 12 and continue with step 603 of FIG 12 In this way the operations of microcomputer 201 are repeat edly performed In FIG 16 operations which reached point PICKUP of FIG 15 proceed to a step 691 to determine whether the AC output from filter 65 has become negative low at testable input T0 which indicates that the positive half cycle is completed If not operations go to a step 693 to determine whether the electrical level used for pickup purposes is no longer exceeded high at testable input T1 If the electrical level is still exceeded low at TI then operations loop back to step 691 until either the electrical level is no longer exceeded in step 693 or the AC output goes negative in step 691 whence a test step 701 is reached If half cycle 185 is occurring operations branch from step 701 to a step 703 to turn on the instantaneous out put relay and close contacts 85 of FIG 1 to trip breaker 52 and interrupter 41 because the instantaneous pickup level is exceeded If half cycle 185 is
77. th in claim 25 wherein the AC voltage has a value of actual volts per Hertz and said generating means also includes means for gen erating a further electrical signal which increases in magnitude during the time when the value of actual volts per Hertz exceeds the pickup value and which decreases in magnitude during the time when the value of actual volts per Hertz is less than the pickup value of volts per Hertz the relay also comprising means for producing a display indicative of the magnitude of the further electrical signal as it increases and decreases in magnitude 31 A protective relay as set forth in claim 25 wherein the AC voltage has a value of actual volts per Hertz further comprising means for supplying a reset control signal representing a reset rate parameter for the relay said generating means also including means responsive to the AC output for generating a third electrical signal that increases in magnitude from an initial value to an accumulated value when the actual volts per Hertz exceeds the pickup value and responsive to the reset control signal for decreasing the magnitude of the third electrical signal from its accumulated value to the initial value in a reset time interval which varies directly with the accumulated value if the value of actual volts per Hertz is less than the pickup value throughout the reset time interval 32 A protective relay as set forth in claim 25 wherein the AC output has half cycles of two
78. tly means that one variable increases when a second variable does whether or not their rela tionship is linear For example the cooling time is greater if the temperature rise due to overexcitation of the protected equipment is greater Advantageously the preferred embodiment provides a reset arrangement which provides a panel setting for a slope parameter in seconds per percentage of accumulated value thereby making the time for reset longer for higher levels of accumulated value in TTTIMER In this way the time interval TDR for reset varies directly with the accumu lated value and the reset slope or rate parameter is independent of the accumulated value As a result the panel setting as a slope parameter more truly models the cooling curve of a protected apparatus resulting in shorter actual reset times for most cases than some fixed reset time that would have to be set long for the worst case In mathematical terms the cooling characteristic of the protected apparatus is given by the equation TA TB TA TRe C 18 where TA is ambient temperature TB is base tempera ture rise above ambient to which the apparatus must cool for reset to be valid and TR is the temperature rise that occurs upon a given volts per Hertz condition persisting for a given time C is the thermal time con stant of the protected apparatus and t is the time re quired for reset Solving equation 18 for reset time TDR t yields TDR C In TR TB 19 Tem
79. ut exceeds the analog sig nal in magnitude the digital computer also being fed by the second comparing means and programmed to pro duce the output signal when an excess is detected by the second comparing means 24 A protective relay as set forth in claim 9 wherein said means for generating includes a digital computer and the relay further comprises a series of light emitting means connected to said digital computer to indicate an accumulation of time toward a trip condition 25 A protective relay for use in an electrical power system with a circuit breaker for connecting and discon necting first and second electrical conductors which are energizable with an AC voltage the protective relay comprising means for sensing the AC voltage to produce an AC output that has zero crossings means for supplying an electrical signal representing a pickup value of volts per Hertz for the relay and means responsive to the AC output and to the electri cal signal for generating an electrical level as a function of both the pickup value and a first time period between a pair of the zero crossings for measuring a second time period during which the AC output exceeds the electrical level and for generating a second electrical signal as a function of the first and second time periods so that the second electrical signal represents a ratio of volts per Hertz ofthe AC voltage to the pickup value of volts per Hertz Hertz 26 A protective relay as s
80. ute a measured value of the ratio M for time trip purposes DAC 331 is a 12 bit National Semiconductor device type no DAC1232 that is controlled by the high and low logic levels on pin P11 from microcomputer 201 at DAC pins X and B1 B2 The WR line is provided to corresponding low active WR1 and WR2 pins of DAC 331 Microcomputer 201 sequentially controls the 12 bit DAC 331 to load all 12 bits from the 8 bit bus 211 A reference voltage for conversion purposes V REF nis provided from input control 303 on a CAL calibration line that supplies an adjustable current from a regulated 9 volt source In counters 321 and 323 the pin mnemonics are as follows CCK counter clock input CCLR low active counter clear input connected to pin P12 for clearing under software control from microcomputer 201 CCKEN low active counter enable input connected to circuit 303 MAG output and pin T1 G low active pin to make tristate counter output active RCD low active carry from counter 323 to CCK input of counter 321 and RCK register clock with internal tristate latch on output connected to an output Q1 from circuit 303 The CCK input of counter 323 is connected to the output Q1 also 8 bit wide outputs of both counters 321 and 323 are connected in parallel to the 8 bit data bus 211 and the counters are read out separately Two OR gates 341 and 343 respectively enable the G pins of counters 321 and 323 OR gate 341 produces an active low when the RD li
81. utput ALM at pin P16 to actuate the alarm output relay and close contacts 71 of FIG 1 When step 615 is completed or the test of step 613 is not met then operations go to a step 617 to deter mine whether the accumulated value in register TTTIMER has reached 100 value for time trip If so operations branch to a step 619 to turn on the Time Trip output on pin P17 to close contacts 81 of FIG 1 and trip the circuit breaker 52 and the interrupter 41 Also in step 619 a reset condition is established by setting RESET to one 1 so that a resetting process can begin paa 5 45 55 60 65 20 After step 619 or if the test of step 617 is not met RE TURN 621 is reached Referring again to FIG 12 operations proceed from subroutine STDCHK 603 to a step 635 to test the TO testable input to determine whether it has gone low indicating that the sinusoidal AC output is negative Until this occurs a loop back to STDCHK subroutine 603 is made Eventually the AC output goes negative at zero crossing 171 of FIG 6 Operations of FIG 12 proceed from step 635 through a program point FREOB to a step 639 In step 639 a test is made using information developed from testable inputs TO and T1 to determine whether the AC output is in its first half period 175 If not operations branch directly to a pro gram point A If so operations proceed to a step 641 to execute the subroutine STDCHK of FIG 13 Then ina step 643 a subroutine for updating
82. wheels at a time Two BCD nibbles 4 bits apiece are respectively output from each of the two addressed thumbwheels so that all 8 of the output lines 235 communicated BCD thumbwheel inputs to inputs 1D 8D of latch 241 In this way the various thumbwheels constitute an example of adjustable means for supplying respective electrical signals representing values of volts per Hertz times and rates to the means for generating e g microcom puter 201 and input control 303 Microcomputer 201 collects the thumbwheel infor mation by addressing input lines 1 8 of thumbwheel switches 230 with respective single high bits and latch ing the switch 230 output on lines 235 into latch 241 with a command WR to latch enable pin LE Outputs 1Q 8Q are tristate outputs that float electrically until a chip enable OR gate 245 supplies an output control signal to pin OC to output the latch 241 contents onto data bus 211 OR gate 245 responds to address bit A6 low and read output RD low Microcomputer 201 is programmed in a conventional manner to segregate and interpret the thumbwheel information as two digit or three digit numbers as indicated in FIG 3 In FIG 7 all pins from PSEN down to P1 7 of mi crocomputer 201 drawn on the right vertical side of the block therefor as well as the pins T1 TO RST and INT on the left side are provided with pullup resistors to 5 volts These resistors are omitted from the draw ing for clarity Bus notation is empl
83. wings DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG 1 a three phase electric power generator 11 is connected by three phase lines 13 to a delta wye unit stepup transformer 21 A neutral N of the generator is conventionally connected by a high resistance ground ing arrangement through a primary 27 of a distribution transformer 31 to ground The distribution transformer 31 has a secondary 33 across which is connected a grounding resistor 35 An exciter 37 produces DC cur rent for a field winding 39 of generator 11 which con trols the AC voltage produced by the generator 11 across three phase lines 13 which AC voltage has a value of actual volts per Hertz Exciter 37 can be a shunt static exciter of electronic type such as one of the SSE type of the assignee Basler Electric Corporation or a rotary exciter on a common shaft with generator 11 the rotary exciter in turn hav ing a field winding which is controlled by an automatic voltage regulator AVR as shown When necessary a field circuit interrupter 41 disconnects exciter 37 from field winding 39 by contacts 43 and closes a set of contacts 45 to instead connect the field winding 39 to a discharge resistor 47 to rapidly reduce the AC voltage produced by generator 11 on lines 13 Unit transformer 21 is in turn connected by three phase lines 49 through a circuit breaker 52 to a three phase bus 55 which conveys electric power to remote lines 56 to a substation load tap changing L
84. yields a further expres sion TIMVAL ETXDT TDR 16 s resetting proceeds the accumulated time TTTIMER is decremented by each value of TIMVAL so that TTTIMER TTTIMER TIMVAL 17 4 788 619 13 In the present work the same quantity TTTIMER acts as a time trip timer when it is incremented by TIM VAL according to equation 4 TTTIMER also acts as a reset timer when it is decremented by TIMVAL by equation 17 It is emphasized that TTTIMER is a register of accumulated value according to the equa tions above and is not an actual timer of clock time In this way the volts per Hertz relay 59 more pre cisely simulates the actual heating and cooling charac teristics of protected apparatus when the time dial and reset dial thumbwheels are properly set Twin objec tives are A to prevent an unduly rapid reset which would produce an erroneous indication of complete reset to an initial value of TTTIMER when the pro tected machine is still hotter than a base temperature and B to reset rapidly enough so that a subsequent excessive but temporary volts per Hertz condition does not cause an unnecessary trip and consequent economic loss Even though any particular unit of protected appara tus has a fixed thermal time constant the actual time required for it to cool from a given temperature rise condition to an appropriate base temperature rise above ambient still varies directly with the temperature rise Varies direc

Use in an electrical power system with a circuit breaker

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