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TVPPA DSC Manual

1. C 6 Single phase Example and Comparison with Full Report continued Report with Voltage Drop and Flicker Calculation continued Load 1 House 2 Circuit Base Voltage 120 240 V Service Wire 1 2 0 AL OH TRIPLEX R N 100 Current Leg 1 Leg 2 Neutral 50 50 PF1 85 Lag 2 85 Lag Voltage Drop Leg 1 Leg 2 Leg to Leg 0 76 0 6 0 76 0 6 1 52 0 6 1 26 1 196 1 26 1 196 2 52 1 196 Fault Current Line to Line Line to Neutral 3 840 A 1 828 Flicker Maximum Threshold of 2 3 TON 1PH HVAC Flicker Starts OnLoad 1 2496 1 per Day 0 Figure C 5 DSC Report page 3 Load House 2 details C 7 Single phase Example and Comparison with Full Report continued Report with Voltage Drop and Flicker Calculation continued Load 2 House 3 16 Circuit Base Voltage 120 240 V Service Wire 1 2 0 AL OH TRIPLEX 100 Current Leg 1 Leg 2 42 58 PF1 85 Lag 2 85 Lag Voltage Drop Leg 1 Leg 2 Leg to Leg 0 38 0 396 1 14V 0 9 1 52V 0 596 0 63V 0 5 1 89V 1 596 2 52V 1 196 Fault Current Line to Line Line to Neutral 3 840 A 2 104 A Flicker Maximum Threshold of 2 3 TON 1PH Flicker Starts OnLoad 1 2496 1 per Day 0 Figure 6 Report page 4 Load 2 House 3 details C 8 Single phase Example and Comparison with Full Report continued Report with Voltage Drop and Flicker Calculation continued Load 3 Hous
2. sin pf VAR Reactive or Imaginary Power S VA volt amps Total or Apparent Power pf power factor This equation identifies Reactive Power as a trigonometric function of Total Power and the power factor In this case when the power factor is unity 1 the Reactive Power is equal to zero 0 D 2 6 Total Load Current S p X 1000 11 e Amps load current as dependent on the Total Power for leg or phase Sip kVA kilovolt amps Total or Apparent Power for leg or phase of load V V volts voltage rating of the system or transformer in question Typically the VA rating of a piece of equipment is given in kVA or VA x 10 The purpose of the 1000 multiplier in this equation is to convert the typical rating of a piece of equipment i e a transformer to VA so that when the voltage rating is taken into consideration the result is in standard Amps with no prefixes or orders of magnitude to worry about NOTE Since unbalanced analysis is being conducted the above equation is used for 30 load currents by calculating each phase current with their respective phase voltages 7 Impedance Z JR X Q Ohms total impedance Q Ohms resistance Ohms reactance gt lt 25 Impedance describes a measure of opposition to current and is a combination of the resistance and reactance in a distribution system Resistance is the real component of impedance and Reactan
3. 10 kVA 1PH UG 10 1 6 1 4 2 1 1 UG 59 N Y N N N 15 kVA 1PH OH 15 1 3 1 0 1 6 1 OH 77 Y Y Y Y Y 15 kVA 1PH UG 15 1 3 1 0 1 6 1 UG 77 N Y N N N 25 kVA 1PH OH 25 1 2 1 7 2 1 1 OH 95 Y Y Y Y Y 25 kVA 1PH UG 25 1 2 1 7 2 1 1 UG 95 N Y N N N 37 5 1PH OH 37 5 1 3 1 9 2 3 1 OH 139 Y Y Y Y Y 37 5 kVA 1PH UG 37 5 1 3 1 9 2 3 1 UG 139 N Y N N N 50 kVA 1PH OH 50 1 1 1 8 2 1 1 OH 180 Y Y Y Y Y 50 kVA 1PH UG 50 1 1 1 8 2 1 1 UG 180 N Y N N N 75 kVA 1PH OH 75 1 0 2 1 2 3 1 255 Y Y Y Y 75 kVA 1PH UG 75 1 0 2 1 2 3 1 UG 255 N Y N N N 100 kVA 1PH OH 100 1 0 2 1 2 3 1 OH 320 Y Y Y Y Y 100 kVA 1PH UG 100 1 0 2 1 2 3 1 UG 320 N Y N N N 167 kVA 1PH OH 167 1 0 2 0 2 2 1 OH 485 Y Y 0 Y Y 167 kVA 1PH UG 167 1 0 2 0 2 2 1 UG 485 N Y N N N 250 kVA 1PH OH 250 1 0 2 3 2 5 1 OH 575 Y Y Y Y Y 250 kVA 1PH UG 250 1 0 2 3 2 5 1 UG 575 N Y N N N 333 kVA 1PH OH 333 0 9 2 4 2 6 1 OH 700 Y Y Y Y Y 500 kVA 1PH OH 500 0 8 2 5 2 6 1 OH 1000 Y Y b Y Y 75 kVA 3PH OH 75 1 0 3 0 3 2 3 OH 390 N N Y Y N 75 kVA 3PH UG 75 1 0 3 0 3 2 3 UG 390 N N Y Y N 112 5 kVA OH 112 5 1 1 3 2 3 4 3 OH 450 N N Y Y N 112 5 kVA 3PH UG 112 5 1 1 3 2 3 4 3 UG 450 N N Y Y N 150 kVA 3PH OH 150 1 0 3 4 3 5 3 OH 585 N N Y Y N 150 kVA UG 150 1 0 3 4 3 5 3 UG 585 N N Y Y N 225 kVA 3PH OH 225 1 0 3 4 3 5 3 OH 810 N N Y Y N 225 kVA 3PH UG 225 1 0 3 4 3 5 3 UG 810 N N Y Y N 300 kVA 3PH OH 300 1 0 3 8 3 9 3 OH 990 N N Y Y N 300 UG 300 1 0 3 8 3 9 3 UG 990 N N Y Y N 500 kVA 3PH
4. Small Multiplier Multiplier that is used when the wire size is 4 0 or smaller Large Multiplier Multiplier that is used when the wire size is larger than 4 0 Runs Inputs Number of Runs listed previously Small Multiplier Inputs Small Multiplier listed previously Large Multiplier Inputs Large Multiplier listed previously Selecting the Save button will enter the values into the database for use when calculating voltage drop for entered circuit models Selecting the New button will clear the fields for the entry of new multipliers into the database Note The new entry will not be entered into the database until the Save button is selected Selecting the Delete button will remove the highlighted selection from the database Selecting the Cancel button will exit the Wire Capacity Multipliers box 17 4 8 5 Transformers To edit the transformer database select Transformers from the Edit Data option under the Tools menu After entering the administrative password the Edit Transformer Data box will display Transformer Data x Transformer Descriptions Transformer Properties 10 1PH Size kVA 25 10 1PH UG R 2 f 2 100 1PH Test X 4 r7 1000 3PH UG 112 5 3PH 2 X 21 112 5 3PH UG 1 Phase Construction No Load Losses w 35 n Available Secondary Connections 167 1PH 225
5. measured in VA Reactive power e VA measured in Real power P measured in Watts The overall relationship between the Total Real and Reactive Power can be explained trigonometrically as diagramed above in the Power Triangle The power factor which can be determined from the phase angle 9 is the ratio between the Real and Total Power D 1 2 Total Power S 02 S VA volt amps measurement of Total Power also referred to as Apparent Power P W watts measurement of Real Power also referred to as True Power Q VAR measurement of Reactive Power also referred to as Imaginary Power This equation shows that Total Power is a combination of Real and Reactive Power 3 Power Factor pf cos pf power factor radians or degrees phase angle phi The power factor is a statement of the efficiency of Real Power to Total Power in the distribution system It can be determined from the phase angle between the Total Power and Real Power This is also the angle between the current and voltage 4 Real Power P Sxpf P W watts Real or True Power S VA volt amps Total or Apparent Power pf power factor This equation identifies Real Power as simply the Total Power adjusted by the power factor The closer the power factor is to unity 1 the more efficient the transmission of real power is from the source to the load In other words the Real Power equals the Total Power 5 Reactive Power Q 5
6. when installed but it can be changed by selecting the Set Administrative Password option from the Tools menu 4 8 1 Acceptable Voltage Flicker To edit the acceptable voltage flicker database select Acceptable Flicker Levels from the Edit Data option under the Tools menu After entering the administrative password the Acceptable Flicker Levels box will display Acceptable Flicker Levels Acceptable Flicker Levels Acceptable Flicker Inrush Frequency Inrush Interval Time Period 32 4 1 8 Hours 31 35 1 1 Hours 30 3 1 30 Minutes 28 2 1 4 Minutes 29 1 5 1 1 Minutes 26 1 1 B Seconds Create New Record 1 amp Flicker EN Inrushes per 1 Seconds Save Delete New Input the acceptable levels for voltage flicker using the available input boxes The levels that display initially are the levels currently stored in the database The following is a brief description for each of the items in the box e D Number assigned by the software to hold the data s place in the database Acceptable Flicker Acceptable percentage of voltage flicker for circuit models including equipment with the defined inrush parameters that follow the value Inrush Frequency The number of inrush operations starts that is acceptable for the associated flicker level in a specified period Inrush Interval In combination with Time Period specifies the period length for the number
7. 0 CU UG 0 000063 0 000041 0 000063 0 000041 315 4 0 SMALL CU UG SINGLE 250 MCM CU UG 0 000053 0 000041 0 000053 0 000041 345 250 LARGE CU UG SINGLE 350 MCM CU UG 0 000038 0 000040 0 000038 0 000040 420 350 LARGE CU UG SINGLE 500 MCM CU UG 0 000027 0 000039 0 000027 0 000039 515 500 LARGE CU UG SINGLE 750 MCM CU UG 0 000018 0 000038 0 000018 0 000038 640 750 LARGE CU UG SINGLE 1000 MCM CU UG 0 000014 0 000037 0 000014 0 000037 750 1000 LARGE CU UG SINGLE 4 ALUG 0 000510 0 000048 0 000510 0 000048 85 4 SMALL AL UG SINGLE 2 ALUG 0 000320 0 000045 0 000320 0 000045 115 2 SMALL AL UG SINGLE 1 0 AL UG 0 000200 0 000044 0 000200 0 000044 150 1 0 SMALL AL UG SINGLE 2 0 AL UG 0 000160 0 000043 0 000160 0 000043 170 2 0 SMALL AL UG SINGLE 4 0 AL UG 0 000100 0 000041 0 000100 0 000041 225 4 0 SMALL AL UG SINGLE 250 MCM AL UG 0 000085 0 000041 0 000085 0 000041 250 250 LARGE AL UG SINGLE 350 MCM AL UG 0 000061 0 000040 0 000061 0 000040 305 350 LARGE AL UG SINGLE 500 MCM AL UG 0 000043 0 000039 0 000043 0 000039 370 500 LARGE AL UG SINGLE 750 MCM AL UG 0 000029 0 000038 0 000029 0 000038 470 750 LARGE AL UG SINGLE 1000 MCM AL UG 0 000022 0 000037 0 000022 0 000037 545 1000 LARGE AL UG SINGLE 6 AL UG DUPLEX 0 000810 0 000036 0 000810 0 000036 70 6 SMALL AL UG DUPLEX 4 AL UG DUPLEX 0 000510 0 000034 0 000510 0 000034 90 4 SMALL AL UG DUPLEX 1 0 AL UG TRIPLEX 0 000200 0 000031 0 000200 0 000031 160 1 0 SMALL AL UG TRIPLEX 1 0 AL UG TRIPLEX R N 0 000200 0 000031 0 000
8. ALF LF Loss factor exclusively utilizes the annual load factor that has been previously calculated ALF Annual load factor ranging from 0 to 1 with a typical value of approximately 0 5 or 50 Loss factor is a formula developed from experience and by experiment to reflect how peak load demands and currents vary over a year for loss calculating purposes The above formula is used primarily for rural electric distributor calculations Refer to REA Bulletin 60 9 dated May 1980 14 Annual kWh Losses Lossywy 8 76 X I X Ryfmr Rw Ry X LF Loss wn kWh kilowatt hours kilowatt hours used due to losses in the system I A Amps current in the system Q Ohms equivalent resistance of the transformer Ohms equivalent resistance of conducting wire Ry Ohms equivalent resistance of the neutral wire LF Loss factor The 8 76 multiplier is a combination of two factors The first factor is the total amount of hours in a given year 8760 hours For a leap year this multiplier changes to include the extra day The second factor is the value of 1000 that is used to produce a final product with the units of KWh 8760 1000 8 76 D 8 15 Annual Loss Cost ALC Lossywy X rates kwn ALC annual loss cost the annual cost due to losses in the system Lossywn kWh kilowatt hours kilowatt hours used due to losses in the system rate aw kWh dollars per kilowatt hour the average cost of a
9. Hour 4 Is Better 3 096 Once Per 30 Minute 2 095 Once Per 4 Minutes 1 596 Once Per Minute 1 096 Once Per 6 Seconds 20 50 100 200 500 100 6 1 2 5 10 FLUCTUATIONS PER MINUTE 2 40 2 5 10 20 40 2 6 12 FLUCTUATIONS PER HOUR FLUCTUATIONS PER MINUTE FLUCTUATIONS PER SEC PCC Denotes Point of Common Coupling typically at meter Frequency of Fluctuations or Western IEEE Sid 141 1925 GE Flicker Studies Northwest Utility RUS Bull 160 3 Once per 8 hours 4 0 60 7 8 3 3 Once per hour 3 5 40 6 0 2 7 7 0 2 5 72 25 6 76 2 5 Once per 30 minutes 3 086 40 49 21 5 2 2 2 63 20 6 7 2 5 Once per 4 minutes 2 0 2 5 3 0 10 2 0 1 0 2 0 5 0 2 5 Ono per mimste 1 5 15 1 994 0 7 1 8 0 6 2 0 0694 2 9 1 7 Once per 6 seconds 1 0 15 12 04 0 7 0 4 06 04 2 5 13 BOV Borderline of Visibility BOI Bordcrlinc of Irritation t See voltige flicker standards summary file licker Alfowance pdf TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX G Acknowledgements amp References Acknowledgements We wish to acknowledge the members of the DSC Project Subcommittee the members of the TVPPA Research and Development Committee and Patterson amp Dewar for all the time and effort put into the development of this tool In addition we wish to especially thank Bruce Harvey for his leadersh
10. OH For the Barn s load the smallest possible wire is a 4 0 AL OH Quadruplex For the Farmhouse s load the smallest possible wire is a 1 0 AL OH Triplex R N R N is used for the Farmhouse because its single phase load is balanced and the R N conducting wire is a lighter choice than the non R N variety C 12 Three Phase Open Delta Example with Errors Then Corrected Lighting TX 3 2 Open Delta 50 kVA Power TX 3 2 Open Delta 25 120 240 V 120 240 V VD 2 46 V 2 05 VD BN 3 36 V 2 8095 VD AB 5 82 V 2 42 VD BC 2 08 V 0 87 Power Factor 77 Powe 00 WARNINGS z 400 AL QUADRUPLEX 50 AB Overloaded 60 6 KVA VD AN 0 58 0 48 VD BN 1 93 1 61 BN Overloaded 35 3 kVA VD BC 0 92 0 38 XXXXX WARNING XXXXX Circuit amp mps 234 Capacity 210 Amps 7 Farmhouse UPLEX G 7 120 240 V 32 120 240 v 12 5 07 TVD 3 11 2 60 TVD AN 4 49 V 3 7 435 gt v 1 215 2 11 W 1 763 TVD BN 7 40 6 17 TVD BN 6 75 5 62 i be YE TVD 10 52 4 3895 TVD 4 19V 007 59 TVD 0 00 V 0 00 Figure C 10 Three phase Open Delta distribution system with a 50 Lighting transformer and a 25 Power transformer one Barn with a balanced three phase 30 load and an unbalanced single phase load with 5 on Leg 1 and 15 on Leg 2 and one Farmhouse with a balanced 25 single phase lo
11. UG 500 1 0 3 9 4 0 3 UG 1350 N N Y Y N 750 kVA 3PH UG 750 1 0 5 7 5 8 3 UG 1650 N N Y Y N 1000 kVA 3PH UG 1000 1 0 5 7 5 8 3 UG 1900 N N Y Y N 1500 kVA 3PH UG 1500 1 0 5 7 5 8 3 UG 2550 N N Y Y N 2000 kVA 3PH UG 2000 1 0 5 7 5 8 3 UG 3000 N N Y Y N 2500 kVA 3PH UG 2500 1 0 5 7 5 8 3 UG 3250 N N Y Y N 62 5 3PH OPEN DELTA UG 62 5 1 1 3 2 3 4 2 UG 234 N N N N Y WIRE DATABASE WIRE CONSTRUCTION WIRE WIRE R C X C R N X N CAPACITY WIRE SIZE WIRE SIZE MATERIAL TYPE TYPE DESCRIPTION OHMS FT OHMS FT OHMS FT OHMS FT AMPS AWG CATEGORY AL CU OH UG S D T Q 8 CU OH 0 000790 0 000130 0 000790 0 000130 80 8 SMALL CU OH SINGLE 6 CU OH 0 000500 0 000120 0 000500 0 000120 110 6 SMALL CU OH SINGLE 4 CU OH 0 000320 0 000110 0 000320 0 000110 160 4 SMALL CU OH SINGLE 2 CU OH 0 000200 0 000110 0 000200 0 000110 210 2 SMALL CU OH SINGLE 1 0 CU OH 0 000130 0 000100 0 000130 0 000100 285 1 0 SMALL CU OH SINGLE 2 0 CU OH 0 000100 0 000100 0 000100 0 000100 325 2 0 SMALL CU OH SINGLE 4 0 CU OH 0 000063 0 000095 0 000063 0 000095 405 4 0 SMALL CU OH SINGLE 250 MCM CU OH 0 000053 0 000092 0 000053 0 000092 440 250 LARGE CU OH SINGLE 350 MCM CU OH 0 000038 0 000088 0 000038 0 000088 530 350 LARGE CU OH SINGLE 500
12. equipment of all types will generally be designed to give satisfactory performance in this range b It is recognized that maintaining voltage levels within Range A on all parts of the system at all times cannot be ensured Due to the economics of operation there may be some system voltages that fall in extremes of Range B and even beyond This may occasionally occur as the feeder reaches its design loading limit at annual or semi annual peak loads c When voltages frequently extend into Range B they should be corrected to conform to Range A requirements within a reasonable time If voltages on any part of the system fall outside the limits of Range B corrective actions should be taken immediately to bring these voltages within Range B requirements within a reasonable time Some types of utilization equipment will not perform satisfactorily or efficiently at the extremes of Range B voltages Many types of utilization equipment may fail to operate and may be seriously damaged or suffer shortened operating life outside Range voltage limits Voltages above these limits of Range B may be especially damaging to the users equipment Table 2 Voltage Drops for Rural Electric Distribution System Design 120 volt base Maximum Percent Volts Volts Drop Drop Substation regulated bus output to last distribution transformer primary 6 67 96 Distribution transformer primary to service delivery connection to consu
13. kilowatt hour of energy The rate variable is a blended annual average cost of both demand and energy charges divided by the total kilowatt hours purchased by the distributor D 9 TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX E Industry Service Voltage Standard Summary Industry Service Voltage Standard Summary The following summarizes the key industry standards and design criteria for electric service voltage Readers are encouraged to refer to the documents referenced for further details and explanations Voltage Conditions 1 Voltage levels will be maintained in accordance with the latest RUS Bulletin 169 4 and or the latest edition of the American National Standards Institute ANST Standard C84 1 The ANSI Standard defines Range A and Range B voltage limits as follows Range A Service Voltage Electric supply systems shall be so designed and operated that most service voltages are within the limits specified for this range The occurrence of service voltages outside these limits is to be infrequent Range Utilization Voltage User systems shall be so designed and operated such that with service voltages within Range A limits most utilization voltages are within the limits specified for this range Utilization equipment shall be so designed and rated to give fully satisfactory performance throughout this range Rang
14. of inrush operations starts that is acceptable for the associated flicker level e Time Period In combination with Inrush Interval specifies the period length for the number of inrush operations starts that is acceptable for the associated flicker level Flicker Inputs the Acceptable Flicker of a new database entry Inrushes Inputs the Inrush Frequency of a new database entry per First Box Inputs the Inrush Interval of a new database entry per Second Box Selects the Time Period of a new database entry 13 Selecting the Save button will enter the values from Voltage Flicker Level Entry into a new line in the database for use when calculating voltage flicker for entered circuit models Note The default data is based on a step curve showing lower acceptable levels for shorter time periods and higher acceptable levels for longer time periods It is possible to enter many different levels of acceptable flicker for various time periods Care should be taken when making these selections to verify that the appropriate flicker level is associated with the intended time period Selecting the Delete button will remove the highlighted selection from the database Selecting the Done button will exit the Acceptable Flicker Levels box 4 8 2 Motors and Other Equipment To edit the motors and other equipment database select Motors amp Other Equipment from the Edit Data option under the Tools menu After entering the administr
15. phase open delta In addition transformers are only allowed one location with no parallel connections 6 3 Fault Calculations The DSC makes fault calculations with the assumption that the primary impedance is zero This technique will always give a higher fault current value than actually possible but this is a standard industry practice for finding worst case values Another assumption is that all current returns through the neutral conductor 6 4 Load and Voltage Drop Calculations load and voltage calculations are based upon the users selection of an industry standard base voltage The voltage is defined at the transformer which is always considered to be a balanced voltage source with a positive phase sequence clockwise rotation The neutral at the transformer is also considered to be the ground reference point for the secondary system being analyzed As with the fault calculations all the current is assumed to return through the neutral conductor One final note is that the DSC makes these calculations assuming a steady state for all load values 26 7 CONCLUSION The DSC represents a collaborative effort between Patterson amp Dewar Engineers Inc P amp D and the TVPPA to aid member staking technicians in the selection and analysis of electrical facilities Every effort has been made to fully explain the functionality of the DSC and anticipate and anticipate likely questions Should users have questions that are n
16. these days primarily due to economics so the absence of this de rating function does not extensively limit the DSC s functionality Customer loads that include either electronic equipment or drives that could promote harmonic distortion being injected into the power source can also contribute to equipment capacity overloads Such evaluation is beyond the scope of the DSC When such service circumstances arise the system engineer is encouraged to refer to the latest edition of IEEE Standard 519 entitled Recommended Practices for Harmonic Control in Electrical Power Systems for guidance Finally one other issue that should be addressed concerning load capacity is how the peak load varies with time The calculation of a load factor is an excellent method for analyzing this issue Monthly Load Factor MLF is calculated by dividing the total estimated kilowatt hours sold by the estimated peak kilowatt demand and then dividing that number by 730 hours the number of total hours in a month Conversely the Annual Load Factor ALF is determined similarly except annual quantities are used with 8 760 hours being available in a year Typical electric consumers on a utility have load factors that vary from 35 to 50 percent The equipment load capacities provided in the DSC are based on such load factors Consumers with load factors greater than these should be evaluated more closely by the system engineer to ensure that the equipment being specifi
17. transformer bank The first load is a Barn with a balanced three phase 30 load at a 0 85 power factor and an unbalanced single phase load with 5 at a 0 85 power factor on Leg 1 and 15 at a 0 85 power factor on Leg 2 The other load is a Farmhouse with a balanced single phase 25 kVA load at a 0 85 power factor The distance from either load to the node pole is 75 feet and the distance from the node pole to the pole mounted transformer bank is 50 feet With these type loads it is typical to see 120 240 V with a 4 wire scheme for the three phase single phase Barn and a 3 wire scheme for the single phase Farmhouse For the purposes of this example all facilities are assumed to be overhead Using the conditions above the kVA ratings for the three phase 120 240 V OH Closed Delta s lighting and power transformers must be calculated The calculations used by the DSC to determine the exact loading of each transformer in a Closed Delta bank are very complex and are dependent upon the impedances of the transformers as well as the size and type of loads For this reason a less accurate but simpler method of estimating transformer sizes is presented here C 11 Three Phase Closed Delta Example continued Creating the Circuit Model continued The easiest way to choose the rating of the lighting transformer needed is to meet the following condition 1 lighting xf mr rating gt 1 25 x total 1g load 3 x total 3g load G
18. used for providing three phase power in a delta or open delta bank Sometimes referred to as Kickers they are typically the smaller transformers in the bank Once all appropriate selections have been made select the Accept button to save the Transformer Properties The Cancel button can be selected at any time to exit the Transformer Properties box without saving the information Once a transformer has been placed nodes or loads can be placed and connected to the transformer 4 2 2 Nodes and Secondary To place a node activate the Node Tool by selecting the icon single click anywhere in the drawing space will place the node at that location and automatically open the Node Properties box Modify Node Properties X Secondary Wire Specifications Wire Description 4 0 AL TRIPLEX RN Selected Wire Capacity Amps Parallel Services Length ft 100 Source Tx Enter the Wire Length in Feet Node Input the specifications for the node using the available input boxes The following is a brief description for each of the input boxes Wire Description Selects the secondary wire connected to the node e Parallel Wire Sets Selects the number of complete secondary wire sets for the particular run of secondary e Length ft Selects the one way distance in feet for the particular run of secondary Source Node Selects the source feed node for the particular run of secondary W
19. 00 7 0 725 0 675 8 0 700 0 650 9 0 675 0 625 10 0 650 0 600 11 0 625 0 575 12 or more 0 600 0 550 MOTORS DATABASE MOTORS RATED PHASE RUNNING EFFICIENCY STARTING STARTING DESCRIPTION HP 1 3 CODE 1 4 HP 1PH MOTOR 0 25 1 0 68 0 65 0 25 M 1 3 HP 1PH MOTOR 0 33 1 0 69 0 66 0 25 M 1 2 HP 1PH MOTOR 0 50 1 0 71 0 68 0 25 L 3 4 HP 1PH MOTOR 0 75 1 0 73 0 70 0 25 L 1 HP 1PH MOTOR 1 00 1 0 75 0 72 0 25 J 1 1 2 HP 1PH MOTOR 1 50 1 0 77 0 74 0 25 J 2 HP 1PH MOTOR 2 00 1 0 79 0 76 0 25 J 3 HP 1PH MOTOR 3 00 1 0 81 0 78 0 25 H 5 HP 1PH MOTOR 5 00 1 0 85 0 80 0 25 G 7 1 2 HP 1PH MOTOR 7 50 1 0 85 0 80 0 25 G 10 HP 1PH MOTOR 10 00 1 0 85 0 80 0 25 G 15 HP 1PH MOTOR 15 00 1 0 85 0 80 0 25 G 20 HP 1PH MOTOR 20 00 1 0 85 0 80 0 25 G 25 HP 1PH MOTOR 25 00 1 0 85 0 80 0 25 G 1 HP 3PH MOTOR 1 00 3 0 63 0 74 0 25 N 1 1 2 HP MOTOR 1 50 3 0 66 0 75 0 25 M 2 HP 3PH MOTOR 2 00 3 0 69 0 77 0 25 L 3 HP 3PH MOTOR 3 00 3 0 73 0 79 0 25 K 5 HP 3PH MOTOR 5 00 3 0 77 0 81 0 25 J 7 1 2 HP 3PH MOTOR 7 50 3 0 79 0 83 0 25 H 10 HP 3PH MOTOR 10 00 3 0 81 0 84 0 25 G 15 HP 3PH MOTOR 15 00 3 0 82 0 85 0 25 G 20 HP 3PH MOTOR 20 00 3 0 84 0 86 0 25 G 25 HP 3PH MOTOR 25 00 3 0 85 0 87 0 25 G 30 HP 3PH MOTOR 30 00 3 0 85 0 87 0 25 G 40 HP 3PH MOTOR 40 00 3 0 86 0 88 0 25 G 50 HP 3PH MOTOR 50 00 3 0 87 0 8
20. 120 240 V 3a 120 240 V 12 Vess TVD 2 41 V 2 017 TVD 3 79 V 3 169 i 21 TVD BN 5 91 4 9236 TVD BN 5 25 V 4 379 AL TVD 8 32 V 3 47 TVD BC 4 72V 1 97 TVD 0 00 0 0095 Figure C 13 3 Phase Open Delta distribution system fully corrected C 16 TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX D Basic Equations 1 Power Triangle The Total Power in a distribution system is the combination of Real Power and Reactive Power components The Real Power is the component that results in a net transfer of energy in one direction or in laymen s terms it 15 the portion of the Total Power that does the work On the other hand the Reactive Power is the component due to stored energy which returns to the source on each cycle This is the portion of the Total Power that just takes up space or in other words reduces the capacity of a distribution system Distribution systems can inherently have Reactive Power which results in the need to have corrective equipment in the system to reduce the Reactive Power This in turn allows as much Real Power as possible to reach the load A distribution system that does not have any Reactive Power is the most efficient for energy transfer This is evident from the fact that the Total Power equals the Real Power in such systems The Power Triangle Total power S
21. 14 Three Phase Open Delta Example with Errors Then Corrected continued Correcting for Insufficient Capacity on the Conducting Wire The next problem to correct in this example is the overloaded conducting wire between the transformer and the node pole Fortunately increasing the wire size for capacity will also decrease the amount of voltage drop due to this piece of conducting wire Consequently the total voltage drop will also decrease and perhaps be reduced to acceptable levels After increasing the size of the conducting wire between the transformer and the node pole until its capacity could meet the demand it is found that the smallest conducting wire for this application is 250 MCM AL OH See Figure C 12 below for an illustration of the removal of the capacity warning seen in Figure C 10 However it should be noted that the total voltage drop still exceeds the 5 0 limit meaning the size of the conducting wire may have to be increased again Lighting TX 30 Open Delta 75 Power TX 30 Open Delta 25 120 240 V 120 240 V VD AN 1 7 4 1 45 VD BN 2 37 V 1 97 VD AB 4 10 V 1 71 VD BC 2 08 V 0 87 Power Factor 77 Power Factor B 1 00 Barn Farmhouse 120 240 V 3a 120 240 V 12 VEN TVD AN 2 63 V 2 20 TVD AN 4 01 V 3 34 4 TVD BN 6 68 V 5 57 TVD BN 6 02 V 5 02 TVD AB 9 32 V 3 88 TVD BC 5 04V 2 1095 TVD CA 0 00 V 0 0095 Figure C 12 Three Phase Op
22. 30 Wye Selects the availability Yes or No of a transformer for use in a circuit model with a three phase wye secondary transformer connection 30 Delta Selects the availability Yes or No of a transformer for use in a circuit model with a three phase delta secondary transformer connection 30 Open Delta Selects the availability Yes or No of a transformer for use in a circuit model with a three phase open delta secondary transformer connection Description Inputs Transformer Descriptions listed previously Select the Save button to enter the values into the database when calculating voltage drop voltage flicker and fault currents for entered circuit models Select the New button to clear the fields for the entry of a new transformer into the database Note The new entry will not be entered into the database until the Save button is selected The Delete button removes the highlighted selection from the database Selecting the Cancel button exits the user from the Edit Transformer Data box 19 5 METHODOLOGY AND INTERPRETING RESULTS 5 1 Methodology and Operational Parameters 5 1 1 Service Development Procedures The typical procedures or steps followed by an electric utility or power supplier to select and layout an electrical service for a new consumer generally fall into one of two categories Routine typical services and major non routine services Routine services refer mainly to ordinary day to day operat
23. 32 54 5 TON 3PH HVAC 4 50 3 0 90 0 90 0 25 48 20 7 1 2 TON HVAC 6 75 3 0 90 0 90 0 25 64 15 10 TON 3PH HVAC 9 00 3 0 90 0 90 0 25 75 88 15 TON 3PH HVAC 13 50 3 0 90 0 90 0 25 113 83 20 TON HVAC 18 00 3 0 90 0 90 0 25 151 77 25 TON HVAC 22 50 3 0 90 0 90 0 25 189 71 3 000 BTU 1PH HVAC 0 23 1 0 90 0 90 0 25 3 45 6 000 BTU 1PH HVAC 0 45 1 0 90 0 90 0 25 6 03 9 000 BTU 1PH HVAC 0 68 1 0 90 0 90 0 25 8 19 12 000 BTU 1PH HVAC 0 90 1 0 90 0 90 0 25 9 64 18 000 BTU 1PH HVAC 1 85 1 0 90 0 90 0 25 14 46 24 000 BTU 1PH HVAC 1 80 1 0 90 0 90 0 25 19 28 ACCEPTABLE VOLTAGE FLICKER LEVELS DATABASE ACCEPTABLE INRUSH INRUSH TIME FLICKER PERCENTAGE FREQUENCY INTERVAL PERIOD 1 096 1 6 SECONDS 1 596 1 1 MINUTES 2 096 1 4 MINUTES 3 096 1 30 MINUTES 3 5 1 1 HOURS 4 096 1 amp HOURS TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX C Sample Calculations Single phase Example and Comparison with Full Report House 1 120 240 V 12 2222 L TVD LL 7 78 V 3 24 TVD LN 3 30 V 2 75 12 100 120 240 VD LL 2 25 V 0 94 m VD LNI 1 02 V 0 86 VD LN2 1 22 V 1 02 Power Factor 0 85 House 2 120 240 V 12 L TYD LL 7 78 V 3 247 TVD LN 3 30 V 2 75 House 4 House 3 120 240 V 12 120 240 V 12 TYD LL 7 78 V 3 2 436 TYD LL 7 78 V 3 24 TVD LN1 2 79 V 2 32 T
24. 320 0 000032 160 1 0 SMALL AL UG TRIPLEX 2 0 AL UG TRIPLEX 0 000160 0 000030 0 000160 0 000030 180 2 0 SMALL AL UG TRIPLEX 2 0 AL UG TRIPLEX R N 0 000160 0 000030 0 000250 0 000031 180 2 0 SMALL AL UG TRIPLEX 4 0 AL UG TRIPLEX 0 000100 0 000029 0 000100 0 000029 240 4 0 SMALL AL UG TRIPLEX 4 0 AL UG TRIPLEX R N 0 000100 0 000029 0 000160 0 000030 240 4 0 SMALL AL UG TRIPLEX 250 MCM AL UG TRIPLEX R N 0 000085 0 000029 0 000130 0 000030 265 250 LARGE AL UG TRIPLEX 350 MCM AL UG TRIPLEX R N 0 000061 0 000028 0 000100 0 000029 320 350 LARGE AL UG TRIPLEX 500 MCM AL UG TRIPLEX R N 0 000043 0 000027 0 000061 0 000028 395 500 LARGE AL UG TRIPLEX 1 0 AL UG QUADRUPLEX 0 000200 0 000031 0 000200 0 000031 150 1 0 SMALL AL UG QUADRUPLEX 2 0 AL UG QUADRUPLEX 0 000160 0 000030 0 000160 0 000030 170 2 0 SMALL AL UG QUADRUPLEX 4 0 AL UG QUADRUPLEX 0 000100 0 000029 0 000100 0 000029 225 4 0 SMALL AL UG QUADRUPLEX 350 MCM AL UG QUADRUPLEX R N 0 000061 0 000028 0 000100 0 000029 305 350 LARGE AL UG QUADRUPLEX 500 MCM AL UG QUADRUPLEX R N 0 000043 0 000027 0 000061 0 000028 420 500 LARGE AL UG QUADRUPLEX 750 MCM AL UG QUADRUPLEX R N 0 000029 0 000026 0 000043 0 000027 495 750 LARGE AL UG QUADRUPLEX WIRE CAPACITY MULTIPLIERS DATABASE OF WIRE CAPACITY MULTIPLIERS SEC SERV WIRE SIZES WIRE SIZES RUNS 4 0 and smaller larger than 4 0 1 1 000 1 000 2 0 950 0 925 3 0 900 0 850 4 0 850 0 800 5 0 800 0 750 6 0 750 0 7
25. 3PH OH oo Qe 225 3PH UG 18 3 wire Yes 7 Wye Yes 52 3f Delta Yes 7 30 OpenDelta Yes 300 3PH 1 Description 25 1PH Data can be entered or edited by using the available input boxes The ratings that display initially are the ratings currently stored in the database The following is a brief description for each of the items in the box Transformer Descriptions Describe the basic characteristics of the transformer The DSC uses this field for selection purposes when creating a circuit model Size kVA Inputs the size of the transformer in R 96 Inputs the resistance of the transformer in percent X 90 Inputs the reactance of the transformer in percent Z 96 Inputs the total impedance of the transformer in percent Phase Selects the transformer s primary connection as either single phase 1 two phase 2 or three phase 3 Construction Type Selects the transformer s construction type as either overhead OH or underground UG No Load Losses W Inputs the watts consumed by the energized transformer without any load attached 1 2 Wire Selects the availability Yes or No of a transformer for use in a circuit model with a single phase 2 wire secondary transformer connection 18 103 Wire Selects the availability Yes No of a transformer for use in a circuit model with a single phase 3 wire secondary transformer connection
26. 9 0 25 G 60 HP 3PH MOTOR 60 00 3 0 87 0 89 0 25 G 75 HP 3PH MOTOR 75 00 3 0 88 0 90 0 25 G 100 HP 3PH MOTOR 100 00 3 0 88 0 90 0 25 G 125 HP 3PH MOTOR 125 00 3 0 88 0 90 0 25 G 150 HP 3PH MOTOR 150 00 3 0 88 0 91 0 25 G 200 HP 3PH MOTOR 200 00 3 0 88 0 91 0 25 G 250 HP 3PH MOTOR 250 00 3 0 89 0 91 0 25 G 300 HP 3PH MOTOR 300 00 3 0 89 0 92 0 25 G 350 HP 3PH MOTOR 350 00 3 0 89 0 92 0 25 G 400 HP 3PH MOTOR 400 00 3 0 89 0 92 0 25 G 450 HP 3PH MOTOR 450 00 3 0 89 0 92 0 25 G 500 HP 3PH MOTOR 500 00 3 0 90 0 93 0 25 G MOTOR STARTING CODE MULTIPLIERS MOTOR STARTING MULTIPLIER CODE A 3 14 B 3 54 3 99 D 4 49 E 4 99 F 5 59 G 6 29 H 7 09 J 7 99 K 8 99 L 9 99 M 11 19 N 12 49 P 13 99 R 15 99 S 17 99 T 19 99 U 22 39 OTHER EQUIPMENT DATABASE OTHER EQUIPMENT RUNNING PHASE RUNNING EFFICIENCY STARTING STARTING DESCRIPTION kW 1 3 kVA 1 TON 1PH HVAC 0 90 1 0 90 0 90 0 25 9 64 1 1 2 TON 1PH HVAC 1 35 1 0 90 0 90 0 25 14 46 2 TON 1PH HVAC 1 80 1 0 90 0 90 0 25 19 28 2 1 2 TON 1PH HVAC 2 25 1 0 90 0 90 0 25 21 38 3 TON 1PH HVAC 2 70 1 0 90 0 90 0 25 25 66 3 1 2 TON 1PH HVAC 3 15 1 0 90 0 90 0 25 29 94 4 TON 1PH HVAC 3 60 1 0 90 0 90 0 25 30 35 4 1 2 TON 1PH HVAC 4 05 1 0 90 0 90 0 25 34 15 5 TON 1PH HVAC 4 50 1 0 90 0 90 0 25 37 94 3 TON 3PH HVAC 2 70 3 0 90 0 90 0 25
27. C calculated fault currents are very conservative in nature System primary source impedance from the service transformer primary bushings to the source substation or delivery point has been ignored This means that the calculated fault current is higher than actual current conditions which allows for future electrical system changes The addition of closer substations delivery points up rated substations and up rated primary lines are among the changes possible Calculating the fault currents in this manner provides for a service design including the consumer s equipment that is impervious to major primary system changes and therefore is adequate for long term use Should the fault current level be determined marginal for customer use of standard service panel designs further review may be warranted Under such conditions the system engineer may review the available fault conditions by utilizing a means outside of the DSC The primary impedance can be added to the service impedance and this may lower the fault current to a level that would allow the customer to utilize standard less expensive service panels The system engineer is cautioned to revise the fault current level provided to the consumer only if it is determined that the primary system is very unlikely to be changed in the future 5 2 4 Voltage Flicker After calculating the voltage drop for a given defined service the voltage flicker can be calculated for any load point Befor
28. MCM CU OH 0 000027 0 000084 0 000027 0 000084 650 500 LARGE CU OH SINGLE 750 MCM CU OH 0 000018 0 000079 0 000018 0 000079 790 750 LARGE CU OH SINGLE 1000 MCM CU OH 0 000014 0 000076 0 000014 0 000076 920 1000 LARGE CU OH SINGLE 4 AL OH 0 000510 0 000110 0 000510 0 000110 120 4 SMALL AL OH SINGLE 2 AL OH 0 000320 0 000110 0 000320 0 000110 155 2 SMALL AL OH SINGLE 1 0 AL OH 0 000200 0 000100 0 000200 0 000100 200 1 0 SMALL AL OH SINGLE 2 0 AL OH 0 000160 0 000100 0 000160 0 000100 225 2 0 SMALL AL OH SINGLE 4 0 AL OH 0 000100 0 000095 0 000100 0 000095 290 4 0 SMALL AL OH SINGLE 250 MCM AL OH 0 000085 0 000092 0 000085 0 000092 320 250 LARGE AL OH SINGLE 350 MCM AL OH 0 000061 0 000088 0 000061 0 000088 385 350 LARGE AL OH SINGLE 500 MCM AL OH 0 000043 0 000084 0 000043 0 000084 465 500 LARGE AL OH SINGLE 750 MCM AL OH 0 000029 0 000079 0 000029 0 000079 580 750 LARGE AL OH SINGLE 1000 MCM AL OH 0 000022 0 000076 0 000022 0 000076 670 1000 LARGE AL OH SINGLE 6 AL OH DUPLEX 0 000810 0 000036 0 000810 0 000036 70 6 SMALL AL OH DUPLEX 4 AL OH DUPLEX 0 000510 0 000034 0 000510 0 000034 90 4 SMALL AL OH DUPLEX 4 AL OH TRIPLEX 0 000510 0 000034 0 000510 0 000034 90 4 SMALL AL OH TRIPLEX 2 AL OH TRIPLEX 0 000320 0 000032 0 000320 0 000032 120 2 SMALL AL OH TRIPLEX 2 AL OH TRIPLEX R N 0 000320 0 000032 0 000510 0 000034 120 2 SMALL AL OH TRIPLEX 1 0 AL OH TRIPLEX 0 000200 0 000031 0 000200 0 000031 160 1 0 SMALL AL OH TRIPLEX 1 0 AL OH TRIPLEX
29. R N 0 000200 0 000031 0 000320 0 000032 160 1 0 SMALL AL OH TRIPLEX 2 0 AL OH TRIPLEX 0 000160 0 000030 0 000160 0 000030 185 2 0 SMALL AL OH TRIPLEX 2 0 AL OH TRIPLEX R N 0 000160 0 000030 0 000250 0 000031 185 2 0 SMALL AL OH TRIPLEX 4 0 AL OH TRIPLEX 0 000100 0 000029 0 000100 0 000029 245 4 0 SMALL AL OH TRIPLEX 4 0 AL OH TRIPLEX R N 0 000100 0 000029 0 000160 0 000030 245 4 0 SMALL AL OH TRIPLEX 1 0 AL OH QUADRUPLEX 0 000200 0 000031 0 000200 0 000031 140 1 0 SMALL AL OH QUADRUPLEX 2 0 AL OH QUADRUPLEX 0 000160 0 000030 0 000160 0 000030 160 2 0 SMALL AL OH QUADRUPLEX 4 0 AL OH QUADRUPLEX 0 000100 0 000029 0 000100 0 000029 210 4 0 SMALL AL OH QUADRUPLEX 8 CU UG 0 000790 0 000052 0 000790 0 000052 65 8 SMALL CU UG SINGLE 6 CU UG 0 000500 0 000051 0 000500 0 000051 80 6 SMALL CU UG SINGLE 4 CU UG 0 000320 0 000048 0 000320 0 000048 115 4 SMALL CU UG SINGLE 2 CU UG 0 000200 0 000045 0 000200 0 000045 155 2 SMALL CU UG SINGLE 1 0 CU UG 0 000130 0 000044 0 000130 0 000044 215 1 0 SMALL CU UG SINGLE WIRE CONSTRUCTION WIRE WIRE R C X C R N X N CAPACITY WIRE SIZE WIRE SIZE MATERIAL TYPE TYPE DESCRIPTION OHMS FT OHMS FT OHMS FT OHMS FT AMPS AWG CATEGORY CU OH UG S D T Q 2 0 CU UG 0 000100 0 000043 0 000100 0 000043 245 2 0 SMALL CU UG SINGLE 4
30. TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 Table of Contents TEXT Introduction Application Overview Software Installation 3 1 Hardware amp Software Requirements 3 2 Installation 4 Program Functions 4 1 Definitions and Symbology 4 2 Building Circuit Models 4 3 Saving Circuit Models 4 4 Opening Saved Circuit Models 4 5 Editing Existing Circuit Models 4 6 Running Calculations 4 7 Printing 4 8 Editing Databases 5 Methodology and Interpreting Results 5 1 Methodology and Operational Parameters 5 2 Interpreting Results 6 Assumptions and Limitations 6 1 General 6 2 Transformer Connections 6 3 Fault Calculations 6 4 Load and Voltage Drop Calculations 7 Conclusion ONA APPENDICES APPENDIX A Equal Employment Opportunity Statement amp Legal Notice APPENDIX B Database Tables APPENDIX C Sample Calculations APPENDIX D Basic Equations APPENDIX E Industry Service Voltage Standard Summary APPENDIX F TVA Flicker Limit Guideline APPENDIX G Acknowledgements amp References TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 1 INTRODUCTION The Distribution Secondary Calculator DSC was created by P
31. VD LNI 2 92 V 2 43 TVD LN2 4 99 V 4 16 TYD 4 87 V 4 069 Figure C 1 Single phase distribution system 120 240V with 100 kVA transformer and four 12 kVA houses as the load Creating the Circuit Model Herein describes the steps taken to create the circuit model shown in Figure C 1 above For a more in depth description of the process for creating your own circuit model please refer to section 4 of this manual First there are certain conditions pre defined such as the size of the load s which the designer cannot alter The conditions that are alterable will typically be the rating of the transformer and the size of the conducting material When creating the circuit model the components have to be input from the source to the load This simply means that the user must start with the transformer then go to the node if there is one and then finally describe the load itself Components may be changed or appended after the fact but the beginning process has the linear flow just prescribed The example illustrated above in Figure C 1 has the following unalterable conditions pre defined there are four houses with 12 kVA of load each and 0 85 power factors two of the houses have balanced loads and two of them have unbalanced loads the two houses with unbalanced loads both have 5 kVA in the first leg and 7 kVA in the second leg there is a pole node 100 feet from the transformer between it and the loads and from this pole n
32. a Delta or Open Delta circuit Note that both sets of inputs are used for four wire services in these circuits The main set is for the three phase portion of the load and the special set is for the single phase portion of the load See Load and Voltage Drop Calculations in the Assumptions and Limitations section for explanation Once all appropriate selections have been made select the Accept button to save the Load Properties The Cancel button can be selected at any time to exit the Load Properties box without saving the information Once a load has been placed more loads and nodes can be placed or the circuit can be analyzed 4 3 Saving Circuit Models To save a circuit model simply select Save or Save As under the File menu at the top left of the screen The DSC defaults to a Saved Projects folder located in the programs installation directory 4 4 Opening Saved Circuit Models A circuit model that has been previously saved can be opened by selecting Open under the File menu at the top left of the screen The Open Project box is displayed Navigate to the appropriate directory and select the desired saved circuit Selecting the Open button will open the selected circuit model Selecting the Cancel button will exit the Open Project box without opening a circuit model 4 5 Editing Existing Circuit Models Sometimes the need arises to edit an existing circuit model Once the circuit model to be edited is open it can be changed by m
33. actor entered This value can be added to other service component costs to determine the economical performance of the service For high load factor loads larger and higher capacity equipment can be justified to reduce losses and overall service costs 25 6 ASSUMPTIONS AND LIMITATIONS As with any computer software the DSC has its limitations To keep the software simple to use several assumptions and approximations have to be made However these assumptions and approximations do not appreciably affect the accuracy of the calculations In fact most are considered to be standard practices for simplifying calculations for everyday use The following subsections clarify the different assumptions and approximations used in the DSC 6 1 General First the DSC makes all calculations based upon a symmetrical system This means that items such as wire are considered to have the same impedance for each leg phase in a span Second variations of impedance for temperature air flow and other conditions are factored in with the equipment data contained in the database The default data uses a defined standard for conditions however the user has the ability to change or add data to account for non standard conditions if desired 6 2 Transformer Connections The DSC limits the transformer connections to commonly accepted industry standards These connections are single phase 2 wire single phase 3 wire three phase wye three phase delta and three
34. ad power factors are at 0 85 Creating the Circuit Model Problems to be Fixed Depicted above in Figure C 10 is a first attempt to set up an Open Delta distribution system circuit model For comparison purposes this distribution system services the same loads as those described earlier in the Closed Delta example presented in this appendix An examination of Figure C 10 shows several problems with this circuit model In any circuit model setup there are always three possible problems that might appear One is the overloading of a transformer The DSC will indicate this problem via a WARNING notice under the transformer s label notice the orange circled portion of Figure C 10 Another problem might be the overloading of conducting wire The DSC indicates this via a red WARNING label on the conducting wire s icon see red circle in Figure C 10 The last problem that may appear is excessive voltage drop The DSC indicates total voltage drops beyond the user input limit with asterisks next to the calculated total voltage drop TVD of the load s see purple circles in Figure C 10 For this example the limit was input as a 5 046 total voltage drop Correcting for Insufficient Transformer Capacity The first problem for correction in this example is the insufficient capacity of the transformer bank As for the Closed Delta bank the calculations used by the DSC to determine the exact loading of each transformer in an Open Delta bank
35. ad the smallest possible wire is a 350 MCM AL UG For the Minimart s 50 kVA load the smallest possible wire is a 1 0 AL UG Quadruplex C 10 Three Phase Closed Delta Example Barn 120 240 V 3a Lighting TX 3 2 Delta 75 kV A TVD 2 07 V 1 7 335 Power TX1 3 2 Delta 25 kVA LO TVD BN 5 80 V 4 84 Power TX2 32 Delta 25 kV A LEE TVD AB 7 87 V 3 28 120 240 V 120 240 V TVD BC 5 48V 2 289 VD 1 30 V 1 08 u TVD 3 55 V 1 489 VD BN 1 93 V 1 60 VD AB 3 23 V 1 349 VD BC 2 69 V 1 1295 VD 1 68 V 0 70 Power Factor 84 Power Factor B 71 Power Factor 99 Farmhouse 120 240 V 12 TVD 3 45 V 2 87 TVD BN 5 15 V 4 29 Figure C 9 Three phase Closed Delta distribution system with a 50 Lighting transformer and two 25 Power transformers one Barn with a balanced three phase 30 load and an unbalanced single phase load with 5 on Leg 1 and 15 on Leg 2 and one Farmhouse with a balanced 25 single phase load power factors are 0 85 Creating the Circuit Model Depicted above in Figure C 9 is an example of a three phase Closed Delta distribution system The process of creating this circuit model is basically the same as previously used with the single phase distribution system and the three phase Wye distribution system The pre defined conditions for this case are the load sizes and the distance of the loads from the
36. age at the point of load utilization and must be supplied within the design limits of the equipment being served Typically equipment is designed to operate at plus or minus ten percent of the equipment nameplate Two standards in the power distribution industry are the American National Standards Institute ANSI Standard C84 1 entitled Voltage Ratings for Utility Power Systems and Equipment and RUS Bulletin 169 4 entitled Voltage Levels on Rural Distribution Systems Appendix E summarizes these standards and guidelines and identifies the proper voltage levels that distributors and utilities are to maintain The design Range A voltage levels in the standards should be utilized when designing services Voltage drops through the transformer and through the secondary wires are proportional to the current through them Voltage is more of a driving force for service adequacy than capacity Typically service wires should be loaded less than 50 percent of full capacity to provide acceptable service voltage 21 5 1 2 3 Service Flicker Voltage drops refer primarily to continuous peak and worst case loading conditions Another voltage aspect that requires review is the voltage transient which is caused by inrush currents that result from motor starting capacitor switching variable speed drives and general large load switching Voltage fluctuation occurring in cycles of time is called flicker If it occurs at a high percentage of base v
37. are very complex and are dependent on the size and type of loads Therefore the same less accurate but simpler method of estimating transformer sizes is presented here This method is valid in this case since an Open Delta bank is basically the same as a Closed Delta bank with one of the Power transformers removed The estimates are considerably less conservative for the Open Delta bank but should be adequate in most cases C 13 Three Phase Open Delta Example with Errors Then Corrected continued Correcting for Insufficient Transformer Capacity continued As before the easiest way to choose the rating of the lighting transformer needed is to meet the following condition 1 lighting xfmr rating gt 1 25 x total 1g load 3 x total 3g load Given that in this example the total single phase load is 45 kVA and the total three phase load is 30 the lighting transformer needs to have a kVA rating of at least 68 75 kV A Also notice from Figure C 10 that the loading on BN of the transformer bank is 35 3 kVA This is the half winding load of the lighting transformer Due to the load unbalance the actual rating of the lighting transformer needs to be at least 70 6 twice the largest half winding load In any case the smallest standard size transformer that can be used has a rating of 75 As can be seen below in Figure C 11 a 75 lighting transformer has been chosen to meet this condition and the overl
38. ative password the Edit Motors and Other Equipment box will display Edit Motors and Other Equipment x Motor Properties Other Equipment Properties c eon y Internal ID 31 Intemal iD 33 20HP 3PH MOTOR 34 25 HP 3PH MOTOR 35 30HP 3PH MOTOR 36 40HP 3PH MOTOR 37 50HP 3PH MOTOR 38 3PH MOTOR 38 75 HP 3PH MOTOR 40 100HP 3PH MOTOR 41 125 HP 3PH MOTOR 42 150HP 3PH MOTOR 43 200HP 3PH MOTOR 44 250HP 3PH MOTOR 45 300HP 3PH MOTOR 46 350HP 3PH MOTOR 47 400HP 3PH MOTOR 48 450HP 3PH MOTOR PANUM Rated HP 110 Running kw Running PF josi Running PF Efficiency joss Efficiency i Starting PF 025 Starting Starting Code z Starting kV Phase Phase Description Description HP 3PH MOTOR Delete New Motor New Equipment Data be entered or edited by using the available input boxes The ratings that display initially are the ratings currently stored in the database The following is a brief description for each of the items in the box D Number assigned by the software to hold the data s place in the database Description Describes the basic characteristics of the equipment and is used for selection purposes when running voltage flicker calculations Type Identifies the equipment as either a motor M or other equipment O Motor Properties Internal ID Same as ID listed previous
39. atterson amp Dewar Engineers Inc P amp D for the Tennessee Valley Public Power Association TVPPA with the intent of aiding member system staking technicians in the selection and analysis of electric facilities in their day to day work Consumer owned utilities have been major contributors to the quality of life enjoyed by Tennessee Valley residents since the mid 1930s Local electric systems are more than utilities they are an active necessary part of the communities they serve The Valley s consumer owned power distributors have only one purpose to provide all ratepayers with the best energy services at the lowest possible cost consistent with sound business practices It is the sincere hope of P amp D that this software will aid member companies in fulfilling this purpose 2 APPLICATION OVERVIEW The DSC is stand alone Windows based personal computer PC software that calculates voltage drop voltage sag flicker and fault current from the secondary connections of distribution transformers to the load connections The DSC user can easily analyze balanced or unbalanced single phase and three phase systems for both overhead and underground construction The main benefits of the DSC follow below Easy to use and does not require detailed engineering knowledge User can print on screen results and save each scenario in a standard Windows file format e Contains database of standard specification data for equipment such as transfor
40. ay This box is a standard Windows style print setup box for selecting and specifying print options Selecting the OK button will display the Print Preview screen This is also a standard Windows style screen that allows the user to preview how the schematic will appear when printed If the preview is acceptable the user can print by selecting the Printer icon Close the Print Preview screen by selecting either the Close button or the x button Note Even though the schematic can be printed in portrait format landscape format is recommended 4 7 2 Printing Reports To print a report of the calculated results for the displayed circuit model select the Print Report option from the file menu The Page Setup box will display This box is a standard Windows style print setup box for selection and specification of print options Selecting the OK button will display the Print Preview screen This is also a standard Windows style screen that allows the user to preview how the report will appear when printed If the preview is acceptable the user can print by selecting the Printer icon Close the Print Preview screen by selecting either the Close button or button 12 4 8 Editing Databases The DSC uses five 5 different databases for modeling and calculating the data related to the entered circuit model Each database is user modifiable with the entry of an administrative password The administrative password is defaulted to DSC
41. cally Follow the on screen instructions If Microsoft NET Framework Version 1 1 with Service Pack 1 15 not already installed then the following advisory window will appear Windows Installer Loader This setup requires NET Framework version 1 1 4322 Please install NET Framework 4 and run this setup again The NET Framework can be obtained from the web Would you like to do this now Selecting the Yes button will open the Microsoft downloads website where the following two components can be downloaded and installed 1 NET Framework Version 1 1 Redistributable Package 2 NET Framework 1 1 Service Pack 1 1 If Setup does not run automatically then run Setup exe in the root directory of the CD to begin the installation process 2 If an Internet connection is not available the components can be installed from the CD The files are located in directories labeled in the same manner as shown above Once Microsoft NET Framework Version 1 1 with Service Pack 1 is installed running Setup will begin the installation of the DSC with the following screen TVPPA Secondary Calculator Software Welcome to the TVPPA Secondary Calculator Software Setup Wizard The next screen depicted below controls the installation directory and the user access of the DSC i TVPPA Secondary Calculator Software Select Installation Folder NN The next screen confirms the installatio
42. ce is the reactive component of impedance Conducting wires as well as other equipment in a distribution system have different levels of resistance and reactance associated with them For example a conducting wire of a specific length has more impedance than a conducting wire of the same material and a shorter length This equation shows that the total impedance has the same relationship to resistance and reactance as Total Power has to Real and Reactive Power D 3 8 Wire Resistance Lx Ohms inherent resistance of wire after its total length has been taken into consideration L Feet wire length per foot inherent resistance of wire as a function of length Often published in units of 2 per 1000 feet in reference tables NOTE This formula is equally applicable for computing the following parameters with the respective inputs exchanged Resistance of Neutral wire in Ohms Reactance of Wire in Ohms Reactance of Neutral wire in Ohms 9 Transformer Resistance y R R LT eae Tes xfmr mr X 100 000 Raga Q Ohms resistance of the transformer Rag numerical value given as a percentage to represent the transformer s resistance V V volts voltage rating of the secondary transformer kilovolt amps transformer s rating The purpose of this equation is to convert the typically given rated percentage impedance of the tran
43. d load is a Minimart with a balanced 50 kVA at a 0 85 power factor The distance from either load to the transformer is approximately 100 feet With these type loads it is typical to see underground conducting wire running from a three phase 120 208 V Wye pad mounted transformer with a 4 wire scheme Using the conditions above the rating for the three phase 120 208 V UG Wye transformer must be determined Given that the total load to be served from the transformer is 150 and then using the previously mentioned rule of thumb of a plus 25 safety factor a transformer rated at 182 5 15 required However in the utility industry there are no standard pad mounted transformers with such a rating Typically what is available are 225 or 300 rated transformers For the purposes of this example a 225 kVA three phase 120 208 V UG Wye transformer has been selected In this example the loads are connected directly to the transformer with two separate conducting wires Since one load is larger than the other it will more than likely require a larger conducting wire The same method as described earlier for the single phase distribution system is utilized start with small conducting wire run the Voltage Drop Calculation tool and re evaluate the components of the system until no problems are apparent From this method the conducting wires depicted in this example are determined For the Fast Food restaurant s 100 kVA lo
44. e 37902 A copy of the applicable TVA regulations may be obtained on request by writing TVA at the address given above LEGAL NOTICE This work was prepared by Patterson amp Dewar as a report of work sponsored by the Tennessee Valley Public Power Association utilizing funds provided by the Tennessee Valley Authority Neither TVPPA nor any member of TVPPA nor TVA nor any person acting on behalf of any of them a makes any warranty or representation express or implied with respect to the accuracy completeness or usefulness of the information contained in this report or that the use of any information apparatus method or process disclosed in this report may not infringe privately upon rights or b assumes any liability with respect to the use of or for damages resulting from the use of any information apparatus method or process disclosed in this report TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX B Database Tables TRANSFORMERS DATABASE CONSTRUCTION NO LOAD AVAILABLE SECONDARY CONNECTIONS TRANSFORMERS SIZE R X 7 PHASE TYPE LOSSES 1PH 1PH 3PH 3PH 3PH DESCRIPTION kVA 15259 OH UG 2 WIRE 3 WIRE WYE DELTA OPEN DELTA 10 kVA 1PH OH 10 1 6 1 4 2 1 1 OH 59 Y Y Y Y Y
45. e 4 Circuit Base Voltage 120 240 V Service Wire 1 2 0 AL OH TRIPLEX RIN 100 Current Leg 1 Leg 2 Neutral 42 58 17 PF1 85 Lag 2 85 Lag Voltage Drop Leg 1 Leg 2 Leg to Leg 0 25V 0 296 1 27V 1 196 1 52V 0 6 0 50 0 496 2 02V 1 796 2 52V 1 196 Fault Current Line to Line Line to Neutral 3 840 A 1 828 Flicker Maximum Threshold of 2 3 TON 1PH HVAC Flicker Starts On Load 1 2496 1 per Day 0 Denotes a value that has exceeded the recommended maximum voltage drop threshold of 5 96 Project Filename Example 1ph 120 240V correct scs Figure C 7 DSC Report page 5 Load 3 House 4 details with footnote that appears at bottom of every page of the report automatically Depicted above in Figures C 3 through C 7 is the DSC report for the circuit model shown in Figures C 1 and C 2 Two significant notes are 1 whether or not flicker analysis details will be printed and 2 whether the load 1s balanced or unbalanced Details from conducting a Flicker Analysis will be placed at the bottom of all pages in the report describing loads see circled portion of Figure C 4 above These details will only appear on the report if a Flicker Analysis is conducted for the circuit model before the report is printed If a load is balanced the Neutral column in the Current section of the report for that load will be zero However if a load is unbalanced the Neutral column will be something other than ze
46. e B Service and Utilization Voltages This range includes voltages above and below Range A limits that necessarily result from practical design and operating conditions on supply and or user systems Although such conditions are a part of practical operations they shall be limited in extent frequency and duration When they occur corrective measures shall be undertaken within a reasonable time to improve voltages to meet Range A requirements Insofar as practicable utilization equipment shall be designed to give acceptable performances in the extremes of this range of utilization voltage although not necessarily as good performance as in Range A Table 1 Voltage Ranges ANSI Standard C84 1 120 volt base Minimum Range Utilization Voltage Non lighting Loads including Service Utilization amp loads lighting Voltage Service Voltage A 108 110 114 126 B 104 106 110 127 Note Caution should be exercised in using minimum utilization voltage as in some cases they may not be satisfactory for the equipment served For example where existing 220 volt motors are used on 208 volt circuits the minimum utilization voltage permitted would not be adequate for the operation or motors E 1 Voltage Conditions continued 2 Basic RUS Recommended Design Criteria a Rural electric distribution systems should be designed and operated to meet the voltage level requirements of Range A in ANSI C84 1 1970 Users utilization electrical
47. e database Selecting the New button will clear the fields for the entry of new wire into the database Note The new entry will not be entered into the database until the Save button is selected Selecting the Delete button will remove the highlighted selection from the database Selecting the Cancel button will exit the Edit Wire Data box 4 8 4 Wire Capacity Multipliers To edit the wire capacity multipliers These multipliers are used to de rate the capacity of parallel runs of wire database select Wire Capacity Multipliers from the Edit Data option under the Tools menu After entering the administrative password the Wire Capacity Multipliers box will display HE Wire Capacity Multipliers Number of Runs Small Multiplier Large Multiplier 4 0 1 1 1 2 0 35 0 325 3 0 8 0 85 4 0 85 0 8 5 0 8 0 75 0 75 0 7 0 725 0 675 8 0 7 0 65 3 0 675 0 625 10 0 65 0 6 11 0 625 0 575 12 0 6 0 55 Runs j 2 Srnall Multiplier 0 6 New Delete Large Multiplier jn 55 Input the multipliers using the available input boxes The multipliers that display initially are the multipliers currently stored in the database The following is a brief description for each of the items in the box Number of Runs Corresponds to the number of parallel wire runs in a secondary service and is used for selection of the appropriate wire capacity multiplier when making calculations for an entered circuit model
48. e for use when calculating voltage flicker for entered circuit models Selecting the New Motor or New Equipment buttons will clear the appropriate properties fields for the entry of a new motor or piece of equipment into the database Note The new entry will not be entered into the database until the corresponding Save button is selected Selecting the Delete button will remove the highlighted selection from the database Selecting the Cancel button will exit the Edit Motors and Other Equipment box 15 4 8 3 Wire To edit the wire database select Wire from the Edit Data option under the Tools menu Upon entering the administrative password the Edit Wire Data box will display Edit Wire D ata Wire Descriptions lt lt 250 MCM AL OH 350 MCM AL OH 500 AL OH 750 MCM AL OH 1000 AL OH 6 AL OH DUPLEX 4 AL OH DUPLEX 4 AL OH TRIPLEX 2 AL OH TRIPLEX 1 0 AL OH TRIPLEX 2 0 4L OH TRIPLEX 4 0 AL OH TRIPLEX 2 AL OH TRIPLEX 1 0 AL OH TRIPLEX 2 0 AL OH TRIPLEX 4 0 AL TRIPLEX z Delete New Description 0 AL OH TRIPLEX Select the Wire Type Single Duplex Triplex Quadruplex Internal ID Do o mc n2 31488 00032 326 05 Capacity Amps fico Wire Size m 2 Wire Size Category Smal AL M Construction Type Wire Trip
49. e the calculation can proceed two service parameters must be defined the number of inrushes per time period and the percent of allowable voltage flicker A typical service may experience one inrush per 8 hour period and an allowable secondary voltage change or flicker percentage of 4 percent is not uncommon If the known inrush condition is predicted to occur less than once per day this level can be increased to 6 percent often with satisfactory results Obviously it is always understood that whenever inrush conditions create annoying conditions for a service s consumer s changes in service design may be warranted and or the consumer should consider ways of reducing the inrush level Flicker is perceived more by consumers having incandescent lighting and is generally annoying to consumers when the frequency of inrushes occurs multiple times a day 24 5 2 5 Economics After calculating voltage drop and peak loading for a given defined service one can determine the service losses in dollars per year The losses are broken down into individual service components e g transformers service wires each leg etc To calculate the losses the annual load factor and the average cost per kilowatt hour in dollars per year need to be input A report listing all the losses by individual components and total circuit losses is generated This dollar amount represents the annual estimated value of the losses at the cost indicated for the annual load f
50. ed The type of wire has two main aspects 1 type of material and 2 type of packaging for the wire s The type of material is usually an easy selection Copper has become very expensive so aluminum has all but replaced it in the utility industry as the preferred conducting wire As far as the packaging triplex conductor wire has been selected for this example to maintain the availability of both 120 and 240 V to each of the houses in this 3 wire system Although triplex is the typical for situations such as this single conductor wires might also be utilized in this application 1 The DSC does not compensate for load diversity therefore the user must take this into account when entering the load sizes For this example the assumption is made that the total load at any given time will be 48 12 for each of the 4 houses 2 Single phase Example and Comparison with Full Report continued Conducting Wire continued In an example such as this where there is a pole node between the loads and the transformer it is typical for the wire between the transformer and the pole node to be larger or at least the same size as the wire between the pole node and the loads The size for each conducting wire must be determined next Automatically choosing the largest conducting wire possible is usually not feasible due to availability expense and construction limitations The advantage of the DSC is that it aids in the selectio
51. ed background box with a warning note The warning note includes the calculated peak load amperes with the capacity amperes of the equipment referenced Equipment capacity limits are listed in Appendix B with the basic environmental conditions on which the capacities were determined Conditions that vary from that should be reviewed closely to ensure that equipment capacity levels are not exceeded Key conditions that may cause a variation of the capacities given in the appendix are ambient operating temperatures multiple conductor runs per phase in conduits and individual phase conductors in individual conduits especially metal conduits If ambient service conditions vary from the base the DSC user should de rate the equipment to fit the expected service conditions The DSC includes a de rating factor for multiple runs of conductors per phase The de rating factors used are given in Appendix B For per phase service conductors in individual conduits present another heat buildup problem In non metallic conduit there is very little heat buildup and conductor capacity does not need to be de rated except for general conduit installation Further de rating is necessary for metallic conduit Heat buildup from circulating currents in the conduit raises the operating temperature of the conductor Such de rating is beyond the scope of the DSC and should be handled directly by the system engineer Very few electric service providers utilize metallic conduit
52. ed can handle the high load factor load and that losses are carefully considered High load factor loads require special service designs considerations and specification especially transformers 23 5 2 2 Voltage Drops Electric service voltage standards e g ANSI Std C84 1 and RUS Bulletin 169 4 state that the service voltage at the customer service point typically utility meter under the Range A design standard should provide a voltage of no greater than 126 volts on 120 base and no lower than 114 volts The calculated voltage drop from the primary transformer bushings to the service point should not exceed 4 0 volts or 3 33 for loads with lighting or 6 0 volts or 5 0 for non lighting loads DSC provides the calculated voltage drop for each service component e g transformer and each service wire sections as well as the total drop to the various loads Drops greater than set levels are indicated with an asterisk The calculated drops of the components help the engineer or technician identify service portions that need to be revisited When designing services it should be understood that if marginal conditions result i e 10 of voltage drop limit further scrutiny is warranted Consumer loads are estimated quantities and if underestimated unsatisfactory service voltage may result Design engineers and technicians should be conservative in their designs to ensure long term service voltage 5 2 3 Fault Currents The DS
53. en Delta distribution system conducting wire overloading corrected C 15 Three Phase Open Delta Example with Errors Then Corrected continued Correcting for Total Voltage Drop TVD Finally the last problem in this example for correction is the reduction of the total voltage drop A good rule of thumb to follow here is that if multiple loads have an excessive voltage drop then the main supplying conductor wire should be the first suspect Further examination of Figure C 12 reveals that there is indeed some substantial voltage drop occurring across the line section between the transformer and the node pole Increasing the wire size will decrease this voltage drop If certain conditions of this example had been different i e the total voltage drop was excessive on only one of the loads then the individual service conducting wire could have been increased in size to fix the problem Depicted below in Figure C 13 is this example of an Open Delta distribution system after being fully corrected It turns out that increasing the size of the conducting wire between the transformer and the node to 500 MCM AL OH was needed to complete the process of correcting the problems in this system Lighting TX 30 Open Delta 75 kVA Power TX 3 2 Open Delta 25 kVA 120 240 V 120 240 V VD AN 1 74 V 1 45 VD BN 2 37 V 1 97 VD 4 10 V 1 71 VD BC 2 08 V 0 87 Power Factor 77 Power Factor B 1 00 Barn Farmhouse
54. h 120 volt base Voltage Voltage Levels Volts Spread Substation Regulated Bus with Regulator E fo Distribution Transformer Primary Terminals Adjacent to substation bus At end of line 8 Volt drop Service Connection Meter Socket At transformer nearest substation bus 118 At end of line 8 Volt drop on primary 114 118 Point of Consumer Utilization At transformer nearest to substation bus Lighting load 112 Non lighting loads At 8 volt drop on primary Lighting load 110 Non lighting load E 3 Voltage Conditions continued 4 Voltage input to Distribution Substations The voltage input to distribution substations should be kept within limits as follows a Substation voltages are kept within the design limits of the substation transformers and other equipment b The substation voltage regulator can maintain the voltages on its output bus within the limits given in the Table 3 4 TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX F TVA Flicker Limit Guideline TVA s Guidelines for Voltage Disturbing Loads Provides Guidelines For Evaluating The Impact of Disturbing Loads TVA Flicker Limit Curve As the frequency FLICKER LIMIT CURVE of variations 5 inerease the allowable limit decreases Note Limit Points at PCC No more voltage variation than Lower 4 096 Once Per Fight Hours 3 596 Once Per
55. hen all appropriate selections have been made select the Accept button to save the Node Properties The Cancel button can be selected at any time to exit the Node Properties box without saving the information Once a node has been placed other nodes or loads can be placed and connected to it 4 2 3 Loads and Services To place a load activate the Load Tool by selecting the icon A single click anywhere in the drawing space will place the load at that location and automatically open the Load Properties box Load Properties Single Phase Circuit X Description Load 0 Connect to Node fi Phase Connection 3 wire Parallel 100 Wire Description 1 AL OH TRIPLEX R N M Load Properties kva Balanced Total kva 20 85 z Source Phase Line 1 50 10 as j Line 2 50 10 85 fe gt wao 0 s s Single Phase Load Delta and Open Delta Only cvs Balanced Total 0 5 las 71 Line 1 0 0 5 fA x line2 0 0 85 a Ez Input the specifications for the load using the available input boxes The following is a brief description for each of the input boxes Description Used as a label for differentiating loads Defaults to the Load number starting at 0 Connect to Node Selects the source feed node for the load s service Phase Type Selects the load as e
56. ine to line voltage Q Ohms equivalent resistance of the transformer Q Ohms equivalent resistance of the conducting wire Ohms equivalent reactance of the transformer Q Ohms equivalent reactance of the conducting wire Fault Current Single phase Line to Neutral I F 1 LN Vin Ry Vin Tr 19 LN E _ 100 375 X Ryfmr Ry Ry 0 5 X Xyfmr A Amps single phase fault current of a line to neutral fault V volts line to neutral voltage Ohms equivalent resistance of the transformer OQ Ohms equivalent resistance of the conducting wire Ohms equivalent resistance of the neutral wire Q Ohms equivalent reactance of the transformer Ohms equivalent reactance of the conducting wire Ohms equivalent reactance of the neutral wire D 6 Fault Current Three phase 30 x Ry Xx fm Xw ls A Amps three phase fault current Vip V volts line to line voltage Q Ohms equivalent resistance of the transformer Ry Q Ohms equivalent resistance of the conducting wire X Q Ohms equivalent reactance of the transformer Xw Q Ohms equivalent reactance of the conducting wire Fault Current Three phase Line to Line IgsgLL EE X Ip 3g Amps fault current of a line to line fault in a three phase system Ira Amps th
57. ing wire is physical It is smaller and lighter than the non R N variety making it easier to install and maintain House 3 is the same as House 1 in every aspect except that it is an unbalanced load The total line to line voltage drop of both houses is equivalent at 7 78 V When analyzing the total line to neutral voltage drops distinctions can be seen between the balanced and unbalanced loads For the balanced load House 1 the load is 6 on each leg For the unbalanced load House 3 the first leg has a load of 5 while the second leg has a load of 7 The analysis shows that the first leg of House 3 has a lower line to neutral voltage drop than the first leg of House 1 and vice versa for the second leg House 3 and House 4 are unbalanced loads with the loading as described above for House 3 House 3 has 2 0 AL OH Triplex conducting wire while House 4 has 2 0 AL OH Triplex R N conducting wire In the case of unbalanced loads having the conducting wire with a reduced neutral does make a difference in the total voltage drop When comparing the second leg s total line to neutral voltage drop between House 3 and House 4 it is seen that House 4 the load with R N conducting wire has a larger voltage drop In some situations the larger voltage drop due to the reduced neutral could cause one leg to exceed the total allowable voltage drop limits Therefore it can be advantageous from an electrical standpoint to utilize the non R N varie
58. ions of a distributor and include applications such as residential farms street lighting small subdivisions and small commercial loads Major services are those required for large commercial industrial loads that merit more thorough engineering supervision and review The procedures or steps for each of these categories may vary between organizations but can be generally summarized as follows under the categories indicated Category A For Routine or Typical Services A System engineering establishes economic design criteria and standards for system construction A2 Designer estimates new consumer load requirements using guidelines established by distributor A3 Designer stakes service using most acceptable and best route A4 Designer selects equipment based on the system standards and may check other options that may be readily apparent A5 Service is released by System Engineering for construction Category B For Major on Non routine Services B1 System engineering estimates and validates the new consumer load B2 System engineering confirms adequacy of primary lines and substation capacity B3 System engineering with assistance from designer stakes service based on most acceptable and best route B4 System engineering reviews options for service and selects equipment based upon sound engineering and economic design criteria B5 Service is released by System Engineering for construction The DSC was p
59. ip in guiding this project DSC Project Subcommittee Adam Newcomb Appalachian Electric Cooperative Bruce Harvey Consultant Jerry Bailey Union City Electric System TVPPA Research amp Development Committee Alex Smith Humboldt Utilities Ben Crane City of Florence Utilities Charles Phillips Gibson Electric Membership Corporation Danny Caples Tippah Electric Power Association Greg Williams Appalachian Electric Cooperative Jack Suggs Oak Ridge Electric Department Jerry Bailey Union City Electric System Kevin Anderson Sand Mountain Electric Cooperative Lynn Robbins City of Oxford Electric Department Mark Kimbell Murfreesboro Electric Department Mark Wesson Chattanooga Electric Power Board Nick Fortson Athens Utilities Board Rick Windhorst Paducah Power System Rody Blevins Volunteer Energy Cooperative Tom Martin Warren Rural Electric Cooperative Corporation TVPPA Administration Roy G Satterfield Jr Chairman TVPPA Jack W Simmons President amp CEO TVPPA Doug Peters Director of Education and Training TVPPA Joshua Mabry Technical Services Engineer TVPPA References Chapman Stephen J Electric Machinery Fundamentals 274 ed New York McGraw Hill 1991 Fink Donald G and H Wayne Beaty Standard Handbook for Electrical Engineers 14 ed New York McGraw Hill 2000 Nilsson James W Electric Circuits 4 ed Reading Addison Wesley 1993 Short T A Electric Power Distributio
60. ither single phase or three phase and the construction type for the service as either overhead or underground Connection Selects the service connection of the load as either 2 wire or 3 wire for single phase and either 3 wire or 4 wire for three phase Wire Description Selects the service wire connected to the load Parallel Wire Sets Selects the number of complete service wire sets for the load Length ft Selects the one way distance in feet for the load s service kVA Amps Input Box Selects the units of the load size as either or Amps Defaults to Balanced Unbalanced Input Box Selects the load as either balanced or unbalanced Defaults to Balanced Total KVA Amps Inputs total size and power factor of balanced loads Displays the total size of unbalanced loads Line Phase Inputs individual line or phase size and power factor of unbalanced loads Labels indicate the line or phase identification and the percentage of the total load Displays the individual line or phase size and power factor of balanced loads e Source Phase Selects the source feed phase of the associated line for single phase loads in a three phase wye circuit Note There are two sets of load size inputs in the Load Properties box The first set is the main set of load inputs which is used for the majority of the load inputs The second special set of load inputs is used only when single phase loads are to be represented in
61. iven that in this example the total single phase load is 45 kVA and the total three phase load is 30 the lighting transformer needs to have a rating of at least 68 75 The smallest standard size transformer that can be used has a rating of 75 which is what was chosen for this example It should be noted that the 1 25 in the above equation 15 a safety factor for typical load unbalance and inrush If a severe unbalance is expected in a system then a larger transformer may be necessary Alternatively in some cases a smaller transformer can be utilized In any case the DSC will provide a warning for overloaded transformers The easiest way to choose the ratings of the power transformers needed is to meet the following condition total 3g load v3 Given that the total three phase load in this example is 30 kVA each power transformer should have a rating of at least 17 32 The smallest standard size transformer that can be used has a rating of 25 which is what was chosen for this example power xfmr rating gt The same method used previously is utilized start with small conducting wire run the Voltage Drop Calculation tool and re evaluate the components of the system until no problems are apparent Thus the conducting wires depicted in this example are determined For the conducting wire running between the transformer and the node pole the most reasonable size is found to be 350 MCM AL
62. lex Material Data can be entered or edited by using the available input boxes The ratings that display initially are the ratings currently stored in the database The following is a brief description for each of the items in the box e Wire Descriptions Describes the basic characteristics of the wire The DSC uses this field for selection purposes when creating a circuit model or smaller and Large for larger than 4 0 Internal ID Number assigned by the software to hold the data s place in the database R C Inputs the resistance of the energized conductor in ohms per foot X C Inputs the reactance of the energized conductor in ohms per foot R N Inputs the resistance of the neutral conductor in ohms per foot X N Inputs the reactance of the neutral conductor in ohms per foot Capacity Amps Inputs the electrical capacity of the energized conductor in amps Wire Size Inputs the AWG or MCM size of the energized conductor Wire Size Category Selects the size category of the energized conductor Small for 4 0 Material Selects the wire s material as either aluminum AL or copper CU Construction Type Selects the wire s construction type as either overhead OH or underground UG Wire Type Selects the wire as either Single Duplex Triplex or Quadruplex conductor Description Inputs Wire Descriptions listed previously 16 Select the Save button to enter the values into th
63. load in this example Since most transformers are of a standard size the designer would typically only have transformers with ratings of 50 75 or 100 available for this level of load In many cases the designer may only have a choice between 50 and 100 transformers for which the conservative choice would be a 100 transformer to accommodate the recommended safety factor For this example a 100 kVA transformer has been chosen to provide extra leeway with all the issues described above as well as the possibility of an expansion taking place in this neighborhood in the form of yet another house on this one transformer While such a possibility is atypical this scenario should be considered If the load exceeds the transformer rating the DSC will report an associated error allowing the designer to realize the problem and make the appropriate corrections by resizing the transformer Conducting Wire Once the transformer has been chosen it is time to select the conducting wire between the transformer and the loads As described earlier the pole node is located 100 feet away from the transformer so this defines the length of the conducting wire connecting the transformer to the pole node Likewise the length of the conducting wires running between this pole node and the individual loads is also pre defined at 100 feet each The length of the wire aside the type and size of wire must also be select
64. ly Motor Properties Rated HP Inputs the rated horsepower of a motor Motor Properties Running PF Inputs the running power factor of a motor Motor Properties Efficiency Inputs the efficiency of a motor Motor Properties Starting PF Inputs the starting power factor of a motor Motor Properties Starting Code Selects the NEC code letter of a motor 14 Motor Properties Phase Selects the motor as either single phase 1 or three phase 3 Motor Properties Description Inputs Description listed previously Other Equipment Properties Internal ID Same as ID listed previously Other Equipment Properties Running kW Inputs the running kilowatt rating of a piece of equipment Other Equipment Properties Running PF Inputs the running power factor of a piece of equipment Other Equipment Properties Efficiency Inputs the efficiency of a piece of equipment Other Equipment Properties Starting PF Inputs the starting power factor of a piece of equipment Other Equipment Properties Starting Inputs the starting of a piece of equipment e Other Equipment Properties Phase Selects the equipment as either single phase 1 or three phase 3 Other Equipment Properties Description Inputs Description listed previously Selecting the Save button will enter the values for the button s corresponding Motor Properties fields or Other Equipment Properties fields into the databas
65. mers conductors motors and HVAC systems that are typically encountered by an electric distributor In addition user defined equipment can be entered and stored e standard systems and voltages encountered by an electric distributor are available for analysis including paralleling conductors for secondary runs and services User modifiable default load power factor provided Power factor for entire system calculated and displayed with results User modifiable default values for power cost cents per kWh and annual load factors provided Losses for entire system calculated and displayed Graphic display of analyzed circuit shown with input information and requested results Units for inputs and results are volts amps KW and percentage of base value e Industry standard data provided and compared to calculated results to determine if the results are within industry standard limits This includes electrical limitations for equipment Results of the comparison displayed on the standard output screen 3 SOFTWARE INSTALLATION 3 1 Hardware and Software Requirements Pentium or higher Windows XP Not tested on other operating systems Adobe Acrobat Reader 7 0 or higher For viewing Manual Microsoft NET Framework Version 1 1 with Service Pack 1 Recommended minimum display resolution of 1024 by 768 pixels Display DPI setting of Normal 96 DPI 3 2 Installation Insert the CD into a CD drive Setup will run automati
66. mers wiring meter or entrance g 4 3 33 switch Utility service delivery point meter or entrance switch to consumers utilization terminal outlet Loads including Lights 4 3 33 90 Non lighting Loads 6 5 00 90 E 2 Voltage Conditions continued 3 Basic RUS Recommended Operating Conditions Voltage level and limit values are based on the following a The outgoing substation voltage is regulated by a suitable voltage regulator as defined in Section A Substations of this exhibit b Theregulator voltage band width setting does not exceed two volts on a 120 volt base c Voltage values used are at the center of the voltage regulator band width d All voltage regulators whether at the substation or out on the line have properly set and functioning line drop compensation LDC e Only sustained voltages apply to these levels and limits The flicker and variations caused by motor starting equipment switching variation of voltage within the voltage regulator band width and similar short duration variations are not considered f Refer to RUS Bulletin 169 27 Voltage Regulator Application On Rural Distribution Systems for detailed guidelines on voltage regulator installation and appropriate settings for voltage level bandwidth time delay range of regulation and line drop compensation LDC Table 3 Voltage Level Limits and Spread for Rural Electric Distribution Systems Measured at center of regulator bandwidt
67. mpedance of transformer Voltage Drop Transformer Three phase Vaoxfmr v3 Zxfmr Vasoxinr V Volts phase voltage drop across the 30 transformer I Amps phase current flowing through the 3g transformer Z4 Q Ohms total phase impedance of transformer Voltage Drop Conducting Wire Single phase Va4aow 2 x I x Zw Vaw V volts voltage drop across the conducting wire for single phase loads I A Amps current going through the conducting wire Zw Q Ohms total equivalent impedance of the conducting wire Voltage Drop Conducting Wire Three phase X I X Zw Vasow V volts voltage drop across the conducting wire for three phase loads I A Amps current going through the conducting wire Zw Q Ohms total equivalent impedance of the conducting wire D 5 11 Fault Current Calculating the fault current under various conditions aids the customer in choosing adequate fault interrupting protection As will be described below there are several different types of faults that can occur on the energized line Therefore all must be considered and the worst case scenario determined See Section 5 1 2 4 amp 5 2 3 in the main text for more information Fault Current Single phase Line to Line I F 1 LL 7 Vit 3 Ran R Ww Xj mr B Xw V IrioLL pee e Rip 2 X Rw Xxfmr 2 Xw A Amps single phase fault current of a line to line fault V volts l
68. n Handbook Boca Raton CRC P 2004 Southwire Company Overhead Conductor Manual 2 ed Carrollton Southwire 2007
69. n of the DSC TVPPA Secondary Calculator Software NN Ei gt Confirm Installation The installer is ready to install Secondary Calculator Software on your computer Click Next to startthe installation Cancel Back The final screen shows successful completion of the installation i TVPPA Secondary Calculator Software lo xi Installation Complete A Secondary Calculator Software has been successfully installed Click Close to exit Please use Windows Update to check for any critical updates to the NET Framework Congratulations The installation process is complete 4 PROGRAM FUNCTIONS 4 1 Definitions and Symbology 4 1 1 Definitions Element A digital representation of a physical piece of equipment Circuit Model The digital representation of a physical circuit defined by individual elements Parent The element that is at the source end of a secondary wire or service Child The element that is at the load end of a secondary wire or service Transformer Element used to represent a transformer or transformer bank Node Element used to represent a wire junction point such as a pole or pedestal The element itself has no electrical characteristics Load Element used to represent a meter point and simulate the actual amount of current drawn at that point Schematic The graphical representation of a physical circuit Wire Run A set
70. n of the most appropriate conducting wire for the application with tools like the Voltage Drop Calculation The Voltage Drop Calculation tool will display possible problems with a circuit model due to undersized components Using the methodology of starting at the smallest sized triplex AL OH UG is also applicable but for demonstration purposes this example is overhead conducting wire and then running the DSC s Voltage Drop Calculation each component s size can be re evaluated and adjusted based upon what kind of problems the DSC describes Typical problems seen are current through the conducting wire exceeding rated capacity or total voltage drop from the transformer to the load exceeding acceptable industry standards The end result of the type and size of conducting wire chosen for this example can be seen above in Figure C 1 Between the transformer and the pole node is 4 0 AL OH Triplex and between the pole node and the loads are varying forms of 2 0 AL OH Triplex This example utilizes reduced neutral R N wiring to some of the loads to demonstrate the differences in voltage drop that will be discussed below in the Comparison section Demonstration of Flicker Analysis House 1 3 TON 120 V Flicker 2 47 5 93 V 100 Acceptable Flicker 4 4 8V 120 240 V Single Phase Flicker 0 29 0 7 V House 2 Flicker 1 24 2 97 V House 4 House 3 Flicker 1 24 2 97 V Flicker 1 24 2 97 V Figu
71. oading problem on the transformer has been remedied Even though the transformer overloading was corrected in this example with a larger lighting transformer for demonstration purposes the process of estimating the Power transformer rating is presented Also as before the easiest way to choose the ratings of the power transformer needed is to meet the following condition total 3g load v3 Given that the total three phase load in this example is 30 the power transformer should have a rating of at least 17 32 The smallest standard size transformer that can be used has a rating of 25 kVA which is what was chosen for this example power xfmr rating gt Lighting TX 32 Open Delta 75 Power TX 3 2 Open Delta 25 kVA 120 240 V 120 240 V VD 1 74 V 1 4595 VD BN 2 37 V 1 97 VD AB 4 10 V 1 7195 VD BC 2 08 V 0 87 Power Factor A e7 4 0 AL OH QUADRUPLEX 50 Power Factor B 1 00 VD AN 0 58 0 48 VD BN 1 33 1 61 VD AB 2 51 1 04 VD BC 0 32 0 38 XXXXX WARNING Circuit Amps 294 Wire Capacity 210 Amps Barn Farmhouse 120 240 V 3 2 120 240 V 12 j cl e TVD 2 40 V 2 00 TVD 3 77 V 3 1495 1 46 TVD BN 6 41 V 5 34 TVD BN 5 75 V 4 79 ZEE TVD 8 81 V 3 67 BC 4 19V 1 75 TYD 0 00 V 0 0095 Figure C 11 Three Phase Open Delta distribution system transformer overloading corrected C
72. ode the four houses are each located 100 feet away C 1 Single phase Example and Comparison with Full Report continued Transformer Given these starting conditions the user may choose design the transformer that will be adequate for these demands Whether there is single phase and or three phase power available in the system it is determined from the transformer However the types of load that are being supplied will have their own set demands on which type of phasing and voltage is preferred The typical house is a single phase 120 240 V load Therefore this example uses a transformer with these parameters The next step is choosing the rating of the transformer With four houses at 12 a piece the summed total power would be 48 kVA Ideally there are no variations spikes flicker or unbalanced loads and a transformer with a rating of 48 KVA could be chosen Since ideal circumstances are rare load variations demand spikes due to household appliances and unbalanced loads are everywhere The designer must take all this into account With these factors in mind there are a few generic rules of thumb that can be followed In a case such as this where the summed total power has been determined to be 48 kVA the rating of the transformer should equal the total load plus a safety factor that is 15 to 25 of the total load Using a 25 safety factor the rating of the transformer would need to be 60 to serve the
73. odeled Phase Selects the equipment as either single phase 1 or three phase 3 Equipment Voltage Selects the operating voltage of the equipment Equipment Description Selects the type and size of the equipment The available selections are from the database If the desired equipment is not available for selection then it must be added to the database See the Editing Databases section of this manual Inrush Frequency Inputs the number of inrush operations starts that the equipment has in a specified period per Selects the time period second minute hour or day for which the Inrush Frequency is to occur Selecting the Calculate button will calculate and display the voltage flicker levels for the circuit model Selecting the Cancel button will exit to the previous mode without calculating any voltage flicker levels 11 4 7 Printing 4 7 1 Printing Schematics To print the schematic for the displayed circuit model select the Print Schematic option from the file menu The Project Information box will display Title Block Information Entry Project Information Name Title Technician Company Electric Company Phone 123345578980 0 7 email jdoe elec_comp com This information is optional however whatever is input will be printed in the title block of the schematic Once the accept button is selected the Page Setup box will displ
74. of secondary or service wires that include one 1 wire each per phase or leg and neutral 4 1 2 Symbology The DSC utilizes different graphical symbols to represent a secondary electrical circuit The following is a list of the different symbols used for representing a model m Single phase overhead transformer Single phase underground transformer e Three phase overhead wye or closed delta transformer bank e Three phase overhead open delta transformer bank e Three phase overhead transformer o EX Three phase underground transformer e e Node Load Wire 4 2 Building Circuit Models As with any electrical analysis software the DSC must first have a digital representation of the secondary electrical circuit that needs to be analyzed This digital representation is called a circuit model The DSC utilizes a combination of graphics input boxes and databases to build a circuit model 4 2 1 Transformers The first step in building a circuit model is to place the transformer Activate the Transformer Tool by selecting the icon single click anywhere in the drawing space will place the transformer at that location and automatically open the Transformer Properties box Transformer Properties Transformer Properties Phase Type Secondary Connection 3 Wire m Nominal Secondary Voltage 20 240 nd Actual Secondary Voltage No Load i 25 250 Numbe
75. oltage lighting and equipment functions will be impacted causing irritation and annoyance to the consumer Flicker allowances are a function of the percent voltage fluctuation and frequency in occurrence The number of consumers served from the primary source feeder is also a factor IEEE Standard 141 discusses and defines the general limitation of flicker that should be followed The default voltage fluctuation limits used in the DSC are those established by TVA They are summarized in Appendix F as well as other industry standards levels As stated earlier these default values can be changed at the discretion of the user 5 1 2 4 Fault Duty When finalizing the configuration of a service the maximum available fault current at the service entrance is information the consumer needs Typically the consumer installs the service panel at his or her home or business That service panel with its main and circuit breakers should have fault interrupting capability greater that the available fault current at the service entrance Residential service panels rated with 200 amperes continuous generally have mains and circuit breakers capable of interrupting fault currents of 10 000 amperes or less Fault current calculations for such typical services are generally not requested by consumers However services requiring higher continuous current capacity generally have higher available fault currents In these situations the consumer often requests that the
76. ot addressed herein please forward any inquiries to Tennessee Valley Public Power Association TVPPA 423 756 6511 Doug Peters Joshua Mabry dpeters tvppa com jmabry tvppa com 27 TENNESSEE VALLEY PUBLIC POWER ASSOCIATION TVPPA Chattanooga Tennessee DISTRIBUTION SECONDARY CALCULATOR Project No DSC 1 APPENDIX A Equal Employment Opportunity Statement amp Legal Notice EQUAL EMPLOYMENT OPPORTUNITY STATEMENT This program is supported by assistance from the Tennessee Valley Authority TVA a Federal Agency Under Title VI of the Civil Rights Act of 1964 Section 504 of the Rehabilitation Act of 1973 the Age Discrimination Act of 1975 and applicable TVA regulations at 18 CFR pts 1302 1307 and 1309 no person shall on the grounds of race color national origin handicap or age be excluded from participation in be denied the benefits of or otherwise be subjected to discrimination under this program In addition no qualified handicapped person shall on the basis of handicap be subjected to discrimination in employment including hiring under the program If you feel you have been subject to discrimination as described above you or your representative has the right to file a written complaint with TVA not later than 90 days from the date of the alleged discrimination The complaint should be sent to Tennessee Valley Authority Office of Equal Employment Opportunity 400 Commerce Avenue Knoxville Tennesse
77. oving adding deleting or modifying the circuit elements To move an element hover the pointer over the element Left click and hold while moving the pointer The element will move with the pointer until the button is released where the element will be placed in the new location Note The DSC does not adjust wire lengths automatically so movement of elements is simply for the convenience and preference of the user Nodes and Loads can be added as described in the Building Circuit Models section Transformer locations cannot be added due to the one 1 transformer limitation See Limitations section An existing element s data be modified by either double clicking the element symbol or right clicking on the element symbol and selecting the Modify option The element s properties box will open as described in the Building Circuit Models section However all fields may not be available for modification depending on the element and circuit configurations See the Limitations section for more information To delete an existing element right click on the element symbol and select the Delete option A delete confirmation box will open Select Yes to delete the element or No to cancel the deletion Note Only elements that do not have children attached can be deleted 4 6 Running Calculations The DSC will calculate voltage drops fault currents and voltage flicker levels for an entered circuit model 4 6 1 Calculating Voltage Dro
78. ps VD To calculate voltage drops for the displayed circuit model select the icon The Maximum Acceptable Voltage Drop box will display A percentage value for the maximum acceptable voltage drop must be entered This value defaults to the ANSI standard of 5 096 and is used for comparison to the calculated values The results of this comparison are used to notify the user of potential excessive voltage drops in the circuit model Selecting the Accept button will calculate and display the voltage drops for the circuit model Selecting the Cancel button will exit to the previous mode without calculating any voltage drops 4 6 2 Calculating Fault Currents To calculate fault currents for the displayed circuit model select the FE icon The calculated maximum available fault currents at the transformer and at each load will display 10 4 6 3 Calculating Voltage Flicker FL To calculate voltage flicker for the displayed circuit model select the icon The Calculate Voltage Flicker box will display Calculate Voltage Hicker x Load Number 0 Phase 1 Equipment Voltage 240 Equipment Description 3 TON 1PH HVAC Inrush Frequency Input the specifications for the voltage flicker causing equipment using the available input boxes The following is a brief description for each of the input boxes Load Number Selects the load at which the equipment is to be m
79. r of Transformers m Transformer s 100 Lighting Transformer 21 Power Transformer s E E Click Accept to save the changes Input specifications for transformer using available input boxes The following is a brief description of each of the input boxes Phase and Type Selects the transformer as either single phase or three phase and the construction type as either overhead or underground Secondary Connection Selects the secondary side connection of the transformer as either 2 wire or 3 wire for single phase and either wye delta or open delta for three phase Nominal Secondary Voltage Selects the ANSI standard voltage for the selected secondary connection Voltages divided with a represent Line to Neutral voltage followed by Line to Line voltage Actual Secondary Voltage No Load Selects the actual voltage at the secondary connections of the transformer if measured with no load attached Number of Transformers Selects the number of transformers needed for the selected secondary connection Transformer s Selects sizes for single transformers and transformers included in a symmetrical bank Lighting Transformer Selects the size of the transformer that provides single phase power in a delta or open delta bank Typically the largest transformer in the bank Power Transformer s Selects the size of the transformers that are
80. re C 2 Single phase 120 240V system with flicker due to HVAC on House 1 Depicted above in Figure C 2 is a demonstration of flicker analysis For more information about flicker please refer to Section 5 1 2 3 of this manual In this case a 3 ton single phase HVAC unit is turning on at a frequency of once a day on House 1 As can be seen the flicker affects all four house loads in this system but the house that directly utilizes the HVAC unit has the worst flicker Fortunately a unit of this size with this starting frequency does not cause extreme flicker in this system and remains within Acceptable Flicker levels C 3 Single phase Example and Comparison with Full Report continued Comparison of Utilizing R N Conducting Wire with Balanced and Unbalanced Loads The purpose of the four house loads in this example is to provide a comparison between balanced and unbalanced loads as well as R N versus non R N conducting wire This comparison is depicted in Figure C 1 above after utilizing the DSC s Voltage Drop Calculation tool House 1 and House 2 are balanced loads of 12 with 0 85 power factors House 1 has 2 0 AL OH Triplex conducting wire while House 2 has 2 0 AL OH Triplex R N conducting wire As can be seen from the lack of difference between the total voltage drops utilizing either R N or non R N conducting wire to supply a balanced load provides the same electrical characteristics However the advantage of utilizing R N conduct
81. ree phase fault current NOTE This fault current is linearly related to the three phase fault current already described above Fault Current Three phase Line to Neutral Vin Ip3o LN REEL Rxfmr T Ry Xx fm Xw Xy Igsoiw A Amps fault current for a line to neutral fault in a 3 phase system V volts line to neutral voltage Ohms equivalent resistance of the transformer Rw Ohms equivalent resistance of the conducting wire Ry Q Ohms equivalent resistance of the neutral wire Q Ohms equivalent reactance of the transformer Xy Q Ohms equivalent reactance of the conducting wire Xy Q Ohms equivalent reactance of the neutral wire D 7 12 Annual Load Factor kWh ALF ___ 8760 x kW ALF Annual load factor ranging from 0 to 1 with a typical value of approximately 0 5 or 50 kWh kWh kilowatt hours the total amount of kilowatt hours consumed that year kW kilowatt the peak value of kilowatt consumption as it occurred that year The 8760 multiplier stems from the total amount of hours in a given year For a leap year this multiplier changes to include the extra day The annual load factor is a useful ratio for comparing the usage to the peak of kilowatt hours in a given year This ratio also becomes useful in the equations to be discussed below and eventually in determining annual losses 13 Loss Factor LF 0 84 x ALF 0 16 x
82. rimarily developed to aid system engineers and technicians in completing Steps Al A4 and B4 Following each step identified above 15 critically important Service design 15 an art that requires solid tools reliable data and proven experience Properly researched estimates and sound judgment are equally important factors 20 5 1 2 Operational Parameters When determining the adequacy of a distribution secondary system five operational parameters must be evaluated Those parameters are Load capacity Service voltage Service flicker Fault duty Economics Selecting the appropriate equipment to meet the estimated service load requirements will result in reliable satisfactory electric service at a reasonable and economical cost for both the power supplier and the consumer 5 1 2 1 Load Capacity Load capacity refers to the capability of the service transformer and secondary wire to handle the estimated peak load conditions for a defined load factor and a defined environmental condition e g summer versus winter peaks overhead versus underground direct buried or in conduit total electric or electric and gas Transformers and secondary wire or cable are current limited equipment that must not be operated above their design limits Operation above the design limits will result in equipment failure costly repair and rework and significant power outages to the consumer 5 1 2 2 Service Voltage Service voltage refers to the volt
83. ro as shown by the circle in Figure C 6 above C 9 Three Phase Wye Example Fast Food 120 208 32 TVD 4 14 V 3 4575 Wye 225 TYD BN 4 14 V 3 4575 120 208 V 120 208 v x TYD CN 4 14 V 3 45 et VD 2 12 V 1 7 6 VD LN mesxi TVD AB 7 17 V 3 45 VD BN 2 12 V 1 76 p wDLL 3 51 1 63 X TVD BC 7 17 V 3 4595 VD CN 2 12 V 1 76 TVD 7 17 V 3 45 VD AB 3 66 V 1 76 Power Factor 85 Lag VD BC 3 66 V 1 76 VD CA 3 66 V 1 7 6 ET U L Power Factors ABC 85 ve ite LIES S ms 15 2 16 Minimart 120 208 v 2 TYD AN 4 70 V 3 9232 TVD BN 4 70 V 3 92 Li TVD 4 70 V 3 92 TVD AB 8 15 V 3 92 TVD BC 8 15 V 3 92 TVD 8 15 V 3 9275 Power Factor 85 Lag Figure C 8 Three phase Wye distribution system with a 225 transformer one Fast Food restaurant load of 100 and one Minimart load of 50 Creating the Circuit Model Depicted above in Figure C 8 is an example of a three phase Wye distribution system The process of creating this circuit model is very similar to creating a single phase distribution system as discussed at the beginning of this appendix As with any situation there are certain pre defined conditions In this case those conditions are the load sizes and the distance of the loads from the transformer One load is a Fast Food restaurant with a balanced 100 kVA at a 0 85 power factor and the secon
84. sformer into an impedance with Ohms units The 100 000 multiplier in the denominator is a combination of two converting factors One factor is that 1000 must be multiplied to the rating of the transforming to convert it from to VA The other factor is that the percentage resistance of the transformer must be converted from percentage to decimal format by dividing by 100 These considerations must be taken into account in order to determine the resistance of the transformer in Ohms NOTE This formula is equally applicable for computing the following parameter with the respective inputs exchanged Xwar Transformer s reactance in Ohms Transformer s impedance in Ohms D 4 10 Voltage Drop Due to System Components In an energized distribution system there will be voltage drop due to the system s components themselves This will happen most noticeably with the transformer and the lengths of conducting wire between the source and the load Below are detailed equations for the various conditions when voltage drop due to these components will take place All equations utilize phasors for calculations just as the software does The results the software displays are displayed as magnitudes for ease of understanding Voltage Drop Transformer Single phase Va 1 xfmr 1 Zxfmr Va oxfar V Volts voltage drop across the 1g transformer I A Amps current flowing through the 19 transformer Zyjmr Q Ohms total i
85. ty of conducting wire when dealing with unbalanced loads However there still are the physical disadvantages of the larger and heavier wire that must be considered CA Single phase Example and Comparison with Full Report continued Report with Voltage Drop and Flicker Calculation Transformer 100 120 240 V 19 Circuit Line 1 Line 2 Line to Line Neutral 183 A 22 217 A 26 33 A 4 1 03V 0 9 1 22V 1 096 2 25V 0 996 Total Power Factor 1 85 Total Power Factor 2 85 Secondary Wire 1 4 0 AL OH TRIPLEX 100 Max Amps 245 Connects Node 110 TX Line 1 Line 2 Line to Line Through Current 183A 217A Wire VD 1 50V 1 396 2 51V 2 196 4 01V 1 7 Total VD 2 54V 2 1 3 73V 3 196 5 26V 2 696 Figure C 3 DSC Report page 1 transformer details C 5 Single phase Example and Comparison with Full Report continued Report with Voltage Drop and Flicker Calculation continued Load 0 House 1 Circuit Base Voltage 120 240 V Service Wire 1 2 0 AL OH TRIPLEX 100 Current Leg 1 Leg 2 50 A 50 A 1 85 2 85 Lag Voltage Drop Leg 1 Leg 2 Legto Leg 0 76 0 6 D 7 65V 0 6 1 52V 0 6 1 26 1 196 1 26 1 196 2 52V 1 196 Fault Current Line to Line Line to Neutral 3 840 A 2 104 A Flicker Maximum Threshold of 2 3 TON 1PH Flicker Starts OnLoad 2 47 1 per Day 0 Figure C 4 DSC Report page 2 Load 0 House 1 details
86. utility or distributor communicate what the maximum available fault current level is at the service point The DSC includes fault current calculation capabilities that provide the utility or service provider this information which allows the consumer to choose the adequate service entrance panel required 5 1 2 5 Economics When designing and establishing corporate standards for electric service economics are the driving force behind what equipment is specified A key economic consideration is the calculated losses of energy in the service equipment These losses are a function of the current going through the equipment the resistance in the equipment and how the load varies with time Annual line losses are determined by finding the square of the current times the equipment resistance times the annual load factor of the load times the cost per kilowatt hour The DSC provides this calculation which can be used by system engineers in establishing corporate standard and methods 22 5 2 Interpreting Results 5 2 1 Load Capacity The DSC determines that the service equipment transformer and service wires have adequate capacity to serve the estimated customer load Once the voltage drop calculation function is used the percent voltage drops are indicated for each phase If the transformer or service conductor capacities are adequate the calculations are shown in a green background box If the capacities are exceeded the prompt is shown in a r

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