Technical Information - Emerson Climate Technologies
Contents
1. amp Copeland Technical information EMERSON Climate Technologies Date of last update 02 08 Ref D7 10 2 1106 0208 E Application Engineering Europe STARTING METHODS AND UNLOADED START FOR SEMI HERMETIC COMPRESSORS 1 1 Ge R RS a or ae 2 2 1 Star Delta Starting Motor Code E Open transition iii 3 2 2 Star Delta Starting Motor Code E Closed Transition cccccccececececeeseeeseeceeeseaeeeeeeseeeeeeseauaeseeeeeeeeeseaaaaees 4 2 3 Part Winding Start Motor Types iii nene aa amana aaa 6 2 3 1 Part Winding Start 2 3 1 3 Motor Code A 6 2 3 2 Part Winding Start 3 5 2 5 Motor Code B A 7 2 4 Resistance Starting G ohasel ii nenea ana aaenaneaaaaa ee 7 2 4 1 Selection of Starting Resistors ii nenea nana aaa aa aaa 7 2 5 Other Method S ARN ERIN RO RR RPR RR N ea PRR RR N N NR RI PI N A IRI N RR 8 2 531 e leegen 8 2 5 2 Reactance Starting eee e eee ame ana aaa ananaaaaaaaaaa 9 2 5 3 Soft Starter Phase Angle Control 9 2 5 4 Synchronous Starting eee eee a ema nene nana amana aaa nana 10 2 6 General Survey SUMMA Y nisiocpa ceia aie abea a gasi da ea abea aan de ati ela a da e aer die bine e dai aa e i e al 10 3 1 MO OC OD COR ee en tee 12 5 1 standard K eine E 13 5 1 1 D25 Motor air or SUCTION gas coole 13 5 1 2 D3S Motor suction gas cooled ii nana aan aaa 14 5 1 3 D4S D8S Cylinder position for unloaded start ss 14 5 2 Beete iata setarea er iii senin e ati ligii a aa i lu teal 15 5 2 1 D2D2. firing angle of thyristors The closer the turn on point is to the voltage zero crossing point the longer the energy is allowed to flow during the half cycle and the higher is the applied voltage to the motor terminals see figure 8 The soft starter is a voltage phase controlling device As already described under position 1 1 it is possible to control the starting current of a 3 Phase motor by modulating the supply voltage Further these devices are providing a voltage ramp soft start where the voltage is increased from an initial value which must be high enough to produce the breakaway torque to the full line voltage in a linear fashion over a user adjustable period of time e g 0 4 0 8 seconds 9 23 D7 10 2 1106 0208 E After the motor start the soft starter is excluded from the supply line by a by pass With this method it is possible to adjust the motor torque to the load torque in optimum fashion and control the acceleration time But one should not forget that the minimum starting current is determined by Minimum required starting torque at motor shaft e g M 0 3M with unloading Torque producing capability of the motor Amount of acceleration torque required all vary with individual compressor type To get an acceptable reduction of starting current compressors are often used with unloaded start As with resistance starting the locked rotor current is then reduced but without energy being dissipated in the
3. In normal Star Delta starting Star contactor K2 and Delta contactor K3 must not be actuated at the same time as that could lead to an arcing short that welds the contacts together or reduces the life of the contactor The current must be interrupted when there is a changeover circuit diagram 7 2 2 Closed transition Star Delta starting avoids this interruption of current by cutting in resistors R7 by way of contactor K10 circuit diagram 6 2 3 After acceleration of the motor in Star speed greater than 0 9 synchronous speed resistors are connected in parallel to the motor winding by contactor K10 This means that the flow of current is not interrupted when the star is opened K2 opens Resistors R7 are now in series with the motor winding and are connected to the motor in delta When delta contactor K3 is actuated the resistors are shortened and cut out K10 opens In oscillograms 4 a b c the current curves of a closed transition Star Delta start with two different resistances R7 are compared with the current curve of open transition starting t a lt H A d d i g e Il Hl i ii it If Wi W M MMM NM WY ANA Wl i i WWW Gell WW Mi Hh Wi O i II Ht Wm si Li iti Figure 4a Star Delta Start Open Transition 4 23 D7 10 2 1106 0208 E m 1 Il dall lit Al D d AAA A AAA AA AR AAA AAA AA AAA d OI d il au i SUL M D M W WA HI Mi Wi WI HA Hi UU Wu Wl II di il
4. A non return valve must be installed in the discharge line to prevent the refrigerant from flowing back from the condenser to the suction side via the bypass The supplied non return valves are selected for full load operation in case of part load operation a replacement NRV with a weaker spring may be necessary The unloaded start equipment in the form of a module including the non return valve can be supplied by DWM Copeland for the single compressor series D2S D D3S D D4S D D6S D D8S D and capacity controlled compressors The TWIN series of these compressors can be correspondingly equipped with two modules Unloaded Start is not required with Direct On Line Starting With DWM Copeland 8 cylinder AW and BW compressors Unloaded Start is not required when starting the compressor on the 1 winding AW 2 3 BW 3 5 4 and 6 cylinder AW compressors mostly require Unloaded Start when starting the compressor on the first winding 2 3 This is when the compressor requires a high starting torque when the motor load is high Condensing higher than 50 C The 8 cylinder AW motor is different to the 4 and 6 cylinder AW motor although they are both 2 3 1 3 part winding start motors They are with different material design For the 4 6 cylinder AW motor to start loaded it would require a redesign and change of material giving an increase in LRA part winding start possibly by as much as 10 calling for a review of installation electrics contac
5. This motor type was replaced by part winding motors with a winding ratio 2 3 1 3 Motor code A e g AWM From January 1994 until September 2005 8 cylinder compressors were equipped with an part winding motor which has the code B e g BWM This replaced the previous motors with motor code A From September 2005 8 cylinder compressors reverted back to AWM motor code A Note The motor code can be found on the compressor nameplate 2 3 1 Part Winding Start 2 3 1 3 Motor Code A This motor winding is divided in a ratio of 2 3 1 3 The current the 1st part winding draws from the mains when it is switched on amounts to approximately 75 of the LRC in the case of Direct On Line Starting Without unloaded Start i e when there is a great difference in pressure the motor does not start until the SCH part winding is cut in after a time lag of 1second 0 1 second also loading the mains with the full LRC The advantage of this type of motor is not realised until Unloaded Start is installed Due to the somewhat higher LRC of the 1 part winding and the better magnetic exploitation compared with a motor with a winding ratio of 2 2 the motor develops higher starting torque so that it accelerates to the rated speed When the 2nd part winding is cut in after a time lag of 1second 0 1 second the current peak is never greater than 75 of the LRC as in the case of a direct start Figure 6 With pre January 1994 8 cylinder co
6. pir Hi di Hill Hi Hit Figure 4b Star Delta Start Closed Transition R7 6 Ohms um Will EE ges eA AAARARAAARAARAARAAAARARSARRAAAARARAAAAAARAARARARAAAAAAAARARAAAAA AL Via t UA M LLL H Vii HL HT wit Figure 4c Star Delta Start Closed Transition R7 24 Ohms to Opening of star point Cut In of resistors R7 tu Open transition tp Resistors R7 in parallel to Closing of delta contactor K3 When a small resistance R7 6 Ohm cuts in the current becomes quite large see figure 4b for current during the period t In extreme cases when R7 falls to zero there is a short and the current short circuits With larger R7 resistance the current drops The higher the R7 resistance the smaller the current when the resistors cut in Compare the currents during the period t in figures 4b and 4c The demand for the greatest possible resistance applies only as long as the star point contactor K2 is closed and resistors R7 are in parallel with the motor winding When the star point contactor K2 is opened resistors R7 are connected to the motor winding in series and a delta connection of the motor is established However the effective phase voltage does not correspond to the delta voltage since the latter is reduced by the voltage drop across R7 The larger R7 is the smaller the effective phase voltage and phase current will be The motor torque declines the speed is reduced In an extreme case
7. and Star connection of asynchronous motor schematic 4 L T Ha am ib Be Vi d f d Sa EE gege ee he d ge seat ae LES Figure 2a 2b M Load Torque Ns Synchronous Speed The following preconditions must be met for the motor to start up in star because of the low torque The load torque M must not be greater than 0 3 of the torque in direct starting During acceleration a speed of more than 0 9 of the synchronous speed should be reached before there is a changeover from Star to Delta From this it can be seen that unloaded start is absolutely necessary in the case of Star Delta starting and that there can be no changeover before the motor has accelerated approximately 1 3 seconds 3 23 D7 10 2 1106 0208 E Note Due to the large displacement the 8 cylinder EW compressor with unloaded start requires pre unloading 5 10 seconds beforehand The oscillogram in figure 3 shows the current curve of Star Delta starting The changeover from Star to Delta must take place at zero current so that there is no arcing short circuit This short interruption is enough for the speed to drop immediately due to the low amount of centrifugal mass and for the renewed current peak to reach approximately 80 in unfavourable cases as much as 100 of the starting current in direct starting Y connection A connection Figure 3 Current Open Transition 2 2 Star Delta Starting Motor Code E Closed Transition
8. maximum 10 times per hour 3 minutes minimum running time for oil pressure monitoring and or faultless supply of oil to the compressor bearings 5 23 D7 10 2 1106 0208 E 2 3 Part Winding Start Motor Types Part winding motors used in our European compressors have 6 separate motor terminals accessible in the terminal box figure 5 terminals 1 2 3 and 7 8 9 Due to the separate connections the parts of the winding can be separately energised during the starting period drawing only partial current from the mains For available models see the sales literature Motor Code F Motor Code A Motor Code B LA LL E 3 07 00 7 In respect to the internal motor design there are several types of Part Winding start motors applied Until August 1983 DWM Copeland used motors with a winding ratio 1 2 1 2 Motor Code F e g FWM The starting procedure is as follows Voltage is applied to the first part winding of the motor to terminals 1 2 3 This results in the mains being loaded with the start current of the first part winding which amounts to 65 of the current in the Direct Start full winding Depending upon the starting conditions it is possible that the motor will not start until the second winding is energised After the full motor winding is connected to the mains after 1 second 0 1 second the full motor start current is reached and the motor will accelerate to full speed Figure 5 Principle Internal Wiring
9. Motor suction gas cooled e esenta sia osii a iii alina a a ie pl ab antena i ia aa nenne 15 5 2 2 D3D Motor suction gas cooled se soimi dei sti Sa seat alma ae ital pa de aa lu ia na i a 15 5 2 3 D4D D6D amp D8D Motor SUCTION gas cooled e eee eee ee eee aaa nea 15 5 2 4 Tandem compressors e g D88SH 5000 Mounting Position of non return valves ccccceeeseeeeeeee enone 16 6 1 Teminat ACM Ail men imediata Abe atena aan titi aa je ei a ae aaa il aa ai iat aa 17 6 2 i teal pu Co AM E 17 6 2 1 ei KI o cz E 18 6 2 2 Sice RI Co cz pp E 19 6 2 3 EE HEIEREN 20 6 2 4 EEN THE 21 6 2 5 circuit EE 22 1 23 D7 10 2 1106 0208 E 1 Terms amp Definitions To prevent misunderstanding some terms used in the following sections are explained here Locked Rotor Current LRC same as Locked Rotor Amps LRA also shown on compressor nameplate The LRA is the current measured after 4 seconds when the motor is fixed cannot rotate and energised at the upper nominal voltage limit e g 420V for AWM D motors at 50 Hz The LRA may be taken as the maximum starting current for the compressor Transient phenomena are not considered Maximum Operating Current I OPER MAX also shown on compressor nameplate This is the highest value of the motor current occurring in the published operating map for the compressor This will normally be at the maximum condensing temperature at the maximum evaporating temperature for the highest pressure
10. ble 1 below may help you to decide which of the normal starting methods is suitable STARTING METHODS Starting Current Direct On Line Star Delta Part Winding Start PWS Resistor Start While connecting to EWM Y FWM 1 2 1 2 AWM 2 3 1 3 BWM 3 5 BWM 2 5 Can be applied the mains Connect terminals 1 2 3 to Start via Start via Jon each motor II the mains first terminals terminals Connect as 1 2 3 7 8 9 with D O L Motor Codes WM T F E A B E F BEE B te ae ee Starting Current D est L Without Unloading During Transition 100 100 100 lt 68 lt 54 lt 90 With Unloading During Transition 80 t0100 Li L2 L3 U V W 1 2 3 1 2 3 1 2 3 7 8 9 a 100 58 50 61 67 60 58 50 33 39 40 60 Table 1 Comparison of Starting and Running Current values for different starting methods with and without unloaded start Note Load reduction with direct starting is not necessary the locked rotor current is not reduced 10 23 D7 10 2 1106 0208 E 3 Unloaded Start For D2 and D3 compressors DWM Copeland use an external method of unloaded start using a very short bypass line fitted with a solenoid valve For D4 D6 and D8 compressors an internal bypass consisting of a special cylinder head is used this is also controlled by a solenoid valve By using a bypass the discharge gas is returned to the suction side without substantially increasing the pressure thus reducing the load on the motor
11. form of heat All thyristor based switching devices produce harmonics towards the motor influencing its characteristics available torque and towards the supply line as well Phase angle control can put a load of harmonics on the mains The technical connection conditions of the power supply companies are decisive It is possible to use motors for Direct On Line start but because the frequency cannot be changed the motor speed cannot be managed Starting frequency of the Soft Starter recommended by its manufacturer and as well of the compressor must be observed 2 5 4 Synchronous Starting A static frequency converter is used to regulate the frequency and the voltage in proportion from a minimum value to the reacted value thus achieving a constant acceleration of the motor Synchronous starting is expensive and therefore not further described here but it can also be used to regulate the compressor cooling capacity via the compressor speed Attention The minimum and maximum speeds of the compressor must be adhered to when regulating compressor power via frequency converters in order to prevent damage for example by lubrication problems 2 6 General Survey Summary Various criteria must be taken into account when deciding which starting method to use Such as What starting current is specified by the Power Supply Company What is specified What torque is required for perfect starting How expensive can the system become Ta
12. imited to a maximum of 0 5 seconds Immediate restarting must be avoided and the number of switching limited to 5 per hour see page 4 2 2 last paragraph Please ask for the precise values number of switching and duty cycle from the resistor manufacturer DWM Copeland cannot supply any resistors but we can inform you of the required resistance values on request 2 4 1 Selection of Starting Resistors This example is supposed to explain how the dropping resistance per phase is calculated Motor data D3SS 100X EWL Mains Voltage Ux 400V Locked Rotor Current I 109 A a 7 23 D7 10 2 1106 0208 E Torque with direct start at rated voltage M Minimum required torque with load reduction M 0 3M Reduced breakaway starting current to keep to M 1 1 e 4M IAM 59 7 A Power Factor with locked rotor COS x 0 63 The Impedance of the motor at switch on U phase voltage phase current E e Ig V3 1 V3 109 The Resistance R ZXx COS 2 12 x 0 63 1 33 Q The Reactance X Zx SID x ZX l COS x 2 12 x 0 776 1 646 Q To limit the breakaway starting current to 59 4 A impedance Z is required with the altered resistance R lt ice Z 400 Br Za 24 387 lo 2350 Ry R R 3 5 1 33 2 17 Q R Dropping resistance per phase 9 2 KS SL 005 a a Combined to make the formula Ry NB Knowledge of COS x is indispensable for calculating the resistance Since the value varies depending o
13. ischarge muffler may be come necessary The manufacturers recommendation must be followed for the valve selection This is very important if the compressor has to operate with capacity control in a large application range over a large pressure ratio or as a two stage internal compounded compressor 5 Installation Instructions The following explanations and drawings serve as an indication for the arrangement of the unloaded start equipment at the compressor 5 1 Standard Compressors 5 1 1 D2S Motor air or suction gas cooled For limits see application envelope shown in Select found on our website www ecopeland com a Unloaded start Components 63 V2 40 00 V 2 41 00 ipa c Mounting position Motor suction gas cooled 13 23 D7 10 2 1106 0208 E 5 1 2 D3S Motor suction gas cooled Pan SES Leet TAG PETIT RANAY gii 2 marking cylinder head ech Sr el Ars RT A 5 NT Sr A we REON N y JN zanse No for thickness of gasket valvaplate compr body Use same thickness or follow instruction supplied with new gaskets Mounting position Control Solenoid Valve Marking 705 RA 001 14 23 D7 10 2 1106 0208 E 5 2 Discus Compressors 5 2 1 D2D Motor suction gas cooled grog Al SKIE a ei CIDUL CD 4 U w V1 12 04 V1 12 03 Unloaded start equipment Parts M
14. ising of the 2 part winding Shorting out of the starting Resistors or the Soft Start device circuit diagram 6 2 2 for the block diagram of the electric circuit of solenoid valve Y3 A non return valve must be installed in the discharge line to prevent the refrigerant flowing back from the condenser to the suction side via the bypass line Care must be taken that in systems with a pump down circuit solenoid valve Y3 must always be closed during pump down 4 Selection Information DWM Copeland cannot supply any unloaded start module for small single stage and two stage compressors smaller than tyoe D2S D2D In these special cases the owner must provide pressure reduction The diameter of the bypass line and solenoid valve should be selected 1 size smaller than the discharge gas line The bypass line between the discharge and suction line must be as short as possible to keep the pressure drop small As a guideline the pressure drop across the bypass line and magnetic valve should be smaller than 3 bar otherwise there would be not sufficient load reduction and the motor would not accelerate because of the high counter torque Care must be taken to avoid the accumulation of condensate and oil in the bypass line 12 23 D7 10 2 1106 0208 E Piston compressors are producing gas pulsations and these pulsations can affect the non return valve in the discharge line causing chattering of the valve and a reduction in life expectancy The use of a d
15. ly companies demand a limit on the LRC there is the question of how to proceed To provide help in making these decisions we describe in this Technical Information the most important methods that can be used to reduce current and the amount by which the LRC can be reduced 2 1 Star Delta Starting Motor Code E Open transition Special wound motors are required for Star Delta starting All the ends of each winding must be free so that they can be wired externally The minimum voltage for which the winding must be dimensioned corresponds to the operating voltage mains voltage in a Delta circuit The DWM Copeland motors which are suitable for this purpose are marked on the nameplate by e g 380 420V A Y start or 220 240V A 380 420V Y During the starting phase the motor is connected in Star circuit diagram 7 2 2 Thus the phase voltage across the motor at the start amounts to only 0 58 1 13 of the actually required voltage The motor is fed with under voltage The current taken from the mains Star current ly drops to one third of the start and operating current that would be needed in a Delta circuit The torque My which amounts to only one third of the torque in Delta Ma operation Figures 2a and 2b below behaves the same way Note Star start of motor compressor only possible with 220 240V mains power Motor code is shown at compressor nameplate example D3DS5 150X EWM a Current and b torque curves with respective Delta
16. mpressors motor code A with unloaded start pre unloading is necessary september 2005 8 cylinder compressors motor code A AWM unloaded start is unnecessary NB Compressor motor contactor K4 may only switch on when K1 has already closed the contacts The contactors must be correspondingly interlocked by auxiliary contacts See connection diagram 6 2 4 6 23 D7 10 2 1106 0208 E a re rr we nn E nm TI eege Loes _ Figure 6 The Part Winding Start 2 3 1 3 Curve for compressors with unloaded start 2 3 2 Part Winding Start 3 5 2 5 Motor Code B Compared with the code A Part Winding motor the torque has been increased both for DOL starting as well as for PWS If the motor without bridges is supplied with power at terminals 1 2 3 we have in effect a true part winding start The start up current is 68 of the value for across the line starting Figure 6 shows the principle current curve for PWS with terminal 1 2 3 connected first The motor accelerates and while connecting terminal 7 8 9 there is no huge current peak As with the other PWS methods the motor terminals 7 8 9 have to be connected to the mains after 1second 0 1second The start of an 8 cylinder compressor with Motor Code B for the A C application range R22 or R407C while using pre unloading and connecting terminals 7 8 9 first to the mains is only under certain conditions possible and has to be clarified
17. n the motor manufacturer it is not indicated here You can receive it on request 2 5 Other Methods In addition to the methods mentioned above there are other possibilities of reducing the current mentioned below 2 5 1 Transformer Start A good but also expensive solution to the problem of reducing the current is provided by a transformer start with which the starting current can be cut to about 33 of the locked rotor current An auto transformer that is connected in Star is used to supply the motor with the voltage required for a perfect start The locked motor current I existing at reduced voltage conditions drops in linear proportion to the voltage supplied to the 3ph motor l e SA U with the voltage transformation ratio i U U primary voltage U secondary voltage However it is not the motor current i e the secondary transformer current that loads the mains but the primary current reduced by the factor of the voltage transformation ratio In general the following applies to the relationship between the mains current and starting current J 8 23 D7 10 2 1106 0208 E As shown in the case of a transformer stari the current taken from the mains is not reduced in linear fashion as with the other methods but by the square of the voltage if the no load current is not taken into account In the changeover phase after the Star circuit of the transformer is opened and before the transformer is shor
18. ordance with sections 2 2 and 2 4 This limit is also required when more than 15 switchings per hour are caused by a thermostat or other sources You will find explanations of applied symbols on the last page All rights and the right to make technical changes are reserved No responsibility is taken for the correctness of the information and no claims can be demanded from these documents 6 1 Terminal Diagram Electronic module INT 69 or INT 69 TM for motor protection M1 44100 L1 amp N Voltage Supply 220 240V 40 60H 1 2 Connection of thermistors 12 Signal lamp 11 14 Control Circuit K Relay making capacity 300 VA at cosp 0 3 Other voltage on request LIN 1 2 12 14 11 6 2 Circuit Diagram Oil Pressure Switch OPS differential 17 23 6 2 1 Circuit Diagram Direct On Line Start 21 22 23 4O0OV 3 Ph 50Hz Li N Control circuit E 1 08 02 D7 10 2 1106 0208 E 18 23 D7 10 2 1106 0208 E 6 2 2 Circuit Diagram Star Delta Start Y A with a pumpdown cycle oil pressure safety control and unloaded start CH ZS A 21 22 23 400V 3 Ph 50 Hz L wescht EENS ET e o o d L3 N DD Ge Ge sf D a 24 25 25 N p O Control cacu e Bose vk ks Ci ke 8 10 la Ki Ho 5 TMO9 7 3 Star Y Start 1 3 seconds Delta A Operation Change over period approximately 0 02 0 1 second Contacts respective valve closed Contacts res
19. ounting position 5 2 2 D3D Motor suction gas cooled Wiii jpg Unloaded start equipment Parts Mounting position 5 2 3 D4D D6D amp D8D Motor suction gas cooled a Unloaded start equipment O a O a re firii N L Hu dE rd LU F es E k d SJ A Za L PA ss ol gasket valvaplate compr A KO DS i or i follow instruction supplied 15 23 D7 10 2 1106 0208 E b Unloaded start mounting position 5 2 4 Tandem compressors e g D88SH 5000 Mounting Position of non return valves 1 Non return valve compressor 2 Control valve of internal unloaded start equipment 3 Non return valve compressor II 4 Muffler 4 6 amp 8 cylinder compressor 5 Connection common discharge line 2 2 e Mt Eu IL E 16 23 D7 10 2 1106 0208 E 6 Electrical Schematic Diagrams and Circuit Diagrams General wiring diagrams circuit diagrams and respective operating sequence plans are presented on the following pages for each starting method described but without any claim to being complete or comprehensive With the exception of Direct On Line Starting all the diagrams are with unload start In addition one example each is provided for preliminary load reduction for series D8S and a pump down circuit A limit on the frequency of operations is not taken into account in the circuit diagrams but it is always required for protection of the resistors in the case of starting methods in acc
20. pective valve opened 19 23 D7 10 2 1106 0208 E 6 2 3 Circuit Diagram Star Delta Start Y A closed transition with unloaded start CH d 21 22 23 400V 3 Ph 50Hz N DER Bi EE i ce all Fi 24 25 2 Control cecuk KS Ki ca 3 31 32 Kal 4 5 iT 27 28 29 CH lt Ill ECH a K 1 2 K 1 21 23 ek K15 K3 K 15 8 red 1 orange e1 pat A SE 27 i wech K 15 9 E 1 41 03 5 112 AA SR z 28 13 m9 i et CC em ai nie TM 09 7 4 PEN EN Star Y Start 1 3 seconds Il Delta A Operation 1 Change over period approximately 0 1 0 5 second a Contacts respective valve closed o Contacts respective valve opened 20 23 6 2 4 Circuit Diagram Part Winding Start Pre unloaded Il II E o Pre unloading 5 10 seconds First part winding 1 0 0 1 seconds Both part windings Contacts respective valve closed Contacts respective valve opened AOOV 3 Ph 50Hz Li N Control cacu D7 10 2 1106 0208 E Attention 8 cylinder compressors with Star Delia start EW require pre unloading With the introduction of new motors in August 2005 the AW motor replacing the BW motor 8 cylinders retain the ability to start loaded without unloading on the 2 3 winding first TMO9 7 5 21 23 6 2 5 Circuit Diagram 1 LA lt 21 22 23 400V 3 Fh 50Hz La L3 N PE Kr tt 5 a4 25 26 Kg Resistance Starting unloaded start Re
21. power is exceeded nationally and regionally different What is decisive are the technical conditions of connection stipulated by the power supply Companies Compliance with the current limitations requires current limiting measures which have to be taken on the electrical installation side and mean a reduction of voltage across the motor terminals except for Part Winding Start motors Since the LRC consumption of three phase motors reduces in proportion to the voltage but the motors torques by the square of the voltage a substantial reduction of current can only be achieved if the load on the motor is reduced at the same time A minimum starting torque of the compressor has to be observed the majority of compressors 30 35 of the torque for D O L start This is limiting the minimum starting current achievable 2 23 D7 10 2 1106 0208 E If for example the LRC has to be halved the voltage has to be reduced to 50 of the operating voltage the torque amounts to only one fourth of the torque at rated voltage and would not longer be enough to start the compressor even if unloaded start were used The compressors that are subject to current limitation must therefore be equipped with unloaded start For exceptions see details of Part Winding Start motors with winding division 2 3 1 3 motor code A like compressor D8SJ 400X AWM to guarantee perfect starting at the minimum required starting torque 2 Starting methods When power supp
22. refrigerant for which the compressor is released The value will not correspond exactly to that observed in the data table given in the Select Software because the table values are at nominal mean voltage Also the data table in Select Software may not show the full operating envelope or the compressor may be released for other refrigerants The voltage at which the maximum current value is taken will normally be the lower nominal voltage limit e g 380V for AWM D motors 50 Hz 1 1 General Remarks Three phase asynchronous motors with squirrel cage rotors are used in the semi hermetic motor compressors made by DWM Copeland They require no maintenance are easy to use and are always suitable for Direct On Line starting With D O L starting the motor is switched directly into the mains by means of a switch The resulting starting current amounts to 4 7 times the maximum operating current see figure1 Note Single phase asynchronous motors are also available for DK Series compressors Current Time Figure 1 Direct On Line starting current In the case of high powered motors the locked rotor current become so large that they lead to disruptive voltage dips in the mains which are indicated for example by flickering lighting or side effects in other loads To prevent these system disturbances power companies limit the permissible size of motors for D O L starting and set a current limit when the motor
23. sistance Starting lt 0 5 seconds Il Nominal operation BI Contacts respective valve closed o Contacts respective valve opened L1 N Control cc u TMO9 7 6 D7 10 2 1106 0208 E 22 23 D7 10 2 1106 0208 E Applied Symbols according to DIN 40719 Electronic module for M1 Oil pressure switch Room thermostat Fuse for control circuit characteristics must be related to maximum load of control mechanism High Pressure Switch Pressure cut oui Safety pressure cut out Low pressure switch Trip timer inside A2 Differential pressure switch in A2 Fuse M1 Fuse M1 Fuse M1 Signal Lamp A1 Contactor M1 Y contactor M1 A contactor M1 Contactor M1 for second part winding Contactor for R6 Contactor for R7 Time delay relay 1 3 s for Y A start Time delay relay 1 s 0 1 for part winding start Time delay relay for resistance starting R6 Time delay relay for pre unloaded start 5 10 s Time delay relay for Y A start closed transition Compressor motor Main switch Resistor in A2 Crankcase heater Thermistors in M1 Intermediate Resistors Resistors Y A start closed transition Auxiliary switch if crankcase heater should heat prior to operation of the compressor Solenoid valve liquid line Solenoid valve unloaded start M1 23 23
24. ted out the motor is still supplied with voltage by part of the transformer the result being that there is no current interruption On this phase the part winding of the transformer functions like a starting reactor However experience has shown that during the changeover from the reduced voltage secondary voltage to full mains voltage current peaks can occur that are dependent on the difference in the voltages between the mains and motor The advantage of the high current reduction is lost again similar to the case with a Y A start 2 5 2 Reactance Starting The method of starting with starting reactors works on the same principles as resistance starting Instead of the resistors reactors are cut into the supply circuits which have to be individually designed for the respective type of compressor and are not as variable as resistors They have not gained acceptance as a means of limiting the current 2 5 3 Soft Starter Phase Angle Control Silicon Controlled Rectifier SCR or Thyristor are the basis on which soft starting systems for 3ph motors described here are built SCR switch from OFF to ON rapidly and remain ON until the current through the device falls to zero at the end of each half cycle in A C supplies By controlling the switch on point of a thyristor relative to the voltage zero crossing in each half wave it s possible to regulate the voltage applied to the motor 400 0 3 3 t Figure 8
25. tors cables etc Mounting Position of Non Return Valve YX ALAS xx RSS LOSS Z 9 24 00 A Compressor Shut off valve B Vibration Absorber C Non Return Valve D To Condenser Non Return Valve The check valves are to be selected in accordance with the table below and mounted as shown in the illustration above This selection facilitates quiet operation over a wide application range without chattering noise caused by gas pulsation If noise should occur during normal or partial load operation it is necessary to match the check valve to the operation conditions Note The Non Return Valve NRVH for Twin parallel compressor operation has a stronger spring than the NRV for single compressor operation 11 23 D7 10 2 1106 0208 E Table 2 Standard Compressors Compressor Non Return Valve Non Return Valve DLH 7 D25 NRV 228022 4S NRV 22S 22 D44S 2 XNRVH 22S 22 D3S D4SJ NRV 28S 28 D44SJ 2 XNRVH 28S 28 D6SF L T NRV22S 22 D66SF L T 2XNRVH 22S 22 D6SA H J NRV28S 28 D66SA H J 2 XNRVH 28S 28 1 also for parallel compressor operation Table 3 Discus Compressors D6DH 7 J 1 also for parallel compressor operation 3 1 Mode of Operation When the compressor is switched on the solenoid valve opens the bypass and holds it open during the starting phase After completion of the starting procedure the solenoid valve closes the bypass That is after Change over from Star to Delta Energ
26. when R7 is infinite and the current equals zero the star delta start is with open transition When the delta contactor is actuated and the resistors shorted out there is a renewed current peak ts in figure 4c which then i e when R7 is infinite corresponds to a start with open transition The smallest possible resistance would be necessary for this short switching phase The optimum resistance of R7 is in between With the resistance it is possible to limit the current to approximately 0 4 of the breakaway starting current in direct on line starting R7 per phase is calculated on the basis of the following rule of thumb U Rated motor voltage in delta n X la Locked rotor current V3 x 0 33 R7 The resistance of R7 calculated with this formula is a guide value To take unavoidable tolerances into account we recommend that R7 be kept variable so that you can match the resistance to the system in optimum fashion Contactor K10 must be dimensioned for the maximum motor voltage delta voltage and half the motor power Due to the thermal load on the resistors and to limit the size it is necessary to keep the duty factor at less than 0 5 second limit the number of switching to 5 per hour and avoid direct restarting However the exact duty cycle and number of switching must be requested from the resistor manufacturer or specified in accordance with the requirements of the compressor system The compressor itself can be started
27. with DWM Copeland case by case When the motor is started via terminals 7 8 9 without bridges the starting current is 54 2 4 Resistance Starting 3 phase The starting methods described in Sections 2 1 2 2 and 2 3 require motors especially built for this purpose free winding ends and divided winding Every 3 phase motor used by DWM Copeland is suitable for resistance starting The motor must be wired so that it can be started directly The ohmic starting resistors R6 are cut into the motor leads between motor contactor K1 and the compressor and shorted out by way of contactor K9 after approximately 0 35 0 5 seconds circuit diagram 7 2 5 The resistances can be sized for any breakaway starting current The current reduction is only limited by the specified minimum necessary torque so that the motor will start faultlessly With the unloaded start from DWM Copeland it is possible to limit the current to approximately 55 of the LRA in the case of a direct start The current peak that occurs when the resistors are shorted out is negligibly small if the speed is greater than 0 9 of the synchronous speed Intermediate resistor shorted out Was AT Penny A ii lui AH AMMAN AA Iri N lili dt II HAAN Mut Im ut d id II Iw wgl dl d L4 MM MII tt Figure 7 Current curve with resistance starting The disadvantage of this method is thai the power is dissipated by the resistors in the form of heat The duty cycle is therefore usually l
Download Pdf Manuals
Related Search