Transformer Size for Large Motor Starting

Calc Calcul ulat ate e Siz Size e of of Tra Trans nsfo form rmer er an and d Vol Volta tage ge dr :Transformer Detail: Transformer Size Transformer Secondary Voltage:(v2) % Impedance: (z)  Allowable Voltage Drop in System: System: :Motor Detail ( Only One No of Motor): Motor Size: Volt (vm): (L-L) Power Factor: Motor KVA

1000 480 5.75% 10% 300 460 0.8 240

Motor Code: (Kva/Hp) InRush Current at Starting:(Enter If you know otherwise leave it blank) Enter Motor Full Load Current( Enter If you know otherwise leave it blank ) Motor Full Load Current: (ILM) Locaked Rotor Current Multiplier: (Min) Locaked Rotor Current Multiplier: (Max) Locaked Rotor Current (L1): (Min) Locaked Rotor Current (L2): (Max) Motor InRush KVA At Starting: (IrsM) How many times Motor Starts per Hours :Calculations: Full Load Current of Transformer : (ILX) Short Circuit Current at Transformer Secondary: (Isc) Max KVA of Transformer at Isc: Q1 Motor InRush KVA At Starting:(IrsM) Voltage Drop at Transformer Secondary Due to Motor inRush: (Vd) Transformer Secondary Voltage :Result: (1) Motor Full Load Current <= 65% Transformer Full Load Current (2) Voltage Drop at Transformer Secondary Due to Motor inRush (3) Transformer Size:(20% Added due to motor starts more than once/Hour)

471 4.10 4.50 1930 2118 1688 2 1203 20919 17391 1688 10% 433  Yes Low 1200

Size of Transformer is Adequate Calculation Formulas: ILX=KVA/(1.732xv2) ILM=(Kwx1000)/(1.732xVmxP.F) Isc=ILx/z Q1=(v2xISCxILMx1.732)/1000 IrsM=(VmxL2x1.732)/1000 Vd=IrsM/Q1

Code Letter (KVA per HP) -Locked Rot or Current 1 2 3

Motor Code

Min

A B C

3.15 3.16 3.56

4 5 6 7 8 9 # # # # # # # # # #

4.1 4.6 5.1 5.7 6.4 7.2 8.1 9.1 10.1 11.3 12.6 14.1 16.1 18.1 20.1 22.5

D E F G H J K L M N P R S T U V

4 4.1 4.5

p due to Starting of Large size Motor KVA Volt

Kw Volt KVA

:Transformer Detail: Transformer Size Transformer Secondary Voltage:(v2) % Impedance: (z)  Allowable Voltage Drop in System: :Motors Detail ( More Than One No of Motor): Total KW of Three Phase Motors: Total KW of Single Phase Motors: Volt: (L-L) Volt: (L-N) Power Factor:

 Amp

Locaked Rotor Current: (Max) Total Three Phase Motors Full Load Current Total Single Phase Motors Full Load Current Total Motors Full Load Current Motor InRush KVA At Starting

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1000 480 5.75% 10% 300 5 460 266 0.8 450% 471 24 494 1772

 Amp  Amp KVA

 Amp  Amp KVA KVA 90% Volt

Kva

:Calculations: Full Load Current of Transform er : (IL) Short Circuit Current at Transfor mer Secondary: (Isc) Max KVA of Transformer at Isc Motor InRush KVA At Starting Voltage Drop at Transformer Secondary Due to Motor inRush Transformer Secondary Voltage :Result: (1) Motor Full Load Current <= 65% Transformer Full Load Current (2) Voltage Drop at Transformer Secondary Due to Motor inRush (3) Transformer Size:

Increase Size of Transformer

Max

3.55 4

1203 20919 17391 1772 10.2% 431  Yes High 1000

4.5 5 5.6 6.3 7.1 8 9 10 11.2 12.5 14 16 18 20 22.4

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KVA Volt

Kw Kw Volt Volt

Amp Amp Amp KVA

Amp Amp KVA KVA 90% Volt

KVA