transformer size for large motor starting 1.6.14

:Transformer Detail:Transformer Size 1000 KVATransformer Secondary Voltage:(v2) 480 Volt% Impedance: (z) 5.75%Allowable Voltage Drop in System: 10%:Motor Detail ( Only One No of Motor):Motor Size: 300 KwVolt (vm): (L-L) 460 VoltPower Factor: 0.8Motor KVA 240 KVA

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) 471 AmpLocaked Rotor Current Multiplier: (Min) 4.10Locaked Rotor Current Multiplier: (Max) 4.50Locaked Rotor Current (L1): (Min) 1930 AmpLocaked Rotor Current (L2): (Max) 2118 AmpMotor InRush KVA At Starting: (IrsM) 1687 KVAHow many times Motor Starts per Hours 2

:Calculations:Full Load Current of Transformer : (ILX) 1203 AmpShort Circuit Current at Transformer Secondary: (Isc) 20919 AmpMax KVA of Transformer at Isc: Q1 17391 KVAMotor InRush KVA At Starting:(IrsM) 1687 KVAVoltage Drop at Transformer Secondary Due to Motor inRush: (Vd) 10% 90%Transformer Secondary Voltage 433 Volt

:Result:(1) Motor Full Load Current <= 65% Transformer Full Load Current Yes(2) Voltage Drop at Transformer Secondary Due to Motor inRush Low(3) Transformer Size:(20% Added due to motor starts more than once/Hour) 1200 KvaSize of Transformer is Adequate

Calculation Formulas:ILX=KVA/(1.732xv2)ILM=(Kwx1000)/(1.732xVmxP.F)Isc=ILx/zQ1=(v2xISCxILMx1.732)/1000IrsM=(VmxL2x1.732)/1000Vd=IrsM/Q1

Code Letter (KVA per HP) -Locked Rotor CurrentMotor Code Min Max

1 A 3.152 B 3.16 3.55

Calculate Transformer Size & Voltage drop due to Starting of Large size MotorCalculate Transformer Size & Voltage drop due to Starting of Large size Motor

3 C 3.56 44 D 4.1 4.55 E 4.6 56 F 5.1 5.67 G 5.7 6.38 H 6.4 7.19 J 7.2 8

### K 8.1 9### L 9.1 10### M 10.1 11.2### N 11.3 12.5### P 12.6 14### R 14.1 16### S 16.1 18### T 18.1 20### U 20.1 22.4### V 22.5

44.14.5

:Transformer Detail:Transformer Size 1000Transformer Secondary Voltage:(v2) 480% Impedance: (z) 5.75%Allowable Voltage Drop in System: 10%:Motors Detail ( More Than One No of Motor):Total KW of Three Phase Motors: 300Total KW of Single Phase Motors: 5Volt: (L-L) 460Volt: (L-N) 266

Power Factor: 0.8

Locaked Rotor Current: (Max) 450%Total Three Phase Motors Full Load Current 471Total Single Phase Motors Full Load Current 24Total Motors Full Load Current 494Motor InRush KVA At Starting 1772

:Calculations:Full Load Current of Transformer : (IL) 1203Short Circuit Current at Transformer Secondary: (Isc) 20919Max KVA of Transformer at Isc 17391Motor InRush KVA At Starting 1772Voltage Drop at Transformer Secondary Due to Motor inRush 10.2%Transformer Secondary Voltage 431

:Result:(1) Motor Full Load Current <= 65% Transformer Full Load Current Yes(2) Voltage Drop at Transformer Secondary Due to Motor inRush High(3) Transformer Size: 1000Increase Size of Transformer

Jignesh.Parmar ,jiguparmar@yahoo.com , www.electricalnotes.wordpress.comCalculate Transformer Size & Voltage drop due to Starting of Large size MotorCalculate Transformer Size & Voltage drop due to Starting of Large size Motor

KVAVolt

KwKwVoltVolt

AmpAmpAmpKVA

AmpAmpKVAKVA90%Volt

KVA

Jignesh.Parmar ,jiguparmar@yahoo.com , www.electricalnotes.wordpress.com