Standard Rating of Electrical Machinery

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848

Standard Size of Transformer (Distribution range)

Transformer Size (Power Transformer and Distribution Transformer)MVA and KVA
Power Transformer in Urban and Semi Urban areas3,6,8,10,16 MVA
Power Transformer in Rural areas1,1.6,3.15,5 MVA
Distribution Transformer16,25,50,63,100,250,400,500 KVA

Standard Size of Transformer of 1Ø and 3Ø (IEEE Standard / ANSI Standard 57.120)

1). Single Phase Transformer (1Ø Transformer)

Transformer range of 5KVA,10 KVA,15 KVA,25 KVA,37.5 KVA,50 KVA,75 KVA,100 KVA,167 KVA,250 KVA, 333 KVA,500 KVA, 1.25 KVA,1.66 KVA,2.5 KVA,3.33 KVA,5.0 KVA,6.6 KVA,8.3 KVA,10 KVA,12.5 KVA,16KVA,20.8 KVA,25 KVA,33.33 KVA used as single phase transformer.  

2). Three Phase Transformer (3Ø Transformer)

Transformer range of 3 KVA,5 KVA,9 KVA,15 KVA,30 KVA,45 KVA,75 KVA,112.5 KVA,150 KVA,250 KVA,500 KVA,750 KVA,1MVA,1.5 MVA,2 MVA,2.5 MVA,3.7 MVA,5 MVA,7.5MVA,8 MVA,10MVA ,12MVA,16MVA,20MVA,25MVA, 30MVA,37.5MVA,50MVA ,60MVA,75MVA, 100MVA used as three phase transformer.

Where,

KVA – Kilo Volt Ampere and

MVA – Mega Volt Ampere

Standard Size of Motor

Motor ranges from capacity rating of 1HP,1.5HP,2HP,3HP,5HP,7.5HP,10HP,15HP,20HP,30HP,40HP,50HP,60HP,75HP,100HP,125HP,150HP,200HP,250HP,300HP,400HP,450HP,500HP,600HP,700HP,800HP,900HP,1000HP,1250HP,1500HP,1750HP,2000HP,2250HP,3000HP,3500HP,4000HP  

Where,

HP – Horse Power

Approximate Revolutions per Minute (RPM) of Motor

Horse Power (HP)Revolutions Per Minute (RPM)
< 10 HPIn a range of 750 RPM
10 HP – 30 HPIn a range of 600 RPM
30 HP – 125 HPIn a range of 500 RPM
125 HP – 300 HPIn a range of 375 RPM

Line Voltage of Motor

Motor Rating in Kilowatt (KW)Line Voltage
< 250 KW440 V (Low Voltage – LV Side)
150 KW – 3000 KW2.5 – 4.1 KV (High Voltage – HV Side)
200 KW – 3000 KW3.3 – 7.2 KV (High Voltage – HV Side)
1000 KW – 1500 KW6.6 – 13.8 KV (High Voltage – HV Side)

Starting Current of Motor

Phase SupplyMotor SizeMaximum Starting Current
Single(1Ø) Phase< 1HPFull Load Motor Current x 6
Single(1Ø)  Phase1HP – 10 HPFull Load Motor Current x 3
Three (3Ø) Phase10 HPFull Load Motor Current x 2
Three (3Ø) Phase10 HP – 15 HPFull Load Motor Current x 2
Three (3Ø) Phase>15 HPFull Load Motor Current x 1.5

Rating of Motor Starter

Motor ranges above > 2.2 KW cannot be connect directly to the supply input voltage if it is connected in delta winding

StarterHP (or) KWStarting CurrentTorque
DOL Starter< 13 HP or < 11 KWFull Load Current x 7Good
Star – Delta Starter13 HP – 48 HPFull Load Current x 3Poor
Automatic Torque Converter> 48 HP or > 37 KWFull Load Current x 4Average
Variable Speed Drive Full Load Current x 0.5 to 1.5Excellent

Transformer Impedance

Mega Volt Ampere (MVA)Impedance %
< 1 MVAImpedance of 5%
1 – 2.5 MVAImpedance of 6%
2.5 – 5 MVAImpedance of 7%
5 – 7 MVAImpedance of 8%
7 – 12 MVAImpedance of 9%
12 – 30 MVAImpedance of 10%
> 30 MVAImpedance of 12.5%