Table of Contents
Standard Size of Transformer (Distribution range)
| Transformer Size (Power Transformer and Distribution Transformer) | MVA and KVA |
| Power Transformer in Urban and Semi Urban areas | 3,6,8,10,16 MVA |
| Power Transformer in Rural areas | 1,1.6,3.15,5 MVA |
| Distribution Transformer | 16,25,50,63,100,250,400,500 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 HP | In a range of 750 RPM |
| 10 HP – 30 HP | In a range of 600 RPM |
| 30 HP – 125 HP | In a range of 500 RPM |
| 125 HP – 300 HP | In a range of 375 RPM |
Line Voltage of Motor
| Motor Rating in Kilowatt (KW) | Line Voltage |
| < 250 KW | 440 V (Low Voltage – LV Side) |
| 150 KW – 3000 KW | 2.5 – 4.1 KV (High Voltage – HV Side) |
| 200 KW – 3000 KW | 3.3 – 7.2 KV (High Voltage – HV Side) |
| 1000 KW – 1500 KW | 6.6 – 13.8 KV (High Voltage – HV Side) |
Starting Current of Motor
| Phase Supply | Motor Size | Maximum Starting Current |
| Single(1Ø) Phase | < 1HP | Full Load Motor Current x 6 |
| Single(1Ø) Phase | 1HP – 10 HP | Full Load Motor Current x 3 |
| Three (3Ø) Phase | 10 HP | Full Load Motor Current x 2 |
| Three (3Ø) Phase | 10 HP – 15 HP | Full Load Motor Current x 2 |
| Three (3Ø) Phase | >15 HP | Full 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
| Starter | HP (or) KW | Starting Current | Torque |
| DOL Starter | < 13 HP or < 11 KW | Full Load Current x 7 | Good |
| Star – Delta Starter | 13 HP – 48 HP | Full Load Current x 3 | Poor |
| Automatic Torque Converter | > 48 HP or > 37 KW | Full Load Current x 4 | Average |
| Variable Speed Drive | Full Load Current x 0.5 to 1.5 | Excellent |
Transformer Impedance
| Mega Volt Ampere (MVA) | Impedance % |
| < 1 MVA | Impedance of 5% |
| 1 – 2.5 MVA | Impedance of 6% |
| 2.5 – 5 MVA | Impedance of 7% |
| 5 – 7 MVA | Impedance of 8% |
| 7 – 12 MVA | Impedance of 9% |
| 12 – 30 MVA | Impedance of 10% |
| > 30 MVA | Impedance of 12.5% |
