Calculate kVA Rating, Primary & Secondary Current, Voltage & Turns Ratio
š” Formulas: kVA = (V Ć I) / 1000 (Single) | kVA = (ā3 Ć V Ć I) / 1000 (Three)
kVA = V Ć I / 1000 (Single) | kVA = ā3 Ć V Ć I / 1000 (Three)
š Transformer Rating Calculator
This tool helps you calculate the kVA rating of a transformer based on primary voltage, secondary voltage, and load current. It also computes primary and secondary currents, turns ratio, and provides standard transformer sizes. Essential for transformer sizing and electrical design.
š Transformer Formulas
Single Phase: kVA = (V Ć I) / 1000 Three Phase: kVA = (ā3 Ć V Ć I) / 1000 Turns Ratio: Nā/Nā = Vā/Vā Primary Current: Iā = (Vā Ć Iā) / Vā
Where: Vā = Primary Voltage (V) Vā = Secondary Voltage (V) Iā = Primary Current (A) Iā = Secondary Current (A)
š Standard Transformer kVA Ratings
kVA
Primary (11kV) Current
Secondary (415V) Current
Application
25
1.3A
34.8A
Small commercial
50
2.6A
69.6A
Small commercial
100
5.2A
139A
Small industrial
200
10.5A
278A
Industrial
315
16.5A
438A
Medium industrial
500
26.2A
696A
Large industrial
630
33.1A
877A
Large industrial
1000
52.5A
1392A
Heavy industrial
1600
84.0A
2228A
Heavy industrial
2000
105.0A
2785A
Power distribution
š Transformer Sizing Guide
Load Calculation: Add all connected loads (kW/kVA) and apply diversity factor
Future Expansion: Size transformer 20-30% above current load for future growth
Efficiency: Distribution transformers typically operate at 95-98% efficiency
Voltage Regulation: Good transformers have 2-5% voltage regulation
Overload Capacity: Transformers can handle 110-120% short-term overload
š” Transformer Types & Applications
Step-Up Transformer: Increases voltage (e.g., 11kV to 33kV)
Step-Down Transformer: Decreases voltage (e.g., 11kV to 415V)
Distribution Transformer: 11kV/415V for local distribution
Power Transformer: 132kV/33kV for transmission
Isolation Transformer: 1:1 ratio for isolation and protection
š§ How to Use This Calculator
Enter primary voltage (Vā) - e.g., 11000V (11kV)
Enter secondary voltage (Vā) - e.g., 415V
Enter secondary current (Iā) - load current on secondary side
Select transformer type - Single Phase or Three Phase
Results include kVA rating, primary current, and turns ratio
ā Frequently Asked Questions (FAQ)
ā How to calculate transformer kVA rating? ā¼
For single phase: kVA = V Ć I / 1000. For three phase: kVA = ā3 Ć V Ć I / 1000. Enter voltage and current to get kVA rating.
ā What is the formula for transformer turns ratio? ā¼
Turns ratio = Nā/Nā = Vā/Vā. For example, 11kV/415V transformer has turns ratio = 11000/415 = 26.5.
ā How to calculate primary current from secondary current? ā¼
Iā = (Vā Ć Iā) / Vā. For a 11kV/415V transformer with 100A secondary current, primary current = (415 Ć 100) / 11000 = 3.77A.
ā What is the difference between single phase and three phase transformer? ā¼
Single phase has one primary and one secondary winding. Three phase has three sets of windings and uses ā3 factor in calculations. Three phase is more efficient for industrial loads.
ā What size transformer do I need for my load? ā¼
Calculate total load in kVA, add 20-30% for future expansion, and select the next standard kVA rating above this value. Use this calculator to verify sizing.
ā What is the standard transformer kVA rating? ā¼