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
š Standard Transformer kVA Ratings
kVA
Primary (11kV) Current
Secondary (415V) Current
25
1.3A
34.8A
50
2.6A
69.6A
100
5.2A
139A
200
10.5A
278A
315
16.5A
438A
500
26.2A
696A
630
33.1A
877A
1000
52.5A
1392A
1600
84.0A
2228A
2000
105.0A
2785A
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
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
ā Frequently Asked Questions
How to calculate transformer kVA rating? ā¼
Single phase: kVA = V Ć I / 1000. Three phase: kVA = ā3 Ć V Ć I / 1000.
What is the formula for transformer turns ratio? ā¼
Turns ratio = Nā/Nā = Vā/Vā. For 11kV/415V, ratio = 11000/415 = 26.5.
How to calculate primary current from secondary current? ā¼
Iā = (Vā Ć Iā) / Vā. For 11kV/415V with 100A secondary, Iā = 3.77A.
Single phase vs three phase transformer? ā¼
Single phase has one winding set. Three phase has three sets and uses ā3 factor. Three phase is more efficient for industrial loads.
What size transformer do I need for my load? ā¼
Calculate total load in kVA, add 20-30% for future expansion, select next standard rating above this value.