Transformer Sizing Calculator
Calculate transformer kVA rating and load capacity for single-phase and three-phase systems
Calculate Transformer Sizing
Voltage requirement of the connected load
Current requirement of the connected load
Additional capacity for future load growth and safety margin
Transformer Sizing Results
Formula used: kVA = I × V / 1000
Transformer type: Single Phase
Input values: 0A at 0V
Example Calculation
Industrial Motor Load
Load Type: Three-phase motor
Load Current: 250 A
Load Voltage: 480 V
Transformer Type: Three-phase
Calculation
kVA = I × V × √3 / 1000
kVA = 250 × 480 × 1.732 / 1000
kVA = 207,840 / 1000
kVA = 207.84 kVA
Suggested transformer size: 225 kVA
Standard Transformer Sizes (kVA)
Transformer Types
Single Phase
120V, 240V residential
Up to 167 kVA typically
Three Phase
208V, 480V, 600V industrial
More efficient for large loads
Sizing Tips
Add 20-25% spare capacity for future growth
Consider starting current for motors (5-7x running current)
Use three-phase for loads above 10 kVA
Consider power factor for accurate sizing
Understanding Transformer Sizing
What is kVA Rating?
kVA (kilovolt-ampere) is the unit used to rate transformers. It represents the apparent power that the transformer can handle, combining both active power (kW) and reactive power (kVAR). Unlike kW, kVA doesn't depend on the power factor of the load.
Why Use kVA Instead of kW?
- •Independent of load power factor
- •Accounts for both resistive and reactive loads
- •Represents total current handling capability
- •Universal rating for all load types
Sizing Formulas
Single Phase:
kVA = I × V / 1000
Three Phase:
kVA = I × V × √3 / 1000
- I: Load current in amperes (A)
- V: Load voltage in volts (V)
- √3: ≈ 1.732 (three-phase factor)
- 1000: Conversion factor to kVA
Transformer Operation
Transformers work on the principle of electromagnetic induction. When alternating current flows through the primary winding, it creates a changing magnetic field that induces voltage in the secondary winding. The voltage ratio is determined by the turns ratio.
Voltage Ratio: Vs/Vp = Ns/Np
Where Vs, Vp are secondary and primary voltages, and Ns, Np are the number of turns
Power Types
Power that does useful work
Power stored and returned by reactive components
Total power (vector sum of active and reactive)