kVA calculator
Pick what you want to find, then enter what you know. You get the amps, kVA or kW for single- or three-phase power, and the next standard transformer size up.
Inputs
Result
kVA to amps chart
Full-load amps for standard transformer sizes.
How it is worked out
A 75 kVA three-phase transformer at 208 V delivers 75,000 / (1.732 x 208) = 208 A at full load. A 200 A single-phase service at 240 V is 240 x 200 / 1,000 = 48 kVA. A generator rated 80 kW at a power factor of 0.8 is 100 kVA.
kVA or kW?
kW is real power, the part that does work. kVA is apparent power, volts times amps, which is what heats the wires and windings. Transformers, generators and UPS units are rated in kVA because their limit is current, whatever the power factor of the load. For heating and lighting loads kW and kVA are about equal; for motors, kVA is higher.
Standard transformer sizes
Single-phase: 10, 15, 25, 37.5, 50, 75, 100, 167, 250, 333 and 500 kVA. Three-phase: 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, 1,000, 1,500, 2,000 and 2,500 kVA. The calculator gives the next size up from your load; the engineer sizes the real transformer from the load calculation, with any growth and motor starting.
For a single circuit in watts, use the watts to amps calculator. For a dwelling service, the electrical load calculator does the NEC 220.82 calculation.
Questions
How do I convert kVA to amps?
Single-phase: kVA x 1,000 / volts. Three-phase: kVA x 1,000 / (1.732 x volts). 75 kVA at 208 V three-phase is 208 A; at 480 V, 90 A.
How many amps is a 45 kVA transformer?
At 208 V three-phase, 125 A; at 480 V, 54 A.
How do I convert kW to kVA?
Divide kW by the power factor. 80 kW at a power factor of 0.8 is 100 kVA.
How many kVA is 100 amps?
24 kVA single-phase at 240 V; 36 kVA three-phase at 208 V and 83 kVA at 480 V.
Is kVA the same as kW?
Only when the power factor is 1. kW = kVA x power factor, so a 100 kVA generator at 0.8 power factor supplies 80 kW.
What size transformer do I need?
Work out the load in kVA and pick the next standard size up: a 60 kVA three-phase load takes a 75 kVA transformer. Leave room for growth and motor starting.
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