What is kVA?

kVA stands for kilo volt-amperes or simply 1000 volt-amperes. It is basically the unit of apparent power and is the product of RMS values of voltage and current.

One kVA is 1000 volt – amperes

What is kVA rating of a transformer?
Nameplate of a transformer with its kVA rating highlighted.

Apparent power

Apparent power is the actual amount of power drawn from the source. It includes both true power and reactive power.

In case of DC, the apparent power is irrelevant. But when it comes to AC, for reactive loads, the current and voltage are out of phase. So, the actual usable power (true power) depends on power factor and is always less than the apparent power.

Read more: Real, Reactive, Complex and Apparent power

AC power sources such as alternators, inverters and transformers are rated in kVA. The output of these devices is independent of power factor of the load.

Calculation of kVA – Apparent power

For single phase, kVA can be calculated using the following formula.

Single phase apparent power,

kVA = (Voltage X Current)/1000

For three phase, kVA can be calculated using the following formula.

Three phase apparent power,

kVA = (√3  X Voltage X Current)/1000 = (1.732 X Voltage X Current)/1000

Calculation of current from kVA

For single phase, current can be calculated from kVA using the following formula.

Single phase current = (kVA X 1000) / Voltage

For three phase, current can be calculated from kVA using the following formula.

Three phase current,

Current = (kVA X 1000) / ( √3  X Voltage) = (kVA X 1000) / ( 1.732 X Voltage)

Summing up

  • kVA is the unit of measure of Apparent power.
  • One kVA is equal to 1000VA.
  • It is calculated by multiplying the RMS value of voltage by the RMS value of current and dividing the product by 1000.
  • In the case of DC, kVA = kW.
  • kVA is independent of the power factor of a load.
  • Alternators, transformers, power supplies and UPS are rated in kVA.

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