How to Convert KVA to KW 3-Phase

How to Convert KVA to KW 3-Phase
••• lisafx/iStock/GettyImages

Power Basics

Power, in general physics, is energy per unit time. Energy in turn is force multiplied through a distance. The standard, or SI, unit for power is watts (W), while the SI unit for energy is joules (J). Time is normally expressed in seconds.

In electromagnetic physics, the principles stand but the units shift. Instead of determining power as W = J/s, power is expressed as the product of potential difference in volts (V) and current in amperes (I). Thus in this scheme:


From these equations, it is clear that a watt is the same as a volt times an ampere, or a volt-ampere (VA). It therefore follows that a kilowatt (kW) is the same as a kilo-volt-ampere (kVA), with each side of the equation divided by 1,000.

Three-Phase Systems and Kilo-Units

In alternating current (AC) power systems, voltage is often delivered in phases, as this is advantageous in terms of reducing energy losses. These phases appear graphically as sine waves, with voltage rising and falling cyclically over short period of time. In a three-phase system, these sine waves overlap, but their cycles start and end at different points in time. The result is that power in these systems is not simply the product of voltage times current, but is instead:


Therefore, if you are working with a three-phase motor, the relationship between kW and kVA is:



Assume you are given a three-phase AC power source with a voltage of 220 V supplying a current of 40 A. What is the power in kilowatts?

First, multiply the voltage and the current to obtain raw volt-amperes:

(220\text{ V})(40\text{ A})=8800\text{ VA}

Then, multiply by the normalizing factor for three-phase systems:

\sqrt{3}(8800\text{ VA} = 15242\text{ VA}

Finally, divided by 1,000 to get the answer in kW (or kVA):

\frac{15242\text{ W}}{1000}=15.242\text{ kW}

Related Articles

How to Convert HP to Amps & Volts
How to Calculate Kva to Amp
Types of Electrical Loads
How to Convert Megawatts to Amps
How to Convert 12 Volt Alternator to 120 Volts
How to Calculate 3 Phase Power
How to Convert KWH to KVA
How to Calculate 3-Phase Line-To-Ground Voltage
How to Calculate Motor Inrush Current
What Is the Difference Between Resistive & Inductive...
How to Calculate Three Phase Amps From Megawatts
How to Calculate 30 KW to Amps
What Is the Unit for Enthalpy?
AC & DC Characteristics
How to Convert 240 Single Phase to 480 3 Phase
How to Convert Horsepower to kWh
How to Calculate the Short Circuit Rating
How to Figure kW Rating of a 3 Phase Electric Motor
How to Change Electrical Amps to Watts