September 10, 2023

Calculation of power in power supply and distribution system

In our dynamic environment system, we often encounter active power, reactive power, power factor and apparent power of power supply and distribution system. Perhaps many of those involved in computer room maintenance and dynamic environment debugging do not know their actual meaning and conversion formula, today we will briefly talk about differences between them.

Active power. Simply put, it is power consumed in circuit. Denoted by letter "P", unit is (W), (kW). It reflects amount of work done by a resistive element, or amount of electrical energy converted into another energy per unit time.

Reactive Power: The power transferred back and forth between an inductive or capacitive element and an AC power source. Denoted by letter "Q", unit of measurement is (VAR), (KVAR). It expresses maximum rate at which AC energy is exchanged with magnetic or electric field energy.

Apparent Wattage: Also referred to as productive power, which is total power that an AC power supply can provide. Denoted by letter "S" and is a unit of measurement (VA), (kav) that is commonly used to indicate power of AC power supply equipment (such as transformers).

Power factor: cosinevoltage and current in an AC circuit > . Denoted by symbol cosΦ.

What is relationship between active power, reactive power, apparent power and power factor? We use a formula to express:



The apparent power of three-phase equipment is S=3*Up*Ip, where Up is single-phase phase voltage and Ip is single-phase phase current.

The apparent power of three-phase equipment is S=√3*U*I, where U represents line voltage and I represents line current.

Active power of three-phase equipment P=Pa+Pb+Pc, where Pa, Pb and Pc — active power of each phase of three-phase equipment (Pa=Ua*a*CosΦa); with symmetrical three-phase load Active power of three-phase equipment P=3U*I*COSΦ.