Apparent Power

In a simple alternating current (AC) circuit consisting of a source and a linear load, both the current and voltage are sinusoidal. If the load is purely resistive, the two quantities reverse their polarity at the same time, and the direction of energy flow does not reverse. In this case, only real power flows.

If the load is purely reactive, then the voltage and current are 90 degrees out of phase and there is no net energy flow. That is, the peaks of voltage are centered at the times when the current crosses zero, and is half positive and half negative. In this case, only reactive power flows—no net transfer of energy to the load occurs.

Practical loads have resistance, inductance, and capacitance, so both real and reactive power will flow to real loads. Power engineers measure power use as the sum of real and reactive power. Alternatively, they measure power factor, the ratio of real power to apparent power, where apparent power is the product of the root-mean-square voltage and current.

The apparent power is the product of voltage and current. Apparent power is handy for sizing of equipment or wiring. However, adding the apparent power for two loads will not accurately give the total apparent power unless they have the same displacement between current and voltage (the same power factor).

Apparent Power: U x I = VA (will be higher or even to real power)

Real Power: U x I x PF = VA

U = Voltage expressed in Volt
P = Power expressed in Watt
PF = Power Factor in %
I = Current expressed in Ampère

U x I = VA (method used by most PDU devices)
U x I x PF = W (method used by the DCMU, 320.000 measurements per second)

How to Use

Racktivity provides this parameter only as additional information, as it can be useful to compare with historical measurements with devices that could not measure the Real Power.