Apparent Power
What is Apparent Power?
Apparent Power (S) is a fundamental parameter in AC technology. It combines both the effectively usable power and the portions that merely oscillate between the power source and the load.
It results from the product of voltage and current and indicates the total power an electrical system must supply or absorb – regardless of how much of it is actually converted into mechanical work, heat, or light.
In practice, Apparent Power is essential for correctly sizing electrical installations, cables, and protective devices, as it reflects the maximum required power capacity. It is measured in Voltampere (VA) and, together with Active Power (P) and Reactive Power (Q), forms the power triangle, which illustrates the interaction of the power components.
Apparent Power provides clear insight into how heavily a system is loaded and which reserves need to be considered.
Practical Example: Apparent Power
Assume an electric motor in a workshop operates at 400 V and draws a current of 5 A. The Apparent Power is calculated as:
S = U × I = 400 V × 5 A = 2000 VA (2 kVA)
However, the motor has a power factor (cos φ) below 1, for example 0.8. This results in an Active Power of:
P = S × cos φ = 2 kVA × 0.8 = 1.6 kW
This means the grid and the cables must be rated for 2 kVA Apparent Power, even though the motor delivers only 1.6 kW of usable power. This example illustrates why Apparent Power is crucial for sizing cables, fuses, and transformers.