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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Reactive power is calculated by
VIcos∅
VIsin∅
VI
IR
VIsin∅
In an A.C. circuit, reactive power represents the portion of power that oscillates between the source and the reactive elements (inductors and capacitors) without being dissipated. It is defined as the product of voltage, current, and the sine of the phase angle between them.
In an A.C. circuit, reactive power represents the portion of power that oscillates between the source and the reactive elements (inductors and capacitors) without being dissipated. It is defined as the product of voltage, current, and the sine of the phase angle between them.
Q=VIsinϕ — The expression for reactive power in A.C. circuits
P=VIcosϕ — The expression for active (real) power in A.C. circuits
Reactive power, denoted by Q, is associated with the magnetic fields in inductors and electric fields in capacitors. Since these components store energy during one part of the cycle and release it in the next, the average real power consumed by them is zero. The magnitude depends on the phase displacement ϕ introduced by these reactive components: Q=VIsinϕ.
Reactive power is measured in Volt-Ampere Reactive (VAR).
It is also known as 'wattless' power because it does not perform useful work.
A phase angle of ϕ=0 results in zero reactive power (purely resistive circuit).
Positive reactive power indicates inductive loading, while negative indicates capacitive loading.
Necessary to establish magnetic fields in motors and transformers.
Used to control voltage levels in power transmission systems.
Increases total current flow (apparent power) in the circuit.
Results in higher I2R losses in transmission lines.
Power factor correction using capacitor banks.
Voltage regulation in electrical grids.
Reactive power is the 'imaginary' part of the complex power triangle.
Option A (VIcosϕ) refers to active power, which is the actual power dissipated by the load.
B is correct — Reactive power is mathematically defined as the product of the root-mean-square (RMS) voltage, RMS current, and the sine of the phase angle difference between them, expressed as Q=VIsinϕ.
Always remember the mnemonic 'Active is Cosine, Reactive is Sine' (AC: Active Cosine) to quickly distinguish between real and imaginary power components.