An reactive power in an A.C. circuit is given by the expression

Question

Question

This question was previously asked in

ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 3

Answer 1

Complex power:

Complex power is a complex quantity that contains both the average power P and the reactive power Q.

S = P + jQ

The complex power delivered to an element is given by

S = V × I∗

S = complex power

V = Voltage across the element

I* = Conjugate of current through the element

Reactive power is a means of measuring the energy flow rate to and from reactive loads.

Apparent power is the maximum possible average power.

The power triangle is shown below.

F1 U.B Madhu 23.03.20 D10

P = Active power (or) Real power in W = Vrms Irms cos ϕ

Q = Reactive power in VAR = Vrms Irms sin ϕ

S = Apparent power in VA = Vrms Irms

S = P + jQ

$S = \sqrt{P^{2} + Q^{2}}$

ϕ is the phase difference between the voltage and current

Power factor $\cos ϕ = \frac{P}{S}$

Power factor can be defined as the ratio of real power to apparent power.

Important Points

Unit of reactive power is Var.

Unit of apparent power is VA.

Unit of total power is Watt.