Question

In the figure given below, a 220 V 50 Hz supplies a 3-phase balanced source. The pressure Coil (PC) and Current Coil (CC) of a watt-meter are connected to the load as shown. The watt-meter reading is _________

(a) Zero

(b) 1600 W

(c) 242 W

(d) 400 W

The question was posed to me in an interview for internship.

The above asked question is from Problems Involving Coupling Coefficient in chapter Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

The correct option is (c) 242 W

Explanation: Watt-meter reading = Current through CC × Voltage across PC × cos (phase angle).

IBR = ICC = \(\frac{220∠120°}{100°}\) = 2.2∠120°

VYB = VPC = 220∠-120°

w = 2.2∠120° × 220∠-120° × cos 240° = – 242 W.