Question

The figure shows a three-phase, delta connected load supplied from a 220 V, 50 Hz, 3-phase balanced source. The pressure Coil (PC) and Current Coil (CC) of a watt-meter are connected to the load as shown, with the coil polarities suitably selected to ensure a positive deflection. The watt-meter reading will be?

(a) Zero

(b) 1600 W

(c) 242 W

(d) 400 W

This question was posed to me in final exam.

I'd like to ask this question from Advanced Problems on Measurement of Power in Polyphase Circuit topic in portion Measurement of Power and Related Parameters of Electrical Measurements

Answer 1

Correct choice is (c) 242 W

To elaborate: 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.