Question

The two-wattmeter method is used to measure active power. The system is a 3-phase, 3- wire system. Then, the power reading is?

(a) Affected by both negative sequence and zero sequence voltages

(b) Affected by negative sequence voltages but not by zero sequence voltages

(c) Affected by zero sequence voltages but not by negative sequence voltages

(d) Not affected by negative or zero sequence voltages

I have been asked this question in unit test.

My question is based upon Advanced Problems on Measurement of Power in Polyphase Circuit topic in division Measurement of Power and Related Parameters of Electrical Measurements

Answer 1

Correct option is (d) Not affected by negative or zero sequence voltages

For explanation I would say: If the phase voltage is unbalanced, then the power reading is not affected by both negative as well as zero sequence voltages. This is a characteristic property of the 2 watt-meter meter since it measures the active power on a three phase three wire system.