Question

Two watt meters, which are connected to measure the total power on a three-phase system supplying a balanced load, read 10.5 kW and – 2.5 kW respectively. What is the total power?

(a) 13.0 kW

(b) 13.0 kW

(c) 8.0 kW

(d) 8.0 kW

I have been asked this question during an interview for a job.

I want to ask this question from Advanced Problems on Measurement of Power in Polyphase Circuit topic in chapter Measurement of Power and Related Parameters of Electrical Measurements

Answer 1

Right answer is (d) 8.0 kW

For explanation: w1 = 10.5 kW

w2 = -2.5 kW

w = w1 + w2 = 8 kW

So, tan ∅ = \(\frac{1.732(w1-w2)}{(w1+w2)}\) = 2.81

Or, ∅ = 70.43

So, cos ∅ = 0.334.