In two wattmeter method of 3 phase power measurement, when does one wattmeter read negative

Electronics and Communication Engineering (ECE) : Measurements and Instrumentation - Quiz(MCQ)

when power factor is unity

when power factor is less than 0.5

when power factor is less than 0.5 lagging

when power factor is greater than 0.5 lagging

Correct Answer : Option (B) : when power factor is less than 0.5

Explanation : When p.f. is less than 0.5 (leading or lagging) one of the wattmeters reads negative.

Recently Updated in Measurements and Instrumentation Questions

In measurements using strain gauge, the dummy strain gauge is used to

compensate for error in voltmeter

compensate for change in temperature

compensate for resistance of strain gauge

compensate for error due to change in voltage of battery

Correct Answer : compensate for change in temperature

A CT is used to feed current coils of wattmeter, energy meter, power factor meter and an ammeter. Then

all coils are in parallel

the coils are in series-parallel

all the coils are in series

None of the above

Correct Answer : all the coils are in series

A permanent magnet moving coil measures

dc value

peak value

true rms value

rms plus dc value

Correct Answer : dc value