GATE 2021 IN – Question 59
A 400 V rms line-to-line, three-phase, three-wire RYB system is measured with two wattmeters as shown. R-line current is $5\angle60^\circ$ A. R-line wattmeter $W_1$ reads ______ W.
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Correct answer: 0 to 0
Explanation
Using the conventional R-phase voltage reference for the stated RYB system, VRB lags VR by 30°. IR=5∠60° A therefore differs from VRB by 90°. W1=Re(VRB IR*)=400·5·cos90°=**0 W**. Use the line-to-line voltage across that wattmeter’s pressure coil.