The current coil of a wattmeter is connected to the CT of R-phase. The potential coil is connected across Y and B phases. The wattmeter measures
A. Active power in R phase
B. Active power of Y phase
C. Reactive power of R phase
D. Power proportional to 3 phase power if the load is balanced
Answer: Option C
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The spring material used in a spring control device should have the following property.
A. Should be nonmagnetic
B. Most be of low temperature coefficient
C. Should have low specific resistance
D. All of the above
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A. The meter is calibrated for AC and it’s error for DC would be high
B. The meter does not respond to DC signals
C. The error is high due to hysteresis effect
D. The error is high due to eddy current effect
A moving iron ammeter may be compensated for frequency errors by
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B. A series inductance
C. Shunt capacitance
D. Series resistance
Wattmeter reading = VPC ICC cos (VPC ^ ICC)
A current coil of wattmeter is connected to the CT of R-phase. So, wattmeter takes the current flowing through the R phase.
Pressure coil is connected across the Y phase and B phase. So, wattmeter takes the voltage VYB
Now, the wattmeter reading is,
W = VYB IR cos (VYB ^ IR)
Let the load angle is ?, the angle between VYB and IR is (90 – ?)
⇒ W = VYB IR sin ? = reactive power of the R phase.
please explain the answer if known to anyone.