Test: Measurement of Power & Energy- 2 - Electrical Engineering (EE) MCQ

A dynamometer wattmeter measures power in a 50 Hz, single phase circuit without error, at all power factors. The resistance of the voltage coil and its series resistance are 400 Ω and 10,000 Ω, respectively. The series resistance has a distributed self-capacitance equivalent to a shunt capacity of 20 pF.What is the self inductance of the pressure coil?

Assertion (A): For measuring the power factor of the load in case of a two-wattmeter method, load may be balanced or unbalanced.
Reason (R): For measuring the power in a three- phase circuit, load may be balanced or unbalanced, source may be balanced or unbalanced but there must be three-phase load connected to three-phase source via three- phase wires.​

The voltage and current in a circuit are given by, v(t) = 5 + 2 sin(ωt + 30°) + 10 sin(3ωt - 60°) and i(t) = 10 + 5 sinωt + 8 sin(2ωt-30°)
The total power consumed in the circuit is

In an electrodynamometer type wattmeter
1. moving coil is iron cored.
2. fixed coil is air cored.
3. air friction damping is used.
4. the fixed coil is connected across the load.
5. the moving coil is connected in series with the load.

Q. Which of the above statements is/are true?

Assertion (A): A wattmeter must be used for the measurement of power in a.c. circuit instead of merely an ammeter and a voltmeter.
Reason (R): Wattmeter measures average active and reactive powers.

Assertion (A): An electrodynamometer type wattmeter reads low when the load power factor is leading.
Reason (R): The effect of pressure coil inductance is to increase the phase angle between load current and pressure coil current when the load power factor is leading.

 The ratio of measured power to true power in case of an electrodynamometer type wattmeter is given by (β = internal angle of pressure coil circuit)

Assertion (A): Phantom loading of energy meter consists of supplying the fixed coil circuit from a circuit of required normal voltage, and the moving coil circuit from a separate low voltage supply.
Reason (R): When the current rating of a meter under test is high, a test with actual loading arrangement would involve a considerable waste of power due to which phantom or fictious loading is done.

A dynamometer wattmeter with its voltage coil connected across the load side of the instrument reads 250 W, If the load voltage be 200 V, what power is being taken by the load?​
(The voltage coil has a resistance of 2000 Ω)

The power flowing in a 3- φ, 3-wire, balanced load system is measured by the two-wattmeter method. The reading on wattmeter -A is 3 kW and on wattmeter -B is-1 kW. The factor of the load is

Holes are filled on the opposite side of the disc of an induction type energy meter to

Two-wattmeter method is employed to measure power in a 3-phase balanced system with the current coils connected in the A and C lines. The phase sequence is ABC. If the wattmeter with its current coil in A-phase line reads zero, then the power factor of the 3-phase load will be