1. Wattmeter cannot be designed on the principle of
- Electrostatic instrument
- Thermocouple instrument
- Moving iron instrument
- Electrodynamic instrument
2. Two wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other (both positive), then the power factor of the load is
3. A single-phase load is connected between R and Y terminal of a 415 V, symmetrical, 3 – phase, 4 – wire system with phase sequence RYB. Load resistance of 100 Ohms is connected in a wattmeter. The power factor of the load is 0.8 lagging. The wattmeter will read.
4. A 300 V, 5 A, LPF wattmeter has a full scale of 300 W. The wattmeter can be used for loads supplied by 300 V AC mains with a maximum power factor of ________
5. Statement (I): The reactive power of the three-phase balanced load can be measured with the use of a single wattmeter.
Statement (II): For measurement of reactive power the current coil is connected to one of the phases of a 3-ϕ network.
6. In case of power measurements by two wattmeter method in a balanced 3-phase system with pure inductive load
- Both wattmeters will indicate the same value but with opposite signs
- Both wattmeters will indicate zero
- Both the wattmeters will indicate the same value same sign
- One wattmeter will indicate zero and the other will indicate same non-zero value.
7. A 3 phase star-connected load is supplied with 440 V and 50 Hz supply, two wattmeter method is used to measure the power in the load. The readings of the wattmeter are 2000 W and – 1000 W. What is the value of the capacitor in μF to be connected in series with each phase of load such that the power is measured by one wattmeter.
- 140.58 μF
- 132.79 μF
- 138.58 μF
- 122.85 μF
8. The apparent power drawn by an AC system is 50 kVA, reading of wattmeter is 20 kW. Reactive power consumed will be
- 45.82 kVAR
- 50 kVAR
- 70 kVAR
- 20 kVAR
9. In a particular test, the readings of two wattmeters are 5 kW and 1 kW. If the second-meter connections are reversed, the total power and power factor are
- 5 kW, 0.6933 lag
- 4 kW, 0.3592 lag
- 3 kW, 0.327 lag
- 5 kW, 0.327 lag
10. Two wattmeters are connected to measure the power consumed by a 3-ϕ load with a power factor of 0.4. The total power consumed by the load as indicated by the two wattmeters is 30 kW. The difference between the two wattmeter readings is _____ kW
- 40.44 kW
- 35.59 kW
- 39.69 kW
- 42.25 kW
11. A 3 phase 500 V motor load has a power factor of 0.5. Two wattmeter are connected to measure the input. They show the input to be 36 kW. The readings of both the instruments are.
- W1 = 36 kW, W2 = 0 kW
- W1 = 9 kW, W2 = 27 kW
- W1 = W2 = 18 kW
- W1 = 45 kW, W2 = -9 kW