1. Which of the following indicating instrument, has/have linear scale ?
- Moving iron meter.
- PMMC meter.
- Thermocouple meter.
- Rectifier type meter.
Select the correct answer using code given below : Code:
(a) Only 1 and 2
(b) Only 2 and 3
(c) Only 3 and 4
(d) Only 2
2. Which of the following instruments will have poorest overloading capacity ?
(a) Moving coil instruments.
(b) Induction type instruments.
(c) Permanent magnet instruments.
(d) Hotwire instruments.
3. Which of the following instrument is free from hysteresis and eddy current errors ?
(a) Moving iron instrument.
(b) Electrostatic instrument.
(c) Moving coil permanent magnet type instrument.
(d) Moving coil dynamometer type instrument.
4. Which voltmeter would you select for measuring 50,000 V direct current ?
(a) Moving coil voltmeter.
(b) Hot wire voltmeter.
(d) Electrostatic voltmeter.
5. What is the correct sequence of the following types of ammeters and voltmeters with increasing accuracy ?
- Moving iron.
- Moving coil permanent magnet.
Select the correct answer using the codes given below. Codes:
(a) 1, 3, 2
(b) 1, 2, 3
(c) 3, 1, 2
(d) 2, 1, 3
6. To increase current measurement range of an ammeter, it is
(a) shunted by a high resistance.
(b) put in series with a high resistance.
(c) put in series with a low resistance.
(d) shunted by a low resistance.
7. How can a milliammeter be used as a voltmeter ?
(a) By connecting a low resistance in parallel with the instrument.
(b) By connecting a high resistance in parallel with the instrument.
(c) By connecting a low resistance in series with the instrument.
(d) By connecting a high resistance in series with the instrument.
8. The primary current in a CT is dictated by
(a) the secondary burden.
(b) the core of the transformer.
(c) the load current.
(d) none of the above.
9. The secondary of a CT is never left open-circuited because otherwise
(a) heat dissipation in the core will be very large.
(b) the core will be saturated and permanently magnetized rendering it useless.
(c) dangerously high emfs will be induced in the secondary.
(d) all of the above.
10. Consider the following statements regarding the causes of error in current transformers.
- Some exciting mmf is required by the primary winding to produce a flux.
- The flux density in the core is not a linear function of the magnetizing force.
- There is some magnetic leakage in the secondary winding.
- There is significant power consumption in the metering circuit.
Of these statements
(a) 1 and 2 are correct.
(b) 1, 2 and 3 are correct.
(c) 2 and 4 are correct.
(d) 1, 3 and 4 are correct.
11. Consider the following statements : A current transformer is used for measurement of large currents to
- isolate the instrument from a high voltage bus bar.
- increase the accuracy of measurement.
- decrease the cost of measuring arrangements.
- extend the range of measurement of a conventional ammeter on ac.
Which of these statements are correct ?
(a) 1 and 2.
(b) 2 and 3.
(c) 3 and 4.
(d) 1 and 4.
12. Instrument transformers are known to introduce magnitude and phase errors in measurements. These are primarily due to
(a) improper connections on the primary side.
(b) measurement errors inherent in the meter connected to the transformer secondary
(c) open and short circuit parameters of the instrument transformers.
(d) none of the above.
13. A current transformer has a phase error of 3°. The phase angle between the primary and secondary currents is
14. What is clamp-on ammeter used for ?
(a) Low ac current.
(b) High ac current.
(c) Low dc current.
(d) High dc current.
15. In case of a PT with the increase in load on secondary side
(a) both of the ratio error and phase angle increase.
(b) the ratio error increases but phase angle decreases.
(c) the ratio error decreases but phase angle increases.
(d) both of the ratio error and phase angle error decrease.
16. The moving coil in a dynamometer wattmeter is connected
(a) in series with the fixed coil.
(b) across the supply.
(c) in series with the load.
(d) across the load.
17. Dynamometer type wattmeters are suitable for
(a) both ac and dc circuits.
(b) only ac circuits.
(c) only dc circuits.
(d) only high voltage ac circuits.
18. The pressure coil of a dynamometer type wattmeter is
(a) highly inductive.
(b) highly resistive.
(c) purely resistive.
(d) purely inductive.
19. In a statement “the wattmeter commonly used for power measurement at commercial frequencies is of the X type. This meter consists of two coil systems, the fixed system being the Y coil and the moving system being the Z coil ” X, Y and Z stand respectively for
(a) dynamometer, voltage and current.
(b) dynamometer, current and voltage.
(c) induction, voltage and current.
(d) induction, current and voltage.
20. A dynamometer type wattmeter responds to the
(a) average value of active power.
(b) average value of reactive power.
(c) peak value of active power.
(d) peak value of reactive power.