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Electrical Measurements Problems on “Advantages of Instrument Transformers”.
1. Instrument transformers can be easily replaced.
a) True
b) False
Answer: a
Clarification: The secondary windings of C.T. and P.T. are standardized. As a result, instruments can be standardized with the ratings of C.T. and P.T. Hence the instrument transformers can be replaced with ease.
2. Instrument transformers provide _________
a) electrical isolation from low rated winding
b) electrical isolation from high rated winding
c) electrical isolation from medium rated winding
d) no electrical isolation at all
Answer: b
Clarification: In an instrument transformer, the low rated secondary windings provide electrical isolation from the high rated primary windings.
3. Instrument transformers give same readings irrespective of number of other instruments connected.
a) True
b) False
Answer: a
Clarification: When instruments are used with instrument transformers, they provide consistent readings. It does not vary with the instrument constants and the number of instruments connected in the circuit.
4. C.T. and P.T. are standardized at _________
a) 50 A and 220 V
b) 25 mA and 2.2 kV
c) 5 A and 110 V
d) 75 nA and 1.1 MV
Answer: c
Clarification: Current transformers are standardized at 5 A of secondary winding current, whereas Potential transformers are standardized at 110 V of secondary winding voltage.
5. A 5A ammeter can measure a current of upto 1000 A using a _________
a) 5/1000A C.T.
b) 1000A C.T.
c) 5A C.T.
d) 1000/5A C.T.
Answer: d
Clarification: A 1000/5A current transformer can be used for measuring a current of upto 1000A by making use of an ammeter with 5A current reading.
6. A 110V voltmeter can measure a voltage of upto 110kV using a _________
a) 110000/110V P.T.
b) 110000V P.T.
c) 110V P.T.
d) 110/110000V P.T.
Answer: a
Clarification: An 110000/110V potential transformer can be used for measuring a voltage of upto 110000V by making use of a voltmeter with 110V voltage reading.
7. How can the meter circuit be isolated from the power circuit?
a) by grounding
b) through electrical isolation
c) by physical separation
d) through mechanical isolation
Answer: b
Clarification: Leads of the secondary winding transformer are brought to the switch board thus separating them from high voltage windings. In this way, the meter circuit is isolated from the high voltage power circuit.
8. How are instrument transformers different from shunts and multipliers?
a) they are all the same
b) they have transformers
c) readings are independent of component values
d) they can be used for high voltages and currents
Answer: c
Clarification: Instrument transformers can be used for extending the range of the A.C. instruments. In instrument transformers, readings are independent of the values of R, L, and C. But in the case of shunts and multipliers, the readings depend on the values of circuit constants.
To practice all areas of Electrical Measurements Problems, .