This set of Electrical Measurements Questions and Answers for Freshers focuses on “Open Circuiting the Secondary Circuit of a Current Transformer”.
1. In a C.T., the primary ampere turns is variable.
Explanation: In a current transformer, the primary ampere turns is fixed. When the secondary circuit is opened, assuming a constant primary current we get a fixed number of primary ampere turns.
2. The secondary circuit of a C.T. is open when?
a) a very high flux density is produced
b) a very low flux density is produced
c) a moderate flux density is produced
d) no flux density is produced
Explanation: When current is flowing in the secondary circuit which is kept open in a C.T., a very high flux density is produced in the core as a result of the absence of demagnetizing ampere turns.
3. High flux density leads to _________
a) a decreased voltage in the secondary
b) a decreased voltage in the primary
c) a increased voltage in the secondary
d) a decreased voltage in the primary
Explanation: High flux density in the secondary winding of a C.T. leads to an increase in the induced voltage in the secondary winding. This may damage the insulation.
4. When primary current flows, secondary circuit should be open.
Explanation: In a current transformer, even when it is not in use for any measurement purposes, the secondary circuit must be closed when the primary current is flowing.
5. High magnetizing forces in the core when removed suddenly lead to ____________
a) no residue
b) partial residual magnetism
c) rupture of the device
d) residual magnetism
Explanation: In a C.T, the high magnetizing forces on the core may leave behind residual magnetism in the core and ratio and phase angle errors.
6. The secondary winding of a C.T. ____________
a) can be shorted
b) can’t be shorted
c) can be opened
d) can’t be opened
Explanation: When a C.T. is used in measurements, it acts as a short circuit. This is because the impedance of the load is negligible due to the ammeter or the wattmeter coil. Thus the secondary winding of a C.T. can be shorted.
7. The secondary winding of a C.T. is opened when?
a) C.T. is magnetised
b) C.T. is demagnetised
c) C.T. is shorted
d) C.T. is opened
Explanation: In a C.T., when the secondary winding is opened by mistake when the primary current is flowing, the C.T. must be demagnetized first fully and then only must be used again in the circuit for any measurements.
8. The rectangular type of C.T. is built of _________
a) L shaped windings
b) T shaped windings
c) A shaped windings
d) Z shaped windings
Explanation: In a rectangular type of C.T., the windings are placed on the shorter limbs. The primary winding is wound over the secondary. The rectangular type of C.T. is built of L shaped windings.
Sanfoundry Global Education & Learning Series – Electrical Measurements.
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