Transformers Multiple Choice Questions & Answers (MCQs) on “Tap Changing Transformers-1”.
1. Why tapping is necessary?
a) To provide a neutral point
b) To vary secondary voltage
c) To control real and reactive power flow in the network
d) For neutral point, variation in secondary voltage, controlling power flow
Answer: d
Clarification: Voltage variation in power systems is a normal phenomenon owing to the rapid growth of industries and distribution network. System voltage control is therefore essential for many purposes as listed above.
2. Common range pf tap changing is __________
a) 5%
b) 7%
c) 15%
d) 10%
Answer: a
Clarification: Adjustment is normally carried out by off-circuit tap changing, the common range being 5% in 2.5% steps. Daily and short-time control or adjustment is carried out by means of on-load tap changing gear, which makes this application easier.
3. How tap changing is achieved?
a) Voltage variation with constant flux and constant voltage turn
b) With varying flux
c) Either by voltage variation or by flux variation
d) Can’t be done by variation in voltage or flux
Answer: c
Clarification: Tap changing may be achieved in one of the three conditions, viz.
(i) voltage variation with constant flux and constant voltage turn,
(ii) with varying flux,
(iii) a mix of (i) and (ii).
4. Negative tapping means ________________
a) less turns than positive tap
b) less turns than principal tap
c) less turns than zero tap
d) more turns than principal tap
Answer: b
Clarification: The principal tapping is one to which the rating of the winding is related. A positive tapping means more turns and a negative tapping implies less turns than those of the principal tap. Tap changing may be achieved by three conditions.
5. Tapping is done at _________________
a) primary only
b) secondary only
c) primary or secondary side
d) on both sides
Answer: c
Clarification: Tapping can be done to either primary or secondary sides. The taps may be placed on the primary or secondary side which depends on construction. Tapping is thus so useful for various applications.
6. Bushing insulators are required when ____________
a) tapping is done near the neutral end
b) tapping is done at the line ends
c) tapping is done
d) they are not required
Answer: b
Clarification: The taps may be placed on the primary or secondary side which partly depends on construction. If tapping is near the line ends, fewer bushings insulators are required. If the tappings are placed near the neutral ends, the phase-to-phase insulation conditions are eased.
7. For achieving large voltage regulation tapping should be done at _____________
a) at the upper ends
b) at the lower ends
c) at the centre
d) anywhere
Answer: c
Clarification: For achieving large voltage variation, tappings should be placed near the centres of the phase windings to reduce magnetic asymmetry. It is generally done on that winding which is placed outside.
8. In case of large voltage variations transformers are tapped at _____________
a) LV
b) HV
c) Both LV and HV
d) Can’t be tapped