This set of Transformers Multiple Choice Questions & Answers (MCQs) focuses on “Distribution Transformers”.
1. Distribution transformers are generally designed for maximum efficiency around __________
a) 90% load
b) zero load
c) 25% load
d) 50% load
View Answer
Explanation: The main difference between power and distribution transformer is distribution transformer is designed for maximum efficiency at 60% to 70% load as they normally don’t operate at full load all the time. Its load depends on distribution demand.
2. In a power or distribution transformer about 10 per cent end turns are heavily insulated _______________
a) to withstand the high voltage, drop due to line surge produced by the shunting capacitance of the end turns
b) to absorb the line surge voltage and save the winding of transformer from damage
c) to reflect the line surge and save the winding of a transformer from damage
d) insufficient information
View Answer
Explanation: End turns produce shunt capacitance while circuit is made ON. Thus, to provide protection from line surge produced by the shunting capacitance of the end turns and to withstand high voltage they are heavily insulated.
3. Distribution transformers have _______________
a) smaller size than Power transformer
b) larger size than power transformers
c) size can be more or less depending on type
d) more weight than power transformers
View Answer
Explanation: Distribution transformers are very likely to be made in a different factory from larger transformers. Being smaller and lighter they do not require the same specialised handling and lifting equipment as larger transformers. Impregnation under very high vacuum and vapour-phase drying equipment is not generally required.
4. Joints are used in distribution transformers because _____________
a) smaller in size
b) economical aspects
c) availability
d) less losses
View Answer
Explanation: Joints form a greater proportion of the total iron circuit in the case of a small distribution transformer core compared to that of a large power transformer and so, measures to reduce losses at the joints will show a greater benefit.
5. How power losses and noise levels are lowered down?
a) By using another core material
b) By using step-lap construction
c) By using Different winding method
d) By using different oil
View Answer
Explanation: The competitive nature of the industry, gives an incentive to provide low losses and noise levels in order to sustain in the market, both of which are improved by using the step-lap construction.
6. Foil windings are used for distribution transformers _________________________
a) low voltage winding
b) high voltage winding
c) for both windings
d) not used
View Answer
Explanation: Foil windings are frequently used as low-voltage windings. In this form of construction, the winding turn, of copper or aluminium foil, occupies the full width of the layer. This is wound around a plain mandrel, with intermediate layers of paper insulation, to form the required total number of turns for the winding.
7. Foil winding provides ________________
a) less mechanical short circuit strength
b) low degree of electromagnetic balance
c) high degree of electromagnetic balance
d) can’t tell by just winding type
View Answer
Explanation: Foil winding arrangement represents a very cost-effective method of manufacturing low-voltage windings and also enables a transformer to be built which has a high degree of electromagnetic balance and hence good mechanical short-circuit strength.
8. Voltage per turn in distribution transformers is ____________
a) very high
b) very low
c) depends on application
d) depends on other components of system
View Answer
Explanation: Distribution transformers because of the small frame sizes resulting from low kVA ratings, the volts per turn is usually very low so that for a high-voltage winding a considerable number of turns will be required.
9. Which of the following can be used for HV winding in distribution transformers?
a) Coil winding
b) Foil winding
c) Cross-over coil
d) Single dash folding
View Answer
Explanation: Another alternative for high-voltage windings is the use of ‘crossover’ coil which shows an individual coil. Each section of the winding, or coil, is itself a small multilayer spiral winding having a relatively short axial length.
10. Which of the following protective component is not provided on small distribution transformers?
a) Overfluxing protection
b) Buchholz relay
c) Overcurrent protection
d) Overcurrent and overvolt protection
View Answer
Explanation: Class C dry-type transformers are those based on glass fibre-reinforced boards, aromatic polyamide paper conductor insulation and similar materials capable of operating at temperatures up to around 220°C. Generally small, lighter transformers are made of this type.
Sanfoundry Global Education & Learning Series – Transformers.
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