Transformer Mcqs


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
Answer & Explanation Answer: B) Buchholz relay

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.

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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
Answer & Explanation Answer: C) Cross-over coil

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.

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Voltage per turn in distribution transformers is ____________

A) very high B) very low
C) depends on application D) depends on other components of system
Answer & Explanation Answer: B) very low

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.

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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
Answer & Explanation Answer: C) high degree of electromagnetic balance

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.

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Foil windings are used for distribution transformers _________________________

A) low voltage winding B) high voltage winding
C) for both windings D) not used
Answer & Explanation Answer: D) not used

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.

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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
Answer & Explanation Answer: B) By using step-lap construction

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.

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Joints are used in distribution transformers because _____________

A) smaller in size B) economical aspects
C) availability D) less losses
Answer & Explanation Answer: D) less losses

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.

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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
Answer & Explanation Answer: A) smaller size than Power transformer

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.

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