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Question-1. What is a Transformer ?
Answer-1: A transformer is a static piece of apparatus which transforms electrical energy from one Circuit to another circuit without changing the frequency. It can be designed to "step up" or "step down" voltages and works on the magnetic induction principle.
Question-2. How does a Transform work?
Answer-2: A transformer has no moving parts and is a completely static solid state device, which insures, under normal operating conditions, a long and trouble-free life. It consists, in its simplest form, of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced to one coil, called the primary, it magnetizes the iron core. A voltage is then induced in the other coil, called the secondary or output coil. The change of voltage (or voltage ratio) between the primary and secondary depends on the turns ratio of the two coils.
Question-3. Can DC Be Applied To Transformers ?
Answer-3: No, direct current can not be applied to transformers. Transformer works on Faraday's law of Electromagnetic Induction for which current in coil must change. If DC is applied current will not change and transformer will not work.
Question-4. What do you understand by the rating of a transformer?
Answer-4: The rating of a transformer is the maximum power which can be drawn from it without the temperature rise in the winding exceeding the safe limits for the particular class of insulation employed .
Question-5. What do you mean by an Ideal Transformer?
Answer-5: An ideal transformer is one in which there should be no losses, the winding should have zero resistance, the leakage flux should be zero and the permeability of core should be so high that the negligible current is required to establish the flux in it.
Question-6. What is the power factor of a transformer?
Answer-6: The power factor of a transformer is very low and lagging on no load. But the power factor on load is nearly equal to the power factor of the load which it is carrying .
Question-7. What are taps and when are they used?
Answer-7: Taps are provided on some transformers on the high voltage winding to correct for high or low voltage conditions, and still deliver full rated output voltages at the secondary terminals. Standard tap arrangements are at two and one-half and five percent of the rated primary voltage for both high and low voltage conditions.
Question-8. Name the winding to which the supply is given?
Answer-8: Primary winding
Question-9. Name the winding from which the supply is taken for load connecting?
Answer-9: Secondary winding
Question-10. What is a step-up and step-down transformer?
Answer-10: In step-up transformer: secondary voltage is greater than primary voltage, turns ratio is greater than 1 and secondary current is less than primary current. In step-down transformer: secondary voltage is less primary voltage, turns ratio is less than 1 and secondary current is greater than primary current.
Question-11. Why is transformer rating in KVA?
Answer-11: Copper loss of a transformer depends on current and iron loss on voltage. Hence, total transformer loss depends on volt-ampere (VA) and not on phase angle between voltage and current i.e. independent of load power factor. That is why rating of transformers is in Kva and not in Kw.
Question-12. What Is Auto-transformer?
Answer-12: In these transformer only one winding is used as primary and secondary. Also, primary and secondary are conductively coupled.
Question-13. What is the use of iron core in a transformer?
Answer-13: The iron core is used in a transformer to provide a continuous easy magnetic path of low reluctance.
Question-14. What is meant by regulation in a transformer?
Answer-14: Voltage regulation in transformers is the difference between the no load voltage and the full load voltage. This is usually expressed in terms of percentage.
Question-15. What is temperature rise in a transformer?
Answer-15: Temperature rise in a transformer is the temperature of the windings and insulation above the existing ambient or surrounding temperature.
Question-16. What Is Single And Three Phase Transformer?
Answer-16: The transformer which works on single phase is called single phase transformer. The transformer which works on three phase is called three phase transformer.
Question-17. What material is used for the cores of a transformer and why?
Answer-17: Lamination of specially alloyed silicon steel (silicon content 4 to 5%) are used due to its high electrical resistance ,high permeability non-ageing characteristics and minimum iron loss .
Question-18. What is an isolation transformer?
Answer-18: As the name suggests it is a transformer used to isolate two electrical circuits. In this transformer, the primary and secondary turns become the same and hence its turn ratio will be equal to 1. It protects the secondary circuit when a fault occurred in the primary circuit.
Question-19. What Are The Advantages Of Shell Type Transformer Over Core Type Transformers?
Answer-19: In shell type transformers the coils are well supported on the all sides and so they can withstand higher mechanical stresses developed during short circuit conditions. Also the leakage reactance will be less in shell type transformers.
Question-20. What Is Stack Factor?
Answer-20: The ratio of total cross section of iron to the total cross section of core is called stack factor.
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