# Transformer interview questions paper-4

51. What are the types of transformers according to transformation?

Ans: (1) Step up transformer & (2) Step down transformer.

52. What do you mean by step up and step down transformer?

Ans: When the transformer transforms low voltage to high voltage it is called a step up transformer and when the transformer transforms high voltage to low voltage it is called a step down transformer .

53. what are the advantages of using a transformer in an a.c. supply?

Ans: The transformer has the following advantages :-

1. Voltage can be transformed from low voltage to high voltage for transmission and high voltage to low voltage for distribution without changing the frequency.
2. As the transformer has on rotating parts there is no frictional losses and were and tear of it .
3. A high voltage or an extra high voltage can be transformed easily by providing good insulation.
4. Its maintenance cost is low.
5. Practically it requires very little attention for its operation.

54. What is ideal transformer?

Ans: The transformer having an overall efficiency of 100 percent is called transformer.

55. What is the condition for an ideal transformer?

Ans : For an ideal transformer, Output =Input i.e. V2 I2 = V1 I1 or E2 I2 =E1 I1 or I2/I1 = E1/E2 = N1/N2 = 1/k i.e. primary and secondary current are inversely proportional to their respective turns .

56. What do you mean by power transformer?

Ans: The transformer which are used up on transmission, lines for the transmission and distribution of relatively large quantities of energy are called power transformers.

57. What do you mean by transmission transformer?

Ans: The high capacity step up transformers , which are used in the generating station for onward transmission of electrical energy, are called transmission transformers.

58.What do you mean by distribution transformer?

Ans: When the transformers are used for distributing the energy from transmission lines and networks for local consumption and the secondaries are directly connected to the consumers load, they are called distribution transformers.

59. What do you mean by lighting transformer?

Ans: A transformer which is used to supply a distribution circuit having no motors connected to it , is called lighting transformer.

60. How does a transformer taken part for wide-spread popularity of a.c. system over d.c. ?

Ans: (1) High voltages of a.c. system can be obtained by using a transformer for transmission of electrical power.
(2) A.C voltages can be increased or decreased without any power loss by using a transformer.

61. Is there any difference of power if the secondary of the transformer is connected in star and delta respectively?

Ans: No. The power will be same .

62.Why is cooling necessary for power transformer ?

Ans: To prevent the damage to the coils and core due to excessive heat accumulated inside the transformers .

63. What are the sources of heart developed inside the transformer ?

Ans : Load current produces heat in the winding and eddy current produces heat in the iron core .

64. what are the important methods of cooling the transformer ?

Ans: The important methods of transformer cooling are as follows :-
1) Cooling by natural air.
2) Air forced type cooling.
3) Oil natural air natural type cooling.
4) Oil nature air forced type cooling.
5) Oil forced air forced type cooling.
6) Oil immersed water forced type cooling.
7) Oil forced water forced type cooling.

65. What do you mean by cooling by natural air ?

Ans: In natural air cooling system is effected by atmospheric air which passes inside the transformer through the holes provided on the casing of the transformer. Here convection process helps in cooling. This type of cooling is applied only in low KVA rating transformer.

66. What do you mine by air forced type cooling?

Ans: In air forced type of cooling, in addition to the natural air cooling air is forced inside the transformer by the arrangement of fans and circulated by introducing ventilating ducts.

67. What do you mean by oil natural air natural type cooling system?

Ans: It is most common system of cooling power transformer and distribution transformer. In this method transformer core and coils are immersed in a tank containing oil. The oil has both the property of cooling and insulating . The cooling tubes are fitted on the tank walls outside the tank through which the heated oil is circulated from the bottom to the top and cooled.

68.How is heat dissipated in oil cooled transformer ?

Ans: During running of transformer the oil in contact with core and coils becomes heated. The heated oil comes in contact with the casing and being lighter goes up through the cooling tubes where the heat is dissipated to the surrounding air. Finally cold having oil comes down and enters the tank again. This process continues in cyclic order so long the transformer is on running operation.

69. What is oil natural air forced type cooling?

Ans: In oil natural air forced type cooling method the oil cooling system is improved by the arrangements of fans which create air blasting.

70. What do you mean by oil forced air forced type cooling ?

Ans : In oil forced air forced type cooling system the oil is circulated through coolers which have cooling fans of exchange heat from oil to air.