71. Malfunctioning of Buchholz relay may be caused due to
- heavy external short circuits
- improper breather action
- dropping of oil level below the relay level during operation
- excessive overheating
72. A Buchholz relay is used for
- protection of a transformer against all internal faults
- protection of a transformer against external faults
- protection of a transformer against both internal and external faults
- protection of a induction motors
73. A shell type transformer is commonly used as it has
- two magnetic paths
- reduced magnetic flux leakage
- reduced copper loss
- both (1) and (2)
74. Spiral core transformer, in which core is made up of steel strip has the advantage of
- minimum losses
- lighter construction
- lesser weight
- all of these
75. Distribution transformer have core losses
- greater than copper loss
- lesser than copper loss
- equal to copper loss
- equal to half of the copper losses
76. Distribution transformers are designed to have maximum efficiency nearly at ____ of full load.
- 100%
- 70%
- 25%
- 10%
77. A distribution transformer is selected on the basis of
- voltage regulation
- efficiency
- all day efficiency
- none of the above
78. Which part of the transformer is subjected to maximum heating?
- frame
- core
- winding
- oil
79. Which of the following methods is employed for cooling of power transformers of rating not exceeding 10 MVA?
- air blast cooling
- natural oil cooling
- forced oil cooling
- natural air cooling
80. Natural air cooling is used for transformers of rating upto
- 100 kVA
- 500 kVA
- 5-10 kVA
- 10 MVA