GETCO Exam Paper (30-11-2008)
In a transformer it is difficult to measure the efficiency by output-input measurement methods because

losses are abnormally high
output is out of phase with respect to input
efficiency of transformer is usually high and hence extremely accurate measurements will be necessary
the output is sinusoidal and hence cannot be measured

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GETCO Exam Paper (30-11-2008)
A buchholz will operate in a transformer whenever there is

saturation of magnetic circuit
large internal fault
any of the above
over load

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GETCO Exam Paper (30-11-2008)
The function of a breather in a transformer is

to suppress harmonics
to provide protection against over currents
to control the level of oil in the tank
to arrest flow of moisture into the tank

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