1000 electrical maintenance question and answers pdf

 What is the use of buchholz relay in the transformer?
It’s a protection relay used in oil immersed transformer to protect the transformer
from insulation failure, core heating or any other type of internal faults, which may
cause the heating of winding beyond the specified temperature. This relay is placed
in between the pipe connecting the conservator and the tank. Generally used in
power transformer of above 500 kVA.

It consists of two operating floats and is operated by two mercury switches
separately provided for the alarm and trip. Due to internal fault (collection of gases)
or leakage of oil if the oil level comes down the alarm relay first operates and then
the trip relay operates to isolate the transformer from the circuit.

 What is the use of explosion vent in the transformer?
It is also a safety device of a transformer, which protects the transformer tank from
the high consequences of the high-pressure gases induced or developed by any type
of short circuit in the transformer by allowing the gas to escape by puncturing the
diaphragm.