A pressure relief valve is a device designed to protect a power transformers during overpressure event. An overpressure event refers to any condition which could cause pressure in the transformer to increase beyond the specified design pressure.
During internal faults of a power transformer, there will be an increase of temperature associated with impurities in oil and some increase in pressure. This pressure is sufficient to damage the transformer. The pressure relief device is applied to prevent the transformer from this dangerous
The pressure relief device consists of a spring which normally is uncompressed an when the pressure increased in the transformer, the spring is get compressed and give a path of gases to go out of the transformer. Compressing the spring may close an electrical contact, and this contact will give trip to circuit breakers associated with alarm.
Figure (48) shows the pressure relief device in the normal condition (before the fault occurrence), while figure (49) shows the fault condition at which the compressed gases are get out from the transformer.
