|The following protective devices
are used so that, upon a fault development inside a Transformer,
an alarm is set off or the Transformer is disconnected from the
circuit. In the event of a fault, oil or insulations decomposes
by heat, producing gas or developing an impulse oil flow.
To detect these phenomena, a Buchholz relay is installed.
The Buchholz relay is installed at the middle of the connection
pipe between the Transformer tank and the conservator.
There are a 1st stage contact and a 2nd stage contact as shown
in Fig. (28). the 1st stage contact is used to detect minor
When gas produced in the tank due to a minor fault surfaces to
accumulate in the relay chamber within a certain amount
(0.3Q-0.35Q) or above, the float lowers and closes the contact,
thereby actuating the alarm device.
Fig. (28). Buchholz Relay
The 2nd stage contact is used to detect
major faults. In the event of a major fault, abrupt gas
production causes pressure in the tank to flow oil into the
conservator. In this case, the float is lowered to close the
contact, thereby causing the Circuit Breaker to trip or
actuating the alarm device.