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amitabh.jpg personal.umich.edu pranavp::A second relay is sometimes used for the tapchanger selector chamber.
The function of the relay is to detect an abnormal condition within the tank and send an alarm or trip signal.
Under normal conditions the relay is completely full of oil.
Operation occurs when floats are displaced by an accumulation of gas, or a flap is moved by a surge of oil.
Almost all large oilfilled transformers are equipped with a buchholz relay, first developed by max buchholz in 1921.
A large fault produces a large volume of gas which drives a surge of oil towards the conservator.
A severe reduction in the oil level will also result in a float falling.
Gas and oil flows buchholz relays are equipped with a number of gas and oil inputs and outputs, including test and sampling facilities transformerworld.
After an alarm or trip signal has been received this must be collected and analysed before the transformer is returned to service.
Gas collection can be done at the relay, or at ground level if suitable arrangements exist.
Clearly the latter is a safer and more convenient option.
Functional tests a test petcock enables dry air to be admitted into the relay to check correct operation.
A trickle of air is equivalent to a gradual accumulation of gas.
A blast simulates an oil surge.
On completion it is important that the relay is bled to remove the air that has been introduced.
Draining a valve in the bottom of the relay enables an oil sample to be taken or the relay to be drained.
As with gas sampling, this facility can be brought down to ground level for enhanced operator safety and convenience.