Electrical Engineering Technology

The Buchholz relay working principle is very simple. Buchholz relay function is based on a very simple mechanical phenomenon. It is mechanically actuated. Whenever there will be a minor internal fault in the transformer such as an insulation fault between turns, break down of core of the transformer, core heating, the insulating transformer oil will be decomposed in different hydrocarbon gases, CO2 and CO. The gases produced due to the decomposition of transformer insulating oil will accumulate in the upper part of the Buchholz container which causes a fall of the oil level in it. Fall of oil level means lowering the position of the float and thereby tilting the mercury switch. The contacts of this mercury switch are closed and an alarm circuit energized. Sometimes due to oil leakage on the main tank air bubbles may be accumulated in the upper part of the Buchholz container which may also cause a fall of oil level in it and the alarm circuit will be energized. By collecting the accumul...

 #What_is_Buchholz_Relay A Buchholz relay is a safety device mounted on (some) oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a “conservator”. Buchholz relays are used as a protective device, as they are sensitive to the effects of dielectric failure that can occur inside the equipment they protect. Buchholz relays are a type of gas detection relay. Buchholz relays have two main elements. The upper element consists of a float. The float is attached to a hinge in such a way that it can move up and down depending upon the oil level in the Buchholz relay container. A mercury switch is fixed on the float. The alignment of the mercury switch hence depends upon the position of the float.  The lower element consists of a baffle plate and a mercury switch. This plate is fitted on a hinge just in front of the inlet (main tank side) of the Buchholz relay in a transformer in such a way that when oil enters in the relay from that inlet ...

  Generally Differential protection is provided in the electrical power transformer rated more than 5MVA. The Differential Protection of Transformer has many advantages over other schemes of protection. The faults occur in the transformer inside the insulating oil can be detected by  Buchholz relay . But if any fault occurs in the transformer but not in oil then it can not be detected by Buchholz relay. Any flash over at the bushings are not adequately covered by Buchholz relay.  Differential relay s can detect such type of faults. Moreover Buchholz relay is provided in  transformer  for detecting any internal fault in the transformer but Differential Protection scheme detects the same in more faster way. The differential relays normally response to those faults which occur in side the differential protection zone of transformer.