What is buclozs relay in transformer?

Answer 1

A Buchholz relay is situated in an inclined pipe between the transformer itself and its expansion tank. It (a) provides an alarm should there be an oil leak or if excessive gas accumulation within the relay and, (b) will disconnect the transformer in the event of a major oil loss or a surge within the oil (caused by a fault within the transformer).

Answer 2

This is a sudden pressure relay. If the transformer is overloaded, it can cause gassing, which will be detected by this (mechanical) relay.

This Question deserves a more elaborate answer

A Buchholz relay consists of a chamber containing two pivoted floats; an upper float and a lower float. The lower float is fitted with a flap which will deflect that float if a pressure wave passes through the relay's chamber. The relay is located in an inclined pipe leading from the top of the transformer to its expansion vessel above the transformer.

An oil leak in the transformer will eventually cause the oil level in the Buchholz relay's chamber to fall. As the oil level falls, the upper float pivots downwards, closing a Mercury switch attached to the float. This activates a warning (alarm) in the substation, but does not disconnect the transformer. If the oil level continues to fall, the lower float also pivots downwards, and a mercury switch attached to that float causes the protection system to disconnect the transformer.

In the event of minor burning within the core of the transformer, gas is generated which bubbles upwards towards the expansion vessel, some of which gathers within the top of the Buchholz relay's chamber. As the gas accumulates, it causes the top float to pivot downwards, closing a mercury switch attached to the float. This activates a warning in the substation, but does not trip the transformer.

In the event of a major flashover between windings, a pressure wave is set up in the oil. This pressure wave passes through the Buchholz relay's chamber, and causes a flap attached to the lower float to deflect that float, closing its mercury switch, causing the protection system to disconnect the transformer immediately.

To summarise. The upper float acts provides a warning of a drop in oil level or an accumulation of gas. The lower float acts to disconnect the transformer if the oil level continues to drop, or a pressure wave passes through the chamber.

(A valve at the top of the Buchholz relay allows any accumulated gas to be collected for testing, as the nature of the gas can be used to indicate the nature of the fault generating that gas(

Answer 3

A Buchholz relay is used to detect

• loss of oil
• presence of gas generated by minor interwinding faults
• catastrophic insulation breakdown

Initially, a loss of oil initiates an alarm. If the oil loss continues, then the relay will initiate disconnection of the transformer.

The presence of gas initiates an alarm.

Catastrophic insulation breakdown initiates the disconnection of the transformer.

Answer 4

A Buchholz relay is a safety monitoring relay that is mounted on top of Transformers. It can detect internal faults in the transformer that is is monitoring.

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