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Examoogle • User • info@examoogle.com • EE-2024-8821
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Buchholz relay is used for transformer rating above
100 KVA
200 KVA
400 KVA
500 KVA
500 KVA
Quick Summary: The Buchholz relay is a gas-actuated protective device installed in oil-immersed transformers to detect incipient faults. According to IS 3639, it is mandatory for oil-immersed transformers with ratings of 500 KVA and above to ensure reliable protection against internal electrical faults.
The Buchholz relay is a gas-actuated protective device installed in oil-immersed transformers to detect incipient faults. According to IS 3639, it is mandatory for oil-immersed transformers with ratings of 500 KVA and above to ensure reliable protection against internal electrical faults.
Pfault∝dtdΦ — representation of fault gas generation due to arcing
The relay is placed in the connecting pipe between the transformer tank and the conservator. When a minor fault occurs, insulating oil decomposes to produce gases that collect in the relay, causing the upper float to tilt and close the alarm circuit. For severe faults, a sudden pressure wave or high oil flow activates the lower float, which trips the circuit breaker to isolate the transformer.
Used for oil-immersed power transformers only.
Categorized as a mechanical protection device.
Capable of detecting internal faults like insulation failure, core heating, and winding short circuits.
Not suitable for external faults or tank leakages.
Detects incipient faults before they become severe.
Simple construction and maintenance.
Applicable only for oil-filled transformers.
Requires minimum oil level to function.
Oil-immersed power transformers.
Large distribution transformers (≥ 500 KVA).
The Buchholz relay is named after Max Buchholz, who invented the device in 1921.
Ratings below 500 KVA generally rely on simpler protection methods like fuses or secondary circuit breakers because the cost-to-risk ratio does not justify the installation of a Buchholz relay.
D is correct — The Buchholz relay is standard protection for oil-immersed transformers rated 500 KVA and above.
Always remember that Buchholz relays cannot function on dry-type transformers as they rely on the generation of gases from the breakdown of insulating transformer oil.