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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Location of buchholz relay is
In main tank
In conservation tank
Between main and conservation tank
None of above
Between main and conservation tank
Quick Summary: The Buchholz relay is a gas-actuated protective device specifically designed for oil-immersed transformers. It is installed in the connecting pipe between the main tank and the conservator tank to detect internal faults early by sensing gas accumulation.
The Buchholz relay is a gas-actuated protective device specifically designed for oil-immersed transformers. It is installed in the connecting pipe between the main tank and the conservator tank to detect internal faults early by sensing gas accumulation.
Vgas∝Fault severity — Gas accumulation rate correlates to fault magnitude
ttrip≈0.1s — Typical operation time for severe internal faults
During an internal fault, the heat causes the transformer oil to decompose, releasing gases. These gas bubbles rise towards the conservator and get trapped in the Buchholz relay, causing a float to drop and trip the circuit breaker. For severe faults, a sudden surge of oil also activates a second element (baffle plate) to disconnect the transformer instantly.
Used exclusively for oil-immersed transformers rated above 500 kVA.
Acts as an incipient fault detector (slow-developing internal faults).
Requires a minimum pipe slope of 1° to 9° toward the conservator to ensure gas flow.
Detects faults at an early stage before they become catastrophic.
Provides protection against inter-turn faults, core faults, and oil leakage.
Cannot be used on dry-type (air-cooled) transformers.
Prone to false operations due to mechanical vibrations or seismic activity.
Oil-immersed power transformers
Distribution transformers with conservator tanks
The Buchholz relay is essentially a gas-actuated relay consisting of two floats; the upper float triggers an alarm for minor faults, while the lower float trips the circuit breaker for major ones.
Option A is incorrect because the main tank is where the core and windings are submerged; gas must leave the tank to be detected.
Option B is incorrect because the conservator is the expansion vessel; placing it here would miss gases generated within the main tank.
C is correct — The Buchholz relay is installed in the connecting pipe between the main tank and the conservator tank to intercept rising gas bubbles generated by internal faults.
Always remember that Buchholz relays are limited to oil-immersed equipment because they rely on the generation of gases from oil decomposition to operate.