Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Which of the protection is provided by buchholz relay?
Short circuit in winding
Earth fault in winding
Local over heating
All of above
All of above
Quick Summary: The Buchholz relay is a gas-actuated protective device installed in oil-immersed transformers to provide comprehensive protection against various internal incipient faults. It detects the accumulation of gas or sudden surges in oil pressure, triggered by arcs, short circuits, or insulation degradation.
The Buchholz relay is a gas-actuated protective device installed in oil-immersed transformers to provide comprehensive protection against various internal incipient faults. It detects the accumulation of gas or sudden surges in oil pressure, triggered by arcs, short circuits, or insulation degradation.
Pfault∝Ifault2 — Relation between internal fault intensity and gas production rate
During an internal fault, the arc decomposes transformer oil into gases like hydrogen, methane, and carbon monoxide. These gases collect in the relay chamber, displacing oil and tilting the float switch to initiate an alarm. If a severe fault causes a rapid pressure wave, the lower float trips the main circuit breaker to isolate the transformer.
Buchholz relay is used exclusively for oil-immersed transformers (rated above 500 kVA).
It cannot detect external faults or faults in the secondary circuit wiring.
The relay operates on the principle of gas accumulation or sudden oil flow velocity.
It provides both alarm (for minor faults) and trip (for major faults) signals.
Detects incipient faults at a very early stage before they become severe.
Simple and reliable mechanical construction.
Applicable only to oil-immersed transformers equipped with a conservator tank.
Cannot detect faults occurring outside the transformer tank (e.g., in bushings or cables).
Oil-immersed power and distribution transformers.
Tap-changing equipment compartments.
Minor faults include local overheating, core insulation failure, and loose electrical connections.
Major faults include phase-to-phase short circuits and earth faults causing sudden pressure surges.
D is correct — The Buchholz relay is designed to detect all internal faults, including short circuits, earth faults, and local overheating, by monitoring gas generation and oil surge within the transformer tank.
Remember that Buchholz relay is a 'slow' protection device; it is not instantaneous and is meant for internal faults, unlike Differential protection which is fast but covers only the transformer zone.