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What should be possible reason if the buchholz relay is operated during energizing of transformer first time?
Vibration of tank
Air bubbles in transformer cover
Both
None of above
Air bubbles in transformer cover
The Buchholz relay is a gas-actuated protective device installed in the pipe between the transformer tank and the conservator. During the first energization, air trapped in the transformer cover, bushings, or cooling tubes can be displaced and move into the Buchholz relay, causing the relay to operate (trip) due to the presence of air bubbles.
The Buchholz relay is a gas-actuated protective device installed in the pipe between the transformer tank and the conservator. During the first energization, air trapped in the transformer cover, bushings, or cooling tubes can be displaced and move into the Buchholz relay, causing the relay to operate (trip) due to the presence of air bubbles.
P=╧Бgh тАФ Pressure exerted by oil column
VgasтАЛ=VtotalтАЛтИТVoilтАЛ тАФ Volume of displaced air
The relay operates on the principle of buoyancy or gas accumulation. When air bubbles are trapped, they collect in the upper chamber of the relay, causing the oil level to drop, which tilts the mercury switch or float to trigger an alarm or trip signal. This is a common phenomenon during commissioning after oil filling, often requiring air purging through the top cover vents.
Buchholz relay is a mechanical protective device for oil-immersed transformers.
It responds to incipient faults that generate gas and air pockets.
The trip contact is usually in the lower section (high-velocity oil flow).
The alarm contact is in the upper section (gas accumulation).
Air trapped during oil filling/topping up causes nuisance tripping.
Detects inter-turn faults before they become severe.
Operates for minor faults like localized overheating or insulation breakdown.
Subject to false operation due to vibrations or seismic activity.
Limited to oil-immersed transformers only.
Oil-filled power transformers.
Distribution transformers with conservator tanks.
Before energizing, the transformer must be 'degassed' or 'vented' to remove air pockets from the top cover and bushings.
Option A (Vibration) is a potential source of nuisance tripping but is usually not the primary cause during initial energization; air bubbles are the standard commissioning concern.
B is correct тАФ Air bubbles trapped in the transformer cover during oil filling migrate to the Buchholz relay upon energization, triggering the alarm/trip contact.
Always remember that Buchholz relays cannot protect against faults in external leads or secondary side faults that do not produce gas inside the main tank.