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The presence of gas inside a transformer’s Buchholz relay can be attributed to internal faults, external factors, and certain special circumstances. Each category has its own underlying mechanisms and implications.
Excessive heating within the transformer is one of the primary causes of gas formation. Short circuits between turns or layers of windings, damage to high-voltage bushings, or flashovers to ground can generate arcs. These arcs decompose transformer oil, producing characteristic gases such as acetylene and ethylene. For example, if a transformer is struck by lightning or subjected to switching overvoltage, insulation breakdown can occur. The resulting discharge leads to oil decomposition and the rapid release of gases, which rise and accumulate in the Buchholz relay.
Faults such as winding short circuits, multiple core groundings, or poor electrical contact can create localized overheating. Elevated temperatures cause the breakdown of both insulating oil and solid insulating materials like paper or wooden structures. This process produces gases such as hydrogen, carbon monoxide, carbon dioxide, and methane. A typical case is insulation damage between laminated silicon steel sheets in the core. The increased eddy currents generate heat, which in turn decomposes surrounding insulation and yields gas that travels into the relay chamber.
The integrity of a transformer’s sealing system is vital. When seals in the tank, conservator, bushings, or cooler become aged, hardened, or cracked, they allow external air to infiltrate the transformer. Loose bolts at flange connections can produce the same effect. In outdoor installations, long-term exposure to sunlight, temperature fluctuations, and environmental stress accelerates gasket deterioration. Air ingress through these weakened seals often results in gas accumulation in the relay.
Sudden environmental or operational changes can alter the transformer’s oil level. A sharp drop in ambient temperature, oil leakage, or improper conservator adjustments can cause the oil surface to fall. Negative pressure inside the tank may then draw air inward. Additionally, gases dissolved in oil may be released due to pressure variations, migrating into the Buchholz relay. For instance, during cold winter nights, oil contracts significantly. If the breather is blocked, negative pressure can form, pulling external air into the system.
When a transformer is newly energized or brought back into service after a major overhaul, residual gas in the oil may not yet be fully expelled. As the unit warms up under load, these gases separate from the oil and rise to the relay. This phenomenon is especially common in the first days of operation and gradually diminishes as the system stabilizes. Similarly, strong external disturbances such as earthquakes or mechanical vibrations can cause false relay operations. In such cases, signals may be triggered even though the gas does not originate from a fault.
The Buchholz relay itself or its secondary circuits may malfunction. For example, a relay might signal gas presence due to a short circuit or grounding fault in its control wiring. In other cases, vibration-induced misoperation may simulate a gas alarm. An illustrative example is a seismic event near a substation, which can jolt the relay’s internal mechanisms and trigger a false alarm. Upon inspection, no fault gases are found, confirming the indication was spurious.
Gas in a transformer’s Buchholz relay is not always a harbinger of disaster, but it must never be ignored. Internal faults such as overheating or discharges can generate characteristic decomposition gases that point to serious risks. External influences, from seal deterioration to oil level fluctuations, may also introduce air or release dissolved gases. Special circumstances like commissioning, maintenance, or even seismic activity can further complicate diagnosis. Careful investigation, including gas analysis and equipment inspection, is essential to distinguish between benign causes and genuine threats, ensuring transformer reliability and system stability.
