What Are You Looking For?
When a light gas relay is triggered, it emits an alarm signal—this must be silenced immediately. The next priority is to inspect the gas trapped within the relay. Judging the gas based on its color, odor, and flammability can offer preliminary insight into whether an internal fault has occurred.
If the gas relay activation is benign—caused by external conditions like oil filtration, refueling that introduces air, ambient temperature drops, or oil leakage leading to a falling oil level—the signal can be reset after validation. Similarly, transitory faults such as an external short-circuit surge or a degraded DC control loop may falsely trigger the relay. In such scenarios, continued transformer operation is permissible post-verification.
However, should there be evidence of a minor internal fault causing gas generation, this must be immediately escalated to supervisory personnel. Any suspicion of an internal anomaly mandates immediate transformer shutdown and an in-depth diagnostic assessment.
When heavy gas protection causes a transformer trip, the likelihood of a major internal failure cannot be discounted. Possible culprits include sudden oil level drops, rapid oil infusion post-maintenance without adequate settling time, or internal arcing displacing oil violently.
First, the alarm must be silenced, and gas from the relay should be meticulously sampled. Analysis of volume, visual characteristics, flammability, and odor aids in diagnosing the root cause. A thorough evaluation includes gas chromatographic analysis of transformer oil and additional targeted testing.
No transformer should be returned to service after a heavy gas protection trip without rigorous diagnostics and clear identification of the fault source.
Transformers rated at 10,000 kVA and above typically employ differential protection based on circulating current principles. Upon tripping due to differential protection, both primary and secondary breakers disengage, necessitating a methodical inspection post disconnection.
Key inspection focal points:
Bushing integrity – any visible damage or insulation breach.
Busbar connections – signs of flashover, charring, or abnormal wear.
Primary equipment within the protection zone – thorough visual and instrument-assisted inspection for defects or anomalies.
If external short-circuits are found to be the cause (outside the differential zone), the transformer may be cautiously energized under no-load conditions for verification. Internal anomalies, on the other hand, demand complete operational suspension pending further investigation.
Upon an overcurrent protection trip:
Immediately silence audible alarms.
Conduct a meticulous review to detect any cascading trip scenarios, checking the trip status of feeder circuit breakers, signal relays, and operating mechanisms for jamming or malfunction.
If the triggering feeder cannot be identified, disconnect all low-voltage side breakers and examine both the low-voltage busbars and the transformer itself. Should all components appear normal, attempt a no-load energization of the transformer. By progressively re-energizing feeders, the offending circuit can be isolated.
If a bus fault is diagnosed and cleared, the transformer can be reconnected. However, if the transformer body is compromised, reintegration is strictly prohibited. Immediate reporting to superiors and awaiting specialized intervention is mandatory.
A failed cooling fan necessitates deactivation of the corresponding cooler unit. The event must be logged, and maintenance personnel alerted. Once repaired or isolated, the unit can be reinstated to service.
If the oil pump or secondary circuit fails and triggers an automatic shutdown, verify whether the backup cooler has seamlessly engaged. If not, activate it manually and proceed with fault diagnostics.
Should a cooler suffer extensive oil leakage, immediate shutdown of that cooling unit is essential. Ensure oil valves are sealed and the power supply disconnected to prevent further deterioration.
If the primary power supply to the cooling unit is lost, the backup supply should auto-transfer. Successful auto-transfer requires a performance check of contactors and manual switching if necessary. If the automatic process fails, manually engage the secondary power route to restore cooling.
Total failure of the cooling system leads to a sharp rise in transformer temperatures. The oil and winding temperatures must not exceed permissible limits. Contact maintenance teams immediately. If power loss is the cause, prioritize restoration within 20 minutes.
For the main transformer, if cooling is not restored within 20 minutes:
Monitor top oil temperature closely.
If below 75°C, operation can continue up to 60 minutes.
If cooling cannot be resumed within 60 minutes, escalate the issue to management and initiate shutdown procedures.
In the event of total cooler failure, decrease transformer load promptly while vigilantly monitoring temperature parameters. If top oil temperature approaches 75°C, initiate immediate shutdown to protect the asset and adjacent infrastructure.
Transformer trip incidents, whether due to gas protection, differential anomalies, or cooling failures, demand a disciplined, procedural approach. Swift diagnostics, precise decision-making, and timely communication with supervisory teams form the backbone of effective fault handling. Each scenario underscores the criticality of proactive monitoring and structured intervention in ensuring transformer longevity and grid reliability.
