BUCHHOLZ RELAY: ALARM vs TRIP

 BUCHHOLZ RELAY: ALARM vs TRIP

A Buchholz relay is a protective device used in oil-immersed power transformers fitted with a conservator tank. It detects developing internal faults by sensing gas accumulation and protects against severe faults by detecting a rapid oil surge.

1. ALARM — Early Warning

How does it work?

A minor or developing internal fault may generate gas inside the transformer.

Gas accumulates in the upper chamber of the Buchholz relay.

The oil level inside the relay falls.

The upper float operates the alarm contact.

An alarm signal alerts the operator.

Possible causes:

Local overheating.

Insulation deterioration.

Minor winding faults.

Core overheating.

Oil leakage or trapped air.

Result: The transformer generally remains in service while the alarm is investigated.

2. TRIP — Severe Fault Protection

How does it work?

A severe internal fault can cause rapid gas generation and a sudden oil surge toward the conservator.

The oil surge operates the lower float or flap mechanism.

The trip contact closes.

The protection circuit energizes the relevant circuit-breaker trip coils.

The circuit breaker opens, disconnecting the transformer.

Possible causes:

Severe internal arcing.

Major winding faults.

Internal short circuits.

Serious insulation failure.

Result: The transformer is disconnected to prevent further damage.

Note : operating mechanisms and responses depend on the relay design and protection scheme.

4. Important Substation Maintenance Points

When a Buchholz alarm or trip operates:

1. Check the relay indication and transformer protection records.

2. Inspect the transformer for oil leakage and other abnormal conditions.

3. For an alarm, arrange appropriate gas sampling and analysis.

4. For a trip, do not re-energize the transformer until the cause has been investigated and the required tests and approvals are completed.

5. Follow the approved substation operating procedure and manufacturer instructions.

Remember: A Buchholz alarm is an early warning; a Buchholz trip is a protective action. Neither should be ignored.

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