How do you detect gas leaks in SF₆ circuit breakers?

Detecting gas leaks in SF₆ circuit breakers typically begins with a preliminary assessment based on monitoring signals and pressure changes, followed by precise localization using various professional techniques, such as qualitative leak detection and the pressure drop method. In field operations, a combination of methods is often employed to enhance detection effectiveness.

The specific detection methods and steps are as follows:

Observe signals and pressure: If the pressure gauge reading gradually drops or the density relay issues a "gas refill" signal under constant ambient temperature, it usually indicates a leak. If the gas pressure suddenly drops to zero, the circuit breaker must immediately be switched to non-automatic mode, and its control power supply disconnected.

Distinguish the cause: When a "gas refill" signal is triggered, first verify the accuracy of the density relay's settings and check for faults in the secondary circuits to rule out false alarms.

In the field, a comprehensive approach-combining multiple detection methods-is typically used.

Qualitative leak detection: This is the most common and straightforward method.

Using a leak detector: Move a portable SF₆ gas leak detector slowly along potential leak points (such as joints, flanges, and valves). An alarm from the instrument indicates the approximate location of the leak.

Limitations: This method is susceptible to false alarms caused by unstable probe movement or wind; it cannot pinpoint the exact leak location, nor can it be used to detect leaks on the main body of energized equipment.

Pressure drop method: This method is simple to implement but offers limited precision.

Procedure: Measure the SF₆ gas pressure using a precision pressure gauge, re-measure after a period ranging from several days to several weeks, and calculate the pressure drop while adjusting for temperature variations.

Auxiliary measure: Compare the unit with other circuit breakers of the same model to improve accuracy and validity.

Sectional isolation method: This method is suitable for circuit breakers with interconnected three-phase gas circuits. When the leak rate is too low to easily locate the source, the detection area can be narrowed down by progressively isolating sections of the gas system. Overall Method: Primarily used by manufacturers, this method involves enclosing the entire circuit breaker within a specially designed sealed container and calculating the annual leakage rate by measuring the concentration of SF₆ gas inside the container; it is rarely used for on-site testing.

Leakage points in SF₆ circuit breakers may occur at the following critical locations:

Porcelain bushing-to-flange connections: Issues such as poor bonding, aging gaskets, or misalignment.

Sliding seal areas: Damaged seal rings or insufficient surface smoothness of the sliding rod.

Pipe fittings and valves: Issues such as loose connections, valves not closing tightly, sand holes in the valve body, or failed seal rings.

Density relay and pressure gauge interfaces: Damaged gaskets or seal rings at the connection points.

Welds: Potential presence of sand holes or areas requiring repair welding.

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