Failure Analysis of Low Insulation of SF6 Relay Contact

The SF6 relay used by the high-voltage circuit breaker is an important protection and control component in the power system. If the circuit breaker fails, it will cause great economic losses. To ensure the reliability of the circuit breaker operation, it is necessary to constantly monitor the indicators of the circuit breaker, especially the SF6 gas, which must meet the provisions of the relevant standards, so as to keep SF6 circuit breaker in a good working condition for a long time. However, when the density relay has the problem of low contact insulation, it may cause the misoperation of the alarm or locking terminal, or the alarm signal may link the locking signal, resulting in both alarm and locking. In the high voltage environment, there may also be electrical breakdown phenomenon, which makes the meter lose a certain function, endangering the circuit breaker and even the safety of the power grid. This paper analyzes the problem of low contact insulation of density relay, and formulates the solution and preventive measures to ensure the safe and stable operation of power grid.

1. Cause analysis of low insulation of SF6 relay contact

The old terminal is fixed by a screw, closed by the sealing ring, but the inner cover has a small hard convex rubber column, not the new O-ring. The hard sealing ring has no shrinkage sealing, and the waterproof effect basically does not work. After a long time of exposure to wind and sun and rain, the sealing ring has the aging phenomenon, so it has a poor quality and has been damaged. Thus, water vapor penetrates into the terminal through the gap and corrodes the metal of the contact position, thus causing a reduction in insulation and the occurrence of induced current. Therefore, under the action of erosion because of the infiltration of rain for a long time, the chemical reaction of rainwater with the negatively charged contact produces a patina. According to the standard, the terminal part of SF6 relay needs to pass the high-voltage breakdown test, including contact to outer shell, and contact to contact. The patina phenomenon reduces the insulation strength, which may cause the misoperation of the alarm or locking terminal, or the alarm signal may link the locking signal, resulting in both alarm and locking.

2. Preventive measures and improvement suggestions for SF6 relay

To check the insulation strength of the junction box (contact and outer shell, contact to contact), to replace or send it to the factory for maintenance when it is below the minimum value specified in the mechanical industry standard; for the old types, add the new O-ring; Install a rain shield on the wiring part. According to the experience of the manufacturer, the installation of rainproof cover can effectively prevent rain erosion and direct sunlight on the density table. Therefore, rain cover is not only an auxiliary measure, but also a major measure to extend the service life of outdoor density relays. In addition to the above preventive measures, it is also necessary to strengthen the acceptance check of density relay (pressure gauge) before putting into operation and seriously implement the relevant measures.

Whether the high-voltage circuit breaker can operate reliably is directly related to the safety of the whole power grid, and has very important significance for the safe and stable operation of the power grid. In the high voltage environment, there may also be electrical breakdown phenomenon, which makes the instrument lose a certain function, endangering the circuit breaker and even the safety of the power grid.

In this paper, by adopting scientific and reasonable on-site check methods for the low insulation of SF6 relay contacts, it is clear that the wires connecting electrical contacts and junction boxes are the main reason for the low insulation, and we timely put forward preventive measures and improvement suggestions such as special inspection and maintenance of density relays combined with power failure, installation of rain cover, acceptance check before operation, etc., so as to ensure the safe and stable operation of the power system.

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