Protective Relays and Breaker Maintenance

To answer your last question first: You may be in danger. Unfortunately, maintenance often gets overlooked until a failure occurs. Everything drifts with time (think "entropy"), although electronic devices are not nearly as susceptible to environmental conditions as older analog equipment.

If the relay is micro-processor based, it performs regular self-checks to detect internal anomalies. If it is solid-state, but not micro-processor controlled, you would have no warning of internal failure. Bear in mind, however, that problems with wiring connections and other equipment external to the relay may also cause reliability problems, and even a micro-processor unit cannot check those vulnerable points. Routine inspection, maintenance & testing is the only way to verify continued proper operation.

As for the breakers, the potential failure points are many:

• Unless they get operated regularly, the lubricants are probably congealed, and possibly contaminated with dust & dirt. The rotating members may have sealed bearings, but circuit breakers have many points where adjacent pieces slide rather than rotate, and bearings don't work there.
• The contacts may become oxidized resulting in a high resistance connection and fire hazard.
• Mechanical springs may lose their responsiveness if kept compressed or tensioned for long periods.
• Wiring connections may become loose from vibration or temperature changes.
• Nearly all 13.8 KV breakers sold in the last 10 years use vacuum interrupters. If the breaker is closed, you have no indication of a loss of bottle integrity until the breaker trips. If there is air in the bottle, it will fizzle, then explode, because the contacts are too close together to quench an arc in air. (I've experienced this, up-close & personal. No one was hurt, but the entire substation was out of service for 3 days for cleanup & repair.) We now hi-pot all vacuum interrupters annually.

I would strongly recommend thoroughly reviewing the equipment manuals for recommended testing and maintenance. The books should give the recommended frequency for each procedure. If you don't have the manuals, you should be able to find them on-line if the plant was built in the late 90's. Additional information can be obtained from IEEE and NETA maintenance standards.

Thanks!!! this has been very helpfull and confirms some of my concerns. Even though the protective devices are new, we may have a variety of problems from not lack of maintenance for so long.

Past experience. We exercised and did P.M work ever year on our 13.8KV switchgear. some even at 6 month intervals.