The relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field that changes the switch contacts. Although it has a simple operating principle and structure, a relay can sometimes fail. These faults can be classified as mechanical and electrical.
Common faults in relays
Identifying relay faults and their causes enables you to fix problems quickly. The most common relay failures are:
Flashover is the trouble where discharge between opposing conductors causes a short-circuit. This often occurs with contacts used with medium and large power. Flashover is dangerous when the current is high.
Welding, locking, or gluing make it difficult to open contacts. Welded contacts are usually caused by high inrush currents as the contacts are closed creating molten or soft metal in the contact area. Welded contacts are also caused by high-frequency switching.
Contact wear is the wear of contacts due to mechanical causes, such as wear during repeated operation. Relays open and close millions of times. Sometimes this repeated operation causes contact wear.
Contact erosion is the expending of contacts due to electrical, thermal, chemical, and other causes all through the repeated operation. Contacts having variable or intermittent contact resistance. This occurs particularly at low current levels because of erosion of the contact materials.
Activation is the failure where contact surfaces become dirty. Dirty contact surfaces increase the possibility of discharge.
Metal oxide, sulfide, and other films are generated on or attached to contact surfaces and cause boundary resistance. If there is a film on the surface of contact and the contacts retouching, the film electrically breaks down and the contact resistance drops rapidly when the contact voltage exceeds a certain value.
Mechanical relays create a humming noise when turned on. Humming noise is continuous during operation. Humming occurs due to mechanical vibration caused by AC poles or a rectifier wave drive with insufficient smoothing.
Abnormal heat generation
If switching arcs occur continuously due to contact chattering, the contact parts generate an abnormal amount of heat, which can lead to contact fusing, dissolution, and welding. This leads to operation failure. Abnormal heat is also generated by wiring and installation failures.
During switching, carbonization occurs (carbon is generated) on the contacting surfaces. This increases contact resistance and leads to contact failure.
Burn damage is caused by problems such as overcurrent, overvoltage, and vibration.
Case surface (top and side) materials that collapse into the inside of the relay obstruct the operation of the components that move inside the relay, which may lead to outer appearance defects, operation failures, and release failures.
This phenomenon causes the top and sides of the case of a relay designed for use with printed circuit boards to swell.
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