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Relay protection should be tested every few years
In a typical industrial application, testing should be conducted at least every 2 years in accordance with NFPA 70B. Protective relay testing may be divided into three categories: acceptance testing, commissioning, and maintenance testing. The protection circuits, CTs, VTs are also checked. Maintenance testing is done in field periodically. Minor repairs done. Primary injection testing takes it one step further by passing actual fault currents through the entire protection chain—current transformers, the relay, and the breaker trip coil. Acceptance testing, commissioning, and startup will include control power tests, current transformer and potential transformer tests, and any other device testing associated with the protective. Mechanical relays, when properly maintained and tested, can last for decades.
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