General purpose miniature relays & protection schemes

[RRaghunath]

I come across of late, even the reputed C&R panel vendors are using general purpose miniature relays for contact multiplication application in protection schemes.

Is this widely practiced? My belief and understnading was that the protection schemes use relays which go through rigorous quality control checks and are designed to be much more reliable than the general purpose ones. After all, many a time an unwanted trip can cause huge production losses, and in the same way not tripping the faulty feeder quickly can also cause big trouble.

Keen to know your experiences / opinions.

Thanks.

 

[ScottyUK]

perhaps slightly OT, but maybe of interest:

ABB used traditional high integrity relays in their bay control units for the ELK series of switchgear which have proven remarkably reliable from the past 15 years. Where we are seeing problems is on the standard mini contactors and pilot relays used for auxiliary functions such as hydraulic pump control, and in interfacing to external apparatus such as the synchroniser. Atmospheric conditions (salt-laden coastal air, wet, cold) have caused surface 'oxidation' - I'm not a chemist; maybe it isn't an oxide - to occur. This causes sporadic and often inexplicable misoperation of parts of the control scheme. I haven't seen a failure which compromises the protection function, but the contact oxidation makes for a frustrating number of problems which impact generation.

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