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Topic Title: Fuse Protection of SCRs
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Created On: 04 February 2014 07:29 PM
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 04 February 2014 07:29 PM
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clarky280

Posts: 83
Joined: 10 June 2008

Hi

It would be great if someone could provide some help on fuse protection of SCRs.

I am currently looking at a fuse selection for protection of an SCR and am using the following method:

* confirm the total clearing i2t of the fuse selected at the prospective short circuit current
* confirm the total clearing time of the fuse at the prospective short circuit current (Pscc)
* check that the i2t rating of the SCR, adjusted for a surge duration equal to the total clearing time of the fuse at the Pscc, is greater than the total clearing i2t of the fuse at the Pscc

Now, as far as I can tell, this takes care of the protection of the SCR from thermal damage due to excessive fault energy. However I have other people telling me that I need to look at the peak let-through current of the fuse to ensure that this does not exceed the peak surge current (ITSM) rating of the SCR. Is this a required step? I was of the impression that the ITSM of the SCR was only used to define its thermal limits...

A steer on this would be much appreciated.

Thanks
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