How to use Hi set function of protection relay

[singpower]

Hi
I know that all of numerical relay have hi set function and I don't know how to use it.
I mean, under what condition it is used and how to select the right setting.

Or any web page, literature that I can look at it? I googled its use in the web and no satisfactory result.

 

[ScottyUK]

High set is a function found on some thermal (IDMT) relays or LV breakers and is typically used to provide an instantaneous trip function when a threshold current is exceeded. It reduces the reach of the thermal overcurrent curve at very high currents.


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I don't suffer from insanity. I enjoy it...

 

[khadisa]

On the relay I have been seeing, they have a hi set different from instateneous and it can be timed.
What we normally do is to provide the IDMT with a higher time than the hi set and a lower current setting. As such the time of relay operation will be graded according to the level of the fault.

 

[ScottyUK]

Thanks khadisa,

I should have said that the hi-set function can have a definite minimum time, whereas the true instantaneous setting is just that - instantaneous.


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I don't suffer from insanity. I enjoy it...

 

[dpc]

Use or non-use of the hi-set or instantaneous function depends on the application. There isn't really a one size fits all answer.

BTW, the term "hi-set" has never really been used in the US. We just call it "instantaneous" and if we add a time delay to it, we just live with that inconsistency or call it a "definite-time" function.

Dave