Lower limit (minimum operating time) of IDMT relay curves

[dicksolder]

Can someone please tell me what the lower time limit is for the normal range of IDMT curves? I.e. for higher MPS ratios (I actual / I set) where the operating time decrease there is some value of t below which one should ignore the calculated time value and use a fixed value representing the minimum time that an IDMT relay requires to operate? (This is where the curve in practice becomes horizontal)

Also how do these cutoff time values vary for:
(a) the different curves (standard inverse; very inverse, extremely inverse, etc.);
(b) electromechanial relays (eg. CDG12) vs. static vs. numerical?

 

[davidbeach]

You've just got to look at the curves. No easy answers otherwise.

 

[dpc]

If this is a critical application, I would say the best approach would be doing some actual testing. But if you are interested in accuracy down to the millisecond, repeatability could be an issue due to temperature variation, lubrication variables, and other maintenance (or lack of).




David Castor

http://www.cvoes.com