Formula for CO-5 (Curve 418245)

Electrical Testing Talk Relay Testing
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Does anyone have the formula for Curve 418245 ?

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I cannot find a formula. Doble protection suite probably has the formula built in the protection curves. I’m sure Omicron probably has the curve in their library. What are you looking to do?

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Someone else’s failure to plan is now my problem.
I’m trying to find a curve and setpoints in a SEL-751A that will get me close to the curve of a CO-5.

After my initial post, I went ahead and wrote out all the expected trip times from the graph in the CO-5 manual for the curve the relays are set with. I compared it with some curves the SEL-751A has. The C4 curve gets me close, at least when the fault is less than 2x Tap, but it will trip at an ever widening pace (quicker) as fault current increases.

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Inverse time curve
Inverse time curve680×605 35.7 KB

Take a look at this. I would assume its a long time inverse

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@Frierfly Did you ever get it figured out? I’m curious :slightly_smiling_face:

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From the ABB manual, a CO-5 is a Long Time Inverse curve. Also, based on the curve plot in the manual linked below, a CO-5 is fairly close to the Long Time Inverse (Schneider Electric) formula, which is the same as the C4 formula, but there is some variance (the C4 curve op times get progressively quicker compared to a CO-5 with similar settings). I handed it over to my boss and said, “Hey, this is what I found.” but I haven’t heard anything about what options were presented to the customer yet.

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