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CT knee point FORMULA

CT knee point FORMULA

CT knee point FORMULA

(OP)



Hello every one!

Am lookin for the exact formula for CT knee point. If any one come up with answer, it'll be helpful. :)

RE: CT knee point FORMULA

(OP)
Is this formula correct??
calculating knee point voltage Vkp
Vkp = {2 x Ift (Rct+Rw)}/ k
Vkp = required CT knee point voltage
Ift = max transformer through fault in ampere
Rct = CT secondary winding resistance in ohms
Rw = loop impedance of pilot wire between CT and the
K = CT transformation ratio

RE: CT knee point FORMULA

So you're trying to calculate what knee-point voltage is required for a specific application?

Sounds like you're leaving out the system x/r ratio.

RE: CT knee point FORMULA



The formula I use for knee point voltage Vk if for example we have a protection class CT rated as 30VA 5P50 :

Vk = K (Pint + Pbn) / Is

where : K = Accuracy limit factor (e.g. 50)
Pbn = CT Rated burden (e.g. 30VA)
Pint = Internal CT burden (e.g. 3-10VA)
Is = CT Secondary Current Rating (e.g. 1 or 5A)

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