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. :)
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RE: CT knee point FORMULA
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
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)