CT knee point FORMULA

[RIYAZAHAMED]

Hello every one!

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

 

[RIYAZAHAMED]

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

 

[scottf]

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.

 

[gilly1]

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)