Answer Posted / shakir mehmood

The formula for Knee Point Voltage is:

Vkp = K * If/CTR * (RCT + RL + RR)

in which,

K = Constant, conventionally taken as 2.0

Vkp = The minimum Knee Point Voltage

If = Maximum Fault Current at the location, in Amperes

CTR = CT Ratio

RCT = CT Secondary Winding Resistnace, in Ohms

RL = 2-way Lead Resistance, in Ohms

RR = Relay Burden, in Ohms

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