WHAT HAPPENS IN DIFFERENTIAL PROTECTION IF CT REACHES ITS
KNEE VOLTAGE POINT?
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Answer Posted / tony
Normally the knee point voltage must be
Vk > 2*Vs
Where Vs is the calculated max. voltage appears across the relay.
Beyond knee point the chara of CT is no longer proportional to the primary current and this cause faulty measuring by relay.Thus if we have higher Vk we can easily with stand higher Vs(fault equivalent seen by relay)
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