Answer / john bosco

knee point voltage definition
when applying voltage in secondary gradually from zero
and measuring current for step voltages, the current raise maintains constant slope up to some level of voltage.
for further raise in voltage secondary current raise do not follow the slope.
the voltage from which 10 % raise gives 50% raise in secondary current called as knee point voltage of current transformer(IEC standard)

saturation voltage is maximum secondary voltage developed across ct for any primary current

protection class CT
formula for VK= Is.ALF.(Rct+Rb)
Is- rated secondary current
ALF- accuracy limit factor
Rct- measured secondary resistance
Rb - rated burden of CT

Answer / thowsif_emerson_csm team

The knee point
is a ten percent ratio error between the
primary input current and the corresponding secondary
output current.

The saturation point involves determining the secondary
voltage necessary to drive the measured current through the
impedance of the secondary circuit.

For More Details,Pls visit
http://www.control.com/thread/1026243854

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