Protection Engineering Basics and Schemes Protection Engineering | Page 17
ALF = I Maximum Primary / I rated primary
Usually CTs have ALF of 5, 10,15,20,30 and 40
But when we are using Metering CT, we called ALF as Safety Factor.
1.1.7 Knee point Voltage:
Knee point voltage is the voltage at which CT starts to saturate, by saturate means errors increase, more excitation current transformed from primary current and secondary current output reduces.
For checking or test purpose we can say that knee point is the point at which 10 % increase in voltage will incite 50 % increase in current.