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 .