What is the purpose of calculating knee point voltage for Current transformers?
Answer A current transformer is an instrument transformer in which the secondary current is substantially proportional to the primary current under normal conditions of operation, and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections. The current transformer works on the principle of variable flux. In an ideal current transformer, secondary current would be exactly equal (when multiplied by the turns ratio) and opposite to the primary current. But, as in a voltage transformer, some of the primary current or the primary ampere-turns is utilized for magnetizing the core, thus leaving less than the actual primary ampere turns to be transformed into the secondary ampere-turns. This naturally introduces an error in the transformation. The error is classified into two: the current or ratio error, and the phase error. The knee point voltage is that point on the magnetizing curve where an increase of 10% in the flux density (voltag
