PROTECTIVE RELAY CLASSES Classification C or K covers current transformers in which the leakage flux in the core does not have an appreciable effect on the ratio or ratios within the limit of current and burden. These instrument and protection CTs are governed by standard IEC 60044-1 in France NF C 42-502. Current Transformer Types And Applications The Talema Group Typically wound CTs L CT accuracy applies at the maximum rated secondary burden at 20 time rated only. Class c current transformers for protection . There are two possible configurations. K classification shall have a knee-point voltage of at least. A current transformer is similar to a electrical power transformer to some extent but there are some difference in construction and operation principle. C three CTs achieving in the neutral connection of their secondary the sum of the three phase currents. The current transformer cores are designed to operate at the class rating 5P 10P up to the nominal accuracy limi...