Transient response of current transformers

In modern HV and EHV power systems more and more emphasis is placed on the ability of current transformers to provide correct operating current to protective relay systems. Relay decisions need to be made while the dc transient component of fault current is still present. The operating current should not be distorted sufficiently to cause maloperation of the protective system. The major cause of concern is the decaying dc transient component of fault current. This component can cause some degree of current transformer saturation and thus operating-current distortion.