Abstract :
Incorrect relay operation has often been related to saturation of current transformers. In many cases, the obvious solution to this saturation problem is an increased core cross-section of the current transformers, in order to allow a larger flux amplitude. In this respect, the transient asymmetrical component of fault currents is one of the most determining factors governing the dimensioning of the core cross-section of current transformers. A new technique using the characteristics of asymmetrical fault currents, has been developed in order to achieve a dynamic control of the core flux, thus allowing a significant reduction of the required cross-section. It is shown theoretically and experimentally that, taking into account all accuracy requirements and overvoltage limitations, the flux control circuit achieves a net reduction of the core crosssection by a factor of at least 3, even in the worst conditions imposed by C.T. or system parameters.
