Calculation of Current Transformer Transient Errors

Transient saturation of current transformers may cause maloperation of protective devices. Therefore there is a need for a method which enables the calculating of transient transformation errors. The method should be simple and based upon the data which are available to the users of current transformers. The method presented adopts the first harmonic approach and uses simplifications which result from experimental study of many oscillograms of current transformers transient states. The simple equations make it possible to calculate aperiodic and first harmonic components of magnetizing and secondary currents in the transient states which involve saturation. The transient errors related to the transformation of the first harmonic may be easily determined, together with the time intervals in which they exceed given limits. Correlation between the method and the full digital model of a current transformer is satisfactory.