Real time compensation algorithm for air-gapped current transformers saturation effects

• A method of correcting the current distortion in air gapped CTs is presented.
• The ratio and phase errors due the gap insertion are also corrected by the method.
• The proposed correction method avoids the CT oversizing.
• The secondary circuit impedances values is not necessary, unlike other techniques.

A platform implemented with digital signal controllers (DSCs) developed for real time studies of the dynamic behavior of the air-gapped current transformers (CTs) used in power grid protection and measurement systems is presented. The implemented algorithms simulate the fault current in an electric power system as well as the transient response of the current transformer. A method for correcting the CT secondary current distortion is presented in the case of gapped core where residual flux is negligible. To estimate the flux, a tertiary winding must be available. The ratio and phase errors, as well as the distortions in secondary current due the core saturation in fault situations are properly corrected by the method. Several cases were tested and the results indicate that the proposed method is very effective in improving the performance of protection schemes based on the current measurement.