To find out the characteristics of insulation faults，this paper studies the primary insulating structure of SF 6 current transformer，and proposes a concept named the equipotential point for analyzing the operation of protection affected by current transformer faults.What has so far been done is:doing a comprehensive research on the requirements of the current transformer equipotential point whatever the installation available，and then abstracting them.Then，summing up the problems of current transformers that cannot meet the requirements of the equipotential point and design habit，and proposing an installation and construction program according to current transformer structure characteristics.This paper studies the relationship between primary winding current and secondary winding current.In the circumstances，the primary and secondary currents are completely out of proportion and may lead to protection malfunction，which is a tremendous impact on the power system.Finally，in face of the current transformer internal fault characteristics，an improvement program for the current transformer primary structure is proposed.