Abstract: During During extreme high-impedance faults on high-voltage transmission lines, the faults exhibit slow-developing characteristics. Prolonged operation under such conditions may cause protection devices to misjudge the situation as a current transformer (CT) disconnection, resulting in the refusal of line protection operation. This paper systematically elaborates on the characteristics of slowly developing high-impedance faults under various operating conditions, analyzes and summarizes the electrical differences between TA disconnection and high-impedance faults, and proposes an optimized logic for TA disconnection identification. The protection system should be capable of adapting to slowly varying faults involving transition resistance grounding to prevent malfunction or failure of protection during line faults.