Research on the Diagnosis of Circulating Current Faults in the Metal Sheath of Cross-linked XLPE Cables under Different Working Conditions

Abstract

This article deeply analyzes the distribution characteristics and variation laws of metal sheath circulating current under various typical fault conditions when XLPE high-voltage single core cables are connected by cross interconnection at 110 kV level. By comparing the different distribution characteristics of circulating current under various working conditions, the fault mechanism is revealed and theoretical basis is provided for state monitoring and protection strategies. By establishing a theoretical model of a cross connected system and based on the principle of electromagnetic induction, five typical fault scenarios are theoretically derived and quantitatively estimated. This article uses PSCAD/EMTDC simulation software to simulate the current values of the sheath ring during normal operating conditions, single-phase grounding short circuit of A-phase core, two-phase short circuit of BC two-phase core, open circuit of A-phase metal sheath, and two-phase short circuit of AB two-phase metal sheath. Compared with theoretical calculation values, it is found that the short-circuit fault of the core will excite a huge sheath current of kA level, and the fault phase current is highly concentrated. The fault of the metal sheath itself will cause abnormal current of 10A level. Among them, the short-circuit between sheath phases significantly increases the fault phase current, while the open circuit of the sheath causes the fault phase current to drop sharply to zero and produce slight disturbance in the non fault phase.