Overview

Cables of 10kV and above are mainly single-core cables equipped with metal sheaths. The magnetic flux generated by the alternating current in the conductor core couples with the metal sheath of single-core cables, inducing high voltage at both ends of the sheath. Therefore, proper grounding measures must be adopted to limit the induced voltage within a safe range (normally ≤50V, or ≤100V with additional safety protections).

For short cable circuits, the metal sheath of single-core cables is commonly grounded directly at one end, while the other end is connected via a gap or protective resistor. For long-distance cable circuits, a three-phase sectional cross-bonding grounding method is applied at both ends.

Regardless of the grounding scheme adopted, intact sheath insulation is essential. Damaged cable sheath insulation will lead to multi-point grounding of the metal sheath, generating circulating current in the sheath. This increases sheath power loss, reduces cable current-carrying capacity, and in severe cases, causes excessive overheating and cable burnout.

Meanwhile, reliable grounding at the direct grounding points of the metal sheath for high-voltage cable lines is critical. If the grounding point fails to connect to earth effectively, the potential of the cable metal sheath may surge to several kilovolts or even tens of kilovolts. This can easily puncture the cable outer sheath, triggering continuous discharge at the breakdown point, which may result in outer sheath temperature rise and even fire hazards.

Product Features

Adopting the circulating current measurement principle, the device monitors the circulating current and its variation on the metal sheath in real time. Under normal single-point grounding conditions, the circulating current on the metal sheath of single-core cables is minimal, dominated by capacitive current. Once multi-point grounding occurs and forms a closed loop with the earth, the sheath circulating current rises sharply, and may even exceed 90% of the main conductor current under serious fault conditions.

It realizes on-line monitoring of multi-point grounding faults on the metal sheath of single-core cables. The system can detect grounding faults timely and accurately, fundamentally preventing cable failures and ensuring safe and reliable operation of cable systems.

Application

This product is designed for on-line monitoring of sheath grounding current of high-voltage single-core cables.