Cable Sheath circulationis the induced current in the metal sheath of a high-voltage single-core cable (usually aluminum or copper sheath) due to the cable's metal sheath being grounded at both ends or at multiple points during the cable's operation. When there is an AC current passing through the cable core, a magnetic field is generated around it. According to Ampere's loop law, the strength of the magnetic field is proportional to the size of the current. For single-core cables, whose metal sheath surrounds the core, this alternating magnetic field generates an induced electromotive force in the sheath. If the sheath is grounded at both ends or at multiple points, a closed loop is formed, and the induced electromotive force drives the electrons to flow, thus generating a loop current. For example, in high-voltage transmission lines, the cable transmits a larger current, generating a stronger magnetic field, more likely to produce significant sheath circulation.
The grounding method of the cable metal sheath is also a key factor in generating sheath circulation. If the two ends of the grounding method, in normal operation, due to electromagnetic induction of the induced electric potential will be formed at both ends of the sheath potential difference, thus generating circulation. Even in the case of single-point grounding, if additional ground paths are formed in the sheath due to external factors (e.g., poor grounding, contact with other metal objects, etc.), loop currents may also be generated.
In real operating environments, the presence of sheathing circulations means that electrical energy is lost. This loss of power not only reduces the efficiency of cable transmission of power, but also increases the operating costs. Moreover, cable sheath circulation will lead to sheath heating, and prolonged heating will accelerate the aging of the cable sheath insulation material, reduce its insulating performance, and may even lead to insulation damage, causing cable failure.
Monitoring and preventive measures
Monitoring methodology:
You can use DX-DLS100-HL Ground Loop Current Monitoring System to monitor cable sheath loop current. Sleeve the ring current transformer on the cable sheath grounding wire, it can real-time measure the size and change of the ring current. At the same time, combined with the intelligent monitoring system, the monitoring data will be transmitted to the background for analysis and processing, and the abnormal ring current situation will be found in time.
Preventive measures:
In the cable design and installation stage, the grounding method can be optimized, such as the use of cross-interconnection grounding method, by changing the location and mode of grounding connection, effectively reducing the sheath ring current. At the same time, strengthening the selection and quality control of cables to ensure that the insulation of the cable sheath is good, is also an important measure to reduce the hazards of sheath ring current.
