| With the rapid development of urban electric power industry, high voltage power cables above 110 kV (110kV inclusive) are used more and more widely. The operations of a large amount of single-core cables are far beyond cable metal sheath's endurance, bringing additional loss to the cable metal sheath and making cable service life shortened. Therefore, the status evaluation of the grounding system of the high-voltage cables becomes necessary.This research focuses on the research strategies in this aspect, especially in the case of 110kV high-voltage cables. In order to control the induced current of single-core cables in actual cable engineering, this paper studies and analysis how induced current of the high-voltage cables' metal sheath varies with bonding methods, manner of arrangement, load condition and operation state. A math mode was established according to the calculation of induced current, so that the induced current could be controlled beforehand through the adjustment of cable arrangement. The voltage and current characteristics of single-point bonding system, double-point bonding system and cross bonding system placed in the manner of horizontal and trial arrangement were analyzed. In the meantime, a program was written to facilitate calculating the absolute and relative value of both earth current and load current. The characteristic of the grounding current in four fault state was analyzed, which included transposition failure, the cross-linking box filling with water, the damage of PVC sheath and the rupture of cross-linking coaxial cable. By comparing the monitoring and calculating grounding current, the fault of the grounding system can be diagnosed. Thus the status evaluation of the grounding system could be established and it provides theory basis and reference data for the running and monitoring of high voltage cables, so that cable-net accident risk could be reduced, improving the safety and reliability of the city grid operation. |
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