Analysis And Online Monitoring Approach Design Of Grounding Induced Circulating Current Of XLPE Power Cable

XLPE power cable is commonly accepted and used more and more widely in power network. In the past 20 years, there has been a lot of rapid research progress about online monitoring of the insulation status of XLPE power cable in home and abroad, many research achievements have been made concerning mainly main insulation status. Adequate investigation and research work prove that: the faults of XLPE power cable took place mainly in the shield and the cable accessories, while the fault rate in the main cable body and the main insulation is relatively low. Based on this, a new idea of metal shield oriented online monitoring of XLPE power cable is brought forward.To get the fault character and criterion of metal shield oriented XLPE power cable, the electricity status of the metal shield of XLPE power cable is systematically analyzed in this paper, and the theoretical analysis of it is also accomplished. The induced voltage of metal shield under any laying modes is modeled and analyzed, and the calculation formula of the induced voltage of metal shield under normal circumstance, or circumstances like over-voltage, thunder, short circuit is given; The circuit model about grounding capacitance current and grounding induced circulating current(GICC) of the metal shield of XLPE power cable is established, the calculation formula of grounding current is derivated, which can be used to easily calculate GICC when the metal shield is damaged or faults occur in the grounding system.Based on the analysis of the electricity status of the metal shield of XLPE power cable, the fault characteristic of grounding loop induced circulating current variation caused by the damaging of metal shield or fault of grounding system is achieved. Therefore, The GICC based online monitoring approach of XLPE power cable is designed in this paper.The experiment is done in the lab by put high voltage on the core of the cable to compare the variation of grounding current in normal and fault situations of metal shield. The results show that the monitoring system of induced circulating current can reflect the insulation status correctly, hence, the approach is feasible, which provides a good foundation for the establishment of GICC based online monitoring equipments of XLPE power cable in the next step.