Analysis And Solution Of Excessive Circular Current In The Metallic Sheath Of High-voltage Cable In Shenzhen

Power cable has many advatages which include of stable transmission of electrical energy, high reliability, being less affected by climatic and environmental factors, covering an area of less, etc..With the rapid development of urban economy, in the process of urban power grid construction, it has been used more and more widely. As of November 2015, the length of Shenzhen 110 k V and more high voltage level power cable is close to 800 km, due to external damage, aging, improper constructing or maintenance and other reasons, the number of high voltage power cables whose circulating current in sheath exceeding a standard increases year by year, in 2014-2015, we detected the number of high voltage cables which have excessive circulation is nearly 40, the operation and overhaul situation of the high voltage power cable is very grim. Therefore, analying the reasons of exceeding the standard and its influence factors of Shenzhen high voltage cable Circulating current in sheath, puting forward effective measures, to ensure the safe and stable operation of the cable has become more and more urgent.In this paper, we calculate the theory of the induced voltage and induced current of single core cable metal sheath, establishe calculation model of single core cable circulating current in sheath, derive the calculation method of sigle core cable circulating current in sheath, and combine with the actual engineering calculation, analyse the influencing factors of sigle core cable circulating current in sheath;Meanwhile, we summarize the the characteristic of the circulating current in sheath with analyzing the common example of circulating current in sheath which exceeds the standard in the actual operation for high voltage cables.In this paper, the reasons of influenceing of the sheath circulation exceeding the standard are mainly uneven for the cross- connection segment, the fault connecting for the cross – connection and demanged for protective layer. We propose, for the new power cables, should try to use the "product" font layout, make sure the cable subsection is even, when the laying condition is changeable,we should choice proper spacing and segmentation according to the load flow and the circulating current in sheath of the cables; in the operation of the power cable, we can find and repair the outer sheath fault, serie small resistance or compensation inductor(reactor) on the groud floor to control the circulation, and the practical effect is good.