Proposals for Protection of Return Cables on SwePol Link

Abstract

The return cable on the SwePol Link has been introduced as an alternative forced by environmentalists due to lack of social acceptance of other solutions. This is why in the proposed solution water and earth have been replaced by two return cables, although from a technical point of view such a solution is less effective. The last, eleventh fault of the return cable took place on 15 October 2012. In eight earlier cases the faults were caused by electrical failures in the cable in the sea and were located between ten and twenty kilometers from the Polish shore and triggered by disturbances in the northern part of the Polish power grid. In this situation it has been suggested to analyze and introduce one or two solutions shown below which may significantly limit the effects and lower the costs caused by return cable faults: a) assembly of additional surge arresters b) return to electrodes – lack of return cables c) ”partial” electrodes working with one return cable d) operation of the link only with earthings on converter stations. To sum up it needs to be stated that: • a relatively cheap way of protecting return cables against electrical failures is installing surge arresters in the cabinet located next to the cable container on the Polish shore • from the suggested preventive measures it seems reasonable to introduce the above mentioned solutions a) and d) simultaneously, as both of them are simple solutions which require neither considerable financial expenditure nor authorizations and may quickly show the expected results.