Research On Relay Protection Technology For UHV GIL-overhead Hybrid Transmission Line

Based on the features of the GIL such as huge transmission capacity,little environmental impact,high reliability and expensive cost,UHV GIL-overhead hybrid transmission line is an essential way for UHV waters crossing power transmission or other complex terrain power transmission over long distance.The relay protection of overhead transmission line will be affected by GIL because of the differences in the structure and electrical parameters between the GIL and overhead line,which may lead to malfunction or rejection in severe cases.Therefore,study on relay protection technology of UHV GIL-overhead hybrid transmission line is of great theoretical and practical value to ensure the safety of GIL equipment and the stability of the system after fault.Firstly,the structure and the way of grounding of GIL are introduced.Then analysis the electromagnetic and electrostatic coupling among the conductor layers of the three phases,the calculation method of the equivalent parameters of the core of GIL is studied and compared with the parameters of the overhead line.Based on the parameters of GIL,the modeling methods of the multiple-segment PI equivalent model with the enclosure segment-connecting and the PI equivalent model with lumped parameters are proposed.The adaptability of differential protection for UHV overhead transmission line is analyzed based on the model of GIL-overhead hybrid transmission line.According to the effect on the differential protection,the differential protection method for UHV overhead transmission line is modified.Based on the “overall differential + section differential” differential protection configuration scheme of GIL-overhead hybrid line,a reclosure strategy for UHV GIL-overhead hybrid transmission line is studied.Finally,the adaptability of distance protection for UHV overhead transmission line is analyzed,and a distance protection method based on lossless line for UHV GILoverhead hybrid line is proposed.Considering the electrical parameters of GIL,a setting method of distance protection for hybrid line is proposed.