Research On Protection Coordination Scheme For Series-compensated Transmission Lines

As a flexible AC transmission technology,series capacitor compensation(series compensation for short)technology has the characteristics of good economy,high equipment utilization,and flexible control.It can effectively improve the transmission capacity of the lines and is widely used in our country’s power grids.The reversion of fault voltage and current components caused by the characteristic of capacitive impedance makes the correct action of traditional line protection have safety risks.How to consider the impact of series compensation on line protection and propose corresponding solutions are important issues that need to be resolved for engineering applications.This paper has carried out the research on the protection coordination scheme of the line with series compensation.The main research contents are summarized as follows:A setting method of inverse-time zero-sequence current protection for double-circuit lines with series compensation is proposed.The time-current operating characteristic of the inversetime zero-sequence current protection and the conventional step-by-step setting method are studied.The misoperation of current protection under fault condition of double-circuit lines with series compensation is analyzed.And the current protection setting method for doublecircuit lines with series compensation is proposed.The calculation example shows that the proposed method takes into account the lumped impedance characteristic of series compensation in detail,effectively avoids the protection misoperation,and has higher protection reliability than the conventional step-by-step setting method.A distance protection setting method that takes into account the operating characteristic of the MOV(metal oxide varistor)of series compensation is proposed.The equivalent impedance of series compensation is under the description of the linearized equivalent model.The operation of the distance protection of the line with series compensation is analyzed.And the distance protection setting method based on the linearized equivalent model is proposed,which realizes the precise setting of distance protection for the line with series compensation.The calculation example shows that the proposed method takes into account the equivalent impedance characteristic of series compensation under specific faults.Compared with the setting method based on the simple series compensation model,the sensitivity of protection operation is improved.A general setting method for current differential protection of multi-circuit lines with series compensation is proposed.The basic principles of the segregated current differential and zero-sequence current differential protection based on steady-state quantities are studied.And the current reversion and protection operation characteristic during an internal fault under the influence of series compensation are analyzed.A general current differential setting method suitable for multi-circuit lines with series compensation is proposed.The calculation example shows that the proposed method realizes the reasonable setting of the current differential protection,improves the sensitivity of protection,reduces the risk of protection fault and enhances the protection reliability.