应对变电站二次直流失电的超高压输电线路相间保护方案

Phase-to-phase protection scheme for EHV transmission line coping with substation secondary DC power loss

变电站二次直流失电会导致本站继电保护装置等设备失去供电电源而无法动作,本站出线发生故障时需要依靠上级变电站的远后备保护进行切除。针对变电站二次直流失电情况下超高压输电线路发生相间短路故障时保护远后备灵敏度不足的问题,提出了一种应对变电站二次直流失电的超高压输电线路相间保护方案。首先,根据超高压电网相间故障时负序电流的自然分布特性,探讨了反时限负序过流保护的远后备应用可行性和相间距离保护的补充特性,确定了相间故障远后备保护的构成思路。接着,研究了助增系数和负序电流对反时限负序过流保护整定时间定值的影响,讨论了临界助增系数的确定方法和反时限负序过流保护的时间定值整定方法。然后,提出了反时限负序过流保护为主、相间距离保护为辅的应对变电站二次直流失电的超高压输电线路相间保护方案。最后,以IEEE 39节点系统和某实际500 kV电网作为仿真算例,对所提方案的有效性进行验证。

Secondary direct current(DC)power loss in the substation will cause all protections and other devices to lose power supply and unable to operate.When the fault occurs on the adjacent transmission line of the substation,it is necessary to rely on the remote backup protection of the superior substation for removal.To solve the remote backup protection insufficiency in case of extra-high voltage(EHV)transmission line phase-to-phase short circuit fault on occasion of substation secondary DC power loss,a phase-to-phase protection scheme for EHV transmission line to deal with substation secondary DC power loss is proposed.According to the natural distribution characteristics of negative sequence current during phase-to-phase fault in EHV power grid,the feasibility of remote backup application of inverse-time negative-sequence over⁃current protection and the supplementary characteristics of phase-to-phase distance protection are discussed,and the method of remote backup protection to cope with phase-to-phase fault is determined.Then the influence of the feeding coefficient and negative-sequence current on the time setting of inverse-time negativesequence overcurrent protection is studied,and the determination method of the critical feeding coefficient and the time setting value of inverse-time negative-sequence overcurrent protection are discussed.Then,a phase-to-phase protection scheme for EHV transmission line is proposed,which is mainly based on inversetime negative-sequence overcurrent protection and supplemented by phase-to-phase distance protection.The IEEE 39-bus system and an actual 500 kV power grid are taken as examples for simulation analysis to verify the effectiveness of the proposed scheme.