不同电压等级的四回线的纵联差动保护方案

New longitudinal differential protection scheme for four-circuit transmission line with different voltage grades

为克服传统纵联差动保护运用在不同电压等级的同杆四回线中容易受到耦合电感的影响,提出了基于反序负序差电流的纵联差动保护方案。不同电压等级的四回线由两个不同电压的等级的同杆双回线构成。对于同杆双回线路,当线路参数完全对称时,系统正常运行或是外部故障时,反向电流分量为零;而当双回线内部故障时,反向环流量存在于双回线的内部,双回线两侧反向电流之和比较大,可以构成基于反向环流量的纵联差动保护。该保护方案不仅可以避开电容电流对于差动保护的影响,而且有较强的抗过渡电阻能力。将该保护方案应用到不同电压等级的四回线的主保护中,保护性能优越,不仅可以可靠动作,还避免了电容电流对保护性能的影响。理论分析和EMTP仿真验证了基于反向分量电流的纵差保护的有效性,保护动作的可靠性。

To solve the problem that the traditional longitudinal differential protection used in four-circuit transmission line on the same pole with different levels will be seriously affected by coupling inductance, a new longitudinal differential protection scheme based on inverse-sequence negative sequence difference current is proposed. Four-circuit transmission lines with different voltage grades generally consist of two double circuit transmission lines at the same tower. However, when line parameters are symmetry, the inverted sequence current is zero when the system operates normally or external faults occur. Once internal faults occur, there is inverted current in the transmission line, and the sam of inverted current at both sides is large, so the differential protection based on inverted current can operate correctly. For this method, the reliability and sensitivity under big fault resistance can be kept. And it will not be affected by capacitive current when it is applied to the main protection of four-circuit transmission line with different voltage grades. The theoretical analysis and EMTP simulation results show that the proposed principle is correct and reliable.