交直流混联电网发电机失步保护与直流低电压保护协调

直流输电站间通信中断情况下,当逆变侧出现故障紧急停运时,整流侧主要依靠直流低电压保护动作实现闭锁。由于整流侧通常采用定功率控制,换流器会出现低电压大电流运行并吸收大量的无功功率,若交流系统强度不够就容易造成整流侧交流母线电压大幅降低,进而引起周围发电厂内机组出现振荡直至失步。文中通过分析一起直流系统长时间低电压运行引起发电机失步保护动作的实例,指出换流站直流低电压保护应与邻近发电机失步保护相互协调,并提出了配合原则。所述原则已应用于实际直流输电工程及其邻近发电厂,显著提高了交直流混联电网运行可靠性。

Coordination of Out-of-step Protection and DC Under-voltage Protection in AC-DC Hybrid Grids

During communication failure between converter stations,if emergency switch off sequence(ESOF) occurs at inverter side due to serious faults,it mainly depends on DC under-voltage protection to block converter at rectifier side.Constant power control is usually employed at rectifier side,therefore,blocking with bypass pair at inverter side frequently leads to low voltage and large current operation mode of rectifier station.This adversely affects the adjacent AC grid and makes the voltage in AC bus of converter station reduce rapidly.As a result,the adjacent generators may start oscillating and even lose synchronism.Based on the analysis of mal-operation of generator out-of-step protection resulting from high voltage direct current(HVDC) under-voltage operation,it is concluded that both out-of-step protection and DC under-voltage protection should coordinate with each other properly,and the principle of setting cooperation is proposed.This method has been successfully applied to HVDC projects and their adjacent AC power plants in China,which improves the performance of protection greatly in AC-DC hybrid grid.