解列后孤岛电网电压失稳机理探讨

电网因故障解列后由于功率缺额孤岛频率一般会下降，而实际电网事故中存在解列后功率缺额情况下孤岛电压失稳且伴随频率上升的现象。利用负荷功率与基本电气量的关系探究网络视在功率传输极限，并从理论上分析电压稳定的静态运行点。通过仿真算例从孤岛网络、负荷电压-功率特性两方面对解列后孤岛电网电压失稳机理进行研究，分析指出解列后负荷视在功率接近网络的视在功率传输极限时，网络极限会制约负荷功率的增长。进一步从各时间断面的视在功率传输极限的角度出发，分析网络极限与马达负荷的制约机理，指出短路故障后马达吸收无功是造成孤岛电压失稳的重要诱因，从而揭示电压失稳后低负荷电磁功率是孤岛低压高频的本质。研究成果可为孤岛电网运行方式安排以及集中切负荷、低压减载措施提供参考。

Study on mechanisms of voltage instability in islanding grid after fault disconnection

Under normal circumstances, the frequency of islanding grid will drop because of power shortage after fault disconnection. However, voltage instability happened with increasing frequency under condition of large power shortage in practical power grid accidents. This paper uses the relationship between load power and basic electrical variables to research the transfer limits of apparent power and to analyze static operation point. And then voltage instability mechanism of the islanding grid after fault disconnection is analyzed from aspect of grid frame and voltage-power characteristic with simulation model. It is pointed out that load capacity will be limited if the load apparent power is close to transfer limit of islanding grid. Furthermore, restrictive mechanism between grid limit and motor load is analyzed by aspect of transfer limit of apparent power at each time section and to point out that reactive power of motor absorbed after short fault is an important cause of islanding voltage instability. And then it reveals that low electromagnetic power after voltage instability is the essential reason of low-voltage with high-frequency question. It provides reference for the operation mode arrangement of islanding grid and control of concentrated load shedding and under-voltage load shedding.