采用新型换流变压器及其滤波系统对换相失败的影响

Influence of novel converter transformer and its filter system on commutation failure

分析了直流输电的换相失败机理及影响换相失败的因素。考虑到新型换流变压器及其滤波系统的阀侧滤波支路会对直流输电系统中各运行变量产生一定的影响,以实验室建立的直流输电系统模拟平台为研究对象,给出了新系统下阀侧无功补偿度的定义,当逆变侧采用新型换流变压器及其滤波系统后,详细分析了多种因素对逆变侧换相失败的影响并得出如下结论:阀侧无功补偿度对换相过程的改善能力不大;直流电流和换相电抗的增加会增大逆变器发生换相失败的几率;越前触发角的增大可有效降低逆变器发生换相失败的几率;不对称故障时,换相电压过零点的偏移会使得与发生单相接地短路相相连的逆变器上、下2个换流阀最易发生换相失败。最后,提出了新系统条件下避免发生换相失败的措施:增大越前触发角或关断角的整定值;适当降低换流变压器的换相电抗;保持换相电压的稳定。

The mechanism of commutation failure in HVDC transmission system and its influencing factors are analyzed. As the novel converter transformer and the branch at valve side of its filter system have a certain influence on the operational variables of HVDC system,the definition of reactive power compensation degree at valve side is given based on a lab simulation platform of DC transmission system. When the inverter adopts the novel converter transformer and its filter system,the influence of different factors on commutation failure are analyzed and the conclusions are：the reactive power compensation degree at valve side has little influence on the improvement of commutation process; the increase of DC current and commutation reactance may increase the probability of commutation failure ; the increase of firing angle may effectively decrease the probability of commutation failure ; the zero-crossing phase shift of commutation voltage may easily cause the commutation failure of two faulty phase converter valves in single -phase grounding fault. Countermeasures are presented：increase the settings of firing angle or extinction angle;decrease properly the commutation reactance of converter transformer;keep the commutating voltage stable.