大型发电机组中变压器后备保护存在问题分析及对策

摘要

Compound voltage over-current and zero-sequence over-current protection are usually used as backup protection for phase and ground faults in generator-transformer unit.Since the boundary of protective zone of these two types of protection is difficult to delimit,it frequently leads to miscoordination with protection in grid side.In addition,it is difficult for protection in grid side to coordinate with the protection in power plant side.Both cases can give arise to misoperation of protection at faults.To meet the requirements of speed,selectivity and sensitivity,phase and ground impedance protection are introduced into generator-transformer unit.The setting principle for impedance protection proposed is discussed in detail and a calculation case is given taking a 750 kV power plant as an example.The scheme has been successfully applied to the large generator-transformer unit and its adjacent grid in Northwest China,which greatly improve coordination of backup protection in power plant side and grid side.%大型发电机组中变压器通常配置复压过流和零序过流保护作为变压器相间和接地故障的后备保护.复压过流和零序过流保护动作边界不易确定,经常与电网侧后备保护失配,在发生故障时可能造成保护的越级跳闸.为此,提出在发电机组变压器中配置相间和接地阻抗保护,并详细介绍了阻抗保护的整定原则,以协调后备保护灵敏性、速动性与选择性的矛盾.分析了应用中需注意的问题,并以某750 kV电厂为例,给出了计算实例.该方案目前已在西北大型发电机组变压器及电厂送出线路中获得应用,提高了电厂和电网侧后备保护的协调配合.