城市电网10kV低阻接地系统中接地变压器零序保护接线方案

Discussion on protection scheme of earthing-transformer in city's 10 kV power network utilizing low earthing resistance mode

为了抑制单相接地时产生的过电压幅值,某些大城市的10kV电网开始采用低阻接地的接线方式。分析了经接地变压器低阻接地方式的城市变电所中,其10kV母线不同位置接地时的零序电流流向以及接地变压器的零序保护逻辑方案,提出采用零序电流方向保护作为主变压器低压侧双分支接线方式的接地变压器零序保护,使保护具有选择性,从而提高了对用户供电的可靠性。

For suppressing the overvoltage caused by a singlephase to ground fault, the low earthing resistance mode utilizing an earthingtransformer is adopted in some of large cities. The direction of zerosequence current and the protection logic of the earthingtransformer are discussed in this paper while the earthing fault takes place at any of 10 kV bus sections in city's substations. The protection scheme based on the direction of zerosequence current is introduced for the earthingtransformer located at lowvoltage side of the main transformer with dualbranches, so as to get higher power supply reliability.