对于小电阻接地系统, 当电网发生单相接地故障时, 由于人为地增加了一个与电网接地电容电流相位相差90°的有功电流, 流过故障点的接地电流就等于电容电流和有功电流的相量和。应该说, 根据零序电流或电阻性电流的大小和方向也是很容易区分故障支路和非故障支路的。

Grid for the small resistance grounding system, when single-phase earth fault occurs, because an artificially increase grid grounding capacitive current of the phase difference of 90 ° active current, flows through the fault point grounding current is equal to and active current phasor and capacitive current. It should be said that according to the size of the zero sequence current and resistive current and direction is also very easy to distinguish the fault branch and the branch. 

　　由于单相接地时故障电流大, 必须切除故障线路, 故其保护配置可为: 限时(瞬时)电流速断保护, 低电压闭锁过流保护, 两段式零序保护, 所有保护均作用于跳闸。对于架空输电线路, 应配置一、二次(或多次)自动重合闸,使得瞬时性故障后可尽快恢复供电, 同时在永久性故障时, 加速继电保护动作于跳闸；对于电缆输电线路, 考虑其故障必定是永久性故障(或永久性故障所占故障比例很大) , 故不必设置自动重合闸。另外, 为保证可靠地切除故障线路, 保护一次设备的安全, 考虑到故障线路的保护或开关存在拒动的可能, 所以应在中性点接地电阻回路中加装电流互感器(TA) ,接入零序后备保护(或称接地电阻零序保护) , 加适当延时后,作用于跳开变压器低压侧开关。

Because when the single-phase grounding fault current is big, must remove the fault lines, so the protection configuration can be as follows: period (instantaneous) current instantaneous fault protection, low voltage lockout overcurrent protection, two sections of zero sequence protection, protection are all on the trip. For overhead transmission lines, should be configured once or twice (or more), automatic reclosing made the instantaneity power can be resumed as soon as possible after a failure, in permanent fault at the same time, accelerate the relay protection action in the trip; For cable transmission lines, consider its fault must be a permanent fault or permanent fault accounted for a large proportion, so don't need to set up automatic reclosing. In addition, in order to ensure the removal of fault lines in a reliable way, to protect the safety of a device, considering the fault lines of protection or the possibility of refusing action switch, so should be mounted in the neutral point grounding resistance loop current transformer (TA), access to the zero sequence backup protection (or zero sequence protection grounding resistance), add the appropriate delay, after apply to jump drive transformer low voltage side switch.