为增大选线定位判据特征量，根据小电流接地故障中性点对地电压的变化特征，提出从系统中性点处向故障系统注入半波直流电流，由中性点对地电压为直流发生装置提供电源，直流发生装置由高压硅堆 D、限流电阻 R 和投切开关 Kd 构成，接于接地变一次侧中性点。直流发生装置仅在单相接地故障发生后短时投入，选线定位结束后即切除。
In order to increase the characteristic value of line selection criterion, according to the variation characteristics of neutral-to-ground voltage of small current grounding fault, a half-wave DC current is injected into the fault system from the neutral-to-ground voltage of the system. The neutral-to-ground voltage provides power for the DC generator. The DC generator consists of high voltage silicon stack D, current limiting resistance R and switching-on switch Kd, which is connected to the neutral-to the primary side of the grounding fault. 。 The DC generator is only put into operation shortly after the single-phase grounding fault occurs, and is removed immediately after the line selection and location is completed.
发生接地故障时，中性点对地电压不为 0，直流发生装置投入后，将会产生半波直流电流，对中性点不接地系统，该直流电流在系统中性点、接地线路接地相、接地点和大地之间形成回路；对消弧线圈接地系统，消弧线圈对地支路有半波直流电流流通。可见，只有故障馈线中变电站至接地点的线路中有直流电流流通，而非故障馈线中没有该直流电流。因此，通过对半波直流电流寻踪可实现故障选线和定位，即为注入半波直流的选线定位原理。
When grounding fault occurs, the neutral-to-ground voltage is not 0. When the DC generator is put into operation, half-wave DC current will be generated. For the neutral-to-ground system, the DC current will form a loop between the neutral point of the system, the grounding phase of the dianbiao.37ix.com.cnjingdianji.37ix.com.cnshusongdaib.07858.net shusongdain.07858.net zhushiguan.07858.netfangdaomenb.89ix.comgrounding line, the grounding point and the earth. For the arc suppression coil grounding system, half-wave DC current will flow between the arc suppression coil and the grounding branch. It can be seen that only the line from substation to grounding point in the fault feeder has DC current, but not in the fault feeder. Therefore, fault line selection and location can be realized by searching half-wave DC current, which is the principle of line selection and location for injecting half-wave DC.