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 K 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 low-current grounding fault, a half-wave DC current is injected into the fault system from neutral-to-ground voltage of the system. The DC generator is supplied with power supply by neutral-to-ground voltage, and the DC generator is switched on and off by high-voltage silicon stack D, current limiting resistance R and switching on and off. The neutral point of the primary side of the grounding transformer is connected with the switch K. 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.