事实上该种选线装置的选线报警最好作为单相接地故障的参考信号，而不能作为直接跳闸的信号。原因是，这套装置以及采集零序信号的电流电压互感器在理论上，可以做到对单相接地故障百分百的正确报警。
In fact, the alarm of this kind of line selection device is better as the reference signal of single-phase grounding fault, but not as the signal of direct trip. The reason is that this device and the current and voltage transformer which collects zero sequence signal can theoretically give 100% correct alarm to single-phase grounding fault.
但是在实践中，正确的接线校线，零序电流互感器的正确选型、配置、安装，以及其他各种复杂的原因，使得选线很难做到百分百正确。
But in practice, correct wiring alignment, correct selection, configuration, installation of zero sequence current transformer and other complex reasons make it difficult to achieve 100% correct wiring selection.