Autoreclose

You are speaking of Auto reclose selector switch positions I suppose. Generally speaking, in transmission substations, the Auto reclose selector switch comes with three positions in addition to OFF position.

'3-pole' refers to trip of 3-poles of Line circuit breaker and subsequent reclose (after dead time) in accordance with the Auto reclose scheme designed for the Line. This is standard and widely implemented in MV as well as HV/EHV lines.

When it comes to EHV lines and some HV lines, 1-pole reclose may be necessary when the power system stabilities show that loss of subject line could cause stability issues. In case of 1-pole trip, power is still flowing through the line in other two phases. Thus there is no complete interruption and there is no loss of synchronism. Of course, 1-pole trip and reclose can only be for single line to ground faults.

If the '1-pole' option is selected, there will be no reclose for three phase or to phase faults.

In '1/3-pole' option, there will be 1-pole trip and reclose for earth faults (single line to ground) and there will be three pole trip and reclose for multi-line faults as well.