Three Phase Auto Recloser vs Single Phase Auto Reclose:
Three Phase Auto Recloser is one in which the three phases of the transmission line are opened after fault incidence, independent of the fault type, and are reclosed after a predetermined time period following the initial circuit breaker opening. For a single circuit interconnectors between two power systems, the opening of all the three phases of the circuit breaker makes the generators in each group start to drift apart in relation to each other, since no interchange of synchronizing power can take place.
On the other hand Single Phase Auto Reclose is one in which only the faulted phase is opened in the presence of a single-phase fault and reelosed after a controlled delay period. For multiphase faults, all three phases are opened and reclosure is not attempted. In case of single-phase faults which are in majority, synchronizing power can still be interchanged through the healthy phases.
In the case of single-phase auto-reclosing each phase of the circuit breaker has to be segregated and provided with its own closing and tripping mechanism. Also it is necessary to fit phase selecting relays that will detect and select the faulty phase. Thus single-phase auto-reclosing is more complex and expensive as compared to three-phase auto-reclosing. When Single Phase Auto Reclose is used the faulty phase must be deenergized for a longer interval of time, than in the case of Three Phase Auto Recloser, owing to the capacitive coupling between the faulty phase and the healthy conductors which tends to increase the duration of the arc.
Advantages of Single Phase Reclosing:
The advantage claimed for single-phase reclosing is that on a system with transformer neutrals grounded solidly at each substation, the interruption of one phase to clear a ground fault causes negligible interference with the load because the interrupted phase current now flows in the ground through neutral points until the fault current is cleared and the faulted phase reclosed.
Dis Advantages of Single Phase Reclosing:
The main drawback is its longer deionizing time which can cause interference with communication circuits and, in certain cases maloperation of earth relays in double circuit lines owing to the flow of zero sequence currents.