Single-pole and three-pole reclosing: secondary arc

Short answer

In single-pole reclosing only the faulted phase opens and recloses, so power keeps flowing through the other two; it requires breakers with independent pole operation and a longer dead time because of the secondary arc. The scheme coordinates the protections, pole discordance, synchronism check and, in breaker-and-a-half, the order between the leader and the follower breaker.

What the single-pole and three-pole reclosing scheme is

The automatic reclosing 79 function closes the breaker again after a transient fault. It is one of the line substation protection schemes. In transmission, how it is done is a scheme decision: open and reclose only the faulted phase (single-pole) or all three (three-pole), and in what order the breakers at each end and in each bay do it.

Most faults on HV and EHV overhead lines are single-phase-to-ground. If only the faulted phase opens, the other two keep carrying power and the two line ends do not separate, which helps system stability.

Which protections are involved and how they are coordinated

Main protections with phase selection: distance and line differential must identify the faulted phase to trip only that pole. See main 1 and main 2.
Teleprotection that allows single-pole tripping at both ends.
Reclosing 79 in one or both main relays, coordinated.
Pole discordance, in the relay or in the breaker mechanism.
Synchronism check 25 and dead line check, for three-pole reclosing.
Breaker failure 50BF with per-pole initiation.
Breaker with independent pole operation, able to open and close each phase separately.

Logic and sequence

Transient single-phase fault:

The main protections at both ends detect the fault and select the phase.
Each end opens only that pole. The single-pole dead time starts.
With the pole open, zero-sequence functions are blocked or adapted, because the line carries unbalance current without a fault.
The secondary arc extinguishes. Both ends close the pole.
The reset time runs; the scheme is ready again.

If the fault evolves to another phase during the dead time, or is multiphase from the start, the trip is three-pole. Depending on the philosophy, a three-pole reclose with synchronism check follows, or the line stays open.

If the fault persists when the pole recloses, the main protections trip all three phases and reclosing is blocked.

Single-pole or three-pole depending on the fault

Is the fault single-phase?
- No, it is multiphaseThree-pole trip; depending on the philosophy, three-pole reclose with synchronism check or line left open
- YesDoes it evolve to another phase during the single-pole dead time?
  - YesThree-pole trip, as in a multiphase fault
  - NoIs the fault still there when the pole recloses?
    - NoThe reset time runs and the scheme is ready again
    - YesThe main protections trip all three phases and reclosing is blocked

Secondary arc

With the pole open, the arc does not disappear at once: the healthy phases feed it through capacitive coupling and, to a lesser extent, inductive coupling. Its duration grows with voltage, line length and load current. On long EHV lines compensated with shunt reactors, a neutral reactor is connected between the neutral of those reactors and ground, sized to compensate the phase-to-phase capacitive coupling and reduce the secondary arc current. Some manufacturers also offer adaptive reclosing, which evaluates the voltage of the open phase and recloses once the arc has extinguished instead of waiting a fixed time.

Breaker-and-a-half: leader and follower

In breaker-and-a-half or ring bus arrangements, each line has two breakers. Reclosing both at once onto a permanent fault exposes both to the fault. The leader-follower scheme makes the leader reclose first and the follower reclose only if the leader succeeded. The bus breaker is often chosen as leader: if it closes onto a permanent fault and then fails, its 50BF trips the bus, while a failure of the center breaker would also take out the other line of the diameter. The choice belongs to the owner. Dual-breaker line relays let you set the leader and follower by setting, or swap them with logic depending on conditions, for example when the leader is open or out of service.

Variants by voltage level

Extra-high voltage: single-pole reclosing is standard practice in many systems, with a single shot and a dead time set from secondary arc studies.
High voltage: single-pole or three-pole depending on the breaker and the transmission owner’s philosophy.
Medium voltage: three-pole, with reclosers and several shots. See radial feeders.
Near large generators: fast three-pole reclosing can expose the shaft to torsional stress; it is evaluated in studies and sometimes avoided.

Design criteria

Single-pole dead time: longer than the secondary arc extinction, based on transient studies of the line.
Pole discordance: timed above the single-pole dead time and coordinated with the one in the breaker mechanism.
Behavior of the ground elements while the pole is open.
Which end closes on dead line and which with synchronism check, for three-pole reclosing.
Breaker capability for the assigned operating sequence. IEC 62271-100 (IEEE C37.04 in North America) defines the sequence O – t – CO – t’ – CO, with t = 0.3 s for breakers intended for rapid autoreclosing, and the alternative CO – t” – CO.

There are no universal dead times: they depend on the line and on the studies. IEEE C37.104 gives the guidance.

How each manufacturer implements it

Siemens SIPROTEC (DIGSI), SEL (AcSELerator QuickSet), Hitachi Energy Relion 670 (PCM600), GE Vernova Multilin UR (EnerVista) and MiCOM (GE Vernova MiCOM Agile P44x/P54x) offer single-pole and three-pole reclosing with open-pole logic. What changes is how the modes are defined (single-pole only, single- and three-pole, three-pole), how two reclosers in M1 and M2 are coordinated, how leader-follower is implemented between the relays of two breakers, and how the ground elements adapt while a pole is open.

Why it fails or misoperates

Pole discordance opens all three phases because its timer is shorter than the single-pole dead time.
Three-pole trip for a single-phase fault: failed phase selection, teleprotection without single-pole tripping, one main relay in three-pole mode.
Trip during the open pole from zero-sequence elements that were not blocked.
Unsuccessful reclose because the dead time is short for the secondary arc.
Both breakers of a breaker-and-a-half bay close onto the fault because the leader-follower logic is missing.

Check the event record: selected phase, opening time per pole, current during the dead time and which function tripped all three phases.

How it is tested

With a three-phase test set (for example, an Omicron CMC 356), single-phase and multiphase faults, transient and permanent, are simulated with the real breaker or a per-pole breaker simulator. Phase selection, dead times, pole discordance, blocking during the open pole and the leader-follower order are verified. It is completed with end-to-end tests and with the breaker pole discrepancy test.

Did your line trip three-pole when you expected single-pole? At Tiza Group we review the events and the reclosing logic remotely. See remote relay configuration or contact us.

References

IEEE C37.104-2022, Guide for Automatic Reclosing of Circuit Breakers for AC Distribution and Transmission Lines.
IEEE C37.113-2025, Guide for Protective Relay Applications to Transmission Lines.
IEC 62271-100, High-voltage switchgear and controlgear – Part 100: Alternating-current circuit-breakers.
S. H. Horowitz and A. G. Phadke, Power System Relaying.

Frequently asked questions

Why is the single-pole dead time longer than the three-pole dead time?

Because with the faulted phase open, the two healthy phases remain energized and feed the fault point through capacitive and inductive coupling. That secondary arc takes longer to extinguish than the arc on a line open in all three phases.

What does pole discordance protection do during single-pole reclosing?

It checks that the three breaker poles are in the same position. During the single-pole dead time the poles are intentionally discordant, so its timer must be longer than that dead time; if the poles are still discordant afterwards, it opens all three phases.

In breaker-and-a-half, which breaker recloses first?

The one the owner defines as leader recloses first; the follower recloses only if the leader succeeded. That way, if the fault is permanent, only one breaker closes onto it. The bus breaker is often chosen as leader, so that a failure of that breaker affects the bus and not the other line of the diameter.