Leader-follower reclosing in breaker-and-a-half schemes

The problem of two breakers per line

In the breaker-and-a-half configuration each circuit sits between two breakers: its bus breaker and the middle breaker of the bay (diameter). The same happens in the ring bus configuration and in double bus double breaker. A line fault opens both of the circuit’s breakers at the local substation and the breaker at the remote end.

Automatic reclosing 79 has to close the line again, but here it has two breakers to command. If it recloses both at once and the fault is permanent, both close onto it and both interrupt fault current again. The middle breaker is also shared: any problem with it affects the other circuit of the bay.

How the leader-follower scheme works

One of the two breakers is designated leader and the other follower:

• The leader recloses after the dead time of the cycle, with the appropriate supervision: dead line or synchronism check 25.
• The follower waits for the leader to close and stay closed for a confirmation time. Then it recloses, usually with synchronism check, because the line is already energized.
• If the leader recloses onto a fault and the protection trips again, the follower is blocked: the line has already shown that the fault is permanent.

In IEC 61850 each breaker usually has its own reclosing instance (RREC), and coordination between them is done with internal relay signals, when the same device handles both breakers, or with GOOSE messages between the relays of each breaker.

Which breaker leads

The choice depends on each utility’s philosophy. A widespread criterion is to let the bus breaker lead, because the middle breaker is shared with the other circuit of the bay: if the middle breaker recloses onto a permanent fault and fails to open, its breaker failure 50BF also takes out the neighbouring circuit. Other designs make the leader the breaker in better maintenance condition or the one with controlled switching.

What cannot be missing is the leader role transfer. If the leader is not available, because it is open and isolated, because its reclosing is blocked by low pressure or because it failed, the follower must take over the role. If the logic does not do this, the line does not reclose. That transfer can be automatic or by selector switch, and it must be indicated in the control system.

Interaction with single-pole reclosing

In transmission, reclosing is usually single-pole for single-phase faults. The leader-follower scheme is applied pole by pole in the same way: the leader recloses the open pole and the follower follows. During the single-pole dead time, pole discrepancy and the line protection must tolerate the open phase. The dead time and secondary arc criteria are in single-pole and three-pole reclosing.

Interaction with 25 and with the remote end

The local scheme is coordinated with the one at the other end. A common practice is for one end to energize the line in dead-line mode and the other to close afterwards with synchronism check. In breaker-and-a-half this combines with the local leader and follower: the first closure of the whole sequence is the leader at the energizing end.

Voltage selection for the 25 is more complex than on a single bus: depending on the position of the other breakers of the bay, the reference voltage of the middle breaker can come from the other line or from a bus. The selection logic must cover every combination.

Interaction with 50BF and other blocking conditions

• 50BF operated on either breaker: blocks reclosing of both.
• Trip by protections that do not allow reclosing (transformer differential in a bay with a transformer, direct transfer trip, bus fault): block.
• Breaker without full duty cycle capability because of gas pressure or a discharged spring: that breaker does not reclose and, if it was the leader, hands over the role.
• Manual close onto a fault: block and, usually, fast trip.

Variants by configuration

• Ring bus: each line sits between two ring breakers, shared with the neighbouring circuits. The scheme is the same, with the complication that an open breaker splits the ring and changes which circuits remain connected.
• Double bus double breaker: no breaker is shared, and the leader is chosen based on the bus or on maintenance.
• Breaker-and-a-third: two middle breakers and the same logic, with more voltage selection combinations.

What goes wrong in practice

• The line does not reclose because the leader was out and there was no leader role transfer. It is one of the causes reviewed in why the recloser does not reclose.
• The follower recloses onto the fault because the block signal arrived late or the confirmation time is shorter than the protection trip time.
• The follower’s 25 does not permit closing because of incomplete voltage selection.
• The middle breaker recloses when it should not and its failure takes out the neighbouring circuit.

How it is tested

In general terms, with secondary injection and the breakers in test, the sequences are run with transient and permanent faults, with each breaker out of service, with the 50BF operating and with every voltage combination for the 25. Between the two line ends, coordination is checked with end-to-end tests.

We can help with your reclosing scheme

At Tiza Group we do the remote relay configuration of leader-follower reclosing, voltage selection for the 25 and 50BF blocking, in high and extra-high voltage. If your line did not reclose or reclosed wrongly, we can quote a relay trip analysis.

Related guides

• Automatic reclosing 79
• Single-pole and three-pole reclosing
• Breaker-and-a-half interlocking
• Voltage selection for synchronism check in double bus
• Dead line live bus closing: 25 modes
• Breaker-and-a-third interlocking
• Substation interlocking: types, levels and logic

References

• IEEE C37.104-2022, Guide for Automatic Reclosing on AC Distribution and Transmission Lines.
• IEEE C37.2, Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations (devices 25, 50BF, 79).
• IEC 61850-7-4, Compatible logical node classes and data object classes (RREC, RSYN, RBRF).
• Siemens, Adaptive Autoreclosure, technical presentation (definition of leader and follower).

Frequently asked questions