Radial feeder protection: recloser and fuse coordination

What a radial feeder protection scheme is

A medium-voltage radial feeder leaves the substation and distributes power along a main line and many laterals, with distribution transformers along the way. Power flows in one direction only. Most faults on overhead sections are transient.

The scheme spreads protection in cascade among several devices, each with its own zone, and uses reclosing to avoid leaving customers without service for faults that clear by themselves. The goal is selectivity: the device closest to the fault operates. It is the most common scheme in the series on substation protection schemes.

Which devices make it up and how they are coordinated

• Feeder relay in the feeder bay: phase and ground overcurrent 50/51 and 50N/51N, sometimes sensitive ground, and reclosing 79. It takes the CT of its bay and trips its breaker.
• Recloser on the main line: a breaker with its own control, fast and slow curves and several reclose attempts.
• Sectionalizer on major taps: counts the openings of the upstream recloser or relay and opens during a dead time.
• Fuses on laterals and at distribution transformers.

Coordination works in pairs, from downstream to upstream:

• Recloser and fuse: in fuse-saving mode, the recloser’s fast curve must clear before the fuse is damaged; the slow curve must let the fuse operate.
• Sectionalizer and recloser: the sectionalizer count must be lower than the number of recloser operations to lockout, so the sectionalizer opens before the recloser locks out.
• Feeder relay and recloser: the relay’s curves and reclosing cycles must give the recloser margin in every operation.

Logic and sequence

For a transient fault on a fused lateral, with fuse saving:

1. The recloser sees the fault and trips on its fast curve; the fuse does not have time to melt.
2. Dead time. The arc extinguishes.
3. The recloser recloses and service returns for everyone.

For a permanent fault on the same lateral:

1. Fast trip and reclose; the fault is still there.
2. The recloser moves to its slow curve; the lateral fuse melts first and isolates the section.
3. The rest of the feeder stays in service.

If the fault is beyond a sectionalizer, it counts the recloser’s openings and, once its count is complete, opens during the dead time; the recloser then recloses successfully onto the healthy section.

Variants

• Rural: long main lines, low fault currents at the far end, several reclosers in cascade and sensitive ground protection.
• Urban with underground sections: reclosing is limited or blocked on cable sections, where faults are usually permanent. In substation medium-voltage switchgear, the bus is often protected with reverse interlocking between the incomer and the feeder relays.
• Industry and mining: in-plant feeders with relays in each bay and, on extensive overhead networks, reclosers.
• Low voltage: breakers with trip units and fuses, without reclosing.
• With distributed generation: sensitivities, directionality and the anti-islanding protection of the plants must be reviewed.

Design criteria

• Maximum and minimum fault currents at each point, from the short-circuit study.
• Fuse curves (minimum melting and total clearing) and the curves of relays and reclosers.
• The utility’s philosophy: fuse saving or fuse blowing, number of attempts, dead times.
• Sensitive and industrial loads that do not tolerate several recloses.
• Inrush currents of the feeder after a reclose.

Margins and curves are defined in the protection coordination study; IEEE C37.230 collects the accepted practices.

How each manufacturer implements it

Feeder relays from Siemens SIPROTEC (DIGSI), SEL (AcSELerator QuickSet), ABB Relion 615 (PCM600), GE Vernova Multilin (EnerVista) and Schneider Easergy / MiCOM (Easergy Studio) offer IEC and IEEE curves, multi-shot reclosing and fuse saving. In reclosers, the device control (for example, those from NOJA Power, SEL’s SEL-651R or Schneider Electric’s) integrates the fast and slow curves and the reclosing sequence. In transmission, the equivalent of feeder reclosing is single-pole and three-pole reclosing. What changes is how curves are assigned per attempt, how operations are counted and how sequence coordination between devices in series is handled.

Why it fails or misoperates

• The feeder breaker trips for a fault on a lateral: fast curve of the feeder relay not coordinated with the recloser, or no sequence coordination.
• The fuse melts on a transient fault: fast curve too slow for the installed fuse, or a fuse replaced with one of a different type.
• Sectionalizer that does not open: count higher than the recloser operations, current below its threshold.
• Healthy feeders tripping because of motor or distributed generation contribution to nearby faults.
• Cold load pickup trip when re-energizing after a long dead time or an extended outage, when the starting current of the loads exceeds the settings.

Check the recloser and feeder relay records first: which curve operated on each attempt and with what current.

How it is tested

The feeder relay and the recloser control are tested by secondary injection: curves, reclosing cycle and lockouts. Reclosers are usually also tested with the test set for their control. Coordination is validated in the study, and in the field the installed settings and fuses are checked against what was studied.

Need to configure a recloser or find out why a whole feeder tripped? Our team configures relays and reclosers remotely. See remote recloser configuration or contact us.

References

• IEEE C37.230-2020, Guide for Protective Relay Applications to Distribution Lines.
• IEEE C37.104-2022, Guide for Automatic Reclosing on AC Distribution and Transmission Lines.
• IEC/IEEE 62271-111 (IEEE C37.60), High-voltage switchgear and controlgear – Part 111: Automatic circuit reclosers for alternating current systems up to 38 kV.
• IEEE C37.63-2024, Standard Requirements for Overhead, Pad-Mounted, Dry-Vault, and Submersible Automatic Line Sectionalizers for Alternating Current Systems up to and Including 38 kV.
• J. L. Blackburn and T. J. Domin, Protective Relaying: Principles and Applications.

Frequently asked questions