Recloser: What It Is, How It Works and Testing

Short answer

A recloser is a medium-voltage circuit breaker with its own control that trips on a fault and automatically recloses a programmed number of times before locking out. Most faults on overhead lines are temporary, so the recloser restores service without a crew and isolates only the section with a permanent fault.

Short answer. A recloser is a medium-voltage circuit breaker with its own protection control. On an overcurrent it trips and recloses automatically following a programmed sequence. If the fault was temporary, service is restored within seconds; if it persists, the recloser stays open in lockout and isolates only the faulted section.

What a recloser is

A recloser is a medium-voltage circuit breaker with its own protection control that detects an overcurrent, trips and recloses automatically following a programmed sequence. If the fault clears, service is restored within seconds. If it persists, the recloser completes its shots and stays open in lockout. For commissioning and settings of the Tavrida Rec15/25 recloser, see use, commissioning and settings guide for the Tavrida Rec15/25.

It exists because most faults on overhead lines are temporary: tree branches, animals, lightning or brief contacts. The reference standard is the dual-logo IEEE C37.60 / IEC 62271-111, which covers ac automatic circuit reclosers for rated voltages above 1 kV.

Reclosers are not used at high and extra-high voltage. There, reclosing is done by a power circuit breaker driven by the auto-reclosing function 79 of the line relay.

Main parts

Poles with vacuum interrupters, encapsulated in solid insulation (epoxy resin or polymers). Older designs used oil or SF6.
Actuator, today almost always magnetic, with capacitors that store the energy for opening and closing.
Current and voltage sensors built into the tank, which feed the control.
Control cabinet with the protection electronics, the local interface, the battery and its charger, and the auxiliary supply from the line or from a voltage transformer.
Control cable that connects the tank to the cabinet.
Communications to the control center, with protocols such as DNP3, IEC 60870-5-104 or IEC 61850 depending on the model.

How it works

The control measures currents and voltages. When an overcurrent exceeds the setting, it orders a trip. It then waits for a dead time and closes. A typical sequence combines fast operations and delayed operations:

Fast operations: clear the fault before a downstream fuse melts, to save the fuse if the fault is temporary (fuse-saving scheme).
Delayed operations: give the fuse on the faulted lateral time to melt and isolate only that lateral when the fault is permanent.

The number of shots, the curves and the dead times are configurable and are defined in the protection coordination study. Other common functions are sequence coordination with downstream reclosers, reset time, cold load pickup, hot-line tag blocking, sensitive earth fault and distribution automation to isolate the faulted section and transfer load. That automation is described in distribution automation.

Types

Three-phase, with three-pole trip and close, the most common on distribution feeders and substation outgoing circuits.
Single-phase, for single-phase laterals.
Single-phase/three-phase, which can open only one phase on single-phase faults and keep the other two in service.
Pole-mounted, pad-mounted or switchgear-mounted, depending on the installation.
Industry and solar plants: used on long overhead networks in mining, oil and agribusiness, and as the connection point of solar plants and distributed generation, where voltage, frequency and anti-islanding functions are enabled in addition to overcurrent.

Associated protection functions

A modern control integrates, depending on the model:

Phase and ground overcurrent 50/51 and 50N/51N with IEC and IEEE curves, and recloser-specific curves. See phase and ground overcurrent protection.
Sensitive earth fault and directional elements 67/67N.
Reclosing 79.
Undervoltage and overvoltage 27/59, frequency 81 and, in distributed generation, rate of change of frequency 81R.
Synchronism check 25 at tie points.

How each manufacturer implements it

Each manufacturer groups and names the functions its own way, and each has its own software:

NOJA Power uses its CMS software for its controls; see the NOJA RC-10 and RC-15 control and the NOJA CMS software.
Schneider Electric uses WSOS software for the ADVC controls of its reclosers; see the ADVC3 control.
Eaton (Cooper) uses ProView for the Form 6 family of controls; see the Eaton Cooper NOVA recloser.
SEL offers the SEL-651R control, configured with AcSELerator QuickSet; see the SEL-651R recloser.
ABB, Siemens and other manufacturers have their own controls and tools: ABB GridShield OVR, Siemens Fusesaver SDR, Tavrida REC, Entec ETR, Arteche Smart RY and GW Viper.

The differences go beyond the software: the names of the proprietary curves, how the shots in the sequence are counted, how settings groups are organized and which conditions block reclosing all change. A setting that works in one control does not carry over directly to another. More on what primary injection validates that secondary injection does not in primary injection: what it validates and when.

Commissioning and maintenance tests

Primary side: contact resistance, insulation resistance, a withstand test across the open contacts to verify the vacuum, and opening and closing times. These tests are similar to those for power circuit breakers.
Control: secondary injection through the control’s test port or primary injection, to verify curves, sequence, dead times, lockout and voltage and frequency functions. See secondary injection.
Auxiliaries: battery autonomy, alarms and communications with the control center.
Integrated functional test: a real operation of the tank from the control with the full sequence.

Common failures

Dead battery or faulty charger: the control loses the ability to operate when the line supply is gone.
Damaged control cable from moisture, rodents or mechanical stress.
Wrong settings group or a forgotten hot-line tag block.
Miscoordination with fuses because of poorly chosen curves.
Trips on cold load or on unbalance on long laterals.
Undetected high-impedance faults.
Loss of communications, which leaves the recloser without remote supervision.

Coordination with fuses: heating and cooling

Coordination between a recloser and a fuse is not a simple comparison of curves, because the fuse heats up with every recloser operation and cools down during every dead time. Three methods are used, and each is useful in a different case:

Conservative method. Ignores cooling and adds up the heating of each operation. It guarantees coordination, but can force a larger fuse than necessary on the source side, with less protection for the equipment (for example, a substation power transformer) and more coordination problems with upstream devices.
Cooling factor method. Adjusts the recloser curves, not the fuse curves, with a factor that reflects the heat left in the fuse after each dead time. It gives more accurate results and allows smaller fuse ratings.
K method. Uses preset factors for common sequences and fuse speeds and sits between the other two.

The criteria change with the position of the fuse:

Fuse on the source side, recloser on the load side. The fuse must not melt before the recloser reaches lockout. The maximum coordinating current is the lower of the interrupting rating of the recloser or of the fuse, and the intersection of the fuse minimum melting curve with the recloser maximum equivalent lockout curve.
Recloser on the source side, fuse on the load side (fuse saving). The fuse must not melt during the fast operations, but it must operate on the delayed ones to avoid lockout. The upper limit is set with the equivalent curve of the fast operations only, not with the lockout curve. The lower limit is the intersection of the fuse total clearing curve with the recloser minimum equivalent lockout curve.

These methods also apply to circuit breakers with a reclosing relay. For the case where both operate at once, see the fuse and the recloser operate at the same time; for the full study, what a protection coordination study needs, and for the protective element, medium-voltage fuse.

Standards that apply to reclosers

IEC 62271-111 and IEEE C37.60 are published as a dual-logo standard. The 2019 edition of IEC 62271-111 (IEEE C37.60-2018) applies to ac automatic circuit reclosers. They can be single-pole or multipole, for overhead, pad-mounted, dry-vault or submersible installation, with rated maximum voltages above 1 kV inclusive. It excludes devices that require dependent manual operation. That edition removed fault interrupters from the title and the scope. When specifying, check that the type test report covers the voltage class, the making and breaking capacity, and the operating duty cycle of the equipment.

We support you with your reclosers

Did your recloser trip or lock out and the reason is unclear? At Tiza Group we review the events and settings remotely with our remote relay configuration service, and we do testing and commissioning in the field, in Colombia or elsewhere on request. Contact us.

References

IEEE C37.60 / IEC 62271-111: ac automatic circuit reclosers above 1 kV.
IEEE C37.104: guide for automatic reclosing of circuit breakers for ac distribution and transmission lines.
IEEE C37.230: guide for protective relay applications to distribution lines.
IEEE C37.2: device function numbers.
Cook and Myers, S&C Electric, recloser and fuse coordination, IEEE PES General Meeting, 2004.
J. L. Blackburn and T. J. Domin, Protective Relaying: Principles and Applications.

Frequently asked questions

Why did the recloser go to lockout and not reclose?

Either it used all its programmed shots and the fault was still there, or a condition blocked reclosing: an active hot-line tag function, a high-current fault programmed to go straight to lockout, a low battery or a settings group different from the one expected. The control's event log shows which one it was.

Why does the recloser trip when load is restored after a long outage?

When service returns, cold load (motors, refrigeration, heating) draws more current than normal for a while. If the control's cold load pickup function is off or poorly set, the overcurrent element reads that current as a fault.

What is the sensitive earth fault (SEF) function in a recloser?

It is a ground element with a very low pickup that detects high-impedance faults, for example a conductor down on dry soil. It must be set above the natural unbalance of the network, according to the coordination study.