Reclosing Relay (Device 79) Testing: Sequence, Timing and Lockout

What it is

A reclosing relay, ANSI device 79, automatically tries to close a circuit breaker after a protective trip. It is used mainly on overhead feeders and lines, where many faults are temporary, caused by lightning, wind, animals or tree contact, and clear themselves once the line is de-energized for a moment. The relay counts attempts, called shots, waits a set dead interval before each close, and gives up and locks out if the fault persists. The test confirms that the device initiates on the right trip signals, closes on schedule, counts correctly, resets after a successful close and locks out when it should. It is applied to stand-alone reclosers, to the reclosing function in a numerical relay and to older electromechanical reclosing relays, and it is run together with the overcurrent elements that initiate it.

Why it is done

Reclosing is a control function that acts on live equipment with no human present, so a flaw in its logic is serious. A relay that recloses too many times keeps feeding a permanent fault, stressing the breaker, the transformer and the line, and may cause a prolonged voltage dip across the system. One that fails to reclose turns a momentary event into a long outage and a crew call. A relay that reclosed after a manual trip, onto a line with a crew working on it, or onto a transformer fault would be a hazard to people and equipment. A fault in the reset logic can leave the counter partly spent. Wiring errors and wrong breaker status inputs are common after retrofits, and a test with simulated trips finds them before the line is in service.

The principle

The device behaves as a small sequencer. A protective trip starts the cycle when the breaker opens and the initiating condition is present. The relay waits through a dead time, long enough for the arc to deionize and the fault to clear, then issues a close command and starts a reclaim timer. If the breaker stays closed through the whole reclaim interval, the cycle is judged successful and the shot counter returns to its start. If the fault returns before then, the next trip advances the count and the following dead time is used, which may be different for each shot. After the allowed number of shots the relay goes to lockout and stays there until it is reset by an operator or a successful manual close. Several conditions can block the sequence: manual trips, manual closes, breaker not ready, low spring or gas pressure, other lockouts, and voltage or synchronism supervision. What is tested is a logic and timing sequence, not an analog quantity.

How it is performed

With the circuit isolated in line with the safety plan, and with the breaker in its test position or its trip and close outputs separated from the mechanism and replaced by indicators, the technician records the relay identification and reads the settings for number of shots, dead intervals, reclaim time and blocking inputs. The insulation of the relay circuits to the frame is measured first. A relay test set or a manual trip signal then simulates each initiating condition, and a breaker status input is supplied to follow the cycle, either from the breaker or from a simulated contact. For each shot the technician watches the close output and times the dead interval from the trip to the close command, then lets the breaker status show closed and confirms the reclaim behavior. Next a repeated trip is applied until the relay reaches lockout, and the number of attempts is compared with the setting. The reset path is checked by a successful sequence, and the blocking paths are checked by applying manual trip, close-ready loss and any supervision input, to confirm that the close output stays quiet. If the device operates with a sync check function, the pairing is exercised too. Settings and wiring are returned to service condition afterward.

What is recorded

The record notes the relay identification and settings, the initiating signals used, the dead intervals measured for each shot, the reclaim behavior, the number of attempts before lockout, the response to each blocking condition, the insulation reading, the test equipment and the as-found and as-left condition of the settings and wiring.

How results are judged

Evaluation is a comparison with the relay's configured logic and the manufacturer's data. The count of shots should match the setting exactly, the sequence should lock out when intended and reset when intended, every blocking condition should hold the close output, and measured intervals should agree with the configured ones within the relay's stated timing accuracy. The reading from the insulation measurement is judged against the table in the standard for the control circuit voltage. Any difference from the previous test of the same device is looked into, even when still within accuracy. The reclosing function is listed among the protective relay tests in ANSI/NETA ATS-2025 for acceptance and ANSI/NETA MTS-2023 for maintenance; consult your licensed copies of both, together with the utility or owner reclosing philosophy, for the criteria and values.