Auto-Reclosing Relay Testing: Dead Time, Sync Check and Dead-Line Check

Auto-reclosing relay testing proves that the reclose logic waits the set dead time, closes only when the sync-check or dead-line condition is satisfied, and blocks reclose after a permanent fault or when the scheme is not charged. It combines a state-sequence test with voltage and angle boundary tests on the check elements.

Key takeaways

• Measure dead time from trip to reclose command, not from fault inception.
• Sync check needs both sides live. If either voltage is below the relay’s live-line threshold, the check fails before the angle is examined.
• Test the angle window in both directions. A 20° setting should reclose at 20° and refuse at 22°, on both lead and lag.
• Respect the charge time. A reclose attempt before the scheme is charged is blocked, and the test will look like a failure.

What does an auto-reclosing test prove?

An auto-reclosing scheme must do four things: wait the correct dead time after a trip, close only when the two sides are safe to connect, refuse to close onto a permanent fault, and block itself when the conditions for a successful reclose do not exist. A test that only checks that the relay recloses proves none of these.

The four checks

How do you wire the VAE-430 for an auto-reclosing test?

Auto-reclosing needs two voltage systems: bus-side voltage and line-side voltage. The VAE-430 provides them without re-wiring: UA, UB, UC for the bus, and the independent UX channel for the line.

If the relay has a single voltage input that is switched internally between bus and line, follow the device manual for the switching logic. The VAE-430’s UX channel lets you keep both voltages connected for the whole test, which is faster and avoids re-wiring between states.

How do you test the reclose time?

Use the 0005 State Sequence module. The sequence is pre-fault (charge), fault, trip, dead time, reclose, permanent fault. The dead time is the interval from the trip contact to the reclose contact.

1. Apply the pre-fault quantities for the full charge time.
2. Apply the fault for 0.7 s and confirm the trip.
3. Hold the post-trip state for the set dead time.
4. Confirm the reclose contact closes at the end of the dead time.
5. Apply the fault again and confirm the final trip with no second reclose.

If the scheme is single-phase, repeat for each phase; the dead time may differ by phase.

How do you test the sync-check angle window?

Set both voltage systems to rated phase voltage, above the relay’s live-line threshold (typically 40 V). Keep the bus voltage fixed and vary the line voltage angle.

1. Set the angle difference to 20° (the setting). Confirm reclose.
2. Set it to 22°. Confirm no reclose.
3. Repeat on the opposite side: −20° reclose, −22° no reclose.
4. If the relay has a voltage-difference element, reduce one voltage until the check fails and record the boundary.

Change the angle slowly. A fast angle ramp may be averaged by the relay’s measurement window, and the result will depend on the ramp rate rather than on the setting.

How do you test the dead-line check?

The dead-line check permits reclose only when the line side is dead. Hold the bus voltage at rated value and vary the line voltage.

1. Set the line voltage to 20 V. Confirm reclose.
2. Set it to 35 V. Confirm no reclose.
3. The boundary should be close to the 30 V setting.

If the relay uses a single voltage input switched between bus and line, follow the device manual for the switching logic; the VAE-430’s UX channel lets you keep both voltages connected for the whole test.

How do you test reclose blocking?

• Manual close. Close the breaker manually, then apply a fault; the relay should trip but not reclose.
• Lockout. Operate the protection lockout or breaker-failure output; reclose should be blocked until the lockout is reset.
• Not charged. Apply a fault before the charge time has elapsed; reclose should be blocked.
• Multi-shot lockout. If the scheme has multiple shots, confirm that the final shot locks out and does not recycle.

What is the pass criterion?

Use the tolerance declared in the relay manual or the commissioning specification. The values above are typical bench criteria, not a substitute for the site specification.

Why does the relay not reclose after a temporary fault?

• Not charged. The pre-fault state was shorter than the charge time.
• Sync check failed. One voltage is below the live-line threshold, or the angle is outside the window.
• Dead-line check failed. The line voltage is above the dead-line threshold.
• Blocking active. Manual close, lockout, or a protection signal is holding the reclose blocked.

Frequently asked questions

What is the difference between sync check and dead-line check?

Sync check requires both sides live and within the angle and voltage window. Dead-line check requires the line side dead. A scheme may use either, or both in different operating modes.

How long should the dead time be?

The dead time is set by the utility and depends on the breaker, the line and the stability study. Typical transmission values are 0.5–1.0 s; distribution schemes are often longer. Test to the setting, not to a rule of thumb.

Can I test auto-reclosing without a breaker?

Yes. A relay-level test monitors the trip and reclose contacts and verifies the logic and timers. A full scheme test with a breaker simulator also verifies the close circuit, the auxiliary contacts and the breaker-failure interaction.

Why does the reclose contact chatter?

The relay may be receiving a fluctuating sync-check condition, or the binary input is picking up a potential-bearing contact with the wrong common polarity. Check the wiring and the input threshold.

Does the VAE-430 support two voltage systems?

Yes. UA, UB and UC form one three-phase system, and UX is an independent fourth channel. That is enough for bus voltage plus line voltage in a single test.

Where VA-TEK test sets fit

The VAE-430 covers auto-reclosing tests with the 0005 State Sequence module and four voltage channels, including the independent UX channel for line-side voltage. The state sequence runs pre-fault, fault, post-trip, reclose and permanent-fault states under time, contact, key or GPS control, and the binary inputs record the trip and reclose contacts. For six-phase schemes, the VAE-660 provides six current and six voltage outputs.

See the relay protection testing hub for the full commissioning sequence, and distance protection testing for the zone tests that usually precede the reclose test.

Standards and references

• IEEE C37.104 — Guide for Automatic Reclosing of Circuit Breakers for AC Distribution and Transmission Lines.
• IEC 60255-1 — Measuring relays and protection equipment: Common requirements.
• IEC 62271-100 — High-voltage switchgear and controlgear: Alternating-current circuit-breakers.

Always test to the approved setting sheet and the relay manufacturer’s instructions. The settings above are examples.

Related guides: underfrequency load shedding testing covers the frequency stage that trips the feeder, and distance protection testing covers the zone tests that precede the reclose.