ODES WT-32 Synchro-Check: Safe Switching Between Dead-Bus and Synchronism Check

TonyZhang
Jan 18
4 min read

Dead-Bus vs Synchronism Check Is Not a “Preference” – It’s a Different Close Logic

In manual synchronizing / automatic synchro-check systems, “dead-bus check” is not just another panel habit. It changes the criterion for closing the breaker:

Synchronism check (synchro-check) – close is permitted only when voltage, frequency and phase angle are within defined limits.
Dead-bus / dead-line check – close is permitted only when the bus/line is confirmed de-energized (or very close to zero voltage).

Switching this mode is therefore equivalent to switching the close permissive philosophy. It must not depend on memory, oral instructions or “which way we usually do it.”

With the WT-32 synchro-check relay, this mode is controlled by a digital input (DI). To avoid ambiguity, engineering should define how to switch, what each state means, and how to test and record it as a formal, traceable requirement.

1. How to Switch Modes: Use the DI Dry Contact (Terminals 7–8)

On WT-32, the synchronism/dead-bus mode is selected via a voltage-free, normally-open dry contact wired to DI terminals 7–8.

Recommended convention:

Dead-bus (loss-of-voltage) check in service
Synchronism check in service

Engineering recommendation:

On drawings and terminal markers, explicitly state:

Do not rely on memory or “local habits.” Treat this DI as a documented operating mode selector, not an undocumented jumper.

2. What the Device Does in Dead-Bus Mode: Loss-of-Voltage Logic

Once WT-32 is switched to dead-bus mode, the close permissive becomes a loss-of-voltage-based decision:

Only when the bus/line voltage is below a defined undervoltage threshold is closing permitted.

From an engineering perspective, that means two things must be clear and documented:

Quantitative undervoltage threshold
Live-bus blocking

Dead-bus mode is essentially: “close only when definitely not energized.” Synchro-check mode is: “close only when both sides are live and synchronized.” The DI state (7–8) flips which of these criteria WT-32 enforces.

3. Three Common Pitfalls on Site

From commissioning and retrofit experience, three mistakes appear repeatedly:

3.1 DI Logic Reversed

The meaning of “contact closed / contact open” is not clearly written in the schematic and as-built records.
Commissioning engineers rely on memory or ad-hoc notes.
At some point, someone assumes “closed = synchro-check” when the device is configured as “closed = dead-bus,” or vice versa.

Mitigation:

Fix the convention (as above) and write it into drawings, terminal lists and operating instructions.

3.2 Mode Switched, But No Re-Test

Mode is moved from synchro-check to dead-bus on the WT-32 DI.
No low-voltage pull-down test is performed to confirm:

Mitigation:

Mode changes must be followed by a structured functional test (see acceptance checklist below).

3.3 Parameters Changed, but Not Saved or Recorded

Parameters (e.g., undervoltage factor, time margins) are changed during commissioning.
Save procedure is not correctly performed, or no read-back is done.
Later, firmware, device replacement or adjustments lead to parameter drift, and nobody has a reliable baseline.

Mitigation:

After any parameter change

4. A One-Page Acceptance Checklist for Mode Switching

To make mode switching repeatable and auditable, treat it like any other protection setting change: use a one-page checklist.

Recommended structure:

4.1 Mode Switching Check

Operate the DI (7–8) through the full cycle:
For each state, record:

Goal:

Confirm that DI state → internal mode → output behaviour is consistent and as documented.

4.2 Criterion Check – Dead-Bus Mode

With WT-32 in dead-bus mode (7–8 closed):

Use a test source to gradually reduce the system-side or incoming-side voltage.
Sweep around the intended undervoltage threshold and record:

Goal:

Verify the dead-bus permissive / live-bus blocking boundary matches the engineering setting.

4.3 Circuit Check – Close Permissive Path

In the actual breaker close circuit, verify:

This step checks the end-to-end wiring and interlocking, not just the WT-32 logic.

4.4 Recording Requirements

On the checklist, record at minimum:

Drawing revision ID
DI state (7–8 open/closed) during each test segment
Voltage / frequency input values during threshold tests
Output contact status and any associated indication
Date/time and signatures of test personnel

This creates a traceable record of how WT-32 was configured and verified when the station was handed over.

Conclusion: Treat WT-32 Mode as a Close Logic Selector, Not a Jumper

Switching WT-32 between synchro-check and dead-bus is not a minor configuration tweak; it is a change in the breaker close philosophy.

To manage it safely:

Use DI 7–8 as a documented mode selector:
Make the undervoltage criterion and live-bus blocking explicit and settable.
Avoid the three common pitfalls: reversed DI logic, “switch without retest,” and unsaved/unrecorded parameters.
Use a one-page acceptance checklist to capture mode switching tests in a consistent, auditable way.

Handled this way, WT-32 becomes a deterministic close-permissive manager, not a source of uncertainty in manual and automatic synchronizing schemes.

If you are planning or retrofitting manual/automatic synchronizing schemes and need to standardise synchro-check vs dead-bus mode management, ODES can help you consult on WT-32 application, request a one-page test matrix template, and learn how to formalise mode switching and acceptance testing in your station standards.