VCB Timing Value(Close-Open operation Timing & Short-Circuit Test Sequence Explanation)

VCB Timing Value(Close-Open operation Timing & Short-Circuit Test Sequence Explanation)

Overview

This article summarizes the response to a customer inquiry regarding the timing for a Vacuum Circuit Breaker (VCB) Close-Open operation, especially when simulating a close into a fault (short-circuit) condition. It also explains related standard operation sequences and considerations during type testing.

1. Understanding Close-Open Operation Timing

  • The customer requested the total time required from manual Close operation to Open operation being executed by the protective relay.

  • Although the Close is manually operated, the Close-Open continuous operation is not expected to cause any operational issue.

2. Standard VCB Operation Sequences

No.Operation TypeDescription
1C (Close)Close operation
2O (Open)Open operation
3CO (Close-Open)Close immediately followed by Open (Trip-Free operation)
4O-0.3s-COOpen-Close-Open Operation / Open, wait 0.3s, then Close-Open sequence (Auto-Reclosing test)

  • CO operation is critical for verifying the Trip-Free function:
    Even if a Close command is executed, the breaker must immediately open if an Open signal is received.

3. Close-Open Operation Time Analysis

  • Close operation time: approximately 36 ms

  • Open operation time: approximately 14 ms

  • Pure Close-Open mechanical time: approximately 50 ms (based on DC12V application)

However, there is additional delay time between the Close completion and the application of the Open command:

  • Delay time (Close to Open signal application): approximately 170–190 ms (typical during testing, but adjusta

    --> Total expected Close-Open time    : approximately 220 ms to 240 ms

Reference: Oscillogram capturing Close and Open coil current profiles.

4. Short-Circuit (Fault) Test Scenario

  • The short-circuit test sequence for VCB follows:

    O - 0.3s - CO - 15s - CO

  • Unlike low-voltage breakers, VCBs must support Auto-Reclosing functionality.

  • During type tests, the most severe condition (15-second interval, instead of 3 minutes) is applied.

In short-circuit conditions:

  • Close operation occurs under asymmetric current.

  • Open operation must occur under symmetric current.

Therefore, the time setting after Close must allow for current stabilization to achieve symmetrical conditions before opening.

5. Customer Considerations

  • The pure mechanical Close-Open operation time (~50 ms) has been provided.

  • However, to ensure proper system simulation, customers must carefully review the additional time required for symmetrical current stabilization (approximately 170–190 ms) based on their specific site conditions and protection studies.

Conclusion

The expected total Close-Open time for the VCB is approximately 220 ms to 240 ms under standard testing conditions.
When simulating closing into a fault, customers should ensure sufficient time settings are applied to meet symmetrical current requirements before initiating Open operations.