How to Determine When to Replace the Vacuum Interrupter of a Vacuum Circuit Breaker

After prolonged use of a vacuum circuit breaker, the vacuum interrupter may reach the end of its service life if any of the following conditions occur. In such cases, replacement should be considered:

1. Exceeding Service or Storage Life

   • If the vacuum interrupter’s storage or service period surpasses the specified validity period (usually 20 years for domestic products, calculated from the delivery date).

2. Decline in Vacuum Degree

   • If the vacuum degree drops to 1.33×10⁻² Pa, as measured using a magnetron vacuum gauge. For glass-shell vacuum interrupters, any significant color change in the metal shield indicates the need for an immediate vacuum check.

3. Excessive Contact Wear

   • When the cumulative wear of the contacts exceeds the product's specified limit (typically 3mm for domestic products).
   • Most vacuum interrupters have a wear warning mark on the movable contact rod. If the wear exceeds the limit, the warning mark becomes invisible when the circuit breaker is closed.

4. Exceeding Short-Circuit Current Interruptions

   • When the cumulative number of short-circuit current interruptions reaches or exceeds the interrupter’s electrical life, as specified in the product manual.

5. Mechanical Operation Limits

   • When the total number of mechanical opening and closing operations exceeds the specified value in the product manual.

Steps for Replacing the Vacuum Interrupter

If the vacuum circuit breaker exceeds its specified number of short-circuit current interruptions or shows signs of vacuum leakage during routine inspections, the vacuum interrupter must be replaced.

1. Remove the Old Vacuum Interrupter

   • Follow the specified order to safely dismantle the old interrupter.

2. Prepare the New Vacuum Interrupter

   • Clean the conductive contact surfaces thoroughly, using a clean cloth or sandpaper.
   • Avoid applying oil to the contact surfaces.

3. Install and Align the New Interrupter

   • Carefully assemble the new interrupter.
   • Adjust the movable conductive rod to ensure it is centered within the interrupter. This prevents rubbing or interference during opening and closing operations.

4. Perform a Power Frequency Withstand Voltage Test

   • Apply voltage between the dynamic and static contacts in the open position to test insulation.
   • Close the circuit breaker and measure the resistance of the main circuit.

5. Adjust Overtravel and Travel Parameters

   • Measure and adjust the circuit breaker’s overtravel and travel to align with the specified values in the product manual.

6. Conduct Operational Tests

   • Perform multiple no-load opening and closing operations (typically dozens of cycles) to verify proper functionality.
   • Only after confirming all tests are successful can the circuit breaker be returned to operation.