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.

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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.

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