How should the vacuum arc extinguishing chamber of an outdoor high-voltage vacuum circuit breaker be maintained?

The vacuum interrupter is the "heart" of a vacuum circuit breaker; its core function is to rapidly extinguish electric arcs. Therefore, its condition directly determines the safety and reliability of the circuit breaker. Because its interior is under high vacuum and has a sealed structure, the core of its maintenance lies in "monitoring" and "prevention," rather than "disassembly and repair."

The following is a detailed maintenance guide, divided into several parts: daily inspection, periodic maintenance, key parameter testing, and replacement procedures.

 

I. Routine Patrols and Inspections (Without Power Disconnection)

These inspections may be conducted whilst the circuit breaker is energised or during de-energisation without disassembly.

Visual Inspection:

Cleanliness: Maintain the cleanliness of the arc-extinguishing chamber's ceramic casing (insulating cylinder), free from significant contamination such as dust, oil, or salt spray, to prevent surface flashover.

Mechanical Damage: Inspect the arc-extinguishing chamber housing for cracks, fractures, or abnormal protrusions. Any physical damage may indicate compromised vacuum integrity.

Discharge Indicators: Examine the arc-extinguishing chamber surfaces, particularly at the end flanges and ceramic-to-metal sealing points, for arc burns, flashover marks, or abnormal corona discharge sounds (more readily detectable during night inspections).

Operational Monitoring:

During circuit breaker tripping and closing operations, listen for abnormal discharge sounds within the arc extinguishing chamber. The normal operating sound of a vacuum circuit breaker is distinctly crisp. Hearing a ‘popping’ or dull thud may indicate reduced vacuum integrity and internal breakdown discharge.

 

II. Regular Inspection and Preventive Testing (Performed During Power Outage)

 

This is the most crucial method for assessing the health status of a vacuum interrupter and must be conducted regularly according to the "Preventive Testing Regulations for Power Equipment" and relevant product manuals.

Vacuum Degree Testing (The Core Test)

Purpose: To directly test whether the vacuum pressure inside the interrupter remains within a safe range (usually required to be below 10⁻² Pa). A decrease in vacuum degree is the main cause of interrupter failure.

Methods:

Magnetic Discharge Method: This is the most commonly used and accurate method. Using a dedicated "vacuum degree tester," a high voltage is applied to both ends of the interrupter, while a pulsed magnetic field ionizes the residual gas inside. The vacuum degree is accurately calculated by measuring the ionization current.

Power Frequency Withstand Voltage Method: This is an indirect but simple qualitative assessment method. A specified power frequency withstand voltage (e.g., 42kV for a 12kV system) is applied between the contacts for 1 minute. If the interrupter can withstand this voltage without breakdown, its vacuum degree is considered basically qualified. This method cannot quantify the vacuum level, but it can effectively screen out failed arc-extinguishing chambers.

Period: It is recommended to perform this test annually after commissioning. Once stable, the interval can be appropriately extended, but new regulations typically require it to be performed every 3-6 years.

Circuit Resistance Test

Purpose: To measure the contact resistance of the entire circuit breaker, including the arc-extinguishing chamber's conductive circuit.

Significance: An abnormally high circuit resistance usually indicates severe wear and poor contact of the arc-extinguishing chamber contacts, or oxidation of the contact surfaces at external connection points. Excessive resistance can lead to overheating, accelerated insulation aging, and a decrease in vacuum.

Standard: The measured value should be compared with the factory value or the previous measurement; the change should not exceed 20%, and it must not exceed the maximum value specified by the manufacturer.

Insulation Resistance Test

Purpose: To measure the insulation resistance between contacts (open position) and to ground (closed position) using a 2500V or 5000V megohmmeter.

Standard: Generally, it is required to be no less than the value specified in the regulations (e.g., above 1000MΩ).

 

III. Indirect Influence and Inspection of Mechanical Characteristics

 

The lifespan of a vacuum interrupter is closely related to the mechanical characteristics of the circuit breaker; improper mechanical parameters can directly damage the interrupter.

Contact Wear Monitoring:

The contacts of a vacuum circuit breaker experience slight wear during each arc breaking and closing. The circuit breaker mechanism is typically equipped with contact overtravel indicators or wear markers.

Maintenance Points: Regularly check the wear markers. When contact wear reaches the manufacturer's specified limit, even if the vacuum test is passed, the interrupter must be replaced. Insufficient overtravel leads to decreased contact pressure, increased closing bounce, and a higher risk of re-breakdown.

Opening and Closing Speed ​​and Synchronization:

Insufficient opening speed results in prolonged arc burning time, burning out the contacts.

Insufficient closing speed or excessive closing bounce leads to prolonged pre-breakdown time and may even cause contact welding.

Regular calibration using a mechanical characteristic tester is essential to ensure that these parameters are within acceptable limits.

Mechanical Operation Inspection:

Perform no-load opening and closing operations to check whether the entire transmission system is flexible and free from jamming. Any mechanical failure could impact the arc-extinguishing chamber.

 

IV. Replacement of the Arc-Extinguishing Chamber

 

The vacuum arc-extinguishing chamber should be replaced immediately if any of the following occurs:

The vacuum test fails.

Breakdown occurs during the power frequency withstand voltage test.

Contact wear reaches its limit.

The arc-extinguishing chamber casing develops cracks or other irreversible physical damage.

The circuit resistance is severely exceeded and cannot be restored by cleaning the external connection points.

Replacement Precautions:

This must be performed by a qualified professional.

Before and after replacement, be sure to check and adjust the mechanical parameters of the circuit breaker (such as opening distance, overtravel, closing speed, etc.) to ensure they match the new arc-extinguishing chamber.

During installation, use a torque wrench to tighten the bolts to the torque specified by the manufacturer to avoid uneven force that could cause the ceramic casing of the arc-extinguishing chamber to crack.

After replacement, a complete set of electrical and mechanical tests must be performed again.

 

Summary: Maintenance Key Points

Observe Frequently:Inspect the exterior, check for damage, and observe for discharge.

Listen Frequently:Listen for abnormal sounds.

Periodicly Test:Measure vacuum level (core), measure resistance, and perform withstand voltage tests.

Maintain Mechanical Function:Check for wear, adjust speed, and ensure smooth operation.

Timely Replacement:Replace any defective components decisively, following procedures.

By following these maintenance strategies, you can maximize the reliable operation of the vacuum interrupter chamber of the outdoor high-voltage vacuum circuit breaker, ensuring the safety of the power grid and equipment.

 

Shaanxi Huadian Vacuum Interruptor, with its superior craftsmanship and rigorous quality control, is committed to becoming your most reliable power protection partner. Please contact us if needed.

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