What are the precautions for installing and using vacuum interrupter?

The vacuum interrupter is the core component of the vacuum circuit breaker. The correct installation and use of it are directly related to the safe and reliable operation of the entire switchgear. The following are detailed installation and use precautions:

I. Pre-Installation Precautions

Inspection and Acceptance:

Appearance Inspection: Carefully inspect the arc extinguishing chamber's ceramic or glass shell for cracks, damage, or scratches. Check the metal flanges at both ends for flatness and no rust, and check whether the guide sleeves of the moving and static contacts are loose or detached.

Vacuum Check: This is the most critical step. Before installation, a dedicated vacuum tester (such as a magnetron discharge tester) must be used to ensure that the vacuum level meets factory standards (usually below 10⁻⁴ Pa). Installing an arc extinguishing chamber that has not been vacuum tested or has failed the test is strictly prohibited.

Document Verification: Verify the product certificate, installation instructions, and other technical documents to confirm that the model and specifications of the arc extinguishing chamber match the circuit breaker.

Storage and Transportation:

Storage Environment: Store in a dry, well-ventilated indoor environment free of corrosive gases. It is recommended to store the circuit breaker upright (moving contact facing downward) and avoid placing it upside down or horizontally to prevent the contact spring from failing due to prolonged stress.

Handle with care: Handle with care during handling, avoiding any impact or vibration, especially on the ceramic housing.

Cleaning:

Gently wipe the arc chamber's outer insulating housing (ceramic or glass) with anhydrous ethanol or acetone to remove surface dirt and fingerprints. Do not use any corrosive chemical solvents or rough cloths.

 

II. Installation Precautions

Installation Direction: Install the arc extinguishing chamber strictly in accordance with the design requirements, ensuring the correct orientation of the moving and static contacts. Typically, the moving contact connects to the circuit breaker's operating mechanism (such as a spring mechanism), and the static contact connects to the upper outlet terminal.

Uniform Force: When tightening the fixing bolts at both ends of the arc extinguishing chamber, tighten them in steps, alternating diagonally to ensure uniform force and prevent cracking of the ceramic shell due to excessive force on one side.

Concentricity and Perpendicularity: During installation, ensure good concentricity and perpendicularity between the arc extinguishing chamber and the circuit breaker body. Improper installation can cause the operating lever to stick, increase friction, affect opening and closing speeds and mechanical properties, and even damage the arc extinguishing chamber.

Connector Installation:

Moving End Connection: The connection between the moving conductive rod and the bellows must be smooth. No excessive torque or radial force should be transferred to the bellows. The bellows is an extremely delicate seal and should not be subjected to torque.

Static End Connection: Ensure a secure connection with low contact resistance.

Installation dimensions: Strictly follow the installation dimension requirements of the circuit breaker, especially the parameters such as the moving contact stroke and overtravel of the arc extinguishing chamber. These parameters directly affect the breaking capacity and mechanical life of the circuit breaker.

 

III. Post-Installation Inspection and Commissioning

Mechanical Characteristics Test: After installation, the circuit breaker must undergo mechanical characteristic tests, including the following:

Contact Opening Distance: The distance between the moving and stationary contacts.

Overtravel (Contact Stroke): The compression distance of the contact spring after contact contact.

Opening/Closing Speed: The average speed and the initial opening/closing speed are measured.

Three-Phase Synchronicity: The synchronization of the three-phase opening and closing.

Bounce Time: The contact bounce time during closing should be as short as possible.

All these parameters must comply with the product specifications.

Loop Resistance Test: Use a loop resistance tester to measure the main circuit resistance to ensure good contact and that the resistance value is within the specified range. Excessive loop resistance can cause overheating during operation.

Power Frequency Withstand Voltage Test: With the circuit breaker in the closed and open states, a power frequency withstand voltage test is performed between the interrupters and to ground to verify that the vacuum insulation strength of the arc extinguishing chamber meets the specified standards. This is an indirect but effective method to verify the vacuum level.

 

IV. Precautions for Operation and Maintenance

Regular Inspections: During normal operation, vacuum circuit breakers should be regularly inspected for abnormal sounds (e.g., normal opening and closing sounds) and overheating (this can be done by observing the color-changing paint applied or using a thermometer).

Monitoring Vacuum Level:

Indirect Method: Regular power-frequency withstand voltage testing of the break is the most common and effective method for monitoring vacuum levels.

Direct Method: Where conditions permit, a portable vacuum tester can be used for regular inspections.

Abnormal Signs: If abnormal flashing or color changes are observed within the arc extinguishing chamber (e.g., disappearance of the internal mirror or the appearance of a red or milky-white glow), this indicates severe vacuum deterioration and the circuit breaker must be immediately shut down.

Overvoltage Protection: Vacuum circuit breakers are prone to generating operating overvoltages (e.g., cutoff overvoltages), especially when interrupting inductive loads (e.g., motors and transformers). Appropriate overvoltage protection devices, such as metal oxide arresters (MOAs) or RC snubber circuits, should be installed according to the load characteristics.

Frequency of Operation: Although vacuum circuit breakers have a long mechanical life, frequent operation within a short period of time should be avoided to prevent fatigue of the operating mechanism and excessive temperature rise in the interrupter chamber.

Replacing the Interrupter Chamber:

Interrupter chambers should be replaced when the vacuum level fails or when the mechanical life has ended.

Must Replace in Groups: Even for a single-phase fault, it is recommended that all three interrupters be replaced simultaneously to maintain uniform characteristics across the three phases.

All mechanical and electrical tests must be repeated after replacement.

 

Summary

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The installation and use of vacuum interrupters is a delicate task. Key points can be summarized as follows:

Before installation: Strictly check the vacuum level, handle with care, and maintain cleanliness.

During installation: Ensure uniform alignment and precisely adjust dimensional parameters.

Post-installation: Conduct performance tests to ensure satisfactory mechanical and electrical performance.

During operation: Regularly monitor the vacuum level and operating status, and ensure adequate overvoltage protection.

Strictly adhering to these precautions is key to ensuring the safe, reliable, and long-term operation of vacuum circuit breakers.

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