Analysis of Common Faults and Countermeasures for Medium-Voltage Vacuum Circuit Breakers

The Role of Vacuum Circuit Breakers in Substation Systems and Common Fault Analysis

When substation system faults occur, vacuum circuit breakers play a critical protective role by interrupting overloads and short-circuit currents, ensuring the safe and stable operation of power systems. It is essential to strengthen routine inspection and maintenance of medium-voltage (MV) vacuum circuit breakers, analyze common failure causes, and implement effective corrective measures to improve substation reliability, thereby delivering greater economic and social benefits.

1. Structure of Vacuum Circuit Breakers

1.1 Basic Components

A vacuum circuit breaker typically consists of the following key components: operating mechanism, current interruption unit, electrical control system, insulating support, and base frame.

Operating mechanisms can be classified into electromagnetic, spring-operated, permanent magnet, pneumatic, and hydraulic types. Based on the relative position of the operating mechanism and the interrupter, vacuum circuit breakers are further categorized as integrated, suspended, fully enclosed modular, pedestal-mounted, or floor-standing types.

1.2 Vacuum Interrupter

The vacuum interrupter is the core component enabling the proper operation of a vacuum circuit breaker. It comprises an insulating envelope, shield, bellows, conductive rod, moving and fixed contacts, and end caps.

To maintain effective arc quenching, the internal vacuum must be preserved—typically at a pressure below 1.33×10⁻² Pa. Significant advancements have been made in the materials, manufacturing processes, structure, size, and performance of vacuum interrupters.

The insulating envelope is commonly made of alumina ceramic or glass. Ceramic envelopes offer superior mechanical strength and thermal stability and are now widely adopted. The moving contact is located at the bottom, connected to the conductive rod. A guide sleeve ensures precise and smooth vertical movement.

To monitor contact wear, a dot marker is placed on the outer surface of the interrupter. By observing the displacement of this marker relative to the lower end, the degree of contact erosion can be estimated.

The current path and arc interruption occur at the contact gap between the moving and fixed contacts. The metallic components are supported and sealed by the insulating envelope, which is welded to the shield, contacts, and other metal parts to maintain vacuum integrity.

The stainless-steel shield, electrically floating and surrounding the contacts, plays a vital role: during current interruption, it captures metal vapor from the arc, preventing deposition on the insulator and preserving internal insulation strength.

2. Common Faults in Medium-Voltage Vacuum Circuit Breakers

2.1 Reduced Vacuum Level

Loss of vacuum is a critical yet often undetected fault. Many installations lack quantitative or qualitative vacuum monitoring equipment, complicating diagnosis.

Vacuum degradation shortens breaker lifespan, impairs current interruption capability, and may lead to catastrophic failure or explosion. Causes include:

• Poor mechanical characteristics such as excessive overtravel, contact bounce, or phase asynchrony.

• Excessive linkage travel during operation.

• Manufacturing defects in the vacuum bottle (e.g., poor sealing or material flaws).

• Leakage in the bellows due to fatigue or damage.

2.2 Insulation Failure

Many vacuum breakers use composite insulation, embedding the interrupter in an epoxy resin housing. However, if the high-voltage parts are not fully encapsulated, environmental factors can compromise insulation.

Heat generated during operation can further degrade insulation performance, increasing failure risk.

2.3 Excessive Contact Bounce and Asynchronous Operation

Prolonged contact bounce during closing and asynchronous opening/closing can result from:

• Substandard mechanical performance of the breaker.

• Defective insulating pull rods or support structures.

• Misalignment between the contact plane and the breaker’s central axis.

2.4 Incomplete Spring Energy Storage

After closing, the spring mechanism may fail to fully store energy due to:

• Premature disconnection of the storage circuit caused by improper limit switch settings.

• Gear slippage due to severe wear.

• Aging of the storage motor.

• High spring tension causing incomplete shaft travel.

2.5 Maloperation and Failure to Operate

• Contact deformation: Soft contact materials can deform after repeated operations, leading to poor contact and phase loss.

• Trip failure: Caused by insufficient trip latch engagement, pin slippage, low trip voltage, or poor auxiliary switch contact.

• Close failure: Results from low closing voltage, deformed linkage plates, incorrect latch dimensions, wiring errors, or poor auxiliary switch contact.

3. Fault Prevention and Remediation Measures

3.1 Preventing Vacuum Degradation

Regular inspection of the vacuum bottle is essential. Use a vacuum tester for quantitative measurement or perform withstand voltage tests for qualitative assessment. If vacuum loss is detected, replace the interrupter and retest travel, synchronization, and bounce to ensure compliance.

3.2 Insulation Failure Prevention and Treatment

Apply APG (Automated Pressure Gelation) technology and solid-sealed pole columns to encapsulate the interrupter and output terminals. This reduces size and shields against environmental effects.

Regularly test insulation performance and predict insulation lifespan using specialized equipment. Follow strict installation, commissioning, and maintenance procedures to prevent human error. Clean and inspect insulators and pull rods regularly to prevent dust-related failures.

3.3 Addressing Contact Bounce and Asynchrony

Insert a flat washer between the insulating pull rod and transmission lever to reduce contact bounce. Adjust the vertical alignment of the contact end face to minimize bounce.

For asynchronous operation, use a switch characteristic tester to measure closing bounce time, three-phase operation times, and phase synchronization. Based on results, adjust the pull rod length within specified travel and overtravel limits to achieve synchronization.

3.4 Resolving Incomplete Spring Storage

• Replace aging storage motors.

• Improve assembly precision of tripping and interlocking components.

• Enhance heat treatment of storage gears to prevent wear and slippage.

3.5 Preventing Maloperation and Failure to Operate

Enhance control circuit reliability by securing auxiliary switch contacts and optimizing linkage mechanisms to prevent deformation or misalignment. Ensure reliable wiring connections.

Maintain a clean operating environment and lubricate moving parts to prevent rust and contamination-induced failures.

For closing circuit faults, inspect the base-mounted auxiliary switch. Use a multimeter to check continuity at the secondary plug. If the plug is open, test continuity between the auxiliary switch terminals and the plug to locate the fault.

4. Conclusion

In summary, to ensure reliable operation of vacuum circuit breakers, enterprises and personnel must identify root causes of common faults—such as vacuum loss, insulation failure, contact bounce, spring storage issues, and maloperation—and implement effective preventive and corrective measures. Proactive maintenance and technical optimization are key to minimizing failures and enhancing the safety, efficiency, and longevity of substation systems.