What factors affect the life of vacuum interrupter?

The lifespan of a vacuum interrupter is a comprehensive concept, generally referring to its electrical and mechanical lifespan. It is influenced by many factors, including design, manufacturing, operating conditions, and maintenance.

These factors can be categorized into the following categories:

Factors Affecting Electrical Life (Related to Interrupting Current)

Electrical life primarily refers to the number of times an arc extinguishing chamber can normally interrupt at rated current, as well as its ability to withstand short-circuit current interruption.

1.Interrupting Current Amplitude and Frequency:

Normal Current Interrupting: Each interruption causes minor electrical wear (evaporation and sputtering) on ​​the contact material. The higher the interrupting current, the more severe the electrical wear.

Short-Circuit Interrupting: This is the most severe test for the arc extinguishing chamber. The enormous arc energy can instantly melt and vaporize the contact surface, causing severe erosion. The wear caused by a single short-circuit interruption can be equivalent to thousands of normal current interruptions. The number of short-circuit interruptions is a key indicator of electrical life.

2.Contact Material:

This is a key factor. The contact material must possess high electrical conductivity, high thermal conductivity, high arc erosion resistance, a low current cutoff value, and good resistance to welding.

The commonly used copper-chromium (CuCr) alloy achieves an excellent balance of these properties. The material composition, proportions, and manufacturing process (e.g., infiltration or sintering) directly impact their lifespan.

3.The role of conditioning:

New contacts may have microscopic burrs and impurities on their surface. By performing several cycles of interrupting a specified current (i.e., "conditioning"), the contact surface becomes smooth and even, achieving a stable operating state, which helps extend their electrical life.

 

Factors Affecting Mechanical Life (Operation-Related)

Mechanical life primarily refers to the number of closing and opening cycles the interrupter and its bellows can withstand.

1.Number of Operations:

The mechanical life of a vacuum interrupter is typically very high (tens of thousands to over 100,000 cycles), but each closing and opening cycle represents a mechanical motion.

2.Bellows Life:

This component is crucial to mechanical life. The bellows are key to dynamic sealing, repeatedly compressing and stretching with the movement of the moving contacts.

3.Influencing Factors:

Stroke and Speed: The greater the contact stroke and the faster the closing and opening speed, the greater the fatigue damage to the bellows.

Material and Process: The material, number of bellows, wall thickness, and manufacturing quality (such as hydroforming or welding) of the stainless steel bellows directly determine its fatigue life.

Once the bellows rupture, the interrupter loses its vacuum, leading to immediate failure.

 

Factors Affecting Insulation Life (Related to Withstand Voltage Level)

Insulation life refers to the ability of the arc extinguishing chamber to maintain a high vacuum level, thereby maintaining high dielectric strength.

1.Maintaining Vacuum:

This is fundamental to insulation life. A decrease in vacuum (i.e., an increase in pressure) causes a sharp drop in dielectric strength, making internal breakdown more likely.

Causes of Vacuum Loss:

Manufacturing Defects: Micro-leaks at the sealing interface of the casing (usually ceramic and metal end caps).

Material Outgassing: Improper handling of arc extinguishing chamber components (such as contacts and shielding) can slowly release adsorbed gases during operation.

Bellows Rupture: This is the most common cause of gas leakage.

Arc Action: Intense arcing can cause the contact material to release trace amounts of metal vapor. While most of this is captured by the getter, it can affect the vacuum level over the long term.

2.Overvoltage:

Although switching overvoltages generated when operating inductive loads (such as motors and transformers) and atmospheric overvoltages from lightning strikes are primarily borne by protective devices such as lightning arresters, excessive voltages can still cause cumulative damage to the insulation within the arc extinguishing chamber or even direct breakdown.

 

External Operation and Environmental Factors

1.Actuator Characteristics:

The circuit breaker's spring-operated or permanent magnet mechanism must ensure that closing and opening speeds, travel, and contact pressures are within the designed range.

Contact Bounce: Excessive bounce during closing can cause arcing and worsen contact wear.

Opening Bounce: This can also cause arc reignition and wear.

2.Environmental Conditions:

Storage: During long-term storage, avoid exposure to moisture, corrosive gases, and extreme temperatures, as these factors may affect external insulation and metal components.

Operating Environment: High humidity, high pollution, and salt spray environments can reduce the insulation strength of the arc extinguisher and may cause surface flashover, but this has no direct impact on its internal lifespan.

 

Summary

The lifespan of a vacuum interrupter is a comprehensive measure, which can be summarized as follows:

Electrical life depends on the cumulative effect of the contact material and the interrupting current (especially short-circuit current).

Mechanical life depends on the fatigue resistance of the bellows.

Insulation life depends on the long-term stability of the vacuum level.

 

Suggestions for extending lifespan:

Reasonable selection: Select an appropriate interrupter based on the actual operating current and the expected short-circuit current, leaving a certain margin.

Proper operation: Avoid unnecessary frequent operation, especially frequent interruption of high currents or short-circuit currents.

Regular maintenance:

Regularly check the mechanical characteristics of the circuit breaker (such as opening distance, overtravel, opening and closing speed, and contact pressure) to ensure the operating mechanism is in good condition.

Perform regular vacuum tests (such as the power frequency withstand voltage test or the magnetron discharge test) to promptly detect interrupters with deteriorating vacuum levels.

Good environmental conditions: Ensure the circuit breaker operates within specified environmental conditions.

In practical applications, the electrical life of a vacuum interrupter is usually exhausted much earlier than its mechanical life and insulation life. Therefore, the electrical wear of the contacts and the ability to maintain vacuum are the two most important indicators for evaluating their remaining life.

 

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