What are the requirements for vacuum interrupters specifically designed for sealed pole assemblies?

The vacuum interrupter specifically designed for encapsulated pole assemblies is the core component of a vacuum circuit breaker. Its design and requirements differ significantly from traditional "bare" vacuum interrupters, as it needs to be encapsulated into a single unit (i.e., an encapsulated pole assembly) using high-quality epoxy resin through an automatic pressure gelation process.

The following are the core requirements for vacuum interrupters specifically designed for encapsulated pole assemblies, which can be understood from four dimensions: technology, materials, structure, and process:

I. Technical Performance Requirements

High Vacuum and Long Service Life:

Initial Vacuum Level: Must be better than 10^-5 Pa, ensuring extremely high insulation strength.

Leakage Rate: Requires extremely low leakage, typically less than 10^{-11} Pa·m³/s, to ensure that the vacuum level does not significantly decrease within the expected service life (usually 20-25 years).

Bellows Life: As a key component ensuring dynamic sealing, its mechanical life (number of opening and closing cycles) must match the mechanical life of the circuit breaker (e.g., 10,000 cycles) and withstand sufficient fatigue testing.

 

Excellent Insulation Performance:

Internal and External Insulation Matching: The external part of the arc extinguishing chamber (i.e., the epoxy resin-encapsulated part) is the "external insulation," and the internal part is the "internal insulation." The insulation design of the arc extinguishing chamber must perfectly match the insulation characteristics of the epoxy resin (dielectric constant, withstand voltage strength) to avoid electric field distortion.

Power Frequency Withstand Voltage: Must meet the requirements of relevant standards (such as GB/T, IEC) for the rated voltage level.

Lightning Impulse Withstand Voltage: Must also meet the standard requirements to ensure it can withstand system overvoltages.

Creepage Distance: The design of the ceramic shell of the arc extinguishing chamber (such as the skirt shape) needs to be combined with the epoxy resin to provide sufficient effective creepage distance to prevent surface flashover.

 

Excellent Switching Performance:

Short-circuit breaking capacity: Capable of reliably interrupting the rated short-circuit current (e.g., 25kA, 31.5kA, 40kA, etc.), with a short arcing time.

Current carrying capacity: In the closed state, it can continuously carry the rated current; in a short period, it can withstand the short-time withstand current (thermal stability current).

Contact welding: Contact welding may occur after the contacts carry a short-circuit current, but it must be ensured that the contacts can be smoothly separated during the opening operation without excessive metal splashing contaminating the inner wall.

 

Low current chopping value and low operating overvoltage:

Especially for applications protecting small inductive currents (such as motors and transformers), the contact material is required to have a low current chopping value to suppress operating overvoltage and protect equipment safety.

 

II. Material and Structural Requirements

Contact Material:

This is the "heart" of the arc extinguishing chamber. Copper-chromium alloy is commonly used due to its:

High breaking capacity

High electrical and thermal conductivity

Low current chopping level

Excellent dielectric strength

The chromium content, material composition, and manufacturing process (such as infiltration method, powder metallurgy) directly affect performance.

 

Shielding System:

Main shielding cover: Used to absorb metal vapor and arc energy generated during the breaking process, preventing them from condensing on the inner wall of the ceramic and causing insulation degradation. It must have sufficient heat capacity and a good fixing method.

Voltage equalizing shield: Optimizes the electric field distribution inside the arc extinguishing chamber, which is crucial for ensuring stable insulation under high voltage.

 

Ceramic Casing:

Typically made of high-purity, high-strength alumina ceramic.

Requires excellent airtight sealing strength and thermal matching with the metal end caps (Kovar alloy) to prevent leakage or cracking due to temperature changes or epoxy resin curing shrinkage stress.

The surface must be smooth and free of defects to facilitate bonding with the epoxy resin and ensure a uniform electric field.

 

III. Process and Adaptability Requirements (This is the key to "specialized" design)

Excellent epoxy resin bonding capability:

Surface treatment: The outer surfaces of the ceramic and metal parts of the arc extinguishing chamber must undergo special treatment (such as sandblasting and coating with a special coupling agent) to form a strong, non-peelable chemical and mechanical bond. This is crucial for preventing "delamination" or the formation of interfacial air gaps due to thermal expansion and contraction during operation.

Bonding strength: Rigorous shear strength testing is required to ensure that the bonding strength is far greater than the stresses that may be generated during operation.

 

Precise dimensional and geometric tolerances:

Since the arc extinguishing chamber is pre-positioned in the mold for casting, its external dimensions, the positional accuracy and perpendicularity of the moving conductive rod, etc., require extremely high precision to ensure accurate positioning in the encapsulated pole and perfect connection with the operating mechanism.

 

Cleanliness and Dryness:

Before being sent to the epoxy resin casting workshop, the surface of the arc chamber must be absolutely clean, dry, free of oil stains, and dust-free. Any contaminants will severely damage the bonding interface with the epoxy resin, creating insulation weaknesses.

 

High Temperature and High Humidity Environment Adaptability:

During the casting process, the encapsulated pole will experience high temperatures (e.g., above 100°C), and the arc chamber must be able to withstand this process without affecting its internal vacuum level and performance.

After encapsulation, the entire pole assembly needs to withstand high temperature and high humidity tests (such as damp heat testing), and the arc chamber itself must not become a weak point in the insulation.

 

Summary

 

The vacuum interrupter specifically designed for solid-insulated pole assemblies is not just a high-performance vacuum switching component; it is a carefully designed system component intended to be "embedded" in epoxy resin solid insulation. Its core requirements can be summarized as follows:

Performance is fundamental: High insulation, strong breaking capacity, and long service life.

Materials are key: Optimized contacts and reliable ceramic-to-metal sealing.

The interface is crucial: A strong and unbreakable bond with the epoxy resin is fundamental to the success of solid insulation technology.

Precision is the guarantee: Strict dimensional and cleanliness control are prerequisites for automated, high-quality production.

 

Shaanxi Huadian Vacuum Interrupter, from material selection to automated assembly, undergoes rigorous testing and refinement at every stage, integrating lean manufacturing and intelligent quality inspection to achieve a "zero-defect" quality standard.If you are interested,please contact us at:pannie@hdswitchgear.com​​​​​​​