What are the materials of vacuum interrupter?

As the core component of a vacuum circuit breaker, the performance of the vacuum interrupter directly determines the circuit breaker's interrupting capacity, lifespan, and reliability. The materials used are carefully selected and designed to meet the requirements of extreme operating conditions such as high vacuum, strong electric fields, high-temperature arcs, and mechanical shock.

Main components and materials of vacuum interrupter

 

1. Insulating Casing
This is the external support and insulation component of the arc extinguishing chamber and must possess excellent insulation, airtightness, and mechanical strength.

Main material: High-alumina ceramic (Al₂O₃ content typically between 92% and 95%).

Reasons for selection:

High dielectric strength: Able to withstand extremely high voltages.

Excellent vacuum tightness: Able to maintain a high vacuum for extended periods, preventing gas permeation.

High mechanical strength: Able to withstand internal and external pressure differentials and mechanical stress.

Excellent thermal shock resistance: Able to withstand the high temperatures and rapid temperature fluctuations generated by the arc.

Excellent metal sealing: Able to achieve a reliable airtight seal with metal electrodes.

 

2. Conductive and Contact System
This is the core of the arc extinguishing chamber, responsible for conducting current and interrupting the arc.

Contact Material (the most critical material):

Requirements: High electrical conductivity, thermal conductivity, low cutoff current (to prevent switching overvoltage), high arc erosion resistance, and low gas content.

Mainstream material: Copper-chromium alloy (CuCr), with a chromium content typically between 25% and 50%.

Advantages of CuCr:

Chromium (Cr): High hardness and a high melting point provide excellent resistance to arc erosion and welding. Under arcing, Cr absorbs gases within the material, maintaining a vacuum.

Copper (Cu): Provides extremely high electrical and thermal conductivity, helping the arc heat dissipate quickly and facilitating arc extinction.

Other contact materials:

CuBi (copper bismuth), CuTeSe (copper tellurium selenide), etc.: Primarily used in applications requiring low cutoff current (such as contactors), but their interrupting capacity is inferior to CuCr.

WCu (tungsten copper): It has excellent arc erosion resistance but poor conductivity. It is mainly used in situations where high voltage, large capacity or high temperature resistance are required.

Conductive Rod:

Responsible for conducting current from the outside to the contacts.

Material: Oxygen-Free Copper (OFC). Its extremely high electrical and thermal conductivity, combined with its extremely low oxygen content, prevents hydrogen embrittlement at high temperatures and ensures stable performance in a vacuum.

 

3. Shield System
This is the "guardian" of the vacuum interrupter, serving multiple functions.

Main Shield (Arc Shield):

Purpose: Protects the ceramic shell from arc products (metal vapor) contamination, condenses and absorbs metal vapor, and promotes arc extinction.

Material: Oxygen-free copper or stainless steel. Oxygen-free copper has excellent thermal conductivity and rapidly cools arc products; stainless steel is less expensive and has good air absorption properties.

Voltage-Shaping Shield (End Shield):

Purpose: Improves the electric field distribution within the interrupter, preventing localized excessive electric fields from causing breakdown.

Material: Oxygen-free copper or stainless steel.

 

4. Bellows
This component enables linear motion of the moving conductive rod in a vacuum environment while maintaining a high vacuum seal. It is one of the components that determines the lifespan of the vacuum interrupter.

Requirements: Extremely high fatigue life (typically tens of thousands to over 100,000 mechanical operations), excellent elasticity, and vacuum tightness.

Material:

Mainstream: Stainless steel (such as SUS304), due to its excellent fatigue resistance, elasticity, and weldability.

Form: Typically a hydroformed, thin-walled bellows.

 

5. End Cap
This is the sealing end face of the arc extinguishing chamber, used for connection to the external conductor.

Material: Valveable alloy (such as 4J29, 4J33, etc.) or stainless steel.

Reason for choosing Valveable alloy: Its coefficient of thermal expansion is very close to that of high-alumina ceramic. During the brazing process, the ceramic and metal expand and contract in unison during heating and cooling, forming a strong, reliable, and airtight permanent seal, preventing cracking due to thermal stress.

 

Summary

Main Functions	Commonly used materials	Key Material Selection Factors
Insulating Housing	Insulation, support, vacuum maintenance	High Alumina Ceramic (92%-95% Al₂O₃)	High dielectric strength, vacuum tightness, mechanical strength, and metal sealability
Contacts	Conducting current, interrupting arcs	Copper-Chromium Alloy (CuCr)	High electrical and thermal conductivity, arc erosion resistance, weld resistance, low current interception, and gas absorption
Conductive Rod	Conducting current	Oxygen-Free Copper (OFC)	Extremely high electrical and thermal conductivity, low oxygen content
Shielding Cover	Protecting the enclosure, condensing vapor, equalizing pressure	Oxygen-Free Copper/Stainless Steel	Good thermal conductivity (copper), gas absorption/low cost (stainless steel)
Bellows	Dynamic sealing, transmitting motion	Stainless Steel (e.g., SUS304)	Extremely high fatigue life, elasticity, and weldability
End Cap	Sealants, external connections	Valveable Alloy/Stainless Steel	Thermal expansion coefficient matches ceramics (valve alloy), making for easy sealing

The scientific combination and precision manufacturing of these materials ensure that the vacuum interrupter can reliably interrupt currents of tens of kiloamperes in an instant and has a service life of up to decades.

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