Benefits of using Elastic Contacts in the new Generation of Vacuum Interrupter

Vacuum Interrupter Based on Elastic Contacts

A vacuum interrupter that utilizes elastic damping elements made of refractory metals and impregnated with a fusible eutectic alloy can be employed in vacuum switching apparatus, especially in systems requiring the switching of large currents (e.g., electrolyzers for hydrogen and metal production) or high-speed switching (e.g., medium voltage direct current). These are also suitable for instantly increasing the switching capacity of existing systems, such as safely boosting the on-load tap changers (OLTC) for wind turbine transformers.

Using elastic contacts removes the limitations on the nominal current magnitude caused by the quadratic increase in compression forces. Consequently, new systems can be designed to be more compact and cost-effective. However, further research and the inclusion of these findings into standards are necessary for their implementation.

Concept of Elastic Contacts in Vacuum Interrupters

At their core, elastic contacts for vacuum interrupters are akin to wire mesh vibration dampers (Fig.1) made from refractory metals and impregnated with low-melting alloys that provide contact through a liquid phase. Early literature refers to them as composite liquid-metal contacts, but this term is not definitive for this specific type of contact, since the liquid phase exists merely as a thin layer on the surface of the refractory wire.

In contrast, the significant characteristics—vibration resistance and contact over the entire visible area—are achieved thanks to the properties of the knitted damper. The design of elastic contacts not only overcomes the limitations of traditional contact materials in high-pressure, high-current applications but also ensures the stability and reliability of equipment operation. This innovation is crucial for enhancing the efficiency and safety of power systems and provides a more flexible and efficient design approach for future electrical engineering projects.

By adopting elastic contacts, the vacuum interrupter technology achieves superior performance and reliability, making it an essential advancement for modern power systems. Further investigation and standardization will pave the way for broader application and integration of this technology in various industries.

Advantages and Challenges of Elastic Contacts in Vacuum Interrupters

These elastic contacts do not exhibit inertial rebound, cannot weld, do not possess conventional contact resistance, and, as will be demonstrated later, are not subject to electromagnetic separation. Given these remarkable properties, one might wonder why such materials have not yet been widely adopted in electrical engineering.

Main Challenges of Elastic Contact Materials in Vacuum Interrupters:

1. Production Technology: Until recently, manufacturing and applying elastic contact materials required expensive equipment, complex thermochemical processes in a hydrogen atmosphere, and specially trained personnel. A significant issue was the poor adhesion of gallium and its alloys to tungsten and other refractory metals.
2. Lack of Consolidated Information: Research on these elastic contacts has not been consolidated into a single source, making it less accessible to specialists.
3. Lack of Systematic Research: Despite their exceptional properties, systematic studies enabling engineers to apply these materials effectively have not been conducted.

Manufacturing Process for Elastic Contacts

The technological hurdle was addressed by the author in April 2024 through the development of a straightforward method for manufacturing and applying elastic contact materials (patent application PCTIB2024/054125). This method is simpler and, in most cases, more economical compared to traditional rigid contacts used in vacuum switching equipment.

Steps Involved:

1. Damper Fabrication: The damper is made from knitted wire—typically tungsten, which was previously used in incandescent lamp filaments—or stainless steel. In special cases, molybdenum, niobium, rhenium, and their alloys can be used. These dampers are readily available from manufacturers.
2. Soldering: The dampers are soldered onto conductors similarly to how rigid contacts are attached.
3. Impregnation with Low-Melting Alloy: The dampers are impregnated with a low-melting alloy that remains liquid under operating conditions. Commonly used are eutectic alloys of gallium, indium, and tin, often with additions like silver to lower the melting point.

Testing Elastic Contacts in Vacuum Interrupters

Switching tests for durability were conducted on a pre-production vacuum contactor specifically designed for elastic contacts. During these tests, the contacts underwent 200,000 switching cycles at 250A in AC4 mode, with currents reaching 600 amperes and voltages up to 690 volts. Overvoltage testing showed that overvoltages were 2-3 times lower than standard norms.

This breakthrough method promises to revolutionize the field of vacuum interrupters by providing superior performance and reliability while reducing costs. Further research and standardization efforts are necessary to fully integrate this technology into broader applications within the electrical engineering industry. By addressing the challenges of production and dissemination of knowledge, these innovative elastic contacts could soon become a staple in modern power systems.