Method description
Electrical contacts build electrical connections between components in overvoltage protections, relays and switches. The requirements for the switch contacts are different depending on the switching power, switching voltage, switching frequency, continuous current, and the starting and breaking current. Accordingly, the requirements for the contacts and the methods to ensure their safe function vary. To prevent oxidation, the contacts can be made corrosion resistant by coatings with precious metals or by operating the contacts in a vacuum, inert gas or oil. Other problems include contact erosion, erosion by spark flashover, or arcing and welding at high power. These problems can be solved by using refractory metals like tungsten.
At the same time a low contact resistance must be ensured. This however can be provided by low-melting but highly conductive metals such as copper and silver. Depending on the requirement, the properties of the high melting metals are combined with those of highly conductive metals. Therefore, alloys are produced in which both components are present in a suitable ratio to each other. This creates contacts with very good welding resistance and good contact resistance. The erosion resistances of TUCOMET® and tungsten-silver alloys even exceed that of pure tungsten. This is due to the cooling effect of evaporating copper (2,927 °C) or silver (2,162 °C) while tungsten begins to melt only at 3,410 °C and therefore remains stable.
Electrical Contacts
Application areas & Materials
Electrical Contacts
- SF6 Circuit Breaker
- On-load Tap-changer
- Load Break Switches
Materials
We recommend the following materials:
- Tungsten/Silver W50Ag, W60Ag, W70Ag, W80Ag
- Tungsten/Copper TUCOMET® 50, TUCOMET® 60, TUCOMET® 70, TUCOMET® 80, TUCOMET® 90
- Tungsten
- Composites W/Cu, WLa/Cu, W/WCu, W/CuCrZr
Contact materials
Tungsten/Silver W50Ag, W60Ag, W70Ag, W80Ag
Tungsten-silver contact materials are characterized by a high conductivity, resistance to erosion as well as welding resistance. In the case of welding the removal force is very low. After a long period of operation tungsten-silver contacts are prone to oxidation and tungstate formation whereby the contact resistance can increase. Due to these properties tungsten-silver contact materials are used preferably in low-voltage switchgears and circuit breakers such as engine circuit breakers, miniature circuit breakers and residual current circuit breakers.
Tungsten/Copper TUCOMET® 50, TUCOMET® 60, TUCOMET® 70, TUCOMET® 80, TUCOMET® 90
TUCOMET® contact materials are also very good at resisting erosion during switching. This erosion is generally flat and uniform. The welding resistance of the materials is good and increases with increasing tungsten content. The tendency to formation of tungstate's is not very pronounced; therefore, contact resistance and chopping gap during the lifetime of the switch remain very stable. TUCOMET® materials are well suited for driving and switching of high currents. Their high thermal conductivity coupled with low thermal expansion makes them very resistant to thermal shock and mechanical stresses. Tungsten is characterized by an extremely low solubility of gases. Correspondingly low is the release of gas in vacuum. For use in vacuum switches, particularly low-gas tungsten-copper contact materials can be supplied. Because of these properties, contact materials made of TUCOMET® are particularly suitable for burn up contacts in circuit breakers, switches and load-break switches between high and medium voltage switchgears. Furthermore, these materials are suitable for electrodes in lightning protection equipment. Low gas TUCOMET® materials are used in vacuum contactors.
Electrical Contacts
Tungsten
Tungsten has the highest hardness and the highest melting point of contact materials. Thus, it is used in arc exposed areas and has good resistance to erosion. Tungsten does not tend to weld and thus has excellent separation ability for safety. Since there is minimal material migration, it is used in applications such as car horns and interrupter contacts. The switching voltage however should be above 6V and the contact force should also exceed 0.5 N. Other applications are found in medium and high voltage switching devices for circuit breakers, switches and load-break switches.