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Protective gas prevents electrical flashover

Vacuum helps saving space and protecting the climate

High voltage can result in an electric short circuit made through the air, even without direct contact. Gas-insulated switch panels prevent this undesired effect. Using vacuum pumps that are very often manufactured by BUSCH, they are evacuated before being filled with insulating gas.

Air does conduct electricity, albeit poorly. At 230 volts, that only results in a harmless little spark – at a light switch, for example. For medium and high voltage lines with several thousand volts, however, electrical flashover is a serious risk. So it’s good to follow the advice about never getting too close to power lines near train tracks or high-voltage grids.

Keeping distance from high voltage

Keeping distance from high voltage sources also applies to objects because electrical flashovers can damage many materials. However, it is not always possible to avoid physical proximity in high-voltage electrical systems. Even after being disconnected, switch elements can remain in the vicinity of live high-voltage cables.

Outdoor switching stations are built with generous distances, so the systems require a good deal of space. For interior spaces there are gas-insulated switching systems that only require a tenth of the space. They are designed as hermetically sealed chambers. The air inside is usually replaced with sulfur hexafluoride (SF6).

Vacuum pumps keep greenhouse gases in check

This gas provides reliable insulation up to a voltage of 1000 kV because it has a dielectric strength that is many times higher than that of air. Unwanted electrical and magnetic alternating fields are not able to form in the first place, and the phenomenon known as arcing is interrupted. When building gas-insulated switching systems, the air is extracted from the chamber using a vacuum pump before it is filled with the insulating gas.

However, SF6 is one of the most damaging greenhouse gases. Therefore, measures need to be taken to ensure that it does not escape into the atmosphere. This is why it is extracted carefully before maintenance work. BUSCH offers vacuum pumps that are ideally suited for evacuation, both before the filling process and before maintenance is performed.
The difference between lightning and electrical flashover

Lightning is the electrical discharge from storm cloud to storm cloud or from the cloud to the earth. This spontaneous electrostatic discharge happens in a fraction of a second. It can result in a spark discharge or as a brief, blazing electric arc. Several million volts are not uncommon; the current flow can be several thousand amps.

When electrical flashover occurs – for instance, from a high-voltage line to a nearby object – a more or less continuous electric arc made of ionized plasma forms. Its temperature can range between 5,000 and 50,000 degrees Celsius. In addition to the longer transfer of current flow through the electric arc, this heat can also have a destructive impact. This power is actively harnessed in arc welding and in the electric arc furnaces of the steel industry. An electric arc between copper wires can already form starting at 12 volts and can be maintained at 30 volts.