What do arc faults and air bags have in common?

Ultra fast earthing switch extinguishes arcs before they can cause any damage

We’re all familiar with electric arcs that occur when a current ‘jumps’ an air gap, if only from the bolts of forked lightning that crash to earth during a thunderstorm. Sometimes, these short circuit currents can be useful, like in arc welding, but an unplanned arc (often referred to as an ‘arc-fault’) can have devastating consequences in electrical equipment. It can reduce a large electrical switchgear cabinet, containing several hundreds of kilos of metal, and costing a significant amount of money, to useless scrap in milliseconds.

As you might imagine, helping customers to avoid arc faults is a top priority. That’s why we at ABB have developed an ultra-fast earthing switch (UFES) that uses air-bag technology for instant results.

In switchgear, arc faults can have a variety of causes; a loose connection, defective insulation, even operator error. When they occur the temperature rises instantaneously to around 20,000°C. That’s well above the melting point of steel, copper and insulation materials. The instant heat vaporizes electrical components and the resulting plasma (ionized gas) explodes, releasing huge amounts of energy, similar to a rocket launch.

In addition to damaging equipment and threatening the lives of near-by workers or others, arc faults also interrupt power supplies, disrupting homes and businesses, hospitals and factories. Outages might be short-lived, but their consequences can be disastrous and long lasting. When it comes to arc faults, prevention is better than cure.

The key is to extinguish the arc before it can cause any damage. ABB’s UFES does this by making a near-instantaneous connection to earth, snuffing out the arc within 4 milliseconds.

This super-fast response is triggered by a light and current sensor that detects a developing arc. This sets off tiny, ultra-fast, gas generators, similar to those used in cars to instantly inflate air bags. In UFES, the gas effectively throws the earthing switch and extinguishes the arc, before it can cause any damage.

The great thing about the UFES is that, in addition to being compatible with new switchgear, it can also be fitted into existing installations, whether they were built by ABB or other suppliers.

Have you ever experienced an arc fault in a substation? Tell us about your experiences!

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