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SF6 Circuit Breakers

SF6 Circuit Breakers

Date posted: May 25, 2016 // Uncategorized

SF6 Circuit Breakers and their Role in Power Engineering

In practice, if asked to give an example of a good electrical insulator, few people are likely to cite something as tenuous as a gas. Actually, quite a number of gasses, including atmospheric air, nitrogen, halogens and their derivatives, have the ability to prevent the passage of electric current. However, the exceptional ability of the gaseous compound known as sulphur hexafluoride to prevent or at least to quickly quench an electrical discharge has made this gas with the chemical formula SF6, a preferred choice for use as an insulator in high-voltage circuit breakers associated with power transmission lines, distributions and switchgear. The use of the gas for such purposes was first patented as far back as 1938, by a German company

In fact, its value in this role is even greater, given that even if this compound should be broken down by the high voltages associated with an electrical discharge, its products of decomposition will normally tend to recombine and to form sulphur hexafluoride once more. Used in both indoor and outdoor applications, these devices provide a safe means by which to interrupt the mains power supply and for outdoor use, they will normally be contained in a ceramic casing that is supported by a pole.

In normal use, the current in these devises is passed between two contacts to provide an unbroken flow. When the SFcircuit breakeris activated by whatever means and for whatever reason, these contacts separate, thus leaving a gap that is instantly filled with a blast of dielectric gas under pressure. Firstly, this acts to cool the resulting arc rapidly from almost 22 000°C to just over 1 700°C, in the space of a few hundred microseconds. In addition, the gas captures any free electrons produced by the discharge to form negative ions that are unable to conduct electricity. If employing a significantly less efficient gas as the insulator, any unchecked, high voltage discharge that may arise as the contacts separate, could easily result in fire and lead to extensive damage to the power installation, as well as to any associated structures.

Despite the effective insulation of the SF6 gas used in circuit breakers, the contacts will eventually succumb to the long-term effects of repeated discharge and will need to be replaced in order to maintain efficient switching. Labotec Industrial Technologies is a supplier of specialised materials and components to South African industries, and sources a wide range of world-class products from leading international manufacturers. Serving industries as diverse as defence, healthcare,, aviation and power distribution, those engaged in the latter sector are assured of the highest quality replacement components as the result of our 40 yearlong partnership with the leading Austrian manufacturer – Plansee.

For use in SFcircuit breakers, we are able to offer tungsten-copper or tungsten-silver contact assemblies complete and ready for installation. Alternatively, we also provide the option of non-machined blanks, either welded or brazed, and consisting of contact heads and carriers made from ELMET materials. Also non-machined, we can supply infiltrated or back-cast blanks made from the same ELMET materials.

LIT Africa has long been synonymous with quality, dependability and service, not just for SFcircuit breaker components, but for all our products.