Load switch

from Wikipedia, the free encyclopedia

Load switches are used in electrical power engineering to switch on and off equipment and system parts in an undisturbed state. The switching capacity of the load switch is specified by the manufacturer and is predominantly at the level of its rated current. Motors cannot be switched with load switches because the inrush current is a multiple of the rated current so that circuit breakers are used for this purpose . In addition to simple load switches, there are also load-break switches .

Basics

If circuits are disconnected under load, an arc occurs in the switch when disconnected . The extinction of the arc is the main problem of the circuit breaker. For this purpose, appropriate technical measures are taken depending on the switching capacity. The rated making capacity and rated breaking capacity of load switches is around twice the rated current .

Arc extinction

Deion chambers are mostly used in the low-voltage area to extinguish arcs , which enclose the separation points of the switching contacts like a chimney. This measure increases the thermal lift of the arc. This lengthens the arc and increases its voltage requirement until it breaks. Arc-extinguishers are built into the arc chamber to deionize and cool the arc so that reignition after the current has passed zero is largely avoided. The extinguishing methods commonly used with medium and high voltage switches using gas, compressed air or liquids are rarely used with low voltage switches.

Areas of application

Various load switches for low voltage

Load switches are used in the low-voltage and medium-voltage range.

Low voltage

Classic load switches for the low voltage range are, for example, the usual light switches . In the case of low-voltage switches, the manual drive predominates as the drive . The most important parameters for low-voltage load switches are:

  • nominal voltage
  • Rated current
  • Rated breaking capacity in kA (rms value) at a certain power factor
  • Nominal making capacity in kA (peak value)
  • Control voltage of the drive (if an electric drive is available)

Medium voltage

In the medium voltage range, load switches are used in systems up to 30 kV. Some medium-voltage load switches (so-called hard gas switches) have arcing chambers made of a polymer: when switching off, after opening the main contacts, parallel switching blades are pulled from switching contacts in the arcing chambers, the resulting arc heats the interior of the arcing chamber, evaporates a small part of the material and the resulting gases extinguish the arc.

Other load switches ( SF 6 switch or gas pressure switch, GIS gas insulated switch ) are located in a hermetically sealed tank filled with sulfur hexafluoride ; the arc is extinguished by this gas. With load switches, the arc can also be extinguished with compressed air (air pressure switch , AIS air insulated switch ), e.g. B. found on electric locomotives. AIS are larger, material and energy intensive than GIS.

Individual evidence

  1. ↑ Réne Flosdorff, Günther Hilgarth: Electrical Distribution. 4th edition. BG Teubner, 1982, ISBN 3-519-36411-5 , pp. 219-227.
  2. ↑ Hans-Günter Boy, Klaus Bruckert, Bernard Wessels: The master's examination in electrical control and drive technology. 10th edition. Vogel Buchverlag, Würzburg 1995, ISBN 3-8023-1556-1 .
  3. ↑ a b Theodor Schmelcher: Handbook of Low Voltage, project planning information for switchgear, switchgear and distribution boards. 1st edition. Siemens Aktiengesellschaft, Berlin / Munich 1982, ISBN 3-8009-1358-5 .
  4. ↑ H. Happoldt, D. Oeding: Electric power plants and grids. 5th, completely revised edition. Springer Verlag, Berlin / Heidelberg 1978, ISBN 978-3-662-06963-9 , pp. 285-286.
  5. ^ Adolf J. Schwab: Electrical energy systems generation, transport, transmission and distribution of electrical energy. 3rd, revised edition. Springer Verlag, Berlin et al. 2012, ISBN 978-3-642-21957-3 .
  6. ^ Klaus Heuck, Klaus-Dieter Dettmann, Detlef Schulz: Electrical energy supply. 7th edition. Friedrich Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-8348-0217-0 .
  7. ↑ Hans-Günter Boy, Uwe Dunkhase: The master's examination in electrical installation technology. 12th edition. Vogel Buchverlag, Oldenburg / Würzburg 2007, ISBN 978-3-8343-3079-6 .

Web links

Commons : Load switches  - collection of pictures, videos and audio files