Oil switch
Oil switches are circuit breakers that are used in high-voltage switchgear in the field of electrical energy technology . In the case of oil switches, the switch is located in a container filled with oil ; the oil is used to extinguish the very hot switching arc that occurs during switching operations . The first oil switches were developed in 1895 by the British company Ferranti .
Initially, the pole or poles were in a kettle filled with oil. The oil serves as an insulating and extinguishing medium, which means that large quantities of oil were necessary. The low-oil circuit breaker was developed in the 1930s. This has a single pole design, with each phase located in its own insulating cylinder. The oil is no longer used for insulation. It is designed in such a way that the oil is injected into the arc when switching. This means that the oil not only cools the arc but also blows it out at the same time. Circuit breakers based on this principle are called flow switches. This principle is also used in hard gas , compressed air and SF6 circuit breakers. Since the 1970s, oil has been increasingly replaced by sulfur hexafluoride (SF6) as an extinguishing medium, including in the SF 6 self-blowing switch .
construction
The switching chamber and the switching contacts of the oil boiler switch are completely under oil in an airtight boiler. The arc creates hydrogen gas in the oil at high gas pressure and with very high thermal conductivity , which extracts heat from the arc and thus, in addition to the electrically insulating properties of the oil and the high gas pressure, low mean free path for charge carriers, leads to extinction. As a consumable, the oil must be constantly renewed in order to remove the decomposition products and impurities in the oil that arise during switching operations.
hazards
At the beginning of the 20th century, oil switches were the only available circuit breakers with a comparatively high short-circuit power in order to be able to safely switch off short-circuit currents in the then newly created electrical energy networks . With high switching currents, so much oil can evaporate due to the switching arc that an overpressure occurs in the gas-tight tank. If the oil pressure vessel cannot withstand the gas pressure inside, a gas leak occurs, including the hydrogen formed by the arc, which in combination with the oxygen in the air forms explosive oxyhydrogen . This triggered the oil switch explosions feared in the early days of electrical switching technology, which could lead to the destruction of the electrical system and damage to surrounding buildings.
literature
- Max Reck (Ed.): ZIPP, Die Elektrotechnik . 6th edition. First volume. Publishing house CA Weller, Berlin 1940, DNB 365694037 .
- Russ Yekley, John Perulfi: Oil circuit breakers. A look at the earlier generation. In: IEEE power & energy, Volume 16, No. 3, May / June 2018, pp. 86–97.
Individual evidence
- ↑ a b Chronicle of electrical engineering: Switches and switchgear: high voltage. VDE-Verlag, requested on August 10, 2012.
- ^ AEG auxiliary book. 8th edition. AEG Berlin, 1960, DNB 571679757 , pp. 5-32.