Gas-insulated pipe conductor
Gas-insulated pipelines (GIL) are transmission lines for high voltages in the field of electrical power engineering . Due to the nature of the construction, electrical power can be transmitted with high voltages and high currents in the smallest of spaces. Therefore, GIL are used, among other things, for diversions, e.g. B. from interiors of switchgear . A major advantage of gas-insulated pipe conductors is their intrinsic safety against fire, which results from their structure.
construction
GIL are made up of two concentrically arranged aluminum tubes. The inner tube is the part carrying the high voltage; operating voltages of up to 500 kV with rated currents per conductor of up to about 5 kA are common . The inner conductor is fixed at regular intervals on post insulators or disk insulators in the outer tube. The space between the inner pipe and the grounded outer pipe is filled with an insulating gas. As a rule, sulfur hexafluoride (SF 6 ) is used at a pressure of approx. 5 bar or a more cost-effective mixture of 80% nitrogen (N 2 ) and 20% sulfur hexafluoride at a slightly higher gas pressure of around 7 bar . Due to the higher pressure compared to normal pressure (1 bar), the mean free path for electrically charged particles such as ionized molecules between the two conductors is reduced according to Paschen's law , which reduces corona discharges and increases the dielectric strength of the insulating gas. The pipe diameters result from the necessary conductor cross-sections; cross-sections of around 5000 mm 2 are common in order to keep the electrical field strength on the inner conductor below certain limits.
The insulating gas used, sulfur hexafluoride, is non-toxic, but has a strong impact on the climate; it has a very strong greenhouse gas potential . The outer tube is rigidly earthed so that no dangerous contact voltages occur. In the event of a possible leak or gas leak, the line must be switched off immediately, as the electrical insulation is no longer guaranteed. Pipe conductors are subject to no external damage and, in contrast to solid-insulated lines, almost no aging and are operationally reliable compared to other energy transmission systems. They also do not represent a fire load , which is particularly important in confined spaces. The individual pipe segments are welded or flanged gas-tight and are tight for life. The effectiveness of SF 6 as a greenhouse gas is therefore hardly relevant, especially in the gas-tight welded GIL systems. No gas needs to be refilled during the 50-year operating life. Additional monitoring of the gas spaces for an early detection of a pressure loss is standard.
Applications
In addition to areas in switchgear, areas of application are electrical conductor systems in urban areas or in scenic areas where overhead lines cannot be used for spatial or optical reasons. GIL are increasingly being used in this area as an alternative to underground cables operated with extra high voltage . The laying can be done above ground or underground in a tunnel or directly in the ground. Depending on the application, GIL systems can do without special cooling. In special cases, an actively ventilated duct may be necessary.
With GIL systems, the capacitance is higher than with overhead lines of the same length. Comparable high-voltage cables have a higher capacitance and require a corresponding compensation device for reactive power when operated with alternating voltage . As a rule, this does not apply to GIL systems.
The first GIL was built by Siemens AG as a double system for a nominal voltage of 420 kV three-phase current 50 Hz and put into operation in 1975. Each system consists of three pipes. It leads through an approx. 600 m long tunnel with a 40 ° gradient from the cavern in the Wehr power plant in the Black Forest to the overhead lines on the surface. As of 2016, it is still one of the world's largest GIL systems.
As of 2013, the largest GIL transmission system implemented with an extension of almost 600 m was set up at the Xiluodu Dam in China . The pipe system consists of seven three-pole pipes that are strung together and have a total length of approx. 12.5 km. The GIL system is used to connect the underground power plant with the overhead lines 460 m higher. The system is operated with 550 kV and is designed for the transmission of 3.9 GW. The GIL was installed in tunnels for fire safety.
The largest GIL system in Europe with an extension of almost 900 m is located in Kelsterbach in Germany. The pipe system consists of two three-phase systems for 420 kV with a total pipe length of 5.4 km. The underground GIL is a replacement for a section of a 380 kV overhead line to create space for another runway at Frankfurt Airport .
literature
- Friedhelm Noack: Introduction to electrical energy technology . 1st edition. Fachbuchverlag Leipzig, 2003, ISBN 3-446-21527-1 .
Individual evidence
- ↑ a b c d Gas-insulated transmission lines. Retrieved July 12, 2014 .
- ↑ Calculation of an SF6 insulated pipe.
- ^ First GIL. Retrieved August 8, 2016 .