Gas-Insulated Transmission Lines
- Description
- Details
- Technical Data
- Benefits
- Applications
- References
Gas Insulated Lines (GIL) provide technical, environmental and operational features which make them a very good alternative wherever the transmission of extra high voltage (EHV) and extra high currents (EHC) is needed within restricted space, e.g. wherever overhead lines cannot be used.
GIL consist of two concentric aluminum tubes. The inner conductor is resting on cast resin insulators, which center it within the outer enclosure. This enclosure is formed by a sturdy aluminum tube, which provides a solid mechanical and electrotechnical containment for the system.
To meet up-to-date environmental and technical aspects GIL are filled with an insulating gas mixture of mainly nitrogen and a smaller percentage of SF6 (sulphur hexafluoride).
GIL can be used in a similar way as power cables, however extending the application range to higher voltages and higher transmission power. At the same time a better operational safety is reached.
GIL proved their reliability in more than 35 years of service experience.
The tubes are made of corrosion resistive aluminum alloy.
Due to their modular design the elements can be combined to deliberate length. Typical GIL installations have a lengths between 100 m and 60 km.
Due to their characteristics, GIL can navigate smooth curves down to 400 meter or sharp angular direction changes in any deliberate angle.
The system comprises mechanical expansion elements so that internal mechanical stress is kept at a minimum.
The tubes are welded together with a computerized orbital welding process. The seams are 100% ultrasonic tested to ensure that the system is absolutely gastight.
For typical applications up to 400 kV the insulation gas is composed of up to 80% nitrogen and only 20% SF6. The gas is not poisonous and can easily be detected.
Mostly GIL are used for transmission systems with 345 kV to 550 kV operation voltages and 2500 A to 5000 A operation current.
Due to their low electrical capacitance reactive compensation is not needed in general.
The enclosure is solidly grounded, thus it is safe to touch the GIL without risk and at the same time the electromagnetic field from the GIL to the environment is reduced to almost zero.
A particle trap is included in the tubes to make an increased lifetime of 50 years or even more possible.
| Nominal voltage (typical) | 220 up to 500 kV |
| Maximum operation voltage | 245 up to 550 kV |
| Nominal frequency | 50 / 60 Hz |
| Nominal short-time current (rms., 1 - 3 s) | 31.5 up to 63 kA |
| Nominal operation current (typical) | 2000 up to 5000 A |
| Withstand voltage vs. earth: AC withstand voltage 1 min Nom. surge-impulse withstand voltage 1.2/50 µs wave Nom. switching-impulse withstand voltage 250/2500 µs wave |
380 up to 620 kV 1050 up to 1675 kVpeak 850 up to 1175 kVpeak |
| Housing and conductor material | Aluminium alloy |
| Insulation gas | Gas-mixture 80% N2 and 20% SF6 |
| Nominal pressure (absolute) | 0.7 MPa |
| Environmental temperatures | -30°C up to +50°C |
| Weight per phase | approx. 50 up to 70 kg/m |
| Capacitance | 55 nF/km |
| Inductance | 0.205 mH/km |
| Surge impedance | approx. 60 Ohm |
| Electrical cross-section of conductor (typical) |
approx. 5300 mm² |
| Electromagnetic field | negligible µT |
| Gas tightness | Sealed for lifetime - no refeed |
Low losses
The resistive losses of GIL are lower compared to cables and overhead lines. The dielectric losses of GIL are negligible. This reduces the operation costs and causes savings. Due to the large outer diameter, the heat dissipation is better than with cables and GIL normally do not require sophisticated cooling systems.
No electrical compensation
Due to its low capacitance, GIL do not require phase angle compensation even for a system length of 60 km or more.
Low electromagnetic fields
The conductor current induces in the enclosure a reverse current of the same size. Consequently the electromagnetic field outside the GIL is negligible. No special shielding is required even in areas which are critical with respect to EMC (e.g. airports or computer centres or in populated areas).
High safety
If an insulation failure would occur in a GIL, the fault arc would be safely enclosed within the outer housing. No influence would occur to the outside. The GIL are fire resistant and do not contribute to fire load. This means optimal protection of persons and environment.
High reliability
GIL technology has proven its reliability since over 35 years in service without any failure up to now.
No ageing
The insulation system of GIL shows no ageing phenomena, neither electrical nor thermal. There is practically no maintenance needed on the GIL for up to 50 years or more.
Operation like an overhead line
The GIL are the ideal addition to overhead lines. The high transmission capability of GIL allows to continue overheadlines underground with one GIL tube per phase, which minimizes space consumption. The GIL allow auto-reclosure switching cycles, consequently no major changes in the operation- and protection schemes of the grid are necessary.
Maintenance free design
Thanks to the technological clear-cut, logical design and the use of high quality materials a practically maintenance free product is achieved which requires external inspection only. The GIL can stay in operation during regular inspection activities.
GIL can be used in all common laying arrangements, which makes them suitable for numerous applications. Be it feeder connections in power plants, transmission systems in tunnels beneath cities or directly buried for overland transmission systems, where overhead lines cannot be used for specific reasons.
GIL can be used horizontally, vertically or in any inclined arrangement.
During service, the fully encapsulated design ensures optimal protection of the GIL against environmental influences.
Since 1975, the long-proven Siemens GIL technology has provided solutions in up to now 29 projects with an overall tube length of about 87,000 meters to customers all over the world. Please find below selected references about Siemens' activities in GIL projects worldwide from 1975 until today. For more detailed information please get in contact with our competence center (contact address on the right-hand side).
Whether above ground, tunnel or directly buried installation - we have the adequate solution for all kind of challenges.
Press releases:
June 15, 2009 - Go-ahead for power pipeline: Siemens and RWE to install extra-high voltage line at Frankfurt Airport as a buried twin gas-insulated line
May 20, 2009 - Pipelines for electrical power: Siemens equips hydropower plant in China with gas-insulated high voltage transmission line
Dec 2, 2008 - Siemens builds gas-insulated high-voltage line for hydropower plant in China - Total tube length 3.2 kilometers with 200-meter long vertical sections
Aug 15, 2008 - Siemens to install an extra-high voltage line for RWE at Frankfurt Airport consisting of a buried, double gas-insulated line
Contact
Telephone: +49 (9131) 7-34660
Fax: +49 (9131) 7-34662