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Visit to the Compressed Air Cable installation by Hivoduct in the utility and service tunnel (WELK) beneath the roadway in the Uetliberg highway tunnel
Posted 2025-01-13
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News
This project was a pilot installation of Compressed Air Cables (CAP) for 245 kV and 4000 A in an existing utility tunnel beneath a Swiss motorway tunnel. The CAP is produced by Hivoduct, Switzerland and this first installation of its kind marks a milestone in the history HV technology.
The purpose of the installation was to demonstrate the feasibility of using existing tunnel infrastructure for transmitting large amounts of electrical energy. The key factors that enable such an installation include the use of compressed air for insulation, the fire-resistant design of the compressed air cables, and the low external magnetic field. The pipes were installed on Hivoduct's proprietary roller system, with continuous monitoring of both pressure and temperature.
By utilizing an existing tunnel, the transmission route is significantly shortened, as the tunnel runs directly and straight through the mountain, compared to an overhead line that would need to zigzag around it.
More than 100 visitors — including grid operators, academics, and other interested parties — were able to experience this new type of high-voltage cable firsthand on-site. The project was supported by Innosuisse.
With Cableizer you can model compressed air cables from Hivoduct and calculate the rating for installations directly in air or buried as well as in air-filled troughs or tunnels. You can calculate them in parallel to traditional cables and other heat sources. Cableizer is the only commercial software on the market able to calculate compressed air cables as well as gas insulated lines which are filled with nitrogen and SF6.
If you have any further questions or require additional information about Hivoduct feel free to contact Dr. Walter Holaus, CEO of Hivoduct.
| flat arrangement | transition | vertical arrangement |
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CAP are based on a coaxial arrangement of a HV conductor inside a grounded, conducting enclosure – like gas-insulated lines (GIL). The basic properties of GIL and the product design and applications are well known and products are tested according to international standard. GIL applications were enabled by the excellent dielectric strength of pure Sulphur hexafluoride (SF6) gas and fluorinated gas mixtures, resulting in compact insulation gaps when using a standard GIS flange design. However, as SF6 is the most potent greenhouse gas, the application of GIL type of products is limited to GIS busbars and exit busducts in connection with gas-insulated switchgear today and will be banned for future new installations.
The larger enclosure diameter requires a larger diameter of the conductor to be near the dielectric optimum of $D_{encl}/D_{c} = e = 2.71$.
This leads to key differences between CAP and XLPE cables.
| Parameter | CAP | XLPE |
|---|---|---|
| Enclosure Diameter | ≥ 150 mm | 40-100 mm (depends on rated current) |
| Conductor Diameter | > 80 mm | As small as possible |
| Conductor Cross Section | > 2200 mm2 | Engineered for rated current: ~1 A/mm2 |
| Conductor Material | Aluminium | Aluminium, Copper |
| Enclosure | 1ph, rigid, 8 mm thick aluminum tube (pressure vessel) | Several layers for protection & shielding |
| Connections | Proprietary boltless flanges every 5 m | Cable joints |