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Gas-Insulated Transmission LineGIL

Gas-Insulated Transmission Line - GIL

The gas-insulated transmission line (GIL) is a system for the transmission of

electricity at high power ratings over long distances. In cases where overhead lines

are not possible, the GIL is a viable technical solution to bring the power

transmitted by an overhead line underground without a reduction of powertransmission capacity.

As a gas-insulated system, the GIL has the advantage of electrical behavior

similar to that of an overhead line, which is important to the operation of the

complete network. Because of the large cross section of the conductor, the GIL has

low electrical losses compared with other transmission systems (overhead lines and

cables).

This reduces the operating and transmission costs, and it contributes to reduction ofglobal warming because less power needs to be generated.

Safety of personnel in the vicinity of a GIL is very high because the solidmetallicenclosureprovides reliable protection. Even in the rare case of an internal failure,

the metallic enclosure is strong enough to withstand damage. This allows the use

of GILs in street and railway tunnels and under bridges with public traffic. No

flammable materials are used to build a GIL. The use of GILs in traffic tunnels

makes the tunnels more economical and can solve some environmental problems.

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If GIL is added to a traffic tunnel, the cost can be shared between the electric

power supply company and the owner of the traffic part (train, vehicles).

The environmental advantage is that no additional overhead line needs to be built

parallel to the tunnel. Because of the low capacitive load of the GIL, long lengths

of 100 km and more can be built. Where overhead lines are not suitable due to

environmental factors or where they would spoil a particular landscape, the GIL is

a viable alternative because it is invisible and does not disturb the landscape.

GIL Construction

The GIL consists of three single-phase encapsulated aluminum tubes that can be

directly buried in the ground or laid in a tunnel. The outer aluminum enclosure is at

ground potential.

Gas-Insulated Transmission Line - Contruction

The interior, the annular space between the conductor pipe and the enclosure, is

filled with a mixture of gas, mainly nitrogen (80%) with some SF6 (20%) to

provide electrical insulation. A reverse current, more than 99% of the conductor

current value, is induced in the enclosure. Because of this reverse current, the outer

magnetic field is very low.

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GIL combines reliability with high transmission capacity, low losses, and low

emission of magnetic fields. Because it is laid in the ground, GIL also satisfies the

requirements for power transmission lines without any visual impact on the

environment or the landscape. Of course, the system can also be used to supply

power to meet the high energy demands of conurbations and their surroundings.

The directly buried GIL combines the advantage of underground laying with a

transmission capacity equivalent to that of an overhead power line.