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 power
transmission 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 of global warming
because less power needs to be generated.
Safety of personnel in the vicinity of a GIL is very high because the solid metallic enclosure
provides 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.
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 - Construction |
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.
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.
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