The
equipment cost of GIS is naturally higher than that of AIS due to the grounded
metal enclosure, the provision of an LCC, and the high degree of factory
assembly.
The GIS
space advantage over AIS increases. GIS can now be considered for any new
substation or the expansion of an existing substation without enlarging the
area for the substation.
A GIS is
less expensive to install than an AIS.
The site development costs for a GIS will be
much lower than for an AIS because of the much smaller area required for the
GIS.
The site
development advantage of GIS increases as the system voltage increases because
high voltage AIS take very large areas because of the long insulating distances
in atmospheric air.
Cost
comparisons in the early days of GIS projected that, on a total installed cost
basis, GIS costs would equal AIS costs at 345 kV.
For higher
voltages, GIS was expected to cost less than AIS.
However, the
cost of AIS has been reduced significantly by technical and manufacturing
advances (especially for circuit breakers) over the last 30 years, but GIS
equipment has not shown any cost reduction until very recently.
Therefore,
although GIS has been a well-established technology for a long time, with a
proven high reliability and almost no need for maintenance, it is presently
perceived as costing too much and is only applicable in special cases where
space is the most important factor.
Currently,
GIS costs are being reduced by integrating functions as described in the
arrangement section above. As digital control systems become common in
substations, the costly electromagnetic CTs and VTs of a GIS will be replaced
by less-expensive sensors such as optical VTs and Rogowski coil CTs.
These less-expensive
sensors are also much smaller, reducing the size of the GIS and allowing more
bays of GIS to be shipped fully assembled.
Installation
and site development costs are correspondingly lower.
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