Substations can be built in part or in whole in overhead or Ground Substation.
However, the cost is high and the need for fire protection and heat dissipation increases the complexity. The following discussion focuses on Bus Design in Ground Substations.
Air-insulated substations (AIS)
The bus and associated substation equipment are exposed and directly visible. An open-air bus can be multi-level or spread over one level. Metal or wood structures and insulation support these bus and power line terminations.
If space permits, the lowered bus layout is generally preferable for aesthetics and easier to conceal in landscapes, walls, and enclosures.
Overhead transmission line termination structures are taller and more difficult to conceal in such an arrangement.
In dry climates, a low profile bus can be achieved by digging out the land area, in which outdoor bus facilities are then located for an even lower profile.
Metal-enclosed or shielded switchgear models that house the bus and associated equipment in a metal enclosure provide an alternative design for distribution voltages. These designs provide a compact, low-profile installation that may be aesthetically acceptable.
Gas-insulated substation (GIS)
Buses and associated equipment can be housed in tube-type enclosures using sulfur hexafluoride or other similar gas for insulation. This not only achieves considerable compactness and reduced site preparation for higher voltages, but it can also be installed lower.
A GIS can be an economically attractive design where space is an important factor, particularly if a building type enclosure will be used to house substation equipment ( see IEEE Std. C37.123-1996 ).
Small sections of overhead or underground cables can be used at substations, although this use is normally limited to distribution voltages ( for example, for feeders or connections between transformers ).
At higher voltages, an underground cable can be used for line inputs or to solve a specific connection problem.
Audible noise, especially discrete sounds constantly emitted (eg from power transformers), is the type of noise that the community may find unacceptable.
Community guidelines to ensure that the noise levels maintained can take the form of government regulations or individual = community reactions (denial of permits, the threat of complaint to utility regulators, etc.).
When noise is a potential concern, field measurements of background noise levels and computer simulations to predict substation impact may be required. The cost of implementing noise reduction solutions (low noise equipment, barriers or walls, noise cancellation techniques, etc.) can become an important factor when selecting a site.
Noise can be transmitted as a pressure wave either through the air or through solids. The majority of cases involving the observation and measurement of noise related to the propagation of noise in the air. However, rare instances of audible transformer noise have appeared at distant vantage points propagating through the transformer foundation and solid rock formations ground substations.
It is best to avoid the situation by isolating the foundations from the bedrock where conditions seem to favor the transmission of vibrations.