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Main single line diagram

Major considerations for the selection of an economical and suitable main single line diagram and switching scheme for a substation are voltage level, site limitation and general and special considerations’وDesign of 33kV switchyard (equipment, SLD, and layout) for small hydro-power plant

Voltage level

Power carrying capability of transmission lines increases roughly as the square of the voltage. Accordingly disconnection of higher voltage class equipment from bus bars get increasingly less desirable with increase in voltage levels. High structures are not desirable in earthquake prone areas.

Therefore in order to obtain lower structures and facilitate maintenance it is important to design such substations preferably with not more than two levels of busbars.

Site considerations

Practical site consideration at a particular location e.g. lack of adequate flat area for layout of equipment in the substation may also influence the choice in such locations. Pollution caused by location near to sea or some other contaminated atmosphere may also affect layouts.

At some locations completely indoor substations may be require former bank as a unit on the high-voltage side only, is shown in Figure 1. The unit scheme is well suited to power systems where loss of large blocks   of a