Many factors influence the selection of the proper type of substation for a given application. This selection depends on such factors as voltage level, load capacity, environmental considerations, site space limitations, and transmission-line right-of-way requirements.

While also considering the cost of equipment, labor, and land, every effort must be made to select a substation type that will satisfy all requirements at minimum costs. The major substation costs are reflected in the number of power transformers, circuit breakers, and disconnecting switches and their associated structures and foundations.

Therefore, the bus layout and switching arrangement selected will determine the number of the devices that are required and in turn the overall cost. The choice of insulation levels and coordination practices also affects cost, especially at EHV. A drop of one level in basic insulation level (BIL) can reduce the cost of major electrical equipment by thousands of dollars.

A careful analysis of alternative switching schemes is essential and can result in considerable savings by choosing the minimum equipment necessary to satisfy system requirements. A number of factors must be considered in the selection of bus layouts and switching arrangements for a substation to meet system and station requirements.

A substation must be safe, reliable, economical, and as simple in design as possible. The design also should provide for further expansion, flexibility of operation, and low maintenance costs. The physical orientation of the transmission-line routes often dictates the substation’s location, orientation, and bus arrangement. This requires that the selected site allow for a convenient arrangement of the lines to be accomplished.

For reliability, the substation design should reduce the probability of a total substation outage caused by faults or equipment failure and should permit rapid restoration of service after a fault or failure occurs. The layout also should consider how future additions and extensions can be accomplished without interrupting service.

Traditional and Innovative Substation Design
Traditionally, high-voltage substations are engineered based on established layouts and concepts and conservative requirements. This approach can restrict the degree of freedom in introducing new solutions.

The most that can be achieved with this approach is the incorporation of new primary and secondary technology in preengineered standards. A more innovative approach is one that takes into account functional requirements such as system and customer requirements and develops alternative design solutions.

System requirements include elements of rated voltage, rated frequency, system configuration present and future, connected loads, lines, generation, voltage tolerances (over and under), thermal limits, short-circuit levels, frequency tolerance (over and under), stability limits, critical fault clearing time, system expansion, and interconnection.

Customer requirements include environmental consideration (climatic, noise, aesthetic, spills, right-of way), space consideration, power quality, reliability, availability, national and international applicable standards, network security, expandability, and maintainability. Carefully selected design criteria could be developed to reflect the company philosophy.

This would enable consideration and incorporation of elements such as life-cycle cost, environmental impact, initial capital investment, etc. into the design process. Design solutions could then be evaluated based on established evaluation criteria that satisfy the company interests and policies.

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