LECCIÓN 1: 

Engineers working on the power station design should consider the character of the load and the necessity for maintaining continuity of service. It should be as simple in the arrangement as practicable to secure the desired flexibility in operation and to provide the proper facilities for inspection of the apparatus.

A review of existing supply installations shows that the apparent combinations are innumerable, but analysis indicates that in general, they are combinations of a limited number of fundamental schemes. The arrangements vary from the simplest single-circuit scheme to the involved duplicate systems installed in big cities where the importance of maintaining continuity of service justifies a high capital expenditure.

In some installations supplying underground cable systems in cities, segregated-phase layouts have been and are still employed to secure maximum reliability in operation. However, their use seems to be on the decline, as the improvement in performance over the conventional adjacent phase grouping is not sufficiently better to justify the extra cost. However, this statement depends from country to country.

This is particularly important in view of the continuing improvement of protective equipment and the more reliable schemes of relaying available today for removing faulty equipment, buses, or circuits.