Most stations initially start with a ring bus scheme which includes
both step-down and generating unit transformers with
provision for expansion to a 1 '/r-breaker scheme in the future.
Generating unit transformers will be connected in the 1 1/r
breaker positions, but step-down transformers will be connected
directly to the main buses via motor-operated switches. The
ring bus with its lower initial cost per line terminal will suffice until
such time as the growth of the 765-kV system requires the
greater reliability of the 1 '/r breaker scheme. The station design
forces conversion to a 1 /2-breaker arrangement when more than
six elements (lines and/or transformers) are to be accommodated.
i(Fig. 1 indicates an ultimate one-line diagram for a major
station.)