Industry standards dictate certain
analytical techniques that adhere to specific guidelines, suited to
address the questions of ac and dc decrement in multimachine systems
in compliance with well-established, industry-accepted practices.
They are also closely linked to and
harmonize quite well with existing switchgear rating structures.
Typical standards are the North American ANSI and IEEE C37 standards
and recommended practices the international standard, IEC 60909
(1988) and others, such as the German VDE 0102-1972 and the
Australian AS 3851-1991.
The analytical and computational
framework in the calculating procedures recommended by these
standards remains algebraic and linear, and the calculations are kept
tractable by hand for small systems.
The extent of the data base
requirements for computer-based solutions is carefully kept to a
necessary maximum for the results to be acceptably accurate. This
type of analysis represents the best compromise between solution
accuracy and simulation simplicity.
The great majority of commercialgrade
short-circuit analysis programs fall under this category. In 7.4.1,
an outline of ANSI and IEEE standards is presented, while in 7.4.2,
the relevant aspects of IEC 60909 (1988) are described. It is not the
intent of these subclauses to fully explore and describe in detail
all pertinent clauses of either standard.
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