Stevenson J. Power system analysis

636

CHA

ER 14

Zhus

METHODS IN CONTINGENCY ANALYSIS

employed or else a

approach. In practice, it is found desirable to maintain

a bue r zone of the external system around the internal system when evaluating

contingencies on the latter. Within the buer zone certain generator (P-V)

buses are retained since they oer a means of voltage and reactive power

support for the internal system.

In faul t studies the individual operating utility represents the neighboring

systems by a reduced equivalent based on the

Zbus

of the external system. This

reduced equivalent corresponds to a submatrix extracted from the external

system Zbus,

as demonstrated in Sec. 14.2. It is worthwhile for the reader to

observe

that the Ward equivalent obtained in Fig. 14.14(a) by gaussian elimina

tion coincides with that obtained in Fig. 14.1O(c) by extracting a submatrix from

the

bus

of System II.

14.7 SUMM

This chapter explains the application of

methods to contingency analysis. It

is shown that these methods are very useful in predicting line-