Coherency-Based Dynamic Equivalents: Applications in Transient Stability Studies

R.W. DeMello, R. Podmore and K.N. Stanton, PAS 95, No.4, July/August 1976, p.1101 (abstracts)

The paper describes the development of a method for determining an equivalent dynamic representation of an external power system for use in transient stability studies. The resulting equivalent is composed of normal power system models element and therefore can be used with conventional transient stability programs. The approach used exploits generator coherency, which is the tendency for groups of generators to swing to gether.

The performance of of the coherency-based dynamic equivalents has been evaluated by tests on 10-generator, 39-bus system and a 295 generator, 732-bus system. Comparison of swing curves have demonstrated that the technique is accurate for both first and successive swings and that the accuracy is unaffected by the prevailing stability conditions. On the larger system, the method has archived greater than 10:1 reduction in the size of the external system representative.

The coherency-base dynamic equivalents have the potential for application as a production tool in planning studies and represent a key step in the future development of on-line transient security monitoring procedures