# Transient Stability Calculations by Computer

It is obvious that a digital computer program can be readily written to carry out the simple studies of Section 8.5. If a load-flow program is readily available, then improved accuracy will be obtained if, for each value of dn, the actual power output of the generators is calculated. At the same time, the effect of the excitation system and the governor movement can be included. Such calculations make use of numerical integration packages based on mathematical concepts. Techniques such as trapezoidal integration provide fast and sufficiently accurate results for many stability studies; more accurate techniques, such as Runge-Kutta (fourth order), predictor-corrector routines, and so on, can be employed if the improved accuracy and longer run times can be economically justified. Most commercial stability programs offer various options for inclusion of generator controls, system switching and reclosing, compensator modelling, and transformer tap-change operation, according to some input criteria. Packages dealing with 1000 generators, 2000 lines, and 1500 nodes are available.

Example 8.4

Consider the network of Figure 8.10. Data for generators, transformers, lines and loads are given in Tables 8.2-8.5

Figure 8.10 Network for Example 8.4

Table 8.2 Generator data

 G1 G2 G3 Rating (MVA) 750 750 250 Xs (p.u) 1.7 1.7 1.6 Rs (p.u) Xd'(p.u) 0.05 0.05 0.06 0.35 0.35 0.3 Xd" (p.u) 0.25 0.25 0.25 Td' (s) 8.0 8.0 8.0 Td" (s) 0.03 0.03 0.03 H(s) 6.5 6.5 6.0

Table 8.3 Transformer data

 T1 T2 T3 Rating (MVA) 750 750 250 Xi (p.u) 0.15 0.15 0.12 R (p.u) 0 0 0

Table 8.4 Line data

 LN1 LN2 LN3 LN4 X(V) 115 115 115 9 R(V) 11 11 11 0.9 Y(mS) 1450 1450 1450 115