Test Cases Library of Power System Sustained Oscillations

Natural oscillation case ND_7 (Back to the homepage)

This case contains two sources, i.e. generators 45 and 159, with different contributions into a single unstable local mode.

System model:

All generators are in GENCLS model.

Parameter D for generators 45 and 159 equals -0.5 and -0.5, respectively.

Parameter D for all other generators equals 4.

All loads are in constant MVA model.

Disturbance:

A three-phase short circuit is added at bus 159 at 0.5s and cleared after 0.05s.

Small signal analysis:

The local mode at 1.41Hz has a negative damping of -0.40%.

Figure 1. WECC 179-bus power system

The specifics of the cases ND_6 and ND_7 is as follows. Sensitivity of real part of the associated eigenvalue to variation of damping coefficient D for generator 159 is two times higher than that for generator 45. Thus, the contribution in negative damping of generator 159 is twice comparing to generator 45 in case ND_7 despite they have the same values of D.