Test Cases Library of Power System Sustained Oscillations

Natural oscillation case ND_1 (Back to the homepage)

This case is a single source - single local mode natural oscillation case, where the oscillation source is generator 45.

System model:

All generators are in GENCLS model.

Parameter D for generators 45 and 159 equals -2 and 1, 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 low damping of 0.01%.

Disturbance location at bus 159 provides the largest excitability of the 1.41Hz mode.

Observation from transient:

Largest oscillation magnitude in bus angle is observed at bus 159, which is not the source.

Figure 1. WECC 179-bus power system

Fig. 2 shows the spectra of oscillations and Fig. 3 shows the rotor angles for generators 45 and 159. This case has one lightly damped local mode 1.41Hz and the source of negative damping is the generator 45.

Figure 2. Spectra of oscillations for the case ND_1

Figure 3. Rotor angles of generator 45 and 159 in the case ND_1

The specifics of this case is that a fault at generator 159 excites the maximal magnitude of rotor angle oscillations at generator 159 while the source of oscillations is actually located at another generator, i.e. generator 45.