Test Cases Library of Power System Sustained Oscillations

Natural oscillation case ND_4 (Back to the homepage)

This case contains single source, one unstable inter-area mode and two poorly damped local and inter-area modes, where the oscillation source is generator 11.

System model:

All generators are in GENCLS model.

Parameter D for generators 6 and 11 equals 5 and -9, 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 6 at 0.5s and cleared after 0.05s.

Small signal analysis:

The local mode at 1.63Hz has a low damping of 0.54%.

The inter-area mode at 0.70Hz has a negative damping of -0.58%.

The inter-area mode at 0.46Hz has a poor damping of 0.68%.

Figure 1. WECC 179-bus power system

Fig. 2 illustrates the case ND_4, where 0.70 Hz mode has negative damping and two other modes (one local and one inter-area) are slightly damped.

Figure 2. Spectra of oscillations for the case ND_4

Figure 3. Rotor angles in the case ND_4. Blue curve is the angle of generator 11 creating negative damping