Observed hybrid oscillations in an electrical distribution system

Slow oscillations, with a period of around 15 minutes, were observed in an 11 kV electrical distribution system. Investigations determined that the oscillations were a result of interactions between tap-changing transformers and switched capacitors. Analysis required a hybrid systems framework, due to the non-smooth (switched) nature of these interactions. It was found that the oscillations could be suppressed by adjusting the lower limit of the capacitor deadband. A grazing bifurcation separated oscillatory from steady-state behaviour.