Interaction between AVR reactive power control and high power ac-dc Converter Control as possible cause of instability

Two oscillatory episodes took place in the Argentinean power system at 22:20 and 22:50, June 7th, 2008. The first one started when a 40 MVAr capacitors bank was disconnected and the second one started when a 500 kV line was disconnected. Both oscillatory episodes produced great variation of active and reactive power in several 330 kV and 500 kV power system nodes. At first sight, these oscillations seemed inter-area electromechanical oscillations, but carried out studies suggest that this oscillatory behavior could be a consequence of interaction between Reactive Power Control of generators and the ac-dc Converter Control of high power loads.