Development of load models for fault induced delayed voltage recovery dynamic studies

As a result of a multiple contingency fault and breaker failure event at two Metro Atlanta 230 kV substations in 1999, Southern Company experienced a wide area voltage depression lasting around 15 seconds. The event resulted in a 1900 MW load loss. Dynamic simulations utilizing standard static stability load models were not successful in replicating the event. However, the actual response of the transmission system was replicated utilizing dynamic simulations with aggregate load models that included the effect of induction motors and distribution system impedances. Since the event in 1999, load has grown exceptionally in the North Georgia region. As a result of the load growth, capital projects are being implemented in Southern Company to appropriately manage the exposure to both NERC reliability standard category B and D fault induced delayed voltage recovery events. Therefore, it is critical that the load models used in dynamic studies correctly represent the behavior of actual load. This is necessary to ensure that the timing and effectiveness of capital projects are appropriately quantified. Both the formulation of the aggregate load models used to replicate the 1999 event, and ongoing efforts to refine the load model used to assess future exposure to fault induced delayed voltage recovery are discussed in this paper.