Transmission system open access versus system reliability: a case history-the MAPP disturbance of June 25, 1998

On June 25, 1998 an event occurred in which a large area of the North American mid-continent area power pool (MAPP) region became separated from the rest of the Eastern interconnection. The separated area had about 14,000 megawatts of generation at the time. While significant load was lost during the event, the fact that the area was exporting and thus had excess generation allowed frequency to stabilize, and most affected systems were reconnected to the grid within an hour after the initial event. The event was triggered by the loss of two major interconnections. A disturbance report for the event made a number of conclusions and recommendations. The report identified a need for improved procedures to quickly return the system to a secure state after a major contingency. Although not cited as a direct cause, the report discusses the difficulty system operators face in the deregulated environment when an outage makes the system not secure to withstand another severe contingency. Current procedures to reduce transfers across an interface prioritize transactions to be reduced and rely on complex system models and software. They are not well suited to rapidly returning the system to a secure state.