Dynamic equivalents using operating data and stochastic modeling

A method is developed to determine equivalents for extensive power systems external to an internal system equipped with a central control computer. These equivalents are needed for different system studies where the internal system is represented in detail, and the external system is represented by the equivalent to simulate the interaction effects of the external system on the internal system for disturbances originating in the internal system. The method uses a generalized Thevenin´s theory for representing the quasi-steady-state performance of the external system and stochastic linear difference equations to represent the dynamic changes in the internal equivalent voltage magnitudes and phase angles. The methods are demonstrated on two test systems.