Small signal analysis of hydro-turbine governors in large interconnected power plants

The paper describes a transient stability program (TSP) based approach to identify numerically, a state-space, small-signal model of the open-loop system seen by the hydro-turbine governor during its normal operation. This single-input multiple-output model is validated successfully by comparing actual closed-loop responses computed in the TSP with those simulated in Matlab using the linearized model. For illustration, three governing systems found in the Hydro-Quebec´s grid are studied: (1) a mechanical hydraulic; (2) a Woodward PID; and (3) a classical Neyrpic´s governor. System performance with respect to the speed of response, interarea modes sensitivity and closed-loop gain and phase margins is assessed, evidencing the somewhat detrimental impact of the derivative control term for interconnected operation. Overall, the small-signal analysis approach devised appears well-suited for determining and/or assessing unit-connected settings of hydro-turbine speed governing systems.