Evaluation of unit connected, variable speed, hydropower station for HVDC power transmission

An economic alternative to the conventional design of a hydropower station which feeds power into a HVDC transmission line is described. A method is developed to operate hydraulic turbines under variable speed to maximize the turbine efficiency, taking the loading and water head connections into account. A 10×100 MW unit-connected hydroelectric power station is analyzed. A 500 MW unit-connection scheme which represents one pole of the above station is simulated in the time domain using the electromagnetic transient program. The harmonic currents flowing in the stator and rotor circuits of the generator are computed, and derating factors at 60 Hz and 70 Hz operation are evaluated. Economic evaluation has been performed for a 10×100 MW hydrostation for both conventional and unit-connection configurations. Savings achieved by adopting the unit-connection scheme are presented