Controlled resistive loads can contribute to damping of electro-mechanical
oscillations. This paper presents an on-off damping controller for a single
machine system. It was used aat a field test in southern Sweden to damp os
cillations of a 0.9 MW hydro power generator. The controller used estimated
machine frequency as input and controlled a 20 kW resistive load via thyri
stor switches. The field measurements are compared to time simulations and
a systematic procedure for tuning the controller is given. the results indi
cate that on-off control of active loads is effective in terms of added dam
ping and that it is simple to tune and implement.