Reducing the effect of penstock pressure pulsations on hydro electric plant power system stabilizer signals

A characteristic trait of Francis turbines operating at low-head is pressure pulsations that occur during certain load levels of the generator. These stem from pressure variations across the turbine due to pulsating flow in the draft tube. This surging action of the water column is related to draft tube geometry and flow rate of water in the penstock. The pressure pulsations cause torque variations on the turbine and corresponding electric power pulsations. If electric power is used as a feedback signal to the power system stabilizer (PSS), then MVAr and terminal voltage pulsations will occur when the generator is operating in the "rough zone". This paper describes field test results for investigating feedforward control from the penstock, draft tube and spiral case pressure to reduce the effects of MW pulsations on PSS output signals. This investigation involved a PSS with generator power as the feedback signal and the PSS tuned for local and inter-area damping