Generator Damper Windings at Wilson Dam

The majority of water-wheel generators now in service have been built without damper windings. Recent technical investigations and laboratory tests have indicated that, in addition to reducing oscillations and improving system stability, damper windings are very effective for reducing high-peak voltages during unbalanced short circuits. This applies particularly under switching conditions of clearing a fault when the load is disconnected from the distant end of a transmission line, and the charging current results in capacitive loading of the unfaulted phases. The existence of similar overvoltage conditions was recognized by the Wilson Dam operating staff and later confirmed by oscillograms during tests. This paper summarizes the studies and tests based on the observed overvoltage conditions and describes a method for adding damper windings to large water-wheel generators which are already installed. Short-circuit tests are extended to generators on a large scale which confirm the earlier theoretical and laboratory tests and demonstrate the advantages to be gained by adding damper windings to other water-wheel generators now in service. The tests show that damper windings in one generator when operated in parallel with another generator without dampers are effective in reducing high-peak voltages during unbalanced faults. Data are given to show the changes in machine reactances due to adding damper windings.