Experience with HVDC - Turbine-Generator Torsional Interaction at Square Butte

Tests on the the modern HVDC system at Square Butte conducted in October 1977 indicated that the HVDC terminal was interacting in an adverse way with an 11.5-Hz torsional mode of an adjacent turbine- generator unit. Subsequent analytical work duplicated the field test observations and was used to develop an understanding of the HVDC-torsional interaction phenomena. As a result of the analytical work, the control system of the HVDC terminal was modified and subsequent tests showed that the changes resulted in stable operation. The paper includes significant field test and analytical results.