Von Karman Hydraulic Vortexes Cause Stay Vane Cracking on Propeller Turbines at the Little Long Generating Station of Ontario Hydro

Abstract

Little Long Generating Station is situated about 500 miles north of Toronto and is one of four plants located close together on the Mattagami River which flows into Hudson Bay. Some 500 MW of power is transmitted at 500 kv to Sudbury and Toronto (Fig. 1). There are two turbines at Little Long Generating Station. Almost immediately from the time when the first unit was being commissioned and operated under load, field reports referred to what was said to be an abnormally high level of noise and vibration. When the second unit came into service, similar findings were reported. About six months after commissioning, the units were unwatered and a detailed inspection indicated that the stay vanes forming the speed ring contained numerous and serious fatigue cracks. The final diagnosis indicated the damage to be a result of what is now usually referred to as von Karman hydraulic vortexes. Because immediate repairs were required and in order to insure the future structural adequacy of the speed ring, it was decided to change the stay vane profile at the same time, in an attempt to eliminate the excitation due to von Karman vortexes, hoping thereby to avoid further damage of the stay ring after the repairs. Recent inspections of both units show that both the modifications and the final repairs were completely successful.