Abstract: A pump turbine makes frequent startup and halt under rapid changes in its working conditions, and its internal flow patterns are usually complicated. During operation under different working conditions, the top cover is subjected to complex water thrusts; the high-strength bolts, tightening it on the seat ring, suffer a great variation in both stress level and its change rate. The bolt stress of top cover is directly related to operation safety, so it is necessary to understand its variations under typical operating conditions. This study conducts a prototype measurement of bolt stress for a unit at the Baoquan pumped storage power station. A resistance strain method is adopted to collect the bolt stress data through measuring micro-strain at four points evenly arranged on the middle section of the stud for various test conditions－bolt preloading process, full load turbine operation, load rejection process, zero flow pump condition, and pump normal operation. This will lay a basis for evaluating the top cover bolts and unit operation safety, and help improve the bolt design.

Key words: pumped storage, pump turbine, bolt of top cover, stress measurement, resistive strain method