When the Cheylas station, equipped with two 250 MW pump turbines under 250m head, was put into service, a large testing programme was undertaken to analyse the behaviour of these machines in main normal and transient operating conditions. The operation of pump turbines requires daily start ups and shutdowns, with or without a change in the direction of rotation. Their frequent operation outside the range of optimum use should not engender abnormal wear of equipment. It is thus important to know the stresses to which these reversible machines are subjected during transient operating conditions, including turbine or pump trip when the gate operating mechamism is blocked in the open position. The present paper analyses the results of tests performed on pump start up, turbine and pump trip with the gate operating mechanism open, on-load cuts and operating in compensator mode. (from English abstract)

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