Abstract: A hydraulic circuit branch of a cooling system in thermal contact with the stator winding of a hydraulic power generator is provided with a feed tube divided into two separate input tube sections. The downstream ends of the input tube sections are connected to respective multiplicities of subsidiary hydraulic circuit branches in the form of winding bars via a pair of semicircular manifolds. The current throughput through the winding bars is monitored by determining the difference between the rates of coolant flow through the approximately identical input tube sections. If the rates of coolant flow or throughputs in the input tube sections differ from one another by an amount which itself differs from a predetermined reference value by more than a preselected threshold, a warning signal is generated indicating that heat removal from the hydraulic power generator is being impaired.