GB1228445A - - Google Patents

Abstract

1,228,445. Hydraulic turbines. INTREPRINDEREA PENTRU RATIONALIZAREA SI MODERNIZAREA INSTALATIILOR ENERGETICE. April 10, 1968 [April 10, 1967], No.17172/68. Heading F1T. A method of operating a hydraulic turbine plant . having first and second control means and a speed control for controlling the speed of the turbine by varying the first control means comprises the steps of operating the first control means to maintain the speed constant and then temporarily operating the first control means as a power control to maintain the turbine output power, instead of speed, constant at its immediately previous value, varying the second control means until the minimum flow through the turbine for that power has been found, and thereafter again operating the first control means as a speed control to maintain the speed constant. The plant includes a Kaplan type axialflow turbine 25 driving a generator 26 supplying a load 27, the turbine having adjustable guide and rotor blades. During normal operation the speed of the turbine 25 and hence the frequency of the generator 26 is maintained constant by comparing the actual frequency f with a reference frequency f o in a comparator 28, the error signal E f causing the governor 14 to alter the angle α of the guide blades so reducing the error to zero. A proportional element 15, which may be a cam, is arranged to alter the rotor blade angle # by an amount appropriate to the change in α so as to maintain maximum turbine efficiency. When the guide blade angle α exceeds a predetermined value a transducer 24 emits a signal p causing switching elements 11, 12, 13 to switch over. Governor 14 now acts to maintain generator power, instead of speed, constant by comparing in unit 29 the actual power P monitored by a sensor 20 with a value P c fed from a memory 21 and corresponding to the power immediately before switch over, the error signal E p causing governor 14 to adjust the guide blade angle α until the power returns to P c . Simultaneously element 12 switches control of the rotor blade angle from cam 15 to a sampling system comprising a servomotor 16, signal generator 17, derivative element 18 and sensor 19. The element 18 compares the change in flow dQ with the change in rotor blade angle d# and the sensor 19 acts to ensure that the angle # is altered to reduce the flow Q to the minimum value for the selected power and thus increase efficiency. The signal p from the transducer 24 accordingly disappears and the switches 11, 12, 13 return to their original positions thereby returning the turbine to speed control. The change from speed to power control may also be initiated by devices 22, 23 detecting changes in the upstream and downstream water levels in excess of predetermined amounts. In a modification, control of the turbine blades is inter-changed so that the rotor blade angle # is controlled by the governor 14 and the guide blade angle α by the cam 15 or sampling system. In a further modification the sampling system is replaced by a manual control of the blade angle.