GB552279A - Improvements in or relating to steam turbine regulating systems - Google Patents

Abstract

552,279. Fluid-pressure servomotor-control systems. AKT.-GES. BROWN, BOVERI & CIE. March 4, 1942, No. 2855. Convention date, March 4, 1941. [Class 135] [Also in Group XXVI] The inlet valves 6 and the interstage valves 7 of an extraction turbine take up positions corresponding to the pressures obtaining in pipes Pf and Pu and in the spaces V, W above pistons 10, 11. These pressures are determined by the positions of the free pistons 10, 11 which move until the pressure Pn, Pe of fluids in pipes 22, 23 and varying in accordance with the turbine speed and the extraction pressure are balanced by the pressures Pf and Pu. These last pressures are applied in mutual support to the piston 10 controlling the inlet valves and in opposition to the piston 11 controlling and interstage valves. The pressure Pn in the pipe 22 varies inversely as the turbine speed by reason of a leak 4 controlled by a speed governor 1, and is admitted freely to the spaces R below the pistons 10, 11. Pressure fluid from a common oil pump 2 passes through a pipe 29 and a diaphragm 17 into spaces T, S and its pressure Pe varies inversely as the extraction pressure in the pipe 27 by reason of a leak 20 controlled by a pressure-responsive device 19. The pressure fluid is admitted freely into the spaces S, T to operate on the underside of a piston flange on the piston 10 and on the upper side of a piston flange on the piston 11. Fluid from the common oil pump 2 is conveyed by the pipe 29 to spaces V, W above the pistons through control ports in the pistons and escapes therefrom by the same ports into a space 18 and a discharge pipe 35. In normal operation, both pistons 10, 11, at a variation of either or both of pressures Pn, Pe, move and opens their control ports to permit the admission of pressure oil into the spaces V, W from the pipe 29, or, the leak of pressure oil from those spaces into the space 18, until the pressures in the spaces V, W re-establish a balance and the pistons 10, 11 return to the positions in which their control ports are closed. The valves 6, 7 simultaneously move to new settings corresponding to the adjusted valves of the pressures Pf, Pu in the spaces, V, W. Special provision is made for abnormal working. When the inlet valves 6 are fully open. A demand for more power can be met only by permitting the extraction pressure to fall. The valves 6 arrive at their fully open position only when the pressure in space V is at its maximum so that a further increase in the pressure in space R due to a fall in turbine speed cannot be balanced by an increase in the pressure in space V. Piston 10 therefore rises until ports B provide a leak for the fluid in spaces S, T and obtain a balance for the piston by reducing the upward pressure on the flange piston. Under these conditions, owing to the fall in the extraction pressure the leak 20 is closed, the pressure Pe is maintained as a function of the turbine speed and both valve groups 6 and 7 are under the control of the speed governor only. When the interstage valves 7 are fully open. An increase in the turbine load or a decrease in the extraction would result in an excessive extraction pressure. To avoid this, the plant is controlled by the extraction pressure. The valves 7 being fully open, the pressure in space W is at its maximum and an increase in the extraction pressure causes the piston 11 to rise until the piston edge C opens a leak from the space R through a valve 14 into the space 18 and obtains a balance by reducing the pressure in space R. The speed governor controlled leak 4 is under these circumstances closed owing to the fall in turbine speed and accordingly the pistons 10, 11 and the valve groups 6, 7 are controlled by the extraction pressure only. In cases where an excess extraction pressure is permissible, the action of the edge C can be prevented by turning a valve 14. When the interstage valves are fully shut. An increase in extraction or decrease in load would result in excessive turbine speed since the pressure in space R having reached a minimum could not diminish further to counterbalance an increase of the pressure of the piston flanges. In this case, the piston 11 moves downwards until ports A provide a leak from space T into space 18 in place of the leak 20 now shut. Both pressures Pn and Pe are thus under the control of the speed governor. When extraction steam is not required. Cock 12 is turned to cut off the leak 20 from the spaces S, T and to substitute a leak 18 of fixed value, and cock 13 is turned to connect the pipe 31 with a space U in which the full pump pressure Pp obtains. In a plant operating alternatively as an extraction turbine and a mixedpressure turbine, the pistons 10, 11 are loaded by springs, the spring on the piston 10 working with the pressure in space V and the spring on the piston 11 working with the pressure in space R.