GB414780A - Improvements in and relating to elastic fluid turbines - Google Patents

Abstract

414,780. Steam turbines. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London, and COLLINGHAM, R. H., 81, Hillmorton Road, Rugby. Feb. 16, 1933, No. 4802. [Class 110 (iii).] In order to prevent racing of turbines when the load is suddenly reduced, means are provided for cutting out or reducing the period of lag of the governor before the steam admission valve commences to close. In operation these means close the admission valve quickly independently of the governor, which subsequently regains control. In Fig. 1, the admission valves 2 are positioned during normal running by an oscillating-vane type servo-motor 7 controlled by a pilot-valve 14 which is influenced by a speed-governor 8 through linkage 9, 10, and a sleeve 11 which regulates the oil-leakage port 12 in the hollow movable centre part 16 of the valve. Normally, pressure oil passing through small ports 15 keeps the centre part 16 in a raised position against the action of a spring 13. A pipe 24 connects the space beneath the centre part to a valve 17, which is normally closed to maintain the pressure in this space. If, however, the load on the turbine is suddenly reduced, a solenoid 18 is energized, the valve 17 is opened thus releasing the pressure beneath the centre part 16, and this part is forced down by the spring 13. The pilot-valve now supplies pressure oil to the servo-motor to close the steam admission valves independently of the governor. The solenoid 18 may be energized when a switch 19 is closed as by the opening of the main switch 23 of the generator circuit. The follow-up rack-rod 6 has a contact 22 adapted to open a switch 20 in the circuit of the solenoid 18 in order to de-energize it as the valves 2 close, so that the governor may again take up control under idly-running conditions. A switch 21 is provided for breaking the circuit on starting-up on no-load, as with the switch 32 open. Fig. 2 shows a modification in which a governor-controlled pilot-valve 36 positions the servo-motor piston 34 of the turbine admission valve 32 under normal conditions, and in which a second pilot-valve 46 is provided. Normally this second valve is inoperative, but should the load be decreased suddenly, as by the opening of the main generator switch 44, a solenoid 49 is energized and lifts the centre-part of the pilot valve 46, so that the pilot-valve 36 is rendered inoperative, and at the same time, pressureoil is admitted to the servo-motor in order to close the valve 32. A contact 40 on the servomotor rod is arranged to open a switch 42 in the circuit of the solenoid 49 as the valve 32 closes in order that the pilot-valve 46 may return to normal position and allow the governor 38 to take up control under idly-running conditions. A switch 41 is provided for breaking the circuit on starting up on no-load.