Patent GB-794583-A (GB)
Title: Improvements in or relating to protective systems for gas turbine propulsion power plants
Inventor: HOOKER STANLEY GEORGE
IPC: F02C3/04
Filed: 1955-06-27
Abstract: 794,583. Gas turbine plant stop-gear. BRISTOL AERO-ENGINES, Ltd. June 19, 1956 [June 27, 1955], No. 18541/55. Classes 110 (3) and 122 (4). In a gas turbine power plant, particularly for aircraft propulsion, comprising a turbine coupled by a mechanical transmission to a screw propeller and a compressor in flow series with and upstream of the propeller-driving turbine and driven by that or a separate turbine, a protective system to prevent overspeed of the propeller-driving turbine in the event of failure of the transmission between it and the propeller comprises a fuel shut-off cock or other means operable in a direction to stop the supply of fuel to the plant by means controlled by electromagnetic means, two electrical switches in circuit with the electromagnetic means and arranged so that the electromagnetic means can only be operated when both switches are in the " on " position, means responsive to the compressor speed for moving one switch to its " off " position when the compressor speed exceeds a predetermined value, and means responsive to a signal dependent on the torque transmitted to the propeller for moving the other switch to the " on " position when the torque falls below a predetermined value. In the arrangement shown a reversible actuator 1 in the form of a geared motor with a split field winding represented by coils C and O is connected to a fuel shut-off cock (not shown) such that energizing coil O rotates the actuator to open the cock and energizing the coil C rotates the actuator in the opposite direction to close the cock. The actuator has two limit switches 2 and 3 respectively operated at the end of the opening movement to break the circuit to coil O at 4 and make a circuit at 5 including a coil 6 of a flag indicator 7 and at the end of the closing movement to break the circuit to coil C at 8 and make a circuit at 9 including a coil 10 of the indicator 7. Switches 2 and 3 are mechanically interconnected so that at the ends of the closing. and opening movements the switches are automatically reset to contacts 4 and 8 respectively. The fuel cock and limit switches may be operated by projections on a block reciprocated by rotation of the actuator 1. Current is supplied to the coil O from a source + through normally closed contacts 11, 13 and 15 and 16 of a starting switch 12, a fire-emergency switch 14 and an electromagnetically operated switch 17 respectively and during normal running the fuel cock is open, this condition being shown by the indicator 7 whose coil 6 is energized at the end of the opening movement. Changing over of switches 12 or 14 to contacts 18 or 19 energizes the coil C and closes the fuel cock. The coil C can also be energized by current supplied through a disarming switch 26 and contacts 21, 22 when the switch 17 is moved to the left by energization of a coil 30 when switches 32 and 34 are closed on contacts 31 and 33 respectively. The switch 17 is held in this position by a spring-loaded latch 28 engaging a notch 47 in the switch. The latch may be withdrawn to reset the switch 17 by moving the switch 26 to engage contact 27 and thus energize a coil 29. The switch 32 is operated by a compressor speed responsive device to close on contact 31 when the compressor speed exceeds a predetermined value. The device may comprise flyweights driven from the compressor shaft or a switch actuated by fluid pressure or electric current varying with the compressor speed. The switch 34 is operated by a diaphragm subjected on one side in the direction to break contact at 33 to liquid pressurized by a torque meter measuring the propeller torque and on the other side to the compressor delivery pressure, the switch being open during normal running and closing only when the torque falls below a predetermined value relative to the compressor delivery pressure. A three-position flag indicator 35 shows an " operated " signal, due to energization of a.coil 36, when switch 17 is operated, an " armed " signal during normal operation when a coil 37 is energized and a " disarmed " signal when neither coil is energized. A switch 43 across the compressor speed responsive switch 32 is provided to enable the system to be tested and the method of testing is described.