Patent GB-487612-A (GB)
Title: Improvements in emergency overspeed tripping gear
IPC: H02H7/093
Filed: 1937-02-05
Abstract: 487,612. Engine stop-gear. ENGLISH ELECTRIC CO., Ltd., and CHITTENDEN, J. P. Feb. 5, 1937, No. 3452. [Class 122 (iv)] Comprises means for testing overspeed trip mechanism without disturbing the normal opera tion of the plant, or leaving the engine unprotected The over-speed mechanism is disconnected and testec while duplicate trip mechanism is thrown into operation. Failure of the overspeed trip gear or of the electric circuits also stops the engine or operates a warning signal. In electricallyoperated gears, one spare set of trip gear may serve a group of engines. A small auxiliary engine-driven generator preferably supplies the energy. In the case of an electric generating station, the supply may be taken from the main alternator, or from auxiliary slip rings on a direct-current, engine-driven exciter. In the arrangement on the left of Fig. 1, which Figure shows two alternatives on the right and left respectively, a synchronous overspeed motor 3 driven from an engine-driven alternator 1 drives means 4 to operate a switch 5 at a predetermined speed. Each such switch makes or breaks a circuit from a battery 6 which energizes a solenoid 7 coupled to the valves &c. for shutting down the engine. An independently-driven, testing-alternator 8 is provided. Each of the motors 3 may be disconnected from its normal supply by a triple-pole switch 12 and connected to the generator 8 by a switch 13 interlocked with the switch 12. The test generator can be run up to and above the tripping-speed which is indicated by a tachometer 9 to test the overspeed device. During the test, the switch 5 is disconnected from the solenoid by a switch 14 which connects the duplicate switch 5a to the solenoid. Each motor operates a switch 10 and thereby an alarm if the motor runs at less than the correct speed. In the arrangement on the right, voltage or frequency-responsive relays 3a are used instead of the synchronous motor. These operate switches 5a when a particular voltage or frequency is reached. Under voltage or under frequency relays 10a operate the switches 10b of warning devices 11a. The switch 14 is interlocked with the switch 12 and is so arranged that it cannot be left in an intermediate position in which both switches are in circuit in parallel. If the switches be adapted to close the circuit of the shutting-down solenoid on one speed, warning means operative at normal speeds are included to indicate any interruption of the solenoid supply. Only one test generator need be provided in a plant including several engines and more than one overspeed trip may be tested at a time by connecting them in parallel. The switches 12, 13, 14 are interlocked. In a further modification shown, only one synchronous motor is provided for each engine, but is adapted to drive through interlocked, disengageable clutch devices, one or other of two trip mechanisms. Other clutches are provided to connect up the testing-motor. Alternatively, one or other of two mechanical trip mechanisms may, through clutches, be connected to the engine shaft or to a testing-motor. In the arrangement shown in Fig. 3, a valve 19 is controlled at excessive speed by a solenoid 7 or by failure of the oil pressure on a device. The two devices are connected to a lever which may also be moved bv hand and which also controls a latch device 18 associated with the valve.