GB359153A - Improvements in and relating to the control of prime movers - Google Patents

Abstract

359,153. Electro - mechanical power transmission systems; control of D.C. motors. GENERAL ELECTRIC CO., Ltd. and SAUNDERS, C. W., Magnet House, Kingsway, London. Sept. 22, 1930, Nos. 28307 and 32244. [Class 38 (iv).] In a ship propulsion system comprising a prime mover and an electric motor arranged to drive a propeller, and a second prime mover arranged to drive a generator for supplying power to the motor, a control device is adapted to control both the electric motor which is arranged to operate at low speeds without the first prime mover and also the first prime mover when the latter is operative. The power supplied to the motor 3, as shown in the Figure, is controlled by varying the field of the generator 5 by means of a rheostat 8 supplied from D.C. mains 29, 30. The lever 75 which controls the supply of fuel to the prime mover 2 is connected to the lever 77 of a rheostat 39 by means of a slotted link 79 which allows the lever 77 a certain freedom of movement. The rheostats 39, 42 are connected across the mains 29, 30 in the form of a Wheatstone bridge, their movable tappings being connected together through the coil 35 of a polarized relay 33, the contact 36 of which moves either to contact 37 or 38 according to the polarity of the potential difference between the tappings and remains in the centre if the p.d. is zero. The moving contacts of rheostats 8 and 42 are coupled together and are mounted on the spindle of an auxiliary motor 12 having two field windings 13, 14 so that it is able to rotate in either direction. When the lever 77 is moved the relay 35 operates causing the motor 12 to move the rheostat arms until voltage balance is obtained, the field rheostat thus being controlled from the lever 77. Reversal of the motor is obtained by reversing the generator field by switches 57, 61 controlled from the reversing handle 52 of the prime mover 2. The isolating switch 47 in the motor-generator circuit is controlled by a relay which allows the circuit to close only when the potential difference between the motor and generator is below a certain value. In the event of over-current a relay 23 operates to close the circuit of a tripping coil 111 which causes the main switch 32 in the D.C. supply circuit to open. The field of the generator reduced to zero and also the isolating switch 47 opens. In the event of overload caused by the lever 77 being moved quickly from the zero load to the maximum load position a relay 26 having voltage and current coils operates and opens the auxiliary motor circuit so that the field of the generator does not further increase until the power has fallen to a value at which the contacts of the relay reclose. In a modification the motor and generator fields are supplied from a small generator driven by the prime mover 6. Further, an arrangement is provided which, when the over-current relay opens, causes the rheostats 8, 42 to return to their initial positions, and when the conditions return to normal the circuit automatically becomes operative, the rheostat hunting round to a suitable position. A magnetic clutch is provided in the shaft of the auxiliary motor 12 which opens when the overload relay 26 operates.