Patent GB-111623-A (GB)
Title: Improvements relating to the Control of Dynamo Electric Generators.
IPC: H02P9/12
Filed: 1917-04-14
Abstract: 111,623. British Westinghouse Electric & Manufacturing Co., (Westinghouse Electric & Manufacturing Co.). April 14, 1917. Systems for continuous current motors only.- In the control of electric generators supplying systems in which frequent stops and reversals of driving plant are necessary, such as in reversing rolling-mills where the voltage of the supply to the driving-motors should respond quickly to the adjustment of the controller, which is used to vary the resistance in the generator field circuit, the resistance in this circuit is automatically and temporarily reduced by a differential relay, which acts when the voltage generated is lower than the normal voltage corresponding to the amount of resistance in the field circuit. In one arrangement mechanically driven generators 80, Fig. 1, alternate with motors 81 the fields 44, Fig. 2, of the generators being supplied through the resistance 43 from a constant source. Motor fields 41 are supplied through the resistance 40 from the constant source and motor fields 37 from an exciter 82 the field 38 of which is excited by the current from the generators 80, a resistance 39 being included in this field circuit. Reversing switches 1-4 and 5-8 are in the generator field circuit and in the motor field circuit 37. The resistance sections are controlled by electric magnetic switches 12-21 for the generator resistance, 26-35 for the motor resistance 40, and 9-11 for the motor resistance 39. Switches 22 and 23 control a shunt round the major part of the generator resistance and switches 26 and 24, 25 a shunt round the motor resistance 40. The differential relay consists of a coil 52, Fig. 4, in shunt to one of the generators, a coil 53 in series with the actuating coils 14-21 of the generator resistance switches and a coil 54 which is energized when the relay contacts 49, 50 are closed to ensure positive closure of the contacts. The coils 14-21 are in parallel. In the " off " position of the controller 45, the switch 11 is closed to shunt the motor resistance 39, the switches 12 and 13 are closed by the switch 61 to cut out sections of the resistance 43 and the switches 26 and 27 are closed to cut out the motor resistance 40; the motor field 41 is energized but the generator field is opened. A switch 65 in the generator field circuit and inter-connected with a field discharge switch is then closed. In position I of the controller the reversing switches for the fields 37, 44 corresponding to the required direction of rotation are closed.. In position II of the controller the generator resistance section switch 14 is closed its coil being in parallel with the coil of switch 26, both being in series with the coil 53 of the relay. If the voltage of the generator does not immediately rise the coil 53 owing to the decreased resistance of its circuit due to the inclusion of switch coil 14 will close the contact 49, 50 and thereby olose the switches 22, 23 to shunt the major part of the generator resistance 43; the excitation will be considerably increased and the voltage of the generators will rise rapidly. The same action occurs at all the generator resistance steps. In position VIII. of the controller the motor field resistance switches 9, 10, which were previously open, close; the switch 28 is closed by an interlock 70 with switch 21, and the switches 29-35 close in sequence after the switch 28 being controlled by suitable interlocks. In positions IX onwards the motor resistance 40 is cut into the field circuit in steps and the motor resistance 39 is cut in with the controller in positions IX, XI, and XIII. Interlocks may be provided between the generator resistance switches 14-21. If during motor acceleration the current is excessive the vibrating relay 59 acts to close the switches 24, 25 so as to strengthen the motor field. When the controller is moved to the " off " position to stop the motors the latter are driven; if the voltage generated by the motors exceeds that of the generators the current in the coils of the switches 57, 59 and 61 is reversed, the series coils of these switches being across a reactive resistance 58. The series coil 63 of the switch 61 now assists instead of as previously opposing the shunt coil 62 and the switch rises to reverse the effects produced by the switch 59 and complete the circuit of the switch 56. If the current during braking is excessive the switch 57, closes the circuits for the switches 12, 13, and the switch 59 opens the circuits of the switches 22, 23 to strengthen the generator field, these switches having been closed by the switch 61 The switch 59 also controls the motor field resistances 24, 25. For driving in the reverse direction the action is the same except that different reversing switches 1-4, 5-8 are closed. In a modification the coil corresponding to the coil 53 of the differential relay is in series with an independent rheostat that is moved in synchronism with the rheostat in the generator field circuit instead of being in series with the actuating coils of the resistance switches. A coil which ensures positive separation of the contacts of the relay is short-circuited when the relay is closed, and energized as the relay opens. The generator fields and the motor fields are in separate series circuits fed from a constant source.