Patent GB-271896-A (GB)
Title: Improvements in or relating to the joint control of the speeds of generating units in electric supply systems
IPC: F01B25/14
Filed: 1927-05-27
Abstract: 271,896. British Thomson-Houston Co.., Ltd., (Assignees of Warren, H. E.). May 28, 1926, [Convention date]. Running generators in parallel; regulation, automatic.-The frequency of an, a.c. distribution system comprising a number of generators or generating stations is maintained constant by means of a standard time-piece. operating locally or from a distance upon the governors of the prime movers driving the generators and biassing those governors to an extent depending upon the accumulated error in frequency. Distant generators may be controlled through modulated highfrequency currents transmitted by radio or over the power mains. Indicators repeating the reading of a dial showing the accumulated error may be operated by the same currents. The invention is described as applied to centrifugal governors controlling steam and hydraulic turbines with electromagnetic and fluid-pressure means for biassing. The operation of the system as a whole or upon any machine may be suspended or modified manually as for instance when synchronizing operations are required. A toothed wheel 29 is driven at a standard speed under the control of a pendulum 23 and escapement 25. An endless band passes over this wheel and over a second toothed wheel 28 driven as by a synchronous motor 22 at a speed proportional to the frequency of the mains 1. The length of the loop 27 which is a measure of the accumulated frequency-error is shown upon a dial 31 and a switch arm 40 is moved over a range of contacts 43 - - 45 in accordance with variations of this length. The governors of prime-movers 5 in stations A, B, C are provided with solenoids 18 which allow freedom of action to the mechanism but are capable of variably biassing it towards closing the throttle valve. At station A a source of current 47 and resistances 46 control this biassing directly from the contacts 43 - - 45. Any desired number of machines in that, station may be controlled by this means. The distant station B is controlled by high-frequency currents sent over the power mains and stations C by radio. Both currents are generated at 48 and modulated by commutator apparatus 49 driven by a constant speed motor 50 and shown in Figs. 2 and 3. A number of toothed wheels 54 one for each of the contacts of the switch 40 operate a series of switches 61. 62 at different frequencies. The high-frequency currents are modulated by one or two of these frequencies according to the position of switch arm 40, i.e. the extent and sense of accumulated frequency-error in the mains. This modulated current is transmitted through transformers 65, 67 and condensers 68, the mains, condensers 69 and transformer 70 to an amplifier 72 at station B and by transformer 63 and aerial 64 to aerial 74 and amplifier 76 at station C. Selective receivers 73 at these stations control the setting of a commutator segment 93 in accordance with the transmitted contacts which by means of brushes corresponding to the series of contacts 43 - - 45 and resistances 46<b>, 46<c> controls the excitation of solenoids 18<b>, 18<c>. The selective receivers are shown in Figs. 6 and 7. A magnet 79 excites armatures 81 carried by reeds 82, 83 tuned to the modulated frequencies. Each reed when vibrating engages its contact 84, 85 and closes the circuit of the appropriate coils of a motor shown in Figs. 4 and 5. This motor has a ring of diametric pairs of magnets 86, 87 and an armature. 90 on the same shaft as an insulating disc 98 carrying the contact 93. An insulating cover carries a series of spring contacts 96, 97 co-operating with the contacts 93. The armature 90 takes up its position according to the magnets, energized by the receiver 73. The shaft carries an indicator which repeats the indication of frequency error given by the dial 31. Fig. 8 shows the application of the invention to the control of a group of water turbines C, D. The centrifugal governors comprise a lever 101 pivoted to a floating lever at 103 and actuating a relay valve 102 controlling the gate motor. The floating lever is supported on an adjustable fulcrum-rod 107 and connected to a dash-pot rod 105 and follow-up rod 106 connected to the gate mechanism. In addition to the usual hand-wheel 108 for adjusting the fulcrum-rod, this modification introduces a spring-loaded piston 109 in a cylinder 111 supplied with oil under pressure controlled by the solenoid 116 and switch arm 40. This piston is coupled to one end of an arm 110 the other end of which is adjustable by the hand-wheel 108 and the fulcrum rod 107 is connected to the arm 110 intermediately. Oil is supplied to pipe 114 under constant pressure from a valves 113 to all the cylinders 111 and the solenoid 116 operates a pin valve 115 to vary the oil pressure in dependence upon the position of the switch arm 40 and the accumulated error of frequency in the electric supply system.