Patent GB-265302-A (GB)
Title: Electric synchronizing systems
IPC: H02J3/42
Filed: 1925-11-06
Abstract: 265,302. British Thomson-Houston Co., Ltd., (General Electric Co.). Nov. 6,1925. Synchronizing dynamo-electric machines; regulation, automatic.- Alternating current systems 1, 2, Fig. 1, are interconnected by switch 3 when they are in phase and operating at the same voltage and frequency, an alternator 56 used to supply the system 1 and driven by a direct-current motor 57 having been automatically brought to the state that the switch 3 can close. Equality of phase between the systems is determined by a valve 10 which impresses on resistors 24, 26 rectified voltages proportional to the system voltages. From the sum of the rectified voltage is subtracted the sum of proportional system voltages bv means of transformers 33, 34. and the resultant impressed between cathodes and grids of a valve 11, When there is equality of phase the resultant anode currents of the valve 11, flowing through coils 4, 5 of switch 3, is a minimum and closure of switch 3 is favoured. Equality of voltage is determined by a valve 12 which impresses the difference of the rectified system voltages across the ends of a resistor 46, which ends are connected in opposite directions across cathodes and grids of a valve 13. The anodes of this valve are in circuit with coils 6, 7 of the switch 3, thus when the system voltages are equal, closure of switch 3 is favoured. Equality of frequency is determined by a valve 14 the potential of whose grids relatively to the cathodes being the difference of voltage produced by tachometer machines 15, 16 coupled respectively to the incoming alternator 56 and a synchronous motor 70 supplied from the system 2. The anodes of the valve 14 are in circuit with coils 8, 9 of the switch 3, closure of which is therefore favoured when the systems 'are operating at the same frequency. The excitation of the alternator 56 is derived from a winding 58 supplied directly from busses 63, 64 and a winding 59 supplied therefrom through a variable resistance 67 operated by a double commutator pilot motor 69. This motor is supplied from the anodes of the valve 13 and thus the rate of decrease of the resistance 67 decreases as voltage equality is approached. Exciting windings 60, 61 on the alternator are switched into circuit with the anodes of the valve 13 when voltage equality has nearly been reached. The excitation of the prime mover 57 and hence the frequency of the alternator is supplied in a similar manner by windings 78 - - 81, the windings 79 being in circuit with a resistance 82 varied by a pilot motor 83 supplied from the frequency determining valve 14, and the windings 80, 81 being switched into circuit with the anodes of this valve when equality of frequency has nearly been reached. The tachometer machines 15, 1& may be replaced by a single machine, the armature of which is rotated by the alternator and the field rotated by the motor 70. In the system shown in Fig. 3, a machine 84 is cross connected between the polyphase systems 1<1>, 2<1>, and drives at a speed depending upon the resultant frequency, a variable resistance 91 for rough adjustment of the excitation of the motor 57, and also a synchronous generator 90 which supplies the valve 14. The anodes of this valve are, as in Fig. 1, connected to the coils 8, 9 of the switch 3<1>, the field regulating pilot motor 95, and the field winding 80. Where the prime mover for the alternator 56 is a turbine, internal combustion engine &c., the pilot motor 83 or 95 is used to vary the excitation of a governor-setting or fuel-controlling coil. Fig. 5 shows a system operating according to the difference in frequency of the power lines 1<1>, 2<1> corresponding lines of which are interconnected by reactors 100, 101,. 102. The resultant current in the reactor 102 isconverted into an alternating current, of a frequency equal to the difference of frequencies existing in the lines 1<1>, 2<1>, by means of a valve 105 and reactor 108 and is impressed upon a resistor 107 from whence it is transferred by a valve 109 and transformer 117 to one winding 119 of a machine 120, the other windings 122, 123 of which are supplied in a similar manner from the reactors 100, 101. The machine 120 thus drives a machine at a rate proportional to the difference of frequencies in the lines 1<1>, 2<1> and is used to operate the switch 3<1> and the pilot motor 83 .which controls the speed of the prime mover. Another system, similar to that shown in Fig. 1 is described, only the power lines 1, 2 are cross connected by reactors. Specification 263,980 is referred to.