Patent GB-294241-A (GB)
Title: Improvements in and relating to synchronism indicating means
IPC: H02J13/00
Filed: 1928-07-06
Abstract: 294,241. British Thomson-Houston. Co., Ltd., (Assignees of Carter, E. F.). July 22, 1927, [Convention date]. Wired wireless systems. -Synchronism between alternating-current circuits is indicated by modulating the output from a transmitter in accordance with the voltage difference between corresponding phases of the two circuits due to their lack of synchronism and indicating the resulting output from the transmitter. Apparatus is shown by which synchronism between a generator 2 at a substation A and the circuit 1 is indicated at an operating station B from which, whem synchronism is attained, the generator 2 is connected to the circuit by means of a switch 3 operated by remote control equipment (not shown). At the substation A are located an oscillation generator 4 adapted to supply high-frequency alternating current to an amplifier 6, both comprising threeelectrode valves the cathodes of which are excited from one phase of the generator 2 through a transformer 10. Transformers 12, 13, 14 have their primary windings connected across the three phases of the switch 3, their secondary windings being connected through rectifiers 18, 19, 20, which may be two-electrode thermionic valves, to the anodes of the oscillation generator 4 and amplifier 6. When an alternating potential exists across the contacts of the switch 3, directcurrent potential is supplied to the anodes of the valves 4, 6, thereby causing high-frequency currents of proportionate magnitude to be supplied to the distribution system 1 through a transformer 7. At the operating station B is located a detector or rectifier 28. which may be a threeelectrode valve, connected to the distribution circuit through a transformer 30. The secondary circuit of the valve 28 is included a direct-current means of an inductance 32 and condenser 33, to the frequency of the carrier currents transmitted by the generator 4 and amplifier 6. In the anode circuit of the valve 28 is included a direct-current instrument 34, the primary winding of a transformer 35, and a source of anode potential 36. As synchronism is approached, the pointer of the instrument 34 vibrates with a frequency equal to the beat frequency between the generator 2 and the circuit 1, synchronism being indicated by a minimum reading and slow oscillations. If the phase rotation of the generator 2 is reversed with respect to the mains, plate voltage will be continuously applied to the anode circuits of the valves 4, 6, there being small pulsations of high frequency compared with those that occur when the directions of phase rotation are alike. These characteristics will be reproduced on the instrument 34, indicating to the operator that the phase rotation of the machine 2 is incorrect. In order to indicate whether the frequency of the generator 2 is above or below that of the mains, a synchroscope 37 is provided having its field winding 38 connected across one phase of the generator 2. The moving system comprises two coils 40, 41, at right angles, in series respectively with an inductance 42 and a resistance 43 and connected across one phase of the mains 1. On the shaft of the synchroscope 37 is fixed a disc 44, with which one end of a lever 45 makes frictional contact, so as to be moved to one side or other in accordance with the direction of rotation of the disc 44. One or other of two contacts 47, 48 is thereby closed, operating one of a pair of relays 56, 58, which closes a circuit through the primary winding of a modulating transformer 53 and one or other of two commutators 66, 67 driven by a motor 49 and having different numbers of segments. The secondary winding of the modulation transformer 53 is connected between the cathode and grid of the amplifier 6, causing the output to be modulated by impulses of a different frequency depending on whether the generator 2 is running too fast or too slow. This may be detected at the station B by audible means, such as headphones, or by relays 61, 62 tuned to the respective modulation frequencies and energizing visual indicators 63, 64.