Patent GB-502151-A (GB)
Title: Improvements in or relating to apparatus for controlling the interconnection of two three-phase electrical systems
IPC: H02J3/42
Filed: 1937-09-10
Abstract: 502,151. Phase difference measurements; synchronizing; electricity supply. REYROLLE & CO., Ltd., A. (Allis-Chatmers Manufacturing Co.) Sept. 10, ]937, No. 24708. [Class 37] [Also in Group XXXV] Apparatus for synchronizing two three-phase systems comprises a pair of phase-responsive members oscillating at the beat or difference frequency in intersecting paths, one member reaching its extreme positions when the systems are in phase opposition and in phase coincidence, respectively, and carrying a first contact in such manner that, shortly before phase coincidence the contact position .depends on the rate of change of phase relationship, whilst the other member carries a second contact and reaches extreme positions when the circuits are in quadrature, the contacts being so shaped as to engage one another prior to phase coincidence at a position of the second contact such that the greater the rate of change of phase relationship the further is the second contact from the phase coincidence position when contact is made. As shown in Figs. 1, 2, apparatus 25 responsive to the phase and frequency difference between two three-phase systems.16, 18, adjusts the frequency of the system 18 through a reversible electric motor 23, controlling the governor 22 of the turbine 21 driving the alternator 19 feeding the system 18, and operates a circuit breaker 17 at synchronism to connect the systems together. To initiate operation of the apparatus, a pushbutton 78 is operated to energize a relay 73 which locks up over its contact a, whereupon solenoids 52, 24, 26 are respectively connected over contacts of relay 73 across the terminals A A<SP>1</SP>, A<SP>1</SP> C, A C<SP>1</SP> of the secondaries of potential transformers 74, 75 and 76, 77 fed from the systems 16, 18 respectively. The armatures 27, 28 of the solenoids 24, 26, Fig. 2; act on a beam 31 pivoted at 32 and biassed to its horizontal position by springs 34, the bracket 33 carrying the beam pivot 32 being rigid with a rod 36 capable of limited vertical movement due to a parallel linkage including levers 37 pivoted at their mid-points. The rod 36 is biassed to the raised position by a counterweight 38 and its movement is limited in both directions by stops 39. The beam 31 thus rocks according to the torque produced by the difference in the pulls exerted by the magnets 24, 26, and moves downwardly according to the sum of these pulls, and the indicating end 42<SP>1</SP> of a pointer 42 rigid with the beam is thereby constrained to move at beat frequency (provided the beat frequency is less than, e.g. 4 cycles a second) over a cyclical path PQRSTP in one direction or the other according to whether the frequency of system 18 is slow or fast. The lateral displacement of the pointer 42 is limited by stops 41 coacting with the armatures 27, 28, to indicate only a range of about 60 electrical degrees either side of the central position shown corresponding to phase coincidence. Frequency adjustment. The beam 31 carries a cam roller 44 which rocks a pivotal contact 46 only when the pointer 421 is travelling along the upper part QPT of its cyclical path, so that if the frequency of system 18 is " slow " the contact 46 is rocked into engagement with contact 48 once during each beat cycle, and into engagement with contact 47 if the system 18 is "fast." If the system 18 is "slow" then once during each beat cycle a relay 84 is energized in series with a timing relay 82 from battery 81, which interacts with a relay 83 to connect the motor 23 in circuit over contacts 84c for a predetermined short period depending on the time delay of the relay 82. The motor 23 is thus operated a constant, amount once during each beat cycle to raise the frequency of the system 18, and, similarly, if the system 18 were "fast," the motor 23 would be operated once during each beat cycle in the reverse direction over contacts 86c of a relay 86 operated similarly to relay 84 but over contacts 46, 47. Synchronizing and connecting the systems. The circuit breaker 17 is operated by a relay 91 to connect the systems 16, 18 together when relays 87, 88, 89 are simultaneously energized. When the beat frequency is less than 4 cycles per second, the armature 53 of the solenoid 52 (de-energized at phase coincidence) oscillates, during lateral movement of pointer 42, a weighted lever 54 carrying a dashpot 62, the piston 63 of which is urged upwardly by springs 66 and is arranged to take up a.position corresponding to the rate of change of the phase difference by virtue of the biassing effect of a spring 57 on the armature 53 and the rate at which the air escapes from the dashpot. The rod 64 of piston 63 carries a contact 51 coacting with a double-spiral-form contact 49 moving with the bracket 29, and also carries a contact 67 coacting with a contact 68 carried by the dashpot 62. Once in each beat cycle at phase opposition relay 87 is operated over contacts 69 on beam 54, and locks up, but if the beat frequency is too high for switching in the breaker, the contacts 49, 51 engage before the contacts 67, 68 in each beat cycle and the relay 87 is released by operation of relay 89 which is itself immediately released. If, however, the beat frequency is less than, for example, one cycle in six seconds, the air is allowed more time to escape from the dashpot 62 as it moves downwards, and contacts 67, 68 make before 49, 51, and energize relay 88 ; relay 87 is already energized, so that when contacts 49, 51 make subsequently, relay 89 also is energized (at a predetermined time dependent on the dashpot adjustment) slightly before phase coincidence, whereupon relay 91 operates and closes the self-holding circuit breaker 17 at phase coincidence. Closing of the circuit breaker 17 de-energizes relay 73 whereupon the whole apparatus 25 and associated relays revert to normal. Modifications:. Figs. 5-10 (not shown), show other arrangements for connecting the solenoids 24, 26, 52 across the transformers 74, 75, 76, 77 in some of which one or more of these transformers may be dispensed with. In another embodiment, Fig. 11 (not shown), the lever 54, Fig. 2, is dispensed with, the solenoid 52 operating directly on a vertically reciprocat. ing member carrying the contacts 51, 67, and the dashpot is replaced by a bellows arrange ment. In a further embodiment, Figs. 13, 14 (not shown), wherein the solenoid 52 is mounted vertically above and operates directly on the dashpot, the solenoids 24, 26 are mounted so as to reciprocate the contact 49 horizontally, no other motion being imparted thereto. Since the phase indicator 421 will then also move horizontally and give no indication as to which system 16 or 18 has the higher frequency, a lamp is illuminated over contacts operated by the dashpot movement only when the systems are approximately in coincidence. A safety circuit is provided to prevent untimety closure of the breaker 17 should the dashpot fail.