Patent GB-908922-A (GB)
Title: Automatic paralleling of alternating current generators
IPC: H02J3/42
Filed: 1961-02-06
Abstract: 908,922. Synchronizing. WESTINGHOUSE ELECTRIC CORPORATION. Feb. 6, 1961 [Feb. 11, 1960], No. 4364/61. Class 38 (4). Means sensitive to the difference in phase and frequency between an A.C. generator to be synchonized and existing energized lines or generators provides an output voltage when these are both within predetermined limits in order to operate a paralleling switch and to effect a change in the sensing means to cause the said output voltage to be maintained until the phase difference between the generator and line generator exceeds a predetermined value. A generator 1 may be paralleled with a generator 2 by means of a breaker 6 having a closing coil 7 energized at synchronism by a current pulse of sufficient length to effect the closing of its contacts but which is not long enough to enable them to close significantly after this point. Voltage control regulators on both generators ensure that the generator voltages are sufficiently close to permit paralleling. A transformer of the primary of which is connected to the phase voltage of the two generators, produces a secondary voltage having a maximum value when the generator voltages are 180 degrees out of phase and a minimum value when these are in phase and having a frequency equal to that of the difference between the generator frequencies. The secondary voltage is rectified by a half-wave rectifier 11 and filtered by resistor 12 and capacitor 13 so as to produce a signal voltage shown in Fig. 2 by the curve V1 modified by the R.C. network to the waveform indicated by a. This signal voltage is adjusted by a potentiometer 14 and applied to the base of a transistor 15 arranged to conduct when this base voltage is above a minimum value Vc. Voltage V 1  drops below the value Vc and produces an output voltage Vo from the now non-conducting transistor 15, when the phase angles of the generators 1 and 2 approach equality, and their difference frequency is within permissible limits for paralleling. The output voltage Vo controls the construction of a second transistor 22 which energizes the operating coil 24 of a relay 23, a contact 25 of which closes to effect the operation of the contactor closing coil 7 when switch 26 has been closed. A second relay contact 28 also closes, connecting an adjustable resistor 27 in parallel with the resitor 12 and effecting a reduction in the signal voltage at the potentiometer 14 the effect of which is shown in Fig. 2 where the signal voltage V1 is seen to be reduced in magnitude as shown by the dotted portion b. This new voltage curve ensures that the output pulse Vo effecting the operation of the contactor 6 is maintained until the point at which the reduced signal voltage V1 rises above the conduction voltage V1, this point being determined by the adjustable resistor 27 so as to correspond to the maximum permissible phase difference between the generators at which time the transistor 15 will again conduct and thus terminate the voltage Vo. By the adjustment of resistor 27 and the potentiometer 14, differing contactor and generator conditions may be accommodated. Specification 861,656 is referred to.