Patent GB-785835-A (GB)
Title: Improvements in or relating to polyphase alternating current supply systems
Inventor: CHILMAN JOHN ALFRED
IPC: H02J3/42
Filed: 1954-10-13
Abstract: 785,835. Synchronizing arrangernents; running generators in parallel. ROTOL, Ltd. Oct. 5, 1955 [Oct. 13, 1954], No. 29486/54. Class 38 (4). Relates to a system in which alternators A1, A2 are driven by separate prime movers T1, T2, and are each connectable to the bus-bars Ba, Bb, Bc of a load network by separate tie-breaker switches TB1, TB2. The alternators may carry individual loads L1, L2 when not connected to the bus-bars, and additional loads may or may not be connected directly to the bars. If the alternator A2 is already connected to the-busbars by the switch TB2, the alternator Al is brought in by moving selector switch 17 to engage contact 17<SP>1</SP>, the two stator windings of a synchronizing machine S1 being simultaneously connected to the bus-bars and to the outputlines of the alternator A1 respectively. A pushbutton switch 16 is then depressed and held, but a closing winding 12<SP>1</SP> of the switch TB1 is not energized through contacts 18<SP>1</SP> since these are interlocked with the switch TB2. The machine S1 controls the speed of the prime mover T1 to obtain synchronism with the bus-bar frequency set by the alternator A2. Contacts 241 are linked with the machine S1 so that they close each time the alternator A1 comes into phaseagreement with the bus-bar voltage within the pull-in range of the alternator, and delay mechanism 28<SP>1</SP> is set in operation. Until a close degree of synchronism is obtained, however, the period of closure of contacts 24<SP>1</SP> is not sufficient to allow the delay mechanism to close contacts 27<SP>1</SP>. Simultaneous closure of contacts 241, 271, energizes the closing coil 12<SP>1</SP> so that both alternators are connected to the bus-bars. A lamp 29<SP>1</SP> indicates that the push-button may now be released. To isolate one of the alternators, a corresponding push-button 141, 14<SP>2</SP>, is depressed to energize either of the trip-coils 131, 132 of the tie-breaker switches. A two-phase induction motor 30 is used for proportioning the load between the alternators when they are in parallel. One phase winding 31 of this motor is adapted to be energized in accordance with the voltage between lines La, Lb of the alternator A2, and the other phase winding is energizable by the difference of the secondary currents of transformers CT1, CT2, the primary windings of which are arranged in the output lines Lc of the two alternators. The armature of the motor 30 and the synchronizing machine S2 operate the governor G2 for the prime mover T2. Once the alternators have been paralleled, the machines S1, S2, become inactive and control of the governor is taken over by the induction motor. To prevent over-loading of the alternator A2, contacts 38 are closed by the motor 30 when it reaches its limit of travel in the loadincreasing direction, these contacts being adapted to energize the trip-coil 13<SP>2</SP> of the breaker switch TB2 independent of the manual switch 142. Contacts 34, 35, are respectively operable by switches TB1, TB2, to isolate the motor 30 when either of the alternators are disconnected from the bus-bars. In a modification, the system comprises three alternators, the selector switch 17 now having three contactpositions, Fig. 2 (not shown). The single pair of contacts 181, 182, is replaced by two pairs associated with the tie-breaker switches in a manner similar to that described. Specifications 515,934, 732,052 and 767,057 are referred to.