[Electric engineering.] . ps will be dark when the machines are insynchronism; by reversing- the connections of one of thetransformers, the lamps would be bright at the voltmeter or synchronizer is in use, the plugswitches connect points o, T and o, 1. 51. Sometimes when a number of alternators are oper-ated in multiple, it is advisable to have their excitersarranged so that they may be operated in multiple also.* Ifone exciter breaks down, the others may then supply thealternator that would ordinarily be supplied by the disabledmachine. Again, in large plants, it is quite cus
[Electric engineering.] . ps will be dark when the machines are insynchronism; by reversing- the connections of one of thetransformers, the lamps would be bright at the voltmeter or synchronizer is in use, the plugswitches connect points o, T and o, 1. 51. Sometimes when a number of alternators are oper-ated in multiple, it is advisable to have their excitersarranged so that they may be operated in multiple also.* Ifone exciter breaks down, the others may then supply thealternator that would ordinarily be supplied by the disabledmachine. Again, in large plants, it is quite customary tosupply all the alternators with their field current from oneor two large exciters that feed into a pair of exciter bus-bars, from which the several alternators are supplied. 52. Running- Alternators Separately. — In manylighting plants, the alternators are not run in multiple; infact, special precautions are taken to see that there is nopossibility of their being thrown in multiple. In such Tp A/fernafor A/°/r. FiG. 63. cases, they are arranged so that the load may be dividedbetween them. This is usually accomplished by usingdouble-pole, double-throw switches, as indicated in Fig. 63,when two alternators are used. The upper set of bus-bars 64 ELECTRIC LIGHTING. § 17 is connected to one alternator and the lower set to theother. The upper terminals of each feeder switch are con-nected to the upper bars and the lower terminals to thelower bars. The feeders are connected to the middle ter-minals as shown. When all the switches are up, the alternatorNo. 2 is not running, and the whole load is carried by No. shown in the figure, circuits 1 and Jf. are on alternatorNo. i, because switches A and D are both thrown 2 is on alternator No. 2. Feeder No. 3 is cut outaltogether, as the switch blades are standing straight outand the circuit is not connected to either pair of is easily seen from the figure that any circuit or combina-tion of circuits may
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