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Four generators in parallel.

with the circuit. One such instrument will answer the purpose for any number of generators. When a differential voltmeter is used it is connected with the bus bars and with the generator that is to be started and the two voltages act against each other. When they are equal the actions neutralize one another, and the instrument indicates zero.

In Figs. 21 and 22 two arrangements are shown for connecting four generators in parallel so as to feed into a number of distributing systems. In the arrangement of a switchboard the effort should be to make the connections as simple as the requirements of the case will permit, but at the same time we must not follow the course of obtaining simplicity by sacrificing points of vital importance; that is, we must not make the connections such that they do not fully accomplish all that is desired. Now, it may happen that we have a building in which it is desired to arrange the circuits so that the current may be turned off a certain portion at a certain hour and that we be able to turn it off from the switchboard. If such be the case, the connections must be such as to enable us to accomplish the result. Again, it may be required to control the lights in several parts of the building from the board, and the switches and connections must be so made that we can control them. Many other reasons may arise that will interfere with the simplification of the switchboard to the greatest possible extent; therefore, it is necessary to know how to proceed when complicated cases present themselves, and the best way to reach this proficiency is by the study of arrangements calculated to meet more or less complex requirements.

Figs. 21 and 22 are cases of this kind, and being ar

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Four generators in parallel to feed a number of circuits.

Another combination of four.

ranged differently, a study of them will serve to throw light upon the subject, and to enable us to decide what combinations can be most advantageously applied in any particular instance.

In Fig. 21 four generators are provided to feed into four external distributing systems, and they are so arranged that any one of the generators can be connected with any one of the distribution systems. The way in which all this is accomplished can be made clear by the explanations that follow:

The four generators G1, G2, G3, G4 are connected with the four switches S1, S2, S3, S4, respectively. The wires marked g leading from the center contacts of the switches connect with the bus marked 5. Bus 6 is the equalizing bus, and it will be noticed that, as in other diagrams previously presented, the wires that connect with it do not lead from the circuit breaker c b. Bus 5 may be the common junction for all the negative, or all the positive wires coming from the four generators. The remaining contact of the S switches is connected with the switches marked A B C D, by means of the wires marked i. These last named switches are of the type called four point, that is, they have four contacts marked 1 2 3 4, and the switch lever, which is pivoted in the center, can swing around so as to make contact with any one of the four points. Each one of the contacts of these four switches is connected with a different bus bar. Thus contact I connects with bus 4 and contact 2 with bus 1, contact 3 with bus 2 and contact 4 with bus 3. With the levers of these switches set as in the diagram, generator G1 feeds into busses 6, 5 and 4, and as bus 6 is the equalizing bus, the current is taken off from busses 5 and 4. The small dis

Still other modifications.

tributing switch si is connected with these busses; hence it is supplied with current from generator GI. Generator G2 connects, through switch B, with busses 6, 5 and 1; hence it will feed into switch s4, which is connected with busses 5 and 1.

In the same way as described in the foregoing, it will be found that generator G3 feeds into the distributing circuit controlled by switch s2, and that generator G4 supplies the circuit controlled by switch s3. If it is desired to connect two of the generators, as, for example, GI and G2, with the same distributing circuit-say with the one controlled by switch s3-then the four-point switches, A and B, are set with their levers covering contact 3. In the same way any of the generators can be set so as to feed into any of the busses. Hence, we have in this construction of switchboard an arrangement whereby any one, or ali, of the generators can be connected with any one of the distributing circuits, but we cannot connect any one generator with more than one circuit at a time. If we desire to so modify the arrangement as to render it possible for the generators to feed into more than one circuit at the same time, all we have to do is to provide switches that will enable us to connect the various busses. Thus, if by means of a switch we connect busses 1 and 2, then generator G4, with the lever of the D switch set as in the diagram, would feed into the circuit controlled by the switches $3 and s4. Switches used to connect the bus bars are called tie switches, and, as can be readily seen, it is a simple matter to so arrange them as to make any connections desired. By means of one tie switch we can connect busses 1 and 2, and by means of another we can connect busses 2 and 3, while a third tie switch will con

Independent distributing systems.

nect busses 3 and 4. Thus, by the use of three tie switches we can connect all the busses from 1 to 4, and then we will have an arrangement that will be precisely the same as those shown in previous figures, with only three busses, under these conditions, for the four connected busses would virtually act the same as one.

If we desire to make the bus-tying arrangement more complete, so as to be able to tie 1 and 3, or 1 and 4, or so as to be able to connect any pair without connecting the others, then the switches will have to be more than threeproviding two-pole switches are used—and their connection will involve more complication. By using three-point switches of the same type as A, B, etc., and providing one for each bus bar, we can connect the bars in any order desired; for suppose we provide four such switches and connect the center of each one with one of the busses, then, by placing the lever over any one of the three outside contacts, we can connect with any one of the other busses.

There is one objection to the arrangement of Fig. 21, and that is that the several distributing systems are not entirely independent, but, on the contrary, all are connected through busses 6 and 5. Now, it is desirable, when the external circuits are divided into several systems, to have these entirely independent, so that if anything goes wrong with one set of circuits it will not interfere with the operation of the others. When the several systems are partially connected, as by the busses 5 and 6 in this figure, it is possible for a ground or short circuit in one to interfere with the operation of the others; hence, if each system is so arranged as to be disconnected entirely, the operation will be more satisfactory.

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