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Connections for distributing circuits.
With the foregoing explanation of the connectior:s of the generator proper with the indicating instruments and the field regulator, we can return to Fig. I and consider the connections with the distributing circuits. In this diagram, the circle A represents the generator armature, and M is the shunt field coil, or more properly, the representation of all the field shunt coils, whatever their number may be. In the same way the coil above JI represents the series coils. The field regulator is at R, the voltmeter at V and the ammeter at Am. The main switch is shown at S, the circuit breaker at f, and the branch circuit switches at d d d. It will be evident at once that it is immaterial in what part of the engine or generator room these various devices are located so long as they are where they can be seen and readily reached when desired. As to the switches d d d, it is not necessary that they should even be in the same room as the generator, for they can be placed at the points where the several circuits branch off. It can be readily realized, however, that if they are located in some systematic order at some convenient point they will not only present a more methodical appearance, but will actually become a greater convenience. A switchboard is nothing more nor less than a board upon which these several devices are arranged in systematic order. For the case shown in Fig. 1 the switchboard would assume the appearance shown in Fig. 11. Here we see that the field regulator is located at the bottom of the board between the main switch S and the circuit breaker C. Before the days of switchboards the field regulator was generally located on the floor by the side of the generator, and the voltmeter, am
Connecting the instruments.
meter and other devices were strewn along the wall wherever there was an available space.
In the regularly organized board of Fig. II the voltmeter and ammeter are located at the top. By tracing the lines that indicate the circuit wires it will be seen that the line runs from the right side brush of the generator to the circuit breaker, and from the central contact of this to the ammeter, by wire a, and thence, by wire b, to wire d to the bottom of the main switch S, from which it passes by f to wire h. The wires h and g are called bus bars, as they form a common terminus from which the several circuits controlled by the small switches s' s' are derived. If the branch circuits L L L are very numerous the board B can be made wider, if there is room in the place where it is located to increase its dimensions in that direction. If such is not the case, its height can be increased, and the s' switches can be placed in two or three rows one above the other. An incandescent lamp placed at k serves to illuminate the board so that the attendant may be able to see the position of the switches and take readings of the instruments at all times.
In Fig. 1 it will be noticed that the ammeter is placed so that all the current of the generator passes through it, but the voltmeter is in a circuit of its own, between the wires N and P. The ammeter is an instrument of very low resistance, and as it measures the strength of the current, all the current must pass through it; but the voltmeter measures the pressure; hence, it must be acted upon by the total pressure, and to be so acted upon, it must bridge the circuit from one side to the other, that is, from wire N to wire P. The amount of current that Leave room behind board.
passes through the voltmeter is very small, owing to the fact that it is wound with fine wire and its resistance is very high. In Fig. 11 the voltmeter wires connect with the busses g and h, but these, as will be found by tracing the wires, are the two sides of the circuit, just as the wires N and P in Fig. I are.
The switchboard should be placed in a vertical position, near the wall, but not so near as to interfere with the thorough inspection of the connections on the back of it. The distance between the wall and the back of the board should be from three to four feet. All the wires are placed on the back of the board, and the switches, circuit breaker and instruments are on the front. The field regulator is also placed on the back, and only the handle projects through to the front.
If it is desired to stop the current, the switch S is opened, and unless the current is not to be used for several hours, it is unnecessary to stop the generator. If we desire to stop the flow of current in any one of the distributing circuits all we have to do is to open the s' switch that controls that circuit. By having the field regulator located on the switchboard, the adjustment of the generator to the proper voltage is greatly facilitated, for the attendant can turn the regulator handle while watching the voltmeter, and thus see just when the proper adjustment is effected.
In some cases it is desirable to arrange the external circuits into two or more independent distributing systems, and to have the connection with the generator so arranged that any one system may be operated alone or all at the same time. If the external circuits are divided into two independent systems, the arrangement of the switch