Two phase Switchboards.

simple switch or a combined switch and circuit breaker. If it is the latter, C C will be fuses, or they may be dispensed with in a cheap construction. At G' a ground detector is placed and is connected with both sides of the circuit as shown, and also with the ground as indicated at G.

Fig. 58 shows a switchboard for one two-phase generator. As in the last diagram, A is the generator, E the exciter, R R' the regulating rheostats, and D the main switch. The current taken from the side terminals of A passes to the two blades of D on the right side, and thence to the line terminals N N', one side of the circuit passing through the ammeter Am'. The top and bottom terminals of the generator are connected with the two left-side blades of D, and this circuit runs to the terminals L L', one side passing through ammeter Am. As will be noticed, two ammeters are provided, one for each circuit, but there is only one voltmeter V, and this is arranged so as to be connected with either circuit by means of the double throw switch S, which connects the primary of H with either one of the circuits, according to the side with which it is closed. The operation of the exciter, and the rheostats R R' is the same as in Fig. 57. The ground detector G' is connected with the center contacts of switch S so that by turning this switch in both directions the two circuits can be connected with the ground detector, one at a time. When it is desired to have the two circuits permanently connected with ground detectors, two of these instruments are used, each one being connected with one of the circuits in the manner shown in Fig. 57.

Fig. 59 shows the switchboard connections for one

Three phase Switchboards.

three-phase generator. As in the two preceding diagrams, A is the generator, E the exciter, D the main switch, R R' the regulating rheostats, H a voltmeter transformer, Am the ammeter, V the voltmeter, G' G' ground detectors, and C C C fuses in the main lines. It will be noticed here that there is only one ammeter, and this is permanently connected in one of the main lines. The voltmeter is also permanently connected with two of the main lines. In a three-phase system this arrangement is possible, because the currents flowing in the three lines are of the same strength, and the voltage between the lines is the same, hence, with two instruments connected as shown, the condition of the current and e. m. f. in the three lines is properly indicated.

These three diagrams show the switchboards arranged so as to deliver the current into a single set of distribution wires, through which it is conveyed to the point where it is utilized. If it is desired to transmit the current through a number of branches, a panel must be added at one side of the board to hold the switches by means of which these branches are connected and disconnected from the circuit. In this case, the terminal wires L L N N' must be connected with bus bars placed back of the added panel, this part of the board being constructed in precisely the same manner as for a continuous current system. If there are a large number of branch circuits, it will make the switchboard more symmetrical in appearance to place a distributing panel on each side.

When alternating current generators are run connected in parallel, it is necessary to provide apparatus by means of which we can know when the machines are running in

proper relation to each other to be connected. With continuous current generators all we have to look after in connecting them in parallel is the voltages of the machines, which must be the same; but with alternating current generators, we must also make sure that they are running at velocities that will make the frequencies the same, and, further, that the currents are in phase with each other; in other words, the machines must be synchronized as to frequency, and the currents must be brought into phase before they can be connected in parallel. The apparatus required to accomplish this, and the way in which it is used, can be clearly explained in connection with the diagrams, Figs. 60 to 62.

Fig. 60 illustrates the synchronizing apparatus for a single phase system. I and 2 represent two single phase generators arranged to be connected in parallel with the two bus bars shown. H and H' are transformers whose primaries are connected with the two machines in the manner shown. If the e. m. f. of the formers are not required, as their only office is to furnish generators is one hundred volts, or thereabout, the trans

secondary currents of low voltage. At a a and b b incandescent lamps are connected in the circuit of the secondary coils of the transformers in the manner shown. Suppose generator I is connected with the bus bars, then the current from it at the instant when it flows upward in the left side line will traverse the primary coil of H in the