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Synchroscopes.

connection with synchronizing lamps, as shown in the diagrams; the lamps determine roughly the condition of the currents, the instrument being used to make the final adjustment. As shown in Fig. 63 the instrument has two pointers, the vertical one being stationary. The other pointer swings to one side or the other, according to the relative frequencies of the two currents. If the frequency

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of the incoming machine is greater than that of the bus bars, the movable pointer will rotate to the right, and if it is slower the pointer will rotate to the left. When the two currents are at the same frequency, the movable pointer will stop at some point on the scale dependent upon the phase relation between the currents. When the two currents are in phase, the pointer will stand in the vertical position directly over the stationary pointer.

The ground detectors used with alternating currents are electro-static instruments, except occasionally in cases where low voltages are used. The ground detector made by the Westinghouse Company is shown in Fig. 67, and the way in which the instruments are connected in a threephase circuit is illustrated in Fig. 68. The tubes placed

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Ground detectors.

around the three-line wires are condensers made in cylindrical form. They consist of two metallic tubes separated by a tube of insulating material. The inner tube is connected with the line conductor, and the outer tube with the instrument. It will thus be seen that there

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is no direct electric connection between the circuit and the ground.

Some of the manufacturers of alternating current machinery make switchboard panels which are provided with the instruments, switches, etc., required to control the particular portion of the system they are designed for, all properly connected with each other. In building a switchboard to take care of an entire plant, these panels are placed side by side and the corresponding parts of the several panels are connected by means of bus bars. A panel of this kind, made by the General Electric Company to control one single phase generator, is shown in Figs. 69 and 70, the first showing the front and the other the back of the structure. Another generator panel, made

Ground detectors.

by the same concern and intended for a three-phase generator, is shown in Figs. 71 and 72. Both of these panels are shown in the manner arranged when intended to control a single generator. When a number of them are placed side by side to control an equal number of

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Ground detectors in three phase circuit.

generators connected in parallel, synchronizing lamps and accessories are provided. Fig. 73 illustrates, diagrammatically, the circuit connections of Fig. 69 together with the synchronizing attachments; and Fig. 74, in like manner, illustrates the connections of Fig. 71. All the parts of these diagrams are plainly marked so as to render further explanation unnecessary.

A switchboard made up of panels, manufactured by the Westinghouse Company, is shown in Figs. 75 and 76.

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