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High tension Switchboards.

by a space of about two feet. There are two incoming three-phase lines, and three groups of three-phase transformers, and the arrangement of the sockets on the switchboard panels is such that either one of the incoming lines can be connected with any one of the groups of transformers. The incoming lines are provided with circuit breakers that have copper primary, and carbon final breaking contacts, both of which are mounted on the end of vertical arms about five feet long which when released swing out to the horizontal position, making an opening of about six feet. One of these circuit breakers is seen at the top of Fig. 82. The three arms are mounted on a single shaft, being strongly insulated from each other, and are arranged so that they may be operated independently or all together. They are operated by means of elctro-magnets, and the lever and connecting rod on the right are used to close the three arms at once, while the smaller lever higher up is for the purpose of opening them simultaneously.

The board, Fig. 83, handles the secondary current from the three-phase groups of transformers that are connected with the high-tension board, Fig. 82. This board has three panels from which three outgoing currents are controlled. Each panel is provided with circuit breakers similar to the high-tension design but of smaller size, the separation of the contact points being about one foot and a half. In addition to the circuit breakers, each panel contain three ammeters, one voltmeter, arranged to be connected across any of the three phases, two intergrating wattmeters, to measure the power passing to the outgoing circuits, and three main switches, the blades of which are protected by hard rubber shields so that they

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Oil break Switches.

may not be touched accidentally. In both these boards it will be noticed that the circuit breakers are separated from each other by large marble slabs, the object of which is to prevent arcs from striking across from one to another when the circuit is opened. • As is shown in the foregoing, switches constructed to handle currents of high voltage have to be made so as

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to make a long break when they open the circuit. This is the case when they break the circuit in air, but if the contacts are separated under oil, the length of the break can be greatly reduced. Oil break switches are made in numerous designs, some of which are arranged to be operated by hand, and others by means of electro-magnets or pneumatic cylinders. Air-break switches intended for high voltages are also made so as to be operated by electro-magnets or pneumatic cylinders.

An oil break circuit breaker operated by electro-magnets is shown in Fig. 84,

These constructions are used when the switch or circuit breaker is of such proportions that it cannot be readily

Power factor meter.

operated by hand. Whether the switch is operated by electro-magnets or compressed air cylinders, a small, manually operated switch is provided to control its movement. If the switch is electro-magnetic, the small operating switch controls the flow of current through its magnets, and thus causes it to open or close at the will of the operator. The pneumatic switches are provided with magnets to open and close the actuating valve, and these magnets are controlled by the small operating switch. The operating switch is generally mounted upon the switchboard, or upon a conveniently located stand, but the main switch itself can be located wherever desired, connecting wires being run from it to the operating switch.

Of late quite a number of devices have been brought out which are for the purpose of rendering the action of some of the apparatus more positive, or to accomplish results that previously existing apparatus did not accomplish. One of the most useful of these devices is an instrument that indicates the power factor of the circuit. This instrument, which is called a "power factor meter," is shown in Fig. 85.



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