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This motor is more powerful than that used for the projector drive motor, and for this reason cannot be connected directly to the power supply line without some special provision being made to prevent an excessively high current from being drawn by the motor upon starting. The starting apparatus used with this motor is illustrated in Figure 27. This starting device consists essentially of a sheet-iron box in which are mounted a line switch for turning the power on and off, a resistor which is connected in series with the motor armature to prevent an overload current from being drawn upon starting, and a contactor which "shorts out" the resistor after the motor has almost reached its normal running speed. The action of this device is as follows:-When the main line switch is closed, a heavy starting current is drawn by the motor. This large current produces what we call a "voltage drop" across the resistor. The connections of the contactor operating coil are made from one side of the line to a point between the motor armature and the resistor. When the motor comes up to speed, the current drawn by the motor "falls off." The lesser current reduces the voltage drop in the resistor, and, since there is less loss through the resistor, the voltage across the coil becomes higher which causes the contactor to close and short-circuit the resistor. The terminals of the coil are then connected directly across the line, and, until the main line switch is opened, the operating coil will keep the contactor closed and the resistor short-circuited.

The generator controls are mounted on the control panel between the two machines. On this panel are located a switch for turning on and off the AC power to the amplifiers, a voltmeter for reading the line voltage supplied by the generator, and a field rheostat for controlling this voltage in the same manner as that described in section 24. In back of the generator control panel is mounted a fuse block containing fuses for the AC line from the generator. These fuses may be replaced when necessary by removing the wire mesh cover. This is done by removing the three nuts on the ends of the three bolts seen protruding from the rear of the panel.


Chapter Three Pages
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
[16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]

[1] [2] [3] [4] [5] [6] [7] [8] [9]
[10] [11] [12] [13] [14] [15]

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