Motion picture operation; stage electrics and illusions a practical hand-book and guide for theater electricians, motion picture operators and managers of theaters and productions - Softcover

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 Excerpt: ... pass through both armatures in series. Thus the counter e.m.f. of both armatures opposes that of the line and they operate at a certain speed. Each motor has a natural tendency to send current in opposition to that impressed upon it by the line. If then the electrodes are brought together, they at once form a short circuit around the armature of B. The current in B reverses and it then begins to act as a generator and sends current through the arc lamp. The current which passes through the armature of A also passes through the arc lamp. A is then a motor and operates B as a generator. The voltage at the arc is less than the line voltage by as much as the counter e. m. f. of motor A amounts to, neglecting the drop in voltage due to resistance. No resistance is needed if the winding is properly arranged and there is not the lsss in heat which goes with the use of resistances. This arrangement can be used with direct-current circuits only. It is not suitable where the supply voltage is very much higher than the voltage used at the arc. A field rheostat is provided to adjust the field strength of B. A is equipped with the ordinary motor-starting rheostat only. Rotary Converter Control.--This is a machine used only where the supply is alternating current. The voltage delivered to the converter must be the same as that desired at the direct-current terminals. This machine has an armature essentially similar to that of a direct-current dynamo. Alternating current is supplied to it at one set of terminals and direct current is taken from the others. This armature acts as motor and generator at the same time. Whatever voltage regulating is necessary with this machine must be done on the alternating-current side. Changing the field strength does not materially affec...

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