Figs. 1,213 to 1,217.—Apparatus which operates successfully on an alternating circuit. The alternating current will operate incandescent lamps, arc lamps, electric heating apparatus, alternating current motors. It will flow through a straight wire with slightly increased retarding effect, but if the wire be wound on an iron bar its strength is greatly reduced.
The size of wire needed to transmit a given amount of electrical energy (watts) with a given percentage of drop, being inversely proportional to the square of the voltage employed, the great saving in copper by the use of alternating current at high pressure must be apparent. This advantage can be realized either by a saving in the weight of wire required, or by transmitting the current to a greater distance with the same weight of copper.
In alternating current electric lighting, the primary voltage is usually at least 1,000 and often 2,000 to 10,000 volts.
Ques. Why is alternating current used instead of direct current on constant pressure lighting circuits?
Ans. It is due to the greater ease with which the current can be transformed from higher to lower pressures.
Ques. How is this accomplished?
Ans. By means of simple transformers, consisting merely of two or more coils of wire wound upon an iron core.
Since there are no moving parts, the attention required and the likelihood of the apparatus getting out of order are small. The apparatus necessary for direct current consists of a motor dynamo set which is considerably more costly than a transformer and not so efficient.