Electrical Engineering ⇒ Topic : Introduction of A.C. Fundamentals
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Sachin
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Introduction We have dealt so far with cases in which the currents are steady and in one direction; this is called direct current (d.c.). The use of direct currents is limited to a few applications e.g. charging of batteries, electroplating, electric traction etc. For large scale power distribution there are, however,many advantages in using alternating current (a.c.). In an a.c. system, the voltage acting in the circuit changes polarity at regular intervals of time and the resulting current (called alternating current) changes direction accordingly. The a.c. system has offered so many advantages that at present electrical energy is universally generated, transmitted and used in the form of alternating current. Even when d.c. energy is necessary, it is a common practice to convert a.c. into d.c. by means of rotary converters or rectifiers. Three principal advantages are claimed for a.c. system over the d.c. system. First, alternating voltages can be stepped up or stepped down efficiently by means of a transformer. This permits the transmission of electric power at high voltages to achieve economy and distribute the power at utilisation voltages. Secondly, a.c. motors (induction motors) are cheaper and simpler in construction than d.c. motors. Thirdly, the switchgear (e.g. switches, circuit breakers etc.) for a.c. system is simpler than the d.c. system. In this chapter, we shall confine our attention to the fundamentals of alternating currents. | |
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