The DC Machine
The DC machines described in this chapter are motors or generators. The term machine is used when the test procedure is the same for both. A motor can be converted to a generator (and vice versa), so the terms motor and generator are used only when the explanation applies to one or the other.
DC generators produce very high-quality power, but (because of maintenance and other costs) AC powered DC drives are used for most motor applications.
DC power is used for some high-voltage power transmission. DC current flows through the whole area of a wire, making it more efficient than AC for long distance transmission. High-voltage AC current uses only the outer portion of the wire. Only two transmission lines are needed with ...