Reference Book
DC may be obtained from an AC supply by use of a rectifier, which contains
electronic elements that allow current to flow only in one direction. DC may
be converted into AC with an inverter or a motor-generator set. DC is used to
charge batteries and as power supply for electronic systems.Motors and Transformers
Electric motors are machines which convert electrical energy into mechanical
energy. There are two types of electric motors - AC motors & DC motors.Both AC and DC motors serve the same function but they are powered,
constructed and controlled differently. The most basic difference is the power
source. AC motors are powered from alternating current while DC motors are
powered from direct current, such as batteries, DC power supplies, or an AC-
to-DC power converter. DC wound field motors are constructed with brushes
and a commutator, which add to the maintenance, limit the speed and usually
reduce the life expectancy of brushed DC motors.
AC induction motors do not use brushes. They have long life expectancies.
The final basic difference is speed control. The speed of a DC motor is
controlled by varying the armature winding’s current while the speed of an AC
motor is controlled by varying the frequency, which is commonly done with
an adjustable frequency drive control.
Transformers are basically very simple static (or stationary) electro-magnetic
passive electrical devices that work on the principle of Faraday’s law of
induction by converting electrical energy from one value to another.
The transformer does this by linking together two or more electrical circuit
using a common oscillating magnetic circuit which is produced by the
transformer itself. A transformer operates on the principles of ‘electromagnetic
induction’, in the form of mutual induction.
Mutual induction is the process by which a coil of wire magnetically induces a
voltage into another coil located in close proximity to it. Then we can say that