14-09-2013, 03:03 PM
Basic Principles and Functions of Electrical Machines
Principles and Functions .pdf (Size: 348.49 KB / Downloads: 246)
ABSTRACT
Recent advances in power electronics and high-
speed microprocessors have led to considerable
attention in electrical machines with regard to
their applications in industrial drives. This paper
brings to the fore, various types of electrical
machines, their operations, and applications, as
well as the method of determining their
parameters. Various ways of protecting electric
machines against overloads and mechanical
faults are also highlighted. It is anticipated that
the work presented in this paper will be of
immense benefit to practicing engineers
especially in areas of machine design,
maintenance, and protection.
INTRODUCTION
The Direct Current (D.C.) machine, the
synchronous machine, and the induction
machine are the major electromechanical
conversion devices in industry [1]. The merits of
the squirrel cage induction machine are:
lightness, simplicity, ruggedness, robustness,
less initial cost, higher torque-inertia ratio,
capability of much higher speeds, ease of
maintenance, etc [2, 3]. The most important
feature which declares it as a tough competitor
to D.C. machines in the drives field is that its
cost per KVA is approximately one fifty of its
counter-part and it possesses higher suitability in
hostile environment.
Electric motors and generators are a group of
devices used to convert mechanical energy into
electrical energy, or electrical energy into
mechanical energy, by electromagnetic means. A
machine that converts mechanical energy into
electrical energy is called a generator, alternator,
or dynamo, and a machine that converts electrical
energy into mechanical energy is called a motor.
Two related physical principles underlie the
operation of generators and motors. The first is the
principle of electromagnetic induction discovered
by Michael Faraday in 1831 [9]. If a conductor is
moved through a magnetic field, or if the strength
of a stationary conducting loop is made to vary, a
current is set up or induced in the conductor. The
converse of this principle is that of electromagnetic
reaction, first discovered by Andre’ Ampere in
1820 [10]. If a current is passed through a
conductor located in a magnetic field, the field
exerts a mechanical force on it.
ELECTRIC MACHINES PROTECTION AND
MAINTENANCE
Electrical and mechanical faults can impose
unacceptable conditions and protective devices
are therefore provided to quickly disconnect the
machine from grid. In order to ensure that
electrical machines receive adequate protection,
extensive testing is performed to verify the high
quality of assembly. After a machine of a particular
type has been type tested for electrical
characteristics, all subsequent machines of the
same type undergo a routine test programme.
CONCLUSION
This paper has presented the basic principles of
electric machines. The basic features and the
conventional method of determining the machine
parameters have also been highlighted.
The authors also elucidated the various ways of
protecting electric machines against overloads and
mechanical faults. Areas of application of electric
machines have been itemized in order to show the
importance of these devices in process industries.