19-01-2012, 01:53 PM
Basic Principles and Functions of Electrical Machines
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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.
CLASSIFICATION OF ELECTRIC MACHINES
There are several methods of classifying electric machines [6]:
• Electric power supply - Electric machines are classified as D.C. and A.C. machines as well as according to their stator and rotor constructions as shown in Figure 1.
• National Electric Manufacturers’ Association (NEMA) Standards - NEMA standards are voluntary standards of the National Electric Manufacturers Association and represent general practice in industry.
BASIC FEATURES OF ELECTRIC MACHINES
The basic structural features of a D.C. machine
are:
• Stator - The stator carries the field winding.
The stator together with the rotor constitutes
the magnetic circuit or core of the machine. It
is a hollow cylinder.
• Rotor - It carries the armature winding. The
armature is the load carrying member. The
rotor is cylindrical in shape.
