الفهرس 
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Abstract
Squirrel cage induction motors are, by all means, the main workhorses of industry for many reasons. The simplicity of construction, the minimum need for maintenance, the inherent safe operation, and the low cost are only examples of these reasons. The other side of the coin depicts their starting characteristics dominated by the high starting currents (typically from 4 to 10 times the rated current in case of direct online starting) and the resulting wild electromagnetic torque transients as well as the incurring mechanical shocks. To reduce these large starting currents, the motor can be started at reduced voltages obtained from one of the various reduced voltage starting techniques. These, however, would also yield a lower starting torque, which means that these techniques may not be able to start all motor loads since the developed torque is highly sensitive to the voltage as it is approximately proportional to its square. Power electronics, it is the new engineering field that conquered the scene in the last few decades. It is concerned with the processing of electrical power using electronic devices. Energy saving, decreasing equipment size, decreasing equipment weight, no environmental pollution problems and let us not to forget that power electronics field is in a continuous improvement are some advantages that made it essential to head towards making full use of power electronics that help with the efficient use of electricity. Using the new technologies in making use of power electronics to control the starting of induction motors depend on the idea of reduced voltage starting techniques of three phase induction motors. Soft starting of an induction motor is one of the most commonly used techniques nowadays to make use of the noticed progress in the power electronics market and the features of the squirrel cage induction motors. Soft starting is considered as one of the reduced voltage starting techniques with some features of micro controllers and protection. One of the most important features of the soft starters is that the motor is started without experiencing a current surge, the supply system will not experience a voltage DROP as that occurs if the motor is started directly and the motor and mechanical system also will not experience a mechanical shock due to the motor starting torque.