MEEN 225 Lecture Notes - Lecture 20: Induction Motor, The Terminal
8 Jan 2018
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Document Summary
The torque-speed characteristics of an induction machine is given as below: The characteristics: braking region nr < 0, s > 1. Torque is positive whilst speed is negative: motoring 0 < nr < ns, 1> s >0. The most common mode of operation: generating nr > ns, s < 0. Squirrel-cage induction motors are frequently started by connecting them directly across the supply line (self-start). A large starting current in the order of 500 to 800% of full-load current may flow in the line. This initial excessive current will affect the operation of other electrical equipment connected to the same line. Also, if a large current flows for a long time, it may overheat the motor & damage the insulation. To avoid problems associated with starting (too high current, too low torque), a variety of techniques are available. An easy way is to decrease the stator terminal voltage (i. e. reduced-voltage starting).
