INDUCTION MOTOR THEORY - PDHonline（感应电动机的理论PDHonline）.pdf

PDHonline Course E176 (3 PDH) Induction Motor Theory Instructor: Jerry R. Bednarczyk, P.E. 2012 PDH Online | PDH Center 5272 Meadow Estates Drive Fairfax, VA 22030-6658 Phone Fax: 703-988-0088 www.PDH www.PDH An Approved Continuing Education Provider www.PDH PDH Course E176 www.PDH INDUCTION MOTOR THEORY Jerry Bednarczyk, PE Course Content INTRODUCTION The AC induction motor is well suited to applications requiring constant speed operation. In general, the induction motor is cheaper and easier to maintain compared to other alternatives. The induction motor is made up of the stator, or stationary windings, and the rotor. The stator consists of a series of wire windings of very low resistance permanently attached to the motor frame. As a voltage and a current is applied to the stator winding terminals, a magnetic field is developed in the windings. By the way the stator windings are arranged, the magnetic field appears to synchronously rotate electrically around the inside of the motor housing. The rotor is comprised of a number of thin bars, usually aluminum, mounted in a laminated cylinder. The bars are arranged horizontally and almost parallel to the rotor shaft. At the ends of the rotor, the bars are connected together with a “shorting ring.” The rotor and stator are separated by an air gap which allows free rotation of the rotor. Typical Induction Motor Rotors The magnetic field generated in the stator induces an EMF in the rotor bars. In turn, a current is produced in the rotor bars and shorting ring and another magnetic field is induced in the rotor with an opposite polarity of that in the stato