Electric Machinery Fundamentals 5th Edition, ISBN-13: 978-0073529547
[PDF eBook eTextbook]
- 704 pages
- Publisher: McGraw-Hill Education; 5 edition (February 17, 2011)
- Author(s): Stephen J. Chapman
- Language: English
- ISBN-10: 9780073529547
- ISBN-13: 978-0073529547
Note: Brand New, Printed in black and white pages.
Chapman continues to share his up-to-date knowledge and experiences in the field in an engaging and understandable style.
“The first five chapters of this book really suffice for a good intro to electric machines. Can’t really say much negative at all except in chapter 7 in the section on the rotor circuit model. Here he uses an ad hoc claim that rotor circuit voltage is directly proportional to slip-true for any positive power of slip at locked rotor and sync, slip 1 and 0 respectively. Linearity totally unjustified. This is done to derive the proper slip dependent impedance. This impedance can be derived from the model and circuit theory taking motion into account with more work and this is valid but too difficult for a basic intro(actually by reference frame arguments the voltage too has a dependence on slip-nonlinear-and is not the constant locked rotor voltage-computer simulation needed). Forgivable considering the scope and intended audience-the claim just comes across as a plausibility which will lead to the slip having the right power-it’s an approximation that most if not all use in circuit model estimates. Nevertheless it deserves a 5-star particularly for treatment of transformers and ac machinery. As an aside I’ll give the justification for the author’s ad hoc claim. In the transformer model which is what is used in chapter 7 to model the 3-phase induction motor, the rotor circuit corresponds to the secondary winding of the transformer. The voltage induced in the secondary winding of the transformer is proportional to the frequency of the field that moves through the winding (through the iron core)-justified in chapter 2-Faraday’s Law applied at the secondary winding with rms averaging of the sinusoidal. This is a fixed or stationary winding with a varying magnetic field moving through it. Our rotor circuit must be viewed as stationary, i.e. we must find the frequency of the magnetic field as seen in the fixed rotor frame, this now looks like the secondary winding. Remembering the frequency of the magnetic field is essentially its angular speed (rotating field at constant speed), the frequency as seen in the fixed rotor frame is the field angular speed in this frame, which is the difference of the angular speeds (at a particular instant for the rotor!), but this is equivalent to slip times frequency of the magnetic field-you know where 2Pi goes. This then is slip times the secondary voltage-approximate since this secondary voltage is an rms value in the transformer equation. Q.E.D. His claim is now justified for the transformer model. The secondary voltage used is the locked rotor rms voltage, so in the end you get an estimate of average torque at a given slip-extended to a torque speed curve. Hope this clarification helps. A second book on power electronics would help. The chapter that used to be included on this was just an outline really.”
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