Up Time Magazine - December 2008/January 2009 - (Page 40) lowest calculated imbalance. If the difference is greater than 2%, positioning the rotor through a second pole face is recommended. Concentric vs. Lap Wound An important consideration when evaluFigure 4 - Peak-to-Peak Inductance Phase 1 to 2 ating RIC data for indication of eccenof the individual phase-to-phase inductance tricity is whether the motor is concentric or lap furthest from the average and multiplying by wound. If a motor is concentric wound, it may 100. With the rotor removed from a three- be built with a pre-existing offset between the phase motor this imbalance is expected to be stator windings and the rotor. less than 1%. With a rotor installed this value varies and is determined by design consider- The concentric wound motor illustrated in Figations such as rotor skew, design air gap, and ure 5 has the stator windings inserted into the other factors that affect rotor/stator geometry. stator slots in a basket form or stacked configuFor a motor in satisfactory condition, this im- ration. Commonly all of the pole groups for balance remains within a plus or minus window phase A are laid into the slots, then all of the of 2 for any rotor position. Some motors may pole groups for phase B, then finally all of the be 5.5% to 7.5%, for example. When perform- pole groups for phase C. This results in a greating a RIC, at the end of positioning the rotor er distance between the rotor and the phase through one pole face, check the highest and A coils than exists between rotor and phase C Figure 5 - Concentric Windings coils. This results in a natural stair stepping indication of the phase-to-phase values seen in Figure 8. Standard lap wound motor windings, which have each coil of every phase equally lapped over the surrounding coils, results in the three phases having equal high/low inductance vales. How does a person identify a concentric or lap wound motor? There are only two absolute methods. One is by taking the end bell off and looking. The other is obtaining the information directly from the manufacturer. However, here are some rules of thumb that should help you distinguish between the two. Here You GO! Introducing the GO, a new mid-range laser alignment tool from Fixturlaser. The new GO is designed to offer the dedicated functionality of the Shaft Hog, while applying the measurement technology of the XA. It fits right into Fixturlaser’s “Express Alignment” philosophy, with large detectors, line lasers, built-in inclinometers, and USB connectivity. Customers have been asking for it, and we’re pleased to reply “here you go”. NEW! GOOD ©2008 Vibralign, Inc. BETTER BEST 40 december/january 2009 http://www.vibralign.com http://www.vibralign.com
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