A special discounted collection of 12 webinar recordings focusing on AC motor windings.

Just $60 for EASA members!

This manual covers horizontal and vertical squirrel-cage induction motors in the 300 to 5,000 horsepower range, low- and medium-voltage. Most of the principles covered apply to other sizes as well. This manual focuses primarily on IEC motors and standards.

This presentation covers induction motor basics for squirrel-cage and wound rotor motors

For those who work almost exclusively with lap or concentric wound three-phase stators, wave wound rotor connections can be a challenge. This is especially true if connection data gets lost or if an existing winding connection is damaged during a failure. In these cases, it is useful to have a practical method for laying out a valid connection diagram. 

Para aquellos que trabajan casi exclusivamente con estatores trifásicos con devanados imbricados o concéntricos, las conexiones de los rotores bobinados con devanados ondulados pueden ser un reto. Esto es especialmente cierto, cuando los datos de conexión se pierden o cuando el fallo en el bobinado provoca daños en la conexión existente. 

Wound rotor (WR) motors represent only a small fraction of all electric motors in service. In reviewing the EASA Technical Support call logs, one would conclude that there are many more wound rotor motors in service. Because many of us do not work on wound rotor motors often, it is understandable that not everyone has a clear understanding of how they differ from a squirrel cage motor. The purpose of this article is to dispel some misconceptions about how they work and to offer valuable tips for failure analysis, repair and testing. Other topics covered include: Secondary voltage Crane applications Testing tips, after assembly

There is much discussion in the industry about how to properly electrically test AC stator and wound rotor windings. Topics include test voltage, procedure, frequency and when to perform the various tests. This article describes how the following standards address these questions:

• NEMA MG 1-2011
• (MG1) IEEE 43-2000
• (IEEE 43) IEEE 62.2-2004
• (IEEE 62.2) IEEE 522-2004
• (IEEE 522) IEEE 1068-2009
• (IEEE 1068) ANSI/EASA AR100-2010
• (AR100) CSA C392-2011 (C392)

These standards are regularly reviewed and coordinated, so some of the information may not match the old yellowed reference taped to your toolbox lid. These updated references should replace anything dated previous to the dates indicated on the standard. AR100 Section 4.3.1 lists the recommended tests for stator and wound rotor windings. They are insulation resistance (IR), winding resistance, growler, phase balance, surge comparison, polarity and ball rotation tests. This article covers the IR, winding resistance and surge tests. Noticeably absent from this list is the ever popular high potential (hi-pot) test. Topics covered also include: IR (or megohm) test Polarization index test Winding resistance test Surge comparison test Hi-pot test.

Quick helpful guidance and tips for test running wound rotor motors.

The slip ring or wound rotor induction motor (WRIM) has been used in a variety of applications. Many of these applications use the WRIM's high starting torque capability while limiting current to start and run very high inertia loads such as hammer mills, rolling mills, centrifuges, and rotary kilns. Other applications utilize the variable speed capability of the WRIM. Probably the most common use of WRIMs for variable speed is in crane and hoist service. Other variable speed uses for the WRIM include wiredraw machines, fans, blowers, pumps and refrigeration compressors. Many of these applications, if designed today, would utilize a standard induction motor and variable frequency drive (VFD), particularly those where speed control is the desired end result. When older WRIMs or their controllers fail, the best solution often is to replace both motor and control. There are situations, however, where the best solution may be to replace the old controller with a VFD and continue to use the WRIM. As always, the more knowledge we have about the equipment we work on the better equipped we are to make good choices about repairing, replacing or upgrading this equipment for our customers. With this in mind, a review of how the WRIM and some of its control schemes work seems appropriate.

The poles for the stator and rotor of the wound-rotor motor must be equal. When rewinding any wound-rotor motor, watch for consequent-pole connections. Grouping alone is not a reliable indicator of poles. The best way to understand the process is to visualize the rotating electrical field in the stator of a wound-rotor motor. The field rotates one direction, so that when the rotor is driven in the opposite direction the passing frequency is increased. If the speeds are the same (i.e., the same number of poles as the drive motor) the output frequency will double.