With the advent of solid-state electronic variable frequency drives (VFDs) in the late 1980s, it was found that the windings of motors used on VFDs failed more frequently than when powered by a utility (sine wave) supply. By the turn of the century, motor manufacturers had gained a better understanding of how VFDs affected motor windings. This article describes the materials and methods associated with inverter duty windings.

Con la llegada de los variadores de frecuencia electrónicos (VFD) de estado sólido a fines de la década de 1980, se descubrió que los bobinados de los motores que funcionaban con VFDs fallaban con más frecuencia que al estar alimentados con la energía convencional (onda sinusoidal). A principios de siglo, los fabricantes de motores habían comprendido mejor cómo los VFD afectaban los devanados del motor, y al igual que los proveedores de materiales electro, aislantes habían desarrollado materiales y métodos para mejorar la confiabilidad de los devanados de los motores alimentados con VFDs. En este artículo, describiremos los materiales y métodos asociados con los devanados inverter duty.

¿Recibió un motor antiguo bobinado con alambre de aluminio? Este webinario explicará como realizar la conversión adecuada de alambre de aluminio a alambre de cobre en máquinas de CA y CC, incluyendo ejemplos para el rebobinado de estatores y campos shunt.

Choosing an appropriate lead wire for a new stator winding is an important task. The manufacturer’s information is not always available, or the number of circuits or external connection may have been changed, requiring a redesign of the lead wire.  

This video shows one step in collecting motor winding data: how to measure magnet wire.

Revised September 2022!
EASA's most comprehensive technical document is available FREE to EASA members. Download the complete manual or just the sections you're interested in.

This webinar recording shares some of the “best practice” rewind methods used by (and learned from) EASA service centers around the world: connection recognition, best insulating materials, wire choices and tips to save time and effort.

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.

Las versiones impresas y en forma de descarga del valioso manual didáctico / recurso de EASA, “Principios de Motores C.A. Medianos y Grandes”, se  ahora disponibles en inglés y en español. El manual incluye gráficos e ilustraciones, fotografías y mucha información técnica sobre máquinas C.A., incluyendo como funcionan, información específica sobre los tipos de encerramientos, fabricación de componentes y aplicaciones.  Muchos de los principios incluidos en el libro aplican a todos los motores C.A., especialmente a aquellos accesorios que fueron asociados en el pasado con las máquinas más grandes (como encoders, RTDs, termostatos, calentadores de espacio, sensores de vibración, etc.).

Filled with practical information, this 118-page handbook (3.5" x 6", 9cm x 15cm) makes a great “give-away” item for your customers and potential customers! Buy this great resource as is OR imprint your company logo and information on the cover to turn it into a great marketing piece for your salespeople!

This webinar focuses on:

• Proper wire measurements
• Metric and AWG sizing
• Aluminum to copper
• Random to form wound and vice versa
• Stator windings, field windings, interpoles
• Using wire combination tables
• Using EASA’s AC Motor Verification & Redesign software

This EASA software is a valuable interactive training tool ideal for training your novice(s) ... and even experienced winders will learn from it. The CD teaches how to wind in a richly detailed, step-by-step approach which includes narrative, animations and video clips, with tests to assess student comprehension. 

This webinar will cover burnout procedures for AC stators: 

• Interlaminar insulation materials / properties
• Core testing before and after
• Processing equipment, controls and records

This webinar recording covers: 

• Importance of core loss testing
• Methods to reduce core losses
• Slot fill improvement without reducing copper

The AC Motor Verification and Redesign software provides easy verification of either concentric or lap windings, as well as redesigns with changes in poles/speed, horsepower, frequency or voltage. The redesign report with original and new winding data is output as an Adobe Reader (PDF) file and can be printed or saved. The program also allows you to search EASA’s extensive motor winding database.

This version of the EASA Motor Rewind Database software takes a large leap forward with the data that it provides members. Most notably, it now has the ability to connect to a live, ever-expanding online database of more than 250,000 windings. This live database will be continuously monitored, updated and corrected as needed by EASA’s Technical Support Staff.

This webinar recording covers:

• Insulation system versus insulation materials
• Stresses imposed on insulation systems
• Insulation system components / functions
• Typical testing of system components / functions

This manual, a companion to EASA's 2-day seminar of the same name, 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 NEMA motors.

When preparing to rewind random or form wound stators, sometimes there just doesn’t seem to be enough room in the stator slot for the desired conductor area and insulation quantities. Common scenarios encountered are redesigns from concentric to lap, changes to higher voltages or aggressive designs from the OEM.

This webinar will look at balancing stator copper losses against insulation reliability.

Before rewinding a stator, EASA strongly recommends winding data verification. We see many cases where failure to invest a few minutes up front costs a service center an additional rewind. One of the most common winding data changes made by service centers is a wire size change. Minimizing the manual calculations associated with this change can increase process efficiency while reducing errors.

When rewinding the shunt fields of a DC machine, it is important to avoid making changes that could negatively impact performance. The recommended practice is to maintain the manufacturer’s winding configuration during the repair. That is, the field circuit connection, turns per coil, mean or average length of turn (MLT) and wire size should not be changed. However, service centers do sometimes encounter issues around wire size availability. The purpose of this article is to provide some guidance for making wire size substitutions when the original size is unavailable.

Although aluminum magnet wire theoretically can be converted to copper magnet wire of about 5/8 of the original wire area, in some cases this is not advisable. In others, it may result in a change in the magnetic strength of a coil or winding. In this article we will address the most common aluminum-to-copper magnet wire conversions as well as how to deal with whether the wire area should be reduced. Topics discussed include:

• AC motor windings
• Shunt fields
• Series fields and interpoles
• Transformer windings

The wires that are associated with most motor and generator windings are copper magnet wires. For some special application machines, there are other wire types that have been used, such as Litz wire (very fine woven strands) or lead wire. In this article, we will address some issues relating to magnet wire type conversions and combinations. The term magnet wire brings to mind the thought that the wire is somehow "magnetic," which is not the case. The reason for the name is that it is wire used in magnetic coils. Thus, they are coils that make use of electro-magnetism. The two physical types are round and rectangular magnet wire. Strictly speaking, square wire is a form of rectangular wire. Topics covered in this article:

• Rectangular to round wire conversion
• Metric and AWG wire conversions
• Wire size combinations

There are many transformers in use rated up to 10 MVA (10,000 kVA) that were originally wound using aluminum conductors. When damaged or when selected for rewind, the aluminum conductor is often replaced with copper conductor. This is usually fairly routine when the conductor changes are undertaken within the bounds of the original transformer design. It is this type of change that will be reviewed in this article. It is not the intent to provide information here for the complete redesign of the transformer. It is important that all coil dimensions remain as close to the originals as possible. In carrying out the type of change outlined above, there are some design issues and differences in material properties that must be considered before proceeding with the work. Some of these issues are:

• The effect that the difference in thermal characteristics of the materials will have on short term overload capability.
• The effect that the different material properties will have on the original blocking and bracing system.
• The effect that the difference in conductivity will have on conductor size.
• The effect that the difference in conductor size may have on coil resistance and reactance.
• The effect that the different conductor size may have on coil size (axial length) and hence its ability to withstand short circuits.

When repairing motors, we often take the lead wire ampacity charts for granted, without giving much thought to how they were developed. Who figured out how much current is acceptable for a specific lead wire, and why are there different ratings for different types of insulation? This article will cover some often-overlooked facts about ampacity.

Learn how proper de-reeling techniques for round magnet wire can help avoid future motor failures.