Mike Howell
EASA Technical Support Specialist

Los bobinados fraccionarios concentrados, en inglés Fractional-Slot Concentrated Windings (FSCW), han sido empleados durante décadas, principalmente en máquinas pequeñas. Sin embargo, el avance continuo en la electrónica de potencia junto con la necesidad de tener máquinas más eficientes y con mayor densidad de potencia está aumentando el uso de este tipo de bobinados en máquinas de diferentes tipos y tamaños.

Por Mike Howell
Especialista de Soporte Técnico de EASA

Los motores de reluctancia conmutada (SRM), también conocidos como motores de reluctancia variable (VRM), tienen su origen a mediados de 1830. Estos motores fueron usados como motores de tracción ferroviaria. Sin embargo, la electrónica de potencia necesaria para controlar satisfactoriamente los SRMs, no fue patentada hasta comienzos de los 70´s. Esto implicaba una conmutación electrónica sincronizada con la posición del rotor. Los centros de servicio están notando un incremento en el número de SRMs que reciben para reparar y algunos de los técnicos no están familiarizados con su funcionamiento. Como cualquier otra máquina rotativa, un conocimiento básico de los principios de funcionamiento puede ayudar a detectar problemas y durante la reparación. Uno de los puntos más críticos para el personal del centro de servicios es entender de antemano que estas máquinas no pueden ser operadas sin un drive especial, el cual normalmente necesita ser suministrado por el usuario final o el fabricante.

Mike Howell
Especialista de Soporte Técnico de EASA

Los avances en la electrónica de potencia en las últimas décadas han permitido el uso de una variedad de máquinas eléctricas rotativas que de otro modo no sería factible. Una de ellas se denomina máquina de reluctancia debido a la forma en la que dichas máquinas producen un torque electromagnético. Una máquina de reluctancia es una máquina eléctrica en la cual el torque se produce por la tendencia de su parte móvil a moverse a una posición donde se maximiza la inductancia del devanado excitado. En un artículo publicado en Currents en marzo de 2020, se trató el tema del motor de reluctancia conmutada (SRM), mientras que este artículo se centrará en el motor sincrónico de reluctancia (SynRM). Demos un vistazo a algunas de sus similitudes y diferencias.

Mike Howell
EASA Technical Support Specialist

Fractional-slot concentrated windings (FSCW) have been used for decades, primarily in small machines. But continued technological advancement in power electronics along with the need for more efficient and power-dense machines is increasing use of FSCW in a variety of machine types and sizes.

Mike Howell
EASA Technical Support Specialist

Reluctance machines offer simple construction, high power density and low cost. Over time, advancement in power electronics will increase the prevalence of these machines in a number of applications, creating repair opportunities for service centers. This recording explores features of synchronous and switched reluctance machines.

• Basic magnetic circuits
• Reluctance machines and torque production
• Slots, poles and phases
• Concentrated windings vs. lap or concentric windings
• Rewind, test and inspection

This recording will benefit service center managers, supervisors and technicians.

This version of Principles of Medium & Large AC Motors manual is now available to address applicable IEC standards and practices. This 360-page manual was developed by industry experts in Europe along with EASA's engineering team. (The "original" version of this book based on NEMA standards remains available as a separate document.)

This manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, information on enclosures, construction on components and applications. Many of the principles included apply to all AC motors, especially those with accessories that are associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters and vibration sensors).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 37 to 3,700 kW (300 to 5,000 hp) range, low- and medium-voltage, most of the principles covered apply to other sizes as well. 

This valuable instructional/resource manual is available in printed and downloadable versions, and focuses primarily on IEC motors.

Sections in the manual include:
(Download the PDF below for the complete Tables of Contents)

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

BUY A COPY FOR YOUR OFFICE

PRINTED BOOK DOWNLOADABLE PDF

This book is also available focusing on NEMA Standards — in both English and Español.

NEMA - English NEMA - Español

Chuck Yung 
EASA Technical Support Specialist 

One of the many interesting things we get to do as repairers of rotating electrical equipment is to rewind the rotating poles of synchronous ma­chines. Handling large poles can present special challenges, but the actual winding process itself can be downright enjoyable—if we are ad­equately prepared. This article will outline procedures that take the mystery out of successful pole winding. The procedures are also helpful for stationary field coils and interpoles. 

One of the first important steps is to draw the connection. Most synchronous rotors are con­nected in series; however, you don’t want to miss a series-parallel connected rotor (Figure 1). 

By Mike Howell
EASA Technical Support Specialist

The switched reluctance motor (SRM), also known as the variable reluctance motor (VRM), originated in the mid-1830s. It was first used as a locomotive traction motor. However, the power electronics necessary for satisfactory control of SRMs were not patented until the early 1970s. This entailed electronic commutation synchronized with rotor position. Service centers are seeing an increase in the number of SRMs received for repair, and some of the technicians encountering them are unfamiliar with how they work. As with any other rotating machine, a basic understanding of operating principles can be useful in troubleshooting and repair. One of the most critical things for service center personnel to understand upfront is that these machines cannot be operated without a special drive, which typically would need to be supplied by the end-user or the manufacturer.

Richard Hughes (deceased)
Pump & Motor Works, Inc.

Proper testing of a synchronous motor is crucial for validating repair, reconditioning or remanufacture. There are several types of synchronous motors and a brief description of each will be given prior to discussing testing.

Topics discussed are:

• Brush type motor
• Watch for resistance value extremes
• Brushless motors
• Performing insulation resistance test
• Performing AC voltage drop test

Mike Howell
EASA Technical Support Specialist

Advancement in power electronics over the last few decades has made it possible to utilize a variety of rotating electric machines that would otherwise not be feasible. One such class of machines is called reluctance machines because of the way they produce an electromagnetic torque. A reluctance machine is an electric machine in which torque is produced by the tendency of its movable part to move to a position where the inductance of the excited winding is maximized. A March 2020 Currents article discussed the switched reluctance motor (SRM) while this article will focus on the synchronous reluctance motor (SynRM). Let’s take a look at some of their similarities and differences.

Charles LeMone
LeMone Technical Services
Roanoke, VA 

Is the induction motor the preferred answer in industrial drive applications? What is happening to the synchronous, DC and wound rotor motor (WRM) in those applications? This paper discusses:

• Observations as customers replace synchronous, WRM and DC machines with the induction motor
• Why synchronous motors are used in industrial applications
• Issues with WRM and soft starters
• A case study of a 12,000 hp 4-pole synchronous motor and a soft starter
• What needs to be done to modernize the older synchronous motor starter?
• How a brushless synchronous motor operates
• Brushless synchronous motor protection