Tom Bishop, P.E.
EASA Senior Technical Support Specialist

The International Electrotechnical Commission (IEC) standard 60529 “Degrees of protection provided by enclosures (IP code)” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “International Protection,” but is sometimes referred to as “Ingress Protection.” The IP code is commonly displayed on metric machine nameplates, which are manufactured to IEC standards.

The NEMA MG1 Motors and Generators standards have adopted the IEC standards for the IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of the IP marking is becoming more common. The purpose of this article is to describe the IP code designations and provide examples of the IP codes for common electrical machine enclosures.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

La norma 60529 de la International Electrotechnical Commission (IEC): “Degrees of protection provided by enclosures (IP code)” trata los grados de protección de las máquinas eléctricas (motores y generadores). La sigla “IP” significa “Protección Internacional” pero a veces se le conoce como “Protección contra Ingreso”. El código IP se muestra comúnmente en las placas de datos de las máquinas métricas, que son fabricadas con normas IEC. 

Las normas NEMA MG1 Motors and Generators han adoptado las normas IEC para las designaciones IP. Aunque no prevalecen en las placas de datos de las máquinas NEMA, la inclusión del marcado IP se está volviendo más común. El propósito de este artículo es describir las designaciones IP y proporcionar ejemplos de los códigos IP para los encerramientos de las máquinas eléctricas más comunes.

Chuck Yung
EASA Senior Technical Support Specialist 

There is now a much-needed DC repair standard, created through the participation of EASA members and industry motor users. The scope, as written in the document, states: “This document covers general recommendations for the repair of DC electric motors and includes guidelines for both the user and the repair facility ... . This standard covers reconditioning, repair and rewind of horizontal and vertical wound-field direct current motors and generators. It applies to all ratings above 0.75 kW (1 hp).”

The standard was created by a group of like-minded industry professionals who recognized the need for a best practice guide specific to DC machines. The working group accomplished the creation of 2455 in fewer than three years, from project authorization request approval to final publication. This document was modeled after IEEE 1068, a widely used electric motor repair standard.

The working group participants were:

*Denotes EASA member 

The working group covered everything from the receipt of the machine, to inspection and testing, to all aspects of repair including rewinding. Beginning with “Diagnostics in user’s plant,” the document recommends specific information gathering by the motor owner/end user to provide as much information as practical to the repair facility. 

Incoming tests for the repair facility are described in detail, with many tests (e.g., voltage drop test) being very familiar to EASA service centers. Nearly a dozen figures will be familiar to EASA members because they were originally published in EASA documents. 

The standard includes specific rewinding tips for fields and armature, as well as assembly and final test recommendations. IEEE 2455 also includes annexes for an Evaluation and Repair form, turn and undercut guidelines, an explanation of commutation, Commutator Condition Guide, sleeve bearing clearance, ventilation and cooling, post-assembly electrical adjustments and bearing currents in DC machines.

Much has been written in EASA publications and elsewhere about the consequences of excessive temperature on a motor’s performance. We know that excessive temperature and moisture are the largest contributors to bearing and winding failures. Understanding the source of the increased temperature will help us to correct the problem and improve the machine’s life expectancy.

A chart included in this article illustrates the theoretical impact of increased temperature on the life of the motor insulation system. This chart only addresses the impact of thermal aging and not various other conditions that will affectthe motor’s life. In other words, it says that for every 10ºC increase in operating tem-perature, the expected life is reduced by one-half. Conversely, if we can re-duce the temperature of the motor by 10ºC, we can expect the life to double. Note that this is true at any point on the curve. However, there is the rule of diminishing returns: at some point the cost of designing and operating a motor to run cooler out-weighs the benefts of doing so.  Here we will explore some of the factors that con-tribute to increased temperature.

Topics covered include:

• Overload
• Ventilation
• Voltage
• Electrical steel (core iron)
• Current density
• Circulating currents
• Harmonics

By Tom Bishop, P.E.
EASA Senior Technical Support Specialist

The International Electrotechnical Commission (IEC) standard 60529, “Degrees of protection provided by enclosures (IP code),” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “international protection” but is sometimes referred to as “ingress protection.” The IP code is commonly displayed on the nameplates of metric machines that are manufactured to IEC standards.

The NEMA MG1 Motors and Generators standards have adopted the IEC standards for IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of the IP marking is becoming more common. In light of this, this article reviews IP code designations and examples of the IP codes for common electrical machine enclosures.

• IP characteristic letters
• IP characteristic numerals
• Typical IP codes

READ THE FULL ARTICLE

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA 

Existe ahora una norma para las reparaciones de CC muy necesaria, creada gracias a la participación de miembros de EASA y usuarios de motores de la industria. El alcance, tal como se describe en el documento, establece: "Este documento abarca recomendaciones generales para la reparación de motores eléctricos de CC e incluye directrices tanto para el usuario como para el taller de reparación... Esta norma cubre el reacondicionamiento, la reparación y el rebobinado de motores y generadores horizontales y verticales de corriente continua con devanado de campo y aplica a todas las potencias superiores a 0,75 kW (1 hp)." 

La norma fue creada por un grupo de profesionales de la industria con ideas afines que reconocieron la necesidad de una guía de buenas prácticas específica para máquinas de CC. El grupo de trabajo logró crear la norma 2455 en menos de tres años, contados desde la aprobación y autorización del proyecto hasta su publicación final. Este documento se basó en la norma IEEE 1068, una norma de reparación de motores eléctricos ampliamente utilizada.

Los participantes del grupo de trabajo fueron: 

*Indica miembro de la EASA

El grupo de trabajo abarcó todos los aspectos, desde la recepción de la máquina hasta la inspección y las pruebas, incluyendo todos lo relacionado con la reparación y el rebobinado. Comenzando con un"Diagnóstico en la planta del usuario", el documento recomienda que el propietario/ usuario final del motor recopile datos específicos para proporcionar la mayor cantidad de información posible al taller de reparación.

Las pruebas de entrada al taller de reparación se describen en detalle, y muchas de ellas (por ejemplo, la de caída de tensión) son muy conocidas por los centros de servicio de EASA. Casi una docena de figuras resultarán familiares para los miembros de EASA, ya que se publicaron originalmente en documentos de EASA.

La norma incluye consejos específicos para el rebobinado de campos e inducidos, así como recomendaciones para el montaje y las pruebas finales. La IEEE 2455 también incluye anexos con un formato de evaluación y reparación, pautas para efectuar el rectificado, ranurado y biselado, una explicación de la conmutación, una guía de condición del colector, holgura de cojinetes de deslizamiento, ventilación y enfriamiento, asi como también ajustes eléctricos posteriores al ensamblaje y corrientes por los rodamientos en máquinas de CC. 

Chuck Yung 
EASA Technical Support Specialist 

Due to economies of scale, the use of cast iron is a popular choice in the manufacturing of NEMA and IEC frames. Cast iron is robust and easily machined. It is dimensionally stable and transfers heat well. However, foundry work is an energy-intense process, not well-suited to limited production runs. 

For larger electric motors, which are manufactured in smaller quanti­ties, the frame is more often fabri­cated from steel. You may have heard various nicknames for this type of construction: “shoe-box,” “skeleton frame,” “bathtubs” or other terms. Those who work on these motors regularly know that the frame requires care in handling, especially those fit­ted with sleeve bearings.