There is now a much-needed DC repair standard, created through the participation of EASA members and industry motor users.

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.

Unlike their AC counterparts, DC machines do not have rotating magnetic fields. Rather, there are fixed magnetic field axes for the field (direct axis) and armature (quadrature axis). Even though the armature is rotating, the magnetic field axis in the armature is fixed thanks to commutation, which allows the direction of current in an armature conductor to change as it passes from the region under one main field pole to the next.

A diferencia de sus homólogos de CA, las máquinas de CC no tienen campos magnéticos rotativos. Más bien, existen ejes de campo magnético fijos para el campo (eje directo) y la armadura (eje en cuadratura). Aunque la armadura esté girando, el eje del campo magnético de la armadura está fijo gracias a la conmutación, lo que permite que la dirección de la corriente en un conductor de la armadura cambie a medida que pasa debajo de un polo de campo principal al siguiente.

Revisit EASA's 2022 Convention & Solutions Expo by buying access to recordings of the general sessions and education events streamed from EASA's website! These recordings provide almost 44 hours of training. Downloadable PDFs of slides and technical papers are included!

EASA's DC Machine Data Sheet provides all the fields necessary on a simple one-page form to accurately record all the details about the machine being repaired.

The lowly brush is underrated and misunderstood. The brush grade, brush pressure and spring tension, as well as the effect of load and humidity are each important to brush performance in DC machines, wound rotor motors, and synchronous machines.

Ground faults, short circuits and bad connections in interpole coils, series coils and compensating windings cause performance problems in DC machines, including brush sparking, flashover, stalling and catastrophic failure. Shunt coils have many turns of relatively small wire and are usually excited by a DC source independent of the armature. Series, interpole and compensating coils in the armature circuit usually are wound with a few turns of heavy wire as these coils carry armature current. For accurate test results, make sure windings are clean and dry. Verify connections of low resistance fields by visual inspection. Apply DC voltage to an assembled field frame and perform a thermography scan to detect problems including uneven heating and loose or corroded connections. Verify that the terminal lead markings are correct. Lead marking should conform to the original equipment manufacturer (OEM) nameplate, NEMA MG1 or IEC 60034-8, whichever is applicable.

Los fallos a tierra, cortocircuitos y malas conexiones en las bobinas de los interpolos, campos serie y devanados de compensación de las máquinas de CC pueden causar problemas de funcionamiento que incluyen: Chisporroteo, flameo (flashover), frenado y fallos catastróficos. Algunas bobinas de campo shunt están bobinadas con muchas espiras y un alambre relativamente delgado y generalmente son excitadas con una fuente de CC independiente a la de la armadura. Por lo general, los campos serie, interpolos y devanados de compensación del circuito de armadura están bobinados con pocas espiras y alambre grueso, ya que por ellos circula la corriente de armadura. Para obtener resultados de prueba precisos asegúrese que los bobinados están limpios y secos y verifique visualmente las conexiones de los campos de baja resistencia. Para detectar problemas de calentamiento irregular o conexiones flojas o corroídas aplique voltaje CC a las bobinas de un estator de CC y realice una inspección termográfica. Compruebe que las marcas de los cables de salida sean las correctas. Estas deben coincidir con los datos de placa del fabricante original (OEM) o con las normas NEMA MG1 o IEC 60034-8, lo que aplique.

For the wide variety of DC motor applications, there are those where a straight shunt motor is preferred and others which seem to require the greater starting torque of a series field. Why are there different field designs and are they interchangeable? What about the nameplates marked “stab shunt” or “str shunt?” The purpose of this article is to clear up lingering confusion about the types of fields as well as the benefits of each.