General guidance for performing brush seating or comutator reprofiling in the field.

Orientación general para realizar el ajuste del asiento de las escobillas o del conmutador en el campo.

This video shows how to adjust the brush neutral position of a DC machine to prevent sparking at the brushes at full load.

The worn carbon brush face indicates the operating conditions. Therefore, it can be utilized by brush experts as a highly effective diagnostic tool for troubleshooting and determination of root causes. If these warning signs shown at the brush face can be identified and proactively addressed in a timely manner, then major unexpected expensive catastrophic failures like flashover or repair of the contact surface can be avoided.

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.

Ever run across brush arcing or vexing commutation issues? This paper, presented at the 2013 EASA Convention, provides a approach to analyzing brush and commutation problems and failures.

The brushes on a 4-pole, 700 hp DC motor were not wearing at the same rate. In this case, rapid brush wear occurred on two adjacent brush rows - one positive and one negative polarity. The other brushes had minimal wear. Electrical tests found no winding faults, and the air supply was clean. Most of us suspect low current-density when rapid brush wear occurs. A lightly loaded DC motor can "dust" a set of brushes in short order. Changing the brush grade (or removing some of the brushes) will usually solve the problem.