A convenient incoming inspection report for basic DC motor conditions and test values.

This inspection report helps record a DC motor's connection as it enters the service center. It is intended for use with 2-, 4- and 6-pole DC machines.

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 Institute of Electrical and Electronics Engineers (IEEE) standard for insulation resistance testing of motor and generator windings that was published in 2002 has been revised. The 2013 edition was published in March 2014. This article examines the changes to the standard.

La norma para realizar las pruebas de resistencia de aislamiento en los devanados de motores y generadores del Instituto de Ingenieros Eléctricos y Electrónicos (IEEE), publicada en el 2002 ha sido revisada. La edición del 2013 fue publicada en Marzo del 2014. Este artículo examina los cambios al estándar.

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.

Occasionally a customer wants a spare DC machine, and you find a replacement that is almost – but not quite – identical. Often, either the original or the spare is compound wound. The customer then asks: “What do the series fields do?” and “Can we just isolate the series leads?”  There are a couple of considerations, but the answer is that “it depends.”

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

When rewinding field coils, there are a couple of common problems that make life difficult for the service center. One problem occurs when the newly rewound set of shunt fields is returned to the service center, roasted again. What causes this, and whether we can improve our winding procedure, has been the subject of much discussion. We all realize that something caused that first failure. If the subsequent failure looks a lot like it - the shunt fields were charred in both cases then it seems logical that the underlying cause could be the same. Sometimes it is. Let's look at why the coil is burnt. Well sure, it got too hot. But why? Is it because the shunts are energized when the machine is otherwise shut down? If so, the fields can be automatically de-energized after "x" minutes of machine inactivity. Installing a timed relay in the controls will avoid future problems. It may be that the customer is able to trace the problem to a new operator, who needs more training.