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Follow these procedures to reduce problems when rewinding field coils

Publication date: 
April 2008
Chuck Yung, EASA Senior Technical Support Specialist
Type of media: 

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.

Field coils
Repair procedures and tips