3 Common Failures In Field Coils & How To Fix

Field coils comprise wounded insulated copper wires with laminated steel cores. Their main purpose and function are to supply excitation for a generator or motor equipment. We have compiled some of the common failures in field coils including overheating, shorting, and overheating which we’ll be going over below and how field coils can be fixed. 


A common failure in field coils is overheating which is often caused by a number of factors such as shorting, vibration, or abnormal noise. This results in the field coil becoming overly hot. High temperatures can cause the coil wires to melt and break the circuit, eventually leading to motor failure. However, in the event of overheating, it is usually impossible for the overheated coil to be repaired, and it is generally recommended that the field coil be replaced.


Shorting happens as a result of unsuccessful insulations among the coils found in generator rotors, thereby causing a large electric current to flow. This generates heat leading to the field coil to overheat and being damaged from melting. It can even cause the entire circuit and electric flow to break.


Another major failure in field coils is earthing which happens as a result of wear and tear over time of the taping around the coil, exposing the coil wire to the metal body of the machine. In this regard, electrical current flows to the ground and becomes negative. Another way that earthing can occur is the build-up of carbon dust, which usually comes from carbon brush wear. When earthing occurs due to the build-up of carbon dust from carbon brush wear, a repair might be possible by performing a steam cleaning and baking the field coils to bring the insulation resistance (IR) up. If this is not the case, the field coils would have to be entirely replaced. 

How to Fix

Generally, you would only be required to replace the field coils when they become overheated and melt as a result. While this may seem difficult, depending on the extent of the damage, the damaged coils can just be removed so that they can be rewound or replaced. Otherwise, you can just send the machine for servicing by a professional engineer.

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