Recently, we were contracted by a drive Company to investigate a fault on a 170kW DC motor. The Leroy Somer motor had been in operation for some time but had suddenly ‘flashed-over’. This term is used when there is arcing from the positive brush arms to the negative brush arms or to earth. If this happens then the brushgear is often damaged and the motor will require removal and refurbishment.
Flash-overs are not uncommon with DC motors since the brushes wear and carbon can be deposited on the inside surface of the motor. This or other contamination can create a low resistance path across the +ve and –ve brush arms. For this reason, it is good practice to have a regular inspection plan to monitor the condition of the brushgear. This will identify problems and with the correct course of action may prevent small issues from developing into a more serious event.
In this particular instance, the motor required a general overhaul;