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Handheld `pen` detects damaging motor discharges

27 February, 2009

SKF has developed a non-contact, handheld instrument for detecting electrical discharges in motors that could be damaging the motor’s bearings.

Motor shaft voltages that discharge to earth through a bearing can cause electrical erosion, lubricant degradation and, ultimately, bearing failure. The increasing use of variable frequency drives (VFDs) has made the problem more severe and widespread.

VFDs can induce currents that increase until they find a path to earth via the motor frame. These currents can pass through the bearings and, when the voltage is high enough to overcome the lubricant layer, discharges occur, damaging the surfaces of the rolling elements and raceways.

Until now, the only ways of detecting this damage have been to remove a suspect bearing and examine it (often after a motor has failed), or to use an oscilloscope – a process that requires expertise, as well as time-consuming wiring and attachment of sensors to the motor.

SKF’s TKED 1 electrical discharge detector “pen” is designed to be held near the motor and to count the number of electrical discharges it senses. It displays the results on a backlit LCD. The count can continue indefinitely, or can be restricted to 10 or 30 second periods, allowing the results to be compared with readings taken from the same motor at an earlier time, or from other similar motors.

The battery-operated, pocket-sized instrument, is designed to be used as part of a preventative maintenance programme.




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