Below is a case study that we took from our Motor Circuit Analysis Book. This book, which was written by Dr. Howard W. Penrose, Ph.D., shares many instances where Motor Circuit Analysis (MCA) was applied to find a variety of faults.

Please note that the following case study was considered true and correct at the time of publication, and has been amended slightly to improve readability.

A motor repair shop was reporting that a brand-new 200 horsepower, 1800 RPM motor was unable to provide enough torque to obtain no-load speed at full voltage with the coupling detached from the load.

A replacement motor was sought and compared to the original using inductive measurements, with changes to the rotor position. When looking at the results, the primary change was to the inductance at the peak of the sine wave. The fault was found to be a large casting void, and its position was identified by a mass of balancing weight on the rotor.

The casting void was also confirmed using vibration analysis, then found by drilling a small hole in the rotor (in the approximate position) and feeding a wire through. The casting void was determined to be close to the rotor core, interrupting the current path.

If you have a success story that you would like to share with us and fellow readers, or if you would like to discuss any of this further, then please do not hesitate to get in touch.