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 series of 150 kVA, 12.4 kV to 208/230 V dry-type transformers were found to be exceedingly noisy. The dB levels required office personnel in the area of the closet transformer to wear ear protection. The manufacturer was contacted, and the noise level was written off as 'acoustics'.

An interesting point about electric motors and transformers is that AC induction motors are basically transformers with rotating secondaries. Using this knowledge (and other concepts developed during a one-year study on Motor Circuit Analysis (MCA) applications for transformer testing), MCA was applied.

The first part of the evaluation was a visual overview of the condition of the windings. It was immediately apparent that the center coils in the transformers were loose. Varnish had flaked away, surrounding the center coil, and the blocks were found to be mounted above the coil and not between the coil and the core.

The only thing that had been holding the center coil in place was the original varnish. MCA tests were performed, and the results (see below) showed a slight turn-to-turn fault in the primary, most likely due to vibration. The finding was confirmed visually when small, dark spots between turns on the outer primary coil were found.

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.