Two Case Studies in Motor Troubleshooting Part 2: Testing, Testing
In order to produce 100 million gallons of ethanol per year, Cardinal Ethanol in Union City, Indiana, has to ensure its equipment operates reliably 24 hours a day, seven days a week. The in-house maintenance team at the ethanol plant schedules shutdowns in the spring and fall for regular maintenance. During the fall 2015 shutdown, four new motors were installed to drive the conveyor belts that feed the corn into the ethanol processing plant.
By December, the maintenance team noticed interruptions in grain flow. Mark Durr, maintenance project manager at the ethanol plant, investigated the grain delivery system and determined that the interruptions in grain flow were being caused by intermittent shutoff of the conveyors. “I instructed my technicians to test all four motors, which ranged from 40- to 60-horsepower. Our meg-ohm meter showed the coils were fine, no short turns and nothing going to ground,” Durr said. “But when we used the All-Test Pro 33 IND, that motor testing instrument showed us the rotors were bad.”
Durr contacted the general contractor who had installed the motors to inform him of the discovery. The contractor was curious about Durr’s conclusion that there was a problem with the rotors. The motors were brand new, and the contractor could not believe that all four motors would have rotor problems. When asked how he came to this conclusion about the rotors being the root cause of the problem, Durr explained to the contractor that he had a de-energized motor testing instrument from All-Test that showed the complete condition of both the stator windings and the rotor.
“I had purchased the AT33 motor testing instrument a little over a year before, shortly after I began working at this plant. We are focused on preventive maintenance to keep this plant up and running, and that means having the right tools to prevent plant shutdowns,” Durr said. “When you have a problem with a motor, a meg-ohm meter, multimeter, and LCR meter (L-inductance, C-capacitance, R-resistance) are not going to tell you if there is a problem with a rotor, but an AT33 will.”
After the motor testing results were shared with the contractor, the contractor made arrangements to replace the motors that were under warranty. The motors were sent to the contractor’s service center to be disassembled and inspected and the service center technicians confirmed that the rotors had, in fact, been the root cause of the motors’ inability to perform as intended.
“The report from the service center, confirming the rotors were bad, was not a surprise to me,” Durr said. “We have used the AT33 quite successfully on several motors, because we know that more common testers don’t have the capability to show rotor health. This is one of the main reasons I bought the testing instrument, because of its ability to test the rotor. In this case, it really came in handy.”
It is critical to inspect new motors and stored motors before they are installed into a system. Spending a few minutes to test a motor before installing it can save thousands of dollars in maintenance, and in some cases, shutdown costs.
The de-energized motor testing instrument, which performs both static and dynamic tests, is a proven asset for revealing the complete condition of the motor rotor and stator windings and also helps the maintenance technician or operator understand if there are any issues with contamination, connections and ground faults.
Author: Mike Schneider
Regional Manager, All-Test Pro LLC