A motor distributor in the Netherlands provided a 17 Kilowatt, 400-Volt motor to a local hospital in 2015. The hospital rented a portable crane to install the motor onto the roof of the building. The motor is used to operate a fan that is mounted on the hospital’s roof. In the spring of 2016, the motor suddenly stopped running, so the motor distributor was contacted for field service, troubleshooting, and on-site support.
The motor had been connected to a Variable Frequency Drive (VFD), and when the motor stopped running, the hospital’s maintenance technician reset the VFD. The motor did start, but unfortunately, the VFD shut the motor down again. Next the technician performed an insulation-to-ground test and determined the motor winding was not shorted to ground. Using a DMM (Digital MultiMeter) he then measured phase resistance and learned the phases were not open. The motor testing tools the technician used pointed to a “good” motor; therefore, they decided to replace the VFD. After the new VFD had been installed, the motor started up, but did not continue to run. Much to the technicians’ chagrin, they were experiencing the same problem; which compelled the hospital’s maintenance manager to contact the distributor who had supplied the hospital with the motor. The responsive motor distributor, who has a service center and support staff, sent one of their technicians to the hospital to test the motor. The service center technician used a meg-ohm meter and Digital Multi-meter (DMM) to determine that the motor was not grounded and the phases were not open; which was no different from the previous test results. Since the motor still did not run, the decision was made to replace the motor. A crane was brought in to remove the motor from the roof of the hospital and allow a replacement motor to be installed. The replacement motor started and operated normally, confirming the new VFD was working as intended. The “suspect” motor was sent to the service center for a more thorough inspection.
3 Minutes of Motor Testing at the Service Center An ALL-TEST PRO 5™ (pictured to the right) was used to perform a de-energized, non-destructive Motor Circuit Analysis (MCA) test at the service providers’ facility. Motor Circuit Analysis evaluates the condition of the electric motor connections, stator, and rotor in just minutes. Using the AT5™, connections were made to the three phases of the motor and a static test was performed. Next, the motor shaft was manually moved during the dynamic portion of the 3-phase test, and at the end of the test the instrument showed the results (as shown on the right). When performing the dynamic test between phases 2-1, it became clear that this was the phase that had the problem.
Owners / Operators Can Reduce Maintenance Costs A 17kW, 400V motor is not expensive, but when it is mounted on the roof of a building, and the owner has to rent a crane to lift that motor for installation and removal, the cost to the owner can become extremely expensive when it comes to maintenance and reliability. If the hospital’s maintenance team had owned and utilized a Motor Circuit Analysis instrument such as the ALL-TEST PRO 5™ or ALL-TEST PRO 33IND™, then they would have been able to tell right away that the motor had been the “bad actor” and not the VFD. Many hours were wasted by ordering and installing a new VFD when it had not been the true cause of the problem.
Distributors and Suppliers Can Improve Quality Assurance:
Motor distributors and suppliers should implement an additional quality control measure prior to delivering new or off-the-shelf motors to their customers. Spending 3 minutes to check the condition of motors will help distributors and suppliers avoid warranty issues and increase customer satisfaction.
Author: Richard Scott, General Manager, ALL-TEST Pro, LLC.