Early inspection revealed a winding fault in one municipal utility district.
by Aaron Schnelle
July 2, 2018

Since 2008, a municipal utility district (MUD) in Texas has worked with Less Watts Inc., a company that specializes in motor reliability and power quality testing for the water and wastewater industry. Less Watts Inc. supports MUDs by providing motor acceptance testing, commissioning and condition monitoring services. When one of the booster stations managed by the Harris County MUD was upgrading its pumps and motors, Stephen Hogue from Less Watts Inc. was asked to perform acceptance testing.

This MUD’s main booster station pumps water into static tanks that are then pressurized to push drinking water throughout the municipal water district. The MUD had scheduled an upgrade to their Well-1 booster station in 2017 and ordered four booster pumps with 75-horsepower motors.

Each pump system (pump, motor and drive) had been mounted on individual skids. Hogue brought a hand-held testing device to the pump suppliers’ warehouse to check the condition of the new motors before they could be officially accepted by the MUD. The device, which is used for de-energized Motor Circuit Analysis (MCA), is specifically designed for troubleshooting motors and commissioning new and rebuilt motors before installation. The testing device enables the operator to identify motor conditions that include winding contamination, stator and rotor unbalance, changes in rotor and stator condition, resistance in windings, contamination and insulation to ground issues.

distribution pumpImage 1. MUD freshwater distribution pump room (Images courtesy of ALL-TEST Pro LLC)

Hogue connected the testing device to the motor box leads and performed static and dynamic tests. He generated reports for each of the motors, with one report showing test results consistent with a developing winding fault in Phase 3-2.

Hogue discussed the test results with the MUD, explaining why his acceptance report showed one motor should not be accepted or approved for installation. Even though the motor was brand new, the testing device showed a defect and provided an alert to the potential of a motor failure. The MUD requested that the questionable motor be returned to the vendor and replaced with another unit. A new motor was delivered a week later, and Hogue returned to the pump supplier’s warehouse with his hand-held testing instrument to test the replacement motor. This time, the new motor passed the acceptance test.

In August 2017, the fully assembled skids were installed at the main booster station. Hogue tested the installed motors prior to startup to make sure all motors were operating as designed. The commissioning went smoothly and the motors have been operating well since startup. Hogue continues to collect operating data on a monthly basis.

“It is important to perform acceptance testing for new and repaired motors,” Hogue said. “Testing your motors before installing them gives you confirmation that the equipment will operate as designed.

“When you install a new or repaired motor, it is better to have the equipment commissioned prior to paying for delivery and installation. Finding out there is a problem with a motor after startup or even after a short period of run time can result in additional maintenance costs, system downtime, and possible challenges in obtaining warranty satisfaction.”

report pageImage 2. Result report page

Lessons Learned

  1. Do not accept a motor if there is proof that it is not operating as intended. The proactive testing initiated by this MUD prior to delivery and installation of the motors helped them avoid additional project costs.
  2. Equipment owners can avoid unscheduled downtime, and even failure, by testing their equipment prior to receipt and installation. Even though motors may be brand new, they should be tested prior to acceptance and installation. If the motor had failed within the first year of operation, the standard parts and labor would likely be under warranty, while the vendor would have been responsible for the materials and replacement. However, if this motor had passed the warranty period, the owner would have had to cover the entire expense.
  3. Mistakes in the manufacturing or repair process can be detected with sophisticated testing instruments.