Electric Motor Diagnosis: Loose Power Connections
A major automotive manufacturer, located in North America with four manufacturing plants, utilizes MCA™ (Motor Circuit Analysis™) to keep their operations running.
A conveyor motor was tested during an annual inspection that operated in the part transfer line. If left operational, without the corrections found conducting predictive maintenance inspections, as coordinated through the Routes feature of the MCA™ Professional Software; the manufacturer estimates a loss of $90,000 in expenses related to unscheduled downtime.
Annual testing for the plant was conducted during a scheduled shutdown. Using the automated routes mode of the & MCA™ Software. A routing plan for testing was created on the PC by the maintenance manager and then uploaded to the ALL-TEST PRO 7™ instrument. This route provides an organized plan for the tech’s to follow for an initial quick preliminary de-energized testing of a group of motors conducted at the motor controller. After completing their annual route testing the data was uploaded to the MCA™ Software.
An initial review of the MCA™ software report titled “Equipment to review,” identified all machines that were in alarm. The report noted an unbalance in resistance and phase angle for a particular conveyor motor (see Figure 1).
The resistance unbalance indicated a possible loose connection. The phase angle unbalance indicates a developing phase to phase short. Based on the finding’s recommendations provided by the MCA™ analysis report (see Figure 2), the tech tested directly at the motor conduit box. The tech found no visible issues upon his initial inspection of the wiring. Next, the tech proceeded to unwire the motor from the building supply wiring and retested the motor wiring only. This test indicated an “OK” condition for resistance and phase angle on the screen of the ALL-TEST PRO 7™ testing device.
The tech determined that the issue could have been a loose wiring connection issue in the motor conduit box. To confirm this theory, the tech reconnected the building supply wiring to the motor properly and retested at the motor disconnect. Again, this test indicated an “OK” condition for resistance and phase angle on the screen of the ALL-TEST PRO 7™ testing device. This confirmed the wiring connection at the motor conduit box was this issue and was corrected by rewiring the building supply connections. Figure 3 below is the uploaded MCA™ analysis report of the successful test at the disconnect. This test shows the motor resistance and phase angle are in a balanced condition and registering an “OK” operating condition.
This MCA™ user confirmed that by conducting PdM testing using the ALL-TEST PRO 7™ de-energized testing device with the support of the Routes feature within MCA™ Enterprise Software, the motor issues were found and resolved before the motor was energized and the manufacturing process reinitiated. The described findings prevented a loss of production and damage to the conveyor, conveyor motor and danger to the operators. This MCA™ user estimates a cost savings of $90,000 by the avoidance of a potential issue occurring during normal operation. This cost savings estimate was based on production losses, additional labor, asset & disposal costs. Some considerations that were not known at the time of the cost estimate was spare motor and lead time which may have increased the potential loss. MCA™ initial motor testing takes about 3 minutes per motor. Testing times can decrease further with the use of additional MCA™ features such as testing using TVS™ values to locate changes in the motor. Having a TVS value provides a cradle-to-grave analysis based on an initial baseline test compared to future testing creating a trending TVS value. This TVS trending value is reviewable on both the MCA™ Software and reference feature on the ALL-TEST PRO 7™, see Tech Tip. Additionally, the MCA™ Software allows managers to designate routes that are easily downloaded to the instrument for based route testing data capture. Once the route testing is completed data is uploaded to the MCA™ software where it can be shared, printed, analyzed, and used for trending. Additionally, a “equipment to review,” report can be generated providing you with a list of motors that require review due to poor conditions found in initial route testing. This report will include supporting “findings” recommendations of the potential issues with them as shown in the situation above. In the above case study, the customer is using MCA™ Enterprise software that is utilized for the four plant locations with one shared database. Routine testing such as this annual testing done by the above auto manufacturer increases plant and staff safety while avoiding shutdowns and delays with throughput.
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