บทเรียนที่ได้รับจากการทดสอบมอเตอร์สมัยใหม่

Authors: Aaron Schnelle, Technical Support, and Richard Scott, General Manager, ALL-TEST Pro, LLC.

 

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During a demonstration of the ALL-TEST PRO 5™ motor circuit analysis tool (no-power motor tester), members of the ALL-TEST Pro technical support team tested a 10HP, 4-pole frameless motor removed from a larger, wet corn milling plant.

This wet corn milling plant, which processes approximately 14,000 bushels of corn daily, pulled this 10-horsepower motor from one of their conveyor belts. The motor displayed a “phase fault” on the frequency converter (VFD) that controls it. Maintenance personnel at the wet corn milling plant identified the motor as “broken,” and a disposal process involving multiple part replacements failed to successfully restart it. The motor was then sent to a motor supplier’s repair center, where it was tested using two ‘conventional’ motor testing technologies: surge testing and induction testing, neither of which yielded conclusive results.

 

The condition of the motor was revealed by the AT5™ power-off tester.

The AT5™ motor circuit analyzer is battery-powered, handheld, and weighs under 2 pounds. After connecting to a three-phase motor, a static test is performed. The motor shaft is then manually moved during the dynamic phase of the three-phase test, and at the end of the test, the instrument displays the results (the entire test takes approximately 2 minutes).

Unlike unsuccessful surge tests (which apply high voltage to the motor windings) and inconclusive inductance tests, the AT5™ instantly detects stator winding faults (see Figure 1).

Although IND testing using the DYNamic option indicates stator winding errors, it’s important to point out that it’s often impossible or impractical to perform “dynamic” testing (which requires slow, smooth rotation of the motor shaft) in the field due to the motor being physically connected to the process or located in an inaccessible position. If dynamic testing is not feasible, the AT5™ unpowered motor testing instrument can still be used for comparative analysis.

 

The comparative analysis was performed using the TVS™ (TVS™) fixed reference test value.

The patented and pending patent methodology of the AT5™ includes obtaining a Reference Test Value Static (TVS™) by performing initial static tests, and a reference TVS™ is generated. The Reference TVS™ is stored in the device’s internal memory or can be transferred to computer software, and subsequent test results can be immediately compared to the Reference TVS™ to instantly identify developing problems or changes to the stator or squirrel cage rotor (the comparison can be viewed directly on the AT5™’s large, easy-to-read display). The TVS™ can then be used as a reference value for that specific motor or other motors of the same manufacturer/type.

This specific case presents an opportunity to demonstrate comparative analysis using TVS™. Identical motors were pulled from the supplier’s stock and subjected to static testing with the AT5™. A 10.9% difference was immediately noticeable between the TVS™ value of the new motor and that of a known “faulty” motor, clearly exceeding the 3% warning threshold and demonstrating that the known faulty motor was in a different condition than its identical twin.

Lessons learned

In troubleshooting situations, TVS™ comparative testing can be performed from the VFD output without removing the motor or disconnecting the load. This comparative test allows plant maintenance technicians to immediately confirm that the motor’s condition has changed from its original installation state. This test, along with fault indication on the variable frequency drive, can accurately identify the cause of motor shutdown, saving time and money compared to simply replacing parts.

It is considered best practice to receive the TVS™ with AT5™ before storing or installing a new motor to make future troubleshooting faster and easier.

For more information on modern motor testing equipment, please visit www.alltestpro.com.

 

About ALL-TEST Pro LLC

Since 1985, ALL-TEST Pro, LLC has provided the most advanced predictive testing and troubleshooting tools for AC and DC motors, coils, windings, transformers, generators, and more to industries worldwide. With a comprehensive suite of testing instruments, software, accessories, and training programs, ALL-TEST Pro has the tools you need to perform advanced non-destructive motor testing and analysis for no-power motor circuit analysis and electrical and power signature analysis. The comprehensive capabilities of its instruments, coupled with reliable after-sales training and technical support, ensure improved productivity, reduced downtime, and a faster return on investment.