Stator Looseness Diagnosed by Electric Motor Testing Tool

Initial Findings

A 6.6 kV motor that is used to cool the temperature of gas after going through a gas phase polymerization process at a Petrochemical plant was experiencing abnormal symptoms. A technician conducted a vibration test and noticed an abnormal vibration. Another test was conducted with no load and the abnormal vibration remained. The root cause of the vibration was still undetermined. A team from Instrument Resource Co. in Bangkok Thailand was contacted to investigate the motor further to try and determine the cause of the abnormal vibration.

Motor Circuit Analysis™ (MCA™) was performed using the ALL-TEST PRO 7 PROFESSIONAL™. By performing a series of tests, the AT7™ identified the problem after performing the DYN test function. This particular test is designed to verify stator and rotor integrity and health. This test requires rotating the motor shaft. ALL TEST Pro’s patented Dynamic Stator and Rotor Signature test found there was an imbalance in the Dynamic Stator Signature.

Dynamic Signature Analysis

The Green line is the Stator signature and represents the deviation of the mean values during rotation for each phase. The two black dotted lines represent the Rotor Signature and include an upper and lower signature.

The motor was disassembled. Loose stator slot wedges were found. These loose stator slots were causing the excessive vibration and imbalance in the Dynamic Stator Signature.

After the motor was repaired and reassembled another set of tests were preformed with the AT7™. The subsequent test showed there was no longer an imbalance in the Dynamic Stator Signature representing the stator health was in good condition.

About ALL-TEST Pro, LLC.

ALL-TEST Pro delivers on the promise of true motor maintenance and troubleshooting, with innovative diagnostic tools, software, and support that enable you to keep your business running. We ensure the reliability of motors in the field and help to maximize the productivity of maintenance teams everywhere, backing every ALL-TEST Pro product with unmatched motor testing expertise.

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Motor Current Signature Analysis on Gearbox Motor

Introduction

Noise and vibration was investigated on a 7.5 horsepower, 1750 RPM, 575 Vac motor and gearbox using the ALL-TEST PRO™ OL (ATPOL) motor current signature analyzer. One set of data requiring less than one minute of data provided the information necessary. The number of rotor bars, stator slots, bearing information and gears was not available. The lack of information did not hinder the ATPOL in immediately identifying the faults.

Discussion Although lightly loaded, the ATPOL automatically identified casting voids (Figure 1), an electrical fault in the stator (Figure 2), gear problems and identified the number of rotor bars (48) and stator slots (36).

Figure 3 shows the automatic analysis display shown in the ATPOL software.

ALL-TEST PRO™ MD Kit

The ALL-TEST PRO™ MD kit consists of:

  • ALL-TEST PRO™ OL motor current signature analyzer
  • ALL-TEST PRO™ 31 and ALL-TEST IV PRO™ 2000 motor circuit analyzers
  • EMCAT motor management software
  • ATPOL and Power System Manager software modules for EMCAT
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