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Taking the Mystery Out of Electric Motors: Stator Analysis and Troubleshooting

When PdMA refers to the Stator Fault Zone in an electric motor, it is referring to the dielectric properties of the insulation preventing current flow between turns, coils, and phases. It’s important to remember that when an insulation short occurs between turns, coils, or phases that the motor is at the lower part of the PF curve and life expectancy may be short. This is why we stress that the goal of predictive/condition-based maintenance technology is to identify conditions conducive to these shorts and fix the condition to ward off a reduced life expectancy.

A variety of root causes should be considered when trying to get ahead of these faults. The following are some potential root causes to consider when identifying conducive environments:

  • Overload – Excessive Heat
  • High Resistance Connection – Circulating Currents
  • External Contamination – Moisture/Conductive Material Intrusion
  • Design Flaw – Wrong Turns/Inverted Coil – Electrical Imbalance
  • Environment – Excessive Ambient/Chemical Attack
  • Excessive Vibration – Excessive Friction Between Turns or Coils
  • Excessive Starts/Hour – Heating
  • Particle Impingement- Rotor Bar, Lamination, Fan Blade, Cooling Slot Separator

Stator fault analysis can be easily performed with the motor running or de-energized (tripped) through Impedance, Voltage and Current, Inductance, and Winding Resistance. Early identification of conducive environments will include additional tests like Resistance-to-Ground, Rotor Influence Checks, Rotor Evaluation Current Signature, In-Rush/Start-Up, Airgap, and Machine Train Analysis.

To see a detailed discussion about Stator Analysis and Troubleshooting view the Stator Tips – Todd and Noah Podcast.  https://www.youtube.com/watch?v=lS3s27ofsSs

Source: https://pdma.com/category/tips/

Do you know what Unplanned Downtime Costs YOUR facility?

Early Identification of Bearing Failure Saves Company Thousands

The early detection and prevention of catastrophic bearing failures alone has justified the existence of predictive maintenance departments within industrial facilities.  For this Decatur Industrial customer, ongoing mechanical bearing failures in the same dryer section of their equipment was a reoccurring problem.

Our experts were brought in to work with the customer’s electrical team to evaluate the motors in the dryer section where they were seeing premature bearing failures.  We were able to identify a bearing failure during a vibration analysis on a critical piece of equipment. It would have eventually progressed and caused an unplanned shutdown.

By identifying the failure early, we prevented a catastrophic failure that would have led to a costly repair or replacement along with associated downtime cost. Instead, we performed a more “routine” repair allowing the customer to get up and running in the most cost-effective way with planned downtime.

Click on individual images to enlarge.

Routine Preventative Maintenance Saves Customer over $30,000

We get it. Preventative maintenance is costly – both in manpower and hard dollars. However, the cost of NOT doing it can be extremely more expensive.

During a scheduled preventative maintenance call at a customer site, a Decatur Industrial technician was inspecting a DC motor for brush wear, condition of the brush springs, and the state of the commutator. The commutator had extensive wear in the brush path. The brushes facilitate the flow of current into the armature so when excessive wear occurs, the motor has a more difficult time maintaining speed and output.

The commutator had a row that was not being used so we removed the spacer to adjust the brush holders onto a new brush path. This allowed the customer to continue using the motor and prevent it being pulled for reconditioning at a cost of $35,000.