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A healthy motor with good Power Quality does not guarantee a reliable system. Overall reliability can be detrimentally influenced by a defective Power Circuit. Studies found that 47% of reduced efficiency in electric motors results from high resistance connections and other Power Circuit anomalies. Power Circuit anomalies create localized heating and degradation that left alone can result in a catastrophic failure or loss of production. Similar to Power Quality, the product of a Power Circuit anomaly is elevated heat. Not only localized heating as a result of the voltage drop across the high resistance connection, but a stator winding temperature increase as a result of the circulating currents flowing though the motor windings in support of the three-phase imbalance. If the motor is already running fully loaded and at design temperature, running with a Power Circuit anomaly can exceed the design temperature, reducing the life expectancy of the motor insulation system.

Power Circuit analysis can be easily performed with the motor running or de-energized (tripped) through In-Rush/Start-Up, Voltage, Current, and Winding Resistance measurements. 

To see a detailed discussion about Power Circuit Analysis and Troubleshooting view the Power Circuit Tips – Todd and Noah Podcast at https://www.youtube.com/watch?v=EAuELl2rlFQ

Source: PdMA

Challenged by the conversion of kW to hp for estimates and quotes? To help, I posted the following in the service center: The conversion formula for kW to hp is arrived at by multiplying the kW x (1.341) = hp (1/1.341 = 0.746; to convert hp to kW, multiply hp times 0.746 = kW). (Example: 15 x 1.341 = 20.115) This post allows my employees to easily cross-reference to our pricing charts.

Another similar experience is when we have discussed RPMs vs. frequency. Utilizing RPM = (120 x Hz)/poles OR poles = (120 x Hz)/RPM. (Example: (120 x 50 Hz)/1500 RPM = 4 poles).

Copyright: EASA

Jacob Voorhies
Technical Education Committee Member
Mid Kansas Winding
Galva, Kansas 
 

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/