Bearing Fluting Specialists Stop the Attack at the source
How to gain Electric Motor Reliability with two initiatives.

How to gain Electric Motor Reliability with two initiatives.

Sunday, April 23, 2023

Purchase right & Install right!!!!!

3Phi Reliability record motor test data from many surveys and use this data to make reliability decisions.

In a recent blog   we explored the relationship of Motor Impedance Imbalance and showed data that directly links this imbalance with winding defects.

A Motor which has Impedance Imbalance runs hotter due to higher energy losses, stresses the winding and therefore shortens its life. Note: I stated the Motor Impedance Imbalance and not just the winding imbalance as the rotor quality greatly affects this overall performance.

A motor with a rotor defect affects efficiency but is likely not measurable by current clamping each phase. A Rotor Influence Check or RIC test should be performed to assess its quality.

A RIC test is measuring the magnetic symmetry of the rotor as it is rotated, and should form a smooth sine wave when measured from a single winding phase.

Good Rotor Test

The article in the link, shows as Impedance Imbalance increases the probability of a winding defect developing is much higher.

Impedance Imbalance is highly Correlated with Winding Defects

After close analysis of 3Phi Reliability database, I had a question.

Why are there still some winding defects in Low Impedance Imbalance Motors? There must be another factor affecting this data.

The answer to that question is "Installation Practice"!!!

When a Motor is installed the resistance should be measured to ensure each phase is not getting a voltage drop. Not only does this stress the winding but creates a point of heat dissipation in I^2R loss.

Motor Losses with Voltage Imbalance

The resistance in each motor phase circuit needs to less than 5% imbalance right back to the supply transformer, measured in milli Ohms or better resolution.

The termination should consider lug surface area and torquing to a correct limit based on Post size and Material. Brass Posts have a lower specification. 3Phi Reliability clients get this termination guideline in their hands on coaching.

High number of Resistive defects in Low Impedance Imbalance Motors

Resistances in Motors vary based on size, and the ALL TestPro MotorGenie has a measurement resolution of 10 milli Ohms, so typically a motor above 45kW should see 0.00 reading on the meter.

A warning limit of 3% imbalance (marked yellow in the MotorGenie test report) and a 5% Alarm Limit (marked red in the MotorGenie test report).

High Resistive Defect found in Isolator

This motor is above 45kW so not only is there an Imbalance of 26% but each circuit winding is well above 10 milli Ohm.

In this example the resistive defect was in the Isolator with poor crimp terminations.

High Resistive Crimp Terminations

3Phi Reliability prefer the use of Hydraulic crimpers which the compression ensures "Cold Flow" of the copper producing a low resistance termination.

In this example the Heat Shrink hasn't yet been installed. Photograph for training purposes.

Reterminated Verified Low Resistance

3Phi Reliability prefer also the us of Beauville Washers, which are a compression washer. Any Thermal cycling during Motor Starts is a source of termination loosening.

Reducing circuit resistances results in eliminating excess thermal cycling and therefore terminations last much longer.  When an initial survey is conducted a large percentage of circuits show looseness.

Poor Compression results in High Resistance

While Thermography  technology is good, waiting for the heat is really chasing your tail in defects. Good installation practice using 3Phi Reliability Termination Guidelines and Electrical Preventative Maintenance stop the source of these defects.

How to get Motor Reliability with two initiatives?

1. Implement an Acceptance Test when purchasing electric motors based on All TestPro test limits. (Spec provided for each Client)

2. Implement coaching of your technicians in installation practice. This can be achieved with remote coaching via video link & AR Glasses.

Try Motor Testing at 3Phi Reliability

Gain Motor Reliability & Return Energy Savings.

No comments yet

Blog  Free Advice on Electric Motor Reliability and Energy Savings

Feel free to Copy Link and use on your Website  (Blue Chain Button)- MENU ABOVE
3Phi Reliability strive to provide interesting and informative topics to clients to Gain Electric Motor Reliability and Return Energy Savings

Gain Electric Motor Reliability & Return Energy Savings

Most of clients make gains on the every first day of implementation. Best Practice Motor Management has a short Return on Investment, improving Electric Motor Reliability and Energy Savings are immediate.