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 https://www.3phi-reliability.com/blog/impedance-imbalance-in-an-electric-motor-wastes-energy 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.
The article in the link, shows as Impedance Imbalance increases the probability of a winding defect developing is much higher.
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.
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.
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).
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.
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.
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.
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.
Gain Motor Reliability & Return Energy Savings.
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