Small Air Compressors on Star Delta Starters typically switch On & Off many times per day which makes them prone to High Resistance defects developing.

These compressors are often arranged with duty & standby compressor, meaning asset owners feel comfortable with the redundancy.  THINK AGAIN, as our testing database shows both Duty and the Standby are affected.

High Resistance defects can be within the Star Delta Starter connections, but a higher number are at the Motor Terminations.

A Resistance Imbalance means the motor winding is not receiving a balance Voltage and places stress on coil and Insulation. When an imbalance has developed and is not identified by Motor Testing the Motor Insulation decays and a shortened service life occurs.

This example shows a Severe Resistance Imbalance, and increasing  level on Insulation Decay using the All TestPro Phase Angle measurement.

Implementing Best Practice Motor Management principles and Motor Testing it is very easy to identify these developing Resistance Imbalances.

Electrical Preventative Maintenance is key to stopping Motor Winding failures.

This example shows a less severe Resistance imbalance before it has Stressed the Motor.

Motor Testing is an effective method to detect these types of early problems. While Thermography is not discounted it requires connections to be in line of sight and under load to be detectable.

The other consideration is Energy, not only will your Compressor motor be Electrically out of balance consuming more power but the Connection loss (I^2R) also is wasting energy.  So Reliability & Energy Savings go Hand n Hand.

A high number of these Air Compressors are under Service Level Agreements (SLA), and while Lubrication, Belts, and Filters tend to be well looked after sadly the Electrical Preventative Maintenance is given no priority. 

It seems it's unacceptable to seize a compressor with no Oil, but OK to run a motor to failure.

My concern is highlighted by 3Phi Reliability's Best Practice Motor Management Program that 100% of these Compressors have the same defect across ALL brands.  It's time to ask for some Electrical Preventative Maintenance from your Vendor.

Here is some more examples:

This last example has obviously been left too long and the Phase Angle Imbalance measurement has started to rise.

Note: These defects have not yet caused  drop in Insulation Resistance as the method is a predictive measurement giving clients more time to plan, similar to Vibration Analysis. 

Mark Gurney Motor Analyst