![motor winding resistance imbalance motor winding resistance imbalance](https://alltestpro.com/wp-content/uploads/2020/09/Motor-Genie-Graph-1024x575.jpg)
When the voltage is high enough to cause an arc between two turns at a fault, the resulting signal can indicate the type and magnitude of the fault. This is used to find turn insulation faults. Unlike the low voltage signal used by motor circuit analysis, surge comparison testing uses high voltage, fast rise signal.
![motor winding resistance imbalance motor winding resistance imbalance](https://easa.com/portals/0/Images/FailuresBrochure/WindingFailure12_web.png)
This change in impedance, combined with the knowledge that the inductance hasn’t changed, gives us indications of what is wrong. If a lower voltage signal with low frequency is used, then the capacitive reactance will have a greater impact on impedance. As windings get contaminated, overloaded, or shorts, the capacitive reactance of the windings change. One of the last measurements that can change due to a winding fault is inductance therefore, a motor’s inductance can be used as a good comparative baseline. By using low voltage sine wave outputs to excite the insulation system and surrounding magnetic steel dipoles, a complete diagnosis can be made by observing their reactive state. The tests up to this point have only been able to give an indication that there is a potential problem. Motor diagnostics have evolved beyond what has been discussed so far. Also, you can test the Polarization Index, which is a ratio of a 10 minute to a 1minute insulation resistance test. A megohmmeter applies a DC voltage from the windings to ground, and the resulting current measured corresponds to the overall resistance of the insulation.Ī megohmmeter can also be used to perform a Dielectric Absorption analysis, which is effectively a ratio between a 60-second and 30-second insulation resistance test.
![motor winding resistance imbalance motor winding resistance imbalance](https://dam-assets.fluke.com/s3fs-public/shaft-imbalance.jpg)
The insulation resistance should regularly be checked with a megohmmeter. As the insulation resistance goes down over the life of the motor, it becomes more susceptible to degradation. A new motor ideally has an insulation resistance of greater than 1,000 megohms. The other resistance is that of the winding insulation. A resistance unbalance (greater than 2%) between the phases could be indicative of a short, loose connections or broken conductors within the motor. To check the resistance of each winding, you need to measure from phase to phase just as was done with the voltage checks. Two of the most basic are the windings and the insulation of the windings. There are different resistance checks you can perform on a motor. This value can be used to see if the motor is overloaded. The result will give you the percent load the motor is being operated at. If a power factor is supplied, you would then multiply all of this by the power factor. These two values are multiplied together then multiplied by 100%. To do this, divide the average voltage by the rated voltage and divide the average current by the rated current. Now that the average voltage and average current have been found, you can calculate the percentage of motor load. The maximum recommended current unbalance is 7%. Once you have all three phase currents, you can find the average and then use the same method to find an unbalanced voltage to check for unbalanced current. The easiest way to measure the phase current is to use a clamp-on ammeter around each of the incoming phases. Ammeter TestingĪs with the voltages, the phase currents can be measured and give you an indication of an issue with the motor. This percentage is multiplied by a certain factor based on the horsepower rating of the motor. To find the voltage unbalance, you first need to find the average of the three phase-to-phase voltage readings as well as the percentage of the readings’ average. Unbalanced voltages lead to unbalanced currents and, in turn, unbalanced magnetic fields, which can lead to adverse operating conditions for the motor. If any of the three values recorded are greater than 5% off, you have an under- or over-voltage that can alter the operating condition of the motor.Īnother thing to check for is voltage unbalance. The maximum recommended deviation is 10%. These values should be compared to the rated voltage, which is normally found on its nameplate. To do this, you should measure from phase A to phase B, A to C, and B to C. When checking a motor’s voltage, it is best to measure phase to phase. Some are more complex and require special analytical instrumentation. Some are simple and can be done with just a voltmeter, ammeter, or ohmmeter. There are many methods for analyzing electric motor faults to predict failures. Motor failure can cause a complete production unit shutdown and millions of dollars in lost revenue.
![motor winding resistance imbalance motor winding resistance imbalance](https://www.rsaworks.com/media/1136/motor-testing.jpg)
They provide rotational force to a large span of equipment from a large 500 HP motor spinning a centrifugal compressor to the small fan cooling your laptop. Electric motors are literally the driving force behind many industrial and residential processes.