To ensure the optimum performance and condition of your machinery, it is important to conduct certain tests that can also prevent costly repairs and unexpected downtime. For instance, Polarization Index Testing is one of these techniques that you can do to keep your machines working properly. Here, we discuss more Polarization Index Testing, its benefits, and uses.
Overview of Polarization Index Testing
Polarization Index or PI testing is designed to check specific issues in a motor including moisture, motor fitness, suitability of the operation, and the gradual insulation deterioration of the machinery. In fact, it is an effective and efficient way to evaluate the performance of a motor. Machines with the higher index for the windings are ideal candidates for this type of test. A minimum polarizing index value of 2.0 is necessary for induction motors.
The life and performance of a motor depend largely on the windings’ insulation conditions. This is why it is necessary to determine the insulation condition through tests such as the Polar Index Tests and Insulation Resistance Testing.
To put it simply, Polar Index testing is more of an extension of the IR test. During an IR test, you will be able to identify and assess the conductors’ insulator resistance to the rotor or the stator. If the resultant resistance comes with a low value, this means the motor is undergoing deterioration. Consider every reading that from the Polarization Index since the values all pertain to the insulator of the motor and its condition.
Performing the Polarization Index Testing
To gain success from polarization index testing, it is important to follow these key steps involved in this process:
- Remove internal and external connections before you begin the testing.
- Discharge the windings to the grounded value.
- Apply a maximum DC voltage between the stator and conductor in the windings.
- Use a Megohmmeter to measure the resistance.
- Obtain a reading at one and 10 minutes so that you can determine the final value.
- Turn the power supply off after you have gotten the readings.
- Use the PI test formula to calculate the final resistance.
- Complete the entire test duration must within 10 minutes.
- Take note of the winding temperature at all times. Perform this portion since the test in single- and three-phase induction motors. This is why you should keep the windings grounded based on the testing procedure performed.
As mentioned earlier, the Polar Index test aims to determine the condition of your motor’s insulators. Since the winding insulation impacts the durability and integrity of a motor, it is important to keep this area in check to avoid untimely downtime and massive expenses for repairs. Hence, you need to make sure that some factors that impact the insulation resistance are under control including the type of insulation, surface area, the age of the material, as well as contamination and moisture.
Insulation resistance also involves various components such as the capacitance, leakage, conduction, and absorption. The capacitance is usually the first to be determined at the onset of the test. As for the conduction, this can stay in zero because of the windings’ dry condition. As for the leakage current, this area remains constant during the Polar Index test.
Benefits and Uses of the Test
There are several reasons why it is important to conduct the polarization index testing. One of these is to take note of the absorption current, which provides information on the insulation’s condition and health. You should also learn more about how the ground impacts motor insulation. This is why the PI testing ratio comes with a 10-minute to a 1-minute resistance.
In addition to these functions, you can also identify the time needed for the polarization of insulation molecules to resist current flow. When adding the current to the windings, molecules begin to align. The alignment rate provides details about the condition of the insulation.
Since the evaluation of the insulation resistance takes place between the conductors and ground during this test, you can obtain more accurate results from testing taped and sealed coils. Just be aware of air exposure skewing the results due to humidity, contamination, and the conductor surface.
To check the condition of your motor’s insulators, it is best to conduct the Polarization Index test properly. By doing so, you can also prolong the lifespan and durability of the motor while preventing unnecessary downtime, loss of profits, and expensive repairs.
(Editor’s Note: This post was originally published in March 2013 and has been completely revamped and updated for accuracy and comprehensiveness.)