24 Mar IEEE Standards documents are developed within the IEEE Societies and part of IEEE Std , IEEE Recommended Practice for Testing. The IEEE Recommended Practice for Testing Insulation Resistance of With the release of IEEE Std , new limitations on the use and evaluation of PI. The revised standard, IEEE Std. , drastically changed a number of traditional testing programs for insulation resistance that had been in place for more.
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This led the IEEE to form a standards committee to address this situation. In such cases, the PI may oeee disregarded as a measure of winding condition. Basically, the insulation system consists of polarized atoms that line up polarize with the applied DC voltage.
If you take the inductance across three phases of a 3-phase machine and compare it to the impedance, changes to capacitance in one or more phases would have a negative effect 43–2000 the impedance, causing the value to fall toward inductance.
The only true way to trend the PI is to perform each test with the winding at about the same iree, over the dew point. The purpose of an insulation resistance Ieee 43-2000 reading is 34-2000 evaluate the condition of the insulation between ieee 43-2000 and ground. The types of insulation ieee 43-2000 in rotating machines have continued to evolve ieee 43-2000 precipitate changes to insulation resistance testing since when IEEE Std. The Evolution of Maintenance — Part 2.
The DC test would identify continuity to ground, ieee 43-2000 a comparison of impedance to inductance would indicate additional winding problems. A standard IR test could be used to accomplish the DC test. DC versus AC voltage testing of insulation. It also 43-2000 an acceptable alternative: For one thing, the fault ieee 43-2000 to have a direct path between the windings and casing of the machine.
Faults on the end-turns of motor windings will also fail to provide a clear path to ground.
However, most windings manufactured after don’t have hygroscopic tapes, and a DC voltage test won’t normally detect problems internal to the insulation system, such as thermal deterioration.
As a result, ieee 43-2000 current ieeee the windings below ieee 43-2000 micro-ohm range require the instrument and test methods used, ieee 43-2000 how to position the conductors, to be extremely accurate.
This may be very difficult in a production environment, ieee 43-2000 extended inactivity of the machinery will have adverse effects on corporate profitability; testing one machine can take as long as 15 minutes. An excerpt from IEEE Std does a good job of explaining the test’s limitations and noting safe minimum values for testing Table:.
The main change has to do with the polarization of new insulation systems based upon temperature because unlike conductors where the resistance increases with temperature, insulation resistance is inversely proportional to temperature so insulation ieee 43-2000 decreases with temperature.
With this in mind, ieee 43-2000 impedance-based test impedance includes resistance, inductance, capacitance, and frequency as opposed to ieee 43-2000 test results, such as resistance and inductance, could be used as the AC test. Prior tothe industry relied on nonstandardized systems to evaluate the polarization of the insulation system. In particular, it identifies the complexities of performing PI and IR tests and notes their limitations.
A Review of Polarization Index and IEEE Std. 43-2000
In addition, PI can only be used on form wound or random wound machines. Unfortunately, the test often ieee 43-2000 to detect many incipient and existing faults. IR tests have very clear limitations when it comes to evaluating the condition of an electric motor for operation.
A poor reading would indicate that additional testing was necessary. Most winding faults start out as internal winding shorts and ieee 43-2000 graduate to insulation faults, although not always.
Therefore, a PI performed on a hot insulation system may be dramatically different than iieee PI performed on a cold one i. This is what makes DC voltage testing ieee 43-2000 viable method for determining the extent of iee to an insulation system. Text format Comments Plain text. If, however, there exists a severe crack through the entire insulation system, it’s possible that an electrical track would be established between the copper conductors and ground, and would appear as ieee 43-2000 low resistance.
In the past, a PI ratio of less than 2. It was then possible to analyze PI by either providing the direct ratio or plotting the readings in steady increments over time.
The lower the current reading, the higher the insulation resistance reading. As they polarize, the insulation resistance will increase.
More information about text formats. This is a change from the version of the standard, where ieee 43-2000 was assumed that PI wasn’t ieee 43-2000 temperature-dependent ieee 43-2000.