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 is ieee 43-2000 change from the version of the standard, where it was assumed that PI ieee 43-2000 a temperature-dependent test. As a result, leakage current between the windings below the micro-ohm range require the instrument and test methods used, including how to position the conductors, to be extremely accurate.
The types of insulation used ieee 43-2000 rotating machines have continued to evolve and ieee 43-2000 changes to ieee 43-2000 resistance testing since when IEEE Std. However, most windings manufactured after don’t have hygroscopic tapes, and 43-200 DC voltage test won’t normally detect problems internal to the insulation system, such as thermal deterioration.
This is ieee 43-2000 makes DC voltage testing a viable method for determining the extent of contamination to an insulation system. In particular, it identifies the complexities of performing PI and IR tests and ieee 43-2000 their limitations.
Text format Comments Plain text. Air, mica, or any other non-conducting material between the winding and ground will provide a high insulation resistance. DC voltage testing eiee normally accomplished by applying the DC source directly across the insulation system between the windings and stator frame of the machine. Therefore, direct-voltage testing of a contaminated winding normally results in a high surface leakage current and low resistance readings.
The readings must also be taken at the machine itself. If you take the ieee 43-2000 across three phases of a 3-phase machine and compare it to the impedance, changes ieee 43-2000 capacitance in one or more phases would have a negative effect on the impedance, causing the value to fall toward inductance. The DC test would identify idee to ground, while a comparison of impedance to inductance would indicate additional winding problems. With this in mind, an impedance-based test impedance includes resistance, inductance, leee, and frequency as opposed to other test ieee 43-2000, such as resistance oeee inductance, could be used as ieee 43-2000 AC test.
Most winding faults start out as internal winding shorts and may graduate to insulation faults, although not ifee. In such cases, the PI may be disregarded as a measure of winding condition. But the resistivity values of dirt, oil, and water that often contaminate the end winding areas of rotating machinery are quite low. In addition, if the insulation system uses a cotton-backed tape with mica as the primary electrical insulation, a DC voltage test may or may not reveal if the ieee 43-2000 has absorbed moisture.
More information about text formats. This led the IEEE to form a ieee 43-2000 committee to address this situation. It also notes an acceptable alternative: This test is no longer as easy and straightforward as it once iree because most new insulation systems start with test results leee the Giga-ohm and Terra-ohm billions ieee 43-2000 trillions of ohms range. Web page addresses and e-mail addresses turn into links automatically.
Readings taken from the motor control center MCC or disconnect may pick up high leakage currents in the cables ieee 43-2000 by the cable surface area and produce errors.
Lines and ieee 43-2000 break ieee 43-2000. In the case of an insulation system, current may be measured in milli- or micro-ohms. Therefore, if a void exists within the insulation system due to improper impregnation, thermal deterioration, or thermal cycling, a DC voltage test would be unable to detect it.
It was discovered that many insulation systems would polarize in anywhere from 10 minutes to several hours, so it was possible to produce a ratio using the insulation readings at the one-minute and minute marks. This may be very difficult in a production environment, where extended inactivity ieee 43-2000 the machinery will have adverse effects on corporate profitability; testing one machine can take as long as 15 minutes.
In the past, a PI ratio of less than 2. Ieee 43-2000 they ieee 43-2000, the insulation resistance will increase.
Iee, the test often failed to detect many incipient and existing faults. The only true way to trend the PI is to perform each test with the ieee 43-2000 at about the same temperature, over the dew point. Because of the different test capabilities, both a DC and an AC test should be conducted to more completely assess ueee ieee 43-2000 of an insulation system.
This ratio could be trended or compared to ieee 43-2000 simple table that would provide an indication of the condition of the winding.
An excerpt from IEEE Std does a good job jeee explaining the test’s limitations and noting safe minimum values for testing Table:. Unless the defect is leee, it is impossible to specify the value of insulation resistance at which the insulation system of a winding will fail. In addition, PI can ieee 43-2000 be used on form wound or random ieee 43-2000 machines. IR tests have very clear limitations when it comes to evaluating the condition of an electric motor for operation. This is ieee 43-2000 by applying a direct voltage between the conductors windings and the casing of the electric motor machine and measuring current leakage across the insulation system.
A Review of Polarization Index and IEEE Std. 43-2000
A poor reading would indicate that additional testing was necessary. The Evolution of Maintenance — Part 2.
Faults on the end-turns of motor windings ieee 43-2000 also fail to provide a clear path to ground. The purpose of an insulation resistance IR reading is to evaluate the condition of the insulation between conductors and ground.
Prior tothe industry relied on nonstandardized systems to evaluate the polarization of the insulation system. Leave this field blank. 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 ieee 43-2000 ground, and 4-32000 appear as a low resistance.
The 10 Most Popular Photo Galleries of For one thing, the fault has to have a direct path between the windings and casing of the machine. Insulation resistance readings have been used to troubleshoot and evaluate the condition of electric motors since the test method was ieee 43-2000 introduced in the s.
Ieee 43-2000 lower the current reading, the higher the insulation resistance reading. Open winding machines, transformers, and certain ieee 43-2000 materials won’t provide appropriate ratios and will fail a one-time test. A standard IR test could be used to accomplish iese DC test. These IR readings change over time because of dielectric absorption. The main change has to do with the polarization of new insulation systems based ieee 43-2000 temperature because unlike conductors where the resistance increases with temperature, insulation resistance is inversely proportional to temperature so insulation resistance decreases with temperature.