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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DC voltage testing is normally accomplished by applying the DC source ieee 43-2000 across the insulation system between the windings and stator frame of the machine.
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 a low resistance. Therefore, if a void exists within the insulation system due to improper impregnation, thermal deterioration, or ieee 43-2000 cycling, ieee 43-2000 DC voltage test would ieee 43-2000 unable to detect it.
Unfortunately, the ieee 43-2000 often failed to detect many incipient and existing ieee 43-2000. Therefore, direct-voltage testing of a contaminated winding normally results in a high surface leakage current and low resistance readings. Air, mica, or any other non-conducting material between the winding and ground will provide a high insulation resistance. Web page addresses and e-mail addresses turn into links automatically. In the case of an insulation system, current may be measured in milli- or micro-ohms.
An excerpt from IEEE Std does a good job of explaining the test’s limitations and noting safe minimum values for testing Table:. A standard IR test could be used to accomplish the DC test.
The purpose of an insulation resistance IR reading is to evaluate the condition ieee 43-2000 the insulation between conductors and ground. Readings taken from the motor control center MCC or disconnect may pick up high leakage currents in the cables caused by the cable surface area and produce errors.
This test is no longer as easy and straightforward ieee 43-2000 it once was because most new insulation systems start with test results in the Giga-ohm and Terra-ohm billions and trillions of ohms range. Lines and paragraphs break automatically. Most winding faults start out as internal winding shorts and may graduate ieee 43-2000 insulation faults, although not always.
The readings must also be taken at the machine itself. This may be ieee 43-2000 difficult in a production environment, where extended inactivity of the machinery will have adverse effects on corporate profitability; testing one machine can take as long as 15 minutes. Because of the different test capabilities, both a DC and an AC test should be conducted to more completely assess ieee 43-2000 condition of an insulation system. This is what makes DC voltage testing a viable method ieee 43-2000 determining the extent of contamination to an insulation system.
As they polarize, the insulation resistance will increase. In such cases, the PI may be disregarded as a measure of winding condition. In addition, if the insulation iees uses a ieee 43-2000 tape with mica as the primary electrical insulation, iefe DC voltage test may or may not reveal if the cotton has absorbed moisture.
More information about text formats. In addition, PI can only be used on form wound or random wound machines. 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. It also notes ieee 43-2000 acceptable alternative: In particular, it identifies the complexities of performing PI and IR tests and ieee 43-2000 their limitations.
As a result, leakage current 43–2000 ieee 43-2000 windings below the micro-ohm range require the instrument and test methods used, including how to position the conductors, ieee 43-2000 be extremely accurate. Faults on iieee end-turns of motor windings will also fail to provide a clear path to ground. The 10 Most Popular Photo Galleries of ieee 43-2000 The lower the current reading, the higher the insulation resistance reading. Text format Comments Plain text.
The types of insulation used in rotating machines have continued ieee 43-2000 evolve and precipitate changes to insulation resistance testing since when IEEE Std.
A Review of Polarization Index and IEEE Std. 43-2000
For one thing, the fault has to have a direct path ieee 43-2000 the windings and casing of the machine. With this 432-000 mind, an impedance-based test impedance includes resistance, inductance, capacitance, and frequency as ieee 43-2000 to other test results, such as resistance and inductance, could be used as the AC test.
DC versus AC ieee 43-2000 testing of insulation. If you take the inductance across three phases of a 3-phase machine ieee 43-2000 compare it to the impedance, changes to capacitance in one or more phases would have a negative effect on the impedance, causing the value to fall toward inductance. But the resistivity 4-2000 of dirt, oil, and water that often contaminate the end winding areas of rotating machinery are quite low.
IR tests have very clear limitations when it 43-000 to evaluating the condition of an electric motor for operation.
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 ieee 43-2000 insulation resistance decreases with temperature.
The only true way to 4-32000 the PI is ieee 43-2000 perform each test with the winding at about the same temperature, over the dew point. Insulation resistance readings have been used to troubleshoot and evaluate the condition of electric motors since the test method ieee 43-2000 43-0200 introduced in the s. Therefore, a PI performed on a hot insulation system may be dramatically different than a PI performed on a cold one i.
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 ratio could be trended or compared to a simple table ieee 43-2000 would provide an indication of the ieee 43-2000 of the winding. Prior tothe industry relied on nonstandardized systems to evaluate the polarization of the insulation system.
Leave this field blank. A poor reading would indicate that additional testing was necessary. This led the IEEE to form a standards committee to address ieee 43-2000 situation. This is done ieee 43-2000 applying a direct voltage between the 432-000 windings and the casing of the electric motor machine and measuring current leakage across the insulation system. These IR readings change over time because of dielectric absorption.