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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It also notes an acceptable alternative: DC voltage testing is normally accomplished by applying the DC source directly across the insulation system between the windings and stator frame of the machine. In particular, it identifies the complexities of ieee 43-2000 PI and IR tests and notes their limitations. The only true way to trend ieee 43-2000 PI is to perform each test with the winding at about the same temperature, over the dew point.
However, most windings manufactured after don’t have hygroscopic tapes, ieee 43-2000 a DC voltage test won’t normally detect problems internal to the insulation system, such as ieee 43-2000 deterioration. 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, direct-voltage testing of a contaminated winding normally results in a high surface leakage current and ieee 43-2000 resistance readings. The DC test would identify continuity to ground, while a comparison of impedance to inductance would indicate additional ieee 43-2000 problems.
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.
iieee This is done by applying a direct voltage between the conductors windings and the casing of the electric motor machine and measuring current ieee across the insulation system. Leave this field blank. In the case of an ieee 43-2000 system, current may be measured in milli- or micro-ohms.
Readings taken from the motor control center MCC or disconnect may pick up ieee 43-2000 leakage currents in the cables caused ieee 43-2000 the cable surface area and produce errors.
This test is no longer as easy and straightforward as ieef once was because most new insulation systems start with test ieee 43-2000 in the Giga-ohm and Terra-ohm billions and trillions of ohms range. The Evolution of Maintenance — Part 2. Air, mica, or any other non-conducting material between the winding and ground will provide a high insulation resistance.
The readings ieee 43-2000 also be taken at the machine itself.
Therefore, a PI performed on a hot insulation system may be dramatically different than a PI performed on a cold one i. Faults on the end-turns of ieee 43-2000 windings will also fail to provide a clear path to ground. 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 resistance decreases with temperature.
Lines and paragraphs break automatically. 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.
An excerpt from IEEE Std does a good job of explaining the test’s limitations and noting safe minimum values for testing Table:. As a result, leakage current between the windings ieee 43-2000 the micro-ohm range require the ieee 43-2000 and test methods used, including how to position the conductors, to be extremely accurate. Open winding machines, transformers, and certain insulation ieee 43-2000 won’t provide appropriate ratios and will fail a one-time test.
But the ieee 43-2000 values of dirt, oil, and water that often contaminate the end winding areas of rotating machinery are quite low.
As they polarize, the insulation resistance will increase. This led the IEEE to form a standards committee to address this situation.
Most ieeee faults start out as internal winding shorts and may graduate to insulation faults, although not always. If you take the inductance across three phases of a 3-phase machine and compare ieee 43-2000 to the impedance, changes to capacitance in one or more ieee 43-2000 would have a negative effect on the impedance, causing the value to fall toward inductance.
In addition, if the insulation system uses a cotton-backed tape with mica as 43-200 primary electrical insulation, a DC voltage test may or iee ieee 43-2000 reveal if the cotton has absorbed moisture. Prior tothe industry relied on nonstandardized systems to evaluate the polarization of the insulation system.
A Review of Polarization Index and IEEE Std. 43-2000
A standard IR test could be used to accomplish the DC test. IR tests have very clear limitations ieef it comes to evaluating the condition ieee 43-2000 an electric motor for operation. The 10 Most Popular Ieee 43-2000 Galleries of It was then possible to analyze PI by either providing the direct ratio or plotting the readings iede steady increments over time. This may be very difficult in a production environment, where extended inactivity of the machinery will have adverse effects on corporate profitability; ieee 43-2000 one machine can take as long as 15 minutes.
Unless the defect is concentrated, it is impossible ieee 43-2000 specify the value of insulation resistance at which the insulation system of a winding will fail. DC versus AC voltage testing of insulation.