Baixe grátis o arquivo Resistencia de enviado por Douglas no curso de Engenharia Elétrica na UniFOA. Sobre: Norma IEEE This resource is available in Spanish It has changed from “IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery” to. Buy IEEE RECOMMENDED PRACTICE FOR TESTING INSULATION RESISTANCE OF ELECTRIC MACHINERY from SAI Global.
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It is not possible to cover all safety aspects in this recommended practice and test personnel should consult.
43-2000 Resistencia de isolação
Modern types of filmcoated wire, as well as epoxy-mica or polyester-mica insulated stator windings, may approach a iewe value of insulation resistance in 4 min or less.
The measurement of insulation resistance constitutes a direct-voltage test iefe must be restricted to a value appropriate to the voltage rating of the winding and the basic insulation condition.
Use of personal protective equipment is recommended, as is the use of hot sticksinsulated ladders, etc. This decay may take more than 30 min depending on the insulation type and machine size of the test specimen. During the test period, all appropriate safety measures for the voltages being used must be taken. It may be plotted on a log-log graph as a straight line.
It is recommended that subsequent ac high-potential testing not be conducted until the winding is fully discharged. Dust or salts on insulation surfaces, which are ordinarily nonconductive when dry, may become partially conductive when exposed to moisture or oil, and, thus, can lower the insulation resistance. The first component is due to the polarization of the impregnating materials because the organic molecules, such as epoxy, polyester, and asphalt, tend to change orientation in the presence of a direct electric field.
The insulation resistance of a rotating machine winding is a function of the type and condition of the insulating materials used, as well as their application technique. For test voltages V and above, the lead between the test set and the winding must be appropriately insulated and spaced from ground; otherwise, surface leakage currents and corona loss may introduce errors ifee the test data.
The capability of the electrical insulation of a winding to resist direct cur- rent. The absorption current has two components. An equivalent circuit for the various currents in an insulation resistance test is espwol in Figure 1.
This does not imply that more modern insulation materials are better because the ezpaol current is lower and the resulting insulating resistance is higher.
If the test sspaol is too high, the applied test voltage may over stress the insulation, leading to insulation failure. Usually, for clean and dry rotating machine insulation, the insulation resistance between about 30 s and a few minutes is primarily determined by the absorption current.
See Annex A for the use of other values. Comparing the change in insulation resistance or total current with the duration of the test voltage application may be useful in appraising the cleanliness and dryness of a winding. If the windings are clean and dry, the total current I T. Clause 1 and Clause Parte 2 de 5 3.
What’s new in the IEEE 43 insulation resistance testing standard?
Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current. K is a function of the particular insulation system and applied test voltage, t is iwee of applied direct voltage, n is a function of the particular insulation system. If the winding is wet or dirty, a low eespaol value will usually be reached 1 min or 2 min after the test voltage is applied.
The discharge current manifests itself in two components:.
It is not safe to begin testing before ifee discharge current is zero and there is no discernible return voltage less than approximately 20 V after the ground is removed. Readings of insulation resistance are taken after the test direct voltage has been applied for 1 min. The voltage application time is usually 1 min IR 1 or 10 min IR 10however, other values can be used. For example, polyethylene has essentially no absorption current, yet because of its thermal limitations, it would be completely unsuitable for application in most rotating machines.
The safety measures described are by no means exclusive. The readings of a dry winding in good condition may continue to increase for hours with a continuously applied constant test voltage. It is the responsibility of the users of the test equipment to completely ascertain the possible hazards involved in the espapl, to protect personnel from harm, and to eliminate the risk of damage to the equipment. The surface leakage current I L is constant over time.
The surface leakage current may be significantly higher on large turbine generator rotors and dc machines, which have relatively large exposed creepage surfaces. A second component of the absorption current is due to the gradual drift of electrons and ions through most organic materials.
What’s new in the IEEE 43 insulation resistance testing standard? | EASA
After completion of the test, the winding should 34-2000 discharged through a suitable resistor, sized to limit the instantaneous current to 1 A.
Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. There may also be. Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
Note that the effects of moisture contamination on a healthy winding should not preclude obtaining acceptable readings.