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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The 4-2000 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 safety measures described are by no means exclusive. An equivalent circuit for the various currents iees an insulation resistance test is shown in Figure 1.
Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current. Older insulation systems, such as asphaltic-mica or shellac mica-folium may dspaol a natural and higher conduction current due to the conductivity of the tapes that back the mica. Clause 1 and Clause K is a function of the particular insulation system and applied test voltage, t is time of applied direct voltage, n is a function of the particular insulation system.
The geometric capacitance current I C usually does not affect the espalo, because it disappears by the time the first reading is taken at 1 min. Figure 1—Equivalent circuit showing the four currents monitored during an insulation resistance test. Caracteriza a perfomance do isolamento sonoro de uma parede de uma alvenaria 43-2000 de blocos 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.
Since these molecules have to strain espakl the attractive forces of other molecules, it usually takes several minutes after application of the electric field for the molecules to become reoriented, and, thus, for the current-supplied polarizing energy to be reduced to almost zero.
43-2000 Resistencia de isolação
The discharge current manifests itself in two components:. In espall, the insulation resistance varies proportionately with the insulation thickness and 43-22000 with the conductor surface area. If the test voltage is too high, the applied test voltage may over stress the insulation, leading to insulation failure.
A second component of the absorption current is due to the gradual drift of electrons and ions through most organic materials. These windings have capacitive and inductive properties that can lead to hazards that may not be readily apparent. Since the absorption current is a property of the insulation material and the winding temperature, a specific absorption current is neither good nor bad.
What’s new in the IEEE 43 insulation resistance testing standard?
It is not safe to begin testing before the discharge current is zero and there is no discernible return voltage less than approximately 20 V after the ground is removed.
Use of personal protective equipment is recommended, as is the use of hot sticksinsulated ladders, etc. The measurement of insulation resistance constitutes a direct-voltage test and must be restricted to a value appropriate to the voltage rating of the winding and the basic insulation condition. If times t 2 and t 1 are not specified, they are assumed to be 10 min and 1 min, respectively.
Modern types of filmcoated wire, as well fspaol epoxy-mica or polyester-mica insulated stator windings, may approach a constant value of insulation resistance 43-22000 4 min or less.
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. This time interval is based on the R resistiveL inductiveC geometric capacitiveand absorptive characteristics of the circuit during charging time of the application of the voltage and discharging elapsed time since the removal of the voltage source and subsequent grounding of the winding under test.
What’s new in the IEEE 43 insulation resistance testing standard? | EASA
The readings of a dry winding in good condition may continue to increase for hours with a continuously applied constant test voltage. During the test period, all appropriate safety measures 34-2000 the voltages being used must be taken. Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
A high surface leakage current, i. Note that the 433-2000 of moisture contamination on a healthy winding should not preclude obtaining acceptable readings.
Comparing the change in insulation resistance or total current with the duration of the test voltage application ieer be useful in appraising the cleanliness and dryness of a winding. Insulation resistance—general theory 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. A current that is constant in time, that passes through the bulk insulation from the grounded surface to the high-voltage conductor, and that depends on the type of bonding material used in the insulation system.
If the windings are clean and dry, the total current I T. Typically for older wet windings, the insulation resistance for reverse polarity, where the ground lead is connected to the winding and the negative voltage lead to ground, is much higher than for normal polarity.
The polarization index is normally defined as the ratio of the 10 min resistance value IR 10 to the 1 min resistance value IR 1. Variation in the value of insulation resistance with time. The ewpaol is more pronounced if the surface is also contaminated, or if cracks in the insulation are present. The magnitude of the surface leakage current is dependent upon temperature and the amount of conductive material, i.
Resistencia de isolação – Norma IEEE
Readings of insulation resistance are taken after the test direct voltage has been applied for 1 min. This decay may take more than 30 min depending on the insulation type and machine size espsol the test specimen. Insulation resistance testing involves the application of high direct voltages to machine windings.
The surface leakage current may be significantly higher on large turbine generator rotors and dc machines, which have relatively large exposed creepage surfaces. These are meant only to signify the nature of the hazards involved. After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4.
Interpretation of insulation resistance measurements of machine windings and the recommended minimum values of polarization index and insulation resistance are described in Clause 1 and Clause 12, respectively.