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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Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. This decay may take more than 30 min depending on the insulation type and machine size of the test specimen. Restriction of personnel access to the high voltages is mandatory. These are meant only to signify the nature of the hazards involved. 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 in the test data.
These electrons idee ions drift until they become trapped at the mica surfaces commonly found in rotating machine insulation systems.
Modern 43-0200 of filmcoated wire, as well as epoxy-mica or iieee insulated stator windings, may approach a constant value of insulation resistance in 4 min or less. 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.
The capability of the electrical insulation of a winding to resist direct cur- rent. During the test period, all appropriate safety measures for the voltages being used must be taken. The total resultant current I T is the sum of four differ- ent currents: Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
To provide greater accuracy around the 1 min point and esaol allow the data to be plotted on log paper, it is also common to take readings at other intervals such as 15 s, 30 s, 45 s, 1 min, 1.
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 effect is more pronounced if the surface is also contaminated, or if cracks in the insulation are present. The quotient of the insulation resistance at time t 2 espsol by the insulation resistance at time t 1.
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. Since the absorption current is a property of the insulation material and the winding temperature, a specific absorption current is neither good nor bad. Insulation resistance testing involves the application of high direct voltages to machine windings.
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. If times t 2 and t 1 are not specified, they are assumed to be 10 min and 1 min, respectively.
A second component of the absorption current is due to the gradual drift of electrons and ions through most organic materials. The absorption current I A or polarization current decays at a decreasing rate.
The conduction current I G iefe well-bonded polyester and epoxy-mica insulation systems is essentially zero unless the insulation has become saturated with moisture. After completion of the test, the winding should be discharged through a suitable resistor, sized to limit the instantaneous current to 1 A.
Resistencia de isolação – Norma IEEE
By definition, the insulation resistance is the quotient of the applied direct voltage across the insulation divided by the total resultant current at a given time. Espaok 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.
If the insulation resistance or polarization index is reduced because of contamination, it can usually be restored to an acceptable value by cleaning and drying. Regardless of the cleanliness of the winding surface, if the winding temperature is at or below the dew point of the ambient air, a film of moisture may form on the insulation surface, which can lower the insulation resistance or polarization index.
Guidelines for test voltages are presented in Table 1. If the test voltage is too high, the applied test voltage may over stress the insulation, leading to insulation failure. Poluicao jeee Isoladores Artigos sobre Poluicao em Isoladores. 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. Before any testing is conducted, the winding insulation must be discharged.
43-2000 Resistencia de isolação
If the windings are clean and dry, the total current I T. See Annex A for the use of other values. Caracteriza a perfomance do isolamento sonoro de uma parede de espaoll alvenaria estrutural de blocos