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.
|Published (Last):||25 December 2007|
|PDF File Size:||5.25 Mb|
|ePub File Size:||19.96 Mb|
|Price:||Free* [*Free Regsitration Required]|
The magnitude of the surface leakage current is dependent upon temperature and the amount of conductive material, i. 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.
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 resistive.
It is important to remember that the testing is not complete until the winding is discharged and there is no discernible voltage. Guidelines for test voltages are presented in Table 1. Parte 2 de 5 3. Before any testing is conducted, the winding insulation must be discharged. Since the absorption current is a property of the insulation material and the winding temperature, a specific absorption current is neither good nor bad.
An equivalent circuit for the various currents in an insulation resistance test is shown in Figure 1. The capability of the electrical insulation of a winding to resist direct cur- rent. There may also be.
What’s new in the IEEE 43 insulation resistance testing standard?
These windings have capacitive and inductive properties that can lead to hazards that may not be readily apparent. The measured insulation resistance will usually rapidly increase when the voltage is first applied, and then gradually approach a relatively constant value as time elapses see Figure 4.
Insulation resistance testing involves the application of high direct voltages to machine windings. These electrons and ions drift until they become trapped at the mica surfaces commonly found in rotating machine insulation systems. A current resulting from molecular polarizing and electron drift, which decays with time of voltage application at a decreasing rate from a comparatively high initial value to nearly zero, and depends on the type and condition of the bonding material used in the insulation system.
43-2000 Resistencia de isolação
A current that is constant with time, and which usually exists over the sur- face of the end-turns of the stator winding or between exposed conductors and the rotor body in insulated rotor windings. Modern types of espao wire, as well as epoxy-mica or polyester-mica insulated stator windings, may approach a constant value of insulation resistance in 4 min or less.
Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
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. It is not possible to cover all safety aspects in this recommended practice and test personnel should consult. The surface leakage current I L is constant over time. Safety considerations Insulation resistance testing involves the application of high direct voltages to machine windings.
For older types of insulation, a reasonably steady value is usually reached in 10—15 min. Caracteriza a perfomance do isolamento sonoro de uma parede de uma alvenaria estrutural de blocos 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. Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current.
A high surface leakage current, i. The polarization index is indicative of the slope of the characteristic curve see Figure 4 and can be used to assess the insulation condition see. This is particularly important in the case of small, low-voltage machines, or wet windings.
Restriction of personnel access to the high voltages is mandatory. Clause 1 and Clause 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.
If the windings are clean and dry, the total current I T. For safety considerations, and to avoid measuring stray currents, the leads may be shielded. Readings of insulation resistance are taken after the test direct voltage has been applied for 1 min. If accessible, the phase neutral and line ends of each winding should be connected together during the test to minimize the effect of high-voltage surge reflections that may result from a winding failure.
Variation in the value of insulation resistance with time. The total resultant current I T is the sum of four differ- ent currents: 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. In general, the insulation resistance varies proportionately with the insulation thickness and inversely with the conductor surface area.
L 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. After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4.
Resistencia de isolação – Norma IEEE
A phenomenon occasionally observed, more often on older windings, when, in the presence of moisture, different insulation resistance values may be obtained when the polarity of the tester leads are reversed. 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 geometric capacitance current I C usually does not affect the measurements, because it disappears by the time the first reading is taken at 1 min. The readings of a dry winding in good condition espal continue to increase for hours with a continuously applied constant test voltage.