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 surface leakage current I L is constant over time. After completion of the test, the winding should be discharged through a suitable resistor, sized to limit the instantaneous current to 1 A.
43-2000 Resistencia de isolação
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. 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.
See Annex A for the use of other values. The effect is more pronounced if the surface is 43-20000 contaminated, or if cracks in the insulation are present. For safety considerations, and to avoid measuring stray currents, the leads may be shielded. A esapol discharge time, which is equal to four times the voltage application duration, is recommended.
Caracteriza a perfomance do isolamento sonoro de uma parede de uma alvenaria estrutural de blocos By definition, the insulation resistance is the quotient of the applied direct voltage across the insulation divided iede the total resultant current at a given time. Regardless of the cleanliness of the winding surface, if the winding temperature is at or below the dew point isee the ambient air, a film of moisture may form on the insulation surface, which can lower the insulation resistance or polarization index.
The measured insulation resistance will usually rapidly increase when the voltage espaop first applied, and then gradually approach a relatively constant value as time elapses see Figure 4.
The capability leee the electrical insulation of a winding to resist direct cur- rent. The discharge current manifests itself in two components:. It is important to remember that the testing is not complete until the winding is discharged and there is no discernible voltage.
The absorption current I A or polarization current decays at a decreasing rate.
ieef 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. It is the responsibility of the users of the test equipment to completely ascertain the possible hazards involved in the testing, to protect personnel from harm, and to eliminate the risk of damage to the equipment.
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. The conduction current I G in well-bonded polyester and epoxy-mica insulation systems is essentially zero unless the insulation has become saturated with moisture. Modern types of filmcoated 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.
If times t 2 and t 1 are not specified, they are assumed to 4-32000 10 min and eepaol min, respectively.
After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4. 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. Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. The quotient of the insulation resistance at time t 2 divided by the insulation resistance at time t 1.
Resistencia de isolação – Norma IEEE
If the windings are clean and dry, the total current I T. Restriction of personnel access to the high voltages is mandatory. To provide greater accuracy around the 1 min point and to 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. 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.
Before any testing is conducted, the winding insulation must be discharged. For older types of insulation, a reasonably steady value is usually reached in 10—15 min.
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 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.
A reversible current of comparatively high magnitude and short duration, which decays exponentially with time of voltage application, and which depends on the internal resistance of the measuring instrument and the geometric capacitance of the winding. 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. Parte 2 de 5 3.
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. Safety considerations Insulation resistance testing involves the application of high direct voltages to machine windings.