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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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.
If times t 2 and t 1 are not specified, they are assumed to be 10 min and 1 min, respectively. If the test voltage is too high, the applied test voltage may over stress the insulation, leading to insulation failure.
The safety measures described are by no means exclusive. Note that the effects of moisture contamination on a healthy winding should not preclude obtaining acceptable readings. It may be plotted on a log-log graph as a straight line.
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. These windings have capacitive and inductive properties that can lead to hazards that may not be readily apparent. Guidelines for test voltages are presented in Table 1. It is recommended that subsequent ac high-potential testing not be conducted until the winding is fully discharged.
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.
The magnitude of the surface leakage current is dependent upon temperature and the amount of conductive material, i.
What’s new in the IEEE 43 insulation resistance testing standard?
For older types of insulation, a reasonably steady value is usually reached in 10—15 min. Use of personal protective equipment is recommended, as is the use of hot sticksinsulated ladders, etc. Older insulation systems, such as asphaltic-mica or shellac mica-folium may have a natural and higher conduction current due 34-2000 the conductivity of the tapes that back the mica. 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.
After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4.
Poluicao em Isoladores Artigos sobre Poluicao em Isoladores. A second component of the absorption current is due to the gradual drift of electrons and ions through most organic materials. 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. 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.
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. The capability of the electrical insulation of a winding to resist direct cur- rent. For safety considerations, and to avoid measuring stray currents, the leads may be shielded.
Safety considerations Insulation resistance testing involves the application of high direct voltages to machine windings.
Caracteriza a perfomance do isolamento sonoro de uma parede de uma alvenaria estrutural de blocos The surface leakage current I L is constant over time. 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.
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.
Modern esapol 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.
Resistencia de isolação – Norma IEEE
This decay may take more than 30 min depending on the insulation type and machine size of the test specimen. If the windings are clean and dry, the total current I T. The absorption current I A or polarization current decays at a decreasing rate.
A minimum discharge time, which is equal to four times the voltage application duration, is recommended. Insulation resistance testing involves the application of high direct voltages to machine windings.
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. 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.
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. 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.
There may also be. 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.
Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. 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 espoal thickness and inversely with the conductor surface area.
Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current.
If the winding is wet or dirty, a low steady value will usually be reached 1 min or 2 min after the test voltage is applied.