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 absorption current I A or polarization current decays at a decreasing rate. The insulation resistance of a rotating machine winding is a function of the type and condition of the insulating 4-32000 used, as well as their application technique.
Espakl time interval is based on the R resistive. If the windings are clean and dry, the total current I T. 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. 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.
After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4. These electrons and ions drift until they become trapped at the mica surfaces commonly found in rotating machine insulation systems.
Figure 3—Types of espoal for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current. Since the absorption current is a property of the insulation material and the winding temperature, a specific absorption current is neither good nor bad. This is particularly important in the case of small, low-voltage machines, or wet windings.
An equivalent circuit for the various currents in an insulation resistance test is shown in Figure 1. The geometric capacitance current I C usually does not affect the measurements, because it disappears es;aol the time the first reading is taken at 1 min.
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. Clause 1 and Clause 43-20000 Use of personal protective equipment is recommended, as is the use of hot sticksinsulated ladders, etc. Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. Figure 1—Equivalent circuit showing the four currents monitored during an insulation resistance test.
What’s new in the IEEE 43 insulation resistance testing standard?
A high surface leakage current, 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. For older types of insulation, a reasonably steady value is usually reached in 10—15 min.
If times t 2 and t 1 are not specified, they are assumed to be 10 min and 1 min, respectively. A minimum discharge time, which is equal to four times the voltage application duration, is recommended. Since these molecules have to strain against 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. A second component of the absorption current is due to the gradual drift of electrons and ions through most organic materials.
During the test period, all appropriate safety measures for the voltages being used must be taken. The safety measures described are by no means exclusive. 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 It is important to remember that the testing is not complete until the winding is discharged and there is no discernible voltage.
Readings of insulation resistance are taken after the test direct voltage has been applied for 1 min. 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 espol conductive when exposed to moisture or oil, and, thus, can lower the insulation resistance.
43-2000 Resistencia de isolação
The total resultant current I T is the sum of four differ- ent currents: This does not imply that more modern insulation materials are better because the absorption current is lower and the resulting insulating resistance is higher. 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.
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. It is recommended that subsequent ac high-potential testing not be conducted until the winding is fully discharged.
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. It is not possible to cover all safety aspects in this recommended practice and test personnel should consult.
This decay may take more than 30 min depending on the insulation type and machine size of the test specimen.
Resistencia de isolação – Norma IEEE
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. These windings have capacitive and inductive properties that can lead to hazards that may not be readily apparent. Insulation resistance testing involves the application of high direct voltages to machine windings.
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. There may also be. 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.
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. 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.