IEEE 43-2000 ESPAOL PDF
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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 eapaol in the test data.
The surface leakage current I L is constant over time. It is not possible to cover all safety aspects in this recommended practice and test personnel should consult. The safety measures described are by no means exclusive.
This does not imply that more modern insulation materials are better because the absorption current is lower and the resulting insulating resistance is higher. By definition, the insulation resistance is espakl quotient of the applied direct voltage across the insulation divided by the total resultant current at a given time.
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.
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. Note that the effects of moisture contamination on a healthy winding should not preclude obtaining acceptable readings. The readings of a dry winding in good condition may continue to increase for hours with a continuously applied constant test voltage.
Resistencia de isolação – Norma IEEE
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. 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.
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. Restriction of personnel access to the high voltages is mandatory. 443-2000 absorption current has two components. A current that is constant with edpaol, 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.
What’s new in the IEEE 43 insulation resistance testing standard?
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.
In general, the insulation resistance varies proportionately with the insulation thickness and inversely with the conductor surface area. 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.
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.
Parte 2 de 5 3. Poluicao em Isoladores Artigos sobre Poluicao em Espaool. 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. For safety considerations, and to avoid measuring stray currents, the leads may be shielded.
For older types of insulation, a reasonably steady value is usually iee in 10—15 min. This decay may take more than 30 min depending on the insulation type and machine size of the test specimen.
Safety considerations Insulation resistance testing involves the application of high direct voltages to machine windings. 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. Guidelines for test voltages are presented in Table 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. 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.
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. 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.
After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4. It may be plotted on a log-log graph as a straight line.