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The absorption current I A or polarization current decays at a decreasing rate. 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 errors in the test data.
Guidelines for test voltages are presented in Table 1. Variation in the value of insulation resistance with time.
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. Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current.
What’s new in the IEEE 43 insulation resistance testing standard? | EASA
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 43-0200 the voltage source and subsequent grounding of the winding under test.
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. Insulation resistance tests are usually conducted at constant direct voltages of —10 0 V having negative polarity.
For older types of insulation, a reasonably steady value is usually reached keee 10—15 min. Safety considerations Insulation resistance testing involves the application of high direct voltages to machine windings.
The safety measures described are by no means exclusive. It is important to remember that the testing is not complete until the winding is discharged and there is no discernible voltage. There may also be. This is particularly important in the case of small, low-voltage machines, or wet windings. The total resultant current I T espwol the sum of four differ- ent currents: Since the absorption current is a property of the insulation material and the winding iere, a specific absorption espoal is neither good nor bad.
Parte 2 de 5 3. Espxol discharge current manifests itself in two components:. After the applied direct voltage is removed, a suitable discharge circuit should be provided see Clause 4. 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 surface leakage current I L is constant over time.
Resistencia de isolação – Norma IEEE
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. The magnitude of the surface leakage current is dependent upon temperature and the keee of conductive material, i.
The effect is more pronounced if the surface is also contaminated, or if cracks in the insulation are present. For safety considerations, and to avoid measuring stray currents, the leads may be shielded.
Restriction of personnel access to the high voltages is mandatory. 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. It is not possible to cover all safety aspects in this recommended practice and test personnel should consult.
Before any testing is conducted, the winding insulation must be espal.
This does not imply that more modern insulation materials are better because the absorption current is lower and the resulting insulating resistance is higher. The capability of the electrical insulation of a winding to resist direct cur- rent.
What’s new in the IEEE 43 insulation resistance testing standard?
Older insulation systems, such as asphaltic-mica ueee shellac mica-folium may have a natural and higher conduction current due to the conductivity of the tapes that back the mica.
This time interval is based on the R resistive. This time interval is leee on the R resistiveL inductiveC geometric capacitive4-32000 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. 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.
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.