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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Figure 3—Types of currents for an epoxy-mica insulation with a relatively low surface leakage current and no conductance current. 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. 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.
A minimum discharge time, which is equal to four times the voltage application duration, is recommended. 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 conduction current I G in well-bonded polyester and epoxy-mica insulation systems is essentially zero unless the insulation has become saturated with moisture.
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. Older insulation systems, such as asphaltic-mica or espall mica-folium may have a natural and higher conduction current due to the conductivity of the tapes that back the mica.
Negative polarity is preferred to accommodate the phenomenon of electroendosmosis. 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.
43-2000 Resistencia de isolação
During the test period, all appropriate safety measures for espaok voltages being used must be taken. Use of personal protective equipment is recommended, as is the use of hot sticksinsulated ladders, etc.
These electrons and ions drift until they become trapped at the mica surfaces commonly found in rotating machine insulation systems.
In general, the insulation resistance varies proportionately with the insulation thickness and inversely with the conductor surface area. Regardless of the cleanliness 433-2000 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 4-32000 resistance or polarization index.
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.
See Annex A for the use of other values. The discharge current manifests itself in two components:. The voltage application time is usually 1 ieeee IR 1 or 10 min IR 10however, other values can be used.
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. 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.
What’s new in the IEEE 43 insulation resistance testing standard?
Since the absorption current is a property of the insulation material and the winding temperature, a specific absorption current is neither good nor bad. The magnitude of the surface leakage current is dependent upon temperature and the amount of conductive material, i.
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. An equivalent circuit for the various currents in an insulation resistance test is shown in Figure 1.
The readings of a dry winding in good condition may continue to increase for hours with a continuously applied constant test voltage. If times t 2 and t 1 are not specified, they are assumed to be 10 min and 1 min, respectively. Note that the effects of moisture contamination on a healthy winding should not preclude obtaining acceptable readings. This does not imply that more modern insulation materials are better because the absorption current is lower and the resulting insulating resistance is higher.
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. Restriction of personnel access to the high voltages is mandatory.
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.
Resistencia de isolação – Norma IEEE
The absorption current I A or polarization current decays at a decreasing rate. Figure 1—Equivalent circuit showing the four ewpaol monitored during an insulation resistance test.
The absorption current has two components. The first component is due to the polarization of the impregnating materials because the organic molecules, such as epoxy, polyester, and asphalt, ieed to change orientation in the presence of a direct electric field.
The quotient of the insulation resistance at time t 2 divided by the insulation resistance at time t 1. Since these molecules have to strain against the attractive forces of other fspaol, 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.