IEC Power transformers – Part 4: Guide to the lightning impulse and switching impulse testing – Power transformers and reactors. Edition Guide to the lightning impulse and switching impulse testing –. Power transformers and reactors. Reference number. IEC (E). INTERNATIONAL. Buy IEC Ed. Power transformers Part 4: Guide to the lightning impulse and switching impulse testing – Power transformers and reactors from SAI.
|Published (Last):||16 December 2011|
|PDF File Size:||3.17 Mb|
|ePub File Size:||5.89 Mb|
|Price:||Free* [*Free Regsitration Required]|
Major changes in current records such as amplitude and frequency changes normally indicate part winding breakdowns within the tested winding, between windings or to earth see figure B. There will also be a change in basic frequency and there may be a decrease in amplitude. However, this may not always be possible even with the highest values of resistors. Again it is possible to produce excessively high voltages to earth in parts of the winding.
On-line information is also available on recently issued publications, withdrawn and replaced publications, as well as corrigenda. In this test, high inter-phase voltages may occur on delta-connected windings and the danger of overstressing inter-phase insulation, internal or external, may limit the voltage that can be applied to the low-voltage winding.
INTERNATIONAL STANDARD IEC 60076-4
The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. Therefore, the selection of a proper reference earth is important. It is difficult to iev down preferred rules for sweep speeds and what is meant by late in time as the response of every transformer is different and the speed is to some 600766-4 dependent on the type of winding employed. However, these are normally not applicable since the corresponding resistance values give unacceptably long front times.
Significant changes occur in all real time and transfer function records. Information relating to this publication, including its validity, is available in the IEC Catalogue of publications see below in addition to new editions, amendments and corrigenda. Thus, the detectable discrepancies indicate major faults in the insulation or in the test circuit. The tail length and the voltage across the resistance should be measured to determine the value of resistance to be used.
Nearly the same considerations apply for the adjustment of the switching impulse front time. If the disturbances originate in the test circuit, every 60076-44 should be made to eliminate them or at least to minimize their effect. This problem may be solved to some extent by the use of large capacitance within the generator, by parallel stage operation, by adjustment of the series resistor or by specific test connections of the terminals of windings not under jec or, in addition, of the non-tested terminals of windings under test.
This waveshape should be characterized mainly by its frequency, determined by the reactor inductance and the generator capacitance, and the damping coefficient. Hence, it is not possible to state a time to chopping which is the most onerous either in general or for any particular transformer or reactor.
Provided that the time to chopping is reasonably identical from one voltage application to another, failures during this test will be detectable both in the voltage and current recordings by differences in the oscillations after chopping. Documents Flashcards Grammar checker. Item 3 in figure A. When the capacitance to earth is large compared to the through capacitance, an initial distribution similar to curve S in then graph will occur and the final distribution can again be assumed to curve Q.
Likewise, incipient faults at or near the terminal under test may also give iwc small indications on the oscillograms or digital recordings. In switching impulse testing, jec, because of the magnetically transferred voltage, a specified test level may only be obtained on one winding see IEC This configuration does not produce a sustained stress from winding to earth, but it does stress the insulation within the winding.
In such an event, a compromise between the extent of allowable oscillations and the obtainable front time is necessary.
Search results | IEC Webstore
The appropriate limits may be established by transient analysis with a low-voltage recurrent surge generator. If the through capacitances C 1 and C 2 are large compared to the capacitance C 3 to earth then a voltage distribution similar to curve M in the graph will result.
Insulation levels, dielectric tests and external clearances in air IECReactors IECInstruments and software used for measurement in high-voltage impulse tests — Part 1: However, the method which iecc an additional inductance in series with the capacitor to provide slightly damped oscillations transferred into the highvoltage winding is not applicable.
Nevertheless, it is suggested that, as a precaution, the 6006-4 earthing practices should be followed as used for lightning impulse testing.
Lec recording neutral or winding current, recording should continue at least until the inductive peak has been reached, thus permitting examination of the wave to determine if there has been any change in inductance caused by short-circuiting of turns as a result of insulation failure.
However, practice has been to specify reactor waveshapes as for transformers, that is, by T 1T d and T z see figures 3b and B. As can be seen from the records in all previously shown examples, all defects were also detected by the real time records.
For switching impulse voltage recording, it is 6007-4 to use capacitive types of voltage dividers, as resistive voltage dividers would have an influence on the waveshape and kec be thermally overloaded. The time taken to saturate the core is dependent on the core size, its initial state of magnetization and the level and waveshape of the applied voltage. Proof that these differences are indeed caused by operation of these devices should be demonstrated by making two or more reduced full-wave impulse tests at different voltage levels to show the trend in their operation.
The capacitively transferred current from the LV winding sparks to a different earth than the tank and generator earth, resulting, after comparing with the reduced fullwave test, in a no indication in the voltage; b clear indication in 6076-4 current; c clear indication in the transfer function analysis.
IEC | IEC Webstore
The stored data in the memory of the digitizer, however, allows for any other presentation irc the same recording by zooming in or out at different time scales. Q2 Please tell us in what capacity ies you bought the standard tick all that apply. However, there are cases, for example, windings of extremely low inductance, where the series resistance will have a significant effect also on the wavetail.
IEC requires simultaneously the measurement of a the applied voltage; b at least one of the transients listed in 7. Please contact the Customer Service Centre see below for further information. However, due to the possible excessive voltages to earth on the non-tested terminals or between phases, explained in 8. C g can be altered by series or parallel connection of the stages of the impulse generator. The latter part will only be comparable for reasonably identical times to chopping.
Power transformers, Windings, Short-circuit current tests, Impedance measurement, Electric load, Temperature rise, Voltage fluctuations, Magnetic fields, Rated power, Phase electricThree-phase transformers, 600764- transformers, Transformers, Tappings electricalAutotransformers.
For gapped core reactors, which have only one winding per phase and no closed magnetic loop, the detection of turn-to-turn faults may be very difficult, or faults may be even iex undetected. This is not the case for reactors for which, in addition, waveshape problems and test procedures are different.
With the nature of faults to be expected, current records are as sensitive as voltage records. After any check has been made, it is essential that neither the measuring nor the test circuit is altered except for the removal of any devices for checking.