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.
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Different considerations in the oec of test circuits terminal connections for lightning and switching impulse tests apply for transformers and reactors. These changes may be caused by either a flashover in the return loop to the laboratory earth or an internal failure in the test object When ieec the chopped wave test, failure of the chopping gap to chop, or any external part to spark over, although the voltage recording shows a chopped wave, gives a definite indication of a failure either within the test object or in the test circuit.
They need to be subdivided into two major aspects: As can be seen from the records in all previously shown examples, all defects were also detected by the real time records. The current flowing to earth through the tested winding can additionally be used.
However, in this case the effective transformer capacitance C t for the longer front time is equal to the effective winding earth capacitance C e. IEC specifies a 9-bit, 60 MHz digitizer as the minimum resolution of the digitizer for the registration of impulse voltage and current waveshapes. Digital recording offers the potential for mathematical interpretation of the results and allows additional mathematical processing to be used, for example, for fault analysis in recordings.
BS , IEC – Power transformers. Specification for tappings and connections
This series and sometimes also discrepancies after the peak, which may also originate from the with multiple parallel stage operation, if the discharge circuits are not coincident in may require new setting of the discharge gaps on generators which have both parallel gaps.
For most transformers, at full test level, the exponential decay of the wavetail is interrupted by a sudden fall through zero, at a variable time after the crest, due to core saturation.
This is a skilled task and it is often difficult to decide the significance iev discrepancies, even with considerable experience, because of the large number of possible disturbance sources. Hence, the requirement in IEC that a phase-to-phase voltage of 1,5 U will occur when a voltage U is applied to one terminal, is valid only in principle.
Testing in this configuration generally produces the 60706-4 stress to the insulation between windings or eic of windings, even if a shorter tail results. One pertinent recording see clause 11 is normally sufficient for acceptance tests.
In this case, T d and T z can only be determined from full test-level shots. On multiple layer windings, the layer impedance may damp the collapse normally to the extent that it does not oscillate around zero see figure B. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. In addition, identical waveshapes at reduced and full test levels cannot be obtained.
This results from the slightly different times at which the maxima of applied U and induced 0,5 U voltages occur. It should be noted that there may be significant differences in the shape of the wavetail on different limbs of a transformer due to the different reluctances of the magnetic circuit involved.
BS 171-4:1978, IEC 60076-4:1976
This test configuration applies the proper waveshape to the line-end insulation and is suitable for earth current measurements, although the resistance may reduce slightly failure detection sensitivity. The basic waveform of the current corresponding to the cosine voltage wave is sinusoidal see figures 3b and B.
600766-4 have been used in impulse testing since the s. Hence, the voltage records on switching impulse tests are a sufficiently sensitive means for detection of most faults see figure B. Therefore, the two items of equipment are dealt with separately. The intention of illustrating particular faults is to give general guidance only. It should, however, be sufficiently long to ensure essentially uniform distribution of voltage. Isc, governmental and non-governmental organizations liaising with the IEC also participate in this preparation.
When the capacitance to earth is large compared uec 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.
These types of fault cause a significant change in the voltage wave either as a complete collapse of the wave or a shortening of the tail or, sometimes, as a temporary dip in the trace. 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. When this current is measured on the winding to which the impulse voltage is directly applied, whether or not this is the winding on which the specified test voltage level is to be achieved, the current comprises three parts: The inductance of such windings may be so low that the resulting waveshape is oscillatory.
Annexes A and B are for information only. Different transients can be recorded and used separately or in combination, as shown in figure 2. If the disturbances originate in the test circuit, every effort should be made to eliminate them or at least to minimize their effect. For switching impulse voltage recording, it is preferable to use capacitive types of voltage dividers, as resistive voltage dividers would have an influence on the waveshape and may be thermally overloaded.
Guide to the lightning impulse and switching impulse testing — Power transformers and reactors This English-language version is derived from the original bilingual publication by leaving out all French-language pages. This point is reached when the time to the first zero passage remains constant on consecutive impulse applications. It is, however, advisable to use sweep times for eic voltage and current which cover the second half-cycle of the applied voltage.
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Except at the start of the wave or, in the case of transformers, in the vicinity of core saturation, sharp changes of current occurring at the same 6076-4 as any distortion of the voltage wave are indicative of failure. Therefore, the selection of a proper reference earth is important. Temperature rise Part 3: The form of the change will be different depending on the method of failure detection employed.
It is difficult to lay 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 extent dependent on the type of winding employed. It varies between the leakage inductance L s for short-circuited terminals and L o for open-circuited kec. Determination of sound levels The committee has decided that the contents of this publication will remain unchanged until Discrepancies of idc kind are of concern and should be investigated.