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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Similar considerations with respect to superimposed oscillations are valid also for singlephase auto-transformers.
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.
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With the non-tested windings short-circuited and earthed usual connectionL t is the leakage inductance of the transformer. Provided that the time resolution is sufficiently high, a more detailed analysis of discrepancies is possible.
When using digital recording techniques, the transfer function analysis as described in clause 10 may be helpful to eliminate this confusion see figure B.
However, the literature and experience regarding transfer function analysis was for many years contradictory. IEC requires simultaneously the measurement of a the applied voltage; b at least one of the transients listed in 7. This circuit was selected for three-phase transformers with both three- and five-limb cores to perform simultaneously testing of the phase-to-earth and phase-to-phase insulation with 1,0 p.
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.
INTERNATIONAL STANDARD IEC 60076-4
The form of the change will be different depending on the method of failure detection employed. The arrangement of the test plant, test 60706-4 and the interconnecting cables, earthing strips, and other equipment is limited by the space in the test room and, particularly, the proximity effect of any 6076-4.
For switching impulses, other parameters apply; these are dealt with in clause 8. The amount of improvement in the tail time with this configuration is dependent on the characteristic of the winding and the values of 06076-4 available. Responses from test object failures — A failure digital recording of a tap changer lead flashover between taps is shown in figure B.
If the through capacitances C 1 and C 2 are extremely large compared to the capacitance C eic to earth, a distribution similar to curve P in the graph will result. It is difficult to lay down preferred rules for sweep 60076- and what is meant by late in time as the response of every transformer is different 6006-4 the speed is to some extent dependent on the type of winding employed.
Thus, the detectable discrepancies indicate major faults in the insulation or in the test circuit. 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 test or, in addition, of the non-tested terminals of windings under test.
It is more important to try to obtain the required voltage level by means of termination resistors kec sufficiently high value. 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. The value of the test voltage is determined according to the principles of IEC It is essential, in acceptance testing, to record at least one of these transients in addition to the applied test voltage: When measuring such overswing, clipping of the recorded waveshape may occur by saturation of the input amplifier in the digitizer in the chosen range.
The number of the required pre-magnetizing impulses 6076-4 their level depend on the level of test voltage aimed for.
Transferred voltage recordings will also indicate the above-mentioned faults. Properly calibrated capacitive bushing taps can be employed as voltage dividers.
However, this sensitivity is accompanied by the possibility of the recordings indicating a number of effects not directly associated with failure. In switching impulse testing, since the rates of change of the impulse voltages and currents are much reduced compared with those in a lightning impulse test and no chopping circuit is involved, the problems of potential gradients around the test circuit and with respect to the reference earth are less critical.
A significant increase, combined with a change in superimposed frequency in a neutral current is indicative of a fault within the tested winding whilst a decrease indicates a fault from the tested winding to an adjacent winding or to earth.
Discrepancies of any kind are of concern and should be investigated. It should be long 660076-4 to ensure approximately uniform distribution throughout the tested winding. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation.
This interconnection of non-tested terminals is not necessary for transformers provided with isc delta-connected winding. For the ief report see clause 11 one pertinent recording is normally sufficient for acceptance tests; for diagnostic testing, however, several records with different sweep times may be required.
Information on the subjects under consideration and work in progress undertaken by the technical committee which has prepared this publication, as well as the list of publications issued, is also available from the following: C g can be altered by series or parallel connection of the stages of the impulse generator.
Power transformers – Part 4 :Guide to the lighting/KS IEC – Full Catalogue Listing
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. 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.
Refer also to IEC NOTE 2 The changes in waveshape shown above are more marked than those which generally result from the presence of non-linear resistors. 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.
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 the current; c clear indication in the transfer function analysis.
For wave analysis, it is important to take samples over the complete waveshape until the wave is completely damped, using the maximum available memory of the digitizer.
It is important to programme the digitizer in such a way that a sufficient number of samples is present to kec the virtual starting-point ied the wave. Evidently, the value of C t for tail considerations is of minor importance in most practical cases see equation A. However, the method which employs an additional inductance in series with the capacitor to provide slightly damped oscillations transferred into the highvoltage winding is not applicable. For windings of small series capacitance, that is, 6076-4 essentially travelling wave behaviour, it may be possible to identify the source of disturbances by evaluating the time difference between the arrival at the neutral of the capacitive and the travelling wave disturbances.
Fort Hood Sentinel Advertisement. The text of this standard is based on the following documents: The sum of items ac and d or of items bc and dis sometimes referred to as line current.
Unless the core magnetization state is identical before each switching impulse application at a given voltage level, identical waveshapes on successive applications will not be obtained. For directly earthed terminals, only the leakage inductance determined by the short-circuit impedance is involved. Kec earthing, rather than direct earthing, of the non-tested winding terminals results in a significant increase in the effective inductance.