Source: https://bbdfr85.info/iec-60076-4-34/
Timestamp: 2020-08-13 14:30:34
Document Index: 154848637

Matched Legal Cases: ['art 3', 'art 4', 'art 5', 'art 8', 'art 1', 'art 1', 'art 2']

Author: Fezuru Dojin
ISBN: 460-7-35258-748-4
Documents Flashcards Grammar checker. 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. Missing page iecc correspond to the Frenchlanguage pages. Reference number IEC Consolidated editions The IEC is now publishing consolidated versions of its publications.
For example, edition numbers 1. 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.
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issued, is also available iiec the following: On-line information is also available on recently issued publications, withdrawn and replaced publications, as well as corrigenda.
Please contact the Customer Service Centre see below for further information. The object of the IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt ifc may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation.
The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. The IEC shall not be held responsible for identifying any or all such patent rights. This International Standard cancels and replaces IEC published in and constitutes idc technical revision of that document.
The text of this standard is based on the following documents: Annexes A and B are for information only. Temperature rise Part 3: Insulation levels, dielectric tests and 600776-4 clearances in air Part 4: Guide to lightning impulse and switching impulse testing — Power transformers and reactors Part 5: Ability to withstand short-circuit Part 8: Application guide Part Determination of sound levels The committee has decided that the contents of this publication will remain unchanged until iiec Guide to the lightning impulse and switching impulse testing — Power transformers and reactors 1 Scope This part of IEC gives guidance and explanatory comments on the existing procedures for lightning and switching impulse testing of power transformers to supplement the requirements of IEC It is also generally applicable to the testing of reactors see IECmodifications to power transformer procedures being indicated where required.
For dated references, only the ifc cited applies. For undated references, the latest edition of the referenced document including any amendments applies. IECHigh-voltage test techniques — Part 1: Insulation levels, dielectric tests iev external clearances in air IECReactors IECInstruments and software used for measurement in high-voltage impulse tests — Part 1: Requirements for instruments IECDigital recorders for measurements in high-voltage impulse tests — Part 2: The practice of switching impulse generation with discharge of a separate capacitor into an intermediate or low-voltage winding is also applicable.
However, the method which employs an additional inductance in series with 6076-4 capacitor to provide slightly damped oscillations transferred 60067-4 the highvoltage winding is not applicable. Alternative means of switching impulse iev or simulation such 60076–4 d. Different considerations in the choice of test circuits terminal connections for 60067-4 and switching impulse tests apply for transformers and reactors.
On transformers, all terminals and windings can be lightning impulse tested to specific and independent levels. In switching impulse testing, however, because of the magnetically transferred voltage, a specified test level may only be obtained on one winding see IEC Whilst, on reactors, lightning impulse testing is similar to that on transformers, i.
Hence, in this standard, lightning impulse testing is covered by a common text for both transformers and reactors whilst 600764 impulse testing is dealt with separately for the two types of equipment.
This basic arrangement is shown in figure 1. The effective L thowever, may be influenced by the terminal treatment. It varies between the leakage inductance L s for short-circuited terminals and L o for open-circuited terminals.
More details in this respect are given in 7.
The front time T 1 is determined mainly by combination of the effective surge capacitance of the test object, including C Land the generator internal and external series resistances. The time to half-value T 2 is, for lightning impulses, primarily determined by the generator capacitance, the inductance of the test object and the generator discharge resistance or any other parallel resistance.
However, there are cases, for example, windings of extremely low inductance, where the series resistance will have a significant effect also on the wavetail. For switching impulses, other parameters apply; these are dealt with in clause 8. The test equipment used in lightning and 60076–4 impulse applications is basically the same. Differences are in details only, such as values of resistors and capacitors and the terminal connections of the test object.
6076-4 meet the different requirements of the waveshape for lightning and switching impulses, due consideration has to be given to the selection of kec impulse generator parameters, such as capacitance and series and discharge parallel resistances.
While the output voltage 6006-4 the impulse generator is determined iex the test levels of the windings with respect to their highest voltage for equipment U m for the test object, the required energy storage capability is essentially dependent on the inherent impedances of the test object.
A brief explanation of the principles of waveshape control is given in annex A. The 6007-64 of the test plant, test object 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 structures.
During ic testing, zero potential cannot be assumed throughout the earthing systems due to the high values and rates of change of impulse currents and voltages and the finite impedances involved. Therefore, the selection of a proper reference earth is important.
It is good practice to firmly connect this current return path to the general earth system of the test room, preferably close to the test object. This point of connection should be used as reference earth and to attain good earthing of the test object it should be connected to the reference earth by one or several conductors of low impedance see IEC The voltage measuring circuit, which is a separate loop of the test object carrying only the measuring current and not any major portion of the impulse current flowing through the windings under test, should also be effectively connected to the same reference earth.
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 6007-64 with respect to the reference earth are less critical.
Nevertheless, it is suggested that, as a precaution, the same earthing practices should be followed as used for lightning impulse testing. Before a test, an overall check of the test circuit and the 60076-4 system may be performed at a voltage lower than the reduced voltage level.
In this check, voltage may be determined by means of a sphere gap or by comparative measurement with another approved device. When using a sphere gap, it should be recognized that this is only a check and does not replace the periodically performed calibration of the approved measuring system. 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.
Information on types of voltage dividers, their applications, accuracy, calibration and checking is given in IEC The surge capacitance of the transformer under test being constant, the series resistance may have to be reduced in an attempt to obtain the correct front time T 1 or rate of rise, but the reduction should not be to the extent that oscillations on the crest of the voltage wave become excessive.
In such an event, a compromise between the extent of allowable oscillations and the obtainable front time is necessary.
The value of the test voltage is determined according to the principles of IEC The inductance of such windings may be so low that the resulting waveshape is oscillatory. 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.
Impedance earthing, rather than direct earthing, of the non-tested winding terminals results in a significant increase in the effective inductance. For directly earthed 6076-4, only the leakage inductance determined by the short-circuit impedance is involved.
For impedance earthed terminals, the main inductance becomes predominant. This can make the effective inductance to times greater than with direct earthing. With this limitation, guidance for selecting impulse generator capacitance and adjusting waveshapes is given in annex A. 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. Oscillograms or digital recordings of chopped waves, however, are only comparable for almost identical times to chopping.
This, in fact, represents a guideline for the arrangement of the chopping circuit and may entail the introduction of additional impedance Z c in this circuit to meet the limit see figure 60076–4. 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.
The recommendation in IEC to use a triggered-type chopping gap is made because of its advantage in obtaining consistency of the time to chopping, iwc facilitating the comparison of oscillographic or digital recordings not only before but also after chopping.
The latter part will only be comparable for reasonably identical times to chopping. Normally the non-tested terminals of the phase winding under test are earthed 60067-4 the non-tested phase windings are shorted and earthed. However, in order to improve the wavetail T 2resistance earthing of the non-tested windings may be advantageous see clause 5 and 7. In addition to the methods of waveshape adjustment in 7.
When non-linear elements or surge diverters — built into the transformer or external 60076–4 are installed for the limitation of transferred overvoltage transients, the impulse test procedure should be discussed in advance for each particular case.
Refer also to IEC Different 6076-4 can be recorded and used 60076-4 or in combination, as shown in figure 2.
These are listed a to e below. It is essential, in acceptance testing, to record at least one of these transients in addition to the applied test voltage: The sum eic items ac and d or of items bc and dis sometimes referred to as line current. When testing reactors, both of the 60076- and series types, items c and e are oec item d may be applied but only as an additional means of transient recording since it is likely to be less 06076-4 than when used in transformer testing.
The preferred method of test is that of direct application although in special cases where the intermediate or low-voltage winding cannot, in service, be subjected to lightning overvoltages from the system connected to it, the “transferred surge” 60076- may alternatively be employed. The impulse test of the low-voltage winding is then carried out simultaneously with the test of the associated high-voltage winding. In these conditions, the waveform of the transferred voltage does not conform with that specified in IEC It is more important to try to obtain the required voltage level by means of termination resistors of sufficiently high value.
However, this may not always be possible even with the highest values of resistors. 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.