IEC 60076-4 PDF

If the above-mentioned methods of wavetail control are still not sufficient to attain the proper time to half-value, a compromise is necessary between either accepting a shorter time to halfvalue or resorting to resistance earthing at the non-tested terminal s of the winding s under test, according to figure A. You may experience issues viewing this site in Internet Explorer 9, 10 or The load capacitance will then reduce the adverse effects of a small series resistor R s. 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. Annexes A and B are for information only. The wavetail half-value and, on occasions, the b Applied impulse test voltage wave recording In order to determine the amplitude of the test wave and to permit detection of any fault which may be present: However, in order to improve the wavetail T 2resistance earthing of the non-tested windings may be advantageous see clause 5 and 7. This waveshape should be characterized mainly by its frequency, determined by the reactor inductance and the generator capacitance, and the damping coefficient.

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If the above-mentioned methods of wavetail control are still not sufficient to attain the proper time to half-value, a compromise is necessary between either accepting a shorter time to halfvalue or resorting to resistance earthing at the non-tested terminal s of the winding s under test, according to figure A.

You may experience issues viewing this site in Internet Explorer 9, 10 or The load capacitance will then reduce the adverse effects of a small series resistor R s. 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.

Annexes A and B are for information only. The wavetail half-value and, on occasions, the b Applied impulse test voltage wave recording In order to determine the amplitude of the test wave and to permit detection of any fault which may be present: However, in order to improve the wavetail T 2resistance earthing of the non-tested windings may be advantageous see clause 5 and 7.

This waveshape should be characterized mainly by its frequency, determined by the reactor inductance and the generator capacitance, and the damping coefficient. However, there are cases, for example, windings of extremely low inductance, where the series resistance ic have a significant effect also on the wavetail.

Therefore, the two items of equipment are dealt with separately. For dated references, only the edition cited applies. The basic waveform of the current corresponding to the cosine voltage wave is sinusoidal see figures 3b and B.

There are, however, cases where the fault occurs before the instant of chopping and then the same considerations apply as for full-wave tests see figures B. Temperature rise Part 3: It varies between the leakage inductance L s for short-circuited terminals and L o for open-circuited terminals.

Depending on the form of the current trace and on the use of linear or exponential sweeps, it may be necessary to use more than one record with different sweep times. 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.

For undated references, the latest edition of the referenced document including any amendments applies. Hence, the normal impulse test procedures as used for lightning impulse tests are required. It is therefore recommended that higher sampling frequencies as mentioned before be used to discriminate noise in the measuring circuit from the actual behaviour of the test object.

Therefore, during a test, the interphase voltages are likely to be higher than 1,5 U if no measures are taken at the non-tested terminals to suppress the eic voltages by means of high ohmic impedance earthing. In these cases, the value of T 2 cannot directly be adjusted according to equation A.

Digitizers have been used in impulse testing since the s. 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 time as any distortion of the voltage wave are indicative of failure. The surge capacitance of the transformer under test being constant, the series resistance jec 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.

The voltage record will normally also satisfactorily indicate any fault on magnetic coupled windings not directly subjected to the switching impulse. Your basket is empty. BS , IEC Information relating to this publication, including its validity, is available in the IEC of publications see below in addition to new editions, amendments and corrigenda.

Item 3 in figure A. Electronic Single-Phase kWh Meter. Impedance earthing of the non-tested terminals of the winding under test may then be applied.

Attention is again drawn to the fact that whilst these oscillograms are typical, it cannot be assumed that a discrepancy found on another transformer or reactor of different voltage, design and manufacture, although apparently similar to one illustrated herein, is caused by an identical fault.

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.

According to equation A. Therefore, the selection of a proper reference earth is important. August Replaced By: This can make the effective inductance to times greater than with direct earthing.

The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. The inductance of such windings may be so low that the resulting waveshape is oscillatory. However, resistive loading causes a significant lengthening of the wavefront at the non-tested terminals, resulting in a phase-to-phase voltage of less than 1,5 U. The form of the change will be different depending on the method of failure detection employed.

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.

The flux in these reactors cannot be directed through the windings on the non-tested limbs. Application guide Part For large values of T 1the damping coefficient will be large thus resulting in a relatively short time T z. Oscillograms or digital recordings of chopped waves, however, are only comparable for almost identical times to chopping. This point is reached when the time to the first zero passage remains constant on consecutive impulse applications.

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.

Even small differences in the instant of chopping, can, for some transformers, give rise marked differences in the oscillation pattern after the chop this pattern being a superposition of the transient phenomena due to the front of the original impulse and the chopping and these differences may confuse comparison between the records of successful applications and those where a fault exists see figure B.

The waveshape is determined largely by the capacitances and resistances of the generator and the impedance of the load. Datasheet — Electronics. This new technology represents a very powerful tool for the future, because it may also be used for on-line condition monitoring, both for dielectric defects and for mechanical defects after severe short-circuits.

The stored data in the memory of the digitizer, however, allows for any other presentation of the same recording by zooming in or out ie different time scales. Related Posts.

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