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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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. This, in fact, represents a guideline for the arrangement of the chopping circuit lec may entail the introduction of additional impedance Z c in this circuit to meet the limit see figure 1. When the indirect method is used, i.
T z cannot be established until the first full-level voltage application is made. The stored data in the memory of the digitizer, however, allows for any other 6076-4 of the same recording by zooming in or out at different time scales. Power transformers, Windings, Short-circuit current tests, Impedance measurement, Electric load, Temperature rise, Voltage fluctuations, Magnetic fields, Rated power, Phase electricIfc transformers, Single-phase transformers, Transformers, Tappings electricalAutotransformers.
This procedure includes reference to measures which may be taken to increase the impulse duration by delaying the possible onset of core saturation.
INTERNATIONAL STANDARD IEC 60076-4
It should, however, be sufficiently long to ensure essentially uniform distribution of voltage. 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. ie
600076-4 Special attention should be given to the amount of overswing to opposite polarity of lightning impulses. 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.
idc These quantities are illustrated in figure 3a. In such cases, higher resolution recording to cover the time to peak and to the opposite polarity of the applied cosine wave is recommended. Click to learn more. L t is influenced by the connection of the non-tested iwc. The form of the change will be different depending on the method of failure detection employed.
For current recordings, it may be advantageous to use, in addition, a shorter sweep time so as to be able to monitor the initial capacitive current in more detail.
BS , IEC – Power transformers. Specification for tappings and connections
Characteristic oscillations will also occur on the voltage wave at the moment 6006-4 flashover see figures B. NOTE 2 The changes in waveshape shown above are more marked than those which generally result from the presence of non-linear resistors.
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. 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.
Standard Number BS It is essential, in acceptance testing, to record at least one of these transients in addition to the applied test voltage: Alternative means of switching impulse generation or simulation such as d.
Please contact the Customer Service Centre see below for further information. Similar but not necessarily identical instants of chopping are achieved by use of triggered-type chopping gaps see figure B.
Guide to lightning impulse and switching impulse testing — Power transformers and reactors Part 5: For windings of small series capacitance, that is, exhibiting 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. The resolution achieved should ensure that a as clear a representation as possible is obtained from the oscillograms, including the higher frequency components near the front of the wave; b the current record is of sufficient duration to permit detection of any discrepancies occurring late in time.
For switching impulses, other parameters apply; these are dealt with in clause 8.
INTERNATIONAL STANDARD IEC
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. While the output voltage of the impulse generator is determined by 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.
Such high opposite polarity oscillation may overstress inter-turn and inter-winding insulation due to high oscillatory stresses which can trigger partial discharges and enhanced electrode mechanisms only due to testing limitations.
The software can subtract the full wave and the reduced wave and show differences on an adjustable magnified scale.
In these cases, the value of T 2 cannot directly be adjusted according to equation A. 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.
Core saturation does not usually occur on reduced-level voltage applications and may not even occur on full-level applications. 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: