When the transformer suffers from short circuit current impact or other impacts, the deformation includes the following:
① The overall deformation of the winding is caused by the impact, tilt, vibration and other external forces during the transportation process, resulting in the displacement of the winding. The size of the deformed winding is unchanged, but the relative displacement of the iron core changes. The inductance and inter cake capacitance of the winding remain unchanged, while the electrical capacity to the ground changes. Generally, the capacitance decreases. In the equivalent circuit, the resonance peak shifts to the high frequency direction. Therefore, in the spectrogram measured after such deformation, compared with the previous ones, all resonance points still exist and do not change, but the peak values are shifted to the high frequency direction (to the right).
② The local deformation between pancakes makes some loose wire pancakes squeezed under the action of short circuit electromagnetic force, and some other wire pancakes are stretched, so the capacitance between pancakes is changed. The consequence of this deformation makes some inductances in the equivalent circuit diagram larger and some smaller; The inter cake capacitance in parallel with the inductor also changes. When measuring the spectrogram, some resonance peaks move to the high frequency direction, and the peak value drops; Some resonance points move to the low frequency direction, and the peak points rise. The deformation area and degree between pancakes can be judged by the change of resonance peak value.
③ Turn to turn short circuit: Theoretically, after the turn to turn short circuit occurs in the winding, the inductance value decreases, the spectrum curve changes significantly, the amplitude increases, and some resonance point peaks disappear. But the theory is like this. In fact, it is difficult to capture this situation. In case of inter turn short circuit during operation, the wire turns will be burnt out, heavy gas will trip, and the pressure relief valve will act. At this time, the chromatographic analysis of transformer oil will also be unqualified, and the transformer will be inspected by hanging the cover.
④ The lead wire is displaced and deformed. When the lead wire is long and not firmly fixed, it will be displaced and deformed during operation. When the lead wire is displaced, the capacitance of two ports changes in the equivalent circuit. When the lead at the signal inlet is displaced but the lead capacitance is connected in parallel with other circuits, its change will not change the spectrum curve significantly; However, the frequency response curve will change significantly after the change of the output terminal lead displacement and lead capacitance, especially in the range of 300kHz~1MHz. Therefore, in the actual test, the neutral point injection signal source is used to prevent the above effects. If the lead to ground capacitance decreases, the amplitude in the frequency band increases, otherwise, it decreases; When the capacitance of the lead to the ground increases, it indicates that the lead moves towards the shell, and when the capacitance of the lead to the ground decreases, it indicates that the lead moves towards the winding.
⑤ The winding is radially deformed. When the winding is subjected to radial force, the inner winding shrinks inward, the diameter becomes smaller, and the inductance becomes smaller. At this time, the distance between the inner and outer windings becomes larger, and its capacitance becomes smaller, which will make the resonance peak in the spectrum move to the high frequency direction, and the amplitude increases.
⑥ The winding is twisted and deformed in axial direction. When the gap between the transformer windings is large or some of the braces are displaced, the winding will be twisted into S-shape in axial direction under the action of electromagnetic force. At this time, some inter cake capacitance and capacitance to ground decrease. On the spectrogram measured, some resonance peaks move towards the high frequency, the amplitude of the resonance peak in the low frequency band decreases, the peak in the middle frequency band rises slightly, and the high frequency band remains unchanged.
