Local deformation means that the total height of the coil has not changed, or the equivalent diameter and thickness of the coil have not changed in a large area; only the size distribution uniformity of some coils has changed, or the equivalent diameter of some coil cakes has changed to a small extent. The total inductance is basically unchanged, so the spectrum curves of the faulty phase and the normal phase will overlap at each resonance peak point in the low frequency band. With the size of the partial deformation area, the corresponding subsequent resonance peaks will be displaced.

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Local compression and pull-out deformation: This kind of deformation is generally considered to be caused by electromagnetic force. Due to the repulsion force generated by the current in the same direction, when the two ends of the coil are compressed, this repulsion force will squeeze out individual pads, causing Parts are squeezed and parts are pulled apart. This kind of deformation generally does not affect the lead wire under the condition that the pressure nails at both ends are not moved: this kind of deformation generally only changes the distance (axial) between the cakes, and the capacitance (between the cakes) reflected in the parallel inductance in the equivalent circuit capacitance) changes. With the leads not being pulled, the high frequency portion of the spectrum will change very little. The whole coil is not compressed, only part of the distance between the cakes is pulled apart, and some of the distances between the cakes are compressed. It can be seen from the spectrogram that some of the resonant peaks move to the high frequency direction with a decrease in the peak value; while some resonant peaks move to the low frequency direction and are accompanied by an increase in the peak value. The deformation area and the degree of deformation can be estimated and analyzed by comparing the position where the resonance peak is obviously shifted, (the number of peaks) and the shift amount of the resonance peak. The high-frequency portion of the spectrogram will change when local compression and pull-out deformations affect the leads. When the degree of local compression and pull-out deformation is large, some resonance peaks in the low frequency and middle frequency bands overlap, individual peaks disappear, and the amplitude of some resonance peaks increases.
Turn-to-turn short circuit: If a metallic inter-turn short circuit occurs in the coil, the overall inductance of the coil will be significantly reduced, and the coil’s obstruction to the signal will be greatly reduced. Corresponding to the spectrogram, the resonant peak of the low frequency band will obviously move to the high frequency direction, and at the same time, due to the decrease of the obstacle, the frequency response curve will move to the direction of decreasing attenuation in the low frequency band, that is, the curve will move upward by more than 2ddB; In addition, the difference between the resonance peaks and valleys on the spectrum curve will be reduced due to the decrease of the Q value. The spectral curves of the mid and high frequency bands coincide with those of the normal coil.
Broken coil strands: When the coil strands are broken, the overall inductance of the coil will increase slightly. Corresponding to the spectrogram, the resonant peak of the low-frequency band will move slightly to the low-frequency direction, and the attenuation in the amplitude will remain basically unchanged; the spectral curves of the mid-frequency and high-frequency bands coincide with the spectrogram of the normal coil.
Metal foreign body: In a normal coil, if there is a metal foreign body between the cakes, although it has little effect on the low frequency total inductance, the capacitance between the cakes will increase. The resonance peak of the low frequency part of the spectrum curve will move to the low frequency direction, and the amplitude of the middle and high frequency part of the curve will increase.
Lead displacement: When the lead is displaced, it does not affect the inductance, so the low frequency band of the spectrum curve should be completely overlapped, and only the curve in the 2ookHz~5ookHz part changes, mainly in terms of attenuation amplitude. When the lead wire moves toward the shell, the high frequency part of the spectrum curve moves in the direction of increasing attenuation, and the curve moves downward; when the lead wire moves closer to the coil, the high frequency part of the spectrum curve moves in the direction of decreasing attenuation, and the curve moves upward.
Axial buckle: Axial twist is that under the action of electric power, the coil is pushed out to both ends. When it is pressed by both ends, it is forced to deform from the middle. If the assembly gap of the original transformer is large or the braces are forced to shift , the coil is twisted into an S shape in the axial direction; this deformation only changes part of the capacitance between the cakes and part of the capacitance to ground because the two ends do not change. The inter-screen capacitance and the capacitance to ground will decrease, so the resonant peak will move to the high frequency on the spectrum curve, the resonant peak near the low frequency will drop slightly, and the resonant peak frequency near the intermediate frequency will rise slightly, and the frequency of 3ookHz~5ookHz will be slightly increased. The spectral lines basically keep the original trend.
Amplitude (diameter) deformation of the coil: Under the action of electrodynamic force, the inner coil is generally contracted inward. Due to the limitation of the inner stay, the coil may be deformed in the amplitude direction, and its edge will be zigzag. This deformation will make the inductance slightly Reduce, the capacitance to ground also changes slightly, so the resonance peak in the whole frequency range moves slightly to the high frequency direction. The amplitude deformation of the outer coil is mainly outward expansion, and the total inductance of the deformation coil will increase, but the distance between the inner and outer coils will increase, and the capacitance of the wire cake to ground will decrease. Therefore, the first resonance peak and valley on the spectrum curve will move to the low frequency direction, and the following peaks and valleys will move slightly to the high frequency direction.