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Common parts of transformer short-circuit damage

time:2020/11/22   source:华天电力  reading:234 time

Corresponding to the part under the iron yoke: The reasons for the deformation of this part are: (1) The magnetic field generated by the short-circuit current is closed by the oil and the tank wall or the iron core. Because the magnetic resistance of the iron yoke is relatively small, it mostly passes through the oil circuit and the iron. The yoke is closed, the magnetic field is relatively concentrated, and the electromagnetic force acting on the line cake is relatively large; (2) The gap between the inner winding set is too large or the iron core is not tightly bound, which causes the two sides of the iron core sheet to shrink and deform, resulting in warpage and deformation of the iron yoke side winding (3) In terms of structure, the axial compression of the yoke corresponding to the winding part is unreliable, and the wire cake at this part is often difficult to achieve the due pre-tightening force, so the wire cake at this part is easy to deform.


Voltage regulation tapping area and corresponding parts of other windings: This area is due to: (1) Unbalanced ampere-turns make the magnetic leakage distribution unbalanced, and the additional leakage magnetic field generated by its amplitude generates additional axial external forces in the coil. The direction always increases the asymmetry that produces these forces. The axial external force is the same as the axial internal force generated by the normal amplitude magnetic flux leakage, which causes the line cake to bend in the vertical direction and compresses the pad of the line cake. In addition, these forces are partially or completely transmitted to On the iron yoke, try to keep it away from the core column, and the wire cake is deformed or turned over to the middle of the winding. (2) The wire cake in this part is to strive for ampere-turn balance or the insulation distance of the tapping interval. It is often necessary to add more spacers. The thicker spacers cause the force transmission delay, so the impact of the wire cake is also Larger; (3) The central reactance height alignment cannot be ensured after the winding is set, causing the ampere-turns to further aggravate the imbalance; (4) After a period of operation, the thicker spacers naturally shrink larger, which on the one hand aggravates the ampere-turn imbalance Phenomenon, on the other hand, the jitter is aggravated when subjected to short-circuit force; (5) In the design time, in order to strive for ampere-turn balance, the magnet wire in the tapping area is selected with a narrower or smaller cross-section wire gauge, which has low short-term force resistance.


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Transposition position: The deformation of this position is common in the transposition of the transposition wire and the standard transposition of the single helix. The transposition of the transposed wire, because the climbing slope of the transposition is steeper than that of the ordinary wire, the opposite tangential force is generated at the transposition place with different turn radius, which is equal and opposite tangential force, As a result, the transposition diameter of the inner winding is reduced and the direction is deformed. The transposition of the outer winding strives to have the same turn radius, so that the transposition is straightened, the inner transposition is deformed toward the center, and the outer transposition is deformed outward, and the thickness of the transposed wire The thicker, the steeper the climb and the more serious the deformation. In addition, there is also an axial short-circuit current component at the transposition, and the additional force generated will increase the deformation of the wire cake. The standard transposition of the single helix takes up one turn in space, causing an unbalanced ampere-turn in this part. At the same time, it has the characteristics of transposition deformation of the transposed wire, so the wire cake in this part is more likely to deform.


Lead wire of the winding: common in the winding of the oblique spiral structure, the winding of this structure, due to the unbalanced ampere turns of the two spirals, the axial force is large, and there is axial current at the same time, so that the corner of the lead wire produces a transverse direction Distortion occurs due to force. In addition, during the winding process of the spiral winding, residual stress exists, which will make the winding strive to restore its original state. Therefore, the spiral structure winding is more likely to be deformed under the impact of short-circuit current.


Between leads: common between low-voltage leads. Due to low voltage, large current flows through the low-voltage leads, and the phase is 120 degrees, so that the leads attract each other. If the leads are improperly fixed, a short circuit will occur.

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