By hvhipot 
Common parts of high-voltage test transformer short-circuit damage
Corresponds to the part under the iron yoke of the high-voltage test transformer. 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 is mostly closed between the oil circuit and the iron yoke. The magnetic field is relatively concentrated, and the electromagnetic force acting on the line cake is also relatively bigger;
(2) The inner winding set gap is too large or the iron core binding is not tight enough, which causes the two sides of the iron core sheet to shrink and deform, causing the winding on the iron yoke side to warp and deform;
(3) In terms of structure, the axial compression of the yoke corresponding to the winding part is the most unreliable. The wire cake in this part is often difficult to achieve the due pre-tightening force, so the wire cake in this part is most easily deformed.
Voltage regulation tapping area and corresponding parts of other windings. This area is due to:
(1) The ampere-turn imbalance makes the magnetic leakage distribution unbalanced, and the additional leakage magnetic field generated by its amplitude generates additional axial external forces in the coil, and the direction of these forces always increases the asymmetry of these forces. The axial external force is the same as the axial internal force generated by the normal amplitude flux leakage, which causes the line cake to bend in the vertical direction and compresses the cushion block 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 line 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. Larger
(3) After the winding is set, the center reactance height cannot be ensured, which causes the ampere-turn to further aggravate the imbalance;
(4) After running for a period of time, the thicker cushion blocks naturally shrink more, which aggravates the ampere-turn imbalance on the one hand, and on the other hand, the beating increases when subjected to short-circuit force;
(5) In the design time, in order to strive for ampere-turn balance, a narrower or smaller cross-section wire gauge is selected for the electromagnetic wire in the tapping area, and the short-term force resistance is low.
Transposition position of high voltage test transformer. The deformation of this part 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. This pair of tangential forces of equal magnitude and opposite direction, 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, resulting in 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 easier to deform.
Lead wire of high voltage test transformer winding. It is common in the winding of the oblique spiral structure. The winding of this structure has a large axial force due to the unbalanced ampere-turns of the two spirals. At the same time, there is an axial current, which causes a lateral force at the corner of the lead wire to be twisted and deformed. Phenomenon. In addition, in the winding process of the spiral winding, residual stress exists, which will make the winding strive to restore its original state. Therefore, the winding of the spiral structure is more likely to be twisted and deformed under the impact of the short-circuit current.
Between the leads of the high-voltage test transformer. It is common between low-voltage leads. The low-voltage leads have a large current flow due to the low voltage and the phase is 120 degrees, which makes the leads attract each other. If the leads are improperly fixed, a short circuit will occur between the phases.