Common parts of dry transformer short-circuit damage

Common parts of dry transformer short circuit damage:

1. The reason for the deformation of the corresponding part under the yoke is:

(1) The magnetic field generated by the short-circuit current is enclosed by the oil and oil tank wall or iron core. Because the magnetic resistance of the yoke is relatively small, it is mostly closed between the oil circuit and the yoke, and the magnetic field is relatively concentrated, and the electromagnetic force acting on the coil is relatively large.

(2) The gap between the inner winding sleeve is too large or the iron core is not tightly bound, so that the two sides of the iron core shrink and deform, resulting in the warping deformation of the iron yoke side winding;

(3) Structurally, the axial compression reliability of the magnetic yoke corresponding to the winding part is poor, and the wire cake of this part is often difficult to reach the preload, so the wire cake of this part is easy to deform.

2. The corresponding parts of the voltage regulator tap area and other windings are in this area for the following reasons:

(1) The ampere-turns imbalance, the magnetic leakage distribution imbalance, due to its amplitude generated by the additional leakage magnetic field in the coil produces additional axial external forces, the direction of these forces always increase the asymmetry of these forces. The axial external force is the same as the axial internal force generated by the normal amplitude magnetic leakage, which causes the wire cake to bend in the vertical direction and compress the diaphragm of the wire cake. In addition, some or all of these forces are transferred to the yoke in an attempt to move it away from the valve stem, and the wire cake deforms or flips into the middle of the winding;

(2) In order to achieve ampere-turns balance or the appropriate insulation distance within the tap interval, more gaskets are often added. The thicker the partition, the slower the force transfer, and the greater the impact on the winding coil;

(3) After the winding is set, the center reactance cannot be highly aligned, which further aggravates the ampere-turns imbalance;

(4) After running for a period of time, the natural shrinkage of the thick pad is very large, on the one hand, it aggravates the imbalance of ampere-turns, and at the same time, it also aggravates the beating when subjected to the short-circuit force;

(5) In the design, in order to achieve the balance of ampere-turns, the enamelled wire in the tap area chooses a narrower or smaller size, resulting in a reduction in short circuit resistance.

3, transposition part: the deformation of this part is often seen in the transposition of the transposition wire and the standard transposition of the single helix. The transposition of a transposition wire is steeper than that of an ordinary wire, so transposition with different turning radii will produce opposite tangential forces. This pair of equal and opposite tangential forces make the transposition diameter of the inner winding smaller and the direction deformed, while the transposition of the outer winding strives to have the same turning radius, so that the transposition is straight, the inner transposition is in the center, and the outer transposition is deformed. The position deforms outwards, the thicker the transposition line, the steeper the climb and the more serious the deformation. In addition, there is an axial short-circuit current component at the transposition, and the additional force generated will aggravate the deformation of the winding coil. The standard transposition of a single helix takes up a circle of space, resulting in an imbalance of ampere-turns in that part. At the same time, it has the characteristics of transposition deformation of the transposition wire, so the wire cake in this part is easier to be deformed.

4. The lead wire of the winding is often used in the winding of the inclined spiral structure. The winding of this structure, due to the imbalance of ampere-turns of the two helical openings, has a large axial force and axial current, so that the corner of the lead produces transverse. Distortion due to force. In addition, during the winding process of spiral winding, there are residual stresses that will make the winding attempt to return to its original state. Therefore, the winding of spiral structure is more prone to distortion under the impact of short circuit current.

5. Leads are commonly found between low-voltage leads. Low voltage leads due to low voltage, large current, phase of 120 degrees, so that the leads attract each other. If the lead is not properly secured, an interphase short circuit occurs.