Short circuit fault solution for power transformers

For the short-circuit phenomenon of the outlet of the power transformer, there are mainly the following possible reasons, and the solution is proposed in a targeted manner:

1. The line cake is bent up and down. This damage is caused by the fact that the wires between the two axial blocks are permanently deformed by the excessive bending moment under the action of the axial electromagnetic force, and the deformation between the two cakes is usually symmetrical.

2. The winding or wire cake collapses. This damage is caused by the fact that the wires are pressed or struck against each other under axial force, resulting in oblique deformation. If the wire is originally tilted slightly, the axial force causes the tilt to increase, and when it is severe, it collapses; the larger the aspect ratio of the wire, the more likely it is to collapse. In addition to the axial component, the end leakage magnetic field also has a radial component. The combined electromagnetic force generated by the leakage magnetic flux in the two directions causes the inner winding wire to invert and the outer winding to be turned outward.

3. The use of flexible wires is also one of the main reasons for the poor resistance of transformers to short circuits. Due to lack of understanding in the early days, or difficulties in winding equipment and technology, manufacturers are reluctant to use semi-rigid wires or design without such requirements. From the perspective of faulty transformers, they are all soft wires. This is very common when AC contactors are shared.

4. Winding winding is loose, improperly changed position or positional climbing, too thin, causing the electromagnetic line to hang. From the point of view of the accident damage, the deformation is often seen at the position of the change, especially the transposition of the transposed conductor.

5. The ordinary transposition wire is used, which has poor mechanical strength and is prone to deformation, stranding and copper exposure when subjected to short-circuit mechanical force. When the ordinary transposition wire is used, due to the large current, the transposition climbing steeply, the part will generate a large torque, and the wire cake at the two ends of the winding will also be generated due to the joint action of the axial direction and the axial leakage magnetic field. Larger torque, resulting in distortion. For example, the A-phase common winding of the Yanggao 500kV transformer has 71 transpositions. Due to the use of thicker ordinary transposition conductors, 66 of them have different degrees of deformation.

6. External short-circuit accidents are frequent. The accumulation effect of electric power after multiple short-circuit current surges causes the electromagnetic wire to soften or internal relative displacement, which eventually leads to insulation breakdown.

7. The radial electromagnetic force causes the diameter of the inner winding to become smaller. The bending is the result of permanent deformation of the wire bending moment between the two supports (internal stays). If the core is tied tight enough and the winding spokes are effectively supported, and the radial electric power is evenly distributed in the circumferential direction, the deformation is symmetrical, and the entire winding is a polygonal star. However, due to the deformation of the iron core, the support is not supported by the support, and the force along the circumference of the winding is not uniform. In fact, local instability often occurs to form a warp deformation.