Analysis of Transformer Short Circuit Accidents

Transformer accidents occur frequently and have a growing trend. From the analysis of transformer accidents, insufficient short-circuit resistance has become the primary cause of power transformer accidents, causing great harm to the power grid and seriously affecting the safe operation of the power grid.

Transformers often experience the following accidents: multiple external short circuit impacts, gradually severe coil deformation, and ultimately insulation breakdown damage; External damage caused by frequent short circuit impacts in a short period of time; Damage caused by prolonged short circuit impact; One short circuit impact can cause damage. The main forms of transformer short-circuit damage are as follows:

1. Axial instability. This type of damage is mainly caused by the axial electromagnetic force generated by radial leakage, resulting in axial deformation of the transformer winding.

2. The wire cake is bent and deformed up and down. This type of damage is caused by the permanent deformation of the wire between two axial pads under the action of axial electromagnetic force due to excessive bending moment, and the deformation between the two pads is usually symmetrical.

3. Collapse of winding or wire cake. This type of damage is caused by the wires being squeezed or collided with each other under axial force, resulting in tilting deformation. If the wire is initially slightly inclined, the axial force promotes an increase in inclination, and in severe cases, it may collapse; The larger the aspect ratio of the wire, the more likely it is to cause collapse. In addition to the axial component, there is also a radial component in the end leakage magnetic field. The combined electromagnetic force generated by the leakage magnetic field in both directions causes the inner winding wire to flip inward and the outer winding to flip outward.

4. The winding rises to open the pressure plate. This type of damage is often due to excessive axial force or insufficient strength and stiffness of its end support components, or assembly defects.

5. Radial instability. This type of damage is mainly caused by the radial electromagnetic force generated by axial magnetic leakage, resulting in radial deformation of the transformer winding.

6. The elongation of the outer winding wire caused insulation damage. The radial electromagnetic force attempts to increase the diameter of the outer winding, and when the tensile stress on the wire is too high, it will cause permanent deformation. This kind of deformation is usually accompanied by insulation damage of the wire, causing inter turn short circuits. In severe cases, it can cause the coil to be embedded, disordered, collapsed, or even broken.

7. The end of the winding is flipped and deformed. In addition to the axial component, there is also a radial component in the end leakage magnetic field. The combined electromagnetic force generated by the leakage magnetic field in both directions causes the winding wires to flip inward and the outer winding to flip outward.

8. The inner winding wires are bent or warped. The radial electromagnetic force reduces the diameter of the inner winding, and bending is the result of permanent deformation caused by excessive bending moment of the wire between two supports (inner braces). If the iron core is tightly tied and the radial support bars of the winding are effectively supported, and the radial electric force is evenly distributed along the circumference, this deformation is symmetrical, and the entire winding is a polygonal star shape. However, due to the compression deformation of the iron core, the supporting conditions of the support bars are different, and the force along the circumference of the winding is uneven. In fact, local instability often occurs, resulting in warping deformation.

9. The fixing of the lead wire is unstable. This kind of damage is mainly caused by the electromagnetic force between the leads, which causes lead vibration and leads to short leads