Main manifestations of short circuit in high voltage test transformer
Transformer accidents have occurred and there is a growing trend. From the analysis of transformer accident situation, the lack of 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 have the following accidents: external multiple short-circuit impact, coil deformation is gradually serious, zui final insulation breakdown damage; external short-term frequent short-circuit impact damage; long-term short-circuit impact damage; a short-circuit impact damage. The main forms of transformer short-circuit damage are as follows:
1. Axial instability. This damage is mainly caused by the axial electromagnetic force generated by the radial leakage and causes the axial deformation of the transformer winding.
2. The line cake is bent and deformed up and down. This damage is caused by the fact that the wires between the two axial blocks are under the action of the axial electromagnetic force, and the bending moment is too large to cause a * deformation, and the deformation between the two cakes is usually symmetrical.
3. 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, and 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.
4. The winding rises to open the pressure plate. This damage is often due to excessive axial forces or the presence of strength, stiffness or assembly defects in the end supports.
5. Radiation instability. This damage is mainly caused by the radial electromagnetic force generated by the axial leakage, which causes the radial deformation of the transformer winding.
6. The outer winding wire is elongated to cause insulation damage. The radial electromagnetic force attempts to increase the diameter of the outer winding, and when the tensile stress acting on the wire is excessive, the deformation is caused. This deformation is usually accompanied by damage to the insulation of the wire, causing a short circuit between the turns. In severe cases, the coil may be embedded, entangled, collapsed, or even broken.
7. The end of the winding is reversed and deformed. In addition to the axial component, the end leakage magnetic field also has a radial component, and the combined electromagnetic force generated by the leakage magnetic flux in the two directions causes the winding wire to invert inward, and the outer winding is turned outward.
8. The inner winding wire is bent or curved. The radial electromagnetic force causes the diameter of the inner winding to become small, and the bending is a result of the *-shaped deformation caused by the excessive bending moment of the wires 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 core, the support is not supported, and the force along the circumference of the winding is not uniform. In fact, local instability often occurs to form a warp deformation.
9, the lead is fixed and unstable. This damage is mainly caused by the electromagnetic force between the leads, causing the leads to vibrate, resulting in a short between the leads.
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