What are the reasons for the short circuit of the power transformer? Follow Anhui Dali Xiaobian to find out. dry-type transformer

Reasons for short circuit of power transformer:

1. At this stage, in the process of the calculation program, a rationalized entity model is created based on the uniform distribution of the leakage electromagnetic field, the same diameter of the turns, and the force at the same position. In fact, the leakage electromagnetic field of the transformer is not evenly distributed. A part of the iron yoke is relatively concentrated, and the special cables in this area are also subjected to great mechanical and equipment forces; the transposed conductor will change the direction of force transmission at the transposition location, resulting in torque; because of the elasticity of the protective layer pad Due to the mold factor, the radial protective layer pads are not equidistantly distributed, which will cause the alternating force caused by the alternating leakage magnetic field to resonate. The direct cause of the deformation of the line pie in the matching position. dry-type transformer

2. Use general transposition wires, which have weak impact toughness, and are prone to deformation, scattered strands, and exposed copper when bearing the force of short-circuit mechanical equipment. When using a general transposed wire, due to the large current and the steep uphill transposition, this position will cause a large torque. In addition, the wire cake at the second web end of the winding, because of the mutual effect of the amplitude and radial leakage electromagnetic fields, will also Causes a large torque, resulting in distorted deformation. For example, the A-phase common winding of Yanggao 500kV transformer currently has 71 transpositions. Because of the selection of thicker general transposition wires, there are 66 transpositions with different levels of deformation. In addition, the main transformer of Wujing No. 11 is all due to the use of general transposed conductors, and the two-terminal wire cakes of the high-voltage winding at the position of the iron core yoke have different rotating and exposed lines.

3. The damage of temperature to the flexural strength and compressive strength of special cables is not considered in the calculation of short-circuit resistance. The anti-short-circuit capability of the scheme designed according to the normal temperature state cannot reflect the specific operating conditions. Generally, the whole process of reclosing is carried out during the operation of the transformer. Therefore, if the short-circuit point cannot be subsided for a while, it will be in a very short time (0.8s). Then bear the secondary short-circuit impact, but because of the impact of the primary short-circuit current, the winding temperature is greatly increased.

4. The winding is loosely wound, the transposition is negligent, and it is too weak, causing the special cable to hang in the air. From the point of view of the damaged part of the accident, the deformation is more common in the transposition, especially in the transposition of the transposed wire.

5. The selection of flexible conductors is one of the key reasons for the poor short-circuit resistance of the transformer. Because of lack of understanding in the initial stage, or the difficulty in winding equipment and processing technology, the manufacturers are unwilling to use semi-rigid conductors or the design scheme does not have these regulations in nature. From the perspective of common faults, the transformers are all flexible conductors.

6. The gap of the suit is too large, resulting in insufficient support points on the special cable, which increases the hidden danger of the transformer's short-circuit resistance.

7. The effect is uneven in the torque force of each winding or each gear, and the short-circuit impact causes the wire cake to vibrate, resulting in excessive bending stress on the special cable and deformation.

8. The winding turns or the middle of the wires are not dry and solid, and the short-circuit resistance is poor. None of the windings that were initially treated with dipping paint were damaged.

9. The poor control of the torque force of the winding leads to the mutual displacement of the wires of the general transposed wires.

10. External short-circuit accidents often occur, and the cumulative effect of the electric driving force after several short-circuit current impacts will cause the special cable to soften or internal relative displacement, resulting in thermal breakdown of the insulating layer.