Causes of transformer short-circuit fault

2022-10-18 17:28:39

71次

There are many and complicated reasons for transformer internal problems and incidents caused by transformer outlet short circuit. It is related to structural planning, raw material quality, process level, operating conditions and other factors, but the selection of electromagnetic wire is the key. According to the analysis of the transformer in recent years, there are several reasons related to the electromagnetic wire.

1. The electromagnetic line selected based on the static theoretical planning of the transformer is quite different from the stress acting on the electromagnetic line during practical operation.

2. At present, the calculation programs of various manufacturers are based on the idealized models such as the uniform distribution of the magnetic leakage field, the same wire turn diameter, and the equal phase force. In fact, the magnetic leakage field of the transformer is not evenly distributed, and it is relatively concentrated in the iron yoke part, and the electromagnetic wires in this area are also subject to large mechanical forces; The transposed conductor will change the direction of force transmission due to climbing at the transposed position, resulting in torque; Because of the factor of the elastic modulus of the cushion block, the axial cushion block is not distributed at an equal distance, which will make the alternating force generated by the alternating magnetic leakage field resonate in a delayed manner. This is also the fundamental reason why the wire cake at the yoke of the iron core, the transposition position, and the corresponding position with the voltage regulating tapping is deformed.

3. The influence of temperature on the bending and tensile strength of the electromagnetic wire is not considered in the calculation of short-circuit resistance. According to the test results, the temperature of the electromagnetic wire is subject to the limit? 0.2 has a great influence. With the temperature increase of the electromagnetic wire, its bending strength, tensile strength and elongation decrease. The bending tensile strength at 250 ℃ decreases by more than 10% and the elongation decreases by more than 40% compared with 50 ℃. However, the average winding temperature of practical transformer can reach 105 ℃ and the hottest point temperature can reach 118 ℃ under additional load Generally, the transformer operates in a reclosing process, so if the short circuit point cannot disappear for a while, it will be subject to the second short circuit impact in a very short time (0.8s). However, because the temperature of the winding increases sharply after the first short circuit current impact, according to the rules of GBI094, the maximum allowable temperature is 250 ℃. At this time, the short-circuit resistance of the winding can have been greatly reduced, which is why most short circuit incidents occur after the transformer reclosing.

4. The general transposed conductor is selected, which has poor mechanical strength, and is prone to deformation, loose strands, and copper exposure when receiving short circuit mechanical force. When selecting a general transposed conductor, because of the large current and steep transposition climb, this part will produce a large torque. At the same time, the wire cake at the two ends of the winding will also produce a large torque due to the combined effect of amplitude and axial magnetic leakage field, resulting in distortion and deformation. For example, the A-phase common winding of Yanggao 500kV transformer has a total of 71 transpositions, because a thicker general transposition conductor is selected, 66 of which have varying degrees of deformation. For other Wujing No. 11 main transformer, the common transposed conductor is selected, and the two end wire cakes of the high-voltage winding at the yoke of the core have different overturning and exposed wires.

5. The selection of flexible conductor is also one of the main reasons for the transformer's poor ability to resist short circuit. Because of the lack of knowledge about this in the early stage, or the difficulties in winding equipment and technology, the manufacturer refused to use semi hard wires or there was no requirement for this in the planning. From the point of view of the defective transformers, they were all soft wires.

6. The winding is loosely wound, and the transposition or correction climbing position is not properly handled, which is too thin, resulting in electromagnetic wire explosion. Seen from the damage direction of the incident, most of the deformation occurs at the transposition point, especially the transposition point of the transposed conductor.

7. If the winding turns or wires are not solidified, the short circuit resistance is poor. There is no damage to the windings treated with dipping paint in the early stage.

8. Improper control of the pre tightening force of the winding results in mutual dislocation of the conductors of the general transposed conductor.

9. The gap between sets is too large, which leads to insufficient support on the electromagnetic wire, which increases the hidden danger of the transformer's ability to resist short circuit.

10. The pre tightening force acting on each winding or gear is uneven, which forms the jumping of wire cake during short circuit impact, resulting in excessive bending stress acting on the electromagnetic wire and deformation.

11. External short circuit incidents are frequent. The accumulation effect of electrodynamic force after repeated short circuit current shocks causes electromagnetic wire softening or internal relative displacement, which eventually leads to insulation breakdown.

HENGFENGSHUAI ELECTRIC, is an electrical enterprise with transmission and distribution industry as its main business, integrating product research and development, manufacturing and trade. Designated suppliers for the world's top 500 enterprises .Its main products include power transformers, medium and low voltage switchgear, distribution panel ,circuit breakers, transmission tower ,Cable and other power distribution equipment .The group has five department: Transformer department, Panel department, power transmission tower department, cable department and electrical engineering department. HENGFENGSHUAI ELECTRIC, has been working hard to provide the best transmission, distribution solutions for users all over the world.【WhatsApp：+86158 5325 2696（Jack） +86158 5326 5269（Alisa）hfs@hengfengshuai.com https://www.hengfengshuai.com 】

label:transformer， power transformers

Website of this article:https://www.hengfengshuai.com/xyzx/251.html

上一篇：What should be paid attention to when using transformers?

下一篇：Reasons for High Oil Level of Special Transformer