I. Fault analysis of transformers in power systems

Transformer is a device that uses the principle of electromagnetic induction to change current. In the power system, the use of transformer is very extensive. It has been proved by experiments and investigations that the fault caused by short circuit of transformer has seriously affected the safety and stability of power transmission. Therefore, in order to reduce the failure probability of the power system, it is necessary to focus on the short-circuit capability of the transformer. The following is a detailed analysis of the causes of short-circuit accidents in transformers:

(1) Defects in transformer structure design

Due to the defects in the structural design of the transformer, the short-circuit resistance is weakly determined to a large extent. At present, China's transformers, manufacturers use static theory to calculate the mechanical force of the transformer. From the static theory, it can be known that the copper wire transformer only needs to calculate the wire stress less than 1600kg/cm2, but in the actual use process, the internal dynamics of the transformer is a complex and complex. In the process of change, the commonly used theoretical values do not directly reflect the actual operating conditions of the transformer, so it is difficult to meet the demand for short-circuit resistance. From the analysis of the more common transformer models, low-loss transformers are still the mainstream products. But how to achieve low loss of transformers, manufacturers have not formed a consensus. In addition, in the low-voltage lead design of the large-capacity transformer, if the lead fulcrum is insufficiently considered, the low-voltage lead forms a cantilever beam. At this time, if the impact of the short-circuit current is encountered, the phase-to-phase short-circuit fault will be caused.

(2) Material quality is not relevant

The insulation quality of the transformer and the mechanical strength of the laminated wood board do not meet the standard requirements, which may also cause frequent short-circuit faults. In order to minimize the loss of winding eddy current, the difficulty of processing and the cost of production and operation, some transformer manufacturers often use thinner wires or ordinary cheap transposition wires in the design process instead of mechanical properties. Semi-rigid wires, these common cheap materials can help companies reduce production and operation costs, but limited by the performance of the material itself, can not meet the short-circuit resistance of the transformer windings. In addition, due to the current uneven level of domestic manufacturers, there is a big gap between the production process and some foreign advanced technologies, so that the density of the insulation board is not enough, and the natural shrinkage phenomenon is also likely to cause transformer short-circuit failure.

(3) There are serious problems in the structure

A serious problem in the structure of the transformer can also cause a short-circuit fault. Since the transformer is transported, hoisted and disassembled from the factory to the start of use, it is inevitably subject to some impact. At this time, if the internal structure of the transformer is not strong, structural problems such as winding displacement and insulation damage may occur due to the impact, which will bury a huge safety hazard for future operation.

(4) Problems with transformers operating in 220kv environment

For 220kv large-capacity transformers, the connection condition of the inner ring is also an important determinant of the occurrence of short-circuit faults. Although the tapping of the inner ring belt can provide a lot of convenience for the operation of the large-capacity transformer, if the tap design is not reasonable enough, the local electric field of the tapped lead wire is disordered, causing partial discharge of the transformer.

(5) Problems in process and equipment

If the manufacturing process and equipment of the transformer cannot effectively ensure that the coil is tightly wound, compacted, and tightened, it will also cause a decrease in the short-circuit resistance and cause a malfunction. Moreover, the insulating block of the transformer is not sealed or the processing work is not in place, and it is possible that the electric power generated in the event of a short circuit causes the wire to be damaged by insulation and is broken down.

When the coil of the transformer is wound, the tension of the wire is not enough or limited by the process and equipment. When the coil is loosely wound, the suspension will be formed, which reduces the short-circuit resistance of the transformer. The binding at the outlet of the coil is not tight enough. It is also easy to cause a short circuit fault of the transformer. If the gap of the wound coil is too large, the inner support of the coil is insufficient to cause the winding coil to deform or collapse, which brings a huge safety hazard to the operation and use in the future. In addition, the clamping force of the transformer core is not enough. After the core is stacked, there is no effective measurement and proper adjustment of the pressure, and the core is not tightly clamped. The displacement is easy to occur during transportation collision, resulting in uneven internal force of the transformer. Serious consequences.

Second, ways to improve the short-circuit resistance of transformers

Due to the important role of transformers in power systems, it is necessary to conduct an in-depth study of their quality and performance. This paper explores the common causes of transformer short-circuit faults, and puts forward some targeted technical methods to improve the short-circuit resistance of transformers. The following specific analysis is carried out:

(1) Calculation of mechanical force and product structure design of improved transformer

The physical structure of the transformer determines its performance. Therefore, it is necessary to optimize and improve the calculation of the mechanical force of the transformer and the design of the product structure, so that the mechanical force distribution of the internal wire is more in line with the actual requirements, and the short-circuit resistance is improved. In the structural design of the transformer, the impact sensing force of the winding structure inside the transformer can be measured by the pressure sensing corrector installed between the pressure plate and the clamp member, thereby providing a reliable guarantee for the structural design of the transformer.

(2) Short circuit test of transformer

By short-circuiting the transformer and analyzing the relevant data parameters, it lays a solid foundation for improving the product structure of the transformer and improving the short-circuit resistance. It is worth noting in this process that the short-circuit test is not only to ensure the manufacturer's products are qualified, but more importantly, to apply safe and reliable technology to the actual production, to avoid some manufacturers only to test and reinforce the transformer. There is no technical promotion in actual production.

In short, with the continuous advancement of science and technology, the continuous improvement of the quality of power system operation and the large-scale operation of ultra-high voltage power transmission and transformation mode, the transformer's short-circuit resistance and the huge loss caused by short-circuit have become transformer manufacturers and operators. An important issue facing the unit and urgently needed to be solved. In order to effectively improve the short-circuit resistance of power system transformers, in addition to the manufacturer's comprehensive improvement in mechanical force calculation and product structure design, it should also pay attention to the quality hazards in process operation, which need to cause transformer manufacturers and operation. The unit is highly valued, which can fully improve the safety and stability of the operation of the power system.

In summary, with the in-depth development of the power grid, it is necessary to improve the short-circuit resistance of the transformer in the power system in order to develop. By improving the short-circuit resistance of the transformer in the power system, it can not only effectively improve the safety of the operation of the mine network, but also shorten the time required to handle the fault, minimize the loss, and also prevent the accident from happening to ensure the safety of the power system. Stable operation.