Influence of transformer winding deformation on winding voltage distribution under lightning intrusion wave impact

Author： GOZ Electric Time：2024-09-27 09:34:05 Read：24

Lightning intrusion wave is one of the important reasons for the damage of substation equipment. The analysis of the overvoltage characteristics of power transformers under the action of intrusion wave has important engineering significance for ensuring the safe operation of transformers. Based on the electromagnetic transient program EMTP/ATP, this paper establishes an equivalent circuit model of lightning intrusion wave and transformer concentrated parameters, focusing on the analysis of the influence of axial deformation and radial deformation of windings on the maximum voltage distribution of windings. The results show that the axial (radial) deformation of the front section of the high-voltage winding will increase (reduce) the maximum voltage of the high-voltage winding on the deformation side and reduce (increase) the maximum voltage of the winding on the non-deformed side; the radial deformation of the medium-voltage winding will reduce the maximum voltage between the deformation position of the medium-voltage winding and the opposite position of the high-voltage winding.

Keywords: power transformer; winding deformation; lightning intrusion wave; maximum voltage distribution

As one of the most important and expensive equipment in the power system, the power transformer is prone to cause huge economic losses and industrial accidents once a failure occurs. In engineering practice, the abnormal operation of the arrester often causes the lightning intrusion wave to directly act on the transformer. Under the impact of the lightning wave, the complex electromagnetic oscillation process in the transformer winding and the static or electromagnetic induction process between the windings will cause overvoltage on the main insulation and longitudinal insulation of the winding, which is easy to cause damage to the winding insulation. In order to reduce such accidents, before the transformer is put into operation, the voltage distribution law of the transformer winding under the lightning impact is studied by simulation, and certain measures are taken at the weak insulation parts. It is an effective means to improve the transformer's impact resistance to timely improve and strengthen the insulation protection of the transformer. However, the transformer winding in operation under the action of lightning overvoltage usually does not immediately break down the insulation, but under the action of the axial force and radial force generated by lightning, it will cause mechanical permanent deformation such as distortion, tilt, collapse, bulge and displacement. In addition to lightning impact, this deformation may also be caused by defects in the design, manufacturing and use of process materials of the transformer, collisions during transportation and installation, or short-circuit current impact during operation. Operation experience shows that transformers with winding deformation still have certain functionality in a short period of time. If lightning overvoltage acts on transformers with winding deformation, the deformation will inevitably be further aggravated, accelerating the insulation breakdown process of the winding.

In recent years, domestic and foreign researchers have conducted a lot of research on transformer winding voltage distribution and winding deformation. Taking a 220kV transformer as an example, this paper establishes a transformer concentrated parameter equivalent circuit model based on the electromagnetic transient program EMTP/ATP. Taking the lightning intrusion wave under actual conditions as the power source, the influence of the axial deformation and radial deformation of the winding on the maximum voltage distribution of the winding is analyzed, and the law of the influence of factors such as the degree of winding deformation and deformation position on the maximum voltage distribution of the winding is summarized, providing a theoretical reference for the insulation design of transformer windings and the diagnosis and maintenance of winding deformation under lightning impulse.

Conclusion

Based on EMTP/ATP, this paper establishes a model combining the lightning intrusion wave power source with a 220 kV transformer concentrated parameter equivalent circuit, focusing on the analysis of the influence of the axial deformation and radial deformation of the winding on the maximum voltage distribution of the winding. The main conclusions are as follows.

(1) Compared with axial deformation, radial deformation of winding has a more obvious effect on the maximum voltage distribution of winding.

(2) The deformation of the front section of the high-voltage winding has the greatest impact on the maximum voltage distribution of the winding. Axial (radial) deformation will increase (decrease) the maximum voltage of the high-voltage winding on the deformed side and reduce (increase) the maximum voltage of the winding on the non-deformed side. The axial (radial) deformation of the high-voltage winding has almost no effect on the maximum voltage distribution of the medium-voltage winding.

(3) The axial deformation of the medium-voltage winding has little effect on the high-voltage (medium-voltage) winding. Radial deformation will reduce the maximum voltage of the medium-voltage winding at the position opposite to the high-voltage winding and increase the maximum voltage at other positions of the high-voltage winding.

Based on the above conclusions, this paper recommends that transformer production units focus on strengthening the radial insulation protection of high-voltage windings and improving the radial insulation strength of windings; it is recommended that operation and maintenance units conduct power outage inspections on operating transformers that have been struck by lightning. If the high-voltage (medium-voltage) winding of the transformer has radial deformation, in addition to paying attention to the deformation degree of the winding deformation part, it is also necessary to focus on checking the insulation structure of the non-deformed side (non-corresponding part) of the high-voltage winding.