Analysis of the influence of lightning impulse on transformer overvoltage characteristics

Author： GOZ Electric Time：2024-09-21 09:35:14 Read：14

Transformers are the main power transmission and transformation equipment in the power supply system. When they are impacted by lightning, the overvoltage changes are an important cause of transformer damage. The EMTP (electromagnetic transient program) simulation method is used to establish the concentrated parameter equivalent circuit model of the transformer, and the changes in the overvoltage characteristics when the transformer winding is deformed due to lightning impulse are analyzed, so as to provide a reference for the safe and stable use of the transformer and improve the stability of the power supply system.

Keywords: transformer; winding; lightning impulse voltage generator; overvoltage; simulation analysis;

Transformers are important power transmission and transformation equipment in the power supply system, which has an important impact on the stability of the power supply system. The production cost of transformers is high, and they have high economic and use value. During the use of transformers, the impact of lightning on transformers caused by the failure or failure of lightning arresters will cause electromagnetic oscillation inside the transformer, which will cause transformer overvoltage and even damage the transformer insulation system. During use, the protection of the transformer insulation system should be strengthened. At the same time, the impact of lightning will also cause the deformation of the transformer windings, resulting in distortion, collapse and other defects, affecting the normal use of the transformer. In view of the change of overvoltage characteristics caused by transformer winding deformation caused by lightning impulse, the deformation and voltage change of the transformer are analyzed in the form of electromagnetic transient program simulation analysis, so as to provide reference for the use and maintenance of the transformer and reduce the damage of the transformer.

Establishment of transformer overvoltage characteristic simulation analysis model

The performance of the high-voltage side of the 220kV transformer under the action of lightning impulse is analyzed, and a model file is established in the electromagnetic transient program to simulate the waveform of lightning for impact. The intrusion waveform of lightning is shown in Figure 1. As can be seen from Figure 1, the peak voltage value is 9470kV, the wave head time is 3.4μs, and the lightning waveform is in the form of oscillation attenuation distribution. A 220kV three-winding transformer is used for analysis. The high-voltage winding of the transformer adopts the connection form of middle outlet, the medium-voltage winding adopts the form of end outlet, and the transformer is a continuous distribution structure.

Figure 1

For the analyzed transformer, the concentrated parameters of the multi-winding transformer with single-panel distribution are established based on the trapezoidal circuit. During the analysis process, only the voltage distribution of the high and medium voltage windings of the transformer is analyzed, and the influence of other voltage changes is ignored. A 110kV cable is inserted at the end of the medium voltage winding as a load, and the grounding capacitance value of the cable is 0.5μF, thereby completing the loading setting of the system. When the transformer is subjected to lightning impulse, the deformation of the winding mainly occurs in the axial and radial directions. Due to the deformation of the winding structure, the internal capacitance, inductance and other parameters change, causing the expansion or distortion of the winding, which changes the overvoltage characteristics of the transformer. Since the high-voltage winding of the analyzed model adopts the middle part, the deformation distribution of the transformer winding is shown in Figure 2. With 52 pancakes as the axis, the lower part of the winding is used as the deformation side, and the symmetrical upper half is the non-deformation side. The front, middle and rear sections of the winding are distributed as shown in Figure 2, and the overvoltage characteristics of the transformer are analyzed.

Figure 2

In the analysis of transformer windings, EMTP is used to build a transformer model under lightning impulse, and the concentrated parameters of the windings are changed to simulate the deformation of the windings under lightning impulses. The concentrated distribution parameters of the windings are selected as 15%, 55%, 95% and 100%, respectively, representing different degrees of deformation of the windings 9. The overvoltage characteristic waveforms on each winding are collected, and the maximum voltage value on the winding coil is analyzed by MATLAB. The distribution curve of the winding voltage is drawn to obtain the overvoltage characteristics of the transformer.