In recent years, more than 50% of the cities in the inland area of our country have suffered from moderate pollution. It can affect the distribution of electric field along the surface of insulator and the pollution characteristics of its surface area, even endanger the safe operation of transmission lines. This paper takes the XSP-160 porcelain three umbrella insulator under the action of 0–±30 kV DC voltage as the research object, and establishes the physical model of the insulator; uses COMSOL software to simulate the electric field of the insulator. The comparison with the results of the wind tunnel test of North China Electric Power University verifies the rationality of the simulation method. In view of the medium pollution environment which often occurs in the inland area, the force of the polluted particles deposited on the insulator under 110 kV DC voltage was analyzed. The distribution characteristics of the electric field along the surface in the clean and three kinds of pollution environment (light, medium and heavy) were simulated and compared. The results showed that: 1) In the moderate pollution environment, the influence of fluid drag force on the movement of polluted particles is greater at the initial stage (0.28–0.33 s); at the late stage (after 0.33 s), the influence of the electric field force begins to increase, and gradually plays a major role in the process of fouling. 2) In the three different polluted environments, the potential along the surface of each umbrella skirt of the insulator increases non-linearly with the increasing of the pollution concentration, and there are apparent potential inflection points near b and l. 3) The pollution particle concentration has the most obvious influence on the electric field along the low-voltage umbrella skirt, whose potential distortion rate can be up to 220 times in the heavy polluted environment.
In recent years, more than 50% of the cities in the inland area have suffered from moderate pollution [
For a long time, scholars have explored the distribution characteristics of the electric field along the insulator surface. In 2014, Zhao [
Bouhaouche et al. [
Although our research predecessors conducted many studies on the distribution characteristics of the electric field along the insulator, and made some important findings, there are a few reports on the distribution characteristics of the electric field along the insulator under different degrees of pollution. Therefore, this study aimed to analyze the stress behavior of dirty particles near the XSP-160 porcelain three umbrella insulator under 110 kV DC voltage by using COMSOL for the light, medium and severely polluted environments that often occur in inland areas. Simulation and comparative analysis of the electric fields along the insulator surface, in three polluted environments, were conducted to study the degree of electric field distortion.
In order to realistically simulate the distribution of the electric field along the surface of the insulator, a layer of virtual “infinite element domain” [
In this model, the steady-state analysis was adopted in the DC electric field. The governing equation [
where
The frequency domain analysis was adopted in the AC electric field. The governing equation [
where
Corresponding to the wind tunnel test [
The 3D physical model was imported into COMSOL software for simulation. The physical model and skirt numbers of the insulator are shown in
Representing the actual situation, the fluid in the physics field of the software was set to air, the steel feet and iron cap of the porcelain three umbrella insulator were set to cast iron, and the umbrella group was set to silicone rubber. According to the air pollution conditions in the natural environment of inland areas [
The distribution characteristics of the electric field along the insulator are influenced by the coupling of three factors in the software: Flow field, electric field and particle field. The boundary conditions of the flow field were set as follows: The front side was a velocity inlet, the rear side was a voltage outlet, and the remaining four sides were set as wall surfaces. The electric field boundary conditions were set as follows: No. 1 umbrella skirt was grounded, No. 3 umbrella skirt was connected to the high-voltage end, and the “infinite element domain” was the electrical insulation boundary. The particle field boundary conditions were set as follows: Particles were released at the entrance, and other boundary condition settings at the entrance and exit were the same as in the flow field.
It can be seen from
NSDD is defined as the mass of polluted particles deposited on unit surface area of insulator. The calculation formula is:
where
The environment with no dirty particles around the insulator is defined as a clean environment, while the environment with dirty particles is defined as a polluted environment. According to the air quality, the pollution concentrations can be set to 0.15, 0.26, and 0.45 mg/m3 for light, medium, and heavy polluted environments, respectively. Selecting the XSP-160 porcelain three umbrella insulator under 110 kV DC voltage as the research object, the stress situation and the distribution characteristics of the electric field along the surface of the insulator in each polluted environment were explored.
According to the relationship between the voltage level and the number of insulators [
The distribution of the electric field along the surface of the insulator was studied with the creepage distance. The creepage distance and characteristic inflection point number of the porcelain three umbrella insulator model are shown in
The electrostatic field module was selected in the clean environment. In the polluted environment, the electrostatic field module and the charged particle tracking module were selected for two-way coupling, with the wind speed of 3 m/s, particle size of 30 µm, density of 2200 kg/m3, and a charge mass ratio of +1.58 × 10-4 C/kg [
The study of the stress of the polluted particles around the insulator provides the basis for the analysis of the distribution characteristics of the electric field along the surface of the insulator, and lays the foundation for the study of its fouling characteristics. Consider the moderately polluted environment as an example. The right-hand rectangular coordinate system was established, the Z-direction was the direction of incoming flow, and the Y-direction was the direction of the insulator suspension, and opposite to the direction of gravity in the system.
The track of the contaminated particles movement is mainly affected by the electric field force, gravity and fluid drag force [
In the X-direction, there is little difference between the fluid drag force and the electric field force. In the Y-direction, the gravity and the electric field force are approximately the same, and the fluid drag force changes greatly with time. In the early stage (0.28–0.33 s), the force condition on the polluted particles is as follows: Fluid drag force > gravity > electric field force. But in the late stage (after 0.33 s), the electric field force plays an important role on the polluted particles. In this late stage the force condition on the polluted particles is as follows: Electric field force > gravity > fluid drag force. In the Z-direction, the force condition on the polluted particles is as follows: Electric field force > fluid drag force.
When the component forces in the three directions are combined into one, the resultant force of the polluted particles is as follows: Electric field force > fluid drag force > gravity.
In conclusion, in the early stage (0.28–0.33 s), the influence of the fluid drag is greater; in the late stage (after 0.33 s), the influence of the electric field force begins to increase, and gradually plays a major role in the process of fouling. It is necessary to study further the distribution characteristics of the electric field along the surface of the insulator because of the distortion of the electric field along the surface caused by the charged particles.
Based on the electrical surface potential as the evaluation standard, the distribution of the electric field along the surface of each umbrella skirt in clean and polluted environment is shown in
Comparing
Voltage ratio (%) | No. 1 | No. 2 | No. 3 | No. 4 | No. 5 | No. 6 | No. 7 |
---|---|---|---|---|---|---|---|
Clean environment | 17.10 | 11.45 | 9.20 | 8.95 | 10.56 | 14.97 | 27.77 |
Environment pollution | 126.74 | 7.67 | 1.78 | 0.67 | 1.44 | 5.78 | 141.87 |
Rate of change (%) | 641.17 | 33.01 | 80.65 | 92.51 | 86.36 | 61.39 | 410.88 |
Comparing electrical potentials in three different polluted environments, it can be found that the electrical potentials of the umbrella skirts of the insulator increase non-linearly with the increase of the pollution concentration, and there are obvious potential inflection points near
where
As shown in
The influence of fluid drag force on the movement of polluted particles is greater at the initial stage (0.28–0.33 s); at the late stage (after 0.33 s), the influence of the electric field force begins to increase, and gradually plays a major role in the process of fouling.
In the polluted environment, the electrical potential of each umbrella skirt is higher than that of the clean environment, and the electric field distortion is serious. The greater the pollution concentration is, the more apparent the potential distortion of the skirts Nos. 3 and 4 will be.
In the three different polluted environments, the potential along the surface of each umbrella skirt of the insulator increases non-linearly with the increasing of the pollution concentration, and there are apparent potential inflection points near
The pollution particle concentration has the most obvious influence on the electric field along the low-voltage umbrella skirt, whose potential distortion rate can be up to 220 times in the heavy polluted environment.