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Power insulators

Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground.
 

Figure 1 - Overhead power line in Gloucestershire, England.

Figure 2 - Ceramic insulator used on electrified railways

Description

For power applications, the electrostatic analysis module of EMS can be used to analyze 3D models of electrode devices and power-line insulators (Figure 3).

The model of interest in this example is a power-line pole with a three-phase insulation scheme. The central-phase line (Figure 4) operates at a phase-to-ground voltage of 80kV rms (phase-to-phase voltage of 138.56 kVrms). The upper and lower lines operate at 40 kV rms. The field is calculated at the point of the AC waveforms, when the center phase voltage is at its peak. The model is composed of aluminum conductor lines and copper clamps (Figure 5). The clamps connect the conductors to the silicon rubber and fibre glass insulators, which in turn connect to the tower. The electrostatic module determines the electric field and the displacement field due to the aforementioned conditions.
 
These fields can be viewed in a full 3D plots and 2D plots showing the field at certain positions in the model. For instance, the electric field is obtained along a segment (Figure 6) that passes through the air as well as the silicon rubber insulator.

         

Figure 3 - Power line with Three-phase insulation scheme               Figure 4 - Close-up view of the middle-phase insulator


               

Figure 5-  Close-up view of the middle-phase insulator.                       Figure 6 - Section view of the middle-phase insulator
                                                                                                                                   with fibreglass  and silicon rubber components




Figure 7 - 3D Model of insulator

 

Study

The Electrostatic module of EMS is used to compute the Electric Field, the Displacement Field, the Potential and the Electrostatic Force density. Also, an important parameter is calculated by EMS, which is the Safety Factor. The parameter is used to identify the breakdown voltage of non-condutor materials.
Materials
In the Electrostatic analysis of EMS, the  required material property is the relative permittivity and the dielectric strength, shown in Table 1.

Results

 The folders contain the Electric Field E, the Electric Displacement D, the Potential distribution V, the Force Density F and the Safety Factor mentioned above. The results table contains the electrostatic energy and the total charge in the fixed voltage bodies. Furthermore, all of the results can be visualized in various formats such as fringe, vector, contour, section, line, and clipping plots. The results can easily be exported, and dissected.
After hiding all components except the fiber and the insulator,  the following Electric Field plot (Figure 8) is obtained:

Figure 8 - Electric Field in the insulator and the fiber (fringe plot)


Figure 9 - Evolution of the Electric Field between two points located at the extremity of the fiber




Figure 10 - Potential in the whole model




Figure 11 - Safety Factor

As shown in the figure (Figure 11) above, the maximum value is  0.378: so there is no breakdown voltage in our model.

Conclusion

To examine if there is a breakdown voltage, the Safety Factor folder in EMS Results is used. It gives the  value of the ratio between Electric Field and Dielectric Strength in a specific point. If the Safety Factor reaches 1,  then there is a risk of breakdown voltage in that point. The Electrostatic Module of EMS helps to avoid the breakdown voltage and the corona effect in such applications. 

References

[1] https://en.wikipedia.org/wiki/Insulator_(electricity)