The Material Properties and Insulation Design for 35kV Flexible and Torsion Resistant Cable

Flexible and torsion resistant cable is one of the key components in wind turbine. Such a cable system needs to withstand the AC electric field and heat dissipation. Therefore, it is of great importance to study the electrical and thermal properties and apply these parameters in cable design. In order to characterize the electric and thermal properties, we measured the breakdown strength, resistance, loss, relative dielectric constant and thermal conductivity of four types of EPR. The breakdown strength of the four specimen ranges from 37 kV/mm to 49 kV/mm, while the resistance distributes in $1.5 \times 10^{14} \Omega\cdot \mathrm{m}$ to $2.5 \times 10^{14}\Omega\cdot \mathrm{m}$. Meanwhile, the relative dielectric constant keeps between 2.5 and 3.5, and the variation of loss is less than 1% when the temperature is below 90 °C. The thermal conductivity is maintained at 0.4 W/(m·K) at 20 °C-120 °C. In the simulation results, under the full-load operating condition, the maximum conductor temperature is 43.8 °C, which is close to 45.3 °C under the numerical calculation of the thermal circuit model. The highest electric field in this case is 3.9 kV/mm. In the case of a transient short circuit, the cable conductor temperature is 50.5 °C, and under the action of operating overvoltage, the maximum electric field strength is 15.6 kV/mm. All of these cases are within the material tolerance range. The result shows that the design structure is suitable for the flexible and torsion resistant cable.