Size control method for non-uniform electrical field distribution of an insulator string for power transmission lines

As a result of rising consumer demand, transmission lines voltages have increased from 154 kV to 765 kV. For 154 kV, 345 kV, and 765 kV transmission lines, 9-10, 19-23, and 30-40 insulators are employed, respectively. When multiple insulators are stringed, the divided voltage safety issue becomes critical. The first insulator is typically subjected to a voltage that is 20% higher. The high-voltage division applied to the insulator in the first stage is likely to result in arc generation. The dielectric breakdown voltages of insulator used in power transmission lines range from 12.8 to 16.8 kV/mm, and the dielectric constant varies slightly depending on the frequency. Herein, for the alumina insulator, the 4.94 cristobalite insulator value was 4.48, and the tan delta value was in the range 0.003-0.006. Based on actual measurements, the finite-element method was applied to analyze the field distribution. The size of the insulator was changed to lower the voltage burden applied to the first insulator string. The sizes used were 185, 250, 375, and 500 mm. By changing the size of the insulator, the voltage applied to the first stage decreased from 27.44% to 6.07%.