A calculation of transient overvoltage for rationalization of insulation design of 22 kV cable system

This paper presents a new approach for a reduction of test voltage for power distribution equipment of 22 kV cable system. EMTP calculations are used in this examination for rationalization of insulation design of 22 kV cable system. From the result of parameter analysis by the typical model of 22 kV cable system, the system condition of distribution line that causes the largest transient overvoltage is determined. In the case of switching surge, there is little relationship between neutral resistance and the overvoltage, and then the maximum per unit value of abnormal voltage is approximately 2 pu. On the other side, in the case of fault surge, the overvoltage increases as the neutral resistance increases, and then the maximum per unit value of the abnormal voltage becomes 2.68 pu. According to the above results, the conventional test voltage for 22 kV distribution equipment could be reduced by approximately 20%.