A Calculation of Transient Overvoltage for Rationalization of Insulation Design of 11.4kV Distribution System

For the rationalization of insulation design of 11.4kV distribution line that consists of existing 6.6kV equipment in use, we had calculated transient overvoltages by EMTP. We investigated the references on the conditions of existing 6.6kV distribution lines, and selected some typical models for calculation. As a result of the parameter analysis by the typical model, we recognized the system condition of the distribution line that caused the largest transient overvoltage. The largest transient overvoltage occurred in the case of reclosing surge. In the case of the reclosing surge, the maximum per unit value of the transient overvoltage became 3.81pu. The maximum voltage is heavily affected by the closing phase and the neutral resistance. Moreover, from the result of calculations considering the effect of surge arrester attached to the current transformer, we found that the overvoltage was reduced to 3.3pu. According to the above result, the conventional test voltage for 11.4kV distribution equipment could be reduced by approximately 30%.