This paper calculates the overvoltage in Tie -Ling 500kV system （including five 500kV lines） in different years

with various connections and under all kinds of operation conditions. The result shows that temporary overvoltage level accords with SD 119-84 and secondary arc current of all lines meets the engineer-ing requirement

except Tie - Tong line. It also demonstrates that when closing and reclosing overvoltages are only limited by different type MO As

terminal switching overvoltage of each line is below 2.0 p. u

and the capacity of energy ab-sorbed in MOA leaves a wide margin .