We analyze the ground resultant electric field distributions under UHVDC and UHVDC parallel doublecircuit transmission lines by Deutsch assumption and measurement. The analysis shows that the calculation of Deutsch assumption is consistent with measurement

so this theoretical calculation method is applicable to prediction of practical resultant electric fields. For parallel UHVDC double-circuit transmission line

the resultant electric field distribution is related with conductors arrangement because of the mutual influence of positive and negative ion flows in space. When two circuits have same polarity on their medial sides

the resultant electric field intensity inside double-circuit transmission line region is higher than that around single-circuit line

on the contrary

when two circuits have opposite polarity on their medial sides

the resultant electric field intensity inside the double-circuit line region is lower than that around single-circuit line. Moreover

with the decrease in the distance between two circuits or the increase in the height of double-circuit transmission line

the resultant electric field intensity inside the double-circuit line region increases

or decreases more larger slope

but the changed amplitude of total electric field increased as the distance of double-circuit transmission lines decreasing or as the transmission lines higher. But the resultant electric field intensity outside the double-circuit line region is almost same with that of single-circuit transmission line.