Abstract: In order to increase transmission capacity of electric power corridor significantly, multi-circuit on the same tower was constructed more and more widely in developed area. However, it’s difficult to realize transposition for multi-circuit on the same tower because of complex conductors arrangement, and electric unbalance degree of the transmission lines would get worse if phases were arranged inappropriately. ATP-EMTP and Matlab programs were applied to electric unbalance degree calculation for the three-layer and six-layer cross-arms tower of 500 kV four circuits on the same tower. According to the comparison of negative sequence voltage and current, lightning trip-out rate and electromagnetic environment, better electric unbalance degree was achieved when commendatory phase arrangement was adopted on three-layer cross-arms tower and diverse phase sequence was chosen on six-layer cross-arms tower. The results also showed that induce voltage and induced current from energized circuits got high when single circuit was maintained. It should be paid much attention to isolated switches selection.

Key words: 500 kV four circuits on the same tower, electric unbalance degree, negative voltage and current, lightning trip-out rate, induced voltage, induced current, diverse phase sequence