EHV Double-Circuit Untransposed Transmission Line-Analysis and Tests

The current unbalance in two 113 mile long, electrically parallel, untransposed 500 kV overhead transmission line sections is studied for conditions in which some or all of the series-capacitor compensation is removed from individual circuits. It is shown that a negative sequence current of over 25% of the positive sequence line current can flow for certain phasing arrangements of the conductors and when one circuit is 70% series-capacitor compensated while the other circuit is uncompensated.