Revenue metering error caused by induced voltage from adjacent transmission lines

A large zero sequence voltage was found to have been induced onto a 138 kV line from adjacent 500 kV lines where these share the same transmission right-of-way. This zero sequence voltage distorted the 2 1/2-element revenue metering schemes used for two large industrial customers supplied directly from the affected 138 kV line. As a result, these two customers were overcharged, on average, approximately 3.5% for 15 years. A description is presented of the work done to trace the origins of the zero sequence voltage, quantify the metering error, and calculate customer refunds which, in the end, totaled $4 million