Common mode forced outages of overhead transmission lines

The studies undertaken by the Task Force addressed the definition and collection of data for common mode outages of multiple transmission lines which are on the same right-of-way for a measurable part of their length. A line-originated common mode outage is defined as an overlapping outage of two or more circuits sharing a right-of-way, from a common event, and due to their proximity on the right-of-way. A preliminary investigation of the available data shows that common mode outage events could be significant in transmission reliability calculations and that most of the data collection procedures are inadequate to provide data needed to evaluate these events. The additional information required to calculate indices of common mode outages is suggested in this paper. A method of calculating these indices is also illustrated.