Analysis of CDM Events in NERC and WECC Power Systems Using TADS Outage Statistics

This paper presents study of the 2015-2020 Common and Dependent mode (CDM) outages of ac circuits and transformers collected by the North American Electric Reliability Corporation’s (NERC’s) Transmission Availability Data System (TADS) during the years 2015 to 2020. The primary objectives of this paper are to: (1) calculate the basic reliability indices for sustained CDM outages of ac circuits and transformers in NERC and Western Electricity Coordinating Council (WECC) systems; (2) calculate the element unavailability in NERC and WECC by voltage class and for all voltages combined; (3) perform the analysis of CDM events by initiating cause; (4) compare the outage statistics in period 2015-2020 with respective indices for previous years 2008-2014. While element unavailability due to CDM outages during this timeframe reduced as compared with the previous 6-year period, multiple-outage events still comprise about 17% of all TADS events, which is a significant factor in transmission reliability calculations.