Table 8.11.B. U.S. Transformer Outages by Type and NERC region, 2012
 

Outage Type Eastern Interconnection TRE WECC Contiguous U.S.
Circuit Outage Counts
Automatic Outages (Sustained) 16.00 -- 16.00 32.00
Non-Automatic Outages (Operational) 48.00 -- 73.00 121.00
Non-Automatic Outages (Planned) 291.00 -- 290.00 581.00
Circuit Outage Hours
Automatic Outages (Sustained) 3,224.13 -- 301.82 3,525.95
Non-Automatic Outages (Operational) 514.28 -- 10.01 524.29
Non-Automatic Outages (Planned) 2,382.76 -- 769.75 3,152.51
Circuit Outage Hours per Outage Incident
Automatic Outages (Sustained) 201.51 -- 18.86 110.19
Non-Automatic Outages (Operational) 10.71 -- 0.14 4.33
Non-Automatic Outages (Planned) 8.19 -- 2.65 5.43

Notes:
An Automatic Outage is an outage which results from the automatic operation of a switching device, causing an Element to change from an In-Service State to a not In-Service State.
A Sustained Outage is an automatic outage with an outage duration of a minute or greater.
A Non-Automatic Outage is an outage which results from the manual operation (including supervisory control) of a switching device, causing an element to change from an In-Service State to a not In-Service State.
An Operational Outage is a Non-Automatic Outage for the purpose of avoiding an emergency (i.e., risk to human life, damage to equipment, damage to property) or to maintain the system within operational limits and that cannot be deferred.
A Planned Outage is a Non-Automatic Outage with advance notice for the purpose of maintenance, construction, inspection, testing, or planned activities by third parties that may be deferred.
Detailed information on the Transmission Availability Data System outage definitions is available at:
http://www.nerc.com/docs/pc/tadswg/Appendix%207%2020101202a%20clean.pdf

Source: U.S. Energy Information Administration, Form EIA-411, "Coordinated Bulk Power Supply Program Report."