Icing on power lines was only one of the issues during that time. Among the problems, the cold actually shut down power plants themselves. And a huge increase in residential natural gas use caused the utilities to shut down many natural gas fired power plants to divert natural gas to their residential customers. (I get the impression that the hassle and danger of turning on millions of pilot lights for residential natural gas customers was a bigger concern than letting the gas fired power plants shut down.)
This article describes that episode and how the blackouts happened.
This had nothing to do with the grid. Grid-related issues are technical. This was not technical. The major problem is the coal-burning power companies did not prepare. The second problem was only minor and it may not have made a difference. Oncor did not have all of the information they needed.
Oncor, which operates the power lines in North Texas, agreed to omit Barnett Shale gas well equipment from rotating outages, but electricity regulators didn't have a database of critical natural gas equipment. So Oncor simply stopped the outages to five counties in the heart of the Barnett Shale gas patch. . . .
Jeanette Isabelle