Executives at Luminant and NRG Energy said in a hearing held by two joint Texas state Senate committees that unusually cold weather in February resulted in power failures despite preparing their plants for the temperature drop, according to a Dow Jones report.

The committees are looking into why the state’s electric grid, operated by the Electric Reliability Council of Texas (ERCOT), couldn’t keep up with demand on Feb. 2 which led them to impose rolling blackouts as a winter storm hit the state. In testimony, the state utility regulator said plants across the state were not adequately prepared for the drop in temperatures and icy conditions. As many as 82 power generating units representing 11,000 MW tripped offline because of the cold weather.

Both NRG and Luminant said they had prepared their plants for the storm by adding heating equipment and deploying more on-site personnel.

Read more news and features on power plant operations and maintenance.

Luminant Chief Executive David Campbell said that even units that had been prepared for weather experienced problems when moisture accumulated in certain equipment and froze. Luminant said it will evaluate the vulnerabilities and add additional heaters.

NRG said it fared better through the weather-driven power crisis. Regional president John Ragan said that the company’s plants fell to 91 percent capacity during the winter weather event.

ERCOT said peak winter demand surpassed 56,000 MW on Feb. 2.