PLANT POWER WAS LOST AT 6:55AM DUE TO A ROLLING OUTAGE DUE TO EXTREME COLD CONDITIONS, INCREASED DEMAND, AND LIMITED SUPPLY. THE OUTAGE LASTED UNTIL 8:13AM. MSHA WAS NOTIFIED AT 7:05AM. FOUR EMPLOYEES WERE IN THE SKIP HEADED DOWN THE SHAFT WHEN THE OUTAGE OCCURED. THEY REMAINED IN THE SHAFT UNTIL POWER RESUMED AND THEY WERE SAFELY HOISTED BACK TO THE SURFACE.