AT 12:50 PM THE CORE DRILLERS LIGHTS WENT OUT. THE HELPER WENT TO CHECK THE CONTROL AND SAW SMOKE. THE DRILLERS WENT TO THE STATION CALLED THE HOISTMAN AND OTHER CREW. A SMALL 480 V TO 120/240 VOLT STEP-DOWN TRANSFORMER HAD FAILED. FUSE PROTECTION SHUT-DOWN POWER NO EVIDENCE OF FIRE. CREWS WERE EVACUATED.