AN ELECTRICAL PROBLEM/SHUT DOWN TRIPPED THE PRS. PLANT OPERATOR NOTIFIED SHIFT SUPERVISOR, AND CALL OUT FOR AN ELECTRICAN BEGAN. OPERATOR BEGAN REDUCING THRUPUT OF PLANT. FIRED HEATER WAS SHUT DOWN, AND FULL SHUT DOWN OF PLANT BEGAN. RAW COAL FEED TO PLANT WAS STOPPED. GATES WERE LOWERED PRGING REACTOR OF COAL. REPORTED TO CONTROL ROOM THAT SMOKE WAS VENTING FROM VALVE.