Brad Palmer says three outages in a week is rare. He says the power system is stable.
The latest outage happened when an electrical line shorted out and caused a blackout for a significant portion of southern and western Pierre.
Three traffic lights went out but police say there were no accidents.
The week previous, there were outages in the city caused by a short in an aging underground cable and by a 3-foot-long bull snake that crawled into an electrical substation and triggered an automatic shutdown of equipment.
The July 15 outage might be connected to the previous weeks blackouts. Palmer says that to restore power, city crews routed extra electricity through other power lines, exposing weaknesses in the system.