Abstract: A system for energy-efficiently operating large capacity cooling pumps in a steam cycle electrical power generating plant which condenses steam using ambient water (e.g., from a lake, cooling tower, or stream) supplied by two or more large electrical motor-driven pumps is disclosed. The system sets reference values for condenser pressure, ambient water temperature, and feedwater flow or electric load, and when conditions change significantly, it cycles on or off one pump, measures and calculates energy efficiency, and depending upon those calculations, either recycles the pump off or on or maintains the status quo and updates the reference values for the plant, and automatically repeats the process upon another significant change of conditions. The system uses a digital computer, sensors, and interface units, for automatically controlling on or off the electric motors of the pumps.