Dennis P. DeCoster Mission Critical West Inc., Redondo Beach, Calif.

Large UPS Technology report: Balancing green and high reliability

Twenty five years ago, the large UPS market—500 kVA and above—was served by two distinctly different technologies: rotary and static. At that time, a rotary UPS for data center applications was a rather kluge-like combination of motors and generators, while a static UPS was a step-wave inverter-based technology (Figure 1). The slow switching statics of the day had many reliability and application issues, while the rotaries were very inefficient but, in many cases, more reliable.