Considerations for selecting and sizing UPS systems for critical loads

The author presents a discussion of considerations for selecting and sizing uninterruptible power supply systems (UPSs). Various applications are discussed and illustrative examples are provided. As the UPS itself is required to maintain continuity of power of appropriate quality, its own protection requirements against input supply disturbances are also discussed. Effective sizing is heavily dependent on identifying types of loads and gathering computer system manufacturer data sheets and start up sequence or procedure and type of electrical distribution system of critical loads. The requirements of distribution are to be considered at the stage of sizing itself. A knowledge of the power tolerance envelope acceptable to loads can determine the UPS output specifications and acceptable tolerances