Definitions

This chapter covers rotating sets capable of providing a continuous, well-regulated power supply to the load irrespective of the normal mains supply. There would appear to be various methods available to create such a system, and they are probably best discussed under two headings: rotating transformer systems and close coupled diesel/clutch/generator sets.

Background

A very early system which one could hardly call a UPS system merely consisted of motor/heavy flywheel/generator system. At this stage engineers were trying to bridge small power transients. The design was not very successful, the system would provide an enormous amount of power. In most designs the output voltage held up for 5 to 10 s but within 1 s the output frequency was out of tolerance. Note that this idea of utilizing kinetic energy has been given a new lease on life due to modern electronic circuitry (see Chap. 8).

For many years prior to the advent of the static system the circuit illustrated in Fig. 6.1 was in use. It consisted of a rectifier and battery charger supporting the load and also charging a battery. The dc supply was used to drive a motor alternator set connected to the load. The fly-wheel was present to provide kinetic energy when the system switched from mains supply to battery supply. At this instant the battery would go from float voltage instantaneously to discharge voltage a drop of some 15 to 17 percent. The regulating device dynamic performance was too poor to cope with this, and...