Reliability of UPS Configurations

An increasing variety of UPS allowing of various configurations and connections are being offered on the market. The main reason for installing UPS is to ensure reliability of supply and it is therefore necessary to judge and compare the reliability of various configurations. This paper defines the basic UPS configurations and develops expressions for the resultant system reliability. We consider only systems where the load is supplied from a busbar (Fig. la). It is of course possible to obtain the required reliability with configurations like Figure lb, but these are outside the scope of this paper, as are systems like the "triport".