High reliability storage systems for genset cranking

In many applications, like hospitals, the reliability of the emergency electrical supply is a critical issue, since the continuity has to be guaranteed at any time. The backup system usually consists of gensets and electrical starters (DC motors), supplied by lead-acid batteries. It is a fact that the latter are responsible for most genset cranking failures occurring in hospitals. Therefore, the reliability of the storage system should be improved to increase the Overall Mean Time Between Failures (MTBF) of the whole backup system. In this paper, eight different electrical storage systems have been modeled and simulated and they have been analyzed and compared from the point of view of reliability; in particular, the possibility of using supercapacitors (together with batteries or even replacing them) has been investigated. A huge number of real data regarding genset failures have been used, from both the literature and direct measurements made on purpose. An accurate statistical analysis has been performed to evaluate the MTBF for batteries, supercapacitors and other components available in the market, considering their actual characteristics. Finally, an innovative hybrid energy storage system has been proposed, based on both batteries and supercapacitors, allowing to triple the MTBF of the cranking storage system.