Uninterruptible Power Supplies (UPS) for data center

The Uninterruptible Power Supplies (UPS) are expensive equipments. Their installation is only profitable, if the costs because of the outage of the power of the supplied system are higher, as the installation/operation costs. Typical application areas are: systems of energy production and distribution, companies using dangerous technologies, (chemical industry), traffic systems, hospitals, data centers. This paper deals with the uninterruptible power supply of data centers. The aim is the short review of the several solutions, and to give a method to select the correct types. It is supposed, that the basic definitions, (MTBF, mean time between failures, A, availability etc.) are of the reader known.