380/400V DC powering option

Many studies have been conducted of a 380V/400V dc (HVDC) powering architecture in telecommunications and data centers. The key driving factors cited in these studies are increased reliability and energy efficiency. Discussion around a HVDC powering architecture has been recently fuelled by two issues. First the rapid increase in rack power density of server based equipment makes it less efficient and more costly to distribute dc power at traditional levels of -48V. Second, the convergence of telecommunications and IP-based internet technologies that increasingly sees server based equipment occupying floor space more traditionally reserved for "telecommunications racks". Servers are usually powered by ac equipment such as UPS. There is little debate that dc systems have traditionally out-performed ac systems on both reliability and energy efficiency. This paper will investigate the relevance of the ac versus HVDC debate on historical grounds. Is this a balanced and independent assessment of current and emerging technology options? Finally, given the traditionally more robust, engineering culture in the telecommunications space, how would a reliability comparison bear out in applying the same culture of rigor to server based technologies? This paper will present a historical comparison of the reliability and energy efficiency between the two architectures. Next, the comparison will be extended to consider present day and new developments. An independent review is presented of current and emerging factors likely to impact the question of ac versus HVDC. This will include advances in UPS systems, some global issues including the use of PDU\´s in North America and the question of HVDC standards. The paper will seek to present a balanced view of what has become a "hot" debate being contested amongst Telcos.