In this paper, we describe 400-Vdc power distribution systems to be used as an energy conservation technology at telecom sites and data centers. We compared the 48-Vdc power distribution systems used at telecom sites with the AC power distribution systems used at data centers, and examined the advantages of DC. However, because of advances in the information and communication services, the 48Vdc system now consumes more electricity. As a solution, we developed a direct-current electric supply system that raised power distribution voltage to the 400-V class. We outline the 400-Vdc distribution systems developed by NTT facilities as well as the rectifier, voltage compensator, and battery charger prototypes.
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