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Higher-voltage Direct Current Power-feeding System
This study aimed to develop and evaluate a shunt module for high direct currents (SMHC) to promote efficient use of DC power. Using offset and gain adjustments, the current-measurement error range improved from ±1.0% to ±0.04%, when measuring a 1000 A current. A real-time temperature correction (TC) function was used to improve the current measurement error from a maximum of 0.35% to less than ±0.04%, before and after the application of TC, respectively, for this current. The linearity evaluation showed the relative deviation to be less than ±0.06% for measured current in the range of 50 A to 1000 A. The measurement uncertainty of the SMHC was evaluated based on the guidelines to realize reliable current measurements. The relative uncertainty with confidence interval 95% (expanded relative uncertainty) for the measurement of 1000 A using the SMHC was estimated to be 0.20%.
NTT Energy and Environment Systems Laboratories has been designing power feeding interfaces to establish direct current (DC) power feeding technology for homes in cooperation with the Green Grid Platform at Home Alliance (GGP@H). A lot of information and communications technology equipment as well as household electrical equipment operates by internally converting mains-supplied alternating current (AC) to DC, so feeding DC to houses from outside should bring various benefits.
Higher-voltage direct current (HVDC) power feeds are attracting attention as an efficient means of supplying 380-V DC electricity to datacenters and telecommunications facilities, and it is expected that this technology will eventually be put to practical use in many places worldwide. In this article, we describe the characteristics of HVDC power feeds and the international standardization efforts related to this technology, including an overview of ITU-T Recommendation L.1200 of May 2012 ("Direct current power feeding interface up to 400 V at the input to telecommunication and ICT (information and communications technology) equipment").
This article introduces work being done by NTT Energy and Environment Systems Laboratories on energy management technologies for datacenters and telecommunication facilities to achieve energy savings by integrating and collaboratively controlling various developed technologies such as lowpower-consumption servers and routers, highly efficient air conditioning for communication equipment rooms, and higher-voltage direct current power feeding.
The Feature Articles in this issue focus on NTT's efforts to introduce environmentally friendly and energy-efficient technology in line with objectives to establish effective business continuity planning and, ultimately, to achieve a sustainable society. The Great East Japan Earthquake in March 2011 was a forceful reminder of the importance of both of these areas. This article presents an overview of NTT's energy management technologies that are bringing us closer to a sustainable society and reviews green infrastructure technologies that help conserve natural resources.
DC power distribution systems for building application are gaining interest both in academic and industrial world, due to potential benefits in terms of energy efficiency and capital savings. These benefits are more evident were the end-use loads are natively DC (e.g., computers, solid-state lighting or variable speed drives for electric motors), like in data centers and commercial buildings, but also in houses. When considering the presence of onsite renewable generation, e.g. PV or micro-wind generators, storage systems and electric vehicles, DC-based building microgrids can bring additional benefits, allowing direct coupling of DC loads and DC Distributed energy Resources (DERs). A number of demonstrating installations have been built and operated around the world, and an effort is being made both in USA and Europe to study different aspects involved in the implementation of a DC distribution system (e.g. safety, protection, control) and to develop standards for DC building application. This paper discusses on the planning of an experimental DC microgrid with power hardware in the loop features at the University of Naples Federico II, Dept. of Electr. Engineering and Inf. Technologies. The microgrid consists of a 3-wire DC bus, with positive, negative and neutral poles, with a voltage range of +/-0÷400 V. The system integrates a number of DERs, like PV, Wind and Fuel Cell generators, battery and super capacitor based storage systems, EV chargers, standard loads and smart loads. It will include also a power-hardware-in-the-loop platform with the aim to enable the real time emulation of single components or parts of the microgrid, or of systems and sub-systems interacting with the microgrid, thus realizing a virtual extension of the scale of the system. Technical features and specifications of the power amplifier to be used as power interface of the PHIL platform will be discussed in detail.
NTT FACILITIES is conducting research and development focusing on the introduction of high-voltage direct current (HVDC) power supply systems to telecommunication buildings, datacenters, and other such facilities. Future applications involving the direct integration of renewable DC energy sources such as solar panels into smart grids are also in view. This article describes our work on the development, construction, maintenance of HVDC systems. © 2015, Nippon Telegraph and Telephone Corp. All rights reserved.
This article describes the development of a higher-voltage (approximately 400 V) direct current power feeding system for information and communications technology (ICT) equipment. It has higher efficiency than conventional alternating current systems, which can reduce the system cost. High-efficiency power feeding systems are an effective way to reduce ICT power consumption as well as low-powerconsumption ICT equipment such as routers and servers and high-efficiency cooling systems.
In recent years, Higher Voltage Direct Current (HVDC) distribution systems have been proposed to reduce power consumption in telecommunication buildings and data centers. NTT FACILITIES and NTT Data conducted verification tests of a HVDC distribution system at a Tokyo data center from January 29 to October 30, 2009. This paper summarizes the results of studies on HVDC distribution systems obtained so far, describes verification tests based on those results, and examines the test results. The verification tests were conducted with the cooperation of domestic and international ICT equipment vendors. We measured the energy savings and stability of the power supply involved long-term powering of ICT equipments (servers and storages) with an HVDC system. The test results show the superiority of the HVDC distribution system over the existing AC system. These test results also validate the HVDC system specifications proposed by the NTT group for standardization. These results may develop the current vigorous discussion of international standardization for HVDC distribution systems.
Reducing the feeding loss of information and communications technology equipment, such as servers and routers, is very effective for reducing the total power consumption in data centers and telecommunication buildings. In this paper, the structure and function of a higher-voltage direct-current (HVDC) power feeding system prototype is presented. This system was developed to reduce power delivery and conversion losses by using 380 V DC. For operational safety, a floating ground system with an earth detector is applied and a fuse and circuit breaker in the power distribution cabinet work in cooperation. The system voltage is around 380 V, and the output power of the rectifier is 100 kW. We describe the advantages of an HVDC power feeding system and show that its basic characteristics are stable.
We outline the specifications and performance of a 400 Vdc power distribution system with a 400 Vdc output rectifier. In 2008, The NTT-group have began developing a 400 Vdc distribution system for reducing power consumption and the usage of materials, such as copper in power cables. In conjunction with this project, NTT facilities has developed prototype rectifiers, a prototype voltage compensator used during interruption periods, and a prototype battery charger. These exhibit higher efficiency than conventional ones and also exhibit high output regulation to adapt charge condition required by valve-regulated lead acid batteries for backup.