Toshimitsu Tanaka

Developing of higher voltage direct-current power-feeding prototype system

High efficiency power feeding systems are effective solutions for reducing ICT power consumption of ICT equipment, such as routers and servers, or high efficiency cooling systems. We developed a higher voltage direct current (HVDC) power feeding system prototype. This system is composed of a rectifier, power distribution cabinet, batteries, and ICT equipment. The configuration is similar to a −48 V DC power supply system. The output of the rectifier is 100 kW, and the output voltage is 401.4 V. We describe the advantage of an HVDC power feeding system and show that its basic characteristics are stable.

Grounding concept considerations and recommendations for 400VDC distribution system

400VDC is becoming a new voltage interface for telecommunication buildings and data centers as well as for ICT equipment. 400VDC interface covers applications for up to 400VDC with a typical nominal voltage of 380VDC. Key drivers for utilizing a higher DC voltage are overall efficiency and reliability gains vs present solutions. However, introduction of a new 400VDC interface brings up some questions about personnel safety and implementation of system grounding. Although DC is considered safer than AC, till now datacom operators have been hesitant to deploy 400VDC because its not as commonly used and well understood as AC. This paper addresses 400VDC grounding issues and recommends high resistance midpoint grounding concept, as an effective way to provide safe operation of 400VDC distribution systems. Today Europe, North America (NA), and Japan telecom/ datacom installations employ slightly different grounding concepts, practices, codes, or regulations. This paper also reviews different grounding models and their implementation praxis in Europe, NA, and Japan. Benefits and the disadvantages of different grounding concepts are discussed and explanation of the reasons for selection of high resistance midpoint grounding as a preferable model for 400VDC distribution system is provided.

Development of power distribution cabinet for higher-voltage direct-current power feeding system

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.

Analysis of wiring design for 380-VDC power distribution system at telecommunication sites

We present a quantitative analysis of the benefits of the 380 VDC power distribution system compared to the current -48-VDC power supply system. The analysis is based on models of typical distribution configurations in global telecommunication sites and takes into account codes, regulations, and practices for wiring and voltage drop comparison between centralized/decentralized 48- and 380-VDC. In 380-VDC applications, the cross-sectional area of the wiring decreases dramatically compared to 48-VDC applications. We also review other benefits of using the 380-VDC distribution system including reduction in wiring costs, reducing the use of copper resources, and increasing space in buildings.

380-VDC power distribution system for 4-MW-scale cloud facility

In February 2014, the NTT Group officially announced that it has launched a high voltage direct current (HVDC) (380-VDC) with a 4-MW-scale power supply system for the Tokyo metropolitan area. Activities, such as international standardization, has led to the commercial commencement of a full-fledged 380-VDC power supply system, demonstration projects, and technology development, which took more than 10 years. For the completion of the 380-VDC power supply system, evaluation, analysis and development, and demonstration of power supply system parts and equipment were necessary. The 380-VDC power supply system is a novel concept completely different from that of AC or 48-VDC systems. There are some technology gaps to provide breakthrough solutions. Prior to development, technology must be codified for the introduction of a safe optimal power supply method, grounding scheme, protection against electric shock, such as overcurrent protection, and stability and noise immunity. Recently, there have been many excellent reports from around the world. This paper focuses on promoting the introduction of our 380-VDC supply system into business and the long-term (over 10 years) development of the 380-VDC power supply system by the NTT Group.

Basic study on grounding system for high-voltage direct current power supply system

The relationship between grounding systems and a high-voltage direct current (HVDC, 380-V DC) power supply system is presented. To assess the effect of grounding system configurations, a simple model of the HVDC power supply system was assumed, and two typical grounding models were evaluated. The noise emission level (conductive disturbance) was measured by using a prototype HVDC rectifier. By use of the measurement results and evaluations, the advantages and disadvantages of these grounding systems are discussed.

Examination progress and development of HVDC power feeding system

A higher voltage direct-current (HVDC) power feeding system for data centers has many advantages and is presently being studied in many countries. This system is composed of a rectifier, power distribution cabinet (PDC), batteries, and ICT equipment, and the configuration is similar to a –48-V DC power feeding system. The power feeding voltage is about 400 V. We developed a prototype of an HVDC power feeding system using commercial fuses in 2008. A prototype of a power distribution cabinet and fuses were developed in 2009. We conducted a basic experiment and confirmed that the characteristics of our prototype are stable. In this paper, we describe the advantages and development of an HVDC power feeding system and the examination progress of standardization.

A practical approach of lightning protection measures for power receiving facilities in telecom building

In this paper, we present a summary of lightning protection measures aimed at securing a more reliable power supply for a telecom building. Based on an analysis of the entry paths of lightning surges into telecom building, we implemented lightning protection measures for the power receiving facilities by strengthening the equipments tolerance to overvoltage surges. This was achieved by using a multistage lightning arrester (LA) to suppress the inflow and outflow of surges, and by introducing surge protective devices (SPDs) in the signal paths. To cover the eventuality of relay equipment damage caused by a lightning strike, we also implemented measures such as redundant undervoltage relays and potential equalization by connecting the earth electrodes together. Of these measures, this paper discusses an example of lightning countermeasures for relays that are at high risk from lightning strikes due to them being directly connected to signal lines from the outside, yet are responsible for important functions such as switching between the mains power supply and emergency backup generator. Since a relays lightning surge breakdown voltage is relatively low, it can be impossible to protect with a commercial surge protector device (SPD). We therefore tried to suppress lightning surge voltages by using a lightning protection unit consisting of an SPD combined with an inductor. A relay has two types of wiring - the zero-phase voltage measurement line between the relay and the pole-mounted air switch (PAS) at the demarcation point between the commercial mains system and the customer equipment, and the -48 V DC control power supply lines between the rectifier and relay. These have two different earthing systems routed to the protective earth and to the -48 V DC earth wire, so we installed lightning protection units at both ports. To verify the effects, we measured the voltage applied to the electronic components inside the relay when a 10 kV lightning surge was applied to each port. As a result, we confirmed that these voltages were below the impulse breakdown voltage of the electronic components, and that the relay was able to continue operating normally.

Development and standardization of higher-voltage direct current power feeding system

We discuss the advantage of highly efficient and reliable higher-voltage direct current (HVDC) power feeding systems and the standardization activities for the power interface conditions in ICT equipment. With the recent spread of Internet services, the power consumption of ICT services is increasing annually. Many data center servicers want to decrease the power consumption of ICT equipment, cooling systems, and power feeding systems. HVDC power feeding systems have recently drawn attention due to their high efficiency and reliability. Such systems are more efficient than AC power feeding systems and are as reliable as conventional -48-V DC power feeding systems. However, the feeding voltage of HVDC systems is DC 380-V, which is higher and different than the conventional voltage of DC -48 V. ICT equipment is needed to change the power supply units interface. Therefore, we are actively standardizing the power interface condition of power supply units in ICT equipment. The European standards bodies of the European Telecommunications Standards Institute and International Telecommunication Union consented to the power interface conditions this year.

Development of PDC and PDU with semiconductor breakers

This paper describes a semiconductor breaker for higher-voltage direct-current (HVDC) power feeding systems. To reduce energy consumption of ICT devices, one effective measure is to manage their power use. To manage the power of individual ICT devices, circuit breakers, which turn ICT device power on and off, must be compact and remote-controllable. Because feeding voltage fluctuations, which occur due to short circuits, can potentially cause a stoppage or failure of ICT equipment, the circuit breaker must be capable of shutting down short circuits without large voltage fluctuations. To control the voltage fluctuations with a compact circuit breaker, we developed a semiconductor breaker with a semiconductor switch. We propose here a circuit configuration of the semiconductor breaker that can control voltage fluctuations. We evaluated the developed semiconductor breaker in an experiment in which we shut down a short circuit using a power distribution cabinet (PDC) and power distribution unit (PDU). The results confirmed that the developed semiconductor breaker was effective in controlling voltage fluctuations.