AC vs DC power in data center

There has been a debate going on for some years if the traditional AC or new DC power distribution is best approach to power a data center. The DC power side has been pushing their technology with claims of quite considerable power savings. In many published articles, expected improvements of 10% to 30% in efficiency have been claimed for DC over AC. I have had my doubts of the numbers on their promises. Now there is some new data on AC vs DC issue available.

White paper compares AC vs. DC power distribution for data centers article tells that a new white paper from APC by Schneider Electric provides a quantitative comparison of high efficiency AC vs. DC power distribution platforms for data centers. The latest high efficiency AC and DC power distribution architectures are shown by the analysis to have virtually the same efficiency, suggesting that a move to a DC-based architecture is unwarranted on the basis of efficiency

A Quantitative Comparison of High Efficiency AC vs. DC Power Distribution for Data Centers paper demonstrates that the best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems. It also tells that most of the quoted efficiency gains in the popular press are misleading, inaccurate, or false (like I have suspected to be for some time). And unlike virtually all other articles and papers on this subject, this paper includes citations and references for all of the quantitative data (which is very good).

The paper first describes that there are five methods of power distribution that can be realistically used in data centers: two basic types of alternating current (AC) power distribution and three basic types of direct current (DC) power distribution. These five types are explained and analyzed.

One AC and one DC, offer superior electrical efficiency. The paper focuses on comparing only those two highest efficiency distribution methods, which are very likely to become the preferred method for distributing power in future data centers. The data in this paper demonstrates that the best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems.

The best AC system is based on the existing predominant 400/230 V AC distribution system currently used in virtually all data centers outside of North America and Japan. Increasing Data Center Efficiency by Using Improved High Density Power Distribution white paper gives details how it could be used in USA. It says that the use of the international 230/400 V distribution system instead of the USA standard 120/208 system can save 56% in the lifetime cost of the distribution system, and save floor space and weight loading.

The preferred DC system is based on a conceptual 380 V DC distribution system (consensus in the literature as a preferred standard) supplying IT equipment that has been modified to accept DC power. In the proposed international ETSI standard for DC distribution for data centers, the 380V DC system is actually created with the midpoint at ground potential to keep the maximum system voltage to ground to within +/- 190 V.

Based on the data I think the 400/230 V AC distribution system is the best way to go in data centers around the world.


  1. Tomi Engdahl says:

    High-voltage relays target electric vehicles

    Fujitsu’s FTR-E1 series of DC switching relays offers 13% higher voltage switching, 77% less power consumption, and a package size that is 40% smaller than similar relays. Intended for the electric vehicle market, these board-mount single-pole relays come with 12 VDC or 24 VDC coils.

    The FTR-E1 relays furnish contact ratings of up to 30 A at 450 VDC (40 A maximum/1 hour) resistive and consume just 900 mW at the rated coil voltage. Their compact package is 43.6×28.3×36.8 mm and weighs approximately 75 g, nearly 60% lighter than competitive relays, according to the manufacturer. In addition, the parts achieve an electrical life of 10,000 operations at 20 A, 450 VDC resistive.

    Devices provide a dielectric strength of 5000 VAC (1 minute) between coil and contacts and 2500 VDC (1 minute) between open contacts.

    Prices for the FTR-E1 series relays start at $29.85 each for 1 to 99 units.

  2. Pathak says:

    The utilization of DC for server farm or system room control genuinely constrains the sorts of IT gear that can be utilized. By and large operation is not down to earth without including a supplementary AC control framework. Reliable quality examinations amongst AC and DC control frameworks are profoundly subject to the presumptions made. A DC control framework is developed of a variety of DC rectifiers providing at least one parallel battery strings. Various late UPS item presentations use a comparable design, with a variety of UPS modules associated with a parallel exhibit of battery strings. Because of their closeness, DC and AC frameworks utilizing these outlines can be straightforwardly looked at.

  3. Tomi Engdahl says:

    Converters target microgrids, data centers–data-centers

    Industrial DC/DC converters from Powerbox operate with an input voltage of 180 V to 425 V and deliver 150 W, 300 W, 600 W, or 750 W of output power for use in microgrids and data centers. The PQB150-300S, PHB300-300S, PFB600-300S, and PFB750-300S series feature a layout optimized for thermal conduction, input/output isolation of 3000 VAC minimum, and single output voltages ranging from 3.3 V to 48 V.

    In lots of 1000 units, the PQB150-300S costs $95, the PHB300-300S costs $140, and the PFB750-300S costs $190.

  4. Tomi Engdahl says:

    How about power in the gas form to the server racks?

    Microsoft makes a ‘crazy’ bet on fuel cells to feed power-hungry data centers

    The tech company is testing the use of natural gas-powered fuel cells that could someday allow data centers — which consume 2 percent of U.S. electricity — to unplug from the power grid. That could translate into big cost savings and, potentially, cuts in carbon emissions.

    Twenty racks of servers sit in a stark, white, well-lit room — a familiar setup for anyone who’s visited one of the data centers that make up the humming infrastructure powering the internet.

    To see what’s special about this one, look up: Sitting on a steel frame above each stack of computer hardware is an electrical cabinet the size of a mini-fridge. Inside is a natural-gas-powered fuel cell.

    That technology, Microsoft engineer Sean James says, could allow future data centers to someday unplug from the power grid entirely.

    By generating electricity close by — literally on top of the computing hardware — Microsoft’s new design eliminates the inefficiency of producing electricity at a distant power plant and transporting it long distancesto data centers. That could trim the energy footprint of the fast-growing data-center business, eliminating a portion of the carbon emissions that fuel global warming, and, in the process, save Microsoft a lot of cash.

    The company’s Seattle trial is preliminary. But if Microsoft’s estimates hold up — and, a big if, the cost of fuel cells comes down — the savings of a fuel-cell-based design spread across the company’s fleet of facilities could total hundreds of millions of dollars.

    James sums up the prevailing view of the plan among the rest of the industry, a group that includes many conservative engineers content to tweak existing designs on the margins: “They think I’m crazy.”

    With demand for those services surging along with high-speed internet use, web giants Amazon, Microsoft and Google, as well as specialists like Digital Realty and Equinix, are scrambling to build warehouse-size data centers across the globe.

    That business is a massive, and growing, consumer of energy.

    Data centers account for about 2 percent of U.S. electricity use, the Department of Energy’s Lawrence Berkeley National Laboratory estimates, up from 0.8 percent in 2000. To cut their costs, companies like Microsoft have designed their newer facilities with energy efficiency in mind. They’ve also reduced their dependence on fossil fuels by buying renewable energy or building their own wind or solar farms.

    But Lucas Beran, who tracks data-center energy economics for IHS Markit, says the industry’s efficiency improvements have started to stall.

    “In the next few years we’re going to be at a crossroads,” he says. “We’ll have to change what we’re doing to maintain those energy gains.”

    Energy experiments

    Microsoft’s fuel-cell concept stems from years of experimentation.

    Mock data center

    Microsoft isn’t the only technology giant dabbling in fuel cells.

    Apple and eBay have used fuel cells to power data centers from a centralized location, essentially replacing the backup generators or grid connections in a typical data-center design with fuel-cell clusters.

    With that clearance,McKinstry, the Seattle-based contractor that built and is hosting Microsoft’s experiment in a formerly vacant space attached to its headquarters, will link the mock data center to the municipal natural-gas grid.

    Gas will be piped to the 20 fuel cells, starting an electrochemical reaction that extracts hydrogen atoms and sends a current of negatively charged electrons to power the servers below.

    Waste products — water vapor and a small amount of carbon dioxide — will be vented out of the building along with the excess heat from the servers.

    In a real data center, the servers would be processing Bing web searches or storing customers’ email. For the purposes of the trial, the 20 racks in Sodo will be filled with dummy data meant to simulate actual workload.

    Microsoft will add methane detectors to guard against potential gas leaks, and airflow monitoring to see how the design deals with exhaust.

    Microsoft researchers, in tests a few years ago with the University of California, Irvine, estimated that when plugged into the power grid, the average data center reaped about 17 percent of the potential energy of the fuel used to generate that electricity.

    The in-rack fuel-cell concept can pull off 29 percent efficiency, Microsoft estimates, because no energy is lost through the long haul from power plant to conversion and consumption, and because the fuel cell’s chemical reaction is more efficient than some industrial-scale power generation.

    Pros and cons

    There is a problem, though. Fuel cells are expensive. Current models cost about twice as much as Microsoft needs to make the concept pay off.

    But the company is optimistic. Fuel-cell manufacturing is a relatively new industry, with most fuel cells bound for relatively niche applications like backup power, cranes and industrial equipment, and specialty vehicles. If big buyers such as Microsoft start lining up for many thousands of them, their costs may come down.

    In that case, the savings would be significant. Microsoft researchers estimate that mass-produced fuel cells would cut the cost of installing a new data-center rack by at least 10 percent, and the costs of operating that rack by 21 percent.

    Those savings pencil out, conservatively, to about $80 per rack, per month. With more than 1 million servers in Microsoft’s worldwide data-center fleet, the potential savings could stretch into the hundreds of millions of dollars a year if the design were rolled out across the board.

  5. Tomi Engdahl says:

    Power Transformers Aim for a Bigger Role in the Smart Grid

    Improvements in power transformers will address the needs of the smart grid. Benefits include enhanced energy security, reduced greenhouse gas emissions, improved urban air quality, and greater grid utilization.

    This is particularly true on the distribution side of electric power, where the total cost of ownership and payback for a utility and the end user over the useful life of a transformer is taken into consideration. According to Metglas Inc., a fully owned subsidiary of Hitachi America Metals Ltd., amorphous metal power transformers are less costly and more efficient than cold-rolled grain-oriented steel transformers.

    The company manufactures amorphous metal power transformers using a proprietary process. The key to Metglas’ rapid-solidification manufacturing process is cooling the molten alloy at a rate of approximately 1 million ºC/s, using a melt spinning technique.

    Metglas says hundreds of utilities are benefiting from amorphous-metal core transformers. By replacing conventional distribution transformers with amorphous-metal types, approximately 27 TWh of core losses in the U.S. alone could result in annual savings.

    Amorphous core technology is also used by the United Kingdom’s Wilson Power Solutions, which is upgrading its products for the smart grid. Its e2+ transformers come with a 17-position on-load tap changer that adjusts the taps automatically to maintain a constant secondary output voltage (relative to input voltage fluctuations). This is done via a volt-ampere reactive relay, where site supply voltages fluctuate, or a constant ±1% output voltage is required.

    Despite the fact that most power transformers are not quite yet ready for the emerging smart grid, there’s room for improvement for incorporating remote diagnostic smart monitoring of a wide range of transformer and system parameters

    Dickinson sees transformers used in power transmission as immediate candidates for integration in the smart grid, with resulting immediate benefits of enhanced energy security, reduced greenhouse gas emissions, improved urban air quality and greater grid utilization.

  6. Tomi Engdahl says:

    Technology Award for Better Electricity Delivery’

    The innovation developed by the Lappeenranta University of Technology “Low Voltage Equal Distribution System for Public Power Distribution” was awarded the Technology Prize by the Finnish Messrs Foundation. The prize for the first time is € 10,000. The award was announced today at the Technology 17 event opened at the Helsinki Fair Center.

    Since 2005, Lappeenranta University of Technology has been researching a power distribution system based on low-voltage electricity (LVDC) in cooperation with industry. The aim has been to develop a more cost-effective way of replacing existing electricity distribution systems with renewable electricity distribution networks to meet future demands.

    - As a result of the research, there is an innovation from active LVDC distribution, where the familiar energy of the history is connected to modern power electronics, network technology and information systems. LVDC’s business potential in Finland is € 40-60 million a year and its estimated global annual market potential is billions in billions, says Professor Jarmo Partanen.

    - Innovation makes it possible to build electricity distribution networks at a lower cost, to improve the reliability of electricity distribution and the lack of security. In addition, similar technologies have many other applications, ships, real estate, electric car charging systems, said sales manager Marcus Bergström from the Exhibition Center as secretary of the prize drawer.


  7. Tomi Engdahl says:

    Data center power market charted for steady increase til 2024: Report

    Key players in the global data center power market, according to the report, include Server Technology Inc., Schneider Electric SE, Rittal GmbH & Co. KG, Intel Corporation, Emerson Network Power, Raritan Inc., General Electric Company, Hewlett-Packard Company, and Eaton Corporation Plc/ABB Ltd.

    Data Center Power Market to Witness Steady Increase by 2024

    Zion Market Research, the market research group announced the analysis report titled “Data Center Power Market: Global Industry Analysis, Size, Share, Growth, Trends, and Forecasts 2016–2024″

  8. Tomi Engdahl says:

    Are Solid-State Transformers Ready for Prime Time?

    It is possible that “solid-state transformers” could reduce the size and weight of power distribution systems, but we’re not quite there yet.

    Several companies are working on technologies that could replace large traditional power transformers with power semiconductors and smaller transformers mounted on circuit boards. Although they are called solid-state transformers, they are really power converters.

    The figure below is a conceptual circuit for a “solid-state transformer” that accepts a three-phase 60 Hz high-voltage input and provides a 60 Hz lower-voltage output. The transistors could be SiC or GaN types with the appropriate specifications. The input circuit converts 60 Hz high voltage ac input to a dc voltage. Then, the dc produces an ac voltage of 10 to 20 kHz that is applied to a step-down transformer. The transformer output is converted to dc and applied to an inverter to produce a lower voltage 60 Hz ac output. The transformer is necessary to provide isolation between the input and output. An advantage of this approach is reduction in size and weight of the transformer because it can operate at a much higher frequency than a 60Hz power transformer.

    Microgrids could be deployed much more rapidly. Grid efficiency could conceivably be increased by up to 8% to 10% because of lower conversion and transmission losses.”

    In describing the advantage of this approach, “that’s 10% less power that you have to generate,” says John Palmour, co-founder and chief technology officer for Power and RF at Cree, a producer of SiCs. “We can replace an 8,000-pound transformer in a substation running at 60 Hz and replace it with one running at 20 kHz in a tiny design. We can shrink it down to [the size of] a suitcase.”

    NC State Report Says Solid-State Transformers Are Ready

    Now, fast foward to July 2017. A North Carolina State (NC State) study using complex computational models found that smart solid-state transformers (SSTs) could be used to let power distribution systems route renewable energy from homes and businesses into the grid. Such a grid would improve efficient use of renewable energy and storage but, to date, this version of the smart grid has been mostly conceptual, the report added.

    “Using this model, we found that SSTs can greatly enhance the functionalities of tomorrow’s power grid,” Chakrabortty says. “However, certain operational boundaries would need to be maintained.”

    Essentially, system designers and operators would need to ensure the system—at every level —is taking into account customer power demand, power generation from renewable sources, and energy storage capacity, in order to avoid providing too much or too little power.

  9. Tomi Engdahl says:

    The Data Center’s backup power to the grid reserve

    Eaton is developing, for example, a service center that provides them with the opportunity to participate in the frequency control of the network with uninterruptible power supplies, ie UPSs. This UPS-as-a-Reserve (UPSaaR) service is the first of its kind in the data center.

    The service provides data center operators with the ability to keep their system within the limits of the power grid and thus avoids network-wide power outages by quickly adjusting the current power consumption. The service is targeted at large data center operators such as cloud service providers and will be brought to the European market by the end of 2017.

    Eaton has developed a service in close cooperation with Fortum. As energy markets move from fuel-based products to renewable energy, energy production itself may become more volatile and the anticipation and balancing of power generation will become more difficult. Network operators buy from service providers, such as energy producers, frequency-controlled operating and disturbance resources to balance electricity consumption and production to maintain frequency.

    Comprehensive tests between Eaton and Fortum have demonstrated that uninterruptible power supply systems and batteries can be safely and efficiently used to perform supply-demand functions without the risk of uninterrupted power supply main operation. Uninterruptible power supply (UPS) can function as part of a virtual power plant, enabling data centers to participate in highly money-intensive frequency-controlled operating or disturbance and demand-driven markets.


    Eaton UPS-as-a-Reserve Solution

  10. Tomi Engdahl says:

    AC versus DC load breaking comparison with a knife switch
    AC Circuit Breaker 230V DC Test

  11. Tomi Engdahl says:

    Why Do Today’s Server Applications Use 54-V BLDC Motors?

    More server manufacturers are adopting 54-V brushless dc motors over traditional 12-V BLDCs to achieve significant savings on a couple of fronts.

    Cloud-based computing refers to a mesh of remote servers that stores and moves data around the world so that we can access via Wi-Fi, local-area network (LAN), or a cellular network.

    These remote servers act as a large storage device that consists of clusters of servers in a warehouse commonly referred to as a server farm. These server farms require a constant ambient temperature (optimal temperature range is between 68° and 71°F) to operate at their highest performance and to minimize any failure. They’re typically cooled by central air conditioning or heated with central heating depending on their location, just like a typical office space.

    Traditionally, server applications have used 12-V BLDC fans to cool the electronics in a cabinet. However, just like automotive applications, 54-V BLDC motors are being adapted for server applications for several reasons.

    Server manufacturers are adopting 54-V BLDC motors over traditional 12-V BLDC motors because it allows them to use one fourth of the current. In turn, motor manufacturers can use thinner ­­copper wire. This also enables motor manufacturers to reduce the size of the motor and, therefore, the overall cost of the motor

    For example, in a 450-W server, 32 W are consumed by the 12-V BLDC fans.

    One issue does emerge when dealing with the electronics that drive a 54-V BLDC fan motor: Server engineers can’t use the old 12-V hardware to drive 54-V motors. They’re required to use electronic components with a higher operating voltage that are suitable for a 54-V power supply with plenty of margin.

    Nonetheless, several hardware solutions on the market can help ease this transition.

    The MIC28514 converts the 54-V supply bus rail to a traditional 12-V power rail with better than 90% power efficiency. As a result, server engineers can continue to use the same motor-control algorithms and proven active components.

    These high-voltage devices make it feasible for server manufacturers to adopt 54-V power bus technology and, in turn, reduce overall system cost by utilizing smaller motors and less copper width on PCB boards and cabling.


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