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.
207 Comments
Ken Gettman says:
I believe that the conclusion presented is likely correct, given that the comparison is done solely on the basis of efficiency. However (without having completely read the whitepapers), today’s push for renewable energy sources (generating DC power) with their associated need to have available energy storage (likely based on DC power), it seems that a direct link, or one with just DC voltage adjustment, would push the advantage to DC distribution and utilization where DC power was the primary source. In addition, many of the auxiliary systems in Data Centers – lighting, HVAC, security, building and power control, etc. – could also be DC for further benefit from the lack of power conversion. This also seems to be the case for microgrid considerations, where power reliability and security concerns dictate the need to either be primarily off-grid or at least have that ability. It is very unlikely that DC will ever replace AC but there seems to be a need for both systems based on the application.
tomi says:
Thank you for your feedback.
I can see your point on DC power distribution in data center on cases where DC power is the primary source.
There is for sure place for DC distribution as well, and I think the 380V DC voltage could be a good candidate for that.
I can agree on your final comment:
“It is very unlikely that DC will ever replace AC but there seems to be a need for both systems based on the application.”
Tomi Engdahl says:
NFPA 70E 2012 Rolls Out New
Electrical Safety Requirements Affecting Data Centers
http://www.emersonnetworkpower.com/en-US/Services/DCN/OOps/Electrical/Documents/SL-24665.pdf
While the importance of electrical safety is clear, understanding the complex regulatory requirements can be difficult. This paper provides an overview of the safety and maintenance changes that most impact data centers; discusses challenges to implementing electrical safety programs; and shares best practices for an effective program for data centers.
Tomi Engdahl says:
Improving HPC Data Center Efficiency with 480V Power Supplies
http://www.appro.com/industry_resources/white_papers/improving_hpc_data_center_efficiency_with_480v_power_supplies/
Traditional AC power distribution systems in North America bring 480V AC power into a UPS, where it is converted to DC to charge batteries, and then inverted back to AC. The power is then stepped down to 208V within the distribution system (PDU) for delivery to the IT equipment. The power supplies in the IT equipment convert the power back to DC and step it down to lower voltages that are consumed by processors, memory and storage.
Server power supplies that operate directly from 480/277 volt power distribution circuits can reduce the total cost of ownership (TCO) for a high performance cluster by reducing both infrastructure and operating cost.
The reason for using low voltage 120/240 volt distribution circuits is safety. The 120/240 volt circuits were never designed to deliver large quantities of power. These inefficiencies are acceptable for a single server but the aggregate losses in a large system with thousands of servers are too large to be acceptable.
The higher voltages do not present a safety issue for these larger systems since they have better facilities and trained maintenance personnel.
Tomi Engdahl says:
Power and cooling: The Oak Ridge way
25 Megawatts, 6.6 tons of cooling, more on the way
http://www.theregister.co.uk/2012/10/16/power_and_cooling_oak_ridge_case_study/
You think you have power and cooling issues? Slip into the shoes of Arthur ‘Buddy’ Bland, Project Director for the Oak Ridge Leadership Computing Facility, and learn how they keep one of the largest computing facilities in the world powered up, yet cool enough to prevent melting.
Oak Ridge is one of the world’s most efficient large data centers with a PUE (Power Usage Effectiveness) score of 1.25.
By comparison, Google has one of the lowest PUE averages at around 1.12 – 1.13, and estimates for typical data centers run from 1.6 to more than 2.0.
Watch the video…
Why 480 volts is better than 240
Tomi Engdahl says:
Powering single-cord equipment in dual path data center environments
http://www.cablinginstall.com/articles/2012/10/dual-path-data-center-power-white-paper.html
“Most high availability data centers use a power system providing dual power paths all the way to the critical loads, and most enterprise class IT equipment offers redundant power supplies and power cords to maintain the dual power paths all the way to the IT equipment internal power bus,” states the paper’s introduction. “In this way the equipment can continue to operate with a failure at any point in either power path.”
“However, equipment with a single power supply [i.e. single-corded data center gear] introduces a weakness into an otherwise highly available data center. Transfer switches are often used to enhance single-corded equipment availability by providing the benefits of redundant utility paths. If not understood, this practice can lead to downtime that would have otherwise been avoided.”
White paper:
Powering Single-corded Equipment in a Dual Path Environment
http://www.apcmedia.com/salestools/SADE-5TNRLE_R1_EN.pdf
The use of dual power path architecture in combination
with IT equipment with dual power supplies and power
cords is an industry best-practice. In facilities using this
approach there are inevitably some IT devices which
have only a single power cord. There are a number of
options for integrating single-corded devices into a
high availability dual path data center. This paper
explains the differences between the various options
and provides a guide to selecting the appropriate
approach.
Tomi Engdahl says:
ABB turns up DC-powered data center
June 6, 2012
http://www.cablinginstall.com/articles/2012/06/abb-turns-up-dc-powered.html
Power and automation technology group ABB and Green, an information and communications technology service provider in Switzerland, announced the official opening of Green’s Zurich-West data center expansion. Based on direct current (DC) technology, the new facility employs HVDC-capable HP servers, and is touted as the most robust application of DC power in a data center to date.
“The implementation of 380 volt DC technology in our data center is part of our long-term energy optimization strategy, a big step that has set a new standard in the industry,” commented Franz Grueter, CEO of Green. “When fully loaded, the system will result in energy savings of up to 20 percent in power consumption from grid to chip and in cooling.”
ABB installed the one megawatt DC power distribution solution for the 1,100 m2 expansion of the 3,300 m2 Zurich-West data center.
“Across all our business areas, customers are asking for improved reliability and energy efficiency, and DC power is an effective solution,”
The company contends that DC systems are less complex than AC systems, making fewer power conversions.
HP provided its HVDC-enabled servers and storage platforms
“Green was looking for an IT partner that could provide HVDC-enabled IT solutions to meet its specific data-center needs,”
Tomi Engdahl says:
Uptime Institute professional services VP Vince Renaud steps forward and “debunks the myth that typical data center deployments are 10kW-20kW per rack.” For years, the data center industry has been warned by vendors that high density racks are coming, but according to the results of a recent survey, “the reality on the raised floor is far different,” contends Uptime Institute’s Renaud.
Source: http://www.cablinginstall.com/articles/2012/05/data-center-density.html
Tomi Engdahl says:
How do we get to a DC-powered home?
http://www.edn.com/electronics-blogs/dave-s-power-trips/4402704/How-do-we-get-to-a-DC-powered-home-?cid=EDNToday
my home is becoming more and more DC-powered. Actually, it is kind of a distributed DC power where some rooms have four or more wall adapters, as well as other devices that convert to DC internally like computers and printers.
According to the Environmental Protection Agency (EPA) in the United States, each person has an average of eight adapters.
Over 100 years ago, Edison and Westinghouse were on each side of the DC versus AC debate. At that time the loads were light bulbs, motors, and heaters. All had DC or AC options. AC had the advantage in that the voltage could be changed with a simple transformer. DC had issues like arcing and connector corrosion.
Combined, the electronics and “other” categories account for 15 percent of the average home total energy use, according to the Consumer Electronic Association2. Others like Greg Reed of the Power & Energy Initiative at the University of Pittsburgh suggest the number is closer to 20 percent.
Reed also predicts that by 2020 the number can reach 50 percent.
Neither Edison nor Westinghouse, and not even Tesla, could have predicted that someday semiconductors would make AC-to-DC conversion easy and efficient. And, furthermore, provide the power and modulation to power lights, motors, and other devices with improved energy efficiency.
So what are we waiting for? Well, we have considerable investment in our AC systems. However, more than 25 percent of the world lives off the grid. These homes easily could accept and benefit from a DC power source, such as solar panels.
The DC-powered home most likely will need two DC buses. The “other,” electronics, and lighting categories could use a low-power DC bus, for example 12V to 48V. However, the heating, cooling, and appliances categories would benefit from a much higher voltage, for example 380V to 400V.
So what is it going to take to push the DC home into the mainstream for grid-connected homes? I think it will take a very well-defined benefit. About five years ago a team of us asked several data center managers what it would take for them to change their system power management solution. The response was a 30 percent energy savings. This was certainly a surprise.
We were thinking a 10 to 15 percent reduction would be attractive.
Of course, it did depend on the cost to make the changes. The real answer was that they wanted a two-to-three year payback. At this point, we are not there yet.
So when do you think we will see the grid-connected DC home?
Tomi Engdahl says:
How to power automated test equipment
http://www.edn.com/design/test-and-measurement/4404894/How-to-power-automated-test-equipment?cid=EDNToday
Automated test equipment (ATE) historically has been built with a centralized power architecture
As instrumentation card requirements grew in terms of count and diversification of channels and loads, distributed power architectures became a necessary choice
A simpler, central “bulk” power device supplied a single regulated higher DC voltage, typically 48V, to a backplane distribution system. Test cards devoted some of their area to DC/DC converters, typically on their periphery, whose outputs closely matched the measurement circuits’ needs.
The “higher density,” “higher dynamic” trend also is challenging at voltages in the 48V range, as higher current requires larger copper cross section within densely populated boards. Some new concepts are being explored today, including factorized power architecture and 400V DC distribution.
Power distribution bills of material are directly affected by one main parameter: backplane distribution voltage. The simple consideration of distribution losses should drive the trade-off in choosing copper cross section.
Table 1 provides a guideline derived from telecom datacenter studies. While ATE requiring more than 20kW are restricted to ATE supporting high degrees of parallel test, it is clear that 48V backplanes may no longer be the best choice, and 400V backplanes with their lower currents are waiting to be exploited once 48V will no longer suffice.
Power distribution network design is a challenge of state-of-the-art test systems. Several trade-offs exist and need to be carefully evaluated within the power system architecture of choice. While distributed power architecture from 48V backplanes is today’s common choice, advanced architectures like factorized power from 400V DC distribution are becoming valuable, because they improve system density by offering higher efficiency and a higher level of granularity.
Tomi Engdahl says:
Virtualization on the plant floor
http://www.controleng.com/home/single-article/virtualization-on-the-plant-floor/d27a965c037a8a3ca3949166cbb3e0bd.html?tx_ttnewssViewPointer=5
Preparing your power distribution system
Virtualization places different demands on your infrastructure than traditional architecture.
By increasing the utilization level of servers, virtualization brings potential to deliver incredible savings in terms of server count, footprint, power consumption, and cooling requirements. However, in order to fully reap these benefits without sacrificing electrical reliability, a few important power distribution challenges must be addressed.
For one, overall power consumption will be lower, but it will be of higher variability and concentration. For example, on an un-virtualized platform, the average server CPU runs at only 10%-15% of capacity. With virtualization, that figure increases to about 70%-80%. As CPU utilization increases, so does power consumption per server.
System availability becomes all the more important as servers are pressed to carry these larger workloads. To protect servers, increase the density of enclosure-level power protection and distribution. Enclosure-based power modules are available that can distribute up to 36 kW in only a few U (rack units) of rack space. These cover four to 45 receptacles in an organized manner to meet the needs of a wide range of power densities.
Traditionally, facility managers could plan for about 60 to 100 W of power consumption per U of rack space, so a full rack of equipment averaged 3 to 4 kW. Today’s blade servers have escalated that figure to 600 to 1,000 W per U, which is steadily growing and may soon reach up to 40 kW per rack.
Five or 10 years ago, a typical computer room was designed to feed one 20 A, 208 V circuit to each rack, or less than 3.5 kW per rack. If you now have to support 20 kW of equipment in each rack, it could take up to six of these 20 A circuits. The existing electrical infrastructure will be unable to support this load growth, and could easily run out of circuits or run out of capacity, especially with the growing prevalence of dual- and triple-corded loads.
Will DC Power Distribution Make a Comeback? « Tomi Engdahl’s ePanorama blog says:
[...] AC vs DC power in data center is talked about lately. 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. Going to DC can help the efficiency compared to USA standard 120/208 system (typically DC systems are 5 to 8 percent more efficient than AC), but best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems at least then powered from AC source. If the power comes from DC source in the beginning, the situation can be different. [...]
Tomi Engdahl says:
IR drop: The ‘gift’ that keeps on taking
http://www.edn.com/electronics-blogs/power-points/4413178/IR-drop–The–gift–that-keeps-on-taking
There’s no getting away from it: one of the oldest manifestations of Ohm’s Law still affects us daily. There’s voltage loss (drop) when current flows through resistance, your basic V = IR.
This phenomenon is so pervasive that I am still amazed that an internal-combustion car can even start
Yes, there are lots of low-power battery-powered devices in use (you can make your own list), but high-current devices are also part of our world. You’ve got home systems which are drawing tens of amps, all the way to servers with 100 to 200 amps/board and kilowatts per rack. That means you are fighting both IR drop and subsequent thermal dissipation.
The solution in many cases, of course, is to trade current for voltage.
I see many otherwise good designs which overlook this consideration. The schematic says “here’s your power” but the physical cabling say “not quite.” It’s easy to inadvertently overlook a fundamental factor such as IR drop when you are worried about hardware issues such as nanosecond signal timing, signal integrity, EMI/RFI, PC board layout, drive currents, I/O, switching, and the many other issues which affect product design.
Tomi Engdahl says:
Report sees steady growth for global data center rack PDU market
http://www.cablinginstall.com/articles/2013/10/rack-pdu-market.html
Research and Markets (Dublin, Ireland) announced the addition of the Global Data Center Rack Power Distribution Unit Market 2012-2016 report to its offering. The firm’s analysts forecast the global data center rack power distribution unit (PDU) market to grow at a CAGR of 13.38 percent over the period from 2012 to 2016.
Unsurprisingly, one of the key factors contributing to this market growth is the increasing deployment of data centers, finds the report. The market has also been witnessing the evolution of alternating phased power.
“Traditional three-phase power distribution divides power into multiple branches within the rack PDU. However, alternating phased power alternates each phase on a per-receptacle basis instead of per branch basis,” explains an analyst from the firm. “In this PDU system, power wiring in simplified as power cords are not required to be laid through the size of the vertical PDU to reach distinct branches. Moreover, servers can be plugged in from the bottom to the top of the rack with lesser risk by installers. Hence, alternating phased power provides noticeable benefits such as shortened cabling, better airflow, improved load balancing, and higher efficiencies.”
Tomi Engdahl says:
Study drills down on effects of data center outages
http://www.cablinginstall.com/articles/2013/10/data-center-outage-study.html
Sponsored by Emerson Network Power, the Ponemon Institute’s 2013 Study on Data Center Outages quirkily reveals that over 80% of “senior level to rank-and-file” IT professionals “say they would rather walk barefoot over hot coals than have their data center go down.”
The study surveys 58 individuals in U.S. organizations who have responsibility for data center operations. Eighty-five percent of respondents reported that their organizations experienced a loss of primary utility power in the past 24 months. Among those organizations that had a loss of primary utility power, 91 percent report their organizations had an unplanned outage.
The study indicates that data center professionals are overwhelmed by unplanned power outages, have waning confidence in electrical utility providers, and feel ill-equipped to minimize the impact of outages.
Tomi Engdahl says:
6 Avoidable Mistakes in Preventing Arc Flashes
https://rapidrequest.emediausa.com/4/Rfi/4105073.EJRGOINN.175819
What You Need to Know About Arc Flashes
Understanding and mitigating the dangers of data center electrical explosions
Arc flashes—the fiery explosions that can result from short circuits in high-power electrical devices—kill hundreds of workers in the U.S. every year and permanently injure thousands more. They can also wreak financial havoc in the form of fines, lawsuits and damage to expensive equipment. Yet, many data center operators are perilously unfamiliar with both the causes of arc flash events and the serious dangers they pose.
This white paper aims to fill that knowledge gap by providing introductory-level information about what arc flashes are, why they’re so hazardous and what steps data center managers should take to safeguard their employees, infrastructure and productivity.
What is an arc flash?
In the simplest terms, an arc flash is the energy release that occurs during an electrical fault when current flows through the air between two live conductors, causing a short circuit. In a residential setting, arc
flashes usually produce little more than a brief flash of light before extinguishing themselves harmlessly. In a commercial or industrial setting, however, voltages are significantly higher, so electrical faults typically release far more energy. As a result, arc flashes in data centers routinely produce powerful explosions marked by searing heat, toxic fumes, blinding light, deafening noise and massive pressure waves.
Arc flash mitigation strategies
Given the grievous dangers they pose, arc flash events merit serious attention from data center professionals. Here are six of the most effective strategies for reducing the frequency, severity and harmfulness of arc flash incidents.
1. Perform a hazard analysis
two standards to help organizations determine how much protection their employees require:
IEEE 1584
NFPA 70E
While arc flash safety standards such as IEEE 1584-2002 are extremely helpful tools, they contain an important gap at present: single-phase-to-ground faults.
2. Reduce available fault current
Though not applicable to environments protected by fuses and current-limiting breakers, data centers that use non-current limiting breakers (NCLBs) can reduce the amount of incident energy released during arc flashes by reducing the amount of available fault current.
Operate with an open tie during maintenance. Maintaining dual electrical feeds helps data centers increase the redundancy of their power supply, and hence the availability of their IT systems. The downside of this power architecture, however, is that it can double the amount of current available when faults occur.
Switch to smaller kVA and/or higher impedance transformers. In the past, server power supplies commonly generated distortion that could overheat electrical transformers. To compensate, data centers often used bigger—and hence stronger—transformers than their infrastructure otherwise required.
Employ high-resistance grounding.
Use current limiting reactors.
3. Shorten clearing time
Just as smaller arc flashes release less energy, so, too, do shorter ones.
Utilize zone selective interlocking. Zone selective interlocking (ZSI) is a protection scheme that uses an “inhibit” signal transmitted from downstream breakers that see a fault to the next breaker upstream. The upstream breaker sees both the fault current and the inhibit signal and therefore delays tripping, allowing the downstream breaker to clear the fault.
Implement a bus differential scheme.
Deploy an Arcflash Reduction Maintenance System.
4. Adopt remote operation
Executing potentially dangerous procedures remotely can shield data center personnel from injuries
5. Predict and prevent faults
One of the most effective ways to prevent arc flashes is to anticipate and eliminate the conditions that cause them.
Monitor insulation integrity. Deteriorating insulation is the leading cause of arc-producing electrical failures. Identifying and repairing compromised insulation before it fails can help avert arc flash explosions.
Monitor pressure junctions.
Use infrared (IR) windows. Using contactless IR thermography technology, IR windows enable technicians to perform IR scans without removing switchgear side panels
6. Redirect blast energy
Equipment that directs arc flash energy away from data center personnel is called “arc resistant.” Arcresistant switchgear, for example, utilizes sealed joints, top-mounted pressure relief vents, and reinforced hinges to contain the energy and heat released by arc flashes and channel them via ducts to an unoccupied area inside or outside the data center
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Tomi Engdahl says:
3-phase switched PDUs available in hardwire and plug-in options
http://www.cablinginstall.com/articles/2014/03/tripplite-415v-pdus.html
Tripp Lite recently introduced eight new 3-phase switched power distribution units (PDUs) in both hardwire and plug-in options. The PDUs provide up to 28.8kW capacity, the company said. “These new PDUs support 415V 3-phase input to the rack, a highly efficient means of power distribution which yields three 240V single-phase outputs for IT loads,” the company said when announcing the products. “This 415V power design has been shown to reduce capital costs as well as inefficient power transformations, increasing data center efficiency and reducing operating expenses.”
“Data center design is constantly evolving and there is a definite need to meet the power demands of high-density data centers in the most-efficient manner possible. With 415A power now growing in the Americas, Tripp Lite’s newest switched PDU models meet this challenge and expand our broad offering of standard, in-stock items.”
Tomi Engdahl says:
Generator ratings and the implications for data centers
https://www.csemag.com/single-article/generator-ratings-and-the-implications-for-data-centers/56ea5433d0351c5b5518ea3e0debea4c.html
Understanding how generator ratings are determined is quite simple, but there is a long list of variables to consider. This reviews the fundamentals of generator ratings and a recent industry discussion about specific ratings for generators in data centers.
The Uptime Institute’s paper specifies that the generator must be “capable of supporting the site load on a continuous basis” and refers to ISO 8528-1 (International Standard for Reciprocating Internal Combustion Engine-Driven Alternating Current Generating Sets), in which four generator ratings are defined: standby, prime, limited running time, and continuous.
As a result, data center designers have specified generators with a “continuous” rating based on the peak demand of the site, which in turn has led to the installation of oversized generators that add unnecessary cost to the data-center design.
Here’s why specifying a continuous rating (as the Uptime Institute recommends) for generators in the data center industry is unnecessary.
When choosing the generator rating, you need to know how many hours per year you expect the generator to be used and what the load profile looks like.
the main causes of a generator’s failure to start or to operate during an outage are not due to engine life, but to fuel contamination, low or dead starting batteries, or a poorly run maintenance program that did not follow the manufacturer’s recommendations.
Tomi Engdahl says:
Electrical distribution equipment in the data center
http://www.cablinginstall.com/articles/2014/03/apc-data-center-electrical.html
A new white paper from APC-Schneider Electric explains electrical distribution terms and equipment types most commonly found in data centers.
Electrical Distribution Equipment in Data Center Environments
http://www.apcmedia.com/salestools/VAVR-8W4MEX/VAVR-8W4MEX_R0_EN.pdf
IT professionals who are not familiar with the concepts,
terminology, and equipment used in electrical distribu-
tion, can benefit from understanding the names and
purposes of equipment that support the data center,
as well as the rest of the building in which the data
center is located. This paper explains electrical distri-
bution terms and equipment types and is intended to
provide IT professionals with useful vocabulary and
frame of reference.
domki says:
Tremendous issues here. I’m very satisfied to look your article.
Thank you a lot and I am having a look ahead to contact you.
Tomi Engdahl says:
Examining data center power system harmonics
http://www.cablinginstall.com/articles/2014/04/green-grid-datacenter-harmonics-paper.html?cmpid=$trackid
A recent white paper from The Green Grid examines data center power system harmonics and provides an overview of this phenomenon’s effects on data center efficiency and reliability. “Harmonic currents can be a major factor in power quality and efficiency issues within a data center and can be a complex subject to understand,” states the paper. “Power quality issues associated with alternating current (AC) power line harmonics…can distort the voltage that is being consumed by information technology (IT) equipment, thereby disrupting the operation of the equipment.”
The paper notes that “ironically, these harmonic currents are usually caused by the power supply units (PSUs) within the IT equipment itself, but there can be other causes as well”
“some devices meant to improve power quality, such as uninterruptible power supply (UPS) systems, can actually create harmonic currents that could interfere with equipment further upstream”
“Harmonic currents are wasted energy that appears as heat.”
DATA CENTER POWER SYSTEM
HARMONICS: AN OVERVIEW OF
EFFECTS ON DATA CENTER
EFFICIENCY AND RELIABILITY
http://www.thegreengrid.org/~/media/WhitePapers/WP55_DataCenterPowerSystemHarmonics.pdf?lang=en
Tomi Engdahl says:
Paper examines different types of electrical meters for data centers
http://www.cablinginstall.com/articles/2013/january/apc-data-center-power-meters.html
A new white paper from APC-Schneider Electric provides guidance on the types of meters that might be incorporated into a data center design, explains why they should be used, and discusses the advantages and disadvantages of each.
The paper notes that there are several different types of meters that can be designed into a data center
Specific types of meters exist for various reasons
Tomi Engdahl says:
Voltage performance monitor sniffs out data center, critical IT equipment failures
http://www.cablinginstall.com/articles/2013/07/ideal-voltage-performance-monitor.html
New from from Ideal Industries, the VPM Voltage Performance Monitor works where the symptoms of poor quality voltage occur: at the point where equipment is connected. The company contends that, when a voltage problem is suspected as a cause of equipment failure, the traditional solution has been to place an analyzer on the main service. However, Ideal notes that this approach misses problems at the branch level where sags, swells, impulses, harmonics and other voltage events can adversely affect electronics.
Tomi Engdahl says:
Connect, monitor and control 16 PDUs via Ethernet cabling
http://www.cablinginstall.com/articles/2014/04/cannont4-smart-pdus.html?cmpid=$trackid
Cannon T4 Inc. recently released a line of power-management solutions that features the ability to use Category 6 patch cords to daisy-chain together as many as 16 power distribution units (PDUs), then monitor and control those PDUs via a single IP address over an Ethernet network.
Each PDU in the series features a 1.8-inch color LCD display, which the company says allows easily readable information such as current, voltage, power, energy consumption in kWh, power factor, humidity and temperature
Tomi Engdahl says:
Generator ratings and the implications for data centers
http://www.csemag.com/single-article/generator-ratings-and-the-implications-for-data-centers/23a32cf195c3ad7c85e1d2e2c480e6a6.html
Understanding how generator ratings are determined is quite simple, but there is a long list of variables to consider. This reviews the fundamentals of generator ratings and a recent industry discussion about specific ratings for generators in data centers.
Tomi Engdahl says:
Mitigating harmonics in electrical systems
http://www.csemag.com/single-article/mitigating-harmonics-in-electrical-systems/0fdc552157dd758226bc8f757fe2b252.html
Although devices using power electronics can produce distortion in electrical distribution systems, it’s up to the engineer to apply effective solutions to mitigate them.
Tomi Engdahl says:
Exploring dc power distribution alternatives
http://www.csemag.com/single-article/exploring-dc-power-distribution-alternatives/b73227a91fc4f74fc233cff10875ddd5.html
Engineers should know when and where the use of dc power distribution is appropriate, and when it is not. In applications where redundancy, immediate transfer capability, high availability, and energy storage are design criteria, direct current power solutions are beneficial.
Applications in which dc power is generated or directly used include:
VFDs
UPSs
Battery technology
Server technology
Mobile phones and tablets
Electric vehicles
LED lighting.
Switching devices are at the heart of dc power distribution systems.
Higher voltage, higher power, and higher temperature semiconductor switching devices continue to be developed and are used commercially at significant production levels.
Inherent to the use of power electronics-based dc distribution systems is the ability to reconfigure the system with power management software. Software can control the dc bus output voltage to initiate load transfer from one dc bus to another dc bus through auctioneering diodes. Similarly, power management can be used to change the dc bus voltage of VFDs for optimal motor efficiency. Power converters also lend themselves to diagnostics, metering, and fault-current limiting.
The switching devices—including thyristors, SCRs, insulated-gate bipolar transistors (IGBTs), and material developments in silicon carbide—enable higher efficiency power converters, motor drives, and UPSs.
In the data center industry, dc battery UPS systems are used extensively to power critical servers during ac power disturbances and source transfers
At the core of data centers are servers and telecommunications equipment that often convert ac power to dc for loads that use 12 V dc. Installations exist that use significant battery rooms and immediately invert through a UPS up to 120/208 V ac, 240/415 V ac, or 277/480 V ac; distributing power; and then converting it back to 12 V dc through multiple converters
Progress has been made in the development of 125, 250, and 380 to 400 V dc system standards.
Standards for 125 and 250 V dc, which are widely used in powering relaying equipment, include:
IEEE 399: dc load flow and short circuit analysis recommended practices
IEEE 485: battery sizing recommended practices
IEEE 946: dc system analysis methods.
The 380 to 400 V dc standards are progressing with UL listed equipment. European Telecommunications Standards Institute and International Telecommunications Union standards have been released including 240 V dc power supply systems for telecommunications.
Data centers also use a significant number of variable speed driven motors for cooling pumps and fans where a redundant dc bus may be beneficial to power multiple drives.
The automotive industry has produced a reliable battery technology, which has driven down the cost of lead acid batteries. The advent of hybrid and full electric vehicles has driven the industry to pursue other higher power density battery technology.
Tomi Engdahl says:
Designing data center electrical distribution systems
Designing efficient and reliable data center electrical systems requires looking through the eyes of the electrical engineer—and the owner.
http://www.csemag.com/single-article/designing-data-center-electrical-distribution-systems/354ee1bceac807a9da6ee540ac413ed2.html
Learning objectives
Understand the preliminary considerations of designing data center electrical distribution systems.
Know how to design efficient data centers that can also accommodate growth.
Identify the codes and standards that apply to designing data center electrical distribution systems.
This article explores data center design through the eyes of both the owner and the electrical engineer. It also discusses the key components of data centers and touches on the codes and standards that apply to data centers and their components.
Capacity: Before deciding anything else, the owner must decide the capacity of the data center (in megawatts). In previous planning efforts, it was common to use W/sq ft. However, today it is more common to discuss kW per rack, which may vary from 5 to 60 kW. This power concentration per rack can also drive cooling system type and capacity, which must be planned for in the capacity. The owner also needs to consider future capacity.
Another big decision is to determine the level of redundancy. Reliability is very important for data centers, and disruptions are costly. But the cost of building a data center increases significantly with higher reliability. Therefore, the owner should decide where to draw the line, and determine how much risk is acceptable.
Reliability and tiers: To classify data centers in terms of reliability, the Uptime Institute created standards referred to as Tiers (see Table 1). Data centers are classified in four Tiers. Tier I data centers don’t have a redundant electrical distribution system, and their components don’t have redundant capacity. Tier II data centers differ from Tier I data centers in that they have components with redundant capacity. Tier III data centers have dual-powered IT equipment and more than one distribution path to the servers. Tier IV data centers have all the features that Tier III data centers have. In addition, Tier IV data centers are fault tolerant in that they have more than one electrical power distribution path. Tier IV data centers have HVAC equipment that is also dual powered and have storage capacity.
Power distribution: Currently, there is debate about what kind of electrical power to use to feed data centers. Should it be ac or dc? Each has merits. Recently, dc power has received increasing consideration because data center computing equipment uses dc power. Having dc power distribution eliminates the need for transformers and ac-to-dc converters on the server floor. Using dc also eliminates harmonics because there is no switching of power. In addition, using dc eliminates conversion steps, which leads to higher efficiency (each conversion step introduces losses), thereby decreasing cost.
However, ac has been the dominating form of power distribution for many years
The benefits of ac include readily available equipment, lower costs, and easier maintenance (because the maintenance crews already know the equipment and the spare parts are readily available). Historically, most ac power distribution systems were designed at 208/120 V. The ever-evolving technologies have helped make the case for using higher ac voltages at 400/415 V, and even 480 V because of the higher power demands and efficiencies delivered by newer electrical equipment.
Power distribution elements: There are many parts to electrical power distribution. It starts with utility transformers, which in large data centers are owned by the data center’s owner. After the power is stepped down from the utility transmission voltage to the distribution level, it goes through distribution switchgear that redirects power to where it is needed. Typically, the power must be stepped down again, more often than not, via substation transformers and through more than one path. The standby power, usually present in today’s data centers, is often introduced at this level, bringing with it the automatic transfer switch equipment. From the ATS, the power goes to the servers (often via a UPS system), where it switches from ac to dc power to be used by the servers. The next layer of distribution includes switchboards and panelboards that feed the auxiliary load, HVAC loads, and regular house loads. Power monitoring systems could also be employed at this point, which could provide very important information on how different pieces of equipment are working and how power is being used.
Going through so many pieces of equipment requires meticulous work.
Relevant codes
The utility service will most likely be medium voltage. Depending on the size and location of the data center, the service could be between 13.8 and 345 kV. The next step is to step down the voltage to a level usable for the servers. Most data center IT equipment works with dual voltage, 100 to 120 V ac and 200 to 240 V ac. The higher voltage—208 or 240 V—increases efficiency, thereby lowering losses. Having servers powered at 415 V ac further increases data center efficiency, making for a better PUE. If the designer decides to use the higher voltage, 415 V, the auxiliary mechanical load would then be at 480 V. This means that autotransformers must be used to take the power from 415 V to 480 V.
At what point does one decide to convert the medium voltage to low voltage (below 600 V)? The answer to this question depends on the size of the data center and the distance from the service drop.
If the service voltage is higher than 13.8 kV, the first transformation will be at the service entrance, stepping down the voltage from whatever the utility voltage is to 13.8 kV. This power is delivered to the data center where the second transformation takes place, stepping the voltage down to 480 V or 415 V.
Redundancy: What sets data centers apart is the level of redundancy. But everything comes at a price. The more layers of redundancy that are added, the more expensive construction of the data center becomes. Granted, having a data center blackout (or brownout) is very expensive as well.
Tomi Engdahl says:
Managing power through networked electrical systems
Engineers should consider the benefits of networking electrical systems—monitoring and controlling power, its usage, and how it affects system reliability.
http://www.csemag.com/single-article/managing-power-through-networked-electrical-systems/6d41a81ad7f1ea9d6615f249a0229c38.html
Tomi Engdahl says:
Specifying a multi-mode UPS in data centers
Engineers should consider lifecycle cost and energy efficiency models for evaluating data center uninterruptable power supply (UPS) systems.
http://www.csemag.com/single-article/specifying-a-multi-mode-ups-in-data-centers/4e23637d5a699764670ccaa415d1b19d.html
Learning objectives:
Understand the impact of uninterruptible power supply (UPS) power conversion technologies on data center power efficiency.
Examine the energy efficiency issues of traditional double conversion UPS systems versus higher efficiency, multi-mode UPS power conversion technologies.
Understand how to apply a lifecycle operating expense (OpEx) versus a capital expense (CapEx) model based on higher UPS power conversion efficiencies.
According to the Uptime Institute, traditional transformer-based UPS devices represent only 12% of a typical data center’s energy consumption, given power use and energy conversion inefficiencies and heat loss. Although they account for only a fraction of the total energy consumption in a data center, even small improvements in UPS energy conversion efficiencies can add up to significant lifecycle operational cost savings. A study by Frost and Sullivan found that the U.S. could reduce its yearly consumption of electricity by up to $3 billion by increasing the energy efficiency of UPS units in data centers from 90% to 98%.
Traditional double conversion UPS units (see Figure 1)—which protect the load during outages—use a rectifier to convert the alternating current (ac) power to direct current (dc) power, and an inverter to provide safe and clean ac power to the load using either the main or battery power.
Unfortunately, in this scenario power efficiency is the price paid for protection. Transformer-based double conversion UPS systems have a typical power efficiency rating in the range of 88% to 92%. As a result, double conversion UPS systems place a steep toll on annual data center energy operating budgets.
Newer three-level insulated gate bipolar transistor (IGBT) UPS technologies, which reduce switching and filtering power conversion losses, offer efficiency levels approaching 97% in double conversion mode, and up to 99% efficiency when operating in energy-saving multi-mode. These new, three-level UPS topologies create new OpEx rationales when designing data center power systems and specifying UPS technologies.
When a multi-mode UPS unit’s responsive monitoring technologies detect any sort of deviation on the main or bypass power path, the inverter is immediately turned on to allow quality power to flow from the double conversion premium protection mode. In the same instant, the static switch on the bypass path from the utility is turned off to block the disturbance from reaching the load.
A variety of disturbance analyzers and fast-switching technologies are employed in combination, including:
An instantaneous adaptive voltage error detector that monitors subtle changes in amplitude and duration
A root mean square (RMS) voltage error detector that computes the RMS of all three UPS output voltages for variances
An output short circuit detector that, after a breaker is tripped, will automatically increase line current to rapidly clear and reset the breaker
A sophisticated transient inverter controller that quickly manages the transfer of the load to inverter power and back again to the bypass path.
All of these advanced monitoring and control systems work in concert to anticipate and respond to a comprehensive set of possible power conditions, creating a transfer switch speed of less than 2 ms. This speed helps to maximize the intermittent transfer to double conversion protection, while maintaining higher multi-mode efficiency for the majority of the time when quality utility power is flowing.
Tomi Engdahl says:
Managing power through networked electrical systems
Engineers should consider the benefits of networking electrical systems—monitoring and controlling power, its usage, and how it affects system reliability.
http://www.csemag.com/single-article/managing-power-through-networked-electrical-systems/6d41a81ad7f1ea9d6615f249a0229c38.html
Energy is a major operating expense for most organizations and, according to EnergyStar.gov, can represent 30% of a typical commercial office building’s operational costs (see Figure 1). However, managing energy usage can be a daunting task. The facility manager is often fighting mounting pressure to lower costs while energy prices are on the rise.
Measurement and verification
There are several aspects of networking electrical systems that must be considered. Step No.1 is to correlate the popular management statement as it relates to energy: “You can’t manage what you don’t measure.” Understanding what drives energy usage is the first key to managing it. Interpreting the data and recognizing what to do with them is the next step in successfully implementing changes in the system to provide the desired end result.
Using the available guidelines is an appropriate starting point for the engineer to design a solution that provides the facility manager with the proper tools to manage energy in the facility.
Some monitoring solutions may be as simple as monitoring the main power service and a few of the high-level distribution feeders. This rather simple system allows the facility manager to monitor the overall power quality and correct it at a system level. This type of monitoring has been around for quite some time; however, this type of approach is not exactly a networked solution. A fully networked electrical system incorporates a much broader range of system components including those that generate energy as well as use it
Fully networked electrical systems are migrating together all aspects of energy consumption and generation
Ensure optimum operation: When a facility’s energy infrastructure is properly designed and commissioned, optimum operating ranges are established based on uncontrollable factors such as weather, occupant load, etc. Over time, the optimum setpoints tend to shift for any number of reasons. The networked system diagnostics may be set to alert the facility manager when equipment is not operating at its optimum setpoint or using more power than anticipated so that corrective action may be implemented. Examples include leaking valves, faulty economizer damper controls, and manual overrides.
Improve reliability and power quality: “Dirty power” is the buzz phrase given to electrical anomalies that exist in a facility. Anomalies such as surges, sags, spikes, and transients can wreak havoc on sensitive equipment if not properly managed. Dirty power originates both outside and within a facility.
Prevent premature equipment failure: Monitoring large motors and HVAC equipment creates a predictive maintenance program by identifying when the equipment performance begins to fall below preset levels or other unexpected anomalies occur.
Tomi Engdahl says:
The world’ first: UL certification for socket-outlet and plug for 10A 400V class DC distribution system
http://www.fujitsu.com/emea/news/pr/fceu_20141208-01.html
NTT FACILITIES, INC. (Minato-ku, Tokyo, President: Kiyoshi Tsutsui) and Fujitsu Component Limited (Shinagawa-ku, Tokyo, President: Koichi Ishizaka) obtained UL(1) certification for its first of a kind socket-outlet and plug for 10A 400V class DC distribution system.
The DC distribution system (voltage level around 400 V d.c. in ICT or similar application) eliminates energy loss by DC-AC conversion and realizes highly efficient electricity distribution.
The DC distribution system has been required to ensure safe operation such as the prevention of arc discharge which occurs by current interruption and electric shock. To meet these requirements, NTT FACILITIES and Fujitsu Component jointly developed a socket-outlet and plug for 400V class DC distribution system. It has been mainly adopted in datacenters in Japan since NTT FACILITIES’ promotion starting in November 2010.
The socket-outlet and plug features following multi-tier safety constructions:
Embedded arc extinguishing magnet assisted module breaks arc discharge in a short time
Control make/break by mechanical slide switch which also prevents withdrawal of plug by mistake
Using flame-retardant safety agency materials
With these safety functions recognized, the socket-outlet and plug for 400V class DC distribution system obtained certification of the safety standard UL 2695(2) for the first time in the world.
Tomi Engdahl says:
PDUs rack up intelligence and global penetration
http://www.cablinginstall.com/articles/print/volume-23/issue-3/features/data-center/pdus-rack-up-intelligence-and-global-penetration.html
Recent market analysis shows that rack PDUs are the fastest growing product group, and intelligent units are growing faster than other types.
A recently published market-analysis report from IHS, titled “Rack Power Distribution Units – 2015″ indicates that the higher-priced rack PDU products are the fastest-growing segment of that market. The report’s analysis also explains why intelligent units are experiencing relatively brisk uptake.
“Global revenue from rack PDUs is forecast to grow 5.6 percent in 2015,”
According to research conducted by IHS, the rack PDU market’s 4.7-percent revenue growth rate in 2014 put it ahead of these other data center infrastructure product groups. Uninterruptible power supplies were the only product group to recede in 2014.
In 2014, the firm says, intelligent rack PDUs accounted for 19 percent of unit shipments globally and 58 percent of revenue. They are forecast to grow more than twice as fast as non-intelligent rack PDUs.
The IHS report also includes detail on the adoption of higher-voltage power architectures, as McElroy referred to in her comments. IHS explained, “Some data centers in North America have begun deploying higher-voltage power architectures. Because of the lower standard voltages in the Americas, this region has transitioned from single-phase rack PDUs to three-phase rack PDUs sooner than other regions. Traditionally, North American three-phase power is 208 VAC whereas European three-phase is 400 VAC. However, new statistics from this study show that there has been some adoption of 400 VAC rack PDUs in North America, where they accounted for more than 5 percent of revenues in 2014.”
Data centers have begun adopting 400 VAC because it reduces the number of electrical drops, IHS said, they can lead to electrical and infrastructure savings, and they contribute to overall efficiency increase. “While the efficiencies gained aren’t enough to justify retrofitting an existing facility with a new power architecture, adoption has been seen in new large data centers,” IHS noted. “The fact that some legacy or specialized data center equipment cannot be powered in 400/240 VAC scheme and would require additional step-downs is a barrier to adoption.”
McElroy added, “The more granular data on three-phase rack PDUs in the report this year will allow us to better understand and track this trend going forward. We anticipate seeing an uptick in the adoption of three-phase 400 VAC rack PDUs if new data center buildouts continue to pursue the higher-voltage power architecture.”
Many technologies exist to enable power-use monitoring, but we will focus briefly here on one technology in particular-Universal Electric Corporation’s (UEC; http://www.uecorp.com) Starline Track Busway Critical Power Monitor.
“With a variety of communications options standard, via wired Ethernet and Modbus, the CPM offers seamless integration with BMS [building management system] and DCIM [data center infrastructure management] packages. An optional 802.11n WiFi version is also available.”
“With the data center/mission critical market’s growing need for energy efficiency, energy monitoring systems are more important than ever,”
IHS’s analysis of the PDU market also included insight into the use of higher-voltage power architectures in North America.
In summing up the white paper’s points, Raritan says, “Whether you operate a large, a medium or even a small data center, it may be time for you to consider deploying high power to at least some of your racks. Good candidates are racks that will be packed with 1U servers, racks with blade servers and racks with data center networks or storage devices. Moving to higher voltages, whether single phase or three phase, reduces transmission losses, which leads to energy savings. Higher voltages, especially when deployed as three-phase power, are a good way to increase rack power capacity without adding to cable clutter and blocking cooling air in under-floor plenums. High power racks, coupled with in-row or overhead local cooling, also eliminate the energy waste from moving air across the room because cooling is now localized.
“There are several high-power alternatives from which to choose,” Raritan says, and includes a handful of examples in the paper. “The best alternative for you depends on your current situation and plans for the future. But high-power deployments, even three-phase 400V, are becoming more common and accepted and should be on your short list of deployment options.”
Tomi Engdahl says:
How does IBM go about supplying almost 8MW to 1.6M microprocessor cores?
A block diagram of a BGQ power distribution system
The Bulk Power Modules (BPM) convert 480VAC to 48VDC for distribution to the midplanes.
Each compute rack supplies around 25KW to its associated cards.
The 480V 3-phase AC supplies four independent power systems, which convert it to 48VDC. From there, the 48V is routed to each node card via two cables, each with an inline fuse. Sequoia uses 96 racks to achieve petaflop performance.
An unpopulated BCQ node card contains multiple 48V-input power supply modules based around Vicor’s Factorized Power architecture (a total of 2.8kW ), plus fibre-optics and other communication circuitry.
Primary processor power is 0.8V @ 130A. A node card contains 32 compute cards when fully populated.
The PRMs translate 48V into a regulated bus voltage and are hot-pluggable. The VTMs act as current multipliers with 32:1 input/output voltage ratio and up to 96% efficiency.
Source: http://www.edn.com/design/power-management/4438985/2/Up-Against-The–Power–Wall–Power-Management-And-The-Path-To-Exascale-Computing
Tomi Engdahl says:
Utility companies typically use medium voltages (5 kV or 15 kV) to distribute power to customers.Commonly used local distribution voltages are 4,160 V, 12.47 kV, and 13.8 kV, while transmission lines that traverse greater distances use higher voltages such as 69 kV and higher. The voltage may be boosted at the production source to a higher voltage for transmission and then reduced to a medium voltage at a neighborhood utility substation. Voltage is reduced again (typically 480 V) at a utility pad-mounted transformer to provide service to an individual building, then reduced to 208 Y, 120 V via a dry-type transformer in a building electrical room
The concept of using the highest voltage available also applies to power distribution within buildings. In large commercial buildings, 480-V, 3-phase, 4-wire power is commonly used to serve large mechanical equipment. Lighting is typically served at 277 V while 120 V power is needed for receptacle loads.
For common 3-phase dry-type distribution transformers, the minimum required efficiencies ranged from 97.0% for a 15 kVA transformer to 98.9% for a 1,000 kVA transformer.
If the load is known to produce harmonics, K-rated or harmonic mitigating transformers should be considered.
Harmonic mitigating transformers are typically very efficient, exceeding the efficiency levels set in NEMA TP 1, although they are exempt from meeting this requirement. The application of harmonic mitigating transformers remains controversial, with some manufacturers only recommending such transformers to correct a known existing problem, while others recommend including harmonic mitigating transformers for new construction projects.
A low-voltage dry-type transformer designed for optimum efficiency at 35% of nameplate load has greater impedance than a transformer manufactured for optimal efficiency at 100% loaded conditions.
Source: http://www.csemag.com/single-article/increasing-transformer-efficiency/266a2aa0de473faed9ffdb9a97ff4162.html
Tomi Engdahl says:
Front-end module performs 380-V to 48-V bus conversion
http://www.edn.com/electronics-products/other/4439666/Front-end-module-performs-380-V-to-48-V-bus-conversion?_mc=NL_EDN_EDT_EDN_today_20150611&cid=NL_EDN_EDT_EDN_today_20150611&elq=2267ca3beabf46a2a58ba5b2164d8d66&elqCampaignId=23409&elqaid=26395&elqat=1&elqTrackId=6b11bf77e15d4511986b4486e0113f59
Operating from a nominal input of 380 V, the VIA BCM DC/DC bus converter from Vicor delivers an isolated 48-V SELV (safety extra low voltage) output from a 9-mm thin module that incorporates EMI filtering, transient protection, and inrush current limiting.
The 1.75-kW VIA BCM modules can be paralleled to provide multi-kW arrays for high-voltage DC distribution in data centers, microgrids, ICT equipment, ATE, and industrial systems. In addition to achieving efficiency of up to 98%, the bus converter provides PMBus digital communication to allow control and telemetry capability within the system design. Module dimensions are 4.91×1.40×0.37 in. (124.77×35.54×9.30 mm).
VIA BCM®
High Voltage Bus Converter Module
http://www.vicorpower.com/via-bcm
Tomi Engdahl says:
Evaluating UPS system efficiency
http://www.csemag.com/single-article/evaluating-ups-system-efficiency/acdb95ef5dddca47ff4575040faa1e93.html
Many modern uninterruptible power supply (UPS) systems have an energy-saving operating mode. Data show that very few data centers put it to use because of the potential risks.
“Eco mode” is a term used with many different pieces of equipment to define a state of operation in which less energy is consumed, which is a more economical operation. When the term is used in reference to a smartphone or car, it generally means some sort of toned-down operation where not all the functions are available and the system runs certain functions at slower speeds to consume less energy. Whether this affects the overall operation of the equipment depends on what task the equipment is performing.
The main function of an uninterruptible power supply (UPS) is to protect the critical load during an outage by supplying backup power from a stored-energy device, and by providing stable voltage and frequency. Similar to other equipment, the intent of running the UPS system in eco mode is to increase efficiency by reducing the amount of energy consumed by the UPS. The Green Grid defines eco mode as “one of several UPS modes of operation that can improve efficiency (conserve energy) but, depending on the UPS technology, can come with possible tradeoffs in performance.”
Tomi Engdahl says:
Implementing microgrids: Controlling campus, community power generation
Microgrids can lower cost and raise reliability for the owner, and for surrounding communities.
http://www.csemag.com/single-article/implementing-microgrids-controlling-campus-community-power-generation/04146d15974998d99b3b1426fb1e80df.html
Microgrids are subsets of the regional electrical grid that have the ability to operate independent, or “island,” from the local utility. Microgrids normally operate in parallel with the utility, but they can operate in an isolated mode when utility service is interrupted or providing poor power quality. The design and operation of microgrids are optimized around the needs of the specific end users they serve. Because of their closer proximity to the end user’s loads, microgrids can provide more reliable and resilient power and a lower net cost of thermal and electric energy than can many utilities. They also are less subject to storm damage than long overhead utility cables. Microgrids can include conventional power generating equipment, energy storage, and renewables.
Tomi Engdahl says:
Evaluating UPS system efficiency
http://www.csemag.com/single-article/evaluating-ups-system-efficiency/acdb95ef5dddca47ff4575040faa1e93.html
Many modern uninterruptible power supply (UPS) systems have an energy-saving operating mode. Data show that very few data centers put it to use because of the potential risks.
“Eco mode” is a term used with many different pieces of equipment to define a state of operation in which less energy is consumed, which is a more economical operation.
The main function of an uninterruptible power supply (UPS) is to protect the critical load during an outage by supplying backup power from a stored-energy device, and by providing stable voltage and frequency. Similar to other equipment, the intent of running the UPS system in eco mode is to increase efficiency by reducing the amount of energy consumed by the UPS.
Does running the UPS in eco mode affect the operation of the UPS, making the overall system less reliable and potentially putting the critical load at greater risk?
When designing a data center, most engineers, owners, and operators focus on the mechanical system and the ability to use free cooling to lower the PUE and increase efficiency. The electrical system, however, also wastes energy in the form of losses due to inefficiencies in the electrical equipment and distribution system. On average, electrical distribution system losses can account for 10% to 12% of the total energy consumed by the data center.
Legacy electrical distribution
In a typical legacy data center electrical distribution system, there are four components that contribute to the majority of the losses:
Substation transformers: transformer no-load and core losses
UPS: rectifier and inverter losses
Power distribution units (PDUs): transformer no-load and core losses
IT power supply: rectifier and transformer losses.
One method of reducing losses that does not affect the operation of the data center is using or replacing equipment like substation and PDU transformers with more efficient equipment. I
Another method of increasing efficiency is to eliminate the equipment with the most losses. This method requires different power strategies, such as implementing higher-voltage ac and dc distribution to eliminate equipment like PDU transformers, UPS invertors, and IT power supply rectifiers. Each of these power strategies has advantages and challenges that impact the operation of the data center, so they must be evaluated when planning a data center.
A third method that manufacturers are recently promoting, and some facilities are starting to implement, involves the operation of the UPS system in some type of economical or eco mode. This mode of operation increases efficiency by eliminating the rectifier and inverter losses in the UPS.
Final thoughts
Traditional eco mode has many negative effects that reduce reliability. Because of that, data center operators and other mission critical type operations previously were not willing to put the critical load at greater risk just to save money on operating costs.
Situations where data center operators tend to be more willing to use eco mode is a UPS system supporting continuous cooling, and a 2N UPS system where only one of the UPS systems (either A or B) is running in eco mode.
The number of transfers from eco to double-conversion should be minimized.
Tomi Engdahl says:
What kind of connectors to use for 400V DC power?
Saf-D-Grid® 400 – up to 30 Amps
http://www.andersonpower.com/us/en/products/saf-d-grid/400-vdc.aspx
First Mate, Last Break Ground Contact
Integral Latch
Hot Plug Rated
Touch Safe / Shock Protection
Arcing Protection
Voltage (AC/DC)
• UL 1977 / CSA 22.2 600
• IEC 400
Current Rating (Amperes) 40
Hot Plug Rated
• 250 cycles 400V @ 440A in-rush
• 250 cycles (UL) 400V @ 20A load
Fault Current Withstand
UL 467 14 AWG, 300A, 4 Sec.
Touch Safety with Connector Housing
IEC 60529 IP20
Tomi Engdahl says:
What’s all the fuss about arc flash and electrical safety?
http://www.csemag.com/single-article/whats-all-the-fuss-about-arc-flash-and-electrical-safety/00b9a89a2dd342799a166ecbba760885.html
Everyone is aware of the shock hazard that is present with electrical equipment, but how aware are you of the arc flash hazard that may be present?
There has been a lot of emphasis on electrical safety within both our company and the construction/operations industry during the last couple of years.
Everyone is aware of the shock hazard that is present with electrical equipment, but how aware are you of the arc flash hazard that may be present? While a shock hazard exists from coming into contact with live energized conductors, an arc flash hazard may be present by just being in the same room with electrical equipment, whether or not the conductors are exposed.
An arc flash is caused by an electrical arcing fault or short between two energized conductors or an energized conductor and neutral or ground. The first component of an arc flash, the available energy in the arcing fault (measured in kilo-amperes or kA), is determined by the available short-circuit current or bolted-fault current at the location of the fault. There are a number of factors that determine this value including the available utility short circuit at the building source, the voltage of the system, the size of transformers and their associated impedance (or resistance to current flow), and the length and size of conductors in the system up to the point of the fault.
The second component of an arc flash is the duration of the arc. This is the most important factor in determining the intensity of an arc flash. A common misconception is that higher-voltage equipment or higher-amperage busways have a higher arc flash hazard. This may or may not be true. Often, the higher-voltage and -amperage systems produce arcing faults that have very high-arcing fault currents, but the upstream overcurrent-protection devices (OPDs) open and clear these faults very quickly.
Most people would say this hazard level is only applicable if the panel door is open with the live conductors exposed. This reasoning is incorrect. The equipment manufacturers test their equipment to withstand the short-circuit current rating and contain any products of combustion to prevent a fire. They do not rate their standard cabinets to withstand arc faults. Therefore, an arc fault incident could cause the enclosure to rupture and subject personnel to high arc flash energy levels in addition to flying shrapnel and other hazards.
So what does this mean for test-and-balance and commissioning personnel? First and foremost, they must understand the hazards that may be present around electrically energized equipment
Personnel must search out the facts and understand the hazards. To do this, a person must be able to read an Arc flash warning label that should be posted on most new equipment.
This label provides all of the required information to determine what is needed to be safe around a piece of equipment. The flash protection boundary indicates the distance from the equipment where an arc flash could cause a second-degree burn to bare skin (1.2 cal/sq cm). Within this boundary, the stated HRC must be utilized to determine arc flash PPE as shown on the label. The shock hazard is also listed. The limited approach for unqualified personnel will typically be the same as the arc flash boundary.
Tomi Engdahl says:
Getting equipment SCCR code requirements right
Complying with the latest NEC and OSHA requirements will improve equipment protection, electrical safety, and power reliability.
http://www.csemag.com/single-article/getting-equipment-sccr-code-requirements-right/9e63e57c0aa3fc85609e7f1f5e005383.html
Short-circuit current rating (SCCR) is the amount of available fault current that an electrical component or equipment can safely withstand, when properly applied. Adequate SCCR is imperative to support a safer workplace and protect equipment. Consequently, OSHA and NFPA 70: National Electrical Code (NEC) have specific SCCR requirements for equipment, such as industrial control panels, industrial machinery, general equipment, and HVAC equipment. Failure to provide equipment with adequate SCCR can have serious consequences including exposure to arc blast, flying debris, electric shock, burns, and others.
An effective SCCR strategy strives to achieve the necessary equipment SCCR with minimal costs, resources, and effort
That said, there are a three basic concepts for developing an effective SCCR strategy:
Determine the available fault current
Define and document the minimum acceptable equipment SCCR requirement
Require all equipment suppliers to provide an SCCR analysis for all equipment specified for a project.
The first step is understanding the available fault current level—the amount of current that would be present in the event of a short-circuit event. Determining the amount of available fault current depends on a variety of variables, including available fault current from the utility (typically, an unknown and subject to change), size of the upstream transformers, fault generation from motors, circuit impedances, voltage drop, short-circuit power factor, and more. The complexity and interaction of these variables can make an exact calculation difficult. That said, a conservative approach can be used to quickly and cost-effectively estimate fault current levels and the amount of SCCR protection required for a specific location.
A “worst-case” available fault current calculation assumes a worst-case condition and is intended to minimize the risk that the calculated available fault current level is too low.
it is critical that all equipment suppliers provide an analysis of the control panel’s equipment SCCR determination
Tomi Engdahl says:
Quarter-brick converters sport digital or analog interface
http://www.edn.com/electronics-products/other/4440915/Quarter-brick-converters-sport-digital-or-analog-interface?_mc=NL_EDN_EDT_EDN_productsandtools_20151130&cid=NL_EDN_EDT_EDN_productsandtools_20151130&elq=4072ffe490124c44843d2e15f3b17184&elqCampaignId=25931&elqaid=29553&elqat=1&elqTrackId=221f6b91596040008d155d1eebf72898
Isolated DC/DC converters in the ADQ500 series from Artesyn deliver 500 W of power for telecom-network and data-center equipment. The quarter-brick devices come in versions that allow digital or analog control and occupy industry-standard DOSA footprints.
Digital-interface converters use the PMBus command protocol for control and monitoring of voltage, current, temperature, and fault reporting. Standard analog control functions include output-voltage trim, output-voltage sense compensation, and remote enable.
The ADQ500 series has an input voltage range of 36 V to 75 V.
ADQ500 Series
500W Quarter Brick
https://www.artesyn.com/power/power-supplies/websheet/575/adq500-series
They have an input voltage range of 36 to 75 V and are primarily designed for use with standard 48 V supplies in computing and server applications, as well as regulated 48V supplies in communications equipment.
ADQ500 series converters have an ultra high efficiency of typically 95.5% at full load and can operate over an ambient temperature range of -40 to 85˚C, making them an ideal choice for the isolated converter in a distributed power architecture supplying power to non-isolated converters. Their open-frame design is optimized for forced air or conduction cooling and an aluminium baseplate option is available for enhanced thermal performance. The conversion technology employs 175 kHz fixed frequency switching to help minimize external EMI filtering requirements.
Standard features protection features are input undervoltage, overvoltage lockout, output overvoltage, output overcurrent and overtemperature conditions.
Tomi Engdahl says:
Expanding the Cool-Power® ZVS Regulator Portfolio
space
New 48 V Buck Regulators Enable 48 V Direct to PoL Step-down Regulation with Peak Efficiency Exceeding 96%
http://www.vicorpower.com/new-products/cool-power-zvs-buck-regulator?utm_source=EEWeb&utm_medium=EmailNewsletter&utm_content=text_120x80_48V-buck&utm_campaign=ACPoL-48V-Buck
Tomi Engdahl says:
Google Joins Facebook’s Open Compute Project
http://hardware.slashdot.org/story/16/03/10/0038246/google-joins-facebooks-open-compute-project
Google has elected to open up some of its data center designs, which it has — until now — kept to itself. Google has joined the Open Compute Project, which was set up by Facebook to share low-cost, no-frills data center hardware specifications. Google will donate a specification for a rack that it designed for its own data centers. Google’s first contribution will be “a new rack specification that includes 48V power distribution and a new form factor to allow OCP racks to fit into our data centers,
Google joins Facebook’s Open Compute Project, will donate rack design
Google pulls back the curtain from some of its data center equipment.
http://arstechnica.com/information-technology/2016/03/google-joins-facebooks-open-compute-project-will-donate-rack-design/
Google today said it has joined the Open Compute Project (OCP), and the company will donate a specification for a rack that it designed for its own data centers.
Google’s first contribution will be “a new rack specification that includes 48V power distribution and a new form factor to allow OCP racks to fit into our data centers,” the company said. Google will also be participating in this week’s Open Compute Summit.
“In 2009, we started evaluating alternatives to our 12V power designs that could drive better system efficiency and performance as our fleet demanded more power to support new high-performance computing products, such as high-power CPUs and GPUs,” Google wrote. “We kicked off the development of 48V rack power distribution in 2010, as we found it was at least 30 percent more energy-efficient and more cost-effective in supporting these higher-performance systems.”
OCP Summit: Google joins and shares 48V tech
http://www.datacenterdynamics.com/power-cooling/ocp-summit-google-joins-and-shares-48v-tech/95835.article
Google has joined the Open Compute Project, and is contributing 48V DC power distribution technology to the group, which Facebook created to share efficient data center hardware designs.
Urs Hölzle, Google’s senior vice president of technology, made the surprise announcement at the end of a lengthy keynote session on the first day of the Open Compute event. The 48V direct current “shallow” data center rack, has long been a part of Google’s mostl-secret data center architecture, but the giant now wants to share it.
Hölzle said Google’s 48V rack specifications had increased its energy efficiency by 30 precent, through eliminating the multiple transformers usually deployed in a data center.
Google is submitting the specification to OCP, and is now working with Facebook on a standard that can be built by vendors, and which Google and Facebook could both adopt, he said.
“We have several years of experience with this,” said Hölzle, as Google has deployed 48V technology across large data centers.
As well as using a simplified power distribution, Google’s racks are shallower than the norm, because IT equipment can now be built in shorter units. Shallower racks mean more aisles can fit into a given floorspace.
Google is joining OCP because there is no need for multiple 48V distribution standards, said Hölzle, explaining that open source is good for “non-core” technologies, where “everyone benefits from a standardized solution”.
Tomi Engdahl says:
The Quest for Server Power Efficiency
APEC still focuses on data center power use
http://www.eetimes.com/author.asp?section_id=36&doc_id=1329224&
Glamour items like energy harvesting and wireless power transfer are likely to make “guest appearances” at next week’s APEC Conference. GaN transistor deployments will be carefully monitored. But on-going efforts to promote data-center energy transfer efficiency retain their “bread-and-butter” utility.
Energy transfer efficiency in data centers — and techniques for improving it — should be at (or near) the top of your list.
Although factory automation and commercial lighting — a rebuilding of our industrial infrastructure — are replacing computing and consumer electronics as the drivers for power product development, voltage regulator products with higher energy transfer efficiency still generate revenues for manufacturers of power management ICs, modules, and power discretes.
When you look at the power distribution chain for a medium-sized data center (about 935 kilowatts in 2014), you can spot pockets of waste and inefficiency. Running 7 days per week, 365 days per year, with (say) a 75% load such a data center will generate a $600,000 annual electricity bill (assuming a cost of 10 cents per kilowatt-hour). A mere one-percent improvement in power train efficiency provides a $6,000 annual savings.
Reducing data center power consumption
It turns out, a huge portion of the electricity bill — up to 60% in legacy equipment — is the cost of running cooling equipment.
The other cooling recommendation, driven by Facebook and the Open Compute Project, may have more demonstrable support. The Open Compute Project, whose members include Google, Quanta and HP, has been promoting standards for hyper scale computing card form factors. These would enable server cards to mechanically interchangeable. The bigger contribution to power management efficiency is in the streamlining of the airflow from the back or the card to its front. While this open frame architecture creates a greater reliance on small fans, it reducts the on-time for the room-sized fans and chillers. (It also jacks up the PUE rating by giving a larger weight to the IT equipment denominator.)
After a reduction in cooling costs, the reductions made by other techniques appear small. But they remain significant. There is consensus among data center systems providers — companies like Schneider Electric and General Electric (these days concentrating on IoT-enabled smart buildings) — that a significant energy savings can be provided by streamlining the power transmission train. This is done chiefly by reducing the number of the voltage conversions in the power transmission chain. Legacy power transmission chains would run the 480V AC coming into a building through a single large uninterruptable power supply (UPS) system, based on a lead-acid battery backup. The UPS would convert the AC to a lower voltage DC, to charge the battery, and then convert the DC back to a higher voltage to distribute to the racks. More contemporary thinking suggests keeping the UPS out of the circuit, putting it in a straight wire “bypass” mode, and switching the UPS back into the circuit only when a power line fault is detected. The high-voltage AC is delivered to the power supplies mounted in the racks. In many cases, the three-phase AC input is put through a transformer to generate single-phase AC, but the rack-mounted power supplies recommended by the Open Compute Project are intended to take a 277V AC input and output 12 volts DC, 480 watts per card.
Tomi Engdahl says:
Keith Lane: I see energy efficiency as the No. 1 trend. On the electrical side, we are seeing more efficient uninterruptible power supply (UPS) systems, 400/230 V system transformers, and topologies that allow for more efficient loading of the electrical components. On the mechanical side, we are seeing increased cold-aisle temperatures, increased delta T, outside-air economizers, and hot-aisle containment. On the information technology (IT) side, the 230 V electrical systems also increase the efficiency of the servers. UPS battery technology is also improving. We are seeing absorbed-glass-mat and pure-lead batteries as well as advances in battery-monitoring systems.
Sty: For many of our commercial-enterprise clients, their headquarters buildings contain a main distribution facility (MDF), an independent distribution facility, and other server rooms that have similar uptime requirements to their main enterprise data centers.
Lane: Increased power densities and modularity of the systems. Over the years, we have seen the average kilowatt per rack increase from 1 kW/rack to more than 10 kW/rack. We are seeing much more than 10 kW/rack in some higher-density areas within the data center. Coordinating the electrical and mechanical systems as well as both the UPS battery type and code-required battery electrolyte containment/ventilation within small data closets with space limitations is critical.
Source: http://www.csemag.com/single-article/data-centers-intricate-design/7ff170677500e930389dc7de73b495a5.html
Tomi Engdahl says:
Energy savings in electrical distribution systems
Consider these energy efficiency options for retrofitting existing and designing new buildings’ electrical distribution systems.
http://www.csemag.com/single-article/energy-savings-in-electrical-distribution-systems/eda3ad616aba5d9352ff4686d632091e.html
The codes and standards associated with energy efficiency establish the minimum energy efficiency requirements needed for the design of new buildings and renovations to existing buildings. The codes, however, are geared toward the efficiency of mechanical and lighting systems. Not a lot of information is provided within these codes to establish energy efficiency measures for the design of the power distribution systems, just the systems that the power distribution systems serve.
ASHRAE 90.1 includes a chapter on power (Chapter 8). Although the standard includes the requirement for transformers to meet the Energy Policy Act (EPAct) of 2005, it does not discuss other aspects of the power distribution system.
The standard also establishes that the voltage drop shall not exceed 2% for feeders and 3% for branch circuits (Chapter 8.4.1). Although ASHRAE 90.1 is not more stringent than NFPA 70: National Electrical Code (NEC) voltage-drop recommendations outlined in the fine point notes (FPNs) section included in Article 210.19, ASHRAE 90.1 does establish voltage drop as a requirement for meeting the standard. An NEC FPN recommends a maximum voltage drop of 5%, with the feeders to not exceed 3%
Copper versus aluminum
Copper and aluminum are the most commonly used materials for conductors, busing in distribution equipment, and windings in transformers. There is a common misconception that because copper is more conductive than aluminum, copper distribution equipment will be more energy-efficient than aluminum. That is not the case. There are other factors to take into account including conductor size, equipment size, cost, and weight of the equipment and conductors.
Depending upon the alloy of aluminum used for the conductors or bus, the conductivity of aluminum is approximately 56% to 61% that of copper. Although the difference in conductivity is significant, this will not significantly affect the overall efficiency of the distribution equipment because the panelboards, switchboards, and transformers because, regardless of the material used, the equipment is still required to meet NEMA and UL standards for temperature rise, which would affect the efficiency of the equipment.
Similarly, although the conductors will be larger, the efficiency of the cables will not be affected.
The cost of the materials is dependent upon the market. However, it is typical to see the following cost savings when using aluminum: 30% to 50% for dry-type transformers, 20% for substation dry-type transformers, 25% for liquid-filled pad-mounted transformers, $1,000 per vertical section for a 1,000-amp switchboard, and $1,500 per vertical section for 3,000/4,000-amp switchboards.
Additionally, in regard to aluminum cable, the voltage drop is a larger factor to be considered because it is less conductive. On average, the equivalent aluminum conductor will reduce the length a cable can be run by approximately 40% to still meet the ASHRAE-recommended 3% voltage drop.
The more significant difference is the reduction in weight, even though the busing/windings of the equipment have increased in size. As an example, a 1,000-amp busway will be approximately 22% larger for aluminum; the copper bus will be approximately 50% heavier. This will dramatically increase as the bus ratings increase. For instance, for a 4,000-amp busway, the size increase to aluminum over copper is approximately 27%; the weight increase is approximately 73%.
Tomi Engdahl says:
Power Distribution Considerations for Data Center Racks
http://www.emersonnetworkpower.com/en-ASIA/Products/RACKSANDINTEGRATEDCABINETS/PowerDistribution/Documents/MPH2%20AU%20Collaterals/Power%20Distribution%20Considerations%20for%20Data%20Center%20Racks%20-%20White%20Paper.pdf
Five major power distribution considerations for data center racks
• At what voltage do you run all the IT equipment?
• What electrical circuits do you bring to each rack?
• Number and type of outlets on the rackmount power distribution units
• What features do you look for within your rackmount power distribution units?
• Remote management of power distribution
At what voltage do you run all the IT equipment?
Most modern day IT equipment typically requires 1-ph power to
operate. However, most IT equipment can accept voltages within
the range of 100V – 250V. The reason is that all manufacturers like
to build universal power supplies that could be used around the
world. In North America, the electrical infrastructure within data
centers is capable of providing 120V (phase to neutral) as well as
208V (phase to phase), requiring data center operators to make
a choice between high and low voltage. In such situations, it is
recommended that customers choose the higher voltage (208V).
ndustry studies have revealed that running servers
at 208V can bring as much as two percent efficiency advantage
to the servers alone.
Outside of North America, choosing the right voltage is not an issue
as the electrical infrastructure provides only one voltage option
(220, 230 or 240V) that falls within the acceptable range.
Most IT equipment today comes with dual redundant power
supplies. To be able to leverage the redundancy built within the
IT equipment, data center operators should plan on bringing a
minimum of two sets of completely independent circuits (N +
N) into each rack.
a recent
survey of 100 large data center operators revealed that 81 percent
had load densities greater than the typical traditional power
density of 3kW /rack.
5 Power Distribution White Paper
While choosing the appropriate circuits to bring to the rack, it is
important to note that all data centers typically have 3-phase power
coming in.
for load densities >5kW / rack, customers should consider
bringing 3-phase power all the way to the rack level. Bringing
3-phase power to the rack level provides several benefits
If a data center operator chooses to use 3-ph power for some or all
the racks, the next decision point is whether to bring in a Wye-
supply or a delta supply to the rack.
Internationally, since all loads require a neutral wire to be able to
run 220 – 240V, a Wye supply is a must. In North America, if the
operators have chosen to run all equipment at 208V, a neutral is not
required and hence, a delta supply could be used. However, if there
is any piece of equipment running at 120V, a Wye-supply should be
used.
Rackmount power distribution units come in vertical
as well as horizontal form factors
Most modern day IT equipment comes with an IEC
input power connector and modular input cords.
In most situations, it makes sense for data center operators to
choose PDUs with IEC outlets.
The PDUs should have the appropriate number
of outlets required to power all IT load within the racks.
In order to ensure the highest availability levels for all mission
critical equipment, it is important that data center operators
consider power distribution units that have metering as well as
switching capabilities.
To minimize chances of overloads, metering capability within PDUs along
with the capability to set current thresholds is very important.
Switching capability defined as the
ability to remotely recycle, turn on or off power, is very important
to minimize the downtime associated with hung equipment.
Sequential startup and shutdown
Unless the electrical circuit is capable of handling
the inrush current of all equipment (which is seldom the case and
is very expensive), starting up all loads within a rack at once can
easily lead to tripped upstream breakers and unavailable loads.
applications running on several
servers can be dependent on each other and hence, they need to
be started up or shutdown in a particular order.
Electronic overcurrent protection: A PDU with just metering
capability can certainly monitor the current draw and send alarms
when programmed thresholds are exceeded.
When current thresholds are exceeded on a branch circuit,
most switched PDUs have the capability to lock any unused
outlets that reside on that specific branch. This ascertains that no
additional equipment gets accidentally plugged into that branch
Remote management
In order to make the maximum utilization of monitoring and control
features, and to help realize the vision of a “lights-out” data center,
it is important that switched and metered PDUs are able to be
managed remotely.
A well planned rack level power distribution strategy is important
to ensure continuous power to all IT equipment and to monitor and
control power consumption.
. Electrically, IT equipment should be chosen to run
within the 200 – 250 range whenever possible. When loads within
a rack exceed 5kW, a 3-phase PDU should typically be chosen while
a 1-ph PDU is good enough for loads below 5kW.
Tomi Engdahl says:
Retainers Improve the Effectiveness of IEC Plugs
https://journal.uptimeinstitute.com/retainers-improve-the-effectiveness-of-iec-plugs/
Today IEC plugs are used at the rack-level PDU and the IT device. IEC plugs backing out of sockets create a significant concern, since these plugs feed UPS power to the device. In the past, twist-lock cord caps were used, but these did not address the connection of the IEC plug at the IT device. Retainers are a way the industry has addressed this problem.
The International Electrotechnical Commission (IEC) plug is the most common device used to connect rack-mounted IT hardware to power. In recent years, the use of IEC 60320 cords with IEC plugs has become more common, replacing twist-lock and field-constructed hard-wired type IEC plug connections. During several recent site evaluations, Uptime Institute has observed that the IEC 60320 plug-in electrical cords may fit loosely and accidentally disconnect during routine site network maintenance. Some incidents have involved plugs that were not fully inserted at the connections to the power distribution units (PDUs) in the IT rack or became loose due to temperature changes fluctuations
Sometimes the cord is longer than the distance between the server outlet and the PDU, so the installer will coil the cable and secure the coil with cable ties or Velcro
This practice adds weight on the cable and stress to the closest connection, which is at the PDU. If the connection at the PDU is not properly supported, the connector can easily pull or fall out during network maintenance activity. Standard methods for securing PDU connections include cable retention clips, plug locks, and IEC Plug Lock and IEC Lock Plus.
Cable retention clips are the original solution developed for IT hardware cable installations
A Plug lock insert place over any C14 input cord strengthens the connection of the plug to the C13 outlet, keeping critical equipment plugged-in and running during routine rack access and maintenance.
C13 and C19 IEC Lock connectors include lockable female cable ends suitable for use with standard C14 or C20 outlets. They cannot be accidentally dislodged or vibrated out of the outlets
The IEC Plug Lock and IEC Lock Plus are also alternatives. Both products have an integral locking mechanism that secures C13 and C19 plugs to the power pins of the all C13 and C19 outlets.
Having a plan to change out older style and suspect cables will help mitigate or avoid incidents during maintenance and change processes in data centers.