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Why is power protection important?
No company can afford to leave its IT assets unprotected from power issues
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Losing power for as little as a quarter second can trigger
events that may keep IT equipment unavailable for anywhere from 15 minutes to many hours
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Some experts believe the U
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economy loses between $200 billion and $570
billion a year due to power outages and other disturbances
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By law, electrical power can vary widely enough to cause significant
problems for IT equipment
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S
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7 percent to 8
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That means that what utility
services promising 208-phase voltage actually deliver can range from 191 to 220 volts
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In the U
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, in fact, it's only 99
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•

The problems and risks are intensifying
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•

Generators and surge suppressors aren’t enough
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Surge suppressors help with power spikes but not with issues like
power loss, under-voltage and brownout conditions
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Once, IT played a supporting role in the enterprise
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When IT systems are down,
core business processes quickly come to a standstill
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The cost of power and cooling
has spiraled out of control in recent years
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Highly-efficient UPS systems
can help with this goal, and products are available today that were not an option even a few years
ago
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Provides backup power when utility power fails, either long enough for critical equipment to shut down
gracefully so that no data is lost, or long enough to keep required loads operational until a generator comes
online
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Conditions incoming power so that all-too-common sags and surges don’t damage sensitive electronic
gear
...
If the AC input supply falls out of
predefined limits, the UPS utilizes its inverter to draw current from the battery, and also disconnects the AC
input supply to prevent backfeed from the inverter to the utility
...
Two of the
most popular single-conversion designs are standby and line-interactive:

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•

Standby UPSs allow IT equipment to run off utility power until the UPS detects a problem, at which
point it switches to battery power
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•

Line-interactive UPSs regulate input utility voltage up or down as necessary before allowing it to
pass through to protected equipment
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Figure 1
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Double-conversion systems
As the name suggests, these devices convert power twice
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The output inverter then processes the power back to AC before
sending it on to IT equipment
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In normal operation, a double-conversion UPS continually processes power twice
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The UPS continues to utilize battery power until the AC input returns to
normal tolerances or the battery runs out of power, whichever occurs sooner
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Static Switch

DC Link

AC SOURCE

AC
Output

Rectifier/Charger

Inverter
Battery

Normal power flow
Stored energy power flow
Recharge energy flow
Emergency bypass power

Figure 2
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Multi-mode systems
These combine features of both single- and double-conversion technologies while providing substantial
improvements in both efficiency and reliability:
•

Under normal conditions, the system operates in line-interactive mode, saving energy and money
while also keeping voltage within safe tolerances and resolving common anomalies found in utility
power
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•

If AC input power falls outside the tolerances of the double-conversion rectifier, or goes out
altogether, the UPS uses the battery to keep supported loads up and running
...
Then it
transitions back to high-efficiency line-interactive mode
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Under normal conditions, they provide maximum efficiency
...
The end result is that data
centers can save tens of thousands a year on energy without compromising data center performance or
reliability
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eaton
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Figure 3
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How do I choose the right UPS for the job?
To ensure that you always end up with the right UPS for your needs, be sure to consider these eight issues
during your selection process:

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Topology
Question number one is should you get a single-conversion, double-conversion or multi-mode UPS? The
answer depends largely on how important energy efficiency is for your organization relative to protection
...
That
makes them a good fit for loads with a higher tolerance for failure
...

Double-conversion UPSs, which provide the highest levels of protection, are less efficient but are usually
the standard choice for protecting mission-critical systems
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Single phase versus three phase
When the utility generates power, it is at the three-phase level
...
Three-phase power
uses three separate “phase” wires, which allow higher power to be delivered to a single point or load
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Single-phase power is delivered through either one or two phase wires, which are derived from the utility
three-phase power system using transformers
...
Three-phase UPSs are generally the preferred choice for
high kVA applications, which are typically more sophisticated and have high compute densities
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Figure 4
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Rating
A UPS’s rating is the amount of load, in volt-amperes (VA), that it’s designed to support
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Use this very basic procedure to
determine the approximate UPS rating your organization requires:
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1
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2
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3
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4
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5
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2, to build in room for growth
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Here are a few additional
considerations to keep in mind:
•

Relying solely on nameplate ratings may lead you to oversize the UPS system, so always use your
equipment manufacturer’s sizing calculator tools as well, if available
...


•

When deploying a centralized power protection architecture, you typically deploy larger kVA UPSs
than you would deploy using a distributed power protection scheme
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Your UPS vendor can assist in applying the proper UPS and rating for these types of applications
...
2
when building in room for growth in the procedure above
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Form factor
UPSs come in a range of form factors that fit into two master categories: rack-mounted and freestanding
...
For companies with more modest needs, deciding
between rack-mounted and freestanding UPSs is largely a matter of data center design philosophy
...
Others prefer to maximize the amount of rack space available for servers by using freestanding
UPSs
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Availability features
Organizations can utilize a variety of deployment options, technologies and services to increase the
reliability of their power protection solution
...
There are three main kinds of
redundant UPS architecture:
•

Zone: In a zone architecture, one or more UPSs provide dedicated support for a specific set of data
center resources
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•

Serial: In a serial architecture, multiple UPSs are connected end to end such that if any one UPS in
the string fails, the others can compensate automatically
...
If any UPS fails completely, the other systems can keep protected
information technology equipment (ITE) loads operational
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eaton
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Zone protection uses separate protected “zones” and may use virtualization software to shift loads
to other zones during failures or maintenance
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UPS 1
AC SOURCE

Output
power
bus

Static Switch
UPS 2

Inverter

Rectifier

Static Switch
AC SOURCE

ITE
Loads
ITE
Loads

Inverter

Rectifier

ITE
Loads

Systems in normal operation
UPS 1
AC SOURCE

Output
power
bus

Static Switch
Rectifier

UPS 2

Inverter

Static Switch
AC SOURCE

Rectifier
Primary power path
Failover power path

ITE
Loads
ITE
Loads

Inverter

Fault

ITE
Loads

Systems in failover operation

Figure 6
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eaton
...
xn)
x1
u1
x2
u2
x3
u3
x4
u4
x5
u5
xn
un

UPS 2

ITE
Loads

Auto Maintenance
Bypass

Battery

Inverter

ITE
Loads

Rectifier

Inverter

ITE
Loads

Static Switch

AC SOURCE

System Control
f(x1
...
xn)
x1
u1
u2
x2
x3
u3
x4
u4
x5
u5
xn
un

Auto Maintenance
Bypass

Battery

Inverter

Figure 7
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Parallel systems must be synchronized together to share the loads
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Figure 8
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Extending battery runtime: A typical UPS battery provides five to 15 minutes of backup power
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Battery management: One of the most important parts of the UPS system is the energy storage system,
which is typically a battery
...
While large
banks of flooded electrolyte batteries for high power (greater than 500kVA) UPS systems need to have the
battery trickle charged, most non-spillable (VRLA, see “UPS energy storage” below) batteries used in
today’s lower kVA UPSs can benefit from a charging technique where the charger turns off and “rests” the
battery
...
This
technique helps increase battery service life by as much as 50 percent
...

Remote monitoring: The best way to address UPS problems is to prevent them from happening in the first
place
...
That enables technicians to make repairs before serious breakdowns have a chance to occur
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Figure 9
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The service
may also include monthly reports on your UPS and its health
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eaton
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To get as much value as possible
from that investment, companies should estimate their needs for the next three to five years when
comparing UPS options
...

Data centers with fluctuating needs or future requirements that are difficult to forecast can employ two
strategies to increase the scalability of their UPS deployment:
•

Deploy UPSs in parallel: Parallel UPS architectures boost scalability as well as redundancy
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•

Use modular UPS products: Some newer UPSs feature modular designs that allow you to add
capacity incrementally as requirements increase
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As
requirements increase, another 12 kW unit can simply be plugged in
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That’s a scalable and efficient
approach to keeping up with escalating power needs that also lowers upfront capital spending and
conserves data center floor space
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Communication software can not only provide real-time notification of UPS status,
but also lets you assign automatic actions to perform in case of a power event
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For the past 20 years, most UPS systems have come with software that would signal one or more servers
that AC power was lost and that the UPS was on battery
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When AC power
was restored, the system would automatically reboot, bringing the system back to its previous state
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Communication was established through an RS232 serial port, or via relays to a simplistic
control port
...
In this type of installation, the UPS is assigned its own IP address on the network and could be
accessed remotely by all servers being powered by that UPS, so each server could be programmed to shut
down or monitor the UPS for power issues
...
With all of these advancements, the typical installation involved servers with single operating systems
and with a single application running on each server
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eaton
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Typical UPS power management software can shut down impacted servers automatically and
gracefully should a power outage threaten to outlast UPS battery capacity
...
Some suppliers of UPS software must ensure that shutdown software
agents are installed on each virtual machine as well as on the host machine
...

Leading-edge UPS manufacturers have developed new software platforms that reduce this management
complexity by integrating their software into virtualization management platforms like VMware’s vCenter® or
Citrix XenCenter®
...
Another benefit is the enablement of automatic live migration of virtual machines in case
of a power outage, as you are no longer limited to the option of shutting down the servers and stopping
operations
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To summarize: logical and complete power management applications can help companies:
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Monitor and administer their UPSs from any location with Internet access

•

Automatically notify key personnel of alarms or alerts

•

Perform orderly, unattended shutdowns of connected equipment, or better, work with virtualization
software to move virtual machines so as to maximize availability of key applications and hardware

•

Selectively shut down non-critical systems to conserve runtime

•

Analyze and graph trends, to predict and prevent problems before they happen

•

Integrate with existing network and management systems via open standards and platforms

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Page 12 of 14

Figure 11
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Services
With proper servicing, a well-made UPS can operate safely and reliably for as long as 20 years
...

Companies in the market for UPS hardware, therefore, should also choose an appropriate UPS service plan
from a service provider with the experience, know-how and resources to provide comprehensive, highquality support
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eaton
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Here are some accessories
worth considering
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Sealed batteries tend to be less expensive, but also wear out sooner
...
Deciding which kind of battery is right
for you basically comes down to whether you’re willing to pay more upfront for batteries that you won’t have
to replace as often
...
Furthermore, due to the toxic chemicals they contain disposing of them is an expensive
and tightly-regulated process
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eaton
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A flywheel is a mechanical device typically built
around a large rotating disk
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When a power
outage occurs, the disk continues to spin on its own, generating DC power that a UPS can use as an
emergency energy source
...

On the plus side, flywheels are smaller and lighter than lead-acid batteries, easier to maintain and free of
dangerous and ecologically-harmful substances
...
However, research shows that more than 95 percent of utility outages last just a
few seconds, so using a flywheel as a complement to batteries during brief power interruptions can save
data center floor space and lower maintenance costs, while also extending the life of your lead-acid
batteries by reducing how often you use them
...

These days, however, many companies can’t afford to be without IT systems for the hours or even days
that may elapse before electrical service is restored
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While UPSs provide brief periods of emergency power, generators
draw on a supply of diesel fuel to keep IT systems operational for anywhere from 10 minutes to seven days
or more
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25 to 3
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The sizing
process should be based on a number of factors, including UPS design, generator and fuel type, so seeking
expert advice from the UPS and generator manufacturer is suggested
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During an extended power outage, demand for diesel can quickly outstrip regional
supplies
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Most companies use both floor-mount PDUs, which provide primary
distribution to server racks, and rack-mount PDUs (also known as ePDUs), which distribute power to
individual servers and other devices
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Conclusion
Businesses today invest large sums of money in their IT infrastructure, as well as the power required to
keep it functioning
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Leaving that
infrastructure defenseless against electrical dips, spikes and interruptions, therefore, is a bad idea
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By familiarizing
themselves with the basics of what a UPS does and how to choose the right one for their needs, data
center operators can ensure that mission-critical systems always have the clean, reliable electricity they
need to drive long-term success
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7 billion
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eaton
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Eaton has approximately 73,000 employees and sells products to customers in more than 150
countries
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eaton
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About the authors
Chris Loeffler is a product manager for Eaton Corporation, specializing in data center power solutions and
services
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Mr
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Mr
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He has also written articles on various UPS topologies for data center and industrial applications
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com
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A 30-year
veteran in the power systems industry, Spears has experience in UPS systems testing, sales, applications
engineering and training—as well as working in power quality engineering and marketing for
telecommunications, data centers, cable television and broadband public networks
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com
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Maintenance bypass, paralleling, UPS topologies, energy management and more are demystified
in complimentary white papers from our online library: www
...
com/pq/whitepapers
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eaton

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