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| UPSonNet NewsLetter Septemeber 2011 |
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UPSonNet
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UPS Upgrading: Costs & Gains
When UPS Turns Power Down
| Spread Your Word On the Globe |
How much to Pay for Best UPS
Backup Battery & UPS Reliability
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Best UPS Battery Technology
UPS Waveform & New Computers
UPSonNet
Specifying the Right Off Line UPS
How to Drop a Protected Computer
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5 Nines Three Phase Scalable UPS
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Redesign UPS & Boost Efficiency
Life Expectancy of UPS Batteries
| How New Modern UPS Systems Protect Critical Load in Unstable Environment |
Editorial Topic by Meir Portnoy: Modern UPS Systems: Power Protection When Lightning
Strikes and Lights Go Down.
Modern UPS systems meet best latest trends offering green, compact and efficient solutions but
err in protecting critical loads in unstable environment.
Since childhood, when we waited for the last minute to prepare for an exam, we continue to
postpone chores that should be done, until we are surprised.
This editorial topic is a result of such recent surprise; who would think that a sudden first seasonal
lightning associated with a short rain shower, will cause a regional power cut that takes the electric
utility service a few hours to fix, causing the lights in an entire region to go down, traffic lights to
stop working, elevators to stop operating, and my computer monitor to become dark.
Regretfully, facts reveal that humanity, in general, is still not convinced that seasonal weather
phenomena do occur, and that the consequences can be foreseen and taking care of. We are
therefore surprised again and again every year; realizing the truth of the old English saying that
"everybody talks about the weather but nobody does something about it".
By February 2009, UPSonNet has performed a study of forty two worldwide power failures
occurring during a single month, each affecting thousand up to hundred of thousands people. The
study showed that most failures happen due to defective equipment which failed in stormy
weather. The learned lessons as well as the causes and remedies for seasonal power outages are
presented in UPSonNet's article: "Carrying On when Weather Storms."
The analyzed cases didn't include even a single UPS failure, indicating perhaps that UPS failure
probability is less than 2.4% of total major power outages. But since February 2009 significant
technological changes have been realized in UPS and related systems. New UPS systems were
introduced, aimed to reduce carbon emission, increase efficiency, compactness, and availability
with decreased costs. These goodies however don't come free; they can adversely affect UPS
ability to protect the critical load, whenever lightning strikes and lights go down.
The following recent technological trends have an impact on UPS ability to withstand utility related
phenomena and outages:
1. Green oriented legislations requiring almost unity power factor at UPS input.
2. Legitimizing Standby and Line Interactive type designs and Eco operational modes in high Power
installations.
3. Implementation of Modular UPS topologies in parallel redundant system configuration.
4. Embracing Blade Server solutions in Data Centers.
All of these were treated at the time and presented on UPSonNet website within Articles or
Newsletters sections. Present newsletter's topic however aims to focus mainly on aspects and
implications of these technologies, in relation to unstable grid environment in stormy and transient
weather conditions.
1. The effect of Input Power Factor Correction circuits on UPS immunity to line voltage
sags and outages.
Latest green oriented legislations demand increasing UPS input power factor, in order to limit utility
pollution caused by input current harmonics. This is generally achieved by designing the Rectifier
of a double conversion UPS with an Active Power Factor Correction (APFC) circuit. Such circuits
use a boost converting rectifier, which increases the DC buss voltage by about 150% to 200%
compared to conventional transistorized or SCR buck converters used in legacy type UPS systems.
Higher DC Buss voltage generally requires increasing the number of series connected backup
batteries in a string, which for three phase 400/230V UPS systems grows to about forty units per
string.
Batteries are the weakest link in any UPS system; our previous newsletter dealing with Impact of
Backup Batteries on UPS Reliability, indicates that UPS's Mean Time between Failures (MTBF)
drops from about 100,000 hours without batteries, to about 20,000 hours with 20 batteries and to
about 10,000 Hours when 40 batteries are used.
MTBF figures are based on average failure rate; most failures occur however during the unfriendly
and stormy season, when batteries are required to support frequent and extended power
interruptions. Such phenomena expose the batteries to destructive, frequent, and deep discharges,
which might sabotage UPS's ability to protect the load, even if a single cell out of the total 240 cells
in a 40 battery string, fails.
2. Eco or High Efficiency operation impact on UPS protection ability with unstable grid.
New trend advocating Off Line operation, typical to Standby or Line Interactive systems, which
for decades was considered inferior and limited to low power less critical systems, is now
recommended by manufacturers as a means to increase UPS efficiency also for the high power
UPS systems. Such OFF Line operation is offered by most Static UPS manufacturers as Eco mode
or High Efficiency regime, which enables to increase UPS efficiencies up to and above 98%.
Eco operation generally means a standby operation via the Static Switch from an Online double
conversion UPS. The UPS is designed to transfer automatically to the double conversion mode
whenever utility voltage deviates beyond programmed levels; sometimes such transfer is based on
site tracking performance, which takes in account also irregularity of utility behavior associated
with stormy weather environments.
The assumption that line voltage behavior can be predicted, or that line excursions are of a
magnitude and speed that can be corrected by fast transfer to online operation isn't always justified.
The speed of transferring the load from Eco ( Bypass) mode operation to UPS's inverter, in order
to correct over voltages associated with lightning induced transients, is dictated by line frequency,
and is delayed up to its half period time; namely to about 8 -10 millisecond, until Bypass current
reaches zero and turns off the conducting Bypass SCR switch . Most electronic loads, and
particularly servers with Active PFC circuit, which boost input voltage, may not be able to
withstand such transients.
Utility undervoltages are more controllable, and can be handled fast enough to promise that the load
will not be exposed to voltages below the safety limits allowed by industry standards such as
CBEMA or ITI curves. Still, unlike double conversion operation mode where load is constantly fed
from UPS inverter, transferring in case of its failure to utility, which is present above 99% of the
time; in Eco mode, latent UPS malfunction might be revealed when line power goes down and the
inverter kicks in; thus the ability of smooth transfer, is subject to UPS health condition and its
ability to absorb full load transient at the worst moment.
Other UPS types, such as certain hybrid and Rotary systems, which are recently getting more
popularity, are practically also Off Line units. Rotary systems may lack the possibility to correct
over voltages. On the other hand, they will better treat short time input voltage sags compared to
static systems, due to the flywheel accumulated energy, which is more reliable than batteries.
The situation becomes however much more severe, because of the short backup times that
flywheel solutions allow; particularly whenever power outages extend beyond a few minutes and
transfer to standby generator is needed. Based on the said UPSonNet 2009 power outages study,
generator starting malfunctions are responsible for 12% of total power outage failures.
3. Effect of Modular UPS topology on Power reliability in Stormy weather.
Modular UPS systems are treated in UPSonNet February 2011 Newsletter titled Pros and Cons of
Modular Uninterrupted Power Supply ( UPS) Systems.
The ability to increase UPS capacity when needed by means of compact and swappable units
offers increased efficiency with lower upfront costs and high N+1 redundancy.
The modular approach may however be more vulnerable in unstable grid environment. Multiple
parallel UPS systems with numerous components can be compared to multiple thin wire strings in a
chain as opposed to two thick ropes approach. The likelihood that the first solution will collapse
under tension, if more than a single thin wire tears down at abnormally tough conditions associated
with stormy weather, is much higher than a single rope failure out of the two available in the
second solution . Thus, the possibility of a second module failure in stormy environment, before
the first failed module was replenished, cannot be ignored.
Additional aspects related to specific design should also be considered. Such consideration should
take in account also the behavior of the parallel modules and their ability to track and share load
during line transients, the impact of possible single point failure, the ability to remove fast enough a
failed UPS before a single component, such as failed Bypass SCR in a single module, turns down
the total system.
4. Effect of Blade Servers on UPS behavior in stormy season.
Blade server solutions were warmly accepted by Data Center industry due to the associated
features, such as high efficiency, compactness and conformity with latest green standard
requirements. Such servers exhibit however a leading input power factor characteristics, which
requires a Blade UPS system designed specifically to work with leading Power Factor loads.
In our June 2011 Newsletter topic, we have described the reason for leading power factor and the
problems associated with UPS Operation With Blade Server Loads. The article indicates that such
loads, when connected to a UPS designed to work with lagging or unity load power factor, can
have negative effects on UPS's loop stability, impacting also on the longevity of UPS filter
capacitors, and batteries.
Unfortunately, Blade servers are frequently connected to an existing UPS, without checking
possible consequences of UPS-Load unsuitability. In numerous cases, particularly when the UPS is
lightly loaded, problems are not revealed by the operator, whereas certain warning signals or
displayed readings are neglected or not associated by maintenance personnel to UPS-Load
inadequacy.
Such latent problems are however liable to appear during the unstable and transient environment,
affecting UPS operation, while particularly impacting on its ability to function properly in redundant
/ parallel configuration and the ability to isolate a failed module, without affecting the total UPS
system.
Surviving the Tough Season
The way to evidence existing installation performance and readiness to survive the stormy season
requires checking system current condition, taking the measures that make sure that the installation
is healthy enough to overcome the stormy period, and consider preferring double conversion over
Eco operational mode until the weather stabilizes.
In addition to the routine checks that should be performed on UPS installation in order to be
prepared for winter, specific tests and scenarios of possible occurrences should be devised and
exercised.
Such tests should include, at least, simulations of utility outage with maximum working load in
normal operational regime with all parallel modules and battery strings in place, and repeating the
test also after removing a redundant module, battery string or generator. Such tests should include,
checking and recording the behavior of total system and of individual battery strings and electronic
modules until generator kicks in, or until battery breaker trips at the End of Discharge.
As part of such test, proper system behavior upon utility restoration should also be verified,
ascertaining smooth transfer to normal operation, while recording the charging values and times, as
well as proper current sharing between UPS modules and battery strings.
In addition, failure of a redundant UPS module and battery strings during normal operation should
be simulated, by isolation of a redundant UPS module and Battery string, as well as by restoration
of such module or battery pack in the manner allowed by the manufacturer (such as hot swapping).
Test records should also include proper operation of alarms and messages, including automatic
notification of the relevant personnel via phone or mail, and verification of appropriate response by
such persons, as needed to correct the situation.
I welcome remarks. Please send to: meirp@upsonnet.com
UPSonNet Website News
As part of UPSonNet business plan for the next year we have performed a review of our current
operations including our regular audience, subscribers and new visitors. The review indicates that
UPSonNet has currently about 12,000 visitors per month, out of which 77% are unique visitors,
whereas 30% are referees from Google and other major search engines.
The review investigated also content and visitor profiles on other unbiased media sources; revealing
that UPSonNet became the prime media source in English, for audience involved or interested in
Power Backup and UPS systems. Whereas 100% of UPSonNet visitors have an interest in this
field, the share of such audience, visiting any other relevant online publishing source, such as
dealing with Power Electronics, IT, Computers and Data Center's, doesn't exceed 5% of total
visitors.
The review also indicates that 55% of UPSonNet traffic comes from USA and Canada, 20% of
visitors come from Europe (mainly UK) and 22% from Far East (mainly India) and Australia.
Visitors' professional profiles reveal that 48% of UPSonNet visitors are engineers; about half of
them are involved in design specifying, consulting and recommending power protection equipment.
Summery of the results as well as additional information, is presented on our new Media Kit, which
is available to potential advertisers by e-mailing to: advertise@upsonnet.com.
Based on the high share of engineering oriented audience, we have already started to present on our
website and on UPSonNet News, also content related to Backup Power components and designs.
In our previous newsletter, we have brought to the attention of Newsletter subscribers that we
intend at the end of the year to publish on UPSonNet website a LI -Ion battery suppliers' guide,
which details main type of UPS batteries and contact details of potential buyers. The inclusion in
the Li Ion guide is currently free of charge for relevant companies.
Interested parties, please write to carole@upsonnet.com, including full name, few sentences
describing your company and relevant products, e-mail phone, task of person to contact, and
country, as well as a link to relevant page on company's website. Please include in subject line: Li
Ion Suppliers Guide.
Whoever missed our last monthly Newsletter can read it by linking to: Charging UPS Batteries- A
Guide for the perplexed user.
UPS Industry News
Companies considering 2012 business plan, may find interesting information about fastest growing
markets, sectors, technologies, Industry players, and expected revenues by region in two World
UPS Market reports, from Pike and from IMS Research companies. Both published on 20,
September 2011, briefs of which are presented on UPS-News.
Based on the reports UPS world market in 2011 is USD 8 Billion, expected to grow by about 6%
per annum to reach USD 10 billion by 2015. The annual growth is expected to be much higher in
certain regions, such as the Far East and Latin America. IT and Data centers are expected to
continue to be the leading sectors, focusing on efficiency, simpler design, reduced cost, compact
and smaller floor space.
We welcome remarks on any Newsletter issue. Please e-mail to: denis@upsonnet.com
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