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| UPSonNet NewsLetter November 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
| | | | | | | | | | | | | | | | | | | | | | |
Redesign UPS & Boost Efficiency
Life Expectancy of UPS Batteries
| Best UPS Spec & Topologies for Now and the Future |
Editorial Topic by Meir Portnoy: The Best UPS Specifications and Topology for protecting
Legacy and Modern Computers.
A comment in our previous monthly newsletter, titled The Best UPS for Today and Tomorrow
indicated that "UPS industry is now at the turning point, where UPS systems are required to
protect both legacy computers, which are still existing and offered on the market, and modern type
computer loads", explaining the need to consider specific points when selecting a new UPS
in order to make sure that the new UPS systems will be able to protect new computers while
operating satisfactory also with legacy computers.
The topic of this newsletter treats main specifications needed from a state of the art UPS, in order
to meet both new and legacy computer requirements. Non technically oriented readers are advised
to read our past newsletter, where certain basic terms used here are explained.
a. Considerations affecting Proper UPS Operation
UPS Output Power Rating
The size of a UPS is dictated by two power related terms: Total (or Apparent) Power measured
by means of Volt Ampere (VA) units, and Active Power (or real power) measured by Watt units.
Both VA and Watt figures are stated by the UPS manufacturer, each should be above the
respected power that the load requires, which should be derived by adding up the total VA ratings
and total Watt ratings of the consumers protected by the UPS. The ratio of Active Power to Total
Power is termed Power Factor.
New computer servers, designed to meet latest green oriented standards, have input power factors
of about 0.96 to 0.99, compared to legacy computers which have power factor figures ranging
from 0.6 to 0.8.
A new UPS should therefore have a Power Factor rating of 0.9 to unity; meaning, that its Watt
rating should not be lower than 90% of its VA rating. This is of particular importance when
single phase UPS systems are considered. Most UPS systems on the market have still Power
factor rating of about 0.7, some don't even declare the wattage rating, until requested.
Hence a Legacy 1000 VA UPS with a Power Factor of 0.7 will be able to power a legacy
computer which needs less than 700Watt to operate , but will not be able to work with a new
1000VA computer that draws 960Watt. To protect a new 1000VA computer load, which needs
960Watt you will need either a legacy UPS of 1370VA if its Power Factor is 0.7 or a New
1000VA UPS with 0.96 Power factor rating.
UPS Output Voltage Regulation
New servers use a power supply with an active power factor correction (APFC) in order to meet
the latest green oriented regulations aimed to eliminate grid polluting harmonics.
Such APFC circuit is based on boosting input line voltage; thus enabling the computer server to
operate with low input voltage of 10% below nominal line voltage, while limiting the upper margin
to 6% above line voltage, resulting in voltage window of 108V to 127V for a 120V utility line and
207 to 244V when a 230V line is applied.
Hence a Double conversion UPS, which offers stabilized output voltage within 2% to 3% will
protect fine any computer server. Whereas Line interactive UPS system, which offers generally
+/-10% output voltage stability, may cause a problem with certain new computer servers which
have APFC power supplies.
UPS Output Waveform
Servers equipped with APFC power supplies require pure sinusoidal voltage to perform correctly;
such voltage is supplied by the line, or by double conversion UPS systems. Most Line Interactive
UPS systems however use non sinusoidal DC to Ac inverters; the server will work fine when line
voltage is available but may malfunction at power outage when the non sinusoidal inverter kicks in.
Hence, any non sinusoidal waveform, including semi sinusoidal or modified sine wave should be
avoided.
UPS Output Power Factor
Legacy UPS systems are designed to work with inductive (or lagging) Power factor loads.
Certain new computers, such as Blade servers have relatively large input capacitors aimed to
decrease EMI caused by APFC circuits. Such servers need UPS systems designed to work with
capacitive or leading Power factor loads of at least 0.9 PF at full load.
UPS Input Power Factor
Latest regulations such as EN 61000-3-2, 61000-3-4 or 61000-3-11 require users to limit parasitic
harmonics allowed to be injected by the UPS into the utility; such harmonic mitigation is achieved
by new double conversion UPS system by means of APFC circuit in the UPS's rectifier.
Line Interactive UPS systems however and Online UPS systems while in Eco mode connect the
load directly to the line, reflecting the nature of the load at UPS input. Unless the load is equipped
with APFC circuits or other measures to mitigate the harmonics, the user should consider
implementing filters or power factor correction devices at the input of a UPS.
Availability & Reliability
Availability of power that protects the critical equipment should be the main concern of UPS user.
UPS system offers power protection as long as it operates correctly. Sooner or later every system
fails and protection becomes unavailable until the UPS is repaired. Availability is therefore defined
as the percentage of the total time when the UPS operates correctly, or Mean Time Between
Failures (MTBF), out of the total time which includes also the Mean Time To Repair (MTTR)
needed to restore the UPS to normal operation. (Availability = MTBF/ (MTBF+MTTR))
Average MTBF figure of a double conversion UPS without batteries is generally about 100,000
hours. Batteries however, reduce dramatically UPS's MTBF figure and therefore dictate its
Reliability and Availability levels . A typical 12 V battery, with five year life expectancy, has an
MTBF figure of about 30,000 hours. Using 38 such series connected batteries in a 230V UPS
reduces its MTBF to 789 hours, and Availability figure for an MTTR of 24 Hours to 97.047%.
This seems apparently fine, but it also means that backup ability of the UPS will be Down 3% of
the time, or 263 Hours (11days) per year, which most users cannot afford.
Similar calculation for a 120V UPS with 24 batteries results in a MTBF figure of 1250 Hours,
Availability of 98.117 %, and UPS backup Down Time of 165 hours per year.
The situation can be significantly improved, by selecting better batteries and a UPS with redundant
ability. Such configuration, generally termed N+1 redundancy includes excess UPS systems that
work in parallel with the N systems needed to supply the load, thus enabling the system to
perform at full capacity even in case of a UPS failure.
Adding a redundant UPS (or UPS battery bank) will increase the MTBF of the said 230V UPS
from 789 to 12969 Hours and of 120V UPS from 1250H to 32552 Hours, thus increasing
Availability of a 230V system to 99.811% and of 120V system to 99.926% , and decreasing
Backup Down Times to 16.5 Hours and 6.5 Hours respectively.
These results still do not meet accepted standards of most data center and IT needs, which
require Availability figures of four (99.99%) and even five nines (to get 5 minutes backup Down
Time). Additional measures should be taken to reach these levels. Such measures may include
using UPS systems with fewer batteries, selecting batteries with longer longevity, adding more
redundant systems (N+2 configuration), and installing battery diagnostic equipment able to reveal
weak battery condition, which should be replaced before failure occurs.
b. Considerations affecting UPS Total Cost of Ownership (TCO).
No UPS specification can neglect cost related consideration; type of UPS, UPS Efficiency,
Scalability and Maintenance should all be taken in account when UPS systems are specified.
UPS Type
Inverters of most standby (generally called backup) UPS systems provide non sinusoidal output
waveforms, and should be avoided for use with modern computers that have APFC Power supplies.
Line Interactive systems, with sinusoidal inverters (called sometimes Smart UPS) provide the
most cost effective solution when both upfront cost and electricity costs are considered. These
systems connect normally the input line to the load, switching to inverter operation when line
voltage exceeds preset setting; they are offered for single phase operation and may be preferred
for less critical applications, provided that loads are equipped with APFC power supplies or other
means to meet EN61000-3-2 or 61000-3-4 standards.
Double conversion UPS Systems called also On Line Systems supply continuously conditioned
power from mains or batteries offering the best power protection with the ability to work in
parallel configuration and solve all line disturbances, for all type of loads in sizes from a few
hundred Watts up to Mega Watts. Online systems are generally the most expensive, considering
both upfront and running costs.
Rotary UPS systems generally resemble Off Line operation like the Line interactive UPS. Such
systems are mainly used in high power installations, offering certain Online features such as
paralleling and redundancy. These systems connect the load to line in normal operation, storing
short time backup energy in a flywheel, which powers the load at utility outage, providing
override time until a backup generator takes over. The high running efficiency and lack of
batteries compensates for the relatively high upfront and maintenance cost.
UPS Efficiency.
The running costs of electricity due to UPS inefficiency should be taken in account in any TCO
calculations. These costs, in addition to the cost of air conditioning needed to extract from the
facility the heat emitted by the UPS system, exceed within a few years the upfront cost of the
UPS , and are therefore of prime importance when selecting a UPS system.
Line interactive UPS Systems and other OFF line regimes such Eco mode offer the highest
efficiencies. New topologies implemented in double conversion UPS systems, such as three level
inverters, and new components such as Silicon Carbide (Sic) diodes, as well as introduction of
APFC based rectifiers, enabled to increase significantly UPS efficiencies of these systems in the
last years.
UPS Scalability
Double conversion and rotary UPS systems can be designed to allow parallel UPS system
operation, enabling scaling up UPS capacity when needed by adding systems to existing
installation. This Go as you Grow approach may have an important affect on UPS's TCO.
Firstly upfront UPS costs can be reduced by installing initially the smallest unit with the lowest
cost needed for current application.
Secondly, running electricity costs are reduced, because UPS systems efficiency is at its
maximum at a load close to nominal UPS rating.
Thirdly, it allows reduce footprint or rack space, which can be put to use for other applications
or purchased when needed.
UPS Maintenance
UPS maintenance whether provided by local manpower or by outsourced service forms also a
significant part of TCO cost. Backup batteries which need replacement form the main factor
affecting UPS TCO figure. Based on the considered above MTBF figures , paying attention to
type of batteries, their longevity, quantity and automatic testing , should be of prime importance
when specifying a UPS.
c. UPS specifications for legacy and new computer requirements
Following are 10 most important specification items to consider when specifying medium and
high power UPS systems,available from major UPS suppliers, needed in order to ensure proper
operation of most current and new equipment:
- 1. UPS Type: Rotary or Line Interactive with sinusoidal Inverter for APFC loads; preferred
Double Conversion UPS with paralleling ability of 4-5 units, for redundancy and capacity.
- 2. Input voltage regulation: – 15% to + 15% of nominal line voltage.
- 3. Input Power Factor: 0.99; or 0.95 and THDI (Total Input Current Harmonics) less
than 3% to 5% at full load
- 4. Output Capacity: 30% above maximum Load rating. ( NEC requires normal load design
not to exceed 80% of UPS rating.)
- 5. Output Voltage Regulation: Line Interactive UPS systems: - 10% /+ 5%; Double
Conversion systems: +/- 1% / +/-3% ( including unbalanced load).
- 6. Output Waveform: Sinusoidal, THDV (Total Harmonic Voltage Distortions): 1-2%
linear load; 3.5 % Non Linear load.
- 7. Output Power Factor Full Load : 0.9 -1.00; Ability to work with leading load power
factor of 0.8 to 0.9.
- 8. AC/AC Efficiency: Online operation: 400V UPS: 94% to 96%; 208V UPS: 92% to 94%.
Eco mode Operation: 97%-99%.
- 9. Number of backup batteries three Phase UPS systems (208 V: 24 to 32;
400V UPS: 32 to 40;
10. Battery Backup Time: 5 to 10 minutes.
For more insight on each of the discussed items please see our following articles:
Raising UPS Efficiency with Eco Mode
UPS Inverter Waveform and New Computer Servers
Mind Watts When specifying a UPS
UPS Operation with Blade Server Loads
I welcome remarks. Please send to: meirp@upsonnet.com
UPSonNet Website News
Our latest interest and Newsletter topics were devoted to the changing requirements for new UPS
systems and new batteries, in order to answer the needs of a changing world seeking for more
efficient, more compact, more green oriented and flexible power solutions. Expanding these
trends with new information and guidance will probably be our main concern during 2012, aimed
to meet the main interest of our audience. We welcome any news from subscriber concerning
these themes.
Towards the New Year, we wish all our friends, customers, visitors and readers the best year;
let it fulfill your wishes and expectations with new and prosperous opportunities.
UPS Industry News
UPSonNet News enable you to see at a glance and become updated about latest UPS industry
news, innovations and trends.
Towards the end of the year many research companies publish new UPS world market reports.
Based on the latest reports presented on UPSonNet News there seems to be a mutual agreement
about the current market; but when future is concerned the different crystal balls show different
pictures. The good news is that despite the uncertain current global market position all reports are
optimistic regarding future of the UPS market .
We welcome remarks on any Newsletter issue. Please e-mail to: denis@upsonnet.com
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