Modular Upss Keep Data Centres Flying

Modular UPS technology has gained momentum overany risk or disruption to the critical load during this
the past few years, especially in data centres.process.
Uninterruptible Power Supplies Limited (UPSL) sales 
director Peter Bentley and operations director John “‘Hot-swappability’ of modules gives
Bladon explain the energy efficiency andUPS systems the ability to continually match their
environmental factors behind this growth.capacity to the size of the critical loads they support.
 This ‘right-sizing’ delivers energy
Ever wondered why modern jet aircraft are equippedefficiency,” asserts Bentley.
with two, and in some cases four engines? ‘For  Meeting the ‘blade server’ challenge
extra power and speed’, is the most commonState-of-the-art modular transformerless UPS
answer. That’s one reason, but there is another,systems – like UPSL’s
arguably more important one – to providePowerWAVE9000DPA™ - are highly efficient (95
redundancy.to 96 percent efficiency between 25 and 100
 percent full load rating), have very low input current
Of the several meanings of the word, the oneharmonic distortion (2 to 3 percent THDi between 30
associated with engineering implies fault-tolerantand 100 percent full load rating) and attract low
design. Fault-tolerant systems continue operating,whole-life costs.
even when one or more of their redundant 
components fail.They are also blade-server-friendly – capable of
 supplying loads with a leading power factor up to 0.9
Bird Strikeswithout the need for UPS de-rating.
Unlike your hot hatch or family saloon, aircraft areBlade-server-friendliness is an increasingly important
equipped with redundant engines so that in the eventconsideration in data centres where the growth of
of one failing - as the result, for example, of a birdthe blade server population is continuing its steep
strike or BASH (bird aircraft strike hazard) - the otherupward trend.
engines continue to support the load. 
 Environmental Issues
“UPS modules are related to a UPS system in thePower consumption in most data centres is continuing
same way that individual engines are related to anto rise rapidly as a consequence of ever increasing
aircraft’s propulsion system,” suggestsround-the-clock demands for more IT services.
Bladon. “The two roles of the engines may be 
regarded as being one for capacity and one forBentley points out that corporations are having to
redundancy (1+1). Modular UPS systems may alsostrike a balance between complying with the
have 1+1 and other more complex N+1 and N+ngovernment’s vision for them to consider the
capacity-redundancy configurations (also referred toeconomic, social and environmental impact of their
as parallel-redundant configurations).”activities, to become more aware of their corporate
 social responsibilities (CSR), and delivering the highest
 possible level of system-availability demanded by their
 customers. “State-of-the-art modular UPS
Modular UPS systemssystems are best equipped to enable corporations to
The introduction of transformerless UPSs into thestrike this balance.”
market - single-phase UPSs in 1994 and three-phase  Increasing share of the data centre market
UPSs in 1997 - paved the way for the developmentBentley says that as a consequence of the many
of rack-format modular UPS systems.benefits they provide, there is an increasing
 momentum for modular parallel-redundant (N+n) UPS
“Transformer-based UPS systems were far toosystems in the market, especially in the data centre
large and heavy to ever become modular,” sayssegment. “Today, over 70% of the UPS
Bladon. “However, light and powerfulsystems that we sell are parallel systems. Three
transformerless three phase UPSs were perfect forfactors have brought this about.
rack-mount, modular configurations.” The 
world’s first three-phase modular UPS system,“Firstly, early parallel UPS systems required
the PowerWAVE9000, was launched by UPSL insystem managers to assign individual UPS modules to
2001.either ‘capacity’ roles or
 ‘redundancy’ roles. Today’s systems
There were two main incentives for thishave the capability to auto-configure, which means
development. The first was that the capacity of UPSthat their UPS modules operate in ‘capacity’
systems could be extended to support the increasedrole if they have to, or in ‘redundancy’ if
critical loads as data centres grew, which they almostthey could do.
invariably do. Nowadays, we know this as system 
scalability.“Secondly, the relative costs and physical size of
 UPS systems have significantly fallen. Today’s
The second was the all important goal of systemmodular 200kVA parallel-redundant systems have a
availability. “By paralleling UPS modules infootprint of less than two computer room floor tiles
parallel-redundant configurations, the availability ofand an impressive power density of 342kW/m2,”
UPS systems, and consequently the availability of thecontinues Bentley.
critical systems that they support, was very 
significantly enhanced,” explains Bladon.“The third and final factor is that the business or
 mission criticality (importance) of the loads powered
Hot-swappable modular UPS systems are cheaper toby UPS systems has increased to the extent that
runparallel-redundancy is no longer a ‘nice to
Unlike aircraft engines, up-market UPS moduleshave’ – it’s an essential.” 
possess the property of ‘hot swappability.’UPSL’s hot swappable
This means that UPS modules can be inserted andPowerWAVE9000DPA™ modular UPS system can
removed from UPS systems while they remainprovide 6 nines availability.
operational. 
 Where continuous power is mission critical, UPS
In a parallel-redundant configuration a module can besystems of the ‘true’-on-line
taken out of service for repair or maintenance whileparallel-redundant hot-swappable modular variety just
the remaining UPS module(s) continue to support thekeep on flying.
load.  Due to ‘hot swappability’ there is not