UPS SYSTEMS
damage are also essential criteria. A
faulty hot-swappable module can be
immediately replaced by a new plug-in
unit, so full UPS capacity is quickly
restored – the mean time to repair
(MTTR) is typically within half an
hour of the module’s failure. The faulty
module can be repaired off-line and
returned to spares stock.
By comparison, if a standalone
UPS system fails, it must be isolated
from the mains supply and repaired
in situ rather than replaced, with fault
finding and repair down to component
level if necessary. This activity carries
a MTTR of typically 6 hours. This
difference in MTTR times clearly
shows the advantage of using hot swap
modular systems when high availability
is a priority. Whereas a free-standing
UPS system with redundancy could
achieve 99.9995 per cent (‘five nines’)
availability, this figure improves to
99.9999 per cent (‘six nines’) for
a hot-swap modular redundant
implementation.
The significance of these figures has
been highlighted in work performed
by the Uptime Institute (www.upsite.
com ). This has generated the term ‘five
nines’ to express high availability. It also
means that hot-swappable modular
systems as in the above example that
achieve 99.9999 per cent availability
are referred to as having ‘six nines’
availability.
Modular UPS systems offer the highest level of power protection
The Best Solution
In selecting a UPS system for high
availability, it is important to ensure
that the chosen solution is fully modular
with hot-swappability. This is because
some vendors offer systems referred
to as ‘fault tolerant’ UPSs to provide
lower-cost redundancy. Systems of
this type have redundant components,
but not all of the major components
are hot swappable. Batteries and
a subset of the power electronics
typically are hot swappable, but often
a high number of critical components,
such as the processor electronics, are
not. Such designs offer high power
availability because they continue to
deliver protected power to the load if
a component fails. However, in this
architecture the failure often means that
42 NETCOMMS europe Volume V Issue 6 2015
the entire UPS has to be shut down for
expensive and time-consuming repairs,
causing system downtime and a major
inconvenience for data centre managers.
Modern, modular UPS systems
offer the highest level of power
protection available because all
critical components, including
batteries, are both redundant and hot
swappable. Both planned downtime
and unscheduled failure outages are
eliminated, while the installation
provides the highest levels of power
availability for data centre critical
loads. These modular UPS solutions
bring commercial as well as electrical
efficiency through their inherent
flexibility and scalability. There is no
need to future proof a data centre with
high excess UPS capacity before it’s
actually needed. I nstead, a modular
system can be efficiently configured to
the existing load requirement, because
modules can be added incrementally
and easily when the load does grow –
often with no interruption to power.
Conclusion
Modern, modular UPS systems can
help data centre managers achieve the
highest possible availability without
sacrificing the highest possible levels of
power efficiency. These non-exclusive
benefits spring from the underlying
transformerless technology. This
technology has significantly improved
UPS efficiency while ushering in
the small, lightweight modules that
allow hot-swappable, redundant
UPS implementations with very high
availability.
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