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MAINTAINING UPS EFFICIENCY
– EVEN ON LOW LOADS While UPSs are valued
72 JUNE 2019
above all for their
availability, their
energy eΠiciency has
also become critical.
As data centres
become larger, more
highly populated
and more numerous,
every percentage
point saving is
accordingly more significant. And energy savings
count, not just commercially, but also for brand
reputation and corporate social responsibility.
Below, Alex Emms, Operations Director at
Kohler Uninterruptible Power, looks at three
methodologies currently available to improve UPS
e€ iciency; transformerless technology, Xtra VFI and
Eco-mode – with Xtra VFI being especially beneficial
at low UPS loads.
Transformerless technology
While early double-conversion online UPSs
used internal step-up transformers, the industry
has generally moved towards transformerless
technology, with ever-growing power capacities
becoming available.
Transformerless technology has an intrinsic
advantage; it significantly improves overall UPS
e€ iciency, increasing it by around 5% to yield a
substantial reduction in heat loss and energy costs
-see Fig.1.
Fig.1: UPS e iciency curve
However, transformerless technology also improves
energy e€ iciency indirectly. Its considerably
reduced size and weight allows transformerless
UPSs to be implemented as relatively small
modules rather than large, floor-standing units.
Among many other benefits, modular technology
allows optimum energy e€ iciency. By adding
or removing modules, UPS capacity can be
incrementally adjusted to ensure that each module
is loaded for best energy e€ iciency, but not
overloaded.
Xtra VFI and low loads
Kohler Uninterruptible Power has further
developed and automated this concept -
sometimes called ‘right sizing’ - with a smart
implementation called Xtra VFI. This automatically
adjusts the number of active modules to match the
current load requirements. Surplus modules are
switched to standby, but remain ready to start up
and transfer to active mode immediately if the load
increases. The e€ iciency improvements achieved by
this mode of operation are especially significant for
loads below 25 percent of full UPS capacity. Fig. 2
shows why this is so.
Fig.2: How Xtra VFI mode enhances energy e iciency for a PowerWAVE 9500DPA
modular UPS running on a low load
Example: The figures below describe a
PowerWAVE 9500DPA UPS operating in Xtra VFI
mode:
Maximum load: 800 kW
Redundancy: N+2
2 x 500 kW frames (10 x 100 kW modules)
Load power: 200 kW
Number of active modules: 4
UPS active capacity: 400 kW
UPS standby capacity = 600 kW
The active modules operate in double conversion
mode, and share the load equally. When the
system calculates the optimal percentage value
for maximum e€ iciency, it allows for the desired
redundancy. The redundancy level for active
capacity and the highest expected load step
are user-configurable to guarantee the highest
protection quality.
A mains failure or alarm deactivates Xtra VFI
automatically, while all modules are switched to
‘active’ status.
Eco-mode
Most UPSs protecting mission-critical loads are
double-conversion, online types. During normal
operation, power flows through their rectifier and
inverter stages before reaching the load; protecting
it from mains
aberrations such
as spikes, surges,
sags and noise. Even
with these stages in
line, modern UPSs
like the PowerWAVE
9250DPA can reach
e€ iciencies of
over 97 percent
– which for many
applications is an
optimum result,
when combined with
the protection also
provided.
However, a
small minority
of applications,
whose loads are
not particularly
sensitive to mains
supply issues, opt
for UPSs with ‘ecomode’
capability;
incoming power can be switched to bypass a UPS’s
conversion stages, removing both their losses and
their protection, to deliver e€ iciencies to 99 percent
or more.
Conclusion
Modular technology is a powerful tool for improving
energy e€ iciency, among other benefits. By using
automated module switching, Xtra VFI ensures that
UPS loading is always enough to achieve optimum
energy e€ iciency. This is particularly e€ ective for
loads of 25 percent or less of full UPS capacity.
kohler-ups.co.uk uksales.ups@kohler.com 01256 386700
link
link
/www.kohler-ups.co.uk
