modular systems
helps to illustrate the issue. For a
baseline case, consider a single UPS
with no redundancy, comprised of four
250kW modules inside a single frame.
Then consider an Internally Modular
arrangement at the same rating. This
differs from the first case by having a
fifth 250kW module for redundancy
purposes. The UPS output bus and
the battery or DC bus is common to all
modules, thereby representing a single
point of failure. In each of these cases
there is a battery module with four
paralleled strings so that failure in one
does not cause failure in all.
Finally, consider a Parallel
Redundant N+1 configuration. In
this case, three separate 500kW
UPSs are connected in parallel
with a common output bus. In this
configuration each module has its
own battery system, which provides
an additional level of redundancy.
Capital cost
Capital expenditure is least, hardly
surprisingly, for the baseline single
UPS with no redundancy. Then
comes the Internally Modular option,
and finally, the most expensive
configuration is the Parallel
Redundant configuration. The
Internally Modular option analysed
is 26.9 per cent lower in terms of
capital cost than Parallel Redundant,
and the non-redundant option is 6.1
per cent lower than Internally Modular.
Capital costs are made up of a
combination of the UPS modules
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