modular systems
additional work that is required includes
more terminations for more electrical
feeds; more units to set in place, more
units to start up and test; and more
control wiring and monitoring points.
With a modular UPS in which
multiple internal modules are used to
increase redundancy, this work can
be done in a factory setting, saving
time and improving the predictability
of the result.
Risk tolerance
themselves, the bypass cabinets, the
back up battery system, assembly
service and cost of installation.
Installation, assembly service and
battery costs were identical or almost
identical for the non-redundant and
Internally Modular options but more
expensive for the Parallel Redundant
system. This can be explained by the
fact that the latter has a separate
battery system for each of the three
modules in its setup, whereas the
other two options only have one
battery system.
Furthermore, the costs of the
extra cabinets required for the Parallel
Redundant option and its larger UPS
modules also increase material and
labour expenses.
24
Deployment time
Speed of deployment also varies
considerably between the N+1 options.
A typical installation of a 1MW UPS
can last between six and eight weeks,
taken up by preparation of the room,
including the concrete housekeeping
pads; delivery and rigging of the UPS;
running conduits for the UPS; pulling
wires and making terminations and
scheduling the start-up and testing.
These installation steps are the
same for the non-redundant design and
the Internally Modular configuration,
apart from having to add an extra power
module for the latter option. But for
a Parallel Redundant configuration,
additional time is required, which can
last for another week or two. The
Fault tolerance varies between
the three different configurations.
Consider the following downtime
risks: failure of the inverter or other
power module, failure of the DC bus,
or the need to bypass the main UPS
for maintenance purposes. All else
being equal (same UPS design, just
different configurations), the Parallel
Redundant configuration is the most
resilient as the remaining UPSs
support the load in those conditions.
Conversely, the non-redundant UPS
transfers to static (or maintenance)
bypass, there will be no battery back
up available, and in the event of a
mains blackout, the IT under load
would be brought down. In the case of
the Internally Modular configuration, a
maintenance event or a DC bus failure
would also leave the IT load vulnerable
to a mains event, although in the case
of inverter or power module failure, the
remaining UPS module would continue
to support the load.
The choice of power back up
strategy must be contingent on many
things, including criticality of IT systems,
likelihood of disruption to mains
power and the cost of any downtime.
Nevertheless the Internally Modular
approach often provides the needed
level of redundancy for a very small
cost premium over having no redundant
back up for the power supply at all.