Hitec
UPS System Configurations Part 2
System Configurations
Hitec Power Protection’s diesel rotary UPS
modules can be delivered in a number of configurations; each
tailored to specific customer needs, from a stand alone UPS to a
distributed redundant Dual Output System. The most common
configurations are the following: Single
Configurations
Fig. 1 shows the typical diagram of a single UPS
configuration. All main components (Diesel, Induction Coupling and
Alternator) are rated to supply the connected critical load.
Fig. 1: Single UPS Configuration For UPS
applications, typically the alternator is overrated to ensure
sufficient short circuit capacity together with voltage and
frequency stability. This excess power can be utilised to supply
non-critical loads. The Diesel is rated sufficiently to supply both
the critical and non-critical loads. This configuration is known as
Dual Output, as shown in Fig. 2.
Fig. 2: Single Dual Output Configuration The
non-critical loads in normal operation are connected to the utility
power. On a utility failure the System will protect the critical
load, while instantaneously disconnecting the non-critical load by
switching off Q5. As soon as the Diesel engine has reached nominal
operating conditions (speed and power), the non-critical load is
connected to the System by switching on Q6.
The benefit of the additional non-critical output
is that it comes at a low cost, much lower than average per kVA
prices for gensets, without the need for additional plant floor
space. MV Systems
For higher power ratings or large centralised UPS
installations, Medium Voltage systems can be considered. The typical
MV UPS configuration is shown in Fig 3. The MV configuration
utilises the proven LV power module components and control systems,
with an additional step-up transformer. Circuit breakers and choke
coil are at MV level. All system configurations
provided hereafter, can also be configured on the basis of this MV
configuration.
Fig. 3: MV Configuration Parallel
Once the total load of the output exceeds the max
power of the largest available unit (2.000 kVA), systems can be
connected in parallel to deliver increased outputs. The max number
of units which can be installed in parallel is limited by the total
deliverable output and short circuit current. At 400 Vac, max 3
units of 1.450 kVA or 2 units of 2.000 kVA can be installed in
parallel. The typical configuration is shown in Fig. 4.
Fig. 4: Parallel Configuration Another typical
application for parallel systems is when redundancy is required. The
most widely utilised configuration is often termed as “N+1”
configuration; when for example two units are required to supply the
critical loads, another (third) unit will be installed to provide
back-up should one unit be unavailable. Inside
Out
The "inside-out" configuration shown in Fig.5
takes advantage of the capacity of the "redundant" unit within an
N+1 system. When all units are in operation, this additional
capacity can be used to supply the non-critical loads. When a unit
is taken out of service, e.g. for maintenance, the non-critical load
will be transferred, without interruption, to the utility supply.
The supply to the critical load is continuously maintained at all
times.
Note that the difference with the parallel system
is that the non-critical load is normally connected to the utility
supply in the parallel configuration, but to the UPS system in the
“inside out” configuration. The non-critical load is fully UPS
protected, as long as the total load (critical and non-critical)
remains below the sum of the critical load capacity of all the
operational units. Whenever the load exceeds this limit, the system
automatically reverts to standard dual-output operation.
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Technical information associated with:
Hitec Power Protection Ltd UPS - Dual Output Design Guide
Hitec Power Protection Ltd UPS - System Configurations part 1
Hitec Power Protection Ltd UPS - System Configurations part 2
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