FIVE APPLICATION CASES OF
CONTROLLABLE SOCKETS THAT YOU
WOULD HAVE NEVER IMAGINED
TWO STAGE POWER DISTRIBUTION
Summary
2
Introduction
3
Application case 1: Unauthorized access
4
Application case 2: Progressive system start-up
5
Application case 3: Programmed load disconnection
7
Application case 4: IP addresses
9
Application case 5: Overload management
11
Load prioritization: a new concept
13
Conclusions
14
Abstract
Controllable sockets are a powerful feature available on the market and recently introduced in the Liebert® GXT4™ product
family. In a separate white paper, “Advantages and efficient use of programmable sockets”, we have explained the way they
work, their advantages and key parameters as well as the criteria behind their activation. While the first paper provides a solid
background about this technology, this document illustrates a series of application cases on how to use it. Some may think
that it is just a feature to enable or disable power delivery to the sockets, but after reading this paper you will discover new
scenarios that might help you have a better control of your protected load, gain extra runtime or define load priority.
Introduction
For those with no background on this feature,
programmable or controllable sockets have the capability
to enable or disable power delivery to a selected group of
output power sockets on an uninterruptible power supply
(UPS). This allows loads to be powered on/off depending
on several conditions which can be configured separately.
The sockets are controlled through the UPS internal
microprocessor and their operation is based on criteria
which can be setup locally via software (USB or RS232
connection) or remotely through web access. Greater
insight is provided in another white paper on the subject,
entitled “Advantages and efficient use of programmable
sockets”.
Vertiv IntelliSlot Port
USB Port Fan
Input Circuit
Breaker
Terminal
RS232
Block
Port
Communications
External
Battery
Connector
Programmable sockets provide an extra level of control
and protection over the secure energy supplied to the
load, thanks to their capability to enable or disable
power at the outputs. Typically, output power sockets
are grouped in one or two sets depending on the UPS
supplier, and there can also be a third group of sockets
that cannot be powered on/off, usually referred to as
“always on”. These deliver power continuously as far as the
UPS is connected to AC mains input, or batteries are not
depleted. As reference, Figure 1 shows the rear panel of
the Liebert GXT4. In this UPS model there are two groups
of controllable sockets plus such group of “always on”
sockets that delivers power continuously.
C14
Input
Programmable
Outlet #1
NonProgrammable
Outlets
Programmable
Outlet #2
Figure 1. Output sockets on Liebert GXT4 UPS including programmable groups as well
3
TWO STAGE POWER DISTRIBUTION
Controllable sockets can bring multiple advantages. To
simplify, these can be grouped in three major areas and
represented along three axes (Figure 2):
yyImproved runtime
yyLoad prioritization
yyLoad progressive disconnection based on specific
criteria (time or battery capacity)
yyBatteries and runtime sized for the target load
profile on battery mode
yyImproved control
yyRemote on/off control of the sockets
yyOverload behaviour management
yyLoad reboot capability
yyProgram and use of a single IP address
yyImproved energy usage
yyLess battery usage because of loads disabled
yyAuthorization for load connection
on the convenient use of controllable sockets, and the
benefits that such solution brings to the user. These
examples are not intended to represent the best or unique
way of application, but are meant to be representative of
what can be achieved in practice. The reader may for sure
find also additional application cases.
Application Case 1: Unauthorized Access
Scenario: An airport with distributed power protection and
UPS typically in the 1-3 kVA range. These can be used for
example to protect computers and ticketing operations
(printer, scanner ...) devices at the boarding gate, etc.
Improve Runtime
Improve Energy usage
Improve Control
Figure 2. Three axes for three areas of advantages
Based on these points, it becomes clear that controllable
sockets are not a “simple switch”, but revolutionize the
way of managing energy and protecting loads. They
allow redefining the role of UPS for all applications below
3 kVA ratings, for which the UPS now also becomes an
“intelligent power management” device, optimizing energy
distribution in a rack and allowing load management and
prioritization, remote control, runtime definition, etc. based
on specific criteria.
In addition to these general advantages that controllable
sockets offer, the next sections will expound five selected
application cases. These will further demonstrate how
technical features can be translated into actual benefits
and bring value for such applications (problem solving).
For each of the five cases, we will first describe the
scenario (which may be intentionally simplified for a
clearer analysis) together with the challenge that needs
to be addressed. Then we will present a solution based
4
Figure 3. Boarding gate with access control
Problem: In an airport, it may happen that even after the
system at the boarding gate is set up, more loads can be
“unintentionally” added to the UPS. This may result in
unexpected runtimes (lower backup time than the system
integrator had specified), overloads or even a complete
system shutdown at the boarding gate.
From the perspective of a system designer or operation
manager, this can be considered as an unauthorized use
or connection to the UPS protected power delivery. A UPS
without controllable sockets does not allow avoiding or
rejecting any extra load that may have been added, which
leads to the above listed series of risks.
This case can be found in other applications such as remote
unattended ATM, reception service desks, office printing
areas in which extra printers may be added, etc.. – basically
most of the cases where the UPS is located remotely to
the IT or system manager, and there is the need to control
which loads are connected and protected by each UPS to
avoid misuse.
Solution: In these cases, the best solution is to use the
capability of controllable sockets to switch-on or switchoff each group. In this way, the IT manager can disable
permanently (or enable if required) one or both groups
of sockets. By doing so, no power is delivered by the UPS
whether the UPS is operating in line mode or in battery
mode.
Benefits: While the benefits of protecting against
unauthorized use are clear, controllable sockets also bring
an extra level of control to the UPS and the loads protected.
For example, the control of the connected loads; the use
of unauthorized loads; a better control of runtimes as no
“unknown” loads will be connected; and avoiding overloads.
Last but not least, the possibility to reboot loads separately.
Runtime
Energy usage
For example, each Liebert® GXT4™ UPS has a configuration
software tool which can communicate with the UPS through
the USB port connection and then apply a specific setup
(Figure 4). It can also use the SNMP/webcard, and do so by
navigating the web browser and selecting the tab for each
group.
Application Case 2: Progressive System Start-up
In this section we will review a case where a complex system
(composed of several electronic or smart sub-systems) can
be progressively activated to “wake-up” in the right way.
Scenario: This second case refers to laboratory diagnostic
equipment used in healthcare applications (hospitals,
medical assistance centers, etc.). To simplify, it can be
composed of a “smart” computer with data storage and
control functionality, and a subsystem in charge for the
analysis (with servo motors, reactants, display, etc.). Out
of the healthcare field, other similar examples of complex
systems can be tooling machines, centralized servers and
Point-of-Sale (POS) terminals in retailing, the combination
of servers and switches for IP addresses, etc.
Control
How to get it done: Control of the sockets can be
performed very easily: either locally with the LCD interface
screen or with a configuration software tool, or remotely in
case the UPS uses a SNMP/webcard and is connected to
an IP network.
Figure 5. Laboratory equipment for analysis
In this case we will describe a very practical example.
Assuming to use a Liebert GXT4 3 kVA UPS, there is a
maximum output power of 2700 Watts. The power of the
control computer may be around 200-300 watts, thus
leaving more than 2000 watts to protect and manage
the loads on the analyzer sub-system (blood analyzer,
chemistry, resonance, etc.)
Figure 4. On/off control for each group of sockets
Problem: In this scenario we need a progressive system
start-up for proper operation, progressively delivering power
to the loads in several steps and with delays between the
different systems. In this simulation case, the analyzer subsystem requires that the data and control computer are
5
TWO STAGE POWER DISTRIBUTION
ready prior to the analyzer. Otherwise the complete system
will not work correctly.
While this is a simplified case, the reasons for the need for a
progressive start may be multiple – to name a few:
yyCorrect system synchronization at start up;
yyHigh inrush currents that would determine an overload if
all the loads were powered simultaneously;
yyNeed for a “warming” period in a sub-system;
Controllable sockets allow to easily solving these issues.
Integrators or system designers will surely appreciate
this flexibility to simplify the design and achieve a better
operation that otherwise would require more complex and
expensive electronics.
Solution: Using the synchronization of sub-systems, as
there are 3 groups of sockets: “always on” which is powered
as soon as the UPS is turned on, group 1 which can be
programmed with a delay, and group 2 which can also be
programmed sequentially with further delay. Thus the loads
can be shed or connected progressively in a maximum of
3 steps of power groups, which is usually enough for most
applications.
These controllable groups can be configured separately,
and with a delay of 30 minutes maximum. Therefore the
solution is to program a delay between the moment in which
the UPS is connected and turned on, thus delivering power
immediately (to the computer in our case, referred to as
Load 1 in Figure 6), and the moment in which it powers the
chemical analysis module (referred to here as Load 2). In
the example the assumption is that a period of 4 minutes is
enough to wake-up the computer (load operating system
and management application), and then start delivering
power to the second sub-system (chemical analyzer). As
a result, once the chemical analysis analyzer wakes-up, the
control computer will be perfectly ready and operative as
an interface.
Even in this scenario the UPS goes one step beyond the
role of simple power protection and actually works as a kind
of “smart power manager”, thus managing the energy flow
through each sub-system in a smart and controlled way
defined by the user.
Energy usage
Start-up
4 minutes delay
Benefits: This is a good example of the extra level of control
and flexibility that controllable sockets bring to users or
system integrators.
The key benefits are related to the flexibility to manage the
groups of loads connected, the capability to synchronize the
start-up as well as the satisfaction of the requirements for
each load (peak currents, warming period, etc.)
How to get it done: There are several ways to set up the
Liebert® GXT4™ UPS using this feature, but one of the
easiest is using the configuration tool bundled with each
UPS. Thus, just connecting their desktop or portable
computer through the USB port, the user can set up the
parameters for Group 1 and/or Group 2 of sockets.
Programmable socket Group 1
Start-up
4 minutes delay
Load 2: chemical analysis module
Load 1: control computer
Figure 7. Liebert GXT4 configuration tool for initial delay setup
Time
Figure 6. Progressive system start-up with a delay
6
Figure 7 shows a screenshot of the configuration tool to
setup the delay for a group of sockets, which is a quite
intuitive process.
It is important to highlight the difference between the “initial
start-up”, intended as the delay when a UPS is connected to
the AC mains, or alternatively the delay period when there
is a mains failure and the UPS returns from battery to AC
mains (either when the batteries are completely depleted
and output power delivery is completely stopped, or when
there is still energy in the batteries). These two cases
are slightly different; however the utmost flexibility of the
Liebert® GXT4™ allows a different time set up for both cases
(see Figure 7).
Application Case 3: Programmed Load Disconnection
Now we will consider a case in which a pre-defined group
of sockets will be configured so as to disconnect the load
when the UPS is running on battery mode.
This particular case is probably the one encountered more
frequently by users interested in controllable sockets.
While the need for an interruption in power delivery is quite
plausible, the key point is defining the criteria for such
interruption. Should it be after a fixed period of time that
the UPS is on battery mode? Should it happen few minutes
before the batteries are depleted? Does it affect the way to
estimate the battery capacity required? As we will see in
the next paragraphs, this case is particularly interesting as it
presents several complex aspects to take into consideration.
Scenario: For this application case we will consider retail
shops with several POS terminals composed of screen, ticket
printer and computer chassis for each. In addition, we will
consider security cameras with their control system, such as
a recorder. The scenario for this simulation is simplified as
a real retail shop may have a number of additional elements
such as lighting, hubs, servers, door controls, etc. While more
complex cases can be evaluated, for the sake of simplicity
Programmable socket Group 1
Figure 8. Retail store
we will consider the POS as the top priority loads to keep
sales and customers flowing, and security cameras as lower
priority. More complex scenarios can be evaluated, but as
said above, it is just for simplicity.
The same solution can be applied in many other scenarios,
like transportation (protection of signalling or information
systems, boarding, lighting, etc.), healthcare (customer
service areas, small computer rooms, lab equipment etc.),
finance, banking, telecom, and so forth.
In the case of our simplified retail shop, we will assume the
following:
yyA POS terminal system with a power consumption of
200 W each and 5 lines, meaning 1000 W of total power
consumption. This load is defined as our top priority load,
so it is crucial to keep it operating as long as possible
according to the target runtime expected by the UPS.
yyA security camera (CCTV) system composed of several
cameras plus the control system manager, with a total
power consumption of 500 W. This load, as per our set
criteria, is defined as lower priority and will be disabled
in case of need, according to several criteria that will be
explained later on.
In a normal operating condition with AC mains input, the UPS
will be protecting the loads against any perturbation that
may occur at the input (swells, brownouts, voltage spikes,
frequency variations, etc.). In the worst case of complete
mains failure, the UPS will be providing backup power to the
top priority loads identified to keep business continuity – in
this instance, POS terminals so that customers can pay and
leave the store with their goods.
Problem: In case of a AC mains failure or out of tolerance,
the UPS switches to battery mode. Having controllable
sockets available, how can we optimize the battery usage to
achieve maximum runtime for the high priority loads? Which
are the criteria to disable sockets and power delivery to the
other loads? What is the consequence of the application of
these criteria? Do we just need to interrupt power delivery
or should we also consider the operating system shutdown?
Solution: There are a lot of alternative answers to these
questions, thus we will address them one by one.
yyThe first step is to define which the priority assigned
to each load is. Assigning a priority means deciding if
that load can be disconnected/disabled while the UPS
is working on battery mode, secondly defining which
criteria for disconnection is to be used (basically time
or battery capacity), and finally grouping the loads in
maximum 3 groups.
7
yyDefining the priority is not deciding whether that load
is important or not – as connected to the UPS, we can
assume all of these are important and require power
protection – but to decide the relative criticality for the
specific application. The decision is based on how long
the loads should remain powered when the UPS is on
battery mode.
yyIn our sample scenario, the CCTV system is defined as lower priority and POS terminals as higher priority.
The key factors to be considered are that battery capacity
is calculated based on the runtime for all the loads (adding
each nominal power consumption), and the need to select
the time delay. This parameter can be selected in a range
from 1 to 30 minutes, which is enough for most applications.
This setup is a good alternative when there is a small
difference between load priorities, so that all of them need
to remain powered as long as possible.
Programmable socket Group 1
yyOnce priorities are defined, then the second step is to
decide the criteria for power disabling. This can be set
with a fixed time or battery capacity criteria.
Assuming that the UPS batteries are fully recharged (100%),
we can consider the typical case of turning off power
delivery after several minutes, for example 5-10 minutes
after a mains failure (see Figure 9). After this time, it is
probable that the interruption of the mains will not be short
and we can expect a long interruption. In this case, most
of the energy in the batteries should be reserved for the
highest priority load. Calculations need to be done for each
specific case; however battery capacity should be selected
mainly based on the target runtime and power needed for
the highest priority load. This option is shown in Figure 9,
and it is generally the most appropriate one when there are
loads with high priority difference.
Programmable socket Group 1
Ex. 5 minutes delay
Load 1: CCTV (500 W)
*Keep
battery
capacity
reserved for
the most
critical load
(POS)
Load 2: POS (5 x 200 W)
Mains
faiture
Time
Figure 9. Immediate disabling of controllable sockets
A second option is to keep both high and low priority loads
powered up as long as possible. For example, assuming
a target runtime of 30 minutes, we can decide to keep
both loads powered up as long as the batteries have
energy stored, with a delay of 5-10 minutes for sequential
disconnection. The timing is represented in Figure 10, so
that it can be easily compared with the previous alternative.
8
Ex. 5 minutes delay
Load 1: CCTV (500 W)
Load 2: POS (5 x 200 W)
Mains
faiture
Time
Figure 10. “Last minute” disabling of controllable sockets
Furthermore, there is a third option to be considered. In the
two former examples, the criterion is based on a fixed time
(in the range of minutes), previously defined by the user
or system integrator. However, the user may also decide to
disable such group of controllable sockets according to the
estimation of remaining battery capacity. This means that
the exact timing for disconnection is not precisely known
beforehand, but the advantage is that the actual battery
capacity status is taken into account. For example, in case
of a series of mains failures, such that there is no time for
the UPS to recharge the batteries to 100% between one
failure and the other, the previous configurations may lead
to unexpected timings. Using the battery capacity status as
a criterion will ensure that whatever the status is, the energy
stored in the batteries is allocated in the best way possible.
Battery capacity for controllable socket disconnection can
be configured from 20% to 80%. Last but not least, the user
can make a combined use of time and battery criteria to
better fit the target runtime for each load.
These considerations allow plenty of flexibility in the
configuration of the loads.
The third and last step regards synchronization with
the operating system (OS) shutdown. Indeed the loads
connected may be for instance a screen (thus passive,
accepting a break interruption), or a server needing a
previous OS shutdown before a stop on power delivery.
When synchronization is required between power delivery
stop by the UPS controllable sockets and the OS graceful
shutdown, we need to use the shutdown software or the
SNMP/webcard to trigger the shutdown. Multiple situations
can be considered here (i.e. servers, USB port, IP network,
quantity of devices, etc.) which should be analyzed
thoroughly to find the appropriate solution. The key take
away is the need to achieve the proper synchronization
between the UPS (responsible for power delivery) and the
shutdown software (responsible for graceful OS shutdown).
Benefits: Utmost flexibility to define load priorities, runtime
for each load, the time intervals and the criteria applied.
Reaching optimum runtimes for each group of loads is one
of the major advantages. Just consider that battery capacity
can be sized according to different requirements without
controllable sockets (all the loads powered and target
runtime). This allows saving the amount of battery used,
or alternatively providing extra runtime for the top priority
loads (assuming the same battery capacity).
Runtime
Figure 11. Time and battery capacity setup page
Application Case 4: IP Addresses
The previous application cases have shown how controllable
sockets bring benefits in terms of control, runtime and load
management. Now we can go one step farther and see how
these help simplify IT assets management.
Scenario: In this case we will analyze a new scenario in the
transportation field, as for instance a railway train station or
airport terminal. Travellers typically rely on the information
panels showing the arrival and departure times as well as
any relevant notice regarding their scheduled travel.
Energy usage
Control
How to get it done: The UPS can be configured either locally
(via display or configuration tool) or remotely (via internet
network) depending on how the specific UPS is designed.
In the case of the Liebert® GXT4™, all the options explained
above can be set up using the UPS configuration tool.
Using a dedicated screen (Figure 11) for each group of
controllable sockets, the user can easily check and configure
each group separately. Bearing in mind that multiple criteria
can be selected, the user needs to make sure that the
chosen socket management setup is appropriate for the
actual application.
Moreover, it is possible to configure a time delay to turn
on specific group of sockets once mains power returns.
Figure 12. Information panels at train station or airport
Each of these information points typically includes 3 or 4
panels (around 75-150 W power each, depending on panel
size and technology) plus a switch or small server (200-300
VA) that manages the flow of information to be displayed.
In total this means a power demand from 1.5 kVA to 3
9
kVA depending on the number of panels and complexity
of the system. Therefore a UPS close or equal to 3 kVA
with six power sockets would be a good solution for power
protection and backup of these information points.
Issues may arise if more panels are added, thus requiring
additional power sockets or an auxiliary power distribution
unit (PDU) connected to the UPS (Figure 13). Besides, the
system manager may prefer to control these remotely,
turning them on or off through the use of a more advanced,
managed PDU.
While this presents no issues from a system design point of
view, but with regards to power administration this means
using 2 IP addresses. Thus the user will need to access a
pre-defined IP address for the SNMP/webcard connected
to the UPS to know the status, alarms or settings, and then
a second IP address to reach the managed PDU and to
execute any power enable/disable action on it.
Where loads can be clustered in 2-3 groups for powering, a
UPS with controllable sockets would be the perfect solution.
For example, the Liebert® GXT4™ allows loads to be
arranged in 2-3 groups that can be enabled or disabled by
the IT systems manager according to the need (see Figure
14). If multiple sockets are required for the connection of
the information panels, a PDU can be connected to each
of these groups. The difference is that now this PDU will be
much simpler (no remote access, no IP address, no switch
capability ...).
UPS
IP Address 1: UNIQUE
A R R I VA L S
A R R I VA L S
A R R I VA L S
UPS + ISWEBCARD
IP Address 1
A R R I VA L S
Controlled PDU
IP Address 2
A R R I VA L S
Figure 14. Power delivery for information panels, with a UPS and a basic
PDU (a single IP address)
A R R I VA L S
Figure 13. Power delivery for panels, with a UPS and a controlled PDU
(x2 IP addresses)
This means more complexity in managing the complete
system, more IP addresses (while there may be restrictions
on the quantity of IP addresses available in the network) and
in some cases also the need to integrate status information
(i.e. SNMP traps) from multiple vendors.
Problem: This scenario shows the complexity of several
devices requiring multiple IP addresses (switch, server, UPS,
managed PDU, etc.), making these more difficult to monitor.
Even in those cases where the number of socket groups in
the PDU is not high, the cost for that PDU will be certainly
higher than for a basic PDU without features for control and
IP monitoring. Is it possible to simplify the system, lowering
the cost and the number of IP addresses required?
Solution: This is an example which combines UPS and
PDU and requires a lot of flexibility to manage the loads,
especially when many separate loads need to be controlled.
10
Benefits: The benefits are related to the use of one simple
device (UPS) for complete power management. Having a
single IP address and interface, the UPS will allow easier
load management. The advantage is even greater if the total
quantity of loads increases, for example, in an airport with
50 information panels and a twofold number of IP addresses
and devices between UPS and managed PDU.
For those applications where loads need to be split in more
than 3 groups, more complex configurations can be set up
using a managed PDU.
How to get it done: Depending on the power consumption,
number of loads and groups required for distinct
management, the user can identify the best combination
of UPS and PDU models. Loads can then be enabled or
disabled remotely through the optional SNMP/webcard or
monitoring software as shown in Figure 4.
To increase flexibility even more, this solution can be
combined with any of the setups explained in the previous
cases so as to configure the minimum runtime while UPS
is operating in battery mode as well as progressive system
start-up.
Application Case 5: Overload Management
This case will assess when controllable sockets can make
the difference in case of unexpected situations such as
overloads.
Scenario: The UPS has multiple loads connected to its
output, with the total power consumption below or equal to
the nominal power of the UPS.
Each load typically has a nominal power consumption,
defined as the power demand when that device is operating
at normal workload or at an average value. There may be
however special conditions due to tolerances (i.e. oscillations
at input supply voltage), abnormal conditions (i.e. a failure
or short-circuit) or other particular conditions (i.e. inrush or
peak currents on an electric motor when started).
Use of the breakers is not to be confused with the
controllable sockets. Breakers manage electrical protection
in case of overcurrent that may damage the device or create
a risk, being these breakers permanently connected. In
contrast, controllable sockets can be used to stop power
delivery but are not intended for electrical protection, and
may be used as either an optional or a permanent feature at
the discretion of the user.
In case an overload occurs while the UPS is working in
on-line mode, the UPS can switch to bypass mode, thus
having an alternative path for power delivery that exceeds
the nominal inverter power capability. Alternatively, if the
overload is severe, the input or output breakers may trip.
But what happens if the UPS is working in battery mode
and there is no chance to use the bypass line? Would
it be acceptable to drop all loads? Or would it be best to
selectively disable any of these loads to keep the others up
and running? Controllable sockets can help in these critical
situations.
 "Always on"
 Group 1
 Group 2
Figure 15. Liebert® GXT4 3000 VA UPS front and rear panel
As a consequence, a perturbation or other problem
generated at the UPS output by any of the loads may cause
it to be “transferred” also to the other loads and determine
the drop of the load itself. In this scenario we will concentrate
on overloads.
For those who are familiar with electrical installations and
the need to manage overloads or short-circuits, this is similar
to the “selectively” concept for the isolation of failures.
Clearly in those cases where a UPS protects several
loads, it is crucial to be able to react selectively to these
occurrences. This is achievable using the breakers (input or
output, depending on the UPS model), an electronic control
and controllable sockets.
As an example, Figure 15 shows the front and rear panels
of the Liebert® GXT4™ 3000 VA UPS. Here we can see the
three different groups of controllable sockets (“always on”,
controllable group 1 and controllable group 2), together with
the input breaker and output protection breakers for these
groups.
Figure 16. UPS with two loads connected and a peak current
For our application case, we will consider an industrial
manufacturing process, or driving a small electric motor
for the access barrier. This is composed of a small
programmable logic controller (PLC) computer plus a
small single phase electric motor regulating the process.
Electric motors generally require a higher starting current
that exceeds the nominal current consumption. This surge
current may exceed in a variable amount of time depending
on the motor type and design, or in other cases it may be
due to an abnormal situation if for instance the electric
motor gets blocked. The UPS needs to be sized to manage
such inrush currents correctly, but this is just to show that in
several cases the UPS needs to manage currents exceeding
the nominal value for short periods. These over currents or
overload conditions may turn off the UPS and consequently
drop all the loads connected. Is it possible to manage these
overloads and keep the most critical loads powered?
11
Problem: The key point is that in most cases the UPS rating
is selected based on the maximum power of the load (thus
with a conservative approach), but in many other situations
the power demanded by the load is evaluated in nominal
conditions only.
In this scenario it is crucial to be able to separately manage
each load in case of an overload condition, and disable a
group of loads in case of overload conditions while keeping
breakers for electrical protection. Controllable sockets,
combined together with breakers where available, can help
manage these conditions.
Solution: A UPS with an overload management feature
grants that even if on battery mode, a group of sockets can
be turned off in case of an overload on the nominal power
of the UPS.
Thus, each group of controllable sockets (group 1 or 2) can
be configured so that in case of overload condition for the
UPS (not referred for that group of sockets), those sockets
will be automatically disconnected. In this scenario with the
PLC computer and the electric motor, the decision would
be to keep the PLC powered and protected as priority load,
and disable the power delivery to the electric motor. The
PLC computer will remain active and continue to provide
alarming and signalling, so that the corrective actions are
implemented.
The overload condition is defined based on the nominal
UPS power, not for that group of sockets. Moreover, in case
the UPS has protection breakers for that group, they may
operate alternatively if the tripping conditions are achieved.
Runtime
Energy usage
Control
How to get it done: The disconnection of a group of sockets
in case of UPS overload can be set up through the display
or configuration tool depending on the UPS. With Liebert®
GXT4™ this can be easily done with the configuration
software, flexibly allowing the user to disable a specific
group or even both.
The advantage of having the “always on” sockets is that
the most critical priority loads connected to these sockets
will remain powered even after programmable group
disconnection. Only in the case of longer overload conditions
or in case that overload remains even after groups 1 and
2 disconnection, then the UPS will be completely shut
down. It is recommended to assess the overload conditions
as described in the UPS user manual to understand the
thresholds.
Users may be reluctant to set up a configuration for each
separate UPS, which may be tedious when managing
distributed systems with many UPS. Liebert GXT4 can make
Again, breakers are intended for electrical protection and
should not be confused with controllable sockets, being
an optional feature for load management and not safety
protection.
Benefits: The possibility to keep several loads powered
even in overload conditions can be vital. Indeed, in those
UPS where this feature is not implemented, the UPS will
completely turn off once the overload conditions are
achieved for a certain period of time, which is defined in the
user manual or technical specs.
Moreover, in this example the user has 3 groups, so
that “always on” will remain powered even in case of
disconnection of groups 1 and 2. This means a more flexible
approach versus other UPS designs where there may be
only 1 or 2 groups managing the loads.
12
Figure 17. How to setup overload operation
the difference thanks to its capability to upload/download its
configuration locally via the USB port. Thus, once the predefined setup is identified as the most convenient, it can be
easily “replicated” or “copied & pasted” via the USB port on
multiple Liebert® GXT4™ of the same rating.
Defining this prioritization of the loads brings advantages
in terms of a longer runtime for the higher priority loads,
extra flexibility, advanced load control, and a more intelligent
battery management that optimizes battery life and runtime.
Figure 18. Liebert GXT4
Load Prioritization: A New Concept
As explained at the beginning of this paper, the feature
of controllable sockets is not only “a switch” to enable
or disable power delivery to a load segment, but a new
approach to load management.
This means that users can decide when to disable power
delivery while the UPS is on battery mode, based on time
delay or battery capacity, but also setup a progressive
system start-up, or define how to react in case of an overload.
The ultimate goal is to keep the top priority loads powered
as long as possible or as configured by the user. Depending
on the characteristics selected, this configuration can be
done locally with a configuration tool (USB) or LCD display.
As described in the various application cases and assuming
the UPS is on battery mode, the criteria to define the load
priority or grouping can be done through:
yyDesired time for load operation
yyBattery capacity
yyOperation in overload conditions
yyProgressive turn-on delay
yyNeed for separate reboot
13
Conclusions
This paper has examined a series of practical application
cases of controllable sockets, a powerful feature recently
introduced in new generation UPS. Through a “hands on”
approach simulating several scenarios, we have defined the
problem, identified a solution and indicated the relevant
benefits achieved. Application cases cover examples in
retail, transportation or healthcare to demonstrate the
flexibility in various fields.
This demonstrates that controllable sockets are not only
capable of enabling or disabling power, allowing new ways
to configure and prioritize your protected loads. Taking full
advantage of the controllable sockets, these can bring a
series of benefits in terms of longer runtimes for prioritized
loads, extra control over these loads and a more efficient
usage for the batteries.
Thanks to advanced capabilities, innovative UPS systems
go beyond the role of simple power protection and actually
work as a kind of “intelligent power manager” or “power
hub” for your applications. Figure 19 shows a smart way to
configure a rack system where the UPS is its “power hub” for
energy distribution, powering and protecting each load and
managing a series of conditions, such as load disconnection,
reboot, remote control, and so on.
Perhaps readers are keen to learn more about potential
application cases and are wondering – is the series to be
continued? The answer is both yes and no – after reading
this paper, we invite you to follow the outlined approach so as
to define your actual scenario, evaluate load priority, define
the best setup, implement it by configuring the controllable
sockets and ultimately benefit of the advantages of
improving your power protection system.
yyWatch the Liebert GXT4 video at:
https://www.youtube.com/watch?v=YphLv2XEJbQ
yyLearn more about Liebert GXT4 controllable sockets
white paper at:
http://vertiv.es
14
Figure 19.Liebert GXT4 intelligent power management
15
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