We are increasingly dependent on electrical and
electronic equipment in our everyday lives. The proper functioning of
this equipment depends on a good supply of electricity. Unfortunately,
many people wrongly assume that the only time to worry about the effect
of power on computer and other electronic equipment is when there is a
total power cut. Of course this kind of protection is essential and one
must never underestimate the effect total power cuts can have on a
business and on our lives. However, nowadays power cuts in the western
world are very infrequent and what has the greatest impact on businesses
are the fluctuations and disturbances in mains power, which are unseen.
Companies need to rid themselves of the risk of the chance that a power
disturbance or blackout could interrupt their bushiness and yet figures
still show that many organisations fail to protect their business with
the correct UPS back up solution.
What a UPS does is not only provide back up power in
the event of complete power failure but also takes the input
electricity, cleans it up and outputs what is called 'pure sinewave'.
For the most part this solution works well for those seeking reliable
power protection and is highly recommended for industries running any
kind of mission critical systems.
PARALLEL UPS SYSTEM WHY DO WE NEED IT?
However, as the world around us continues to change
the need for businesses to be up and running 24/7 mean organisations
need an even higher level of reliability. Today, competition. extended
shopping hours more demanding customers, virtual shopping, mobile
connectivity, the Internet, to name just a few things, have combined to
change the face of the world in which companies and organisations must
To have computer systems, electrical and electronic
equipment, phone lines up and running is now so critical to an
organisation's survival that failure due to power problems cannot be
tolerated. Organisations such as banks, Internet Service Providers,
telecommunication companies and anyone surviving in the thriving
e-commerce industry cannot afford to have their business to go down at
anytime. If it does it can lead to loss of profits and loss of customers
perhaps the most damaging effect of all.
For piece of mind they need to know that their chosen
back up solution can never fail. They need to know that if anything goes
wrong with one UPS then another takes over at once. Organisations need
redundancy. And the solution? To run a parallel UPS system.
WHAT IS A PARALLEL UPS SYSTEM?
Put simply a parallel UPS system means the linking
together of two or more UPS units in parallel so that in the unlikely
event one fails the other can automatically take up the load. When
buying a UPS in a situation that requires a redundant solution there are
two types to investigate. You can install a parallel redundant system or
an isolated redundant system.
Redundancy in an isolated (or standby) system
configuration depends completely on the on the successful transfer of
the load by the on-line (primary) UPS to its bypass and the graceful
acceptance of that load by the stand-by (secondary) UPS. Theoretically,
it could be a 100% load step, which is a serious transfer.
To successfully obtain a transfer it requires the
following four step procedure:
The primary unit must recognize that a transfer is
The primary unit must ensure that the transfer is
- Bypass source is available - Bypass source is in
Voltage is within accepted limits
Frequency is within accepted limits
The actual transfer action has to take place:
Static switch must turn on
- The primary unit's inverter must disengage
- If there is a wrap-around breaker, it must close
The secondary UPS must accept the load step and
maintain a voltage variation within limits that are acceptable to the
critical load. Actually, since the secondary unit is not supporting any
load, one cannot be certain it is operational and will accept the
transfer at all until it is attempted. What a time to find out there is
These four steps are in series. If any one of the
four steps fail, the transfer fails and the load will be dumped.
Remember. this is an emergency situation. There is no room for a slip.
If the reason for transfer is a faulted bus, the transfer must take
place TWICE before the load bus is attached to a power source capable of
clearing the fault (through the bypass of the secondary UPS). If the
reason for transfer is a failed primary UPS, the module cannot be
isolated for repair because the secondary UPS is feeding the load
through the bypass of the primary UPS. If there is a maintenance bypass,
the load can' of course, be transferred to it but if UNPROTECTED power
is acceptable, why spend the money for redundancy?
A parallel redundant systems, and the systems which
Invensys Power Systems strongly supports, has a number of advantages
that increase the availability of protected power to the load and gives
the customer fewer things to worry about where support of the critical
load is concerned.
With a parallel redundant system the following six
points outline the advantages:
two most critical elements in the isolated redundant scheme are
eliminated: Execution and Acceptance of the load transfer.
Qualification stage is minimised because the normal operation of a
parallel redundant configuration is for the modules to share the load,
which means they must be in sync for both voltage and frequency.
a module is taken off line for maintenance, the remaining module AT
WORST will suffer a 50% load step, which substantially reduces the risk
of voltage variations outside the limits of the critical load (its safe
to say the risk is eliminated). You can be sure the on-line module is
operational and will accept the transfer because it is already sharing
unit that is off-line is isolated so maintenance can be performed.
power to the load is maintained by the on-line unit and automatic
transfer to bypass is still an option if necessary.
a faulted bus occurs, only one transfer is required to reach a power
source (the feeder bus) capable of clearing the fault.
To make a parallel system work you will always rely
on the transfer to bypass happening successfully with the secondary
module always accepting the load gracefully. But if it doesn't you are
back to where you started. A parallel redundant system eliminates the
possibility of this happening.
HOW TO PARALLEL? REDUNDANCY AND CAPACITY?
When installing a parallel redundant system, in other
words to get two or more units to run parallel and share the load the
units must be locked to exactly the same phase. You must then
synchronise the modules, connect them together through the collective
buses of the system thus allowing them to share the load between them.
The system is now ready to achieve redundancy. Load
the system with power equal to the total demand of all the loads minus
the demand of a least one module. This ensures that failure of any one
UPS will not corrupt the power, will allow one to isolate the damaged
module whilst the functioning UPS modules seamlessly take over without
the load ever noticing the transfer.
Doesn't all this sound great. However we still have
one problem. Traditionally a parallel redundancy configuration is
achieved by having a common paralleling logic circuitry in the system.
This logic circuitry gives out individual commands to all the different
units. Unfortunately this can lead to a single point of failure for the
whole system because if the logic circuitry system fails the whole UPS
system will be in trouble. And so what you are left with is a very
complicated configuration that at the end of the day and whilst this
gives you a 98% solid power protection it does not eliminate the risk of
a single point of failure keeping you from receiving 100% peace of mind.
That is exactly why the Powerware Hot SyncŪ
technology was developed. An industry leading paralleling technology in
its own right, the patented Hot SyncŪ enables you to setup a parallel
redundant system giving you 100% conditioned power at all times. Its
unique digital design eliminates the system-level single
point-of-failure inherent in traditional parallel UPS modules and
exponentially increases the reliability of the overall system.
HOW DOES IT WORK?
Hot SyncŪ allows two or more UPS units to cover the
same load in parallel and redundant configuration, by working in
complete synchronisation without being wired together. No common logic
is needed h1 this patented design It provides automatic load sharing and
module level redundancy with nothing other than the power connecting the
Hot SyncŪ does not require any centralised commands
to function. All units are able to function on their own and make
decisions simply by looking at their own output, the UPS modules do not
need any communication between them to load share or to remove a faulty
module from the load bus. If one module fails the other or others
continue supplying the load and the failed UPS module is immediately
isolated from the critical bus while the other UPS takes over the full
load. This means there is no single point of failure, no crashes and
most importantly no downtime. In short the critical load remains 100%
It manages to share the load by making minute changes
to the output phase angle 1000 times per second. If one of the UPS
modules detects that it is getting ahead of the other it will push its
extra load back to the other module until finally the load is evenly
shared. If the load changes all UPSs will see it instantaneously and in
tile same the way. That's why an even load share is maintained even if
the load varies.
Phenomenal growth of super-servers, telecommunication
switching centres, and other large, centralised computing operations,
has created a market need for extremely large power solutions. This need
typically exceeds the capacity of a single UPS module. To address this
shortfall, Hot SyncŪ enables UPS modules to be tied together to create
a UPS solution that protects the entire system, and allows additional
modules to be added as capacity needs grow. It allows customers to
expand effortlessly from a single-module system to a two-module
redundant system and, potentially, to an eight-module system. The
scalability of this system provides customers the flexibility to add the
power protection as their application grows. And it also makes
redundancy for these very large systems a reality. increasing system
availability and overall reliability.
Invensys Powerware is a leading global provider of
engineered power solutions. Offering the broadest range of product and
services available today, Invensys Powerware integrates a full line of
AC and DC power systems, power management software, remote monitoring,
turnkey integration services and site support, providing a seamless
solution. Powerware systems and services deliver the high nines of
availability demanded by today's digital economy. Powerware products and
services are utilized in local and wide area networking, data and voice
over IP, co-location facilities, fixed-line and wireless communication
networks, and industrial manufacturing. Invensys Powerware is
headquartered in Raleigh, NC, and is part of Invensys plc.
Invensys plc is a global leader in production
technology and energy management. The group helps customers improve
their performance and profitability using innovative services and
technologies and a deep understanding of their industries and
Invensys Energy Management works with clients
involved in the supply, measurement and consumption of energy and water,
to reduce costs and waste and improve the efficiency, reliability and
security of power supply. The division includes Energy Management
Solutions, Appliance Controls, Climate Controls, Global Services,
Metering Systems, Powerware and Home Control Systems. These businesses
focus on markets connected with power and energy infrastructure for
industrial, commercial and residential buildings. The company also
serves the specialized rail, wind-power and electronic manufacturing
(power components) markets through Invensys Rail Systems, Hansen
Transmissions and Lambda, respectively, in its development division.
Invensys operates in more than 80 countries, with its headquarters in
The writer is Product
Marketing Director EMEA, Invensys Powerware