For Data Centres, power protection systems must be available every second of every day and therefore maximizing system availability must be the overriding objective of any installation. Availability is best described as the percentage of system uptime achieved in a year. To achieve maximum availability, all single points of failure within the UPS need to be removed. Over the years, many improvements have been made in relation to UPS technology and configurations to increase availability.
Availability requires duplication and redundancy which naturally introduces inefficiencies, thereby increasing energy requirements. For example: thirty years ago, the only way to achieve redundancy was to install a number of standalone UPS modules in a parallel topology. These stand-alone systems could be pretty big, for example: 60KVA UPS weighed around 600kg and was the size of a double wardrobe! In addition to the UPS modules were the associated battery systems.
The introduction of transformer-less technology in the early 1990s, by Filippo Marbach, dramatically increased efficiency, decreased size, weight and reduced costs. The true modular UPS concepts, introduced after the year 2000, resulted in even further improvements
The 4th Generation true modular UPS systems now available, provide a significant improvement over previous system designs. This is because each module contains all the power elements of a UPS – rectifier, inverter, static switch, display – and critically – all control and monitoring circuitry. This places it above other current designs that have a separate, single static switch assembly and separate control or intelligence modules as there is no single point of failure. Availability for our CumulusPower UPS which incorporates this Distributed Active Redundant Architecture (DARA) system is now ‘nine-nines’ or 99.9999999%. Hot-swap capability lowers the Mean Time to Repair (MTTR) to only around three minutes.
Scalability and flexibility are also important when installing a system to ensure the continual ‘right sizing’ of the UPS. A system which is too small will be overloaded, compromising reliability and availability. One which is too large will waste energy, be inefficient and costly to run. CumulusPower offers a flat efficiency curve across the whole load range, particularly at lower loads which are inherent in parallel redundant UPS configurations. CumulusPower offers 97% efficiency even at these low loads.
Duplication and redundancy of UPS components must also apply to the communication cables between UPS modules. The most simple communications bus is a single cable. If this breaks or becomes disconnected, the entire system could be compromised.
For this reason, the ring circuit was introduced to the majority of modern UPS systems. If the circuit breaks the signals can simply communicate the other way around the ring. The recent introduction of the Triple Mode communications bus increases system availability even further.
Like its name suggests, there are three paths of communication between UPS modules and frames made up of three separate ring circuits. Three brains communicate with three other brains – it’s the belt, braces and buttons approach.
We liken Triple Mode to the comparison of a tightrope walker. If a tightrope breaks, the consequences will be dramatic and far-reaching. In the same way, a single communications bus is far more precarious than a Triple Mode ring connection which is more like a bridge with multiple supports. Here the single points of failure are completely removed. Even if one or several bridge struts fail, the others will support the load. It does beg the question: how would you prefer to cross the chasm?
UPS technology has seen huge developments over the years. With reductions in footprint and increases in efficiency and availability, the Total Cost of Ownership is now significantly lower. The most modern UPS have become about as close to perfect as possible, keeping in mind there will always be some losses due to the very nature of switching. The incorporation of Triple Mode communications buses further mitigates the risk and moves us further towards power protection perfection.
The team at CENTIEL has been at the forefront of UPS development over the several decades. Our goal is clear: to achieve the ultimate availability of power for our client base. Our leading-edge technology, backed-up with our comprehensive maintenance contracts ensure our clients’ power has the very best protection at all times, now and in the future.
Originally featured in UK Power August 2018
Presenting a paper at the recent Data Centre World conference, Mike Elms posed some searching questions on the subject of fourth generation modular UPS technology. Here, he details that presentation considering the challenges of achieving Tier IV availability, achieving very low PUE and how the latest UPS technology can help achieve the apparently mutually exclusive objectives of Tier IV availability plus very low PUE.
Can fourth generation technology improve datacentre availability above that required by Tier IV (99.995%) and help achieve a power usage efficiency (PUE) less than 1.1?
The primary objective of any datacentre is to achieve the highest possible availability. The Uptime Institute created a tier system (Tiers I-IV) for datacentres. Tier IV fault tolerance (Availability) certification is the highest and requires 2N or 2N+1 duplication/redundancy to give 99.995% availability. Being awarded Tier IV status is advantageous for both the client as it provides the highest level of security of supply and the datacentre as it can receive increased revenue for this enhanced service.
The secondary objective of any datacentre is the highest possible efficiency. The Green Grid has suggested a metric known as power usage efficiency (PUE) which can be calculated by dividing the total datacentre power by the ICT Power, ie total power suppied to the facility divided but useable IT computing power. However, this gives datacentres an Availability versus PUE dilemma: the Uptime Institute’s Tier IV availability requires duplication and redundancy which naturally introduces inefficiencies, thereby conflicting with The Green Grid’s low PUE requirements.
At this point, it must be noted that the two big users of power in a datacentre are: power protection systems (UPS) and HVAC (air conditioning). One Tier IV mega datacentre belonging to Facebook in Lulea, is built inside the Arctic Circle. They have access to free cooling due to its geographical location and it is also built near hydro-power plants which offer multi-path, environmentally clean, reliable power. However, medium and micro datacentres (i.e. almost all datacentres) do not have the opportunity or budget to build inside the arctic circle and are built in and around city and town centres. As a UPS provider, a datacentre’s location is outside of our control but in this article we can consider how the latest UPS technology and innovation can combine the dual benefits of very high availability and very high efficiency in this medium and micro arena.
Tier IV using Monobloc UPS
If a datacentre needs “N” power: an N system has 1 UPS module, an N+1 system has 1 “module” of redundancy, a 2N system has 100% duplication (i.e. two independent paths that are normally refered to as “A” and “B”) and a 2N+1 system has both duplication and redundancy.
If we consider a 2N datacentre with a 100% design load (i.e. two UPS systems, one supplying A and the other B) the maximum load on each UPS in normal operation would be 50%. If the same UPS systems were in a 1+1 parallel redundant configuration (the most common parallel configuration) then there would be two UPS modules supplying A and two supplying B and therefore the maximum normal load on each UPS would be 25%.
However, datacentres never operate at 100% of their design load so if we consider a 2N datacentre with a more realistic 60% (of the design load) as an actual load the maximum normal load on each UPS would be only 30%. If the same UPS systems were in a 1+1 parallel redundant configuration the maximum normal load on each UPS would now be only 15%.
As can be seen in Figure 1, even with the latest transformerless design UPS modules there is >3% difference in operating efficiency between the UPS loaded at 50% and the UPS loaded at 15%. When you consider that datacentres are running 24x7x365 and need a lot of power, 3% “wasted” energy represents a significant amount of power and therefore money over the working life of the datacentre.
What the above demonstrates is that using monobloc UPS and the Uptime Institute’s Tier IV “2N” and/or “2N+1” suggestion(s) to achieve Tier IV levels of availability directly conflicts with The Green Grid’s requirement for a very low PUE. But what if 4th Generation Modular UPS were used? 4th Generation Modular UPS has a number of features which ensure high availability AND reduce PUE.
4th generation modular UPS
From an operating efficiency perspective, 4th Generation modular UPS technology has two very distinct advantages over the previous technology. These advantages are a class leading “true on line” efficiency curve (see Figure. 2 below) and the ability to enter what is commonly known as an “active sleep” mode. Active Sleep Mode is a user enabled function which only becomes active when the actual load is low enough (as defined by the user). In this mode, all UPS modules in excess of those needed to fully support the load with the required levels of redundancy are put into an active sleep which keeps all UPS monitoring and circuitry alive but inhibits the actively sleeping UPS from switching power, thereby eliminating their switching losses and increasing system efficiency.
Tier IV using 4th generation modular UPS
Using exactly the same examples as above, our 2N datacentre with a 100% design load (i.e. two UPS systems, one supplying A and the other B) the maximum normal load on each UPS would still be 50%. However, if the same UPS systems were in an N+1 parallel redundant configuration where N was, say, 5 modules, then there would be 6 UPS modules supplying A and 6 UPS modules supplying B but this time the maximum normal load on each UPS system would be increased to 42%.
As previously stated, datacentres never operate at 100% of their design load so if we consider a 2N datacentre with a more realistic 60% (of the design load) as an actual load the maximum normal load on each 5 module UPS system would still be 30%, however, if the same UPS systems were now in a 6 module parallel redundant (i.e 5+1) configuration and active sleep was enabled the maximum normal load on each fully switching UPS module would now be 75%.It is a given that to minimise power losses (and hence minimise PUE) a UPS needs to operate at the best point of its efficiency curve. A system which is too small will be overloaded, compromising reliability and availability. A system which is too large will waste energy, be inefficient and costly to run. It will also cost more than necessary to purchase and maintain due to its size. Scalability and flexibility is therefore essential to ensure the continual ‘right sizing’ of the UPS and is easily achievable with the latest 4th generation modular UPS. The efficiency curve of 4th generation modular UPS is also much flatter with efficiencies of greater than 96% now achievable even with vey low load levels in the teens. This is how 4th generation modular UPS, when correctly configured, can help minimise PUE.
We have shown above how system configuration can minimise PUE but does the same configuration maximise availability? Availability is MTBF divided by the sum of MTBF plus MTTR. Availability is maximised when Mean Time Between Failure (MTBF) is maximised and Mean Time To Repair (MTTR) is minimised.
4th generation modular UPS maximise MTBF in a number of ways. Distributed active redundant architecture (DARA), provides a significant improvement over previous UPS system designs. With DARA, each module contains all the power elements of a UPS – rectifier, inverter, static switch, display – and critically – all control and monitoring circuitry. This places it above older designs that have a separate single static switch assembly and separate control or intelligent modules (and therefore single points of failure).
As all 4th generation UPS modules are 100% complete UPS, the fast, simple “hot swap” replacement of a faulty module guarantees a UPS repair regardless of the problem. The key point is therefore speed of repair and a 4th generation modular UPS module takes less than 3 minutes to replace and MTTR is minimised.
The combination of very high MTBF and, most importantly, class leading MTTR, means that 4th generation modular UPS availability of 99.9999999% (“nine 9s”) is achieved. An independent white paper, validated by a leading Swiss university, showing how and why “nine 9s” is achieved in more detail, can be downloaded from the Centiel UK website (www.centiel.co.uk)
The author: Mike Elms is sales and marketing director at Centiel UK Ltd
Originally featured in Data Centre Review April 2018
Uninterruptable Power Supplies Limited (UPSL), a Kohler Company, today announced the arrival of its new lithium-ion battery solution for UPS systems, providing a range of enhanced technical features and practical benefits for critical applications across the country.