South Africa's fast growing economy places a high demand on production which cannot afford downtime due to power outages. Loss of production results in loss of revenue and with power failures being at the centre of some of these problems, companies are increasingly looking at specialised power protection to avoid this scenario. This can be seen in the fact that more uninterruptible power systems (UPSs) are now being installed as they have become a necessity rather than a 'nice to have'.
Protection against power failures is not the only advantage gleaned from a UPS system - they also have an inherent capability to regulate the mains supply and also to isolate the critical load from any irregularities on the mains supply that may be caused by voltage surges and dips.
Choosing the correct UPS for your application
How you go about choosing a UPS is absolutely critical, as the wrong UPS for the application can further compound existing problems. Too many people are suckered into purchasing UPSs that are completely unsuitable for their application, with decision making criteria being overshadowed by that one nemesis, 'the price'. Far too often the initial cost is given too much attention, with both the operational risks and downtime due to malfunction not being carefully considered.
Typically, there are two types of on-line double conversion UPSs available, the one being transformer-based and the other a transformerless unit. But… there are also significant technological differences that result in differences in both physical size and the cost of the two types of UPS systems. These differences are of paramount importance when the long-term operational performance of the UPS is being investigated and one should remember that when the primary reason for purchasing a UPS is to provide maximum protection and avoid costly downtime, that the initial cost should not be the defining criterion.
By definition a transformerless UPS (sometimes called a solid state UPS) is exactly what the name implies: a unit without the large input rectifier/charger transformer. The result is a smaller footprint, a lower component cost and, consequently, a smaller price tag.
But this is not all good, due to the fact that in most environments the quality of supply can be degraded, creating voltage transients which can affect a transformerless UPS just as badly as the equipment the UPS is intended to protect. Yes, one can install an isolation transformer but this ends up being more expensive than considering a transformer-based UPS in the first instance.
Similarly, consideration must be given to extended battery back-up applications as typically the standard solid-state type machines often do not have sufficient capacity in the rectifier charger to accommodate larger battery sets and the batteries then do not get charged at the correct rate to ensure full performance when called upon.
On the positive side, solid state UPSs do have the advantage of low input stage harmonic reflection, making them far more suitable when generators are involved as a source of extended alternative to mains supply. But one should not forget that these solid state UPSs still require protection from mains power whilst mains power is present. Also, the solid-state type UPS is generally more technologically advanced, offering additional features such as parallel redundancy, battery management programs (see picture), and advanced performance monitoring.
In applications where downtime is simply not an option, parallel redundancy is the best solution, reducing the risk of downtime by a factor of 10.
Smaller UPSs, typically below 5 kVA in rating, are also available in line-interactive technology, a hybrid technology between off-line entry-level machines and the proper on-line double conversion design. Whilst line interactive UPSs have their niche in the power protection arena, engineers need to understand that these systems have lower price tags for very specific technical reasons. Most line interactive UPSs simply will not work off generators as they are very susceptible to frequency variations, and some generators do struggle to maintain their output at 50 Hertz. The battery then becomes a source of alternative power and eventually when the battery is flat the UPS simply 'powers off'. Another downside is that this constant micro discharge from the line interactive UPSs batteries is similar to the detrimental effect that ripple current creates, resulting in shortened battery life and lower backup times.
So, in short, speak to the experts when it comes to UPS usage and the expected degree of protection.
Maintenance
Simply having a UPS installed does not mean that you are now home free. Far too often, maintenance of the UPS system is completely overlooked. Just like any other equipment, a UPS system requires ongoing maintenance to ensure that when called upon, it will perform to expectation. Poor environmental conditions are the single largest contributor to UPS failure. Environmental temperature, both very high and very low, will have an extremely adverse effect on battery performance and life expectancy. Meissner offers maintenance contracts for UPS systems that include periodic servicing, battery performance evaluations and site critiques. This creates a preventative maintenance culture that is pro-active rather than re-active and ensures that UPSs are always operating at their optimum. All Meissner's Maintenance Contract customers receive priority response and preferential spares pricing over non-contracted customers.
Professional consultants
So… do not just rush out and purchase the cheapest UPS you can source. Ask yourself, if the UPS is so cheap, what am I missing, or what vital components have been omitted in the design. Speak to your electrical consultant or a supplier such as Meissner for the correct advice on choosing the correct UPS for your application.
Meissner runs countrywide seminars on an ongoing basis and covers issues such as how to correctly specify a UPS, and how a UPS's battery is rated. There are batteries… and then there are batteries that are suitable for UPS applications. Watch that price, as far too often a low budget determines the quality of the power protection system eventually purchased, and unscrupulous suppliers are willing to part customers from their hard earned cash in return for expensive problems and higher risks than are actually necessary.
For more information contact Graham Beyleveld, Meissner, +27 (0)11 824 0202, [email protected], www.meisner.co.za
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