partly because its continuous operation is essential to the organisation’s viability. Critical loads include computer and communications systems, industrial process control, medical equipment, point of sale terminals and online transaction processing hardware. Within these loads, brownouts or sags can cause equipment malfunction or rebooting where computers believe they are being re-started. Spikes can damage load equipment, while surges can degrade switched-mode power supplies and cause premature equipment failures. The potential for data loss and corruption is equally serious.
Protection Possibilities Critical loads can be protected from these power problems. Uninterruptible Power Supplies (UPS) offer the most comprehensive protection currently available. UPSs are solid-state assemblies that connect to the incoming mains supply and feed power to the site’s critical load. UPS systems contain batteries that store electrical energy when the mains supply is available, and feed it to the critical load whenever the mains supply is compromised. A UPS must also have a rectifier, battery charger and an inverter to convert the DC battery power into an AC mains supply level to suit the critical load. All modern UPSs also include a bypass system and a switch allowing direct connection of the critical load to the incoming mains supply when required. These components are typically
arranged in dual conversion configuration in which, during normal operation, the incoming mains supply is rectified and used for float-charging the battery, then inverted back to the critical load AC level. During mains failure, the charger shuts down and the battery takes over the mains supply by discharging through the inverter. This topology offers the best possible protection for the critical load for two reasons. Firstly, whenever the mains fails or falls outside acceptable limits, transfer to the battery is invisible to the load, which suffers no power interruption or disturbance. Secondly, the inverter and rectifier act as a barrier to mains borne noise and transient voltage excursions,
as well as providing a well-regulated output voltage. The load enjoys protected power at all times, irrespective of whether it is supplied from the mains or the UPS battery.
UPS Factors When the case for UPS protection becomes clear, suppliers can advise on suitable products matching them to site requirements. However, site managers can start by considering the key factors relating to UPS deployment and maintenance as an efficient and effective power protection facility. These include taking advantage of the latest technology, maximising UPS availability, choosing suitable battery autonomy, and making adequate provision for repairs and maintenance. Trends in UPS development over
recent years have had a significant impact on their size, and consequently on their resilience to failure, availability and maintainability. Originally, UPS designs typically included a transformer to boost the inverter output to a level compatible with the critical load requirement. Since the 90s, advances in semiconductor technology have eliminated the output transformer, yielding a significant reduction in UPS size and weight, and improving energy efficiency. This has allowed the more recent concept of modular design, where the smaller, lighter implementation means that a UPS can comprise a number of independent modules in a rack rather than one large standalone installation. Repair of a failed module can
be achieved simply by a ‘hot-swap’ replacement, an operation that can be completed in about half an hour, compared with the six hours usually needed for in-situ repair of a standalone system. The UPS’s availability, which is a comparison between the equipment’s Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR) is also significantly improved, with up to 99.9999 percent being possible. Battery autonomy refers to the time
for which a fully charged UPS battery could support the critical load during a mains failure. It depends on the battery capacity compared with the
Trends in UPS development have had an impact on their size.
critical load size. 95 percent of all mains disturbances last either for less than five minutes or for several hours. A battery autonomy time of 10 to 30 minutes, depending on site requirements, is therefore standard. Some loads must remain online even if a mains failure or problem lasts for several hours, a requirement not realistically supported by battery autonomy times. A typical solution to this is to use a generator, in which case the UPS’s role is to provide sufficient battery autonomy for the generator to start-up and supply power. Maintenance of modular systems
becomes easier as repairs require less skill as well as less time, and stockholding is simplified. However, a preventive maintenance program is always recommended, especially for batteries with a finite life. Regular inspection of batteries and other key components can ensure that problems are resolved before they cause failure. Reputable UPS suppliers can advise on and offer service plans for planned maintenance together with callout support appropriate to the needs of each specific site load.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60