Main Power
Online Uninterruptible Power Supplies
Ensuring uninterrupted power is a vital part of any organisation’s business continuity planning and can be achieved with the correct deployment of suitable uninterruptible power supplies (UPS). Different types of UPS can be used as stand-alone solutions or in conjunction with one another other. The three main static UPS topologies are as follows: Online (‘On-line’) or Double Conversion VFI (Voltage and Frequency Independent, Line Interactive VI (Voltage Independent)and Offline (‘Off-line’) or Passive Standby.
So what are the main characteristics of an Online Uninterruptible Power Supply? The only UPS for completely break-free supply. An online uninterruptible power supply (UPS) maintains power voltage and frequency variations within prescribed limits and is independent of any fluctuation in supply. It’s not just complete power failure that can affect a modern power-hungry business. The online UPS also conditions mains power to counter the potentially damaging consequences of sags, surges and other everyday power problems.
Because of this combined power protection and power conditioning capability, the online UPS is the preferred choice for critical data and voice processing systems and remote mobile telecommunication sites where there may be a high risk of damage from local lightning strikes and high-energy transients. Furthermore, an online UPS can also act as a frequency converter providing 50/60Hz or 60/50Hz. There are also solutions for 400Hz applications.
Of the three main UPS topologies, the online uninterruptible power supply is the only one that can provide completely break-free protection if the mains supply should fail. And, in the event of the UPS developing a fault or suffering an overload, the online UPS is designed to deliver safe failure to mains. This is achieved through an automatic system bypass.
Typical online UPS applications. Online UPS from manufacturers such as Riello UPS are typically used for specialist operations. They can be easily modified using a range of accessories and ‘small batch’ production techniques. Typical applications for the online uninterruptible power supply include the following: rail equipment requiring extended runtimes, remote telecom sites, industrial applications requiring specialised air filters, water treatment works requiring UPS with raised plinths and high ingress protection, scientific sites at altitude or in tropical areas, military applications requiring ruggedised assemblies, remote sites where only renewable energy sources are available and medical applications requiring isolated supply.
Online UPS are particularly suitable when it’s necessary to expand large-scale Power over Ethernet (PoE) implementations, requiring an upgrade to the current level of UPS protection. Maybe the existing uninterruptible power supply is no longer large enough to power the entire infrastructure or, as in the case of a telecom application with existing line interactive UPS installation, perhaps the available runtime duration is not long enough. When business continuity planning has reached this stage, it may be time to upgrade to an online UPS for maximum power protection.
Sizing an online UPS for current and future needs. Regardless of the application, correct sizing is essential to avoid over- or under-specification that wastes resources or leaves parts of the network vulnerable. Then, once the current load requirement has been correctly established, it is prudent to include an allowance for future expansion. The most common approach is to allow for 25% load expansion within five years. For online UPS (above 10kVA), additional capacity, along with higher operating resilience, can be achieved by adding more modules into an existing system using a parallel architecture.
Whatever the requirements of a business’s power continuity plan, and whatever the eventual uninterruptible power supply solution, the first step should always involve seeking the advice of a reputable UPS manufacturer with a proven track record in power protection. Whether for an online solution or one of the other UPS topologies, a modern consultative UPS specification process ensures that uninterrupted power for mission critical facilities are easy to achieve.
About the Author
Robin Koffler is the General Manager for Riello UPS Ltd the UK subsidiary of Riello UPS (RPS S.p.A) a leading European manufacturer of Uninterruptible Power Supplies and a co-author of The Power Protection Guide(ISBN 978-0-9554428-0-3)- available from Amazon.com
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