Tip

Choosing the best uninterruptible power supply for your organisation

Power failures are infrequent, but nevertheless they do still occur, thus every business should review its contingency and emergency power plans.

There are two main components in a complete emergency power system -- power generation and protection -- and these are provided by:

  • an auxiliary or emergency power system
  • an uninterruptible power supply (UPS)

An auxiliary or emergency power system provides generated power, usually via a diesel generator, but gas, petrol or hydrogen in the case of fuel cells may also be used. However, there's a delay before a conventional generator reaches operating power and can supply electricity. This gap in supply can cause problems for computers and the applications running on them, so a generator isn't enough to provide a reliable power supply.

This is where the uninterruptible power supply comes in. An uninterruptible power supply provides stored power, usually from lead-acid batteries, but it can also come from NiCad batteries and flywheel systems. Its primary roles are to provide near instantaneous protection from input power interruptions and short-term power in the event of a power failure.

Uninterruptible power supplies correct a variety of poor power quality problems. A sag in power can occur when an air conditioning unit turns on, while power spikes -- brief, high-energy bursts -- are typically caused by lightning or malfunctions in the power supply. Line noise -- usually

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caused by nearby equipment or frequency variations -- and brownouts -- extended periods of under voltage -- are all smoothed out and corrected by an uninterruptible power supply.

The short-term power supplied by an uninterruptible power supply presents enough time in which to shut down protected equipment safely, or to bring an auxiliary power source on-line, which can deliver more sustainable power. For many smaller organisations, a generator is not a viable option. Cost and maintenance are obvious issues, but there can be problems such as location, planning permission, size, noise, heat and exhaust fumes. In such a situation, choosing the best uninterruptible power supply is even more important.

Desktop computers should be supported by an off-line uninterruptible power supply with an Automatic Voltage Regulation (AVR) transformer -- often described as line interactive -- or, if the organisation can afford it, a slightly more expensive on-line uninterruptible power supply . The main advantage of an on-line UPS is its ability to provide an electrical firewall between the incoming power and the equipment connected to it. An on-line uninterruptible power supply may be necessary when the power environment is noisy, such as in industrial settings, for larger equipment loads like data centres, or when operation from an extended-run backup generator is necessary, because electrical interference from other machines -- even a vacuum cleaner -- can disturb power waves. Critical servers should be protected with an on-line double conversion UPS, filtering the input power and controlling output voltage and frequency.

Wherever possible, choose an uninterruptible power supply that has the ability to initiate a controlled shut down of the equipment it's protecting, and check that it can support the equipment's load and sensitivity. The battery runtime depends on the type and size of batteries and rate of discharge -- which, in turn, is based on the type of equipment connected to it -- and for most uninterruptible power supplies  is relatively short, five to 15 minutes being typical. In order to bridge longer supply interruptions, you will need extended-runtime UPSes with extra batteries.

In small offices, a cheaper option is to use laptops instead of desktops that are connected to the mains power via power strips, which include surge protection. This setup only requires the investment of an uninterruptible power supply for the office server. However, it is best to avoid relying on a single uninterruptible power supply, as it can be a single point of failure. It is better to use multiple smaller uninterruptible power supplies to provide greater redundant power protection.

Many servers and more powerful desktops can accept more than one power supply, so. in the event of one power supply failing, one or more other power supplies are able to power the load. Redundancy can be further increased by connecting each power supply to its own uninterruptible power supply. This provides double protection from both a power supply failure and a UPS failure. This configuration is referred to as 2N redundancy. If the budget does not allow for two uninterruptible power supply units, then plug one power supply into the mains power via a power strip and the other into the UPS, making sure each power supply can power the entire server by itself.

If your operations require constant power with no breaks and high reliability, then you will need a generator or generators in addition to uninterruptible power supplies with switchgear, so the generator can start automatically on a mains failure. In such situations, seek professional advice from a company specialising in power protection.

Also, power supply equipment needs to be maintained. A UPS manufacturer's standard warranty is normally only two years, and UPS batteries do decline in efficiency. Regular controlled tests of the system need to be carried out to ensure power can be restored within an acceptable timeframe.

Installing a suitable, uninterruptible power supply is a proactive and cost-effective decision. It helps ensure profitability and employee productivity won't suffer during any type of power disruption, as you can keep your electronic systems running. Doing so also avoids lengthy recovery periods and the need to re-input data. Even if your equipment is insured, the insurance won't cover any loss of goodwill or reputation if your level of customer service is affected. Lightning rarely strikes twice, but make sure you're ready, and install either an emergency power source, or test that the one you have is up to the job.

About the author:
Michael Cobb, CISSP-ISSAP, CLAS is a renowned security author with more than 15 years of experience in the IT industry. He is the founder and managing director of Cobweb Applications, a consultancy that provides data security services delivering ISO 27001 solutions.

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This was first published in March 2011

 

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