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One of the most important questions for IT managers remains: 'Is there an effective power quality support system in place to prevent anomalies causing operating problems and facilitate an orderly shutdown on power failure?' If the answer is no, it will not matter how reliable the IT equipment being used is because its inherent sensitivity to power anomalies will cause continual and often inexplicable operating problems.

The malfunction of an electrical device due to an anomaly in its power supply may have limited consequences. However, if this device is serving other units, the adverse effects could be dramatic. Installing an uninterruptible power supply (ups) with online topology to provide power outage protection and line conditioning is a reliable and cost-effective insurance against the adverse effects of power failure.

But what is the likelihood of damaging power aberrations occurring? According to statistical data from the Electrical Power Research Institute, 92% of all power quality events relate to sags to below 90% of nominal line voltage. The remaining 4% includes surges, spikes, waveform distortions, frequency variations and noise.

Sags (undervoltages) that would not even make a light blink have the potential to reboot or disable a computer, corrupt its data or damage its components. The most vulnerable parts are the switch mode power supply, a common item at the front-end of most electronic equipment, and the variable speed drive, such as is in a computer hard disk.

Surges (overvoltages) can cause breakdown or sparkover of the electrical insulation and damage semiconductors. In particular, surges can cause serious disruptions in computer communication ports and all multiport appliances. Long-term exposure to low levels of transient overvoltages will degrade electronic components and circuitry, which reduces the equipment's life and increases the chance of failure.

It is estimated that 80% of sags are caused by factors within a building, such as equipment stopping and starting. They are also caused by external factors affecting the utility distribution system, such as damage to overhead power lines. Surges may occur due to power switching, static discharges or lightning.

Even a single improperly protected node in a network can cause serious damage in the event of failure. Why take such a risk when the cost of protecting the equipment is negligible compared to the cost of down time?

The benefits of online ups
There are different ups technologies available according to the type of equipment to be protected, the amount of power and how critical the data applications are.

An off-line ups is typically used for stand alone pcs and office peripherals. This turns on back-up batteries if the mains supply fails.

The next level of protection is known as line-interactive, as it has an internal device that allows input voltage regulation within a certain range – 625%. This provides some power conditioning using a 'buck and boost' function, which reduces transfers to the battery thereby increasing its life.

The highest level of protection is provided by online ups technology. This is the most appropriate for a retail operation that has electronic equipment networked to a server. This type of ups maintains a clean consistent voltage at all times because the input power is constantly conditioned and regenerated by a rectifier/inverter circuitry. Unlike the other options, it can fully correct sags, frequency variations and waveform distortions. Also, the inverter is continually on, so in the event of an outage back-up is instantaneous, with no start-up or switching required.