UPS (uninterruptible power supply) device is a critical object in the data centre technological infrastructure. And besides, it is important without reference to the computing amount (and consequently also to the power of the devices), which is processed at the data centre.

The UPS system has most probably been encountered daily by anyone who has spent some time in the IT industry or has simply worked for a company that has employed people responsible for the technologies to provide uninterrupted operation of the IT system in cases when there is a short-term interruption in the power supply. It was especially important for so-called desktop computers, which in comparison to laptops do not have their own alternative power source except the 220V voltage provided by the internal building power network. Many of us remember such cases with fearful hearts and minds – will or won’t the last piece of work or even all the information stored on the hard drive of the computer be lost.

Despite the fact that the first impression makes one consider that an UPS device is comparatively primitive and choosing it might only be basically related to the necessary electricity power which has to be provided in the case of a short-term power interruption, there are several things to consider when choosing optimal devices.

In comparison to backup generators, which provide alternative electricity power for devices of the data centre in situations when there is a fault in the power supply, providing it for hours and, if necessary, even for days, UPS provides a different function.

UPS provides an uninterrupted, stable power supply to devices in order to level out the changes in power voltage and short-term interruptions. The mentioned short-term events are too transitional to be reacted to by a backup generator system, but their damage can be identical to a fundamental electricity power interruption that lasts for several hours.

Thus the task of a UPS is not only to serve as a short-term backup power source in the case of a power supply interruption, but also to level out the voltage in cases when there are voltage fluctuations in the basic power connection. As already mentioned such short-term voltage fluctuations may cause the same damage to an IT system as short-term interruptions of the voltage supply.

In a way UPS may be compared to a power source such as a battery, where the storage of electric power is provided by chemical processes. Despite the fact that there is one basic task for all UPS devices – to provide a stable power supply for devices in cases of short-term power fluctuations in the central electric power supply, devices of various types with different parameters are available.

UPS devices are divided into 3 mains types:

1. The so called standby or the so called offline UPS device is the simplest and cheapest solution, which basically provides the provision of short-term backup power in cases when the power supply is temporarily terminated entirely. While the central power supply is provided, the UPS device charges its battery. As soon as the voltage supply is interrupted, UPS switches to the power supply source and provides a short-term power supply to devices, so that the device administrator is able to activate a more reliable backup supply solution or to correctly shut down the devices, so that the power interruption does not cause irreversible damage to them. In the case of a data centre such devices cannot be used, because in principle they do not provide protection from voltage fluctuations which do not result in complete power supply interruption.

2. Interactive UPS system. The basis for this UPS device is a solution that provides uninterrupted current flow. The device is actually active the whole time. As soon as there are fluctuations in the current, the voltage is stabilised by electronics and the device battery. Due to the principle of its operation, devices of this type are also able to provide a stable voltage supply for technologies in situations where the current supply is not principally interrupted, but there are changes/fluctuations in the voltage.

3. Double conversion (online) UPS devices provide the greatest protection against various voltage quality problems. Instead of switching from the central current supply to the UPS battery, these devices transform the input alternating current to direct current and back. Part of the direct current is used to charge the UPS device accumulator, but the remaining current is converted back to provide the devices with alternating current power. Such a system practically eliminates any risk of electric power fluctuations. But it also has its flaws. This is the most expensive system, and it also creates greater loss in power and thus also effectiveness when consuming energy, which is necessary for transforming the alternating current into direct current and back. An additional side effect is the production of heat, which is created while the device is operating. This creates an additional power consumption position for cooling devices.

In the case of introducing data centre technology it is important to precisely evaluate the most appropriate UPS solution, as well as to provide correct development of the UPS connection scheme. Regarding this matter it might be useful to seek advice from experts who work with the construction of critical systems and have implemented such solutions in practice.

But no matter what type of UPS device is being used, one must remember that it is only a short-term solution for cases of current fluctuations or short-term power supply damage. It is actually a solution that provides extra time to activate the basic backup power system – diesel generators.