During storms or when the national network of electrical energy falls, we have an alternative, namely the energy back-up system (or UPS system).The UPS (uninterruptible power supply) is an electrical apparatus which provides emergency power to a consumer(when the main input power source fails).
The process of choice of such systems is done in several stages.
In the first we have to determine its purpose (for what it is used, the power requirements, the identification of the according UPS type); then the parameters of the identified UPS are analyzed ( its availability, maintenance, security, cost/function assessment).
If many electrical systems (such as: conditioner air, ventilation, warming systems) can tolerate the lack of energy, there are many critical systems for which functionality termination is not desired. The most common purpose of using a UPS is saving data from an IT system, but at a close examination, this area can be extended. The purpose of using a UPS may be various: from the support of servers and workstations to support an emergency lighting system or a medical equipment in a surgery room.
The UPS equipment is recommended to be oversized, but at the right level. This is because of two main reasons: for the effective management of peak consumption and for the possibility for other consumers to be added afterwards (without having to purchase a new UPS ). Usually, the “oversize” is done within a percent of 30%.
For a correct dimensioning of the UPS system power, it is good knowing that if we have a usual system with a 17” monitor, then we probably need a power of 500VA; for a 19” monitor we’ll need a power of 650VA. If together with these we use a laser or ink-jet printer, then the above power needs to be augmented by 150-200VA.
An UPS energy accumulator is manufactured from lead or nickel-cadmium. Usually, at a 100% charge , the UPS autonomy (or back-up time) is between 3-10 minutes, but in some models this can be extended (by additional batteries installed inside the UPS).
The main types of UPS are: the stand-by (which is the simplest and cheapest technology), line-interactive and double-conversion (which is the most complex and most expensive technology), hybrid topology (double conversion on demand), ferro-resonant, DC power and rotary UPS.
If the stand-by UPS protects against voltage drop and shock (transients phenomena), the line-interactive UPS protects also against voltage variations (it is additionally a multi-tap variable-voltage autotransformer, which is a type of electrical transformer that can add or subtract power, thereby increasing or decreasing the output voltage of the transformer).
If the network voltage is between 205 to 235V, then a stand-by UPS is recommended; if the voltage does not fit into that scale or if it has fluctuations , then a line-interactive UPS is recommended .
The double-conversion UPS is recommended for industrial settings (when the power environment is ‘noisy’) or for data centers (larger equipment loads) or when operation from an extended-run backup generator is necessary.
