FOCUS on POWER


UPS


Getting a jump start


The UPS comes in many different sizes. It also performs different functions, getting the correct system is vital – though not easy. Ambrose McNevin offers a guide on where to start


Early 2011 and already we’ve have some significant product announcements in the uninterruptible power supply (UPS) space.


Riello entered the flywheel UPS market through a distribution partnership with Vycon. Emerson Network Power, or rather the part of Emerson now known as Chloride, powered by Emerson, said 300, 400 and 500kW versions of its transformerless Chloride 80-NET product were shipping in Europe, Middle East and Africa, Asia and Latin America. While Uninterruptible Power Supplies, part of Kohler, unveiled a compact PowerWAVE 5000/TP UPS System.


But before we get lost in the forest of new products and their bespoke terminology and brand names, here is a short guide to the UPS market.


Power frequency variations


THE UPS ABC We hear a lot of talk about the limits of what a UPS can do in terms of load and efficiency and there is a remarkable level of confusion about this in the market. But let’s take a step back even from this. What is a UPS for?


In a nutshell, when faced with common electrical disturbances (see figure 1) a UPS must be able to supply high quality or clean power to the load during large voltage amplitude fluctuations – that is when the quality of the power is not good enough for the load. It must also ensure continued supply during total power outages (when the mains is lost it must kick in within milliseconds and power the load through local energy storage devices such as batteries or flywheels). It must maintain this


DC components


Other disturbances include notching, electric noise and inducted low frequency voltage and oscillatory transients. Source: Emerson


power while the alternative power source, usually diesel generators crank up. The UPS, therefore, must be matched to the load it is expected to provide during a brown out - but this is not as simple as it sounds.


Riello offers a short guide. Firstly, it says, on rear panel labels and in user manuals hardware manufacturers often rate power usage unrealistically high. It is not uncommon to see loads running at only 50% of this. In addition, any ratings given may be in Amps or Watts. There can also be a difference between in-rush (start-up) and running power. (See the power update on


page 60 in the main magazine for a guide to end the confusion between Amps and Watts)


It is important, therefore, when sizing UPS to carefully consider: apparent power (VA – a unit of measure for the apparent power drawn by an electrical device); active power (Watts – a measure for the real power or active power dissipated by the load) and Power Factor (PF – sometimes referred to as displacement power factor or phase power factor). It is the ratio of real power to apparent power in an alternating current (AC) circuit. The higher the input power factor, the more efficient the UPS will be.


Harmonics and inter-harmonics Voltage fluctuations and flickers


Figure 1: The electrical supply quality depends on several types of disturbances that can be briefly summarized in the following categories


Voltage dip (sag) and interruptions


Voltage imbalance


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