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UPS Jargon Buster

If you’re trying to specify a UPS system, you’ll find yourself confronted, as with any technology, by a fair amount of jargon – which could be confusing if you’re not familiar with it. Our Jargon Buster below is intended to clear away any such confusion and to help you decide the best UPS for your requirements. 

Availability is a measure of how much time per year a UPS system is operational and available. UPS availability is a function of mean time between failures (MTBF) and of mean time to repair (MTTR). 

Hot-swap modules
Hot-swap modules can be safely plugged into or removed from a UPS system without having to interrupt power to the critical load or expose it to raw mains power. Assuming the system has redundancy (additional module(s) to protect the load whilst one module in swapped out).

kVA or kilovolt-ampere (1000 volt-amperes) is a measure of the apparent power rating of a UPS or other power device. It is the vector sum of actual (or active) power in kW, and reactive power. kVA relates to a UPS system’s maximum permissible current, while kW describes its power-handling capacity. The less reactive a load is the smaller the difference between its kVA and kW rating.

Power Factor (pf)
Power Factor is the relationship between actual/active power (W or kW) and apparent power (VA or kVA), where power factor = W/VA. Ideal (direct current loads or resistive) loads have unity power factors, while reactive loads have a power factor value between 0 and 1. Low power factors are undesirable as they create large reactive currents which increase energy costs and impose higher equipment ratings without performing useful work.

Redundancy is whereby a UPS has additional power module(s) so that in the event of a fault, replacement or other disturbance to one power module, the UPS system remaining power modules are capable of maintaining power protection to the critical load. The faulty module can then be replaced without disturbance to the load, redundancy gives installations/sites more resilience.

Lead acid battery (VRLA = Valve Regulated Lead Acid)
Lead acid batteries are the most used battery type for stationary applications. Expected life for this kind of batteries is typically a 3-5 year or 8-10-year, installation/cycle/environment dependent. One disadvantage of lead-acid batteries is usable capacity decrease when high power is discharged. For example, if a battery is discharged in one hour, only about 50% to 70% of the rated capacity is available. Other drawbacks are lower energy density (lead has heavy specific weight) and the use of lead, a hazardous material prohibited or restricted in specific environments and applications.

Nickel-cadmium battery (NiCd)
Compared to lead-acid batteries, NiCd batteries have a higher power density, a slightly greater energy density and the number of cycles is higher. NiCd batteries are relatively rugged, are the only batteries capable of performing well even at low temperatures in the range from -20 °C to -40 °C, and their life expectancy is still good even at high temperature, so they are used in warm countries and in applications where high temperature is a constraint. 

Lithium-ion battery (Li-ion)
Li-ion batteries have a high gravimetric energy density, meaning that a Li-ion battery solution is lighter and needs less floor space compared to LA or NiCd batteries. For Li-ion batteries, the calendar life (over 10 years) and cycle life (thousands of cycles) are very good even at high temperatures.

Static Transfer Systems (STS)
Static Transfer Systems (STS) are intelligent units that transfer the load to an alternative source when the primary source is out of tolerance or no longer present. This ensures "high availability" of the power supply for sensitive or critical installations. The purpose of STS devices is to ensure the redundancy of the power supply to critical installations by means of two independent power sources, increase power supply reliability for sensitive installations, facilitate the design and expansion of installations that guarantee a high availability power supply, and increase the overall site flexibility, allowing easy and safe maintenance or source replacement.

Fast EcoMode
FAST EcoMode is whereby the UPS supplies the critical load via its bypass line, this increases the efficiency of the UPS as it is not conditioning the output like it would be if in online mode. In the event of the supply having impurities or fault, the UPS will transfer the output supply from the bypass line to the inverter output, having a minimal transfer time.

If you need a little extra help with deciphering the UPS jargon, be sure to get in touch with our Technical Services department who will be more than happy to help you with your search for the best UPS for the job.

Download our Jargon Buster.

22 May 2019