A UPS's output rating is shown as 2000VA/1800W. I understand that the power factor here is 0.9, but the device or load I will connect to the UPS might have pf<0.9 or pf=1 (for light bulb.) From my understanding, the real and reactive power will vary based on my load's pf. Then why does UPS specif Contact online >>
A UPS''s output rating is shown as 2000VA/1800W. I understand that the power factor here is 0.9, but the device or load I will connect to the UPS might have pf<0.9 or pf=1 (for light bulb.) From my understanding, the real and reactive power will vary based on my load''s pf. Then why does UPS specific a fixed pf? Isn''t it enough just to mention the VA rating?
With the loads presented to a domestic UPS being resistive (incandescent lamps) / inductive (ceiling fans) / capacitive (CFL / LED lamps), the probability of the reactances cancelling out does exist.
The UPS manufacturer may hence assume a power factor of 0.9 (midway between 0.8 & 1!) and give the rating in kW in addition to kVA.
There is no need to specify wattage for the UPS as VA rating is enough and complete. However, since a layman generally understands wattage best, the manufacturer has also specified its capacity as 1800 watts assuming a power factor of 0.9 for the load. If the load is theoretically assumed as completely resistive ( power factor 1), the same 2000VA UPS will deliver 2000 watts.
First reason is redundancy/simplicity. Not everybody can calculate 2000 VA/1800 W = 0.9 PF. But more importantly, it is mentioned due to marketing reasons. Most early UPS systems were designed to handle output with 0.6 PF. Marketing people realized that people associate high PF values with better products so they use high PF numbers to justify higher prices.
UPS manufacturers first tried to lure buyers using higher VA ratings. In other words, higher VA rating = much more expensive unit. But, it is cheaper to add extra components to increase VA ratings, compared to increasing the W rating which is the actual power used by the load. Designing system which can give out more actual power also costs much more $$$. Using VA values was a way to inflate prices.
Marketing departments are now pushing that the higher power factor is worth paying more. In the past they could sell 2000 VA/1800 W UPS with a high price tag. Now they need to justify why 2000 VA/2000 W UPS costs even more.
Some even try to push 1800VA/1800W UPS more expensive than 2000 VA/1800 W UPS due to higher PF. Although, it should be cheaper to manufacture. In reality, one could just put 1800 VA/1800 W sticker on a 2000 VA/1800 W device.
Here is a quote from Peter Gross of APC (according to this article)
"When someone buys a 100 kVA UPS designed with a .8 power factor, inreality he is buying the equivalent of an 80 kVA UPS that has unitypower factor rating," says Gross. "They pay for a 100 kVA UPS, but inreality, with the load approaching unity power factor, they only getan 80 kVA system, only 80% of the UPS capacity they thought they werebuying."
Unfortunately in that article there is some APC propaganda also. It is hard to find objective references nowadays. :(
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Power factor (pf) is the differencebetweenactual energy consumed (Watts) andtheapparentpower (Volts multiplied by Amps)in an AC circuit is calculated as a decimal or percentage between 0-1pfand 0-100%i.e.0.9pF = 90%.
The nearer the power factor is to unity (1pf), the closer the two waveforms are inphase with each other and the device uses power more efficiently, hence why power factor relates to UPS efficiency.
Convention stipulates thatinductive loads are defined as positive reactive power, with capacitive loads defined as negative reactive power.But power factor is neverdescribed as positive or negative, it is either lagging or leading.
Theseare loads where the current waveform lags behind the voltageby a factor equal to the load’s reactance, typically between 0.5and 0.95.
In the below image, a 2300VA load with a lagging0.766 pfwould have a real power value of1762 W(1.76 kW).
Loads with a leading power factor have a current waveformthat leads the voltage by a factor equal to the load’s reactance, usually between 0.8 and 0.95.
Traditionally, UPS systems were designed to support loads with unity or lagging power factors.
However, modern uninterruptible power supplies can alsonowhandle leading power factors doesrequire careful planning during installationthough,asleading power factorscan place an overload on the UPS that it may notrecognise.
Blade servers are thebest example of a load with a leading power factor. They are capable of greater processing power within less rack space than traditional file serversand have been widely adopted in the telecoms and data centre sectorsbecause of advantages such assimplified cabling and reduced power consumption.
There are several ways to try and reduce the impact of leading power factors, includingincreasing the size of the UPS, but the most common approach isto useactive harmonic filters withpower factor correctionon the output.
This delivers a more acceptable load to the UPS, but it does reduce efficiency, take up more floor space andincrease capital costs.
However, the output factor varies between different types of UPS. For standby UPS or Line-interactive UPS, the UPS input power factor equles to the output factor.
Reliable power for a sustainable world
Power Factor (PF) is a key concept to understand when evaluating UPS systems and the devices they support. Simply put, the power factor is the ratio of real power (measured in Watts) to apparent power (measured in Volt-Amps or VA). It’s a measure of how effectively the electrical power is being converted into useful work in an electrical system. A power factor of 1, or unity, indicates that all the supplied power is being used effectively, with voltage and current perfectly in sync. In an ideal world, all devices would have a power factor of 1, but in reality, this is rarely the case.
In relation to UPS systems, the power factor is crucial because it affects the actual amount of power that a UPS can deliver to its connected devices. UPS systems are typically rated in VA, but the actual power they can supply, in Watts, is determined by the power factor. For example, a UPS with a 1000 VA rating and a power factor of 0.7 can only deliver 700 Watts of power. Understanding the power factor is therefore important for correctly sizing a UPS system. If only the VA rating is considered, the UPS might end up being undersized, leading to potential overloading and operational issues. Therefore, when choosing a UPS, it’s important to consider both the VA rating and the power factor to ensure it can deliver the required power to your devices.
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