Power Factor

Thank you for helping me regarding Power Factor.  Oft times, my ignorance and my struggle to get past the misunderstanding of a concept is quite frustrating.  If you wouldn't mind my taxing your patience a bit further, I'd like to exemplify my inferior understanding of Power Factor with an example, and ask a few more questions.

Let's say I purchase a unit of electronic hardware.  Let's say this unit has a Power Factor of less than 1.  So the electric utility company charges me, somehow ( by way of a power meter that measures kW-hours?).  So I am charged by the Real Power that the unit uses, though the Apparent Power is required to be supplied by the utility company.  If the difference between Real and Apparent powers is negligible, no big deal, apparently, for the utility company.  I am undercharged according to the utility company's rate, so I assume that rate compensates for the Power Factor of most users.  

Now let's say I implement thousands of these electronic units, and the utility company, by way of the increased demand on their generators, can no longer ignore the difference between my Real Power usage and my Apparent Power usage.

Q: Isn't it true that generators must take into account the Power Factor of the load they are supplying?  Why not the same for an UPS system, whose battery-supplied direct current will be inverted to alternating current?  Let's say my UPS system is rated for 200 kVA. If electronic equipment supplied by the UPS batteries has a certain load as well as a Power Factor of 0.7, then my UPS system can only support 140 W worth of the equipment, given that the Power Factor of the equipment tells me this equipment will cause higher current draw such that the power usage is

 140 kW / 0.7 --> 200 kVA.     Real Power = 140 kW, Apparent Power = 200 kVA

Q: Is there no meter that measures the extra current draw that would put this Power Factor issue to rest? 

Q: When implementing a newly purchased electronic unit whose manufacturer has listed the Wattage on the unit, I can calculate the expense of running the unit from the Watt rating. Isn't the Power Factor of the unit also known by the manufacturer, and couldn't the Power Factor be included with the unit?  



asked 7/5/2013
Dwain Seppala3
Dwain Seppala

3 Answers

Pattabhiraman

 sir delivered excellent explanation that is enough ...

answered 10/19/2013 Rajendra 6
Rajendra
Q: Isn't it true that generators must take into account the Power Factor of the load they are supplying?  Why not the same for an UPS system, whose battery-supplied direct current will be inverted to alternating current?

Yes, even for generators the power factor should be maintained at about 0.9 lag to optimally utilise the engine capacity. For this automatic power factor compensation systems can be provided. In earlier days when APFC systems were not available, the alternator used to be derated to utilise the full capacity of the engine.

In modern UPS units, the out put power factor is automatically maintained at about 0.9 to 0.98 lag irrespective of the connected load. 

Q: Is there no meter that measures the extra current draw that would put this Power Factor issue to rest?

There is no meter to directly read the apparent current. However using a trivector meter you can calculate the apparent and real value of power / current.

Q: When implementing a newly purchased electronic unit whose manufacturer has listed the Wattage on the unit, I can calculate the expense of running the unit from the Watt rating. Isn't the Power Factor of the unit also known by the manufacturer, and couldn't the Power Factor be included with the unit? 

Your energy meter reading will reflect only the real energy (in Wattshour/KWh) consumed based on which you make the payment. The reactive power does no useful work and hence is not considered in energy reading. In bigger installations, the power factor plays an important role in deciding the rating of transformer, D.G's, cables, switch gear etc. Higher the power factor (towards unity), lower will be capacity of capital equipment's required. Also if you draw more reactive power from utility grid, you will be penalised by the board as the utility infrastructure is inefficiently used. Typically for such installations, APFC systems are provided to maintain high power factor.  Hence maintaining a better power factor is given more importance in bigger installations.

answered 7/11/2013 Pattabhiraman 74
Pattabhiraman

Q: Isn't it true that generators must take into account the Power Factor of the load they are supplying - The power factor of the system (for a  area) will be kept at 0.9 or 0.8 by installing suitable pf correction equipments at high voltage Sub stations.UPS is not the only load ,there will be other loads which also cause the pf to fall.

Q: Is there no meter that measures the extra current draw that would put this Power Factor issue to rest?  - Trivector meter ,Multi functional meter

answered 7/9/2013 ram31 66
ram31

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