I was at a testing facility recently and had a chance to peek at some of their load data when I noticed that the when the test was running it would operate with a pf between 75-85 however for a certain part of the test [for an hour or two in a 6 hour period] the kw would drop [+/- 10%] however the pf would drop to 12% and the kVA thru the roof. They are using dyno’s to simulate real world conditions. Just curious of anyone has experience with test cells operating in this manner and what would be causing the low PF’s one individual indicated that it was the way at which the test is setup [programmed] to run that creates the low power factor conditions? It did not seem to be a concern as this was one part of a larger facility just trying to wrap my head around it..
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Low PF
- Thread starter Mike01
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Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike...
Was the facility testing various loads, including VFDs?
Reards, Phil Corso
Was the facility testing various loads, including VFDs?
Reards, Phil Corso
The Great Sarducci
Member
- Location
- Detroit, MI. USA
Hey Mike,
As with any case of low pf, the culprit is almost exclusively caused by inductive loading. In practice, there is virtually no such thing as a capacitive load. Therefore, power factor will almost never go leading below unity (unless several capacitive components are suddenly introduced into a system when pf is being corrected too closely to unity; which can also be an issue). Whenever you see a poor power factor condition on a large industrial system, it is entirely due to a lagging power factor resulting from the introduction of inductance on the line. In my profession, I actually work around open-loop dyno test cells quite often, and can relate to what you are seeing. My guess is this period of low pf during the test may very well be due to the energizing of additional motors, transformer fed loads, etc. Especially if these circuits are using inline reactors to boost the inductance on some of the motors (a common practiced in many older industrial motor drives). A 0.12 pf does seem extremely low, and probably means that either A) the facility isn't equipped with properly sized pf correction capacitor banks to combat the huge inductive loads, or B) They aren't using them at all. I would hope that there is some kind of pf correction upstream of the test cell to keep this sort of low reading from reaching the main facility metering equipment. Because if there's one thing the power company loves to write-up big, costly penalties for (and rightfully so from their perspective), its a utility customer that is throwing massive VARs back onto the grid.
As with any case of low pf, the culprit is almost exclusively caused by inductive loading. In practice, there is virtually no such thing as a capacitive load. Therefore, power factor will almost never go leading below unity (unless several capacitive components are suddenly introduced into a system when pf is being corrected too closely to unity; which can also be an issue). Whenever you see a poor power factor condition on a large industrial system, it is entirely due to a lagging power factor resulting from the introduction of inductance on the line. In my profession, I actually work around open-loop dyno test cells quite often, and can relate to what you are seeing. My guess is this period of low pf during the test may very well be due to the energizing of additional motors, transformer fed loads, etc. Especially if these circuits are using inline reactors to boost the inductance on some of the motors (a common practiced in many older industrial motor drives). A 0.12 pf does seem extremely low, and probably means that either A) the facility isn't equipped with properly sized pf correction capacitor banks to combat the huge inductive loads, or B) They aren't using them at all. I would hope that there is some kind of pf correction upstream of the test cell to keep this sort of low reading from reaching the main facility metering equipment. Because if there's one thing the power company loves to write-up big, costly penalties for (and rightfully so from their perspective), its a utility customer that is throwing massive VARs back onto the grid.
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