Our local ultility company for years had a surcharge if power factor was below .9. ( non residential customers ) At my first plant 50 years ago we would start up a 125 HP Synchronous motor with out a load and think they called it over excitement to produce above a1 power factor while the ultility guy was on his way to our switchgear room/ meter room. Amazing how the heck cheating lack of quality control communist china gets away with making millons of LED lamps with very low power factor. A word of caution to you young sparkies: Do not install a VFD on any motors that have their own power factor capacitors between starter & motor without first disconnecting the capacitors. We had a contractor install two 40 HP VFD'S and could not get them to work. I looked at it and after disconnecting the PF Capacitors drives ran great.
Does Improving Pwr. Factor Lower Bill?
- Thread starter designer82
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Wow never know they made 24 pulse VFD'S. In a newer building we had 18 pulse on every motor 50 HP & larger except for a soft start on a 250 HP fire pump. Talked to service techs from two different companies and neither were fans of the 18 pulse drives.
The distortion factor was minimal on these drives also. They were 24-pulse units.
As others have stated, it depends on the rate structure.
We don’t charge for poor PF as we are mostly residential.
Actually, out of 40,000 meters, if we implemented PF charges, it would only affect 4-5 of the larger industries we have. Two of them are on express feeders.
I think the last time we looked we explored .17 per kVAr
We don’t charge for poor PF as we are mostly residential.
Actually, out of 40,000 meters, if we implemented PF charges, it would only affect 4-5 of the larger industries we have. Two of them are on express feeders.
I think the last time we looked we explored .17 per kVAr
kwired
Electron manager
- Location
- NE Nebraska
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- EC
Early 90's at a plant we did all the electrical work in they were first introduced to power factor penalties and we were to install individual capacitors on each motor of I believe 7.5 hp and up. For most part all those motors had motor controllers remote from the equipment so we spent a lot of time mounting capacitors and wireways between them and controllers and getting all ready to make final connections on a down day for quite a bit of them.
Come back the day after most were put on line, only to find blown fuse indicators lit up on two of three lines on everything that was running at the time. A 250HP drive of older design (the PWM type that eventually replaced it was maybe a 1/4 size of this one) and the distortion it was putting on the supply was the culprit. At the time we ended up putting some larger capacitor banks with line reactors between them and the source as the PF correction method. They would turn them on/off as needed depending on production load levels so to speak.
That drive and it's distortion on the supply line had caused other issues now and then when new equipment was installed.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
Getting into details I'm not so familiar with, but I will agree that as time has gone by many these drives are not as much a problem as older ones were when it comes to having enough distortion to effect other items.
The 250 HP drive I mentioned in my other little story there, I got called early in the AM while my boss was on vacation because it wouldn't start. I knew very little about this thing at the time. All I could do is look at what it was doing and try to see if I could find any solutions in what paperwork we had for the thing, and then make some calls once it was late enough to actually contact anybody from some the contacts found in said paperwork. I was probably only 21 maybe 22 at the time and didn't have a lot of experience yet, and practically no experience with such drives other than I understood they varied frequency to vary speed of the motor.
Luckily one the production workers noticed a valve had been left open and the turbo fan this thing drives was full of water. Took an hour of so to drain it, but it ran fine after that. Thing couldn't accelerate the fan well enough in that water and must been shutting down on overload. Did not have the UI that today's drives have that are easier to understand what it is trying to tell you.
You probably know that variable drives were my forte. DC drives, AC, synchronous....... Quite were variable frequency drives. One of the things we made sure of was the DC reactors - they have to keep ripple sufficiently low for distortion requirements. Some people make it insufficient or even zero.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
You probably made what you would call better units at about retirement time then you made when you first started doing this as well.
I've even came back to things I originally installed and thought "what was I thinking" or "I have learned since then".
I we constructed them for scratch to meet best practice. Why else would I?
kwired
Electron manager
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- NE Nebraska
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- EC
Over time you didn't change some your practices as you seen the benefits of the new practice? Or maybe even tried something new, only to discover it introduced other issues and had to either revert back to what you were doing or make additional changes?
You didn't have overall more efficient drives at the end of your career than at the beginning?
Open Neutral
Senior Member
- Location
- Inside the Beltway
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- Engineer
I've often wondered about VFD's, PF, and distortion of the line. Back in the dark ages when I took the optional senior year Electronic Power Control course, we didn't even discuss it. Now, I'm hard pressed to think of a constant {across the sine wave} load in a residence: lighting? PWM LED; stove, ditto; HVAC? VFD, etc. Maybe the electric water heater is straight resistive. Now the EU has PF restrictions that have changed the design of wall-warts and PC power supplies.
I wonder if POCO's are concerned about harmonics and their pole pigs.
I wonder if POCO's are concerned about harmonics and their pole pigs.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I really think that probably varies depending on where you are at and what the majority of the load is on their system.
Here the dwelling load is pretty minimal on the rural system, within towns/villages it maybe the other way around though. The major rural loading here is irrigation loads during the months between May and September. When those are at peak demand usually in July and August the dwelling loads look like nothing in comparison.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
So, are you telling me that the little gizmo I bought to plug into a 120V outlet in my home isn't going to reduce my electric bill by 80%???
At the beginning of my career we didn't AC PWM variable frequency drives.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yeah, sure.So, are you telling me that the little gizmo I bought to plug into a 120V outlet in my home isn't going to reduce my electric bill by 80%???
Oh, and I have a nice bridge for sale…
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Deltaforce
Member
- Location
- India
- Occupation
- Electrical Engineer
Above power factor1 can?
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
The switch mode power supplies now common in consumer electronics have atrocious power factors and dump all kinds of ugly transients into the grid. The problem is that they are so numerous, and their contribution is so small on a per unit basis, that it would never pay to try and wrangle them all to get above 0.90 pf.
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