We have a city waste water treatment plant in our tiny city, paying a large penalty for a pf of 59%.

Plant was federal project with all the overkill redundancy and intrinsically safe sensor circuitry.

Only 6 years old. Most all motor load is on vfds.

Most everything works well. I've been called a dozen times or so for repairs.

Where would I start looking for the low hanging fruit?
My knowledge predates vfds.
My meter doesn't do harmonics. thd

Will I need to update my equipment to even get a sense of what's going on?

My wife is in charge of another building in town. Library. After obtaining a grant for an updated AC system, she was taking heat for utility bill. 83% in her building. Only two suspects there. Compressor load and lighting.

I believe the city should look into the treatment plant first.
Is my assumption of vfds having good pf wrong?

 

VFD's can be the culprits, the service supplier here will bring in a team to assess and record the P.F. and recommend suitable Capacitor correction.
Max.

 

Call the supplier of the vfds. They will likely have a simple, safe, standardized solution for you.

 

VFD's can be the culprits, the service supplier here will bring in a team to assess and record the P.F. and recommend suitable Capacitor correction.
Max.

That was my first suggestion to the city.

Back in the day, I worked for a contractor when pf correction was just becoming popular. We just had the power company give us the recommendations. Just as you suggest.

My wife, and city, claims they (power company) have no interest in helping.
Their suggestion is to call a contractor.
I am an electrical contractor (licensed in the state), but have no recent knowledge when vfds are in the mix.

The city doesn't understand the savings potential. I don't have the confidence or experience to guaranty results.

Can you explain in general terms how the vfds with capacitor input power supply busses lead to poor pf?

Understand the effect on thd but not how this relates to pf problem.

I asked if penalty was for distortion and was told it is specifically for pf.

 

Call the supplier of the vfds. They will likely have a simple, safe, standardized solution for you.

I'll give it a shot.

 

What about a meter suggestion to localize the problem?
All I have is an amprobe acd-30p.
http://content.amprobe.com/DataSheets/ACD30P.pdf

Without thd.

I remember a job a while back. My fluke was reading over 600vac upstream 50' from a small 10hp vfd. (480 volt system)

Special meter or filtering must be required.

As general practice, I use input reactors on my jobs.
Haven't checked yet, but don't remember seeing them on this job.

 

Options

Read the technical press

http://www.waset.org/journals/waset/v78/v78-344.pdf

Get a specialist contractor in

http://www.sml.ltd.uk/power_factor_correction.html

Do it yourself - work it out from the texbook

http://books.google.co.uk/books?id=...factor correction in pumping stations&f=false

One suggestion, however, most pumping stations have some redundancy so you can take measurements / experiment on some plant that is offline for maintenance.

Look also at the type of motor. If you have the old slow moving type spreader bars in the treatment system their motors can be inefficient.

Is there any UV treatment involved? The UV generator probably has an opposite phase PF to the motors.

 

The problem may not be the big VFDs. Look for lightly loaded induction motors in air handling or pumps - especially if the are running under no load conditions. The post above says waste plants rotate demand through different sections. If so, do any pump motors or blowers continue to run with no load?

See this document from ABB claiming that FVDs prevent the need for PF.

here
Especially the note in the last paragraph.

 

The problem may not be the big VFDs....True from what I read....... Look for lightly loaded induction motors in air handling or pumps - especially if the are running under no load conditions. The post above says waste plants rotate demand through different sections...very small plant... If so, do any pump motors or blowers continue to run with no load?......modern designed, automated plant with mostly vfds. I'll check

See this document from ABB claiming that FVDs prevent the need for PF..........I'm puzzled

here
Especially the note in the last paragraph.

Again, this is why I'm puzzled. All except two motors are are on vfds now.
I've been under the assumption that one advantage of vfds is better pf.

I guess I'll start with those.

 

VFD's can be the culprits,
Max.

Can you explain or link?
My understanding contradicts.

 

Can you explain or link?

I phoned a couple of contacts I have who are engineers that are with the service provider, and they say it is not so much P.F. that is a problem but Electrical noise from VFD's.
In the past I have usually used 3ph chokes either just on the motor side and in some case input and output.
Max.

 

Can you explain or link?
My understanding contradicts.

See
microchip VFD


rockwell automation

 

I phoned a couple of contacts I have who are engineers that are with the service provider, and they say it is not so much P.F. that is a problem but Electrical noise from VFD's.
In the past I have usually used 3ph chokes either just on the motor side and in some case input and output.
Max.

That's what my research led me to believe.

The pf problem then, still eludes me, as the cities cost penalty is for pf not harmonics. Unless I've been given false information.

As in previous post. I also use input reactors. Just as "good practice". Output reactors are specialized and only required on long runs, I believe.

ps.
Your contacts didn't hint that they monitor and penalize for noise did they?

 

See
microchip VFD


rockwell automation

A lot to digest.
Mostly things I've found in my searches.

An explanation for poor pf on vfd systems doesn't jump out.

Think I will concentrate on the non-vfd loads first as I don't have proper equipment for the others.

 

A lot to digest.
Mostly things I've found in my searches.

An explanation for poor pf on vfd systems doesn't jump out.

Think I will concentrate on the non-vfd loads first as I don't have proper equipment for the others.

That is the best plan from my point of view.

 

Your contacts didn't hint that they monitor and penalize for noise did they?

No they don't.
Max.

 

The problem may not be the big VFDs. Look for lightly loaded induction motors in air handling or pumps - especially if the are running under no load conditions. The post above says waste plants rotate demand through different sections. If so, do any pump motors or blowers continue to run with no load?

See this document from ABB claiming that FVDs prevent the need for PF.

here
Especially the note in the last paragraph.

Excellent article and worth the full read. Pat attention to the comments about lightly loading, as this applies to transformers as we'll. I'd get out the single line drawings to map out a strategy. Request your annual usage data from the utility as they likely have hour by hour usage with pf. Compare that with plant loading.