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Bad Power Factor

Bad Power Factor

Bad Power Factor

(OP)
Hello,

Recently a pumping station was upgraded and the 'part-wind' starters and power factor correction capacitors for three 60hp 480 pumps were replaced with ABB ACQ580 variable frequency drives.

Ever since this upgrade, the power factor has dropped every month, dropping from 90% PF (with the old starters and PFCC) to 19% this month!

Needing some input on what could be causing the problem?

Thanks

RE: Bad Power Factor

Where is this power factor being measured, and by what? The output of an AFD is highly non-linear.

RE: Bad Power Factor

(OP)
This installation has been in service for a year now, and every month the 'electric bill'
indicates a 10% loss, now it has leveled out to around 20%. This is a rural electric
utility.

RE: Bad Power Factor

Typically, all equipment removed during an upgrade becomes the property of the contractor.
If this is a Displacement Power Factor issue, buy the original capacitors back from the contractor and reinstall them.
If this is a Distortion Power Factor issue, I'll let others comment.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

(OP)
What kind of issues 'could' we have with the VFD's? (Adding the capacitors)

RE: Bad Power Factor

Dear Mr DonQ (Electrical)(OP)20 Feb 23 20:09
"...What kind of issues 'could' we have with the VFD's? (Adding the capacitors) "
1. In general, the introduction of the VFD will affect the system.
2. Consider the following cases:
(a) if the pf correction capacitors are connected on the main busbar; your system voltage could be affected by the VFD if you have a weak utility source. The capacitors will fail one-by-one depending on how badly the voltage is distorted. Suggestion: Remove them immediately as the load connected to the VFD do NOT require pf improvement capacitors. However, the other loads may require the caps, in this case check the cap current.
(b) if the pf correction capacitors are connected on the load circuit (i.e. after the VFD), remove them immediately! There shall be NO pf correction cap after the VFD. Attention: these caps will fail very quickly!
3. Check the capacitor current. Some of them may have had failed already.
Che Kuan Yau (Singapore)

RE: Bad Power Factor

Quote (donq)

every month the 'electric bill'
indicates a 10% loss, now it has leveled out to around 20%
Donq, given that the power factor is being measured by the utility, the first thing I would check is the metering data, if it is available. Metering on many commercial installations in Australia provide 30min interval data with volts, current, real power, reactive power, power factor etc. Accessing this information would provide a very good indication as to how/when the poor power factor is being recorded. I suspect it is measured as kwh/kVA over a specific interval defined by your utility or regulator. Perhaps this poor power factor is recorded during the "worst" 30min interval of the month which might point to the cause.

If changes were made to the installation's metering during the pump station upgrade, it is possible that the metering was compromised. There are 40 ways to wire up 3 CTs to a 3 phase meter (3 x 2 x 2 x 2 x 2) and only one configuration is correct. All too often one of the other 47 other options has been inadvertently installed.

Another problem that I have seen is when there are renewables on site, the active load on site could be substantially offset by the behind the meter renewables. As net P reduces, Q remains constant and the PF drops.

I would have thought that the VFDs would be able to display power factor. If available, it would be worth checking such displays before assuming the VFDs are at fault.

RE: Bad Power Factor

(OP)
Very good point, I'll check the 'power factor' information on the drive(s), I'm sure its there somewhere!

RE: Bad Power Factor

I doubt the drive will do any incoming power metering.

You'll need to put some power metering equipment on the system and try to determine what is happening. A drive with a line reactor should have a power factor above 90%. A drive connected directly to line power shouldn't cause the power factor to be anywhere close to 19%.

I was involved with a site that had poor power factor and nothing seemed to help it. I don't know exactly what was wrong because after a bunch of testing to give data to push back to the utility it ended with the customer signing an NDA with the utility.

RE: Bad Power Factor

(OP)
When the drives were installed, at the same time the electric utility upgraded the service from a 480v corner grounded delta
to a 277/480v wye. Line and load reactors were installed with the drive also. Thanks for all the help!

RE: Bad Power Factor

How much time the pump run each month?

[anecdote]
I have seen locations with water pumps that only a few minutes in some months and many hours in other months. The pumps themselves have power factor correction applied either via capacitors or by a VFD, so the power factor is good when the pumps run most of the month. In months where the pumps don't run much, the power consumption consists primarily of reactive power for transformer excitation. I have seen power factors lower than 19% for this kind of situation.

Replacing an older transformer that has high real power losses with a modern transformer that has low real power losses could make the power factor even worst in months that the pumps do not run.
[/anecdote]

Another item to verify is that the power factor measured by the utility is lagging rather than leading. Keeping the capacitors and added VFDs with near unity power factor could have pushed the site to delivering reactive power to the grid.

RE: Bad Power Factor

The worst PF I have seen was under 10% on a large unloaded transformer.
That translated to a 90% penalty, (On a very low bill.)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

(OP)
Each pump will run approx. 3 to 4 hrs a day. The pumps are set-up to only run at 55 Hz to keep
the filter tanks from over-flowing. Thanks.

RE: Bad Power Factor

Seat of the pants engineering.

Quote (Respectfully)

3. Check the capacitor current. Some of them may have had failed already.
An old and wise maintenance Guru shared the following tip:
"Whenever you walk past a capacitor bank, run your hand across the capacitor cases. If one is cooler than the others, it has probably failed."
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

(OP)
The power factor correction capacitors were removed when the VFD's were installed.
Thanks..

RE: Bad Power Factor

The ACQ580 lists the drive with a power factor 0.98. I am stumped how you could be at 0.19 with 3 hours of run time per day.

Does the monthly kWh on your bill still seem reasonable? Did the utility replace the metering when the service was converted from delta to wye-grounded?

RE: Bad Power Factor

(OP)
I'm still trying to find out if the utility changed-out the metering, I really believe they have
something wrong on their side!

RE: Bad Power Factor

I think the main question remains - how is this being measured and where is it being measured? It is 100% possible they are reporting for an entirely different customer entirely, simple billing error. Or their equipment has failed. Or some other reason.

I feel like those IT support calls where someone says their computer doesn't work, so the IT guy says "check to see if it is plugged in" and the response is that the building power is out and they don't have enough light to see if it is plugged in.

RE: Bad Power Factor

Then again, many utilities have a clause that allows them to measure the highest phase and multiply by three. So if you are very poorly unbalanced, you could be seeing the higher bill.
If the service was changed, the metering likely was changed to accommodate.

RE: Bad Power Factor

(OP)
When the electric service was replaced, a backup generator and automatic transfer switch were also
installed for the pump station. It looks like the generator would be constantly running if the incoming
power was excessively unbalanced. But I didn't setup the transfer switch either.

RE: Bad Power Factor

Quote:

If the service was changed, the metering likely was changed to accommodate.
That once got me a free trip from Canada to Central America.
The utility changed the transformers at a seafood freezing plant.
They put the metering connections back as they thought that they had found them.
Originally there were 120/240 Volt transformers connected in series wye to give 240/416 Volts.
The metering potential coils were connected to the 120 Volt terminals on the transformers.
Unfortunately, they connected the meters to the 240 Volt terminals instead of the 120 Volt terminals.
I physically verified each wire from the meters to the transformers on the roof.
That took a couple of days.
The plant had been double billed for an entire season.
The utility repaid about $100,000 to the plant operator.

Quote:

It looks like the generator would be constantly running if the incoming
power was excessively unbalanced. But I didn't setup the transfer switch either.
That is not a safe assumption.
The transfer switch doesn't care about unbalanced power.
It looks at incoming voltages.
If any one phase voltage drops below the set point, the transfer switch calls for back-up.

Been there, done that.
I had a customer whose set would not transfer back when the grid was restored.
The transformer bank had one transformer on the wrong tap and the voltage was low on one phase.
The voltage was above the trip point so the service would stay on the grid, but when service was restored after an outage, due to hysteresis in the voltage monitoring circuit, the voltage was not high enough to transfer back to the grid.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

If the utility re-did the metering likely they moved it to their side of the transformers.
And with that PF it sounds like they screwed up the wiring.
Insist that they come out and monitor the actual values with separate equipment, not using the installed CTs and taps.
They are charging you for that PF, and it is wrong.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Bad Power Factor

(OP)
Yes, they are charging...thanks

RE: Bad Power Factor

Quote:

If the utility re-did the metering likely they moved it to their side of the transformers.
Not likely. That is not a trivial, conversion nor is it something that will be done accidentally.
Metering on the utility side of the transformers will require high voltage PTs and CTs.
Expensive and not something that will be lying around.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

DonQ,
Have you requested an explanation as to how the PF parameter is determined for billing purposes and then asked for the underlying data? In my area, the PF charge is based on the coincident PF at the time of peak demand. Maybe the wrong data is used, or the metering is just plain incorrect. If it is a metering problem, then getting the data is going to be a very important path to proving it.
With a bit of luck, you should be able to get a CSV file (here they are at 30min intervals), which will quickly reveal if Watts and VARs make sense. I've attached an example below - please forgive the lack of column alignment.

Date Exp kWh Exp kvarh Imp kWh Total Imp kvarh Total
1/11/2020 12:30:00 AM 10.096 6.528 0 0
1/11/2020 1:00:00 AM 9.512 5.84 0 0
1/11/2020 1:30:00 AM 9.524 5.844 0 0
1/11/2020 2:00:00 AM 9.492 5.748 0 0
1/11/2020 2:30:00 AM 9.436 5.76 0 0

RE: Bad Power Factor

At a utility I'm familiar with, "average" power factor is calculated from the billing period Wh and varh. Anything below 95% is applied to the demand to become the "billing" demand (90% average pf would cause billing demand to be 105% of demand). The very worst outcome was when a school redid their ballfield lighting off season. Once the work was complete, the lights were tested; setting the 15 minute monthly demand. Once the testing was complete, the lights were turned off for the remainder of the month. The transformers feeding the lights remained energized, however. The no-load varh from these transformers caused the average pf to be extremely low. I would check with the utility to see just how the pf and penalty are calculated.

RE: Bad Power Factor

The school seems to have hired a bad electrical advisor, and bad project manager.
Likely the project manager was the school principal, who while educated at the university level would have had little practical experience.
Which is sad as they likely could have asked for help from the local utility. I say ask, but in some rural areas the REA may not have had anyone with the knowledge to help them on staff.

This should say something about the demand for people with electrical background. Then again, in the REA example above, as I have seen, they likely would not be willing to pay such a person the prevailing wages.

RE: Bad Power Factor

We had a customer with an unused warehouse. As I understood, the main breaker on the transformer secondary was open, so no load on the transformer.
Unfortunately, this installation had primary metering, so the KWHr consumption was the no load losses of the transformer.
The PF was close to zero and the penalty was close to 90%.
90% of very little was still very little.
The General Manager happened to see a power bill with 90% penalty and called our firm.
Some one went down and pulled the primary switch.
The problem went away.

Quote (stevenal)

Once the work was complete, the lights were tested; setting the 15 minute monthly demand.
I have had customers with demand tariffs that were the greater of;
The present month demand,
or
90% of last month's demand.
A one time high demand would impact billing for 10 months.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: Bad Power Factor

HOPEFULLY you removed the PFC capacitors when you installed the VFDs, otherwise you have killed the VFDs...

If you are measuring PF on the output side of the VFD, that is totally useless information and is 100% irrelevant.

If you are measuring PF on the input (line) side of the VFD, and your metering equipment is not suitable for measuring in a harmonic-rich environment, then it is likely giving you erroneous information. It's not simple and cannot be undertaken lightly. The VFD should be correcting the displacement PF to about .95 or better, which is what the utilities measure and assess penalties for.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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