Bad Power Factor 1

[DonQ]

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

 

[DonQ]

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.

 

[waross]

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.

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!

 

[EdStainless]

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

 

[DonQ]

Yes, they are charging...thanks

 

[waross]

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!

 

[EnzoAus]

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

 

[stevenal]

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.

 

[cranky108]

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.

 

[waross]

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.

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!

 

[jraef]

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