Power Quality Issues 2

[wesles24]

Hello,

I am trying to understand how harmonics from a few new oil wells with large variable speed motors can cause a few residential washers to stop working. They worked fine until a new substation with a delta wye transformer was recently energized. This substation serves the oil wells as well as the problematic residential loads. After some tests and monitoring we believe it is the third harmonic caused by the variable speed motors causing the washers to not work. They work fine when ran from a generator. I am trying to understand how this happens? Also, any recommendations on how to fix the problems would be appreciated. I have found a few power quality filters that may work.

Thanks for any help

 

[waross]

That raises a lot of questions;
Are you working for the home owners, the utility or the oil companies?
The first step is to check the voltage. If this is a simple case of low voltage, then filters may be a waste of time and money.
An oscilloscope check for harmonic content may be a good idea.
If the voltage is good, than shut off the oil well pumps.
It is not permitted in most jurisdictions to cause distortion power factor which will interfere with other users of utility power.
The pumps may be run on generators to maintain production. While on generators, the power quality issues may be investigated, identified and resolved before the pumps are reconnected to the grid.
In many jurisdictions correcting poor quality power to a residential customer is the responsibility of the local utility.
Under many tariffs, if a utility determines that a user is causing high levels of distortion that are affecting other users, then the utility has the right and responsibility to force the problem user to correct the issue at their expense. In extreme cases, the utility may disconnect the problem user.
But, to repeat, check the voltage first. That is a utility issue.
A call to the Utilities regulator may prove productive.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[wesles24]

I am with a utility,
while the washer was under load, it was checked with a Fluke 87 meter to check for min/max voltage deflection, there was less than 1/2 volt. Also, no stray voltage found. Hz is steady at 60 Hz, but other tests/oscope checks ran to show that the 3rd harmonic presence is very high.

 

[waross]

What was the actual voltage?
Does your utility have standards for maximum allowable distortion at the Point Of Common Coupling? (The connection point of the well pumps)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

I've seen a few power electronic loads with active power factor correction front ends struggle with badly distorted voltages. Do you have any waveform disturbance around the zero crossing? Multiple zero crossings was eventually pinned down as the cause in that case.

The solution is likely a filter, either a tuned harmonic trap or an active filter. The latter is likely to get expensive as the power level rises, and the reliability is lower than a passive solution, but it will adapt well to changing conditions and a varying harmonic profile. The passive filter will be optimised for a specific set of conditions and be less effective as the operating state moves away from that optimised condition. I'd assume that the oil company would pay for mitigation measures in preference to being disconnected from the supply. ;-)

 

[itsmoked]

You likely want to the remediation at the pumps to constrain the problem to near the cause.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[wesles24]

Waross: I will have to talk to some people on that one, but the voltage was not an issue I know and we do not want to shut the oil sites down. if we were to do an active filter, it should be placed parallel to the source of the problem correct (as close as possible to the oil pumps?) there has been talk of placing the filter close to the residential load where the washers are having issues. But from what I have read, I am thinking that harmonics are bad for the transformer and other electrical components and that the

 

[itsmoked]

Are these 'problem' motors all at one site or distributed at several locations?

What are their sizes, kW or HP?

What exactly are the motors being driven/controlled by? Makes/models would be very useful in getting to the details.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jghrist]

Three-phase variable speed drives create harmonic currents of orders 5, 7, 11, 13, 17, 19 ... It would be unusual for the drives to be the source of third harmonic currents. What are the transformer connections serving the oil wells? Delta-wye connections would block third harmonic currents.

IEEE Std. 519 gives limits on a customer's harmonic current levels. I suggest measuring the harmonic current distortion at the oil well service points. If the distortion exceeds IEEE Std. 519 limits, then you may have a case for requiring the oil well owner to install mitigation of some sort.

 

[jraef]

I agree with jghrist, the VFDs would not be the source of 3rd order harmonics. In a 3 phase bridge rectifier, the third order harmonics is creates, assuming a balanced voltage, will neutralize each other, as do even order harmonics. It is the odd order non-triplen harmonics that are problematic.

it's far more likely that if there are light fixtures or other single phase power supplied electronics in those pump stations, that those are the source of your 3rd order harmonics. It's also possible that the issue causing your appliances to not function is related to common mode noise, not harmonics. If not installed properly, common mode noise inherent in the operation of a VFD can cause all nature of problems with other sensitive electronic systems. Likewise with EMI/RFI issues, also due to a lack of attention to installation details. I would spend more investigation time on those areas rather than harmonics.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[mikekilroy]

Maybe it is worth backing up and re-examining WHEN the issue began... You said:

I am trying to understand how harmonics from a few new oil wells with large variable speed motors can cause a few residential washers to stop working. They worked fine until a new substation with a delta wye transformer was recently energized. This substation serves the oil wells as well as the problematic residential loads.

Unless you didn't write this clearly, it appears you are saying the "new" oil wells worked fine and did not cause residential issues - until AFTER installation of a new transformer... Wouldn't that mean the issue is the new transformer and not the oil wells?

Perhaps a simple solution would be to move the residential loads off THIS transformer?

You have been asked to share scope pictures, but it seems you only have max/min digital voltmeter readings? How do you KNOW it is 3rd harmonic noise causing the issues if you have not scoped the voltage yet?

You have been asked for the motor sizes, voltages, vfd model numbers... Lots of folks here know lots of different brands and designs - no telling WHAT will pop up if you share? It is being ASSUMED your VFDs are simple diode front ends - better answers can be given if you share what you actually have? We once had a certain type transformer added to a machine tool installed in a corporate 3 story building and when it turned on all the clocks in the building ran backwards - active front end on the large vfd on the machine... share more?

http://www.KilroyWasHere<dot>com

 

[LionelHutz]

You have determined that 3rd harmonics are the issue. Before you can solve the problem, you need to determine what is causing the 3rd harmonics.

As one example of something that should be fixed instead of masked-over with some filter. Many VFDs use 3 diodes and 3 SCRs in the rectifier. The SCRs are first off so the initial turn-on power goes through 3 small diodes and a resistor to charge the bus, using the 3 main rectifier diodes to complete the circuit. Then, once the bus is charged the 3 main SCRs in the rectifier are gated-on to make the full 3-phase rectifier. However, if the gating circuit on one SCR fails then the rectifier has one phase running 1/2 wave rectified.

 

[wesles24]

I meant to say that that everything was fine until a new substation was brought online. The transformer has a delta-wye connection. I am working on getting more details and will update as soon as I have what you all are asking for. I do appreciate all the feedback, I agree that we should backup and look at everything again. Thanks again, I will update soon!

 

[waross]

Are the washers on the same distribution circuit?
What is the distribution voltage?
Is the transformer wye well grounded?
Are the distribution transformers line to neutral or line to line?
How far from the sub to the washers?
How far from the sub to the well pumps?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

Are there any capacitors on the distribution system? Maybe the new transformer is in resonance with the capacitors at a critical frequency (180 Hz), while the old transformer, of a different size and/or impedance had a different resonant frequency. If the capacitor and source reactance are in parallel resonance at 180 Hz, then any third harmonic current would cause a large third harmonic voltage.

 

[mikekilroy]

Agreed to consider capacitors.

So in reality, it is as originally stated: both oil pumps with VFDs AND residential dc brushless zero cross detect motor controllers in new washing machines (another assumption) worked fine together UNTIL the transformer was added to the picture.

So it begs for info: WHAT was the exact (details please?) distribution scheme BEFORE the new transformer was added?

http://www.KilroyWasHere<dot>com