Synchronous Reactance Controller for Energy Reduction 8

[ibkenb]

I am an electric utility power engineer and have been asked to evaluate a "Synchronous Reactance Controller" that promises our customer up to 10 % energy savings. Personnally, I think it is snake oil, but in fairness I would like to know if anyone has evaluated such a system and would share their results.

The device promises VAR correction which lowers the KVA demand and our associated charges. However, it also promises to filter the harmonics out of the supply voltage and to balance the three phase voltages. I am sure there are some efficiency savings with the harmonic improvements, but I do not know how to quantify them.

I cannot obtain information on the internals of the device and since it is connected in a shunt (parallel) I am at a loss as to how it may balance loads/voltage.

 

[busbar]

The product of RMS voltage and current produces apparent power (voltampere) quantities, but that number will always be equal or larger than that of apparent power defined as square-root-of-the-sum-of-squares of real and reactive powers. For years many considered these to always be equal, but that is not always the case with nonsinusoidal current and voltage waveforms

If the first customer is generating excess reactive power to push his var demand surplus back through the meter, does he have any financial or operating incentive to continue in this mode? I don’t think that leading-power operation typically reduces his electric bill. It may be appropriate to figure that efforts in reducing harmonic currents at the meter will pay off in reduced kVA demand, and this could be seen as an indirect means of minimizing harmonics on the utility-owned facilities.

It seems like we agree on the difference in measurement algorithms, but disagree on the relative ‘fairness’ of the two.

 

[dpc]

The new reactive power tariffs used by Bonneville Power Authority (BPA) provide for a penalty if power factor is worse than 0.97 lagging **or leading**.

I don't know if they are actually penalizing for leading pf, but under their new rate structure, they could, assuming they can meter it.

dpc

 

[electricuwe]

busbar,

in my example in post dated May 2nd the first customer initially operates still with lagging power (I didn't state that explicitly). With the second power customer his power factor is reduced beyond the limit of 0,95 by harmonic currents injected by the second customer into his capacitor bank. Do you really think that the first one should pay for that ?

 

[busbar]

electricuwe, I had not imagined such a condition. It sounds like 0.95 must be a significant breakpoint in the billing structure. It does not seem at all fair to the first customer, when his power factor at the meter should show reactive export.

Is this an issue that could be posed to the serving utility, particularly if previous billing records could demonstrate a change in their reactive billing with the addition of the second customer? Is there any chance that customer one’s meter also has 4-quadrant var registration? That may help resolve the matter, but the utility could stand firm by their rates, especially if they have been “approved” by some governmental or municipal agency.

 

[jbartos]

Suggestion: It appears that the metering alone will not solve the problem since one may be paying for someone else shortcomings. Rather than paying a penalty for the lower power factor and harmonic content, it would be better to tackle those globally by installing necessary hardware and share the cost based on an "amount of culpricity." This way the harmonics will be reduced (not staying there while penalties are being paid, some potentially unjust), and power factor compensated (also on shared bases).

 

[electricuwe]

If a billing scheme should include distortion power and be fair to all customers it would need meters able to determine the direction of power or reactive power flow for every harmonic separately. I guess that it will be possible to design such a meter, but I do not think that this would be a good approach.

 

[busbar]

There are some fairly sophisticated “meters” out there [correspondingly priced I bet], but a big problem I see is defining a rate schedule that won’t cause aneurysms.

It’s possible the harmonic recipe could be divided into odd, even and triplen quantities. FFT-type analysis can give angles all over the place, making ‘direction’ sort of elusive. Certainly voltage being utility-based and current being strictly customer-based gets garbled.

There are some other characteristics that seem to have importance to utilities, or their regulatory cohorts.

http://www.arbiter.com/pdf/1133a_direction_harmonic_flicker.pdf

 

[stevenal]

Busbar

Regarding your 1st May 3rd post:
The IEEE dictionary has two definitions of reactive power for non-sinusoidal quantities. One sums the components of the individual frequencies as electricuwe has said. The other uses the Pythogorean relationship between real and apparent power, seeming to contradict you. Are the two definitions not equivalent? Both definitions define reactive power in terms of apparent power rather than vice versa.

 

[busbar]

Good question. stevenal, I am caught between 1990 and 2000. 1990 here is IEEE 90EH0327-7-PWR Nonsinusoidal Situations: Effects on the Performance of Meters and Definitions of Power. 2000 in this case is IEEE 1459-2000 Trial Use Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Non-Sinusoidal, Balanced, or Unbalanced Conditions. Here, 1459 is taking longer than anticipated to digest. I apologize that I do not have ready access to latest IEEE dictionary.

Emanuel, P. Filipski, et al, have IEEE/PES Power System Instrumentation and Measurements papers commenting on the IEEE-dictionary Pythagorean power relationship, and their proposals for updating it. The label ‘distortion power’ is sometimes used, but I’m not sure if that is a IEEE-defined term. One charming illustration is:

http://67.115.161.42/images/1459ub.fig4.jpg

Problems become very real when, for example, the 3-side relationship is used for sizing PF capacitors. Based on the Pythagorean difference of real and apparent power measurements, where there are significant harmonics, you can get in trouble—to the point of fuses being ineffective in protecting capacitors from overcurrent suicide. I have witnessed a number of cases of LV/MV can rupture, and in these the process took milliseconds to complete.

 

[MarkAthay]

ibkenb,
I've had some experience with customers contesting their electric bill claiming that the revenue power meter was being driven fast by the harmonic currents. We had one consultant in town that liked to push this theory onto his customers to enhance his business and push for his special black boox to filter harmonics.

Harmonic currents have a positive, negative, and zero sequence value to them, depending on the harmonic number. Some harmonics want to push the meter faster, some want to push it backwards. Because of the stiffness of the utility bus at the high-side of the typical utilization transformer, the typical customer with his harmonic currents has little effect on the voltage waveform of adjoining customers being served by a different utlization transformer, USUALLY. Voltage harmonics push AC motors both faster and slower than the base frequency. This results in heating and a reduction in the available capacity in the motor. There are two losses here, electrical heating losses, and loss of equipment capacity or availability. For the manufacturer, these are real losses, even though he may not be aware of the cause of his "weak" motors.

I believe it was an IEEE paper that covered the accuracy of revenue metering in the face of heavy harmonics. The result was that while it was possible to mess up the metering in the laboratory by injecting extremely heavy harmonic currents, in the real world the amount of error harmonics would induce would be negligible. This is talking about measuring the real power.

There is one problem in measuring reactive power with revenue meters, there is no standard established on what constitutes reactive power, at least not for revenue meters. This was as of 5 years ago anyway. I know the mathematics can be crunched out and ..... Is reactive power all non-fundamental power / current flow? How about all current flowing 90 degrees out of phase with the voltage? Some people ascribe to the former, I follow the latter.

A case study.....

Park City, Utah had some severe harmonic problems. Being a rural (but expensive) area the electrical system wasn't that stiff. During the winter a preponderance of the electrical load was the ski resorts, which are dominated by variable speed drives on ski lifts and snow making equipment. One part of town had their clocks running fast whenever a particular ski lift was running because the harmonics were so bad. Most drives were 6 pulse. Ski lift motors were between 300 hp and 1000 hp. The revenue metering was running fine, both real power and reactive power metering. Nothing was noted out of the ordinary. Eventually a system-wide study was funded jointly between the utility and the ski resorts to solve the harmonics problem. Harmonic filters were strategically installed on 480 volt buses, and all new drives had to be 12-pulse or higher. Without the filtering any shunt capacitors would likely of had a difficult life with the voltage harmonics. This was the most extreme case I've seen. In this case filters and shunt capacitors were the answers to the problem, and at a much lower cost.

I have seen studies done on synchronous reactance controllers. They were all being installed on transmission systems. Because almost all transmission systems are well balanced, balancing the voltage is almost a non-issue. They do a good job fixing power factor, and because of the high-speed nature of the electronics, they can straighten out the voltage waveform quite well if you have voltage harmonics. The main application for these units is dynamic system stabilization and high-speed correction & manipulation to affect load flows on transmission systems. I don't know the voltage your's will be installed on. I have heard that thy've come out with 15 kV class units with similar capabilities, and I think even some 600 volt class units. A 10% reduction in total power consumption sounds like someone slipped a cog, or at least a decimal point. Ask for their calculations. If they won't give them to you then assume that it's a smokescreen and a sales pitch.

Mark

 

[stevenal]

Busbar,
From IEEE 100-1992 (dictionary):

D=(U^2-S^2)^0.5
D=(U^2-P^2-Q^2)^0.5

D=distortion power
U=apparent power
S=phasor power
P=active power
Q=reactive power

All nice and neat, at least it was in '92.

 

[busbar]

I agree with you, stevenal. But, the 1990 papers collection already mentioned seems to devote quite a bit of effort hashing over the weakness of the IEEE 100 definitions; particularly those for Q and D. I don’t think there are any ANSI C12 revenue meters that have power/energy registers for the D quantity, much less a utility rate structure that makes use of it. That’s what Filipski, Emanuel and others were “complaining” about. There seems to have been a fantastic number of manhours devoted to getting IEEE 1459-2000 out, and I think it’s going to take awhile for may utilities to buy in to. The definition for D in IEEE 100-1992 looks all nice and neat, but there seem to be a fair lot of scholarly, respected and published detractors to it. Blazing A-to-D converters and ‘computers under glass’ [modern revenue meters] have helped us get a handle on recognizing the pervasive nature of D. From the revenue perspective, not everyone has bought into S derived from the ‘convenient’ product of rms V and I. I suppose I was lucky to be first introduced to it 20 years ago, were I came across situations where the simple version of Ohm’s law didn’t always work out, and, for a while that was a trial to appreciate.

 

[electricpete]

Just my two cents. I don't think that D has any physical significance other than a fudge factor to account for the vector difference between U and S. (D=sqrt(U^2-S^2) is the only defintion.

Q is defined similarly as the vector difference between S and P... but Q has a physical signficance. We can trace the flow of reactive power from sources to sinks and see the voltage drops.

D is of course associated with the harmonic content... but the same value of D could be associated with distortion of the current or distortion of the voltage... and may arise from many different patterns of harmonics. The value D in itself doesn't tell a whole lot.

 

[electricuwe]

Depending on phase shift of harmonic voltage and harmonic current of each harmonic number you can have active or reactive power for every harmonic number. But these products are very small compared with the product consisting of the fundamental and a harmonic. These products are neither active or reactive power but just distortion power.

 

[electricpete]

Good point eu. If we express current and voltage both as sum of sinusoids (each at a harmonic series of frequencies), then there will be product terms of the same frequency and product terms of different frequencies.

All of the product terms of different frequencies must be associated with distortion power.

As to the product of terms of same frequencies, they will have an in-phase component and a quadrature component. The in-phase component clearly can be associated with real power. The quadratue component clearly associated with reactive power if we're talkig fundamental. A little fuzzier if we're talking about the quadrature compoent of same-frequency harmonics... do we want to call it reactive?

I guess that is a minor semantic point. U will be sqrt of sum of squares of ALL product terms. Which terms exactly you choose to group into Q is not terribly important.... depends on your purposes..... just have to group those that you have not already captures into D.

To sum up what distortion power means.... it is associated with (sum of squares of) those terms that we do not include in our definitions of P and Q.

It makes a little more sense after you pointed that out, eu.

 

[jbartos]

Suggestion: Visit

http://www.laplaceinstruments.com/ac2000.htm

http://www.laplaceinstruments.com/6100032.htm

http://www.laplaceinstruments.com/ac1000.htm

http://www.laplaceinstruments.com/Harmonic/Ac2app.htm

(for flickermeter)

http://grouper.ieee.org/groups/harmonic/iharm/docs/docs.html

(for interharmonic distortions, etc.; however, there is no notion of any interharmonic distortion power, yet)
etc. for more info

 

[ElectroJoe]

Hi...

Almost 3 years later...Has it ever been determined if the synchronous reactance controller technology has been proven to work? The president of the company I work for has approached me on this and referred me to this company:

http://www.correctioncontrols.net/

I am going to have to hire someone to analyize our company's power quality before deciding a course of action.

Any thoughts?

 

[stevenal]

The technology is as old as synchronous motors, and has been used as an alternative to capacitors about that long. see Busbar's 4/26/02 response above. Seems like they are repackaging the SOS and making it sound like something new.

 

[jraef]

In general I had no problem with their statement of improved power quality, extended equipment life and decreased operating costs, because correcting power factor problems does accomplish that in general. Where they lost me was in this statement under the "How" tab.

"SR System technology creates a “flywheel” effect in the tank circuits which “dumps” current back into the system. This allows electrical equipment within the facility to function with the same voltage, torque and capacity it originally had before the installation of the SR System, while requiring less current from the utility company. This translates into lower Kw or Kva Demand and lower Kwh on your electric bill."

The part about requiring less current from the utility and lower kWH is a severe stretch. In the first place, you either have a flywheel or you don't. What is a "flywheel effect"? If it is a flywheel, it may in fact help to "dump" current back into the system, but it would later on require current (energy) to replace it. "YOU CAN'T GET SOMETHING FROM NOTHING" They then use the nebulous term "tank circuit" as a description, yet what is that? Free energy? WOW!!! Why isn't everyone jumping on this band wagon? Why doesn't the government set up massive banks of "tank circuits" all over the world and solve all of our energy problems? It must be a conspiracy of those rich money-grubbing utility fat cats!!!! You get my drift.

And another thing. Poor power factor shows up as losses in the transformers etc., which costs the utility inhaving to supply reactive power for it, but unless they pass that cost on to you in the form of power factor related charges, who cares? If your utility does have a power factor demand charge you may see some savings in the dollar amount on the bill, but not from lower kW consumption.

In my opinion they are banking on the fact that the vast majority of users do not understand how the utility charges them for their power consumption. A common thread in all scams is the complex mixture of truth, truisms and the fiction you are trying to pedal. I'll stop short of calling this a scam because there are definite benefits to improving power quality, but when they try to peddle the "energy savings" issue it starts to smell a little fishy IMHO.

"Venditori de oleum-vipera non vigere excordis populi"

 

[jraef]

By the way ElectroJoe,
For future reference it is better to start a new thread and reference this old one when you have your own question. You can reference it by highlight-copy-and-pasting the thread number at the top into the body of your new thread. It will show up as a direct link, like this Thread237-20884.

"Venditori de oleum-vipera non vigere excordis populi"