# Harmonic filter problem ---- computer harmonic analysis using EasyPower software



## azzaman77 (Nov 25, 2010)

I will just apologize to everyone in advance because of my English,, as well as for long post, I just don't know how shorten it







..



I'm expirencing some problems (that are more "theoretical" nature) with harmonic filters.. I can't seem to find how to properly calculate the values for inductance and capacitance of "notch" filter..

Actually, I have designed notch harmonic filters for 5th and 7th harmonic in EasyPower,, using thompson relation,, but my real problem is to determin reactive power request at the point of installation of filters..
Here You can see some "print screens" of my project (it's pretty simple one) that consists of 4 loads, 1 linear and 3 nonlinear.. transformer is able to atenuate "triplens" but, because at my loads 5th, 7th, 11th and 13th harmonics are dominant,, I still have significant current THDi at PCC point of sistem if filters are OFF..


filters off:


filters on:



impendance characteristics @ bus 3:



My problem here is, how to precisely calculate "capacitor bank" and how to determin "voltage" required by programme, please look at the filter data box (notch filter):

I've set aprox. voltage level of 430V (because main is 400V) just to perform calculation,, and it seemed to work, but I'm looking to find formula for it's precise calculation..
The only information provided by programmes "manual" and "help" is:
Filter Data:
• Resistor: Resistance of resistor of the filter in ohms.
• Inductor: Real and imaginary impedances (ohmic resistance and inductive reactance) at system frequency in ohms.
• Capacitor Bank (1 and 2): The reactive power of capacitors for the system frequency in MVARs at the voltage level specified in kilovolts
… which doesn't helps me very much..


Other thing, about reactive power calculation,, my loads are set in kW and kVAr,, so if I just "add" those kVArs I'm not sure if I'm geting proper value for my capacitor bank.. Lets say, for example, if my linear load is set as: 100 kW and 20 kVAr, and other three, ASD 40 kW and 5 kVAr, Fluo. lighting 25 kW and 5 kVAr,, and PC center 30 kW and 5 kVAr,, simple problem is how should I properly add those to gain value for reactive power request by my loads.. I asume that linear load would have "ohmic" character, ASD drive "inductive",, and Fluo and PCs "capacitive" character,, so simple adding (20+5+5+5=35 kVAr) is definatelly questionable,, more proper way would be "phazor" addition.. but interesting fact is that if I set my filters capacitor bank to 0.035 MVAr it provides better THDi atteunation than it's if I set it to phazor value 20,616 kVAr,, I supose that programe is not able to differ those "load character" differences.. 



Once knowing this "voltage" and "capacitance" it's simple to calculate "inductance" using Thompsons relation..
Here are also the links for my calculation of those filters, as well as "reverse" calculation (that's the way I found to calculate my filters) of filters that are provided in example in the users guide of this book (I'm going to apologize again, now for two reasons, first is those materials are not in English, since I'm from _adriatic region_, but You can see/look only at calculations…. other reason for apologize is "messy" pdfs because my scanner just got broken, so I was using my camera).. 
"_primjer iz knjige_" would be "example from the book" and "_računanje filtera_" would be my filter calculation..

example form the book (please notice that "2.filter" and "3.filter" are notch 5th and 7th filters respectively….. how come is Xc value different for both filters and it's close to 20 MVAr set by the load?……. there You can also see those voltages like 120 kV that are set "in decimal"):
http://rapidshare.com/#!download|583l3|432528052|Primjer_iz_knjige.pdf|313

calculation (please look on the page 3. for calculation of my filters,, and on page 2. for reverse calculation of filters from book example):
_http://rapidshare.com/#!download|569tl2|432527002|racunanje_filtera.pdf|4058_


_Every help is warmly wellcome







..
_
Kind Regards,, azzaman77..


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## 10492 (Jan 4, 2010)

Why are you trying to build a filter for the 5th, and 7th harmonic?

What do they do? 

They are just there, floating around minding there own business.

FWIW, I have no clue what that software is or does. sorry.


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## azzaman77 (Nov 25, 2010)

Dnkldorf said:


> Why are you trying to build a filter for the 5th, and 7th harmonic?
> 
> What do they do?
> 
> ...


Sure, I'm sorry for not saying anything about the EasyPower, but I'm not sure how is this helping very much :blink:,, is't simple, but powerfull software for short circuit/power flow/harmonics/relays analysis..

Those filters are not just there,, they're here to provide low impendace sink to 5th and 7th harmonics currents,, similiar you can see at the example from book..

I know that those two are not enough for best results, i would have to use active filtering,, but I'm ok with that, and I'm just looking for way to calculate them more precisely..

Thanks for Your comment ..


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## 10492 (Jan 4, 2010)

Don't mind me. I just hooked up with some good mistletoe, and read your "theoretical", as "theatrical".:laughing:


So, in a nut shell, you're looking at building a 300hz, to 360hz filter?


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## azzaman77 (Nov 25, 2010)

Dnkldorf said:


> Don't mind me. I just hooked up with some good mistletoe, and read your "theoretical", as "theatrical".:laughing:
> 
> 
> So, in a nut shell, you're looking at building a 300hz, to 360hz filter?


Actually those are 240 Hz and 340 Hz filters,, because you never use exact harmonic order to calculate with it,, it's allways little less (about 0,2 less) to ensure security tolerance..

5th harmonic filter resonance freq:
4.8 x 50 Hz = 240 Hz

Speaking about european 50 Hz systems,, but there's no difference in calculations I'm looking for..

7th harmonic filter resonance freq:
6.8 x 50 Hz = 340 Hz


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## 10492 (Jan 4, 2010)

azzaman77 said:


> Actually those are 240 Hz and 340 Hz filters,, because you never use exact harmonic order to calculate with it,, it's allways little less (about 0,2 less) to ensure security tolerance..
> 
> 5th harmonic filter resonance freq:
> 4.8 x 50 Hz = 240 Hz
> ...


 
No idea why I put 5 and 6. I'll reference the mistletoe again.

I used 60hz.


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## MDShunk (Jan 7, 2007)

All this talk about harmonics got me thinking about this:


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## azzaman77 (Nov 25, 2010)

MDShunk said:


> All this talk about harmonics got me thinking about this.............................


 Hahaa,, You're silly :laughing: :001_tongue:  ,, and this guy rocks ..

Anyways,, here are more pics,,

Current spectrum of loads:
[IMG=http://img340.imageshack.us/img340/5039/izrezakm.jpg][/IMG]

And spectrum @ primary side of transformer:
[IMG=http://img23.imageshack.us/img23/2280/spectrumatprimary.jpg][/IMG]


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## Josue (Apr 25, 2010)

MDShunk said:


> All this talk about harmonics got me thinking about this:


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## brian john (Mar 11, 2007)

There are a few posters on mikeholt.com tat may be able to give you insight into your question.


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## azzaman77 (Nov 25, 2010)

brian john said:


> There are a few posters on mikeholt.com tat may be able to give you insight into your question.


Thank You,, I've just registered there :thumbsup:..


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## Shorty Circuit (Jun 26, 2010)

azzaman77 said:


> Actually those are 240 Hz and 340 Hz filters,, because you never use exact harmonic order to calculate with it,, it's allways little less (about 0,2 less) to ensure security tolerance..
> 
> 5th harmonic filter resonance freq:
> 4.8 x 50 Hz = 240 Hz
> ...


Canned computer design of filters usually doesn't work well, especially if the filters have very high Qs. Among the problems that aren't taken into account which can affect both Q and Fc are parasitic inductance and capacitance not evident in your calculations and differences between the capacitance printed on the capacitors and their actual values. Even heating of the conductors can change the R value of the equation. The higher Q is, the more critical accurate tuning becomes. 

To design and get one to perform you need a way to adjust C and L with the actual load either by having adjustable inductors and capacitors or by adding or subtracting to their numbers usually in small increments and then watching the waveform on an oscilloscope or better yet a real time spectrum analyzer. When the notch filter coincides directly with the harmonic, you'll see the peak disappear. Don't be surprised if Q is too sharp or the "harmonics" do not occur at single frequencies but over narrow bands. Also don't be surprised if the filtering effect drifts with increasing or decreasing load.

A better choice might be to design a sharp low pass filter say with an F3 of 80 to 90 hz, say a second, third or fourth order filter. This will surpress all of the harmonics simultaneously, the higher the harmonic, the greater the supression.

I've never trusted the zig-zag transformer design and haven't bought one. It seems to me that unless the phases are perfectly balanced, it won't work, there's nothing to cancel the harmonics against. This is the real world case, not the laboratory case where it should work perfectly. Also different current phase shifts due to different pfs on the different phases may reduce the cancellation effect.

Harmonics can wreak havoc on transformers and feeders. Skin effect heating can be very pronounced. This manifests itself in overloaded neutrals, which creates a very dangerous risk to electrical loads on Wye connected systems. An open neutral due to overload caused by harmonic heating could destroy many of the loads connected to the neutrals as can be seen by a simple circuit analysis of phase to phase voltages across loads which are suddenly in series between phases when the neutral is open.

IMO the best method for dealing with high harmonic loads is to use harmonic rated equipment such as K rated transformers. Personally I spec out K-13 aluminum winding transformers as the best bang for the buck. They are not much more expensive than K-4 rated transformers and are much more effective. I haven't found instances where K-20 or K-30 was justified. Panelboard manufacturers like Square D now recognize the problem and often supply 200% rated neutrals as standard. You can also buy transformers twice the size you need and just derate them by 50%. I don't see any advantage to buying K rated transformers over that option. It's usually slightly cheaper and you get the advantage of running the phase wires at far lower than rated capacity. For some reason I don't understand, the prices of transformers including aluminum winding transformers is sky high compared to where they were say 15 years ago, much higher escallation than other equipment. I'm trying to find out why. I know in the US energy efficiency laws have driving the cost up a lot.


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## brian john (Mar 11, 2007)

Shorty:

Are there negative trade off to using higher K rated transformers (than what may be required for the specific application), such as higher secondary available fault currents? 

In addition if you needed a 75 kva k-13, could you use a larger transformer? The issue is with additionally heating so you could minimize the heating effects with a larger transformer?


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## Shorty Circuit (Jun 26, 2010)

brian john said:


> Shorty:
> 
> Are there negative trade off to using higher K rated transformers (than what may be required for the specific application), such as higher secondary available fault currents?
> 
> In addition if you needed a 75 kva k-13, could you use a larger transformer? The issue is with additionally heating so you could minimize the heating effects with a larger transformer?


 
I'm not aware of any drawbacks to higher K-rated transformers besides size and cost. As I said, you should be able to get equivalent results by just doubling the size of the transformer and derating it. For example, if you need a 75 KVA K-13, just buy a 150 K-1 and treat it like a 75. The cost is about the same. Check with your distributor and see what he thinks about that, then let me know.


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## azzaman77 (Nov 25, 2010)

> Canned computer design of filters usually doesn't work well, especially if the filters have very high Qs. Among the problems that aren't taken into account which can affect both Q and Fc are parasitic inductance and capacitance not evident in your calculations and differences between the capacitance printed on the capacitors and their actual values. Even heating of the conductors can change the R value of the equation. The higher Q is, the more critical accurate tuning becomes.


 I really appriciate your opinion,, and even though that in my chase I don't believe that these details are relevant (because my load doesn't change over time, so as heating of conductors don't,, and I mentioned earlier that I know this wont work well, but it's only for my studying purposes),, I'm still interested in influence of parasitic inductance and capacitance and other you mentioned, on more precise calculations..



> To design and get one to perform you need a way to adjust C and L with the actual load either by having adjustable inductors and capacitors or by adding or subtracting to their numbers usually in small increments and then watching the waveform on an oscilloscope or better yet a real time spectrum analyzer. When the notch filter coincides directly with the harmonic, you'll see the peak disappear. Don't be surprised if Q is too sharp or the "harmonics" do not occur at single frequencies but over narrow bands. Also don't be surprised if the filtering effect drifts with increasing or decreasing load.


This is interesting..
I wander what you concider as "Q" (do you think on capacity of capacitor bank or maybe quality factor Q of the filter)? I would say I understand that filtering effect changes with change of load.. That is why this resonant frequency must be safely away from any significant harmonic or other frequency component that may be produced by the load. Filters are commonly tuned slightly lower than the harmonic to be filtered to provide a margin of safety in case there is some change in system parameters that would raise the notch frequency. If they were tuned exactly to the harmonic, changes in either capacitance or inductance with temperature or failure might shift the parallel resonance higher into the harmonic being filtered.. This could present a situation worse than one without a filter because the resonance is generally very sharp (look at the picture of impendance frequency scan)..



> A better choice might be to design a sharp low pass filter say with an F3 of 80 to 90 hz, say a second, third or fourth order filter. This will surpress all of the harmonics simultaneously, the higher the harmonic, the greater the supression.


I believe you know why you're recomending this solution, but seems like I can't really understand it :001_huh:..
Here's the current spectrum on delta winding (primary) of transformer:
http://img23.imageshack.us/i/spectrumatprimary.jpg/




> IMO the best method for dealing with high harmonic loads is to use harmonic rated equipment such as K rated transformers. Personally I spec out K-13 aluminum winding transformers as the best bang for the buck. They are not much more expensive than K-4 rated transformers and are much more effective. I haven't found instances where K-20 or K-30 was justified. Panelboard manufacturers like Square D now recognize the problem and often supply 200% rated neutrals as standard. You can also buy transformers twice the size you need and just derate them by 50%. I don't see any advantage to buying K rated transformers over that option. It's usually slightly cheaper and you get the advantage of running the phase wires at far lower than rated capacity. For some reason I don't understand, the prices of transformers including aluminum winding transformers is sky high compared to where they were say 15 years ago, much higher escallation than other equipment. I'm trying to find out why. I know in the US energy efficiency laws have driving the cost up a lot.


This also sounds logical to me, but I'm still wandering how does this helps to prevent harmonics entering Distribution (on PCC),, besides only helping transformer to "ride-trough" these conditions?? I would say it's only recomended when there's no danger of disturbing sensitive loads or exceeding limits set in standards........... I mean, what are the limits for current THDi @ PCC,, I know voltage is limited to 5% THDu according to IEEE 519, and to 8% in europe..


Anyways.. Thank You very much for your effort, and good advices :thumbsup:..
I would say, I want to start with simple notch filter designs for now,, and I'm willing to lear more ..


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## Shorty Circuit (Jun 26, 2010)

azzaman77 said:


> I really appriciate your opinion,, and even though that in my chase I don't believe that these details are relevant (because my load doesn't change over time, so as heating of conductors don't,, and I mentioned earlier that I know this wont work well, but it's only for my studying purposes),, I'm still interested in influence of parasitic inductance and capacitance and other you mentioned, on more precise calculations..
> 
> 
> This is interesting..
> ...


I can't give you a course in filter analysis and design here. I recommend that you study it in an electronics course, exactly the same principles apply. Most elementary courses up to the high school level use canned formulae which are often used blindly. The real understanding comes with deriving the models, mathematical equations, and manipulating them. It also requires coures in waveform analysis. You'll need a couple of years of calculus, Fourier analysis, and some courses in electrical engineering for that. You can try some textbooks from the library for starters. I'm sure there are also many websites that can give you detailed explanations. 

BTW, "Q" sometimes called the "resonance magnification factor" is a comparison of how sharp the filter is, that is its amplitude divided by its bandwidth. Very high Q filters are extremely effective over a very narrow range of frequencies. The filter you need depends on fully understanding your exact application.

Harmonic rated transformers do not surpress harmonics, they are merely designed to be robust enough to withstand their effects. Harmonic cancelling, mitigating, or surpressing circuits have varying effect. A good state of the art UPS is usually very effective at cancelling harmonics by using principles of negative feedback to add harmonic components 180 degrees out of phase to the distorted waveform.

Harmonics usually arise because of the effect of SMPSs, that is switching mode power supplies found in most mondern electronics including fluorescent ballasts. They are cheap, efficient, and generate lots of harmonics that can spell trouble but they are a fact of life.


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## azzaman77 (Nov 25, 2010)

> I can't give you a course in filter analysis and design here. I recommend that you study it in an electronics course, exactly the same principles apply. Most elementary courses up to the high school level use canned formulae which are often used blindly. The real understanding comes with deriving the models, mathematical equations, and manipulating them. It also requires coures in waveform analysis. You'll need a couple of years of calculus, Fourier analysis, and some courses in electrical engineering for that. You can try some textbooks from the library for starters. I'm sure there are also many websites that can give you detailed explanations.
> 
> BTW, "Q" sometimes called the "resonance magnification factor" is a comparison of how sharp the filter is, that is its amplitude divided by its bandwidth. Very high Q filters are extremely effective over a very narrow range of frequencies. The filter you need depends on fully understanding your exact application.


Thank You again, I'm aware of facts you're saying,, and I'm already reading about this Q factor  ..




> A good state of the art UPS is usually very effective at cancelling harmonics by using principles of negative feedback to add harmonic components 180 degrees out of phase to the distorted waveform.


I'm not sure I understand this eather,, this would be a priciple of active harmonic filter.. 

Wouldn't UPS devices even add to harmonic problems?? Since they are also nonlinear loads, unless you mean using a 12-pulse rectifier in place of a 6-pulse set which will reduce the levels of THDi, and when coupling this with a passive filter will provide further reduction to around 4%.. For a transformerless uninterruptible power supply, THDi levels of less than 4% can be achieved by installing an active harmonic filter. New today's UPSs with harmonics-corrected, power factor-corrected insulated-gate bipolar transistor (IGBT) technology are recommended.. So, all I know that UPS can only cause additional problems related to harmonic distortion..


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## Shorty Circuit (Jun 26, 2010)

azzaman77 said:


> Thank You again, I'm aware of facts you're saying,, and I'm already reading about this Q factor  ..
> 
> 
> 
> ...


Modern state of the art UPSs have circuits which deal effectively with both load generated harmonics and harmonics generated back at the source. Look at models from Eaton and Liebert for specs. Contact their distributors. This is not really new by the way, it's been SOP for many many years.


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