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Hi. My name is costas. I start my master thesis and i face a problem. i take measurements in a hybrid renewable energy system (with photovoltaics and a wind turbine) to see the produce power quality of the system (i take measuremets after the inverter). From measurements i notice that i have big harmonig currents. I want to know if anybody have the IEEE standards for power quality (current, voltage) to compare them with the values of the measurements i take and also if there is a way to reduse this harmonics in the real system. Thanks.
costas said:
Hi. My name is costas. I start my master thesis and i face a problem. i take measurements in a hybrid renewable energy system (with photovoltaics and a wind turbine) to see the produce power quality of the system (i take measuremets after the inverter). From measurements i notice that i have big harmonig currents. I want to know if anybody have the IEEE standards for power quality (current, voltage) to compare them with the values of the measurements i take and also if there is a way to reduse this harmonics in the real system. Thanks.
Most relevant IEEE standard regarding harmonics is IEEE: 519-1992,, here's link to simple pdf that contain tables with standard limits for THDi and THDu http://www.calvin.edu/~pribeiro/IEEE/ieee_cd/chapters/pdffiles/c9pdf.pdf ..
Hope that helps ;)..
Regards,, Alen..
Leading PF can cause the safety devices (circuit breakers and contactors) to fail over time.
This is the first time I've ever heard of this. Could you please expand and give a technical reason why this may occur.
Prezado Jim
eu sou engenheiro eletrico e trabalho com manutenção predial,UPS, cabling e data centers.
eu moro em Brasilia DC Brazil e presencio no dia a dia tudo o que Vc relatou no texto acima.
SEUS COMENTÁRIOS SÃO ÓTIMOS.
poucos profissionais entendem de harmonicas, a literatura é superficial ou muito academica.
os filtros ativos são a melhor solução no meu ponto de vista, mas no Brazil são muito caros.
as harmonicas são um problema mundial e a situação só tende a piorar com o acesso a computadores e todos equipamentos eletronicos presentes nos lares, escritorios e industrias.
temos uma invasão de produtos chineses com fontes com FDP perto de 1 ou capacitivos e com alta THI.
meu principal cliente é o GOVERNO FEDERAL e o menor preço é fundamental, acima da qualidade.temos predios com energia trifásica 380/220 Volts , porem com cargas predominantemente monofasicas com harmonicas de sequencia zero.
os computadores são ligados comumentemente em 120 Vac ( F,N,T); em alguns casos utilizam transformadores isoladores K-20 delta- estrela.
cuidam do primario e esquecem da fonte das harmonicas
Although we are talking about an entirely different field of “filters” I must comment that many of my commercial clients for hvac filters have begun discussing the “harmonic filter” issue frequently. Out of curiosity, I did some research and find that this article is likely the most comprehensive one on the net regarding this subject. Admittedly, I do not have the brain power to intelligently discuss this issue. But I must say that anyone who does have that capacity has a Texas “hats off to you” salute for your level of intelligence and comprehension. Now I know what blog to recommend to my clients I will surely send some traffic your way! Best regards! John Mauldin, Dallas, Texas
WOW!!! Thank you for your very kind words.
The knowledge expressed here is the result of 39 years of work in the power electronic field. First with AC and DC motor speed controls and then ative harmonic filters. But I have to say a lot of other people have teught me much over the years. Without competent engineers to discuss issues with there would be much confusion and poor assumptions.
Please, do send others to this site. I hope everyone that comes and learns passes it on to another.
Thank you and Regards,
Jim
HI, Joe,
Safety devices and contactors are designed to operate with leading voltage, not leading current, on an AC system. When a safety device or contactor opens it is designed to break the voltage which then stops the current flow.
If the contactor opens with leading current, the voltage is still present and arcing occurs. The arcing causes damage to the contact surfaces. The amount of arcing depends upon the voltage present when the conacts are separated. As the phase angle (displacement power factor) becomes more and more leading the instantaneous voltage level increases toward the peak of the sinewave of the voltage and more damage will occur.
The problem is the pitting (chunks of metal are pulled from the metal surface) upon each activation due to arcing. As the amount of pitting increases the actual surafce area left is less and less on the contacts. At some point the contact surfaces are eroded sufficiently to either they weld shut upon the next occurence or prevent closure because not enough surface is present.
Hope this helps.
Regards, Jim
Hi, Alen,
Most of your attachments have been removed from the Blog content. I have not been able to review most of what you sent.
Obviously, this is not the correct media for your investigation.
Please psot your email and I will get back to you.
Regards,
Hi, Joe,
It looks like the last response I posted for you did not make it here. So, I will do it again.
Contactors and circuit breakers deisgned for AC voltage systems operate on the principle of breaking the voltage before the current is interrupted. In this manner the energy supply – voltage – has been removed and the contacts open stopping current (and voltage).
If current leads voltage, the contacts must break the current before it breaks the voltage. This causes the source (voltage) to continue as the current is interrupted. The result of this is a high energy arc according to the level of voltage broken. As the power factor goes more leading the instantaneous voltage rises on the AC voltage waveform toward the peak voltage at 90 degrees.
The issue is what happens to the contacts when the voltage is still present and supplying energy. This energy must arc to between the contacts. Each arc lifts the metal content at the point of arc. Over time the contact becomes heavily pitted.
At some point one of two results will occur. One is the conatcts will weld closed and prevent opening the contacts. Thus continued supply of power to the load. The other is if the contacts are open, they may not close because there is an irregular surface and lock in cannot occur.
Regards, Jim
Jim said:
Hello, Owen, Garage and Kerstein,
I don't know where this discussion come from but I will offer some comments.
Direct on line (DOL) AC motors are the worldwide standard to produce mechanical work from electricity. No dispute. Its huge.
DOL AC motors provde fixed speed operation. They are dependable and last a long time if environmental conditions are maintained to standard.
DC motors are only used when variable speed is needed and a DC controller (DC drive) is required.
So any discussion about comparing DC and AC motors requires a discussion about the motor controllers also.
DC motors are more efficient than AC motors. Typically DC motors are 97-99% efficient. AC motors are not more than 94% efficient (check the manufacturers' tables).
DC drives are 99% efficient. AC motor speed controls (PWM VFD) are at best 97-98% efficient. Typically about 97%.
But efficiency is only one part of the discussion. Maintainence is another issue. DC motors require maintenence for the brushes. AC motors need grease and they run forever.
DC drives are simple and less costly and easy to maintain. PWM VFD are more complex and do require more maintenece than DC drives.
DC motors are considered special and have relatively long deliveries. AC motors for DOL use are stocked and readily available. For a given size rating, the DC motor is larger physically.
AC motors to be used with PWM VFD require a different design than do standard DOL AC motors. NEMA and other bodies have defined how these differ. Needless to say the AC motor that operates on VFD should be special.
Trade offs abound.
Generally, PWM VFD with AC motors are used as a preference over DC dirve and motors – today.
Regards,
nice discussion , u can use the general manafactued motor with the VFD drive. But now a days motor is specially desigened for the VFD and it will give you better result. specially ABB motor.
But brother DOL is a unversal applicaiton and still it is used in the industry due to natuie of its cost and maintenance naturre but modern factories who has good budget they are using the soft starter.
Well where u need a precession of control , like paper industry , still u need those dc drive anyway good discussion
Jim said:
Hi, Alen,
Most of your attachments have been removed from the Blog content. I have not been able to review most of what you sent.
Obviously, this is not the correct media for your investigation.
Please psot your email and I will get back to you.
Regards,
Hi and thanks for your help,, I really appreciate it ;)..
You can find my e-mail above this post by clicking on “little red button – with person logo” named “view user profile”..
But there it is to: alen.matanovic@gmail.com
I've prepared detailed paper with my problem to send you :)..
Regards, Alen..
Dear Jim,
Actually i am in the filed of power quality, and visit industries to do harmonic analysis.
I have some questions in my mind that i want to ask you,
1. Reason for selecting 189Hz detuning frequency, for the detuned filters??
2. If the particular industriy is having total current harmonics of say 25% ithd (without capacitors), customer used to ask me what will be the possible reduction of harmonic with detuned or tuned filter.Is there any formulae or Matlab simulation software available to calculate this % reduction in iTHD, 5th , 7th ,11th level after connecting passive filters.
If you could help me, i will be very glad. By this i can commit customer that after connecting passive filters harmonic levels will come down to below 5-6% as per IEEE norms. I know there are verious factor involve in this to calculate exact reduction.
You are requested to guide me.
wull i want to know one thing that i am choosing my final year project on design an fabrication of power factor improvement pannel, well after reading these all topics i am confused that , in this pannel which is basically for industries, should i use harmonic filters also or not? and one important thing what change can i bring in my project?
Jim Johnson said:
Thanks for the compliment. The subject is not simple – it gets tough to make it simple.
A PF capacitor when placed in an electrical system has a resonant frequency based upon the inductance of the electrical system (from any point) and the capacitance of the PF capacitors. The PF capacitors are installed parallel to the loads. Adding a reactor in the parallel portion of the circuit in series with the capacitors modifies the frequency of the PF capacitor bank and thus the resonant frequency of the PF capacitor bank in the electrical system. This is 'detuning.'
PF capacitors will interact with all frequencies present in the electrical system. When harmonics are present this is harmfull to the capacitors. The harmonic currents will overheat the PF capacitors to shorten its life or trip its thermal safety devices. Detuning can be designed to 'block' most of the harmonic currents or can be designed to permit the current of one harmonic frequency to flow into the capacitors. The 'blocking' design is considered 'detuned' within the industry. The design that permits a harmonic order to flow into the capacitors is called a 'tuned' capacitor or a harmonic filter.
Detuned and tuned capacitor systems are typically of two application philosophies. One is an electrical system solution where one large bank is used for a group of loads or used at the utility connection. Local and worldwide suppliers of these exist. However, a harmonic study is required for these types of solutions. Be sure the company chosen can provide this before equipment is purchased.
The second philosophy is to place a small tuned capacitor system at each nonlinear load to provide harmonic suppression for the electrical system. To be sure that these small tuned banks do not interact with each other (when more than one is installed) or overload due the presence of other sources of harmonics, a series reactor on the source side of the filter section is required. The series reactor is sized for the full load current of the nonlinear load on which applied.
The tuned filter also provides leading reactive current that must be evaluated within the system to determine if problems may occur due to excessive leading PF. The manufacturers of these type of filters tend to be localized operations within individual conutries. They exists in many countries.
The result of properly applying either device will relieve the utility of conducting VARs and specific harmonics and permit green generation technologies to be more easily employed.
Regards
wull i want to know one thing that i am choosing my final year project
on design an fabrication of power factor improvement pannel, well after
reading these all topics i am confused that , in this pannel which is
basically for industries, should i use harmonic filters also or not? and
one important thing what change can i bring in my project?Jim said:
WOW!!! Thank you for your very kind words.
The knowledge expressed here is the result of 39 years of work in the power electronic field. First with AC and DC motor speed controls and then ative harmonic filters. But I have to say a lot of other people have teught me much over the years. Without competent engineers to discuss issues with there would be much confusion and poor assumptions.
Please, do send others to this site. I hope everyone that comes and learns passes it on to another.
Thank you and Regards,
Jim
hi jim
i am eagerly waiting for ur reply!
wull i want to know one thing that i am choosing my final year project
on design an fabrication of power factor improvement pannel, well after
reading these all topics i am confused that , in this pannel which is
basically for industries, should i use harmonic filters also or not? and
one important thing what change can i bring in my project?regards umer
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