- This topic has 10 replies, 2 voices, and was last updated 9 years, 1 month ago by Anonymous.
2010/10/15 at 9:05 am #10245FrancoisParticipant
When professionals want to manage an electrical system in a new installation or after retrofit or extension of an existing installation, it is important to consider the Harmonic currents emitted by the non linear loads connected to the distribution system.
The non linear loads or products producing harmonics can be as example, for industrial equipments: welding machines, battery chargers, variable speed drives for electrical motors, uninterruptible power supplies, or for office equipments or household appliances: TV sets, fluorescent lighting, light dimmers, etc…
I think that it is sometimes the only best solution to mitigate harmonics at the equipment level by using passive filters or active filters. But you can also consider that the good solution is to mitigate at the installation level. For instance, an active filter can be located at the input of the main supply network in order to mitigate harmonics of all equipments, or for a group of non linear loads.
From the utility point of view, it is mandatory to comply with limits required by standards at the PCC. PCC is the Point of Common Coupling located in the public supply system, closest to the installation concerned, at which other installations (customers) are connected. National or international standards suggest limits to comply with at the PCC, like the Total Voltage Distortion THD.
Some parameters are to be considered at installation and equipment level like Isc, Ssc, Rsc, in order to know what harmonic limits are required. Considering your experience on the field, do you think it is easy to collect that kind of information? And do you know what are the different harmonics mitigation solutions, available for your installation?
I will be glad to react to other point of views.
Martial Patra2010/10/15 at 9:06 am #11542AnonymousGuest
There is now a better solution to Harmonics rather than passive and active filters that usually damp the harmonics energy down to the ground.
A new method utilizes unsaturable zigzag reactor that convert this back to useful Electric energy.
This is called Electroflow, now represented in 107 countries, including USA, Europe, switzerland France Canada.
Check the website Electroflow.2010/10/15 at 9:06 am #11543AnonymousGuest
No passive or active device designed to mitigate harmonics converts harmonics ‘back to useful Electric energy.’ In fact, all of the passive and active harmonic mitigation devices consume some small amount of real power (useful energy) in order to operate.
Unsatuarable zigzag reactors are also known as zigzag transformers. There are two main uses for these devices.
1) Neutral current mitigation: The device attaches to the neutral and the three mains conductors. It is designed to conduct the third harmonic (the largest and most harmful harmonic on the neutral) to the mains conductors equally per phase. This process reduces the neutral harmonic away from the loads beginning at the point of connection to the neutral and increases the harmonic current on the mains. But since it is divided equally on the mains, it has a much less detrimental effect on the mains.
2) Multipulse rectifiers: Autotransformers can be designed with zigzag secondary connections to create phase shifting that results in reduced harmonic current on the mains side of the transformer. The equipment are three phase loads with two or more rectifiers. In some cases, two or more independent nonlinear loads may be connected in this fashion to create a quasi-multi-pulse system.
To reitierate the important point, no harmonic mitigation device, passive or active, converts harmonics back to useful electrical energy. All harmonic mitigation equipment consume some level of real power while functioning.
The purppose of harmonic mitigation equipment is to limit the effects of harmonics on the mains side of their connection within the electrical system to permit fuller utilization (increase energy efficiency) of the electrical system. This also stops the detrimental heating and voltage distortion that causes other equipmnet to fault or fail.2010/10/15 at 9:06 am #11544AnonymousGuest
1st of all I am glad to read all things about Electrical system. and i hope you will provide help to us time to time.
Sir I am a associate Engineer (Hired) in Karachi electric Supply Company I have worked 4 years on Distribution network HT,LT over head & Under ground system now I supervising the Installation of 1PMT
project problem with me that I have DAE in Auto mobiles. & my Expearance is in electrical side company says submit the electrical certificate for become as our employment please help me in this regard. My mail address is email@example.com if any certification is available online I can pass the examination. sir please any one help me.2010/10/15 at 9:06 am #11545AnonymousGuest
Can you explain harmonics in layman’s terms, it’s effects, causes, and remedies?
I’m doing some work at a manufacturing plant that has 20-30 VFD’s from different manufactures and we are having issues with harmonics.
We have changed out some “inferior” drives and improved somewhat, but still have issues.
What effect does current harmonics have? How do they effect the system i.e.
would one bad drive affect the incoming service and/or all equipment/or drives?
Also same question with voltage harmonics.
John Bouchard & Sons Co.2010/10/15 at 9:06 am #11546AnonymousGuest
Dear Electrical Professionals, had understand the destructive effect of Harmonics, as it create unwanted heat enrgy, causes loss of memory of computers, causes disturbance of electronic controllers, causes early rewinding of motors as it destroy winding insulations and foremost as it causes error in Electric Meter readings normally the error increases whaqt the electric meter reads, which is advantageous to Utilities.
What I need to know please, is what are particular effect of Voltage Harmonics and what the Current Harmonics destructively do in a Electrical system?2010/10/15 at 9:06 am #11547AnonymousGuest
respected electrical professional can you please provide me with the circuit diagram on the following topic because its urgent . and this should be carried out using active filter and not passive filter .
Harmonic Mitigation: Filtering harmonic currents from the neutral of three phase systems with single phase non-linear loads
my email address is( firstname.lastname@example.org)2010/10/15 at 9:06 am #11548AnonymousGuest
Hi, glad to explain
Harmonics in layman’s terms : Bacteria or germs that appear under the microscope of a unhealthy blood sample.
Any signal that travels at frequency which is diffrent from the system fundamnetal frequency is a harmonic. In a 50 Hz system a 60Hz current is considred a harmonic. On the contrary, a 50 HZ current is considred a harmonic in 60HZ system.
Voltage harmonics generally increase transfomer’s eddy losses, overload capacitors ” can be RFI caps at the input of VFDs.
while current harmonics increase heat losses as voltage drop across transfomers windings as well resonance in capcitor banks.
the best approach in manging harmonics in a multi VFD installation is to use line reactros , this should probaply fix 60% of the problem then adecision will have to be made to apply a suitable harmonic mitigation technique. From My experience assuming the VFDs donot have line reactors , the reactors should significantly rectify the problem.2011/09/10 at 10:39 am #12485AnonymousGuest
we just finished the mall project & in this peak summer we checked harmonic study & found 04 nos of panel are showing total demand distortion limit is as per below detail
R % TDD = THDI x (I1/IL) =22% x (830/1565.7)=11.7%
Y % TDD = THDIx (I1/IL) =22% x(814/1565.7) =11.4 %
B% TDD = THDI x(I1/IL ) =21%x (853/1565.7 )=11.4%
%total demand distortion (%TDD)
LV MDB Isc /IL 41.5 TDD R11.7% Y 11.4% B 11.4% as per IEEE 519 1992 standards 8% is acceptable limit we need metegation plan how we can close this issue by doing less modifaction in the system & expence wise total 4 nos of MDB,s are same value , the active load in this panels is VFD,s lighting ,motors ,chillers with inbuilt VFD , fan coil units ,air handling units2011/12/21 at 1:39 pm #12742AnonymousGuest
Deep thought! Thanks for cornitubting.2012/12/14 at 4:06 pm #13290AnonymousGuest
I have a situation that I am confused about. I recently installed some Leviton Flourescent closet fixtures with integral IR sensors in a residence. The customer called me back stating that they turn on by themselves with no occupancy and the doors are shut. It is a newer house (5 years old). The Leviton rep stated that if there are ceiling fans on the same circuit they may create harmonics in the line that may cause them to trip on. I ran a new dedicated circuit to the panel and replaced all 4 of the existing fixtures with new ones from a new batch and am still experiencing the same problem. On my last trip it was noted that when one of the bathroom fans is turned OFF it turns on the lights in the adjacent room, and the lights also trip on when the T-stat calls for the furnace to turn on. The Utility put monitoring equipment at the site and found the THD was
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