Reactive Power Compensation
Reactive Power Compensation
(OP)
Hi everyone,
I've just been assigned a new project regarding Reactive Power Dynamic Compensation, which is kinda new for my employer in my country, as it is for me. I am going to be formally taught about it later on but I really want to get acquainted with it before training and all I know as of now is that it involves injecting and absorbing VAr from the power grid when needed by means thyristors controlling a set of reactor and capacitor banks as well as filtering the 5th and 7th harmonics (in this case). I would like to know why the 3rd harmonic (which is usually the most harmful for three phase grids) is not accounted for as well as any other helpful information about this technology. Any information would really help. Thanks in advance.
Cheers!
P.D. I don´t know if this will help but being a Mechatronics Engineer I am not too familiar with power transmission, I do know a bit more than the basics but I wouldn't call myself an expert so ABC types of answers are welcome too!
I've just been assigned a new project regarding Reactive Power Dynamic Compensation, which is kinda new for my employer in my country, as it is for me. I am going to be formally taught about it later on but I really want to get acquainted with it before training and all I know as of now is that it involves injecting and absorbing VAr from the power grid when needed by means thyristors controlling a set of reactor and capacitor banks as well as filtering the 5th and 7th harmonics (in this case). I would like to know why the 3rd harmonic (which is usually the most harmful for three phase grids) is not accounted for as well as any other helpful information about this technology. Any information would really help. Thanks in advance.
Cheers!
P.D. I don´t know if this will help but being a Mechatronics Engineer I am not too familiar with power transmission, I do know a bit more than the basics but I wouldn't call myself an expert so ABC types of answers are welcome too!






RE: Reactive Power Compensation
RE: Reactive Power Compensation
The 3rd harmonic usually cancels out on mono-phasic grids, but in three-phase grids the harmonic series is not zeroed at the common point, therefore it isn't cancelled.
Cheers!
RE: Reactive Power Compensation
Can you expand on If this is what the rest of us know as a single phase circuit, then how does cancellation occur?
You might also look at how triplen harmonics behave when they reach a delta/star transformer. Conventional wisdom is that they are trapped by the delta and can not propagate into the upstream system.
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RE: Reactive Power Compensation
Yeah, I'm talking about single phase circuits, I'm sorry my english is getting rustier by the day.
About triplen harmonics, thats what I was referring to, on single phase circuits the harmonic is unable to propagate to the rest of the system and as it turns out, I was thinking of unbalanced three phase circuits in which the triplen harmonics are not trapped by the delta.
I am having a hard time understanding the different harmonics present on the system and how they are managed to improve the power factor. It is of my understanding that the spikes generated by the control system bring a huge number of harmonics with them, some of them are absorbed by the delta and higher orders by the set of filters we will design. There are more harmonics in the system obviously, those that come from the grid and alter the power factor of the overall system, they are filtered by the same means (then again that's my understanding, I may be wrong).
The harmonics issue is only one part of the actual problem, the SVC's main task is to compensate for the fluctuations of reactive power when big loads (i.e. factories) are switched on and off. For this the system uses phase angle modulation to set a bank of reactors and capacitors on and off, the closed loop control is also a mistery to me as I've seen several ways of doing it, including fuzzy logic. I would like to know if there is a standard way of designing the control system, or which is the most common way of doing it.
Thanks very much.
RE: Reactive Power Compensation
The reasson for 5:th and 7:th harmonic filter is because
these harmonics are generated from the TCR(Thyristor Controled Reactor), also other harmonics are generated but 5, an 7 are generated with highest amplitude.
The amount of harmonics depends on the fire angle.
Check out www.abb.com/facts for more info about SVC applications.
/Gestur
RE: Reactive Power Compensation
Third harmonic is usually canceled in TCR because TCR is connected in delta. It is always good engineering practice to devise grid (transformers connection, nonlinear consumers grouping etc.) to cancel out as much of third harmonic as possible.
Sometimes, even capacitor banks (or filter banks) are switched on/off by thyristors or IGBT’s because of very different working regimes in the rest of the grid (for example high consumption of reactive power and no consumption at all, all happening in 1-10 minutes period). Then, if you have control only through TCR, you can not maintain high power factor throughout all the regimes, hence you have to disconnect filter (capacitive) banks from time to time. This capacitor switching also inputs higher harmonics into the grid.