. . . we transmit 75MW to a distance by AC line transmission line and we get 72MW in Receiving end.

If we do same work with DC line will we get 72 MW in receiving end regardless of economical cost.

If you make the conductors larger, you'll get more useable power. Voltage drop is a function of conductor resistance and current, e. g. V = I X R. High voltage AC is used for long transmission lines so that current is minimized. It's difficult to transmit high voltage DC and efficiently reduce it to useable levels.

No. There will be a greater transmission loss in your DC line. To get 72 MW, you will need to start with a greater MW value; maybe 75 or higher.

Quote ronseto "No. There will be a greater transmission loss in your DC line. To get 72 MW, you will need to start with a greater MW value; maybe 75 or higher."

I assume that you are including the conversion process of AC to DC to AC. Otherwise that statement would not be true. Either way you would need to transmit more than 72 KW to end up with 72 KW at the end.

With DC transmission, the losses are bound to be lower than AC. Skin effect for sure, maybe others things i guess. AC is used because step up and step down is easy resulting in transmission at very high voltages and consequently low currents.

However, 800kV DC transmission is now a reality. Economically feasible too.

Here is a link: siemens hvdc

For those who do not have time to see the link, here is the start....

I will give you some information

DC lines only provide a more economic alternative than AC lines if the transmission distance is long enough to offset the investment for the converter stations. There is no universal break-even distance beyond which the DC transmission can be considered as advantageous. Local conditions and system requirements can play a major role in the decision to adopt a DC transmission. As a rough indication a transmission distance of more than 800 km could be considered as a threshold beyond which the DC transmission alternative can be taken into account. So far DC transmission as a whole has been competitive with equivalent AC systems only in specific cases due to the high investments of converter station.

Now regarding to your question,

A DC bipolar line having the same voltage as the peak phase to ground voltages of an AC three phase line can transport with the same current approximately the same power.

Here

for more information to your question please refer to Overhead Power lines Planning, Design and Construction Book by (F.Kiessling.P.Nefzger.J.F.Nolasco.U.Kaintzyk. )

I don't understand how you can mix peak voltages with rms currents in the same formulae and come out with all these results!

If these lines were copied from a reference I tend to believe that you should check if there was any misprints and start with " and finish with " so that we know where and when you added your own contribution.

** how can Pdc = 2 x Udc x Idc ? I believe that Bi-polar means here 2 lines: a live and a neutral (or the 2nd return conductor). Are we on the same wave length? I yes, then remove the 2.

*** On th AC power formula for a 3 phase system, a square root of 3 is what you need and not a 3(?). can you explain please because I was a bit lost here.

thanks

You seem to have been offended! sorry if I tried to understand your input but could not ... but after all, this forum is to try and help others to understand some concepts and sort some cloudy or foggy knowledge.

On the other hand, there are some ethical issues concerned here. I hope you got the gist (maybe you felt offended?) Anyway, there is no need to answer back in the way you did: just ignore my comment. it was for others maybe to question the input. If you answer then it should be to clear my confusion and not just to hide behind some offended behavior. Don't worry, you don't need to answer this comment unless you want to clarify on the subject first introduced .

Thank you for your understanding.

This is the normal reply/response from somebody that dont know the subject anyway, but he is good at googling. When he needs to explain what he googled he becomes like this one. Just like this fool that grabbed the keyboard in haste at the start, now he is stumped. However, I commend you for your handling of the guy.

What kind of an ignorant reply was that? I bet you just copied and pasted the information out of wikipedia or equivalent. You just showed what an ignorant pig you are. You are the one with problems so address this before you post again. It is clear you have issues.

Blind pig, reference has already been given by Hameedullah. You all guys instead of arguing with him why dont you check the reference.

and read what he has mentioned

"A sinusoidal voltage with a peak amplitude of 1 volt has the same effect as a dc voltage of 0.707 volts because the ac voltage of 1 volt peak or 0.707 volts rms is as effective as a dc voltage of 0.707 volts."


He has mentioned that Udc = sqr(2)Uac this Uac is peak to peak


Vpeak-peak = 0.707Vdc or Udc = sqr(2)Uac

I dont see any problem. No one has right to personal attack and shame on all you guys instead of refering to reference, you are attacking Hameedullah.

let me to explain the AC and DC voltages relationship and hope you can understand my words.

A sinusoidal voltage with a peak amplitude of 1 volt has the same effect as a dc voltage of 0.707 volts because the ac voltage of 1 volt peak or 0.707 volts rms is as effective as a dc voltage of 0.707 volts.

Some advantage of DC line:

1- DC lines present lower power losses

2- DC lines present lower switching over voltages and therefore require lower clearances to towers

3- DC lines introduce no problem of stability as the interconnected systems do not operate in synchronism

4- DC line have the great ability to interconnect systems of different frequencies through back to back converter stations

5- DC lines present reduced levels of short circuit powers and do not contribute to increase short circuit levels of neighboring systems.

Some Disadvantages of DC against AC

1- Dc lines can not directly supply loads. They require converter stations, rectifying station at the sending end and an inverting station at the receiving end

2- DC lines can not economically be tapped with intermediate substations to supply consumers

If you want any one to understand your words, then first improve on your writing (English is a languish and you need to improve you grasp of it).

Also, we are not here for you to lecture us about the basics of a subject like electricity. You can explain an intricate concept or guide us into your thoughts but stop being pedant and condescending, Just state your opinion about the subject clearly and avoid too many errors. If we comment on some errors it does not mean that we consider you ignorant. We only point it out for the sake of clarity and you should appreciate it and try to read back what you wrote etc.

This is not a University or a school of engineering for you to impose your knowledge, Just help out when possible and when willing.

First, please do not use condescending language here about anyone's technical knowledge. Even when you are correct in your knowledge it diminishes you. When you change your story after putting people down, well I'll let the community decide that.

Second, your latest relationship between AC equivalent voltages and DC voltages seems to disagree with your earlier statement. You now approximately agree with my statement since 0.707≈1/√2. So don't lecture me about AC Root Mean Square voltages. Explain why your earlier post said that DC voltage is the same as the Peak AC voltage, but then in the exact same line of your earlier post it states that the DC voltage is the peak AC voltage times √2.

Third, there are synchronization advantages that DC power transmission have but power loss is not a built in advantage. It all depends on how well designed are comparable power transmissions systems. Edison's DC power distribution was removed from Manhattan long ago because it was inefficient.

Synchronization is an additional problem that DC power transmission avoids. If you have just one power source driving just one location load then there will never be any synchronization problems. But when one is connecting one power grid into another grid, then getting both grids to synchronize with each other gets to be near impossible.

Now to properly identify which power transmission technique will be most efficient and effective will require a critical item not found on this web site, a contract for services rendered.

dear ,

very good question, but little confusing.

Transmitting AC power is with 3 conductors, making losses in 3 conductors.

Transmission Power ( AC ) = Power recedived + I2R losses in 3 conductor + corrona losses

Transmission Power (DC) = Power received + losses in AC-DC/&DC-AC conversion +I2R losses in 2 conductors. (Normally, DC voltage is amplified at EHVT level - toreduce I2R losses very very low) but , for the sake of comparision, let us assume the same voltage levels for AC RMS / DC voltages,

even though, the power conversion losses are very very low, to the tune of less then o.5%, & the DC voltage transmission will be having more effificency.

iNFACT, BENEFITS OF dc voltage transmission are

1. Less capital cost, as structure & conductor cost is low.

2. Low I2R losses

3. Zero Corona losses

That is why, now a days, power transmission on DC is preferred, & distribution is made on AC.

When you transmit power via a cable or overhead line there will be unavoidable losses due to resistance,corona etc.To compare ac transmission with dc transmission for a given power,distance,voltage etc it is better to use a software as manual calculation is cumbersome.Or else vary the voltage and analyse using a software to determine at which voltage ac or dc becomes economical.For proper evaluation you should consider terminal equipments like transformer,converter,protective relays etc too.

I would like to add another point related to power transmission through AC or DC voltage line. In AC transmission there would be problem of stability in case of any system fault or disturbance. As given in power equation below

P = V_S*V_R* Sind/X

Where V_S is sending end voltage, V_R is receiving end voltage , d is phase difference between sending end and receiving end voltage and X is reactance (inductive and capacitive both) of the transmission circuit. So there would be some limitation on the amount of power transmission as d reaches 90⁰. In case of DC transmission this limitation would get eliminated due to elimination of circuit inductance. This is the advantage of DC transmission over a longer distance, and if I am not wrong, reason for development of DC transmission.

jvrj:
No one has right in this forum to personal attack.If someone wants to ask question, he should ask in a good way. I did not answer him for Pac = 3 Uac*Iac*cosx because I have already mentioned the voltage line to ground not line to line.

by the way, It is not good to talk against someone if you dont know him and I dont care you are saying about googling or searching but the important is learning and knowing.

LAA_Lucke:

I have already given reference book for my post. I was really offended by asking question method against me and book.

The answer for Pac = 3 Uac*Iac*cosx was already clear for line to ground voltage not line to line volage.

Anyway, it was just my post for OP. If my post consists of too many errors let him to ignore my post.


redfred:

I am really happy what you are saying. It is a good question and I have already given two explaination about AC and DC. I have also given the book reference and if it looks still wrong for you, you can refer to the reference once.

I am really unhappy from this forum administrator. Because by name of guest, people make some nonsense words. I kindly request the administration of this forum, to take an action for these guests.

Yes,

As it is, the Administrator is not at all responsible for the knowledge sharing content, & what discussions going on are purely as a guide, what kind of actions do you expect ?

regards

I agree with you Harry, but it seems this guy wants to be the tin god, but when somebody objects or questions, as happened today, he takes offence.Maybe the admin should remove posts like his, then there won't be Guests calling him names. However, its best forgotten. I want to improve my Googling anyway.

You know? I can't resist but to still post this last one. I promise that I will not answer any of your comments again just for the sanity of the forum.

*** If you are talking of Line to neutral (or Ground as you like) and still you deal with a 3 phase system, then a √3 comes in and not a 3. If not 3 phases, then why complicate the issue, just deal with a single phase and then no room for a 3 again. You seem to be confused on the polarities , number of conductors and then a multiphase system...as seen again with the 2 multiplier in the next formula in question. ***

End of discussion from this end.

Thank you for paying attention and good to have you arround.

Ok LAA Lucke:

This is a good way asking question and now I will reply you too.

LAA Luck, Dont worry about √3 that must be in three phase power equation or not. It is all math contribution and you can write in thousand ways through math.

Let me prove it for you, why there is a 3 and not √3. See below

Any way, it is not important issue.

I have no problem in AC and DC transmission which one is good and which one is bad. But I only post this equation for OP because he has mentioned regardless of economical.

That post just gives good idea and that's why I posted with reference.

Anyway, I would like to say thanks for redfred and you because you both pay attention to equestions. But I dont care those who speaks nonsense without any contribution.

Ok, Fine we call it a day for this.

There is a flaw in your statement. If you transmit a certain amount of power from the sending end you will never get the same amount of power at the receiving end.Even if you design a line where L=C,the line resistance,corona etc will account for loss of power.You may try a super conductor .

I don't think that anyone has claimed a lossless power transmission. The question is will DC necessarily have less loss than AC. I say that one can design either system to have less loss than the other. One will quickly reach a point where the available room for improvement will make cost versus benefit a major concern. But there will always be room for improvement. But you are quite correct that there must always be some power lost regardless of the transmission system.

Dear all (redfred, LAA_Lucke, and OP )

Regarding to my first post and redfred questions(Vrms, Vdc and peak) and LAA Lucke question ( why there is 2 in DC equation and why there is 3 ) please see the below link and hope it will give you all some good idea. It is another book by an other author. Please read carefully page number-132

Electrical power systems By C L Wadhwa

Ham, Dont fret but these all guys need to improve their basics.

It seems like CR4 is fast becoming the joker's paradise. Lack of basic english ones at that.

Ops! engineering forum not english forum.

It is possible either way but like you have rightly mentioned, cost is the main determinant of the issue at stake.

Transmission of AC power is done with the help of transformers among other transmission equipments. Stabilized receiving end voltage is either compensated from the generating station or through buster stations.

The transmission voltage is that high to enable affordable transmission line project cost; particularly in cutting down the size transmission wires. By reducing the size of the wire, the weight is reduced, that also will affect the size of the support pylons, pin insulators etc.

The attenuating problems in AC transmission is deferent from that of DC transmission, while it will be easier and cheaper to transmit AC, DC will cost thrice as much; since the cable size and voltage required to carry the loads will remain the same from source to the receiving end. The transmission pylons will be made much stronger to with stand such weight of cables. Compensating for voltage drop at the receiving end can only be achieved at the supply source. If the line is too long, the source excitation limit can be exhausted.

DC transmission with converters is also very costly since two converter station will be involved, one at the sending and one at the receiving end. The short comings of paragraph 2 is solved by the high cost of converters in this case.

Dickson

Peace to everyone.

The power requirement is about what is used in electric train top lines and tram ways.

Europe has chosen for DC at about 10 kV operational voltage. And efficiency is the reason to use it.

Dynamo generators and motors are both designed for these voltages.

Only rho (specific resistance) and contact resistance losses are applicable in this case.

It turns out to be a matter of inductance, phase synchronism and distance with AC, plus of course also rho and contact resistance, and transformation losses.

If you can work with HVDC in the provider AND the same value in the receiver, IMO DC beats AC over long distances, like in the train line example.

i have watched many threads peter out with new ones coming in, and we don't know whether the OP got what s/he wanted. In this case, OP being a guest, we will probably never know.

However, for me, this thread has given some "collateral knowledge"... not that i will probably ever need to use it, being firmly ensconced in low voltage.

My rudimentary reasoning that DC transmission would have less losses than AC due to no skin effect, maybe no proximity effect etc, was shaken by some of the posts.

Still i can't shake the feeling that the lowest losses will be when only I²R loss is left, which cannot be any lower than what DC transmission will have? Or am i missing something here ?

So, Edison, maybe, was right after all, though Tesla was right everywhere else ? (There is a video from TED, courtesy MIT that demonstrates wireless transmission, came my way via a Globalspec newsletter, but that's another story)

Please people, when you have the time, please put me out of my misery