# Power transmission

Discussion in 'General Electronics Chat' started by GOURABGHOSH1990, Oct 15, 2009.

1. ### GOURABGHOSH1990 Thread Starter New Member

Mar 12, 2009
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what is HVDC(high voltage direct current) transmission? How does it decrease the power loss during transmission?

and......... can anybody please give me idea about what are the actual reasons for power loss in transmission?

Any help with above topics will be heartily appreciated ...............

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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It's a means of sending electrical energy from one geographical location to another. Instead of sending the energy as alternating voltage / current along the conductors a DC voltage / current is sent.

Power losses in DC transmission will be primarily due to joule heating (I^2xR losses) in the conductors. In HVDC transmission losses will also occur as corona discharge - as in HVAC transmission. To decrease joule heating losses in either format (DC or AC) the voltage is made as high as practicably possible so that the I^2 factor in the losses is minimized. In DC transmission you only need two conductors for the current to flow - one if you use the earth for the return path. Also assuming the the DC transmission voltage is equal to the allowable crest value of an alternating voltage on an AC transmission, then the conductor efficiency in the DC case is double that of a single phase AC case and 50% higher than that of a 3-phase AC case.

Because AC transmission offers so many advantages by comparison, HVDC is probably only employed where it is technically impracticable to use HVAC. For instance, if you have to transmit power a long distance via an underwater cable, HVDC is a good choice where cable capacitance mitigates against efficient HVAC transmission.

HVDC may also offer some advantages for supply network stability & control by effectively isolating two asynchronous AC systems in which an interconnecting HVDC link exists.

3. ### wr8y Active Member

Sep 16, 2008
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Well, there must be SOME advantage, because I remember reading that the connection between east and west in the USA is a DC link.

Must be some BIG AC/DC convertors!

A google of "DC link between east and west grids" yielded many links of similar interconnections worldwide.

4. ### GOURABGHOSH1990 Thread Starter New Member

Mar 12, 2009
3
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thank you sir ................

In high voltage DC power transmission, high voltage is applied between which points?
Is it applied across the transmission line? If it is so, Then if voltage is increased then(I^2xR) should increase because with voltage (I) should increase.

what are the major disadvantages of high voltage dc transmission? I mean why is it not broadly used?

Can you please prescribe me a good book for studying these energy transmissions?

How bright is the future of the technology of power transmission by optical fibers and wireless power transmission?

Last edited: Oct 15, 2009
5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Normally HVDC transmission is part of an over-arching AC generation and transmission system. So where the link starts and ends there are terminal facilities which perform the necessary AC-to-DC and DC-to-AC conversions, at either end of the HVDC line. The process can be bi-directional where you may, for instance, want to take advantage of time zone differences in the occurrence of peak load demands to load share in sufficiently geographically separate locations.

Suppose a DC link has a rated transmission capacity of 1000MW. In simple terms .... if the system voltage is 100 kV then the rated system current will be 10 kA. If the system voltage is 500 kV the rated system current is 2 kA - and so on. So for the same conductor size (CSA) a higher voltage leads to lower I^2*R losses for equal values of power transmission.

The more relevant point is the comparison between AC and DC line transmission - where DC has the edge over AC in that specific area [i.e. transmission line economy]. The costs of the technically more complex terminals weigh against DC. So AC has the overall edge when the power system as a whole (generation / transmission/ distribution etc) is considered. Its much 'easier' to transform AC to different voltage levels than DC for instance.

Didn't Mr Edison and Mr Tesla start the AC/DC debate?

As far as books go - I don't know. Why not do a search on the web. I imagine all of this is well documented at several sites. And someone will be advertising a book somewhere. I seem to get a link result to at least one book on most (technical type) searches I run.

6. ### ELECTRONERD Senior Member

May 26, 2009
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Yes, they did; and Mr. Tesla won the debate so we use AC to power our modern homes.

Oct 13, 2009
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