Why DC supply is not used in high voltage transmission over long distances?

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  • Anonymous
    1 decade ago
    Favorite Answer

    DC is battery and they do not generate a current. They store energy for use upon demand. They also do not store enough energy to maintain transmission for long periods.

  • Ubi
    Lv 5
    1 decade ago

    Actually DC is used in some high voltage transmission applications, but only in certain situations that warrant it. bijay sums up some of the advantages of HVDC transmission (although there are still corona problems just like in AC transmission). AC transmission is better than DC transmission in almost all cases.

    High voltage DC is used pretty much only when the economics dictate that it is beneficial to do so. DC has the advantage that fewer conductors are required than 3phase AC which can be a substantial cost savings. On the other hand, the AC must be converted to DC, sent down the line and then converted back to AC so that customers can actually use the electricity, which can be a substantial increase in cost (conversion equipment and maintenance).

    So it turns out that when the length of the transmission line is very long, the cost savings beat out the increased costs. Thus, the utility company decides to install the necessary conversion equipment, lines and towers to transmit high voltage DC.

    One example of HVDC in America would be the Pacific Intertie. It is a very long line that connects the Pacific Northwest to customers in southern California. It was authorized in the 1960's and built using Swedish HVDC technology.

    Check out the Wikipedia articles for more details on advantages/disadvantages of high voltage DC transmission that I have not covered.

  • Anonymous
    4 years ago

    Most of that is correct, except krk is confusing. Europe uses 50 hertz ac except for some very long distant and underwater cables which are HVDC = high voltage direct current power lines. USA has two HVDC lines which import electricity from Canada, plus several more for various reasons. Wikipedia has a mostly correct article with the title HVDC. DC is rarely used for distribution to homes anywhere since 1915, but dc = DC has some advantages and a pilot program community may be built soon, somewhere. If an appliance is labeled AC or DC that means performance will be acceptable with either. If the circuit is dc, the amps are dc, the volts are dc and the watts are dc. If the circuit is ac the volts are ac, the amps are ac, the watts are ac, the impedance is ac, the VA = volt-amperes are ac, the KVA is ac, the phase is ac, the pf =power factor is ac. Neil

  • 1 decade ago

    it is not true that DC supply is not used for high voltage transmission.

    lets got to the basics to get to the answer.

    power is supplied by flow of current and current is flow of charge.

    on a conductor , charge resides only on the surface. never inside the conductor.

    DC current can be defined as a unidirectinal current of a certain magnitude.

    all this charge that is flowing will be on the outer surface of the conductor only. the outer surface has got a limitation on the accomodation of number of charge carriers as the no of atoms on the surface arae limited. this will result in increased resistance to the current flow, which will be a loss generating component.

    and at higher voltages , there will be corona effect and capacitance effect.

    since the voltage is unchanging, the conductor and the earth surface ill act as two parallel plates of a capacitance and there is eery chance of diacharge if insulations are not properly maintained.

    since the current is uni directional, the magnetic field generated around the conductor will be of a constant magnitude which wll attract any other magnetic material in the vicinity.

    keeping all these things in mind and the surface area required to conduct the requisite amount of power, AC transmission is preferred in most of the cases. but DC will prove to be economical at certain places where the conductor is expensive to procure and maintain.

    note: this question cannot be explained ina jiffy but needs agood knowledge of electrical engg. hope u got the answer to the question but u can refer to any book on power systems which will discuss HVDC transmission.

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  • 1 decade ago

    Supply voltage ( both AC and DC ) drops while it travel through HT lines over a distance. This drop is compensated by using booster transformers and again it reaches its peak value and again travel over a distance.

    This is only easily possible in case of AC transmission. Boosting up DC transmission is a complex task and very much costly.

    As such HT transmission over a long distance is avoided in case of DC.

  • 1 decade ago

    It is not true that DC supply is not used for HV transmission.The advantage is more power can be transmitted in a single conductor with out any phase angle and corona problem.Further there shall be no inductive losses.However any supply is to be converted to AC for obvious advantage. The conversion cost is high, because.DC requires higher insulation than AC for same voltage rating and therefore it is not used for long distance transmission due cost factor.Since any supply system needs isolation form other supply sources to avoid voltage and frquency fluctuation,DC transmission is being used in india to connect different grids in the country.

  • 1 decade ago

    A/C power can be increased or decreased very simply with transformers.

    Increasing or decreasing d/c voltage is not a simple task and better done at the far end of the transmission lines when know what voltage is needed.

    A/C through a rectifier and then filtered with a capacitor and maybe a voltage regulator if you require d/c voltage.

    Light bulbs,motors and most appliances operate on a/c current.

    All in all the most efficient and simple method of energy transmission is with a/a current!

  • Anonymous
    1 decade ago

    It's a lot easier to step-up or step-down an AC Voltage that requires a simple transformer with adquate cooling mechanism but it does not require any sophisticated full wave rectifiers to convert to DC at the input or output point. The cost for a rectifier at a very high voltage could be exhorbitant.

  • 1 decade ago

    DC doesn't transform as easily as AC. You can take a low AC voltage with high current, step the voltage up very high (which reduces the current ie, power = constant), push it over a distance and transform back down at the other end. By reducing the current flow over the distance, you save power. The same process can be applied to DC but at much higher cost and power loss.

  • 1 decade ago

    DC will not work with conventional transformers. Transformers are used to step up / step down the voltage as required, and are a cheap and effective way of doing this.

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