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Direct Current Transmission – Kimbark
The Swedish State Power Board decided to use alternating ‘-eurrent for the north-to-south transmission already mentioned. The initiative in exploring the use of mercury-arc valves for dc transmission was taken by the General Electric Company. Thus was demonstrated a feature of dc transmission that has been important in several subsequent instalIations: The fortunes ofwar prevented completion ofthe project, and in such plant and pertinent documentsas survived were taken to the U.
Practical ground electrodes were developed, and kimbarj kinds of valves and converter control were tested. Most long overhead ac kimbak require series compensation of part of the induetive reaetanee.
Direct Current Transmission – Kimbark – Livro de HVDC do Kimbark
In the figure, one bank of series capacitors for this pur pose is shown at the middle of the tine. Therefore three-pole switching is always used to clear permanent faults, although such a fauIt may involve only one conductor.
Exp1 queda livre Experimento de queda livre. Tfansmission two smaller experi 2’mentsB1. Next the converter voltages would be raised to equality with those of the respective yransmission converters, after which switches I would be closed.
The tine itself usually has two conductors, aIthough some Iines have only one, the return path being in the earth or seawater or both. They transmitted 4 MW at kV a distance of 3 mi 5 km over an existing line from a station ia the Charlottenburg district of Berlin to one in the Moabit district. One of the mercury-arc valves was replaced by an air-cooled thyristoi’ assem bly, which also has performed well.
The ac line, of course, also has this reversibility. A representative single-circuit dc link is shown in Figure le. In this respect a homopolar line is preferable to a bipolar tine in cases where continuai ground current is.
Direct current transmission – Edward Wilson Kimbark – Google Books
B4,S Power of 0. Perhaps an additional belief was that there was no future in dc transmission. This kimbzrk so, two parallel three-phase circuits are required for reliable transmission see Fig. The capability of ali converters would then be usable, and the power normally carried by two conductors would then be carried by one. The whole switching operation would take about 0.
Their ratings have increased, however, with surprising kibark, and it seems certain that such valves will soon replace mercury-arc valves in HV dc use. The ac input at Mechanicville was at a frequency of 40 Hz, and the output at Schenectady was at 60 Hz.
Kimbarl are also several grading electrodes placed between the control grid and the anode for obtaining a more uniform potential gradient than would otherwise existo The grading electrodes are kept at the desired potentials by connecting them to taps on an externaI resistance-capacitance potential divider the ends of which are connected to the anode and control grid.
Either converter, however, can function as rectifier or inverter, permitting power to be transmitted in either direction. The hornopolar Iink has two or more conductors ali having the same polar ity, usually negative, and always operates with ground returno In the event of a fault on one conductor, the entire converter is available for connection to the remaining conductor or conductors, which, having some overload capability, can carry more than half of the rated power, and tranmsission the whole rated power, at the expense of increased tine loss.
The converter at the sending end is called a reetifier, and that at the receiving end an inverter. EHV transmission links, hvdd on a lower-voltage ac network, or inter eonnecting two such networks, or connecting distant generating plants to an ac network, are compared as to their principal components and the arrange ments thereof, according to whether the line operates on ac or dc.
Each terminal has two converters of equal rated voltages in series on the dc side. If both neutrals are grounded, the two poles can operate inde pendently. Russian engineers have concentrated on single-anode valves, which so far appear to have been less successful than hvxc ASEA valves.
The bus-tie switches I are normally open.
A demonstration of dc transmission using grid-controlled steel-tank mercury-arc conversion trandmission given at Zurich, Switzerland, inat the Fifth Swiss National Exhibition. The current ratings are to A per anode. In a bipolar scheme reconnection of the whole converter to one pole of the line is more complicated and is usually not feasible because of graded insulation.
Large inductances ealled de. Long two-cireuit ac links are usually sectionalized by means of intermediate switching stations for severa reasons.
The breakers are required, however, for clearing faults in the transformers or for taking the whole dc link out of service. If the transformers are operated as an integral part of the link, only 10w-voItage circuit breakers are required. The Une loss would be four times its normal value, somewhat diminishing the delivered power.
Livro – Whitebook Livro – Whitebook. A fuIl-scale km mi overhead line between a hydroelectric plant at Volgograd, formerly called Stalingrad, and the Donets Basin was energized. These reactors are usually placed at intermediate switching stations and are so indicated in Figure Ih.
Lamm inhas considerably increased the peak inverse voltage that the valves tranxmission withstand. At both ends of the tines are converters, the components of which are transformers and groups of mercury arc valves. Present-day mereury-are valves for high-voltage transmission, known as excitrons, have, in addition to the anode and the mercury-pool cathode, an transmizsion electrode for starting the arc, one or more excitation electrodes for maintaining the are, and a control grid that prevents the are from reaching the anode until it is desired that the valve begin to conduct.
These breakers are not used for clearing faults on the dc line or most misoperations ofthe valves, for these faults can be cleared more rapidly by grid controlof the valves. At present these are not capable of handling the highest voltages and powers required for HV dc transmission.
Constant-current operation was chosen because the hot-cathode tubes then used couId not withstand the high short-circuit currents expected to occur on a constant-voItage system. It aided further development ofvalves by permitting them to be tested under service conditions. One pole of a four conductor line is shown in Figure Id, with two converters per terminal.
On many long EHV lines, shunt reactors are required for limiting the voltage, especially at light loads, but they may be required even at full load.