The most comprehensive book for HVDC Transmission by: Edward Wilson Kimbark. You received this message because you are subscribed to the Google Groups ” EEE – B ( – )” group. To unsubscribe from this group. Direct current transmission, Volume 1. Front Cover. Edward Wilson Kimbark. Wiley-Interscience, – Technology & Engineering – pages.
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Valves for HV dc transmission are invariably of single-phase eonstruction, in contrast to the polyphase valves with mercury-pool cathode formerly used extensively in low-voltage rectifiers for industrial and railway application. Long two-cireuit ac links are usually sectionalized by means of intermediate switching stations for severa reasons. 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.
The ac line, of course, also has this reversibility. B4,S Power of 0. Plans have been announced for doubling the voltage and power on the existing cable by the addition of a new thyristor valve group to each terminal, thereby doubling the voltage. The line transmits 20 MW at kV through a single-conductor cable, with return path through the sea and earth. The bus-tie switches I are normally open.
At both ends of the tines are converters, the components of which are transformers and groups of mercury arc valves. Among these are a limiting the deerease in stability power Iimit attributable to switching out one circuit to clear a fault or for line maintenance, b Iimiting the overvoltage when a line is energized from one end, c providing a place for the connection of grounding transformers to limit the overvoltages of the unfaulted phases with respect to ground when one phase is faulted to ground, and d for con nection of intermediate loads or generation.
The breakers are required, however, for clearing faults in the transformers or for taking the whole dc link out of service. Figure la shows a single-eircuit three-phase ac line.
It aided further development ofvalves by permitting them to kimbaark tested under service conditions. The ac input at Mechanicville was at a frequency of 40 Hz, and the output at Schenectady was at 60 Hz. Present-day mereury-are valves for high-voltage transmission, known as excitrons, have, in addition to the anode and the mercury-pool cathode, an ignition electrode for starting the arc, one or more excitation electrodes for maintaining the are, and a control grid that prevents the vurrent from reaching the anode until it is desired that the valve begin to conduct.
Next the converter voltages would be raised to equality with those of the respective adjacent converters, after which switches I would be closed.
EHV transmission links, superposed 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. M uch of the time when power is delivered to Gotland, there are no generators in operation there, the only synchronous maehine being a condenser.
Power is adjusted automatically to maintain rated frequency 50 Hz in Gotland. Most long overhead ac tines require series compensation of part of the induetive reaetanee.
In this respect a homopolar line is preferable to a bipolar tine in cases where continuai ground current is.
This system of grading elec trodes, invented by U. Therefore three-pole switching is always used to clear permanent faults, although such a fauIt may involve only one conductor. A representative single-circuit dc link is shown in Figure le.
The current ratings are to A per anode. One pole of a four conductor line is shown in Figure Id, with two converters per terminal. Direet-current links are classified as shown in Figure 2. Norrnally they operate at equal current; then there is no ground current.
Three-phase tines curretn be operated, directt for a very short time Iess than 1 sec with one or two conductors open, because such operation causes unbalanced voltages in the ac system and interference in parallel telephone lines. Each pole would be switched independently of the other.
The distance is far toa great for ac eable transmission. Either converter, however, can function as rectifier or inverter, permitting power to be transmitted in either direction.
The converter at each end of the line had 12 hot-cathode glass-envelope thyratrons in 6 series pairs. The Swedish State Power Board decided to use alternating ‘-eurrent for the north-to-south transmission already mentioned. The whole switching operation would take about 0. In the event of a fault on one conductor, the other conductor with ground return can carry up to half of the rated load. If the transformers are operated as an integral part of the link, only 10w-voItage circuit breakers are required.
The converter at the sending end is called a reetifier, and that at the receiving end an inverter.
A demonstration of dc transmission using grid-controlled steel-tank mercury-arc conversion was given at Zurich, Switzerland, inat the Fifth Swiss National Exhibition. Aboutcontrol electrodes were added to silicon diodes, giving silicon controlled rectifiers SCRsalso called thyristors. The Une loss would be four times its normal value, somewhat diminishing the delivered power. Parte 1 de 6.
These breakers are not used for clearing faults trnsmission the dc line or most misoperations ofthe valves, for these faults can be cleared more rapidly kimbafk grid controlof the valves. B1S The line carried 5. Intermediate generation raises the stability limit of the link. The neutral points junctions between converters are grounded at one or both ends.
Each valve has two anodes working in parallel. Practical ground electrodes were developed, and various kinds of valves and converter control were curent. Large inductances ealled de. The United States transmissiin inactive in the field of dc transmission, however, for nearly 20 years. Power fiow is normally from the mainland to Gotland but is sometimes in the opposite direetion.
The capability of ali converters would then be usable, and the power normally carried by two conductors would then be carried by one. The larger of these, rated at 20 MW, was installed at the Edgar Thompson plant of the.
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. In the figure, one bank of series capacitors for this pur pose is shown at the middle of the tine.
The phrase “transmission link” denotes the transmission line proper together with its terminal currentt auxiliary equipment. If both neutrals are grounded, the two poles can operate inde pendently.