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83-513: The Vlasina flows out from the Vlasina Lake at an altitude of 1,213 m. Lake used to be a large, muddy peat bog , but in 1947-1951 the Vlasina was dammed by the long, earth dam and the bog was turned into an artificial lake. The river flows to the north, between the mountains of Čemernik on the west, and Gramada on the east. It flows through Crna Trava , regional and municipal center, and

166-687: A plateau called Vlasina in the municipalities of Surdulica and Crna Trava . The lake is most easily accessible from the southwestern side, by a 19 kilometres (12 mi) long section of the M1.13 road from Surdulica , which itself lies 10 kilometres (6.2 mi) east of the Niš - Skopje motorway on the E75 European Route . The road extends west, towards the Bulgarian border crossing at Strezimirovci , some 20 kilometres (12 mi) away. Along

249-415: A brush with the lines, and reduces the overall danger of the lines slightly. These types of lines are often seen in the eastern United States and in heavily wooded areas, where tree-line contact is likely. The only pitfall is cost, as insulated wire is often costlier than its bare counterpart. Many utility companies implement covered line wire as jumper material where the wires are often closer to each other on

332-475: A bundle of conductors is similar to the field that would surround a single, very large conductor—this produces lower gradients which mitigates issues associated with high field strength. The transmission efficiency is improved as loss due to corona effect is countered. Bundled conductors cool themselves more efficiently due to the increased surface area of the conductors, further reducing line losses. When transmitting alternating current, bundle conductors also avoid

415-470: A bundle. Spacers must resist the forces due to wind, and magnetic forces during a short-circuit. Bundled conductors reduce the voltage gradient in the vicinity of the line. This reduces the possibility of corona discharge. At extra high voltage , the electric field gradient at the surface of a single conductor is high enough to ionize air, which wastes power, generates unwanted audible noise and interferes with communication systems . The field surrounding

498-430: A comparative porcelain or glass string. Better pollution and wet performance is leading to the increased use of such insulators. Insulators for very high voltages, exceeding 200 kV, may have grading rings installed at their terminals. This improves the electric field distribution around the insulator and makes it more resistant to flash-over during voltage surges. The most common conductor in use for transmission today

581-431: A conductor is a flexible object with uniform weight per unit length, the shape of a conductor strung between two towers approximates that of a catenary . The sag of the conductor (vertical distance between the highest and lowest point of the curve) varies depending on the temperature and additional load such as ice cover. A minimum overhead clearance must be maintained for safety. Since the temperature and therefore length of

664-436: A ground conductor (shield wire, static wire, or overhead earth wire). The ground conductor is usually grounded (earthed) at the top of the supporting structure, to minimize the likelihood of direct lightning strikes to the phase conductors. In circuits with earthed neutral , it also serves as a parallel path with the earth for fault currents. Very high-voltage transmission lines may have two ground conductors. These are either at

747-716: A highest system voltage of 1100 kV and India is currently developing a 1200 kV (highest system voltage) line which will initially be charged with 400 kV to be upgraded to a 1200 kV line. Suspension insulators are made of multiple units, with the number of unit insulator disks increasing at higher voltages. The number of disks is chosen based on line voltage, lightning withstand requirement, altitude, and environmental factors such as fog, pollution, or salt spray. In cases where these conditions are suboptimal, longer insulators must be used. Longer insulators with longer creepage distance for leakage current, are required in these cases. Strain insulators must be strong enough mechanically to support

830-426: A kilometer). Insulated cables can be directly fastened to structures without insulating supports. An overhead line with bare conductors insulated by air is typically less costly than a cable with insulated conductors. A more common approach is "covered" line wire. It is treated as bare cable, but often is safer for wildlife, as the insulation on the cables increases the likelihood of a large-wing-span raptor to survive

913-488: A large football field, small sports field and weightlifting room. Touristic attractions could include the numerous churches from the 19th century in the area. Also, the region is known for many popular local legends, which include myths of the giant water beasts, fairies and the now submerged bridge which was allegedly built by the Crusaders on their way to Jerusalem . An ambitious project for development of tourism

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996-452: A mixture of meadows and high-altitude forests, especially birch , beech , pine and juniper (the former two indigenous, and the latter chiefly introduced by afforestation of the western shore). The indigenous trees downy birch and yellow beech (characteristic for its ever-yellow leaf color) stand out among the species of trees. Sundew is the only carnivorous plant in Serbia and

1079-399: A modest range of services. There is a youth resort, Omladinsko Naselje, at the lake, with over 200 beds. It has not been maintained for a while, though in 2019 and 2021 its full renovation was announced. Along with regular tourists, they often host sporting teams from Serbia and abroad, as the lake is a popular destination for summer training due to its high altitude. Sporting grounds include

1162-401: A phase and neutral) up to as many as six (three phase conductors, separate neutral and earth plus street lighting supplied by a common switch); a common case is four (three phase and neutral, where the neutral might also serve as a protective earthing conductor). Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains. Overhead line is designed on

1245-411: A pole is placed in the ground, then three crossarms extend from this, either staggered or all to one side. The insulators are attached to the crossarms. For an "H"-type wood pole structure, two poles are placed in the ground, then a crossbar is placed on top of these, extending to both sides. The insulators are attached at the ends and in the middle. Lattice tower structures have two common forms. One has

1328-404: A pyramidal base, then a vertical section, where three crossarms extend out, typically staggered. The strain insulators are attached to the crossarms. Another has a pyramidal base, which extends to four support points. On top of this a horizontal truss-like structure is placed. A grounded wire is sometimes strung along the tops of the towers to provide lightning protection. An optical ground wire

1411-405: A staggered array line is often used. Along a staggered array line the conductor cables for the supply of the earth net of the transmitting antenna are attached on the exterior of a ring, while the conductor inside the ring, is fastened to insulators leading to the high-voltage standing feeder of the antenna. Use of the area below an overhead line is limited because objects must not come too close to

1494-657: A variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or "armless" construction with conductors supported on insulators attached to the side of the pole. Tubular steel poles are typically used in urban areas. High-voltage lines are often carried on lattice-type steel towers or pylons. For remote areas, aluminum towers may be placed by helicopters . Concrete poles have also been used. Poles made of reinforced plastics are also available, but their high cost restricts application. Each structure must be designed for

1577-610: Is aluminum conductor steel reinforced (ACSR). Also seeing much use is all-aluminum-alloy conductor (AAAC). Aluminum is used because it has about half the weight of a comparable resistance copper cable (though larger diameter due to lower specific conductivity ), as well as being cheaper. Copper was more popular in the past and is still in use, especially at lower voltages and for grounding. While larger conductors lose less energy due to lower electrical resistance , they are more costly than smaller conductors. An optimization rule called Kelvin's Law (named for Lord Kelvin ) states that

1660-405: Is 10.5 metres (34 ft) and its maximum depth is 34 metres (112 ft), near the dam. The central part of the lake is wide and 10 and 15 metres (33 and 49 ft) deep. Its eastern coastline is jagged, with two bays: larger Biljanina bara and smaller Murin zaliv separated by Taraija peninsula. The southern part of the lake, between Bratanov del peninsula and the mouth of Božićki kanal

1743-466: Is 12,741 hectares (31,480 acres), of which 9.6 hectares (24 acres) are in the 1st level of protection (islands of Dugi Del and Stratorija), 4,354 hectares (10,760 acres) in the 2nd level and 8,377 hectares (20,700 acres) in the 3rd level of protection. In the summer of 2018, both the citizens and the tourists, so as the administration of the Surdulica municipality reported the record low water level in

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1826-694: Is a more advanced version with embedded optical fibers for communication. Overhead wire markers can be mounted on the ground wire to meet International Civil Aviation Organization recommendations. Some markers include flashing lamps for night-time warning. A single-circuit transmission line carries conductors for only one circuit. For a three-phase system, this implies that each tower supports three conductors. A double-circuit transmission line has two circuits. For three-phase systems, each tower supports and insulates six conductors. Single phase AC-power lines as used for traction current have four conductors for two circuits. Usually both circuits operate at

1909-638: Is a semi-artificial lake in Southeast Serbia . Lying at an altitude of 1,211 metres (3,973 ft), with an area of 16 square kilometres (6.2 sq mi), it is the highest and largest artificial lake in Serbia. It was created in 1947–51 when the peat bog Vlasinsko blato (Vlasina mud) was closed off by a dam and submerged by the waters of incoming rivers, chiefly the Vlasina . The lake lies at 42°42′N 22°20′E  /  42.700°N 22.333°E  / 42.700; 22.333 on

1992-458: Is planned for the Vlasina area by the country's Development plan and the Ministry of Tourism, and it is included in the 2005 "21 projects for the 21st century" plan. The planned facilities include a new tourist center Novi Rid , with 1,000 beds and shopping center, tourist center Krstinci with 350 beds, center "Džukelice" for summer sports, a marina for sailboats (motorboats are forbidden on

2075-423: Is preferable to use more than one conductor per phase, or bundled conductors. Bundle conductors consist of several parallel cables connected at intervals by spacers, often in a cylindrical configuration. The optimum number of conductors depends on the current rating, but typically higher-voltage lines also have higher current. American Electric Power is building 765 kV lines using six conductors per phase in

2158-458: Is referred to as " Moby-Dick " by the local population, and is the largest such formation in the Balkans. It is overgrown with dense vegetation, including birch trees. Carried by the water currents and strong winds, in 2016 "Moby-Dick" almost reached the shore near the "Vlasina" hotel, softly attaching itself to the bank and becoming a major tourist attraction. Previous such occurrence happened in

2241-468: Is shallower (2 to 6 metres or 6.6 to 19.7 feet), with swampy coasts and peat. The "working level of reservoir" is projected between the altitudes of 1,205.26 m (3,954.3 ft) and 1,213 m (3,980 ft). There are two permanent islands on the lake, along its eastern coast: Dugi Del (7.84 hectares or 19.4 acres) and Stratorija (1.82 hectares or 4.5 acres). Both islands are covered with green areas and forests. Along with those islands, one of

2324-495: Is the chance that they will not "unhinge" from the bank when the water rises. Head of the local protection enterprise accused EPS of lowering the water level to produce more electricity rather than to renovate the plant. The EPS stated that "in the period to come", they will start to pump the water from the Lisine Lake into the Vlasina. Current tourist capacity includes around 300 beds in hotels "Vlasina" and "Narcis", offering

2407-425: Is unique to the Vlasina region. It is estimated that over 300 herbal species in the region are medicinal. The lake is home to 16 species of fish. These include: Brown Trout , Ohrid trout , Rainbow trout , European perch , European eel , Eurasian minnow , Mediterranean barbel , grass carp , common carp , crucian carp , Prussian carp , tench , roach , common chub , pumpkinseed and others. Ohrid trout

2490-519: The Black Sea drainage basin and it is not navigable. During the summer, large amounts of water from the river are used for irrigation of the surrounding arable land. Water is especially used in the lower course, known for the vegetable production. There is a small dam in Vlasotince, close to downtown, with a reservoir and the beach. By the 2020s, plans were made to build 55 mini hydros in

2573-510: The ACCC conductor uses a carbon and glass fiber core that offers a coefficient of thermal expansion about 1/10 of that of steel. While the composite core is nonconductive, it is substantially lighter and stronger than steel, which allows the incorporation of 28% more aluminum (using compact trapezoidal-shaped strands) without any diameter or weight penalty. The added aluminum content helps reduce line losses by 25 to 40% compared to other conductors of

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2656-622: The Aegean Sea in Greece. As the lake, via its outflow Vlasina, belongs to the Black Sea drainage basin , this way the artificial bifurcation was created. Flora and fauna of the lake, and the entire surrounding Vlasina region, are rich, and include several endemic species. It features over 850 species of flora and over 180 species of vertebrates , including rare species of mammals, reptiles and amphibians. The lake's surroundings are

2739-477: The conductor increase with increasing current through it, it is sometimes possible to increase the power handling capacity (uprate) by changing the conductors for a type with a lower coefficient of thermal expansion or a higher allowable operating temperature . Two such conductors that offer reduced thermal sag are known as composite core conductors (ACCR and ACCC conductor ). In lieu of steel core strands that are often used to increase overall conductor strength,

2822-569: The conductors in the span with insulators. The first type is easier to build as it does not require insulators in the span, which may be difficult to install and to maintain. Examples of compact lines are: Compact transmission lines may be designed for voltage upgrade of existing lines to increase the power that can be transmitted on an existing right of way. Low voltage overhead lines may use either bare conductors carried on glass or ceramic insulators or an aerial bundled cable system. The number of conductors may be anywhere between two (most likely

2905-483: The dangerous areas of the Helicopter height–velocity diagram , and the pilot must be qualified for this " human external cargo " method. For transmission of power across long distances, high voltage transmission is employed. Transmission higher than 132 kV poses the problem of corona discharge , which causes significant power loss and interference with communication circuits. To reduce this corona effect, it

2988-444: The design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower. More rigid structures may be intended to remain standing even if one or more conductors is broken. Such structures may be installed at intervals in power lines to limit the scale of cascading tower failures. Foundations for tower structures may be large and costly, particularly if

3071-560: The energized conductors. Overhead lines and structures may shed ice, creating a hazard. Radio reception can be impaired under a power line, due both to shielding of a receiver antenna by the overhead conductors, and by partial discharge at insulators and sharp points of the conductors which creates radio noise. In the area surrounding the overhead lines it is dangerous to risk interference; e.g. flying kites or balloons, using ladders or operating machinery. Overhead distribution and transmission lines near airfields are often marked on maps, and

3154-689: The erosion. Especially hit are the sections between Crna Trava and Svođe, and between Svođe and Babušnica. The town of Vlasotince was flooded in 1948. On 26 June 1988, after a period of heavy rains, Vlasina valley was a site of catastrophic floods. Extreme downpours and heavy storms affected river's watershed area in the municipalities of Vlasotince, Crna Trava, Babušnica, Pirot and Leskovac. Upper and central watershed sections received 100 to 200 litres per square metre (2.0 to 4.1 imp gal/sq ft) with an absolute peak in Rakov Dol , with 220 litres per square metre (4.5 imp gal/sq ft). This

3237-455: The form of a catenary , and much of the analysis for construction of transmission lines relies on the properties of this form. A large transmission line project may have several types of towers, with "tangent" ("suspension" or "line" towers, UK) towers intended for most positions and more heavily constructed towers used for turning the line through an angle, dead-ending (terminating) a line, or for important river or road crossings. Depending on

3320-400: The full weight of the span of conductor, as well as loads due to ice accumulation, and wind. Porcelain insulators may have a semi-conductive glaze finish, so that a small current (a few milliamperes) passes through the insulator. This warms the surface slightly and reduces the effect of fog and dirt accumulation. The semiconducting glaze also ensures a more even distribution of voltage along

3403-430: The ground conditions are poor, such as in wetlands. Each structure may be stabilized considerably by the use of guy wires to counteract some of the forces applied by the conductors. Power lines and supporting structures can be a form of visual pollution . In some cases the lines are buried to avoid this, but this " undergrounding " is more expensive and therefore not common. For a single wood utility pole structure,

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3486-506: The grounded conductor strung below the phase conductors to provide some measure of protection against tall vehicles or equipment touching the energized line, as well as to provide a neutral line in Wye wired systems. On some power lines for very high voltages in the former Soviet Union, the ground wire is used for PLC systems and mounted on insulators at the pylons. Overhead insulated cables are rarely used, usually for short distances (less than

3569-624: The lake area. The best known kladenac (cold water spring), noted for its cold water and most visited by the tourists, is the Sveti Nikola ( Saint Nicholas ) spring. The dam is located in the northwestern part of the lake. It is an embankment dam , built of a concrete core with an earth-filled cover. First plans for the power plant were made in the Kingdom of Yugoslavia , during the Interbellum . Construction ran from 1946 to 1948, when

3652-430: The lake because of the repairs on one of the four Vrla hydro power plants, but that no harm will be done. The reconstructed power plant, Vrla I, was built in 1955 and it was stated that the renovation "was necessary" and that the works will be finished by October 2018. By October other floating islands got stranded, the boat traffic was made more difficult and the water level dropped by 4 to 7 m (13 to 23 ft). In

3735-640: The lake near the dam: Čemernički kanal from the west and Strvna from east. The construction of the entire Vrla complex of 4 power plants was finished in 1958. The water from another artificial lake, Lisina, on the Božička Reka, is being partially rerouted into the lakes watershed. As the Božička Reka is the longer headstream of the Dragovištica , which in turn flows into the Struma in Bulgaria which empties into

3818-414: The lake's most famous features are the floating islands . They didn't exist in the former peat bog and began appearing after 1948, when the lake was created. They are formed when at high water level, loose chunks of peat 0.5 to 2 metres (1 ft 8 in to 6 ft 7 in) thick break off the shore. It is estimated that the peat chunks took 5,000 years to form. There are up to 30 floating islands at

3901-407: The lake), a number of ski lifts and facilities for Nordic skiing . By this plan, by 2021 Vlasina was to get a heliport and an airfield for smaller airplanes. Nothing of this happened, and in 2022 another ambitious plan for the neglected tourism center was announced, which would include an investment of €500 million and 10,000 new jobs. Announced as the "eco-icon of Europe", the project was to follow

3984-486: The lake, on the Vrla River, with a total capacity of 125 megawatt-hours (450 GJ). A part of the hydroelectric system is the pump station "Lisina", which pumps in water from the nearby Lisina Lake , chiefly in summer months. Vlasina Lake is also fed by numerous streams, descending from the surrounding mountains. The water level varies, depending on the water influx and drainage of the dam. Two artificial canals enter

4067-485: The lake. Municipality issued a statement saying that the sudden water discharge at the dam may destroy the part of the plant and animal life in the lake. Numerous boats and barges were stranded, such as the "Moby-Dick", the largest floating island on the lake. It is estimated that the level fell for up to 5 m (16 ft). The Elektroprivreda Srbije (EPS), a state-owned electric utility power company admitted that they are forced to discharge larger amounts of water from

4150-418: The length of the chain of insulator units. Polymer insulators by nature have hydrophobic characteristics providing for improved wet performance. Also, studies have shown that the specific creepage distance required in polymer insulators is much lower than that required in porcelain or glass. Additionally, the mass of polymer insulators (especially in higher voltages) is approximately 50% to 30% less than that of

4233-413: The line are generally made of aluminum (either plain or reinforced with steel , or composite materials such as carbon and glass fiber), though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises. A major goal of overhead power line design is to maintain adequate clearance between energized conductors and the ground so as to prevent dangerous contact with

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4316-444: The line, and to provide reliable support for the conductors, resilience to storms, ice loads, earthquakes and other potential damage causes. Today some overhead lines are routinely operated at voltages exceeding 765,000 volts between conductors, with even higher voltages possible in some cases. Overhead power transmission lines are classified in the electrical power industry by the range of voltages: Structures for overhead lines take

4399-409: The loads imposed on it by the conductors. The weight of the conductor must be supported, as well as dynamic loads due to wind and ice accumulation, and effects of vibration. Where conductors are in a straight line, towers need only resist the weight since the tension in the conductors approximately balances with no resultant force on the structure. Flexible conductors supported at their ends approximate

4482-473: The mid-1990s. During the extremely low water level, it was reported in August 2018 that the island was partially stranded on dry ground. Another major storm and strong wind, detached Moby-Dick on 15 August 2020, which after four years continued to float on the lake surface. The temperature of the water reaches 21 to 23 °C (70 to 73 °F) in the summer months, making for refreshing swimming. It freezes in

4565-459: The normal operating voltage and surges due to switching and lightning . Insulators are broadly classified as either pin-type, which support the conductor above the structure, or suspension type, where the conductor hangs below the structure. The invention of the strain insulator was a critical factor in allowing higher voltages to be used. At the end of the 19th century, the limited electrical strength of telegraph -style pin insulators limited

4648-412: The optimum size of conductor for a line is found when the cost of the energy wasted in the conductor is equal to the annual interest paid on that portion of the line construction cost due to the size of the conductors. The optimization problem is made more complex by additional factors such as varying annual load, varying cost of installation, and the discrete sizes of cable that are commonly made. Since

4731-588: The outermost ends of the highest cross beam, at two V-shaped mast points, or at a separate cross arm. Older lines may use surge arresters every few spans in place of a shield wire; this configuration is typically found in the more rural areas of the United States. By protecting the line from lightning, the design of apparatus in substations is simplified due to lower stress on insulation. Shield wires on transmission lines may include optical fibers ( optical ground wires /OPGW), used for communication and control of

4814-494: The pole, such as an underground riser/ pothead , and on reclosers, cutouts and the like. Because power lines can suffer from aeroelastic flutter driven by wind, Stockbridge dampers are often attached to the lines to reduce the vibrations. A compact overhead transmission line requires a smaller right of way than a standard overhead powerline. Conductors must not get too close to each other. This can be achieved either by short span lengths and insulating crossbars, or by separating

4897-523: The power system. At some HVDC converter stations, the ground wire is used also as the electrode line to connect to a distant grounding electrode. This allows the HVDC system to use the earth as one conductor. The ground conductor is mounted on small insulators bridged by lightning arrestors above the phase conductors. The insulation prevents electrochemical corrosion of the pylon. Medium-voltage distribution lines may also use one or two shield wires, or may have

4980-435: The principle of one or more overhead wires situated over rail tracks. Feeder stations at regular intervals along the overhead line supply power from the high-voltage grid. For some cases low-frequency AC is used, and distributed by a special traction current network. Overhead lines are also occasionally used to supply transmitting antennas, especially for efficient transmission of long, medium and short waves. For this purpose

5063-596: The purpose of hydroelectricity production, some of the Vlasina's tributaries were rerouted through canals into the Vlasina Lake, thus making them part of the Vrla watershed. Those tributaries are Mlađenica, Čemernica and all the right tributaries to the Strvna river. This way, an artificial bifurcation and stream capture were formed. The Vlasina drains an area of 991 square kilometres (383 sq mi). It belongs to

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5146-497: The pylons; often some circuits are installed later. A disadvantage of double circuit transmission lines is that maintenance can be difficult, as either work in close proximity of high voltage or switch-off of two circuits is required. In case of failure, both systems can be affected. The largest double-circuit transmission line is the Kita-Iwaki Powerline . Insulators must support the conductors and withstand both

5229-497: The reduction in ampacity of a single large conductor due to the skin effect . A bundle conductor also has lower reactance , compared to a single conductor. While wind resistance is higher, wind-induced oscillation can be damped at bundle spacers. The ice and wind loading of bundled conductors will be greater than a single conductor of the same total cross section, and bundled conductors are more difficult to install than single conductors. Overhead power lines are often equipped with

5312-509: The reservoir was first filled. It is 239 metres (784 ft) long, 139 metres (456 ft) wide at the base and 5.5 metres (18 ft) at the top, and 34 metres (112 ft) high (of which 25.7 metres or 84 feet is above the ground). The reservoir it creates has a volume of around 1.65 cubic kilometres (0.40 cu mi). Of these, 1.05 cubic kilometres (0.25 cu mi) is usable for hydroelectric exploitation. The system of 4 hydroelectric plants called Vrla (I-IV) lies downstream of

5395-415: The river flow being supposedly regulated. Subsequent analysis showed a number of flaws in the design of the protected catchment . In the next period, a solidarity settlement was built in Vlasotince and new bridges were constructed in the villages Manastirište, Tegošnica, Stajkovac, Ravni Dol and Donji Dejan. A book commemorating the event, Događaj za zaborav i nezaborav ( Event for oblivion and remembrance )

5478-441: The same diameter and weight, depending upon electric current. The carbon core conductor's reduced thermal sag allows it to carry up to twice the current ("ampacity") compared to all-aluminum conductor (AAC) or ACSR. The power lines and their surroundings must be maintained by linemen , sometimes assisted by helicopters with pressure washers or circular saws which may work three times faster. However this work often occurs in

5561-404: The same voltage. In HVDC systems typically two conductors are carried per line, but in rare cases only one pole of the system is carried on a set of towers. In some countries like Germany most power lines with voltages above 100 kV are implemented as double, quadruple or in rare cases even hextuple power line as rights of way are rare. Sometimes all conductors are installed with the erection of

5644-405: The shallower bays the water receded significantly and they have been described as "desolate". The EPS claimed that the works will last for only 30 days and that water level has to be reduced to 1,206.5 m (3,958 ft) but continued to claim that no harm will be done. University of Belgrade Geography Faculty contradicted the company's claim. The longer floating island are stranded, the greater

5727-528: The strictest ecological rules. More or less, the same attractions and structures were planned, as per the 2005 plan. Local ecological groups doubted such a massive and expensive project, especially at such high standards, will be done. Overhead power line An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors (commonly multiples of three) suspended by towers or poles . Since

5810-448: The surrounding air provides good cooling , insulation along long passages and allows optical inspection, overhead power lines are generally the lowest-cost method of power transmission for large quantities of electric energy. Towers for support of the lines are made of wood (as-grown or laminated), steel or aluminum (either lattice structures or tubular poles), concrete, and occasionally reinforced plastics. The bare wire conductors on

5893-482: The time. Driven by the wind, they float from one shore of the lake to another, carrying the flora and fauna, and serving as shelter and a food source for fish. For that reason, they are an attractive target for fishermen, however it is forbidden to visit them or disturb them because of the unique animal and plant ecosystems, though walking on them is practically impossible since they don't have solid ground. The largest such island has an area of 2 hectares (4.9 acres), it

5976-602: The town of Vlasotince and western parts of the low Leskovac Field, part of the composite valley of the Južna Morava. After the villages of Batulovce and Stajkovce , the Vlasina empties into the South Morava, east of the Leskovac 's eastern suburb of Mrštane . The river's valley, from the Vlasina Lake to the town of Vlasotince is narrow, defile-like with steep sides prone to heavy erosion. Downstream from Vlasotince,

6059-537: The valley expands and the rivers starts to meander. Right before its confluence with the South Morava, the Vlasina branches into several arms, stretching for 400 metres (1,300 ft). During the high water levels, this entire confluence area is flooded. The longest tributaries are Tegošnica (41 kilometres (25 mi)), Lužnica (38 kilometres (24 mi)), Pusta Reka (20 kilometres (12 mi)), Gradska Reka (17 kilometres (11 mi)), Bistrica (14 kilometres (8.7 mi)) and Rastovnica (11 kilometres (6.8 mi)). For

6142-631: The villages of Brod , Krstićevo and Jabukovik , where it reaches the Lužnica mountain and receives the Gradska from the right. The river bends to the west, along the southern slopes of Lužnica, and receives from the right the Tegošnica (at Donje Gare village) and the Lužnica (at Svođe ). As the Vlasina continues on the southernmost slopes of the Suva Planina and Babička Gora mountains, it reaches

6225-572: The voltage to no more than 69,000 volts . Up to about 33 kV (69 kV in North America) both types are commonly used. At higher voltages only suspension-type insulators are common for overhead conductors. Insulators are usually made of wet-process porcelain or toughened glass , with increasing use of glass-reinforced polymer insulators. However, with rising voltage levels, polymer insulators ( silicone rubber based) are seeing increasing usage. China has already developed polymer insulators having

6308-459: The watershed of Vlasina. After the negative backlash which followed construction of mini hydros in other parts of Serbia, and action of the local environmentalists, the municipality of Vlasotince banned such facilities on its territory in March 2021. Usually a calm river, Vlasina is infamous for catastrophic, torrential flooding, which cause major damages. The entire watershed of the river is prone to

6391-451: The west shore, the regional road R122 leads across the dam towards Crna Trava in the north. The plateau is surrounded by the mountains of Čemernik , Vardenik and Gramada . Geological and hydrological surveys showed that lake used to existed in this area in distant history. The lake runs north–south for a length of about 9.5 kilometres (5.9 mi) and has a maximum width of approximately 3.5 kilometres (2.2 mi). Its average depth

6474-415: The winter and the ice crust can be as much as 2 metres (6 ft 7 in) thick. The temperature also varies with location and depth. In the village of Topli Dol south of the lake, there is a water factory "Vlasinka", producing high-quality mineral water called " Vlasinska Rosa ", a renowned brand in Serbia. It was purchased by The Coca-Cola Company in 2005. There are some 70 natural water springs in

6557-419: Was absolute daily maximum in the entire Serbia. Instead of an average discharge of eleven cubic metres per second (390 cu ft/s), the Vlasina swelled 145 times, to 1,600 cubic metres per second (57,000 cu ft/s). Tidal wave was nine metres (30 ft) tall and, to make things worst, smashed the town during the night. Both the discharge and the height of the wave were never recorded previously. It

6640-473: Was cut off on 36 locations. Apart from Vlastince, huge damage stroke the villages of Dobroviš, Tegošnica, Gornji Orah, Svođe, Dejan, Kruševica, Boljare, Manastirište, Konopnica and Stajkovce. All crops were destroyed and the livestock population was decimated. In total, the area affected by the catastrophe covered more than 1,000 square kilometres (390 sq mi), and caused a damage of around US$ 1 billion (or 355 billion of current Yugoslav dinars), despite

6723-593: Was estimated that the river collected and carried over 230,000 tons of sediments in the 26–27 June period. Military was dispatched to help the residents. In Vlasotince, 1,700 buildings were flooded, 120 were completely destroyed, so as 55 artisan shops, while all major companies and economic organizations were disabled. Numerous streets were washed away, so as 17 bridges along the river, town's bus station, power station and all generators, sports fields, post offices, city waterworks, overhead power lines and Vlasotince's famous "Park" garden. The Vlasotince-Crna Trava trunk road

6806-541: Was published by Dragoljub Stanojević. The Vlasina again flooded its valley in 2008. During the floods in January 2021, the army was again deployed. Severe rains and ensuing floods caused power outage in the entire municipality of Vlasotince and cut the supply of the drinking water. The river also brought large amount of garbage which clogged the small dam in town. Vlasina Lake Vlasina Lake ( Serbian : Власинско језеро , romanized :  Vlasinsko jezero )

6889-432: Was stocked and it successfully adapted to the environment, making it a popular for fishing. Birds includes gray heron , mallard , tufted duck and cormorant . Mammalian species include wild boars , wolves , foxes , hares , roe deer and feral horses . By the decision of Government of Serbia in 2006, the Vlasina region is protected as a nature preserve of special interest at category I. The total protected area

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