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1.2 EARLY TELEGRAPH LINES
In 1812, Baron Schilling detonated a mineunder the Neva River at St. Petersburg, Russia, by using an electrical pulsesent through a cable insulated with strips of India rubber. This is probablythe earliest use of a continuously insulated conductor on record. One of theearliest experiments with an underground cable was carried out by FrancisRonalds in 1816. This work was in conjunction with a system of telegraphy consistingof 500 feet of bare copper conductor drawn into glass tubes, joined togetherwith sleeve joints, and sealed with wax. The tubes were placed in a creosotedwooden trough buried in the ground. Ronalds was very enthusiastic over thesuccess of this line, predicting that underground conductors would be widelyused for electrical purposes and outlining many of the essentialcharacteristics of a modern distribution system.
The conductor in this case was firstinsulated with cotton saturated with shellac before being drawn into the tubes.Later, strips of India rubber were used. This installation had many insulationfailures and was abandoned. No serious attempt was made to develop the ideacommercially.
In 1837, W. R. Cooke and Charles Wheatstonelaid an underground line along the railroad right-of-way between London’sEuston and Camden stations for their five-wire system of telegraphy. The wireswere insulated with cotton saturated in rosin and were installed in separategrooves in a piece of timber coated with pitch. This line operatedsatisfactorily for a short time, but a number of insulation failures due to theabsorption of moisture led to its abandonment. The next year, Cooke andWheatstone installed a line between Paddington and Drayton stations in London,but iron pipe was substituted for timber to give better protection frommoisture. Insulation failures also occurred on this line after a short time,and it was also abandoned.
In 1842, S. F. B. Morse laid a cableinsulated with jute, saturated in pitch, and covered with strips of Indiarubber, between Governor’s Island and Castle Garden in New York harbor. Thenext year, a similar line was laid across a canal in Washington, DC. Thesuccess of these experiments induced Morse to write to the Secretary of theTreasury that he believed “telegraphic communications on the electro-magneticplan can with a certainty be established across the Atlantic Ocean.”
In 1844, Morse obtained an appropriationfrom the U.S. Congress for a telegraph line between Washington and Baltimore.An underground conductor was planned and several miles were actually laidbefore the insulation was proved to be defective. The underground project wasabandoned and an overhead line erected. The conductor was originally planned tobe a #16 gage copper insulated with cotton and saturated in shellac. Fourinsulated wires were drawn into a close-fitting lead pipe, which was thenpassed between rollers and drawn down into close contact with the conductors.The cable was coiled on drums in 300-foot lengths and laid by means of aspecially designed plow. Thus, the first attempts at underground constructionwere unsuccessful, and overhead construction was necessary to ensuresatisfactory performance of the lines. After the failure of Morse’s line, noadditional attempts were made to utilize underground construction in the UnitedStates until Thomas A. Edison’s time. Gutta-percha—a natural, thermoplasticrubber—was introduced in Europe in 1842 by Dr. W. Montgomery, and in 1846 wasadopted upon the recommendation of Dr. Werner Siemens for the telegraph linethat the Prussian government was installing. Approximately 3,000 miles of suchwire were laid from 1847 to 1852. Unfortunately, the perishable nature of thematerial was not known at the time and no adequate means of protecting it fromoxidation was provided. Insulation troubles soon began to develop andeventually became so serious that the entire installation was abandoned.
However, gutta-percha provided a verysatisfactory material for insulating telegraph cables when properly protectedfrom oxidation. It was used extensively for both underground and submarineinstallations.
In 1860, vulcanized rubber was used for thefirst time as insulation for wires. Unvulcanized rubber had been used on severalof the very early lines in strips applied over fibrous insulation for moistureprotection. This system had generally been unsatisfactory because ofdifficulties in closing the seam. Vulcanized rubber proved to be a much betterinsulating material, but did not become a serious competitor of gutta-perchauntil some years later.
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1.2早期電報(bào)線(xiàn)路
在1812年，在俄羅斯彼得堡泥瓦河底，席林男爵能過(guò)橡膠帶絕緣的電纜引爆了水雷。這可能是可記錄的最早使用連續(xù)絕緣的案例。還有一個(gè)最早的案例是在1816年由弗朗西斯.羅那德進(jìn)行的。這項(xiàng)工作用于連接一個(gè)500英尺的電報(bào)系統(tǒng)，裸導(dǎo)體穿到玻璃管中，并用套管連接到一起，并用石蠟密封。這些管子被木餾油浸漬后埋到地下。羅那德被這次試驗(yàn)的成功所鼓舞，預(yù)言地下電纜將被廣泛應(yīng)用于電力系統(tǒng)，并描述了現(xiàn)代電力系統(tǒng)的很多基本特征。
最初，導(dǎo)體在穿入管道前，用飽和浸漬蟲(chóng)漆的編織物進(jìn)行絕緣。后期又使用印度橡膠帶絕緣，但是這種方式因過(guò)多的絕緣失效而被放棄。同時(shí)，在商業(yè)上也沒(méi)有強(qiáng)烈的開(kāi)發(fā)意愿。
在1837年庫(kù)克和查爾斯，在倫敦的尤斯頓和卡姆登之間的鐵路沿線(xiàn)，敷設(shè)了五芯電報(bào)線(xiàn)路。這種電纜用松香浸漬的棉織物絕緣，然后安裝在浸漬瀝青的木制隔離套中。這條線(xiàn)路令人滿(mǎn)意的運(yùn)行了一段時(shí)間，但是由于濕氣的入侵，導(dǎo)致大量的絕緣失效，最終被放棄。下一下，庫(kù)克和查爾斯在輪頓的帕丁頓站和德雷頓站之間，敷設(shè)了另外一條線(xiàn)路，用鐵管取代木套，以更好的抵擋溫氣入侵。但一段時(shí)間之后，絕緣失效依舊發(fā)生，這條線(xiàn)路最終也被放棄。
在1842年莫爾斯在紐約敷設(shè)了一根電纜，用黃麻浸瀝青絕緣，包覆印度橡膠帶。下一年，另外一條線(xiàn)路被敷設(shè)，穿躍了華盛頓的一條河道。這些成功的經(jīng)驗(yàn)，促使莫爾斯寫(xiě)信給財(cái)政大臣，他相信“可以實(shí)施穿躍大西洋的電報(bào)通信計(jì)劃。
在1844年，莫爾斯獲得國(guó)會(huì)的撥款，建立一條從華盛頓到巴爾的摩的電報(bào)線(xiàn)路。敷設(shè)了一條幾公里的地下線(xiàn)路，在隨后絕緣被證實(shí)失效。這個(gè)地下工程被拋棄，并被建立了一條架空線(xiàn)路。這個(gè)線(xiàn)路最初計(jì)劃用4芯16號(hào)的銅導(dǎo)體，浸漬蟲(chóng)漆的棉織物絕緣；然后絕緣線(xiàn)芯穿進(jìn)鉛密封的管道中，但鉛套通過(guò)導(dǎo)輪，導(dǎo)致鉛套與導(dǎo)體緊密接觸。這種電纜每個(gè)電纜軸能裝300英尺，并通過(guò)特殊設(shè)計(jì)的裝置放線(xiàn)。
因此，第一次地下電纜的償試是失敗的。架空電纜成為了保證使用效果的必然選擇。在美國(guó)，莫爾斯地下電纜的失敗后，地下電纜的開(kāi)發(fā)處于停滯狀態(tài)，一直到愛(ài)因斯坦時(shí)代，才重新開(kāi)啟。
在1842年，蒙哥瑪利博士將杜仲橡膠引進(jìn)歐洲，在1846年沃納博士建議將杜仲橡膠應(yīng)用于電報(bào)電纜，并被普魯士政府所采納。在1847至1852年間，大約敷設(shè)了3000公里的這種電纜。不幸的是，當(dāng)時(shí)天然橡膠的易腐爛的性沒(méi)有被發(fā)現(xiàn)，也沒(méi)有可靠的方式保護(hù)橡膠氧化。絕緣問(wèn)題很快變得極其嚴(yán)重，最終整個(gè)線(xiàn)路被放棄。
但是，如果能很好的阻止杜仲橡膠被氧化，它就成為了一種令人豐常滿(mǎn)意的絕緣材料。它被廣泛的應(yīng)用在地下和水下線(xiàn)路。
在1860年，橡膠的硫化工藝被應(yīng)用于電纜行業(yè)。在早期的一些線(xiàn)路中，非硫化橡膠被用于纖維絕緣的濕氣保護(hù)。這種系統(tǒng)，密封接頭相當(dāng)困難，并不能另人滿(mǎn)意。硫化橡膠已經(jīng)被證實(shí)是一種更好的絕緣材料 。但是，之后的很多年，硫化橡膠一直沒(méi)有成為杜仲橡膠的有力競(jìng)爭(zhēng)者。