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.

1.2早期电报线路

在1812年，在俄罗斯彼得堡泥瓦河底，席林男爵能过橡胶带绝缘的电缆引爆了水雷。这可能是可记录的最早使用连续绝缘的案例。还有一个最早的案例是在1816年由弗朗西斯.罗那德进行的。这项工作用于连接一个500英尺的电报系统，裸导体穿到玻璃管中，并用套管连接到一起，并用石蜡密封。这些管子被木馏油浸渍后埋到地下。罗那德被这次试验的成功所鼓舞，预言地下电缆将被广泛应用于电力系统，并描述了现代电力系统的很多基本特征。

最初，导体在穿入管道前，用饱和浸渍虫漆的编织物进行绝缘。后期又使用印度橡胶带绝缘，但是这种方式因过多的绝缘失效而被放弃。同时，在商业上也没有强烈的开发意愿。

在1837年库克和查尔斯，在伦敦的尤斯顿和卡姆登之间的铁路沿线，敷设了五芯电报线路。这种电缆用松香浸渍的棉织物绝缘，然后安装在浸渍沥青的木制隔离套中。这条线路令人满意的运行了一段时间，但是由于湿气的入侵，导致大量的绝缘失效，最终被放弃。下一下，库克和查尔斯在轮顿的帕丁顿站和德雷顿站之间，敷设了另外一条线路，用铁管取代木套，以更好的抵挡温气入侵。但一段时间之后，绝缘失效依旧发生，这条线路最终也被放弃。

在1842年莫尔斯在纽约敷设了一根电缆，用黄麻浸沥青绝缘，包覆印度橡胶带。下一年，另外一条线路被敷设，穿跃了华盛顿的一条河道。这些成功的经验，促使莫尔斯写信给财政大臣，他相信“可以实施穿跃大西洋的电报通信计划。

在1844年，莫尔斯获得国会的拨款，建立一条从华盛顿到巴尔的摩的电报线路。敷设了一条几公里的地下线路，在随后绝缘被证实失效。这个地下工程被抛弃，并被建立了一条架空线路。这个线路最初计划用4芯16号的铜导体，浸渍虫漆的棉织物绝缘；然后绝缘线芯穿进铅密封的管道中，但铅套通过导轮，导致铅套与导体紧密接触。这种电缆每个电缆轴能装300英尺，并通过特殊设计的装置放线。

因此，第一次地下电缆的偿试是失败的。架空电缆成为了保证使用效果的必然选择。在美国，莫尔斯地下电缆的失败后，地下电缆的开发处于停滞状态，一直到爱因斯坦时代，才重新开启。

在1842年，蒙哥玛利博士将杜仲橡胶引进欧洲，在1846年沃纳博士建议将杜仲橡胶应用于电报电缆，并被普鲁士政府所采纳。在1847至1852年间，大约敷设了3000公里的这种电缆。不幸的是，当时天然橡胶的易腐烂的性没有被发现，也没有可靠的方式保护橡胶氧化。绝缘问题很快变得极其严重，最终整个线路被放弃。

但是，如果能很好的阻止杜仲橡胶被氧化，它就成为了一种令人丰常满意的绝缘材料。它被广泛的应用在地下和水下线路。

在1860年，橡胶的硫化工艺被应用于电缆行业。在早期的一些线路中，非硫化橡胶被用于纤维绝缘的湿气保护。这种系统，密封接头相当困难，并不能另人满意。硫化橡胶已经被证实是一种更好的绝缘材料 。但是，之后的很多年，硫化橡胶一直没有成为杜仲橡胶的有力竞争者。