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1.5PAPER INSULATED CABLES
The firstimportant line insulated with paper was installed by Sebastian de Ferrantiin 1890 between Deptford (on the south side of the River Thames) andthe City of London, for single-phase operation at 10,000 volts [3]. Some ofthese mains were still in use at the original voltage after more than 50 years.The cables consisted of two concentric copper conductors insulated with widestrips of paper applied helically around the conductor and saturated with arosin-based oil. The insulated conductors were forced into an iron pipe filledwith bitumen and installed in 20-foot lengths inside train tunnels under theriver. This system operated successfully for 43 years and may be the source ofthe “40 year life” of power cables [4].
In theperiod between 1885 and 1887, cables insulated with helically applied nar-rowpaper strips saturated with paraffin and later in a rosin compound and cov-eredwith a lead sheath (very similar in design to those used at the present time)were manufactured in the United States by the Norwich Wire Company. Thesewere the first flexible paper-insulated cables, and all subsequent progress hasbeen made through improvements in the general design.
Paper-insulatedcables were improved through the following years by:
Theintroduction of the shielded design of multiple conductor cables by MartinHochstadter in 1914. This cable is still known as Type H.
LuigiEmanueli’sdemonstration in 1920 that voids due to expansion and contraction could becontrolled by the use of a thin oil impregnating fluid and reservoirs. Thispermitted the voltages to be raised to 69 kV and higher.
The1927 patent by H. W. Fisher and R. W. Atkinson revealed that the dielectricstrength of impregnated paper-insulated cable could be greatly increased bymaintaining the insulating system under pressure. This system was not usedcommercially until the 1932 installation of a 200 psi pressur-ized cable inLondon.
Impregnatedpaper became the most common form of insulation for cables used for bulktransmission and distribution of electrical power, particularly for operatingvoltages of 12.5 kV and above, where low dielectric loss,low dissipation factor, and high ionization level are important factors indetermining the cable life.
Impregnatedpaper insulation consists of multiple layers of paper tapes, each tape from 2.5to 7.5 mils in thickness, wrapped helically around the conductor to beinsulated. The entire wall of paper tapes is then heated, vacuum dried, andimpregnated with an insulat-ing fluid. The quality of the impregnated paperinsulation depends not only on the proper-ties and characteristics of the paperand impregnating fluid, but also on the mechanical application of the papertapes over the conductor, the thoroughness of the vacuum drying, and thecontrol of the saturating and cooling cycles during the manufacturing.
Originally,most of the paper used was made from Manila-rope fiber. This was erratic in itsphysical properties and not always susceptible to adequate oil penetra-tion.Increased knowledge of the chemical treatment of the wood (in order to obtainpure cellulose by the adjustment of the fiber content and removal oflignin), the con-trol of tear resistance, and the availability of long fiberstock resulted in the almost universal use of wood pulp paper in cables after1900.
Theimpregnating compound was changed from a rosin-based compound to a pure mineraloilcirca 1925, or oil blended to obtain higher viscosity, untilpolybutene replaced oil circa 1983.
Paper-insulated,lead-covered cables were the predominant power cables of all the large,metropolitan transmission and distribution systems in the United States, andthe rest of the world, throughout the twentieth century. Their reliability wasexcellent. It was, however, necessary to have a high degree of skill for propersplic-ing and terminating. A shift toward extruded dielectric cables beganabout 1975 in those metropolitan areas, but the majority of the distributioncables of the large cities remained paper-insulated, lead-covered cables as thecentury ended.
Considerableresearch has been carried out by the utilities, technical organizations, andmanufacturers of cables to obtain improved paper and laminatedpolypropylene-paper-polypropylene (PPP, now used in transmission cables) tapesand insulating fluids that are able to withstand high, continuous operatingtemperatures.
Impregnatedpaper insulation has excellent electrical properties, such as high dielectricstrength, low dissipation factor, and dielectric loss. Because of these prop-erties,the thickness of impregnated paper insulation was considerably less than forrubber or varnished cambric insulations for the same working voltages.Polyethylene and cross-linked polyethylene cables in the distribution classesare frequently made with the same wall thickness as today’s impregnated papercables.
１.５紙絕緣電纜
在1890年，紙絕緣電纜首次被用在英國的德弗德弗和倫敦之間，整個(gè)項(xiàng)目是由塞馬斯蒂安.德.弗蘭蒂推動。電纜為單相10000伏。一些電纜，在50年后，仍可運(yùn)行在原工作電壓下。電纜是由兩根同軸的絕緣銅導(dǎo)體組成，絕緣是由寬紙帶螺旋繞包而成，并浸漬松香基的油。絕緣導(dǎo)體被穿進(jìn)鐵管中，填充瀝青。然后安裝在河底的管道中，這些電纜每20英尺為一節(jié)。這個(gè)系統(tǒng)成功了運(yùn)行了43年，這也可能是電力電纜“40年壽命”的由來
在1885和1887期間，美國諾威奇電纜公司用窄紙帶浸漬石蠟做為絕緣，然后再浸漬松香，最后鉛護(hù)套（這種設(shè)計(jì)已經(jīng)非常近似現(xiàn)代電纜）。這是第一個(gè)紙絕緣柔性電纜。并且在后續(xù)的設(shè)計(jì)中，又有一系列的改進(jìn)。
在接下來的幾年里，紙絕緣電纜被持續(xù)改進(jìn)著:
１.在1914年，馬丁開發(fā)了多芯導(dǎo)體的電纜。這種電纜被命名為“H型”。
２.在1920年，路易吉證實(shí)，氣隙的擴(kuò)張和收縮可以通過輕質(zhì)防腐油和儲油裝置來改善。這使電壓可以升到69KV及以上。
３.在1927年，費(fèi)希爾和艾特金森申請了一項(xiàng)提高紙絕緣電纜電壓的專利。當(dāng)給絕緣系統(tǒng)施加壓力時(shí)，可以顯著的提高絕緣介質(zhì)強(qiáng)度。但這種系統(tǒng)在1932年才實(shí)現(xiàn)商業(yè)化。在倫敦安了一條工作在200psi的紙絕緣電力電纜。
浸漬紙絕緣成為了大規(guī)模電力傳輸及分配的最通用模式。尤其對于12.5kv及以上的電力系統(tǒng)。紙絕緣具有低介電損耗，低介質(zhì)損耗角，高介電常數(shù)。這此特性對電纜的壽命都很有利。
浸漬紙絕緣是由多層紙帶，螺旋繞包而成，每層紙帶的厚度在2.5至7.5mils（譯者注:1mil是千分之一英寸）之間。然后紙絕緣被整體加熱，真空干燥，用絕緣液體浸漬。紙絕緣的品質(zhì)不僅是由紙帶和油的特性所決定的，同時(shí)也受紙帶包覆情況，真空干燥程度，以及在加工過程中浸漬和冷卻的情況影響。
起初，大部分的絕緣紙是由麻纖維制作的。這種絕緣紙的物理特性不穩(wěn)定，而且不能充分勝任油的穿透。隨著木制品加工技術(shù)的提升，抗張強(qiáng)度和長纖維含量都得到了有效控制。在1900年后，木漿絕緣紙，得到了廣泛應(yīng)用。
大約在1925年，浸漬油由松香基的混合物，發(fā)展成純礦物油或都其混合物，以提高粘度。直到1983年，聚（異）丁烯才取代了礦物油。
在美國及世界各地，整個(gè)20世紀(jì)的大規(guī)模輸配電系統(tǒng)，被紙絕緣和鉛套電纜所壟斷。但是，這種電纜對接頭和端子的要求很高。大約1975年，擠出絕緣電纜開始在一些大城市應(yīng)用用。但是，到20世紀(jì)結(jié)束時(shí)，大部分大城市的電力傳輸系統(tǒng)依然使用紙絕緣和鉛護(hù)套電纜。
機(jī)構(gòu)、研發(fā)組織和電纜廠，進(jìn)行了大量的研究，來改善紙絕緣電纜。開發(fā)了層疊結(jié)構(gòu)的PPP絕緣（聚丙烯-紙-聚丙烯，現(xiàn)在應(yīng)用于變壓器電纜）。同時(shí)也開發(fā)出了能夠承受更高溫度的絕緣油。
浸漬紙絕緣具有極其優(yōu)秀的電性能，例如高介電強(qiáng)度，低介質(zhì)損耗角正切值和低介電損耗。由于這些特殊，在相同電壓下，浸漬紙絕緣比橡膠絕緣及浸漬麻布絕緣的厚度要薄。通常紙絕緣電纜的厚度和現(xiàn)在輸配電領(lǐng)域聚乙烯及交聯(lián)聚乙烯的絕緣厚度一樣