一 交聯(lián)電纜接頭故障原因及處理方法-交聯(lián)電纜接頭運行狀況
6-10KV高壓動力電纜在水利工程和電力系統(tǒng)運用非常廣泛,其完好的接頭和附件對機(jī)電設(shè)備安全、經(jīng)濟(jì)、可靠運行和供電安全是非常重要的。設(shè)計良好、施工合理的電纜接頭,經(jīng)實際運行證明,在大多數(shù)情況下是可以長期使用的。但交聯(lián)電纜由于載流能力強(qiáng),電流密度大,對導(dǎo)體連接質(zhì)量要求就更為嚴(yán)格。對接頭所要求機(jī)械的電氣的條件日益從嚴(yán)越來越高,特別是6-10KV電動機(jī)電纜,各種接頭將經(jīng)受很大的熱應(yīng)力和較高激烈程度與持續(xù)時間的短路電流的影響。所以說交聯(lián)電纜附件也不是附屬的,更不是次要的部件 ,它與電纜是同等重要,必不可少的部件,也是與安全運行密切相關(guān)的關(guān)鍵產(chǎn)品。交聯(lián)電纜在國外已普遍應(yīng)用,國內(nèi)廣泛采用雖然僅10余年,目前還存在一些問題,但隨著技術(shù)的發(fā)展,附件的配套,質(zhì)量的提高,工藝的完善,交聯(lián)電纜已有替代油紙電纜的趨勢具有廣闊、深遠(yuǎn)的發(fā)展前景。
二交聯(lián)電纜接頭故障原因及處理方法-交聯(lián)電纜接頭故障原因分析
由于電纜附件種類、形式、規(guī)格較多;質(zhì)量參差不齊;施工人員技術(shù)水平高低不等;電纜接頭運行方式和條件各異,致使交聯(lián)電纜接頭發(fā)生故障的原因各不相同。由于交聯(lián)電纜與油紙電纜的介質(zhì)不同,接頭發(fā)生故障的原因有很大的差異,油紙電纜接頭發(fā)生故障主要是絕緣影響,而交聯(lián)電纜接頭發(fā)生故障主要是導(dǎo)體連接。交聯(lián)電纜允許運行溫度高,對電纜接頭就提出了更高的要求,使接頭發(fā)熱問題就顯得更為突出。接觸電阻過大、溫升加快、發(fā)熱大于散熱促使接頭的氧化膜加厚,又使接觸電阻更大,溫升更快。如此惡性循環(huán),使接頭的絕緣層破壞,形成相間短路,引起燒毀。造成接觸電阻增大的原因有以下幾點。
1、工藝不佳。主要是指電纜接頭施工人員在導(dǎo)體連接前后的施工工藝。
(1)連接金具接觸面處理不佳。無論是接線端子或連接管,由于生產(chǎn)或保管的條件影響,管體內(nèi)壁常有雜質(zhì)、毛刺和氧化層存在,這是不為人們重視的缺陷,但對導(dǎo)體連接質(zhì)量的影響,頗為嚴(yán)重。特別是鋁表面極易生成一層堅硬而又絕緣的氧化鋁薄膜,使鋁導(dǎo)體的連接要比銅導(dǎo)體的連接增加不少麻煩,工藝技術(shù)的嚴(yán)格性也要高得多。造成連接(壓接、焊接和機(jī)械連接)發(fā)熱的主要原因,除機(jī)具、材料性能因素外,關(guān)鍵是工藝技術(shù)和責(zé)任心。施工人員不了解連接機(jī)理,沒有嚴(yán)格按工藝要求操作,就會造成連接處達(dá)不到電氣和機(jī)械強(qiáng)度。運行證明當(dāng)壓接金具與導(dǎo)線的接觸表面愈清潔,在接頭溫度升高時,所產(chǎn)生的氧化膜就愈薄,接觸電阻就愈小。
(2)導(dǎo)體損傷。交聯(lián)絕緣層強(qiáng)度較大剝切困難,環(huán)切時施工人員用電工刀左劃右切,有時干脆用鋼鋸環(huán)切深痕,往往掌握不好而使導(dǎo)線損傷。剝切完畢雖然不很嚴(yán)重,但在線芯彎曲和壓接蠕動時,會造成受傷處導(dǎo)體損傷加劇或斷裂,壓接完畢不易發(fā)現(xiàn),因截面減小而引起發(fā)熱嚴(yán)重。
(3)導(dǎo)體連接時線芯不到位。導(dǎo)體連接時絕緣剝切長度要求壓接金具孔深加5mm,但因產(chǎn)品孔深不標(biāo)準(zhǔn),易造成剝切長度不夠,或因壓接時串位使導(dǎo)線端部形成空隙,僅靠金具壁厚導(dǎo)通,致使接觸電阻增大,發(fā)熱量增加。
2、壓力不夠?，F(xiàn)今有關(guān)資料在制作接頭工藝及標(biāo)準(zhǔn)圖中只提到電纜連接時每端的壓坑數(shù)量,而沒有詳述壓接面積和壓接深度。施工人員按要求壓夠壓坑數(shù)量,效果如何無法確定。不論是哪種形式的壓力連接,接頭電阻主要是接觸電阻,而接觸電阻的大小與接觸力的大小和實際接觸面積的多少有關(guān),與使用壓接工具的出力噸位有關(guān)。造成導(dǎo)體連接壓力不夠的主要原因有以下3點。
(1)壓接機(jī)具壓力不足。近年壓接機(jī)具生產(chǎn)廠家較多,管理混亂,沒有統(tǒng)一的標(biāo)準(zhǔn),特別是近年生產(chǎn)的機(jī)械壓鉗,壓坑不僅窄小,而且壓接到位后上下壓模不能吻合;還有一些廠家購買或生產(chǎn)國外類型壓鉗,由于執(zhí)行的是國外標(biāo)準(zhǔn),與國產(chǎn)導(dǎo)線標(biāo)稱截面不適應(yīng),壓接質(zhì)量難保證。
(2)連接金具空隙大?，F(xiàn)在交聯(lián)電纜接頭多數(shù)單位使用的連接金具,還是油紙電纜按扇型導(dǎo)線生產(chǎn)的端子和壓接管。從理論上講圓型和扇型線芯的有效截面是一樣的,但從運行實際比較,二者的壓接效果相差甚大。由于交聯(lián)電纜導(dǎo)體是緊絞的圓型線芯,與常用的金具內(nèi)徑有較大的空隙壓接后達(dá)不到足夠的壓縮力。接觸電阻與施加壓力成反比,因此將導(dǎo)致增大。
(3)假冒偽劣產(chǎn)品質(zhì)量差。假冒偽劣金具不僅材質(zhì)不純,外觀粗糙,壓后易出現(xiàn)裂紋,而且規(guī)格不準(zhǔn),有效截面與正品相差很大,根本達(dá)不到壓接質(zhì)量要求,在正常情況下運行發(fā)熱嚴(yán)重,負(fù)荷稍有波動必然發(fā)生故障。3、截面不足 將交聯(lián)電纜與油紙電纜的允許載流量,在環(huán)境溫度為25℃時,進(jìn)行比較得出的結(jié)論是:ZQ2—3×240油紙銅芯電纜可用YJV22-3×150交聯(lián)銅芯電纜替代。因為YJV22-3×150交聯(lián)電纜的允許載流量為476A;而ZQ2-3×240油紙電纜的允許載流量為420A,還超出56A。ZLQ2-3×240可用YJLV22-31×50替代,因為交聯(lián)3×150鋁芯電纜的載流量為364A,而油紙3×240鋁芯電纜的載流量才320A,交聯(lián)電纜還超出44A。如果用允許載流量計算,150mm2交聯(lián)電纜與240mm2油紙電纜基本相同,或者說150mm2交聯(lián)電纜應(yīng)用240mm2的金具連接才能正常運行。由此可見連接金具截面不足將是交聯(lián)電纜接頭發(fā)熱嚴(yán)重的一個重要原因。4、散熱不好。繞包式接頭和各種澆鑄式接頭,不僅繞包絕緣較電纜交聯(lián)絕緣層為厚,而且外殼內(nèi)還注有混合物,就是最小型式的熱縮接頭,其絕緣和保護(hù)層還比電纜本體增加一倍多。這樣無論何種型式的接頭均存在散熱難度。現(xiàn)行各種接頭的絕緣材料耐熱性能較差,J-20橡膠自粘帶正常工作溫度不超過75℃;J-30也才達(dá)90℃;熱縮材料的使用條件為-50～100℃。當(dāng)電纜在正常負(fù)荷運行時,接頭內(nèi)部的溫度可達(dá)100℃ ,當(dāng)電纜滿負(fù)荷時,電纜芯線溫度達(dá)到90℃,接頭溫度會達(dá)140℃左右,當(dāng)溫度再升高時,接頭處的氧化膜加厚,接觸電阻隨之加大,在一定通電時間的作用下,接頭的絕緣材料碳化為非絕緣物,導(dǎo)致故障發(fā)生。綜上所述增加連接金具接點的壓力、降低運行溫度、清潔連接金屬材料的表面、改進(jìn)連接金具的結(jié)構(gòu)尺寸、選用優(yōu)質(zhì)標(biāo)準(zhǔn)的附件、嚴(yán)格施工工藝是降低接觸電阻的幾個關(guān)鍵因素。
三 交聯(lián)電纜接頭故障原因及處理方法-提高交聯(lián)電纜接頭質(zhì)量的對策
由于交聯(lián)電纜接頭所處的環(huán)境和運行方式不同,所連接的電氣設(shè)備及位置不同,電纜附件在材質(zhì),結(jié)構(gòu)及安裝工藝方面有很大的選擇余地,但各類附件所具備的基本性能是一致的,所以應(yīng)加強(qiáng)以下幾點措施來提高接頭質(zhì)量。(1)必須選用技術(shù)先進(jìn)、工藝成熟、質(zhì)量可靠、能適應(yīng)所使用的環(huán)境和條件的電纜附件。對假冒偽劣產(chǎn)品必須堅決抵制,對新技術(shù)、新工藝、新產(chǎn)品應(yīng)重點試驗,不斷總結(jié)提高,逐年逐步推廣應(yīng)用。(2)采用材質(zhì)優(yōu)良、規(guī)格、截面符合要求,能安全可靠運行的連接金具。對于接線端子,應(yīng)盡可能選用堵油型,因為這種端子一般截面較大,能減小發(fā)熱,而且還能有效的解決防潮密封。連接管應(yīng)采用紫銅棒或1#鋁車制加工,規(guī)格尺寸應(yīng)同交聯(lián)電纜線芯直徑配合為好。近年長沙和沈陽電纜廠附件廠提供的交聯(lián)電纜接頭用壓接管,使用效果較好。(3)選用壓接噸位大、模具吻合好,壓坑面積足,壓接效果能滿足技術(shù)要求的壓接機(jī)具。做好壓接前的界面處理,并涂敷導(dǎo)電膏。(4)培訓(xùn)技術(shù)有素、工藝熟練、工作認(rèn)真負(fù)責(zé),能勝任電纜施工安裝和運行維護(hù)的電纜技工。提高施工人員對交聯(lián)電纜的認(rèn)識,增強(qiáng)對交聯(lián)電纜附件特性的了解,研究技術(shù),改進(jìn)工藝,制定施工規(guī)范,加強(qiáng)質(zhì)量控制,保證安全運行。由于交聯(lián)電纜推廣應(yīng)用時間較短,電纜附件品種雜亂,施工人員技術(shù)水平高低不等,加之接頭的接觸力和實際接觸面積是隨著接頭在運行中所處的各種不同的運行條件而在變化,所以交聯(lián)電纜各種接頭發(fā)生故障的原因也就各不相同,除發(fā)熱問題外,對于密封問題、應(yīng)力問題、聯(lián)接問題、接地問題等引起的接頭故障也應(yīng)予以重視。
XLPE cable joint operation of a state
6-10KV high voltage power cables used inwater conservancy and electric power systems is very extensive,well-fitting and accessories of their mechanical and electricalequipment safety, economic, reliable operation and security ofelectricity supply is very important. Well designed and reasonable construction of the cable connector, the actual operation proves that in most cases can be long-term use. However, XLPE cable as carrying capacity, current density, on conductors connected to the more stringent quality requirements. Joints required for the electrical machinery increasingly strict growing conditions, especially the 6-10KV electrical cable joints will undergo a great variety of thermal stress and high intensity and duration of the short-circuit current. So do not cross-linked cable accessories is a subsidiary, more than secondary components, it is as important as the cable, the essential components is closely related with the safe operation of the key products. XLPE cable has been widely used in foreign countries, although widely used in China only 10 years, there are still some problems, but as technology development, attachment support, quality improvement, process improvement, cross-linked cables have replaced oil-paper cable The trend has broad, far-reaching prospects.
Second, cross-linked cable connectorFailure Analysis
Because the cable attachment types, form, size large; of varying quality; construction workers high and low level of technology; cable joint operation mode and conditions vary, leading to cross-linked cable joint failure for different reasons. XLPE cable and the media of different oil-paper cable, connector failure is very different reasons, the main oil-paper cable connector is the insulation of the failure, and failure of cross-linking the main cable connector is a conductor connection. XLPE cable allows high operating temperature, on the cable connector to put forward higher requirements, so that joint heating problem becomes more prominent. Contact resistance is too large, the temperature rise faster, make joints of heat than thermal oxide film thickening, and also allows greater contact resistance, temperature rise faster. Such a vicious circle, so that damage to the insulation joints to form a white short-circuit, causing an explosion destroyed. Increased contact resistance caused by several reasons.
1, the process is poor. Mainly refers to the cable joint construction workers in the construction process before and after conductors.
(1) connected with a contact surfacetreatment of gold poor. Either terminal or connecting tube, as the conditions of production or storage, management is often the body wall of impurities, burrs and oxide layer exists, it is not important for people to defect, but the quality of conductors, is rather serious. Particularly easy to generate a layer of hard aluminum surface of the alumina insulating film but to make the connection of aluminum conductors than copper conductors connected to increase a lot of trouble, the strictness of technology should be much higher. The connection (crimping, welding and mechanical connections) the main reason for fever, in addition to equipment, materials, performance factors, the key is the process technology and responsibility. Construction workers do not understand the connection mechanism of action is not in strict accordance with technical requirements, it will cause the connection not reach the electrical and mechanical strength. When the crimping operation proved a gold surface and the more clean the contact wire in the joint temperature rises, the more the resulting thin oxide film, the less contact resistance.
(2) conductor damage. Greater intensity of cross-linked insulation stripping cutting difficult, circumcision when the construction workers the right plan with the electric knife cut the left, sometimes simply mark with a hacksaw circumcision deep, often not good at leaving wire damage. Stripping is completed, though not very serious cut, but the line core creep bending and crimping, it will result in increased damage or injuries at the conductor fracture, finished crimp difficult to find due to reduced cross-section caused serious fever.
(3) conductors are not in place when the wire core. Conductor connection cut length requirements stripping insulation crimp fitting hole depth plus 5mm, hole depth but non-standard product is easy to cause the length of strip cutting is not enough, or when the string of bits by crimping the wire ends to form the gap, with a wall thickness of gold alone conduction, resulting in increased contact resistance, heat increases.
2, the pressure is not enough. Today information technology and standards in the production of connectors that the cable connection diagram only when the number of pits at each end of the pressure, but did not elaborate crimp crimp area and depth. Construction personnel required number of pressure enough to press pit, unable to determine how effective. Whatever the form of pressure connection, joint resistance is mainly the contact resistance, contact resistance and contact force size and the size and the number of actual contact area is related to the use of crimping tools on the tonnage output. Not enough pressure caused by the main conductor connector has the following 3 points.
(1) insufficient pressure crimping machines. In recent years, many manufacturers of crimping machines, chaotic management, there is no uniform standard, especially in recent years, the production of mechanical pressure clamp, pressure is not only narrow pit, and the pressure of the upper and lower die after receiving the bit can not match; purchase or production of some manufacturers Foreign type pressure clamp, because the implementation of the foreign standard, and the nominal cross-section suited to domestic wire, crimping difficult to guarantee quality.
(2) connection fittings big gap. Now most of the units cross-linked cable connector used to connect the equipment, or oil-paper cables produced by fan wire terminals and the pressure to take over. Round and fan theory of effective core cross-section line is the same, but the actual operation compared to crimp the two effects vary considerably. XLPE cable conductor is the twist of the round wire core tight, with the usual gold with a larger diameter after crimping the gap enough to reach the compression force. Contact resistance is inversely proportional to the applied pressure, so will lead to increase.
(3) poor quality of fake and shoddy products. Fake gold material with not only impure, the appearance of rough, cracks easily after pressing, and specifications are not allowed, effective and genuine cross-section vary widely, and thus fail to crimp quality requirements, under normal circumstances, running a serious fever, the load is slightly fluctuations inevitable failure. 3, the cross-section less than the XLPE cable and allow the carrying capacity of oil-paper cable, at an ambient temperature 25 ℃, comparison and concluded that: ZQ2-3 × 240 oil-paper copper cable available YJV22-3 × 150 cross-linked copper cables instead. Because YJV22-3 × 150 cross-linked cable to allow for the carrying capacity of 476A; and ZQ2-3 × 240 oil-paper cables carrying capacity to allow for the 420A, but also exceed 56A. ZLQ2-3 × 240 YJLV22-31 × 50 can be replaced, because cross-linking 3 × 150 aluminum cable carrying capacity for the 364A, and 3 × 240 oil-paper containing the flow of aluminum cable before 320A, XLPE cable has exceeded 44A. If allowed to load flow calculation, 150mm2 and 240mm2 XLPE cable is basically the same oil-paper cable, or the application of 240mm2 150mm2 XLPE cable connection to the gold with normal operation. This shows that lack of connection fitting cross-section will be cross-linked cable connector is an important cause of severe fever. 4, the heat is not good. Wrapping type connector and a variety of casting joints, not only over the cable around the insulation layer is cross-linked insulation thickness, but also marked with the mixture inside the enclosure is the smallest type of heat shrink connectors, the insulation and protection layer also increased over the cable body more than doubled. No matter what type of joints exist in cooling difficult. Insulating materials of various joints of the existing heat resistance is poor, J-20 self-adhesive rubber with normal operating temperature does not exceed 75 ℃; J-30 has only reached 90 ℃; thermal conditions for the use of materials -50 ~ 100 ℃. When the cable is in normal load operation, the joint internal temperature up to 100 ℃, full load when the cable when the cable core temperature reaches 90 ℃, the temperature will reach 140 ℃ joints around, when the temperature rises again, the oxidation of joints membrane thickening, contact resistance become larger, the role of a certain power of time, the joints of the insulation material insulation for non-carbonation, resulting in failure. To sum up contacts to increase the pressure connection fittings, reducing operating temperature, clean the surface of metal materials connected to improve the structure connection fittings size, the standard accessories of high quality, strict construction process is to reduce the contact resistance of several key factors.
Three cross-linkedto improve the Quality of the cable connector
XLPE cable joints as the environmental and operating in different ways, the connection of electrical equipment and different positions, cable accessories in the material, structure and installation techniques have great choice, but all kinds of accessories on the essential performance the same, so the following measures should be strengthened to improve the joint quality. (1) must use advanced, mature technology, reliable, able to adapt to the environment and conditions used in the cable accessories. Of counterfeit and shoddy products must be firmly resisted, the new technologies, new processes, new products should focus on testing, review to improve, year after year and gradually popularized. (2) The material quality, size, section to meet the requirements, can be safe and reliable operation of the connection fittings. The terminal should be used as oil-blocking, because the general section of a larger terminal, can reduce fever, but also effectively solve the moisture seal. Connecting pipe should be used copper rods or 1 # aluminum car system processing, size should be the same cable core diameter of cross-linked with as well. In recent years, Changsha and Shenyang Cable Factory Accessories Factory provides cross-linked cable fittings pressure to take over, use the better. (3) selection of crimping large tonnage, fit the mold well, pit area of foot pressure, the pressure to meet the technical requirements take effect crimping machines. Good interface treatment before crimping and coating conductive paste. (4) well-established training techniques, technology proficiency, serious and responsible, competent operation and maintenance of cable construction and cable installation technicians. Construction workers to improve the understanding of cross-linked cable, XLPE cable accessories enhance understanding of the idiosyncrasies of technology, process improvements, development of construction specifications, strengthen quality control to ensure safe operation. Promote the use of XLPE cables as short time, cable accessories species messy, high and low level of technology ranging from construction workers, plus the joint contact force and the actual contact area, with the joints in the operation in which a variety of operating conditions and in change, so all kinds of XLPE cable joint failure will vary because, in addition to heating problems, the sealing problems, stress problems, connection problems, due to grounding problems should also be emphasis on joint failure.
