一 交联电缆接头故障原因及处理方法-交联电缆接头运行状况
　　6-10KV高压动力电缆在水利工程和电力系统运用非常广泛,其完好的接头和附件对机电设备安全、经济、可靠运行和供电安全是非常重要的。设计良好、施工合理的电缆接头,经实际运行证明,在大多数情况下是可以长期使用的。但交联电缆由于载流能力强,电流密度大,对导体连接质量要求就更为严格。对接头所要求机械的电气的条件日益从严越来越高,特别是6-10KV电动机电缆,各种接头将经受很大的热应力和较高激烈程度与持续时间的短路电流的影响。所以说交联电缆附件也不是附属的,更不是次要的部件 ,它与电缆是同等重要,必不可少的部件,也是与安全运行密切相关的关键产品。交联电缆在国外已普遍应用,国内广泛采用虽然仅10余年,目前还存在一些问题,但随着技术的发展,附件的配套,质量的提高,工艺的完善,交联电缆已有替代油纸电缆的趋势具有广阔、深远的发展前景。
二交联电缆接头故障原因及处理方法-交联电缆接头故障原因分析
　　由于电缆附件种类、形式、规格较多;质量参差不齐;施工人员技术水平高低不等;电缆接头运行方式和条件各异,致使交联电缆接头发生故障的原因各不相同。由于交联电缆与油纸电缆的介质不同,接头发生故障的原因有很大的差异,油纸电缆接头发生故障主要是绝缘影响,而交联电缆接头发生故障主要是导体连接。交联电缆允许运行温度高,对电缆接头就提出了更高的要求,使接头发热问题就显得更为突出。接触电阻过大、温升加快、发热大于散热促使接头的氧化膜加厚,又使接触电阻更大,温升更快。如此恶性循环,使接头的绝缘层破坏,形成相间短路,引起烧毁。造成接触电阻增大的原因有以下几点。
　　 1、工艺不佳。主要是指电缆接头施工人员在导体连接前后的施工工艺。
　　 (1)连接金具接触面处理不佳。无论是接线端子或连接管,由于生产或保管的条件影响,管体内壁常有杂质、毛刺和氧化层存在,这是不为人们重视的缺陷,但对导体连接质量的影响,颇为严重。特别是铝表面极易生成一层坚硬而又绝缘的氧化铝薄膜,使铝导体的连接要比铜导体的连接增加不少麻烦,工艺技术的严格性也要高得多。造成连接(压接、焊接和机械连接)发热的主要原因,除机具、材料性能因素外,关键是工艺技术和责任心。施工人员不了解连接机理,没有严格按工艺要求操作,就会造成连接处达不到电气和机械强度。运行证明当压接金具与导线的接触表面愈清洁,在接头温度升高时,所产生的氧化膜就愈薄,接触电阻就愈小。
　　 (2)导体损伤。交联绝缘层强度较大剥切困难,环切时施工人员用电工刀左划右切,有时干脆用钢锯环切深痕,往往掌握不好而使导线损伤。剥切完毕虽然不很严重,但在线芯弯曲和压接蠕动时,会造成受伤处导体损伤加剧或断裂,压接完毕不易发现,因截面减小而引起发热严重。
　　 (3)导体连接时线芯不到位。导体连接时绝缘剥切长度要求压接金具孔深加5mm,但因产品孔深不标准,易造成剥切长度不够,或因压接时串位使导线端部形成空隙,仅靠金具壁厚导通,致使接触电阻增大,发热量增加。
2、压力不够。现今有关资料在制作接头工艺及标准图中只提到电缆连接时每端的压坑数量,而没有详述压接面积和压接深度。施工人员按要求压够压坑数量,效果如何无法确定。不论是哪种形式的压力连接,接头电阻主要是接触电阻,而接触电阻的大小与接触力的大小和实际接触面积的多少有关,与使用压接工具的出力吨位有关。造成导体连接压力不够的主要原因有以下3点。
　　 (1)压接机具压力不足。近年压接机具生产厂家较多,管理混乱,没有统一的标准,特别是近年生产的机械压钳,压坑不仅窄小,而且压接到位后上下压模不能吻合;还有一些厂家购买或生产国外类型压钳,由于执行的是国外标准,与国产导线标称截面不适应,压接质量难保证。
　　 (2)连接金具空隙大。现在交联电缆接头多数单位使用的连接金具,还是油纸电缆按扇型导线生产的端子和压接管。从理论上讲圆型和扇型线芯的有效截面是一样的,但从运行实际比较,二者的压接效果相差甚大。由于交联电缆导体是紧绞的圆型线芯,与常用的金具内径有较大的空隙压接后达不到足够的压缩力。接触电阻与施加压力成反比,因此将导致增大。
　　 (3)假冒伪劣产品质量差。假冒伪劣金具不仅材质不纯,外观粗糙,压后易出现裂纹,而且规格不准,有效截面与正品相差很大,根本达不到压接质量要求,在正常情况下运行发热严重,负荷稍有波动必然发生故障。3、截面不足　将交联电缆与油纸电缆的允许载流量,在环境温度为25℃时,进行比较得出的结论是:ZQ2—3×240油纸铜芯电缆可用YJV22-3×150交联铜芯电缆替代。因为YJV22-3×150交联电缆的允许载流量为476A;而ZQ2-3×240油纸电缆的允许载流量为420A,还超出56A。ZLQ2-3×240可用YJLV22-31×50替代,因为交联3×150铝芯电缆的载流量为364A,而油纸3×240铝芯电缆的载流量才320A,交联电缆还超出44A。如果用允许载流量计算,150mm2交联电缆与240mm2油纸电缆基本相同,或者说150mm2交联电缆应用240mm2的金具连接才能正常运行。由此可见连接金具截面不足将是交联电缆接头发热严重的一个重要原因。4、散热不好。绕包式接头和各种浇铸式接头,不仅绕包绝缘较电缆交联绝缘层为厚,而且外壳内还注有混合物,就是最小型式的热缩接头,其绝缘和保护层还比电缆本体增加一倍多。这样无论何种型式的接头均存在散热难度。现行各种接头的绝缘材料耐热性能较差,J-20橡胶自粘带正常工作温度不超过75℃;J-30也才达90℃;热缩材料的使用条件为-50～100℃。当电缆在正常负荷运行时,接头内部的温度可达100℃ ,当电缆满负荷时,电缆芯线温度达到90℃,接头温度会达140℃左右,当温度再升高时,接头处的氧化膜加厚,接触电阻随之加大,在一定通电时间的作用下,接头的绝缘材料碳化为非绝缘物,导致故障发生。综上所述增加连接金具接点的压力、降低运行温度、清洁连接金属材料的表面、改进连接金具的结构尺寸、选用优质标准的附件、严格施工工艺是降低接触电阻的几个关键因素。
三　交联电缆接头故障原因及处理方法-提高交联电缆接头质量的对策
　　由于交联电缆接头所处的环境和运行方式不同,所连接的电气设备及位置不同,电缆附件在材质,结构及安装工艺方面有很大的选择余地,但各类附件所具备的基本性能是一致的,所以应加强以下几点措施来提高接头质量。(1)必须选用技术先进、工艺成熟、质量可靠、能适应所使用的环境和条件的电缆附件。对假冒伪劣产品必须坚决抵制,对新技术、新工艺、新产品应重点试验,不断总结提高,逐年逐步推广应用。(2)采用材质优良、规格、截面符合要求,能安全可靠运行的连接金具。对于接线端子,应尽可能选用堵油型,因为这种端子一般截面较大,能减小发热,而且还能有效的解决防潮密封。连接管应采用紫铜棒或1#铝车制加工,规格尺寸应同交联电缆线芯直径配合为好。近年长沙和沈阳电缆厂附件厂提供的交联电缆接头用压接管,使用效果较好。(3)选用压接吨位大、模具吻合好,压坑面积足,压接效果能满足技术要求的压接机具。做好压接前的界面处理,并涂敷导电膏。(4)培训技术有素、工艺熟练、工作认真负责,能胜任电缆施工安装和运行维护的电缆技工。提高施工人员对交联电缆的认识,增强对交联电缆附件特性的了解,研究技术,改进工艺,制定施工规范,加强质量控制,保证安全运行。由于交联电缆推广应用时间较短,电缆附件品种杂乱,施工人员技术水平高低不等,加之接头的接触力和实际接触面积是随着接头在运行中所处的各种不同的运行条件而在变化,所以交联电缆各种接头发生故障的原因也就各不相同,除发热问题外,对于密封问题、应力问题、联接问题、接地问题等引起的接头故障也应予以重视。

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.