IEEE 1637-2010 en Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV C 46 kV《额定电压5 kV - 46 kV交流电电力电缆用端子选择指南》.pdf

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4、on to photocopy portions of any individual standard for educational classroom use can also be obtained through the Copyright Clearance Center. Introduction This introduction is not part of IEEE Std 1637-2010, IEEE Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV 4

5、6 kV. This guide was developed within the IEEE Insulated Conductors Committee of the Power the closer the lines, the higher the stress. The coaxial configuration of a shielded power cable keeps the electric stresses symmetrical and under control as long as the cable components are left intact. To fa

6、cilitate electric stress control at the end of a shielded-power cable, the insulation shield is removed axially for a distance sufficient to prevent interaction between the conductor and the insulation shield. When the insulation shield is ended, this leads to a concentration of electric stress at t

7、he shield terminus (see Figure 2). Shielded-power cable terminations are designed to relieve this concentration of electric stress at the insulation shield terminus. Figure 3 shows how this electric stress is overcome with a geometric type of electric stress control and Figure 4 shows how this elect

8、ric stress is overcome with non-linear types of electric stress control. Figure 1 Dielectric field sat shield terminus without gradient material 3 Copyright 2010 IEEE. All rights reserved. IEEE Std 1637-2010 IEEE Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV 46

9、 kV Figure 2 Dielectric field at shield terminus without gradient material Figure 3 Dielectric field at shield terminus with geometric electric stress control Figure 4 Dielectric field at shield terminus with gradient material electric stress control 4 Copyright 2010 IEEE. All rights reserved. IEEE

10、Std 1637-2010 IEEE Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV 46 kV 4.2 Parts of termination A shielded power cable termination may be comprised of several elements. All terminations must have an electric stress control component. In addition, terminations m

11、ay include the cable end seal, the connector, and electro-chemical track resistance on the surface of the termination between the insulation shield terminus and the cable conductor. 4.2.1 Cable end seal Class 1 terminations provide a seal to keep the environment out of the cable and when necessary,

12、keep any gas, liquid, or semi-solid in the cable. 4.2.2 Connector When terminating a shielded power cable, a connection has to be made from the cable conductor to a piece of equipment. Termination connections used for power cables are most commonly compression connectors, but can be soldered, welded

13、, bolted, or fastened by means of a set screw. It is imperative that prior to the installation of the connector, the cable conductor strands and connector be clean and free of contaminants and corrosion, including surface oxidation. This helps to make a solid, permanent connection. Regardless of wha

14、t type of connection is used, all terminations require a connector that is listed as follows: a) is compatible with the cable conductor metal b) seals the power cable conductor, in combination with other termination components, from the entry of environmental contaminants into the conductor or the l

15、eakage of fluids, when present, from the conductor 4.2.2.1 Compression Connectors Compression connectors are either copper, aluminum, or a combination of both (bimetallic). Copper cable conductors can use either a copper connector (CU rated) or a dual rated aluminum connector (AL/CU rated). Dual rat

16、ed connectors often employ an intermediate metal between the copper and aluminum, usually in the form of a tin and/or zinc coating on the aluminum connector. Only aluminum connectors or dual rated connectors are applied to aluminum cable conductors. In some cases, a transition from aluminum to coppe

17、r is needed. For example, aerial connections, where an aluminum cable conductor connects to a copper conductor, require a transition connector. In this instance, a bimetal connector provides the transition. A commonly used bimetal termination connector has an aluminum barrel with a copper stem. The

18、transition area of the connector may have an intermediate metal at the interface or the interface may be spun welded to eliminate access of air and moisture to the metal junction. This type of connector is sometimes referred to as a pin connector. Compression connectors for aluminum conductors requi

19、re an inhibitor to fill the area between the conductor strands and the interior connector wall. Inhibitor generally comes preinstalled within the connector and is critical to its function. Inhibitor should not be removed from a connector. Inhibitors are intended to limit the formation of oxidation o

20、n the metal surfaces within the connector and on the surfaces of the cleaned conductor strands. Inhibitors also serve to limit moisture intrusion into the connector and may include particles to enhance electrical contact between the metals. Because the inhibitor can contain conductive particles, exc

21、ess inhibitor squeezed out of the connector should be cleaned away in the area between the end of the connector and the cable insulation. This helps avoid contamination of the insulation 5 Copyright 2010 IEEE. All rights reserved. IEEE Std 1637-2010 IEEE Guide to Select Terminations for Shielded Alt

22、ernating-Current Power Cable Rated 5 kV 46 kV surface during termination assembly and helps avoid contamination of insulating fluids that may fill some types of terminations. Compression indents on a connector can create sharp metal protrusion off the edge of a connector, commonly referred to as fla

23、shing. In most cases, these protrusions should be removed to avoid damaging components within the termination during the assembly process. Once the proper connector is selected, the manufacturers recommendation for tooling and installation shall be carefully followed in order to provide a proper con

24、nection. It is very important to follow the tooling recommendations and installation procedures required for the connector. Selection of the proper tool and die combination is important to maximize electrical contact between the connector and the various strand layers within the conductor without ov

25、erly reducing the mechanical strength of the conductor at the transition to the connector. A poor connector installation leads to problems with the cable termination during the service life of the cable system. 4.2.2.2 Soldered and welded connectors Soldered and welded connectors require the applica

26、tion of heat. The choice of this type of connector can depend on the environment of application and the type of support equipment available. For example, use of a torch in a confined space can consume the oxygen, requiring adequate ventilation to meet safety requirements. Confined spaces can also po

27、se an issue when volatile solvents are used to clean cable ends. Vapor concentrations and flammability of the vapor become important issues. When heat is applied to a connector, it is conducted into the surrounding materials. When these materials are polymers with relatively low melting points, cabl

28、e insulation and shields can become damaged or even burn. To maximize conduction of current across a welded or soldered joint, care should be exercised to fill internal voids within the connection with solder or the weld material. Similarly, the metals are required to all bond together properly, mak

29、ing it necessary that a minimum temperature be reached. Fluxes may be required to maximize metal flow and bonding for a good electrical connection. 4.2.2.3 Bolted and Set Screw Connectors Bolted and set screw connections should be torqued to the manufacturers specifications. Special tooling may be r

30、equired for this purpose, although “break away” connectors are becoming more common. On “break away” connectors, the bolt or set screw is designed to shear in two at the required torque. Oxidation inhibitors should be applied to bolted and set screw connectors. 4.2.3 Electric stress relief A shielde

31、d power cable is composed of a conductor, a conductor shield, insulation, a coaxial insulation shield, a metallic shield or sheath, and may or may not have an overall jacket. The conductor shield and insulation shield are generally formed of semiconductive material that is compatible with the cable

32、insulation. The coaxial conductor and insulation shields cause the electric field within the cable insulation to be uniformly distributed, thus allowing optimization of the insulation thickness. Metallic shields are available in a wide variety of designs, including tapes, wires, and straps that are

33、applied in helical, longitudinal, or corrugated designs. Many factors influence the choice of a metallic shield design, including such issues as shield losses, short circuit duty, magnetic forces during faults, and historic practices by the user. 6 Copyright 2010 IEEE. All rights reserved. IEEE Std

34、1637-2010 IEEE Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV 46 kV When a cable ends the insulation shield and metallic shield have to be separated from the conductor and conductor shield, a sufficient distance to reduce the electrical interaction between the t

35、wo. This separation may be accomplished with a gradient type material as shown in Figure 4 or with geometric stress grading in the form of a force fit slip-on molded or taped termination, as shown in Figure 3. When the insulation shield is ended abruptly, a destructively high electric field is prese

36、nt at the insulation shield terminus. This electric stress must be relieved to provide a long life for the installation. 4.2.4 Electro-chemical track resistance The surface of the termination insulation that lies between the conductor and the insulation shield terminus is under electric stress and i

37、s susceptible to electric discharge that can cause erosion and chemical decomposition of both the cable and termination. This vulnerable area can be protected by the choice of materials and/or the geometry of the termination. This track resistant outer housing must be in contact with the metallic gr

38、ound to bleed off leakage current. This allows the leakage current to travel from the track resistant material directly to metallic ground without eroding other areas of the system. 5. Mounting When selecting terminations for shielded power cables, consideration should be given to mounting requireme

39、nts insofar as how they are to be attached and supported on the pole, structure, or enclosure in which or on which the cable is to be terminated. The weight of the cable, the height of the riser, and the type of structure to which it is to be attached leads to different mounting configuration requir

40、ements. 5.1 Riser pole mounting Cables in conduit or under a U-guard that attach to a riser pole are generally considered as requiring outdoor terminations and usually connect to some disconnecting means, either a switch or fused cutout. The weight of the termination and the weight of the attached c

41、able affect the type of mounting required. When a light weight polymeric termination is used and the cable weight up the pole is supported by a nearby grip, bracket, or mounting band, the termination may be attached directly to the disconnecting device without other means of support. This typically

42、applies to smaller cables that are extruded dielectric and not too heavy, generally of the 200 A rating. This is done utilizing a pin connector crimped onto the cable conductor and connected to disconnect. For larger and heavier terminations, due consideration of the strength and rigidity of the dis

43、connecting device is required. If the device is rigidly supported, the cable termination may be bolted to the device using a flat pad lug of some other suitable means of connection. Otherwise, separate support of the cable and termination is required by attaching the cable to either a mounting band

44、or support bracket. A separate jumper lead is then required from the termination to the connecting device. In addition to weight, the stiffness of the cable and its bending radius from the cable support point to the termination should be considered. Stiff cables, usually with large conductors, can p

45、lace significant mechanical forces on a termination and its mounting as daily load cycles create expansion and contraction of the cable conductor. The minimum bending radius of the cable should be considered to avoid damaging cable components and placing stresses on the cable that could lead to fail

46、ure during elevated temperature operation. On large cables, which can be extremely stiff, it may be necessary to include an S-bend in the cable under a termination to compensate for thermal expansion and contraction effects on cable length that get translated into mechanical forces on the terminatio

47、n and its mounting. 7 Copyright 2010 IEEE. All rights reserved. IEEE Std 1637-2010 IEEE Guide to Select Terminations for Shielded Alternating-Current Power Cable Rated 5 kV 46 kV If heavier terminations, such as porcelain, are required or specified, separate mounting brackets are needed for rigid su

48、pport, since these terminations are not suitable for hanging or attaching directly to the disconnect device. The above terminations and mountings generally apply to extruded dielectric cables with concentric neutrals or tape shields that are single, paralleled, or triplexed. Other types of cables th

49、at are laminated with metal jackets that are more rigid, or three conductor cables, may require lead wipes, trifurcating assemblies, spreader heads, or special accessories that are considerably heavier and require independent mounting brackets. These terminations require jumper leads from a connector on top of the terminator to the disconnecting device. 5.2 Structure mounting Varying conditions and configurations may be found in substations, switch yards, or other areas that may consist of one or more circuits with various forms of bus work on fixed structures.