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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Types of contact connections. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric installation work There are various technological ways of making contact connections current-carrying parts of electrical installations: electric welding with contact heating and carbon electrode, gas-electric, gas, thermite, contact butt and cold pressure welding, soldering, crimping, twisting, tightening with bolts (screws), etc. Electric welding with contact heating used for terminating, connecting and branching aluminum wires with a cross section of up to 1000 mm, as well as for connecting aluminum conductors with copper; resistance heating welding using filler materials - for connecting and terminating aluminum stranded conductors of wires and cables with a cross section of up to 2000 mm2, carbon electrode electric welding - for connecting aluminum tires of various sections and configurations; gas-electric welding - mainly for joining aluminum and copper conductors. The advantage of gas-electric welding is that it is performed without fluxes, the disadvantage is relatively bulky equipment plus the use of expensive gas. For this reason, gas-electric welding is mainly used for the contact connection of aluminum alloy busbars and copper busbars. It is used to connect copper and aluminum wires of various sections and configurations. gas welding (this requires bulky equipment). Thermite welding connect steel, copper and aluminum wires and tires of all sections. It is most expedient to use it for connecting bare wires of power lines in the field. To perform thermite welding, simple equipment is required, it is technologically simple, but it is characterized by an increased fire hazard. Another requirement is the creation of special conditions for the storage of thermite cartridges and matches. Thermite-crucible welding is used when connecting steel strips of ground loops and lightning protection cables. Butt welding It is applied at connection of aluminum tires with copper. Cold pressure welding it is used when connecting aluminum and copper busbars of medium sections and single-wire wires with a cross section of up to 10 mm. Its implementation does not require additional materials and contact fittings. Connections of aluminum and copper wires of any section are performed soldering; this method does not require sophisticated equipment, but is laborious. Crimping used to make contact connections of aluminum, steel-aluminum and copper insulated and bare wires with a cross section of up to 1000 mm both in cable and overhead lines. When terminating and connecting conductors, it is especially necessary to carefully select lugs, sleeves, as well as punches and dies. Twisting wires and their connection using connectors are used on communication lines. The use of the contact connection method depends on the materials of the conductors to be connected, the section, shape and voltage of the electrical installation, and the installation conditions. Overhead lines (wires) up to 1 kV in spans are connected by twisting in oval tubes, single-wire wires can be connected by twisting followed by soldering or overlap welding (butt welding of single-wire wires is not allowed). In the loops, the wires of the anchor supports are connected with anchor and branch wedge clamps, twisting in oval tubes, flat or hardware pressed clamps and welding. The preparation of conductors for a contact connection is carried out depending on the method of making the connection. So, when connecting or terminating stranded wires by soldering, the ends are cut in steps or with a bevel at an angle of 55 °, so that contact is formed between the tubular part of the tip (sleeve) and the wires of each layer. When terminating or connecting sector or segment cores with a special tool or using pliers, they are rounded so that the core can easily enter the cavity of the tubular part of the tip or sleeve. Preparation of the contact ends of flat conductors for welding includes straightening and edge processing. In order to ensure metallic contact between the connected conductors, their contact surfaces are preliminarily cleanse from all kinds of films, using washing, chemical dissolution of films and mechanical cleaning; often these methods are used together. Effective mechanical cleaning in combination with rinsing or dissolution. Methods for cleaning surfaces are selected depending on the materials of the contact elements, the presence of protective metal coatings on them, the type of films and the method of making the contact connection. The easiest way to clean surfaces is mechanically, using steel and carded brushes. The contact surfaces of aluminum conductors are cleaned especially carefully, having previously applied a layer of technical vaseline or other protective lubricants to prevent re-oxidation of the surfaces of the connected elements. Under a layer of lubricant, with the help of special brushes, the internal ones clean the contact surfaces of aluminum oval or tubular connectors. Rotating brushes are used to clean the contact surfaces in specialized harvesting areas. Surfaces covered with oil films are preliminarily degreased with solvents, and then mechanically cleaned to a metallic sheen. The surfaces to be joined are protected to prevent re-contamination. The protection is chosen depending on the method of making the contact connection, the material of the contact elements and the operating conditions of the connections. So, in contact welding or soldering, the surfaces of the elements to be joined are protected from oxidation by fluxes, and if a connection is used with bolts, crimping or twisting, then contact lubricants. Protective contact lubricants (pastes) must have high adhesion, have a relatively high degree of dropping, be chemically neutral, stable over time and elastic. Capacitor vaseline, quartz vaseline paste, etc. are used as protective contact lubricants and pastes. Lubricants are applied in a thin layer. The correct and high-quality performance of operations for connecting, branching and terminating the cores of wires and cables determines the reliability of the operation of internal and external electrical wiring. These wiring elements must have the necessary mechanical strength and low electrical resistance, while maintaining these properties for the entire period of operation. For electrical wiring, wires and cables with aluminum and copper conductors are used. For economic reasons, electrical wiring is usually carried out with wires and cables with aluminum conductors. However, aluminum has properties that contribute little to the reliability of the connection. One of them is increased (compared to copper) fluidity and oxidizability with the formation of non-conductive films. Aluminum oxide creates a large contact resistance, leading to poor electrical contact and excessive heating. The oxide film creates difficulties when soldering and welding wires, since it has a melting point of 2050 ° C, while the melting point of aluminum itself is only 660 ° C. The film from the contact surfaces must be removed and measures taken against its secondary occurrence. For this, quartz-vaseline or zinc-vaseline pastes are used, as well as ZES lubricant. Copper conductors are also covered with an oxide film, but it does not significantly affect the quality of the contact connection and is easily removed. A large difference in the coefficient of linear thermal expansion of aluminum compared to other metals also leads to contact failure. Therefore, aluminum wires must not be pressed into copper lugs or attached to copper contacts of devices. Even during normal operation, after some time, the wires in the places of bolted and screwed connections of aluminum conductors should be periodically tightened, since when the ambient temperature changes, they can become very hot. During long-term operation, aluminum begins to "flow" from an area with a high pressure to an adjacent area under a lower pressure. Therefore, screw and bolt contact connections of aluminum conductors must not be pinched. In particularly unfavorable conditions are the contacts of aluminum conductors with other metals in outdoor wiring. Under the influence of moisture contained in the environment, a water film with electrolyte properties appears on the contact surfaces and a so-called galvanic couple is formed at the junction. Aluminum here acts as a negative pole and "loses" metal particles, is gradually destroyed, and the contact is destroyed. Aluminum compounds with copper and brass are especially unfavorable in this respect. Such contact surfaces must be protected from moisture penetration with quartz-vaseline paste, ZES lubricant or coated with a third metal - tin or POS-type solder. During operation, screw and bolt clamps of aluminum and copper wire connections require control and periodic tightening. However, for electrical wiring, for example, in country houses, this method of connecting conductors the most acceptable, since it is simple and does not require special tools and equipment for connecting wires. The design of the clamp for connecting aluminum conductors must provide the following properties: - constancy of pressure on the wires when their fluidity appears; - a device that protects the wires from spreading out from under the contact screw; - galvanized parts. These requirements are met by a clamp specially designed for connecting aluminum conductors. The spring washer of the clamp ensures constant pressure on the connected wires, and the stop prevents the wire from being squeezed out from under the contact clamp. In some designs, the spring washer and the spread limiting stop are made in the form of a single sprocket washer. It is necessary to assemble the clamp with all the details, since the absence of any of them will necessarily lead to poor contact.
The termination of aluminum conductors under the screw clamp is carried out in the form of a ring, for copper conductors - in the form of a ring and a rod. Connection sequence of aluminum conductors with a cross section of up to 10 mm: 1) from the end of the core, the insulation is removed for a length sufficient to make the ring. The knife is directed at an angle of 10-15 ° to the surface of the wire, so that, cutting off the insulation, it slides along the surface of the core. You can not hold the knife perpendicular to the wire, as in this case you can cut and break the core. To remove insulation from wires with a cross section of up to 4 mm, special KSI pliers are used; 2) the core is cleaned with sandpaper or glass paper to a metallic sheen and lubricated with a thin layer of quartz-vaseline paste; 3) the prepared end of the core is bent into a ring with round-nose pliers. The wires should be bent clockwise, i.e. in the direction of rotation of the screw. The inner diameter of the ring should be slightly larger than the diameter of the contact screw; 4) the wire is clamped with a screw on the contact output plate, screwing it into a threaded hole or tightening it with a nut. Flexible copper conductors with a cross section of 1-2,5 mm are terminated in the form of a ring, followed by a half-wire in the following order. About 25-30 mm of insulation is removed from the wire, the strands are cleaned with sandpaper to a metallic sheen, the wires are twisted into a rod, bent into a ring, the ring is covered with rosin or its solution in alcohol, then dipped for 1-2 s in molten P0S-40 solder. After cooling, the wire is insulated to the ring. A stranded copper current-carrying core with a cross section of 1,0-2,5 mm in some types of connections is terminated in the form of a rod with half-solder P0S-40 solder. Contact clamps of socket outlets up to 10 A and switches from 4 A and above allow the connection of copper and aluminum wires with a cross section of 1 to 2,5 mm, and for switches of 1 A - only copper conductors of wires with a cross section of 0,5 to 1 mm. The connection of aluminum wires in the clamp must be carried out with an end in the form of a ringlet, copper wires - in the form of a ringlet and a rod. The ring of aluminum wire before being put into contact is cleaned and lubricated with quartz-vaseline or zinc-vaseline paste. In socket outlets up to 10 A, no more than two copper or aluminum wires with a cross section of up to 4 mm2 can be connected to one contact. The connection of aluminum or copper wires of electrical wiring with copper wires of lighting fittings is carried out using a special clamping block. The wires are clamped between plates having notches and threaded holes for clamping screws. Spring-loaded split washers must be put on the screws.
In luminaires, incandescent lamp holders have contact clamps for a ring, as well as a plug-in type for connecting straight ends of copper conductors of wires. When connecting the wires, it must be remembered that the central contact of the cartridge is connected to the phase wire, and the contact connected to the base sleeve is connected to zero. It is recommended to additionally insulate the wires coming out of the cartridge with a PVC tube. A method of connecting and terminating aluminum and copper wires and cables by crimping has become widespread, which provides reliable electrical contact and the necessary mechanical strength, and is also easy to perform. Crimping is performed with manual tongs, mechanical and hydraulic presses using replaceable dies and punches. To connect the cores of wires and cables, sleeves are used, for termination - lugs. Technological procedure for crimping aluminum conductors in connecting sleeves and ending with cable lugs: 1) depending on the cross section of the current-carrying conductors of wires and cables, the type and dimensions of the connecting sleeves and cable lugs are selected. For crimping conductors with a cross section of 2,5 to 10 mm2, connecting aluminum sleeves of the GAO type are used; for sections more than 10 mm - connecting sleeves of the GA type. Termination of cores and cables is carried out using tubular aluminum lugs of the TA type or copper-aluminum lugs of the TAM type; 2) select dies and punches in accordance with the standard sizes of connecting sleeves and tips; 3) check the presence of factory grease in the sleeves and tips. In the absence of lubrication, the sleeves and tips are cleaned with a metal "brush" and lubricated with a protective quartz-vaseline or zinc-vaseline paste; 4) remove the insulation from the ends of the cores: when terminating - at a length equal to the length of the tubular part of the tip, when connecting - at a length equal to half the sleeve; 5) clean the ends of the current-carrying wires with sandpaper or a cordolent brush to a metallic sheen, wipe with a cloth soaked in gasoline, and immediately cover with quartz-vaseline paste; 6) put a tip or sleeve on the prepared and pressed cores. When terminating, the core is inserted into the tip until it stops, when connected - so that the ends of the connected cores are in contact with each other in the middle of the sleeve; 7) install the tubular part of the tip or sleeve into the matrix and pressurize; 8) having processed the sharp edges of the sleeves, the connection is isolated. It is not allowed to press a copper tip onto an aluminum core, as the connection will be fragile due to the large difference in the coefficient of linear thermal expansion of copper and aluminum. The procedure for crimping copper conductors and cables: from multi- and single-wire wires, the insulation is removed along a length of 20-25 mm, the wires to be connected are laid in parallel, without twisting them together. Then they are wrapped with two layers of copper or brass foil 0,2 mm thick and 18-20 mm wide and the junction is crimped with press tongs. Crimping of single- and multi-wire conductors with a cross section of 4 mm or more is carried out in copper tubular lugs of the T type or in connecting copper sleeves of the GM type. All operations are performed in the same sequence as for aluminum wires and cables, with the exception of the application of quartz-vaseline and zinc-vaseline paste. It is forbidden to make crimping with a hammer and chisel. By soldering and welding, wires are connected and branched in cases where all the others cannot be used - crimping, screw clamps and welding. Soldering requirements are the same: it must ensure the reliability of electrical contact and the necessary strength. To obtain high-quality soldering, it is necessary, firstly, to choose the right solder, and secondly, to remove the oxide film of the contact surfaces to be joined. When connecting copper wires, the oxide film is removed before soldering, when connecting aluminum wires - during the soldering process. Soldering creates a good electrical contact, but this connection is fragile, so the wires must be twisted before soldering. Soldering of copper conductors with a cross section of 1,0-10 mm2 is carried out with a soldering iron. For soldering, soft tin-lead solders of the POS brand are used. When soldering copper wires, the oxide is removed by cleaning the surfaces with sandpaper or a file. As a flux, rosin or its solution in alcohol (1: 1 ratio of parts), as well as soldering fat, is used. When soldering copper wires, it is not recommended to use etched hydrochloric acid or ammonia as a flux, since they have a destructive effect not only on the oxide film, but also on the copper wire itself. The heating temperature of the soldering place should be 30-50 ° C higher than the melting temperature of the solder and flux. Low temperature gives the so-called cold soldering, which has low mechanical strength and creates an unreliable electrical contact. To prevent damage to the insulation, a section of the core 2-3 mm long before the insulation cut is not tinned. In the process of soldering, the oxide film is removed from the surface of the connected cores mechanically (under a layer of molten solder) or chemically (by using special fluxes). At a certain temperature, they destroy the oxide film. This is the peculiarity of soldering and welding of aluminum conductors. After soldering, flux residues must be carefully removed, as they can cause destruction of the contact. Soldering aluminum conductor connections in humid air is not recommended due to possible corrosion. The places of soldering are protected from moisture by protective covers. Soldering single-wire conductors with a cross section of 2,5-10 mm can be done with solder A using a soldering iron, other solders (TsO-12, TsA-15) using a gasoline blowtorch. Solder A is resistant to corrosion, convenient for soldering and tinning wires. The aluminum oxide film is destroyed mechanically when the wire is rubbed with a solder stick, so flux is not needed when soldering. The connection and branching of copper conductors with a cross section of up to 6 mm (Fig. 33) is carried out by soldered twisting. Twisting with subsequent soldering is a method of connecting and branching single-wire copper and stranded wires of the brands PR, PV, PRHD, PRD with a cross section of 1,5-6 mm in open electrical wiring on rollers and insulators. This method of connection and branching is also used in electrical wiring performed by flat wires PPV and others, when branch boxes do not have inserts with contact clamps, as well as in some other cases. For example, when connecting a copper wire branch from an overhead line with a cross section of 4-6 mm with copper input wires with a cross section of 2,5 mm. The method of connecting wires with a twist is simple in execution, but it requires subsequent soldering of the connection, since even a well-made twist has a transient contact resistance several times higher than with other connection methods - crimping, soldering, welding, bolted or screw connection.
When twisted, the wires have few contact points and when current flows through the connection, the contact can overheat, which can sometimes cause a fire. For this reason, a twisted connection without soldering is not allowed. The technology for connecting and branching copper wires is as follows. To connect 2 pieces of wire, it is necessary to tightly twist the wires of the conductive wires so that they do not unwind, and cross the wires. The end of the left wire makes 8-10 turns around the right wire, and the end of the right wire makes 8-10 turns around the left wire, but in the other direction. The twisted joints must be at least 10-15 diameters of the connecting wires. The connection is crimped with pliers and soldered with POS-30 or POS-40 solder. The soldered twist is insulated for the entire length of the connection with the obligatory capture of the unprotected wire insulation. The connection between two twisted wires is performed in a run. When soldering single-wire aluminum conductors with a cross section of 2,5-10 mm, the connection and branch are made in the form of a double twist with a groove (Fig. 34). The insulation is removed from the cores, cleaned to a metallic sheen with sandpaper or cord tape, overlapped with a double twist to form a groove at the point where the cores touch.
The connection is heated with a blowtorch or soldering iron to the temperature at which the solder begins to melt. Solder stick A is rubbed with force on one side. As a result of friction, the oxide film is torn off and the groove begins to be tinned and filled with solder. Similarly, the cores are tinned and the groove is filled with solder on the other side. At the same time, the outer surfaces and places of twisting of the cores are tinned. After cooling, the junction is isolated. Welding is used for terminating and connecting current-carrying conductors of wires and cables of all sections and for aluminum conductors with copper conductors with a conductor cross section of not more than 10 mm. This connection method requires the use of special fluxes, welding machines and other special equipment. Author: Bannikov E.A.
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