On railways in Russia they use two power supply systems: constant and single-phase alternating current. Traction on three-phase alternating current has not become widespread, since it is technically difficult to insulate closely spaced wires of two phases contact network(third phase - rails).
Electric rolling stock is provided traction motors DC, since the proposed AC motor models do not meet the requirements for power and reliability. Therefore, railway lines are supplied with a single-phase alternating current system, and special equipment is installed on locomotives that converts alternating current into direct current.
Rules technical operation rated voltage levels on current collectors of electric rolling stock are regulated: 3 kV - at DC and 25 kV - at alternating. At the same time, voltage fluctuations that are permissible from the point of view of ensuring motion stability are determined: with direct current - 2.7...4 kV, with alternating current - 21...29 kV. On certain sections of railways, a voltage level of at least 2.4 kV for direct current and 19 kV for alternating current is allowed.
The main parameters characterizing the power supply system of electrified railways are the power of traction substations, the distance between them and the cross-sectional area of the catenary.
On railways electrified using direct current, traction substations perform two functions: they reduce the voltage of the supplied three-phase current and convert it to permanent. All equipment supplying alternating current is located in open areas, and rectifiers and auxiliary units- in enclosed spaces. From the traction substations, electricity enters the contact network through the supply line - the feeder.
The main disadvantages of the DC power supply system are its polarity, relatively low voltage and the inability to ensure complete electrical insulation of the upper track structure from the lower one. Rails, which serve as conductors of current of different polarities, and the roadbed represent a system in which an electrochemical reaction is possible, leading to metal corrosion. As a result, the service life of rails and artificial structures is reduced. To prevent this, apply appropriate protective devices(anode grounding switches, cathode stations, etc.).
For this purpose, traction substations are placed close to each other (10... 20 km) and the cross-sectional area of the catenary wires is increased.
With alternating current, the efficiency of using electric traction increases, since the required power is transmitted through the contact network at a lower current strength compared to a direct current system. Traction substations in this case are located at a distance of 40... 60 km from each other. Their task is only to reduce the voltage from PO...220 to 25 kV, therefore their technical equipment is simpler and cheaper than that of DC traction substations. In addition, in a single-phase alternating current system, the cross-sectional area of the overhead wires is approximately half as large. Open areas are used to place equipment at traction substations with alternating current. However, the design of locomotives and electric trains using alternating current is more complex and their cost is higher.
As a result of the influence of the electromagnetic field of alternating current on metal structures and communications located along the railway tracks, voltage dangerous to people appears in them, and interference occurs in communication and automation lines. Therefore, special measures are taken to protect structures. Costs for protective measures such as improving electrical insulation between rails and ground, replacing air lines cable or radio relay, account for 20...25% of the total cost of electrification work.
The joining of contact networks of lines electrified with direct and alternating current is carried out on special railway stations. In a number of cases, when the creation of such stations seems impractical, dual-power electric locomotives are used, operating on both direct and alternating current.
The energy consumed by railway transport is spent on providing train traction and powering non-traction consumers: stations, depots, workshops, train traffic control devices.
The power supply system of electrified railways includes power plants, regional transformer substations, networks and power lines, which are called external power supply. Internal or traction power supply includes traction substations and electric traction network.
Power plants produce three-phase alternating current with a voltage of 6...21 kV and a frequency of 50 Hz. At transformer substations, the current voltage is increased to 750 kV, depending on the transmission range electrical energy to consumers. Near places of electricity consumption, the voltage is reduced to 110...220 kV and supplied to regional networks, to which traction substations of electrified railways and transformer substations of roads with diesel traction are connected.
The traction network consists of contact and rail wires, which represent the supply and suction lines, respectively. Sections of the contact network are connected to adjacent traction substations.
Railways use direct current systems with a rated voltage of 3000 V and single-phase alternating current with a rated voltage of 25 kV and a frequency of 50 Hz.
The main parameters characterizing the power supply system of electrified railways are the power of traction substations, the distance between them and the overhead contact area.
DC traction substations perform two functions: they reduce the voltage of the supplied three-phase current and convert it into direct current. The voltage level at the pantograph of electric rolling stock with direct current in any block section should be no more than 4 kV and no less than 2.7 kV, and in some areas no less than 2.4 V is allowed. Taking these requirements into account, DC traction substations are located nearby from each other (10...20 km) with the maximum permissible cross-section of the contact wire.
AC traction substations serve only to reduce the AC voltage (up to 27.5 kV) received from power systems. On routes electrified with alternating current with a rated voltage of 25 kV, the distance between traction substations is 40...60 km. The cross-sectional area of the contact network wires in a single-phase alternating current system is approximately two times smaller than with direct current. However, the design of locomotives and electric trains using alternating current is more complex and their cost is higher.
The joining of contact networks of electrified lines on different current systems is carried out at special railway stations.
A contact network is a set of wires, structures and equipment that ensure the transmission of electrical energy from traction substations to pantographs of electric rolling stock.
The contact network consists of consoles, insulators, support cable, contact wire, clamps and strings and is mounted on metal or reinforced concrete supports(Fig. 22.1).
Simple (on secondary station and depot tracks) and chain overhead contact networks are used. A simple catenary consists of a free-hanging wire that is attached to supports. In a chain suspension (Fig. 22.1), the contact wire is not suspended between the supports freely, but is attached to the supporting cable using wire strings. Thanks to this, the distance between the surface of the head and the contact wire remains almost constant. The distance between supports with chain suspension is 70...75 m.
The height of the contact wire above the surface of the rail head at hauls and stations must be at least 5750 mm, and at crossings - 6000...6800 mm.
The contact wire is made of hard-drawn electrolytic copper of a special profile (Fig. 22.2). It can have a cross-sectional area of 85, 100 or 150 mm2.
Contact network supports are made of reinforced concrete (up to 15.6 m high) and metal (15 m or more). The distance from the axis of the outer track to the inner edge of the supports on hauls and stations must be at least 3100 mm. On existing electrified lines and in difficult conditions, it is allowed to reduce the specified distance to 2450 mm at stations and to 2750 mm at hauls.
To protect the contact network from damage, it is sectioned (divided into separate sections - sections) using air gaps (insulating interfaces), neutral inserts, sectional and mortise insulators.
Air gaps are designed to electrically isolate adjacent areas from each other. The air gap is made in such a way that when the current collector of electric rolling stock passes, the mating sections are electrically connected. At the boundaries of the air gaps, contact network supports are installed that have a distinctive color.
A neutral insert is a section of a contact network in which there is no current at all times. The neutral insert consists of several air gaps connected in series and, when passing electric rolling stock, provides electrical insulation of the mating sections.
Stages, intermediate stations, groups of tracks in station parks are divided into separate sections. The connection or disconnection of sections is carried out using sectional disconnectors placed on the supports of the contact network or using sectioning posts. Sectioning posts are equipped with protective equipment - automatic switches from short circuits.
To ensure the safety of service personnel and other persons, all metal structures (bridges, overpasses, traffic lights, hydraulic pumps, etc.) directly interacting with the elements of the contact network or located within a radius of 5 m from them are grounded or equipped with shutdown devices. Also, in the zone of influence of the contact network, all underground metal structures are isolated from the ground to protect them from damage by stray currents.
Contact network structure: 1 – support; 2 – traction; 3 – console; 4, 9 – insulators; 5 – support cable: 6 – contact wire; 7 – string; 8 – clamp
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24. Basic diagrams and designs of the contact network
Dimensions of contact network devices. The normal height of the contact wire above the level of the rail heads on hauls is assumed to be 6250 mm, at stations - 6600 mm. The minimum height must be no less than 5750 mm on hauls and 6250 mm at stations, the maximum - no more than 6800 mm.
The distance from the front edge of the supports to the axis of the track is assumed to be 3100 mm on straight sections of the stage and stations, in recesses when the supports are located behind the ditch - 4900 and 5700 mm, in cramped conditions on stages the dimensions are reduced to 2750 mm and at stations - to 2450 mm.
The distance from the reinforcing wires suspended on the contact network supports on the field side to the ground in the middle of the span must be at least 6000 mm, and the distance from them to the slope of the excavation must be at least 4500 mm.
In artificial structures, the distance from the elements of the pantograph and parts of the contact network that are energized to the grounded parts of structures and rolling stock should be 200 mm in the DC and 350 mm AC sections.
Mating anchor sections. The contact network consists of separate anchor sections 1200-1600 m long. To ensure the transition of the pantograph runner from the contact wire of one anchor section to the contact wire of the next, various coupling schemes for these sections are used. The connections must ensure a smooth transition of the pantograph and uninterrupted current collection for the accepted speeds on the site. On stages, simple and elastic connections are used. In places where the catenary is sectioned, insulating connections are made, and in places powered by different phases on alternating current roads, where the pantograph cannot short-circuit adjacent sections, insulating connections with a neutral insert are used (see paragraph 25).
With a semi-compensated suspension, when the speed does not exceed 70 km/h, simple connections are made according to a two-span scheme (Fig. 76, a). Between anchor supports 1 and 3 there is a transition 2, on the console of which the supporting cables of both anchor sections are suspended in one double saddle. Contact wires are suspended on strings to the supporting cables and anchored on supports 1 and 3 by 0.5-0.6 m and above the normal height of the wire in the span.
The electrical connection between the wires of the anchor sections is made using longitudinal connectors. At the intersection of the contact wires, a boundary pipe 1-1.5 m long is installed so that when the runner passes, the rise of any wire in this place causes the rise of another. At the intersection of contact wires, sparking and increased wear are observed, so two-span coupling is used on the secondary tracks of stations.
Rice. 76. Simple two-span (a) and elastic three-span (b) coupling of anchor sections
On the main tracks of stations and stages with semi-compensated and compensated suspensions, elastic three-span couplings of anchor sections are performed (Fig. 76, b). Between the anchor supports 1 and 4 there are two transitional ones 2 and 3. The anchored branches of the contact wires between these supports in plan are placed parallel at a distance of 100 mm with an elevation at the transitional supports of 200 mm relative to the working contact wire. The pantograph moves from one wire to another more calmly in the middle of the transition span.
Air shooters. The transition of the pantograph from the contact wire of one station track to another is ensured by air switches, which are formed at the intersection of two converging overhead contacts. At the intersection of the contact wires, a restrictive tube 1-1.5 m long is installed on the lower wire.
At high speeds, the air arrows must be fixed, that is, the wires must be held in the position required for reliable operation using clamps. Therefore, crossings of wires are carried out near a flexible or rigid crossbar or a support is specially installed (Fig. 77).
The fixing devices are located at a distance of 1-2 m from the intersection of the contact wires in the direction of the arrow point; the intersection of the contact wires must be between the axes of the converging paths and separated from them at a distance of 400 mm. In the vertical plane, this intersection is located where the distance between the inner edges of the converging crosspiece rails is 730-800 mm.
Non-fixed arrows are used on secondary routes where traffic speeds are low.
Retainers. To create zigzags of the contact wire on straight sections of the track and offsets at supports on curves, clamps are used. The clamps should be lightweight and easy to move in vertical and horizontal planes. 
Rice. 77. Layout of a fixed air switch on a turnout
Rice. 78. Diagrams explaining the operation of compressed (a) and stretched (b) clamps
The clamps are made curved so that when the contact wire is pressed, the pantograph skid does not touch them. Depending on the direction of the zigzag, the clamps work in tension or compression. With a positive zigzag (see Fig. 76, b, support 1), a compressive force acts on the latch, and with a minus one (support 4), a tensile force. For a compressed clamp (Fig. 78, a), the vertical component N of the force is directed downward, which increases the concentrated mass and rigidity, and for a stretched clamp (Fig. 78, b) it is directed upward, which reduces the concentrated mass and rigidity when the pantograph passes under this clamp. In the latter case, the conditions for current collection will be better, and the wear of the contact wire will be less. If possible, compressed clamps are replaced with reverse articulated clamps and consoles with reverse clamping posts (see Fig. 91, d).
According to their design, clamps are divided into rigid, articulated, flexible and reverse. The articulated clamp (Fig. 79, a, b) consists of 1 main and 2 additional rods. The additional rod works in tension. It is attached to the main rod using a special rack 3. The main rod is suspended with two strings from the supporting cable at a distance of 1.5-2 m on both sides of the console. In this case, only the load from the weight of the additional rod is transferred to the contact wire. In areas with two contact wires, clamps are used for each contact wire with additional rods. 
Rice. 79. Direct articulated (a), reverse articulated (b) and flexible (c) clamps
Reverse clamps are installed on straight sections of track with positive zigzags and on supports located inside curves. When supports are located on the outer side of curves of small radii, flexible clamps are used (Fig. 79, c), which consist of a curved clamp 4 and wire 5 with a diameter of 5-6 mm, attached to an insulator 6 at the support.
Strings and clamps. Vertical strings are made flexible or link. The strings are connected to the wires of the chain suspension with string clamps of a boltless design (previously bolted clamps were used). Boltless clamps are 3-4 times lighter than bolted clamps, which leads to a reduction in metal costs for their production and simplifies installation work. In a semi-compensated suspension, when the strings are distorted, sliding strings are used (Fig. 80).
Catenary suspension in artificial structures.
Due to the insufficient size of the artificial structure, when installing a catenary system in it, it is impossible to use standard designs. Therefore, under bridges and overpasses (Fig. 81, a), if their height is sufficient, the suspension is passed under the structure and: insulated bumpers are installed to prevent it from being pressed against the structure. If the height of the structure is insufficient, an insulated insert is cut into the supporting cable and a bypass is arranged, secured to the contact wire or away from the track (Fig. 81, b). Other solutions are also possible.
Rice. 80. Sliding string:
1 - hard triangle: 2 - ring 
Rice. 81. Schemes for the passage of catenary under a pedestrian bridge and overpass:
I - fence shield; 2 and 5 - support cable bumpers; 3 - sliding string; 4 - insulated insert; 6 - bypass
Contact network supports are installed so that the structure is located in the middle of the span.
On bridges with driving below, the design of the contact suspension depends on their dimensions. If the height of the bridge is insufficient, the supporting cable is suspended on U-shaped brackets or special rotary consoles above the wind connections of the bridge (Fig. 82, a), or inside them on transverse cables or other structures, Fig. 82, b).
The installation of contact networks in tunnels is the most difficult. It is made in the form of a chain suspension with a small structural height (400-500 mm) and short span lengths (15-25 m). The suspension is strengthened on an insulated console installed in a niche in the upper part of the tunnel, or on flexible insulated connections.
Rice. 82. Schemes for the passage of contact suspension on bridges with driving below:
1 - bumper; 2 - bracket; 3 - clamp; At GR - rail head level
The height of the contact wire in and under artificial structures is usually less than in neighboring adjacent areas. On the approaches to the structure, a gradual decrease in the height of the contact wire is provided.
Contact network is a set of devices for transmitting electricity from traction substations to EPS through current collectors. It is part of the traction network and for electrified rail transport it usually serves as its phase (with alternating current) or pole (with direct current); the other phase (or pole) is the rail network. The contact network can be made with a contact rail or with a contact suspension.
In a contact network with a catenary suspension, the main elements are the following: wires - contact wire, supporting cable, reinforcing wire, etc.; supports; supporting and fixing devices; flexible and rigid cross members (consoles, clamps); insulators and fittings for various purposes.
Contact networks with catenary suspensions are classified according to the type of electrified transport for which it is intended - railway. mainline, city (tram, trolleybus), quarry, mine underground rail transport, etc.; by the type of current and rated voltage of the EPS powered from the network; on the placement of the contact suspension relative to the axis of the rail track - for central current collection (on mainline railway transport) or lateral (on industrial transport tracks); by type of contact suspension - simple, chain or special; on the specifics of anchoring the contact wire and support cable, connecting anchor sections, etc.
The contact network is designed to operate outdoors and is therefore exposed to climatic factors, which include: temperature environment, humidity and air pressure, wind, rain, frost and ice, solar radiation, the content of various pollutants in the air. To this it is necessary to add thermal processes that occur when traction current flows through network elements, mechanical impact on them from pantographs, electrocorrosion processes, numerous cyclic mechanical loads, wear, etc. All contact network devices must be able to withstand the action of the listed factors and provide high quality of current collection in any operating conditions.
Unlike other power supply devices, the contact network does not have a reserve, so increased reliability requirements are placed on it, taking into account its design, construction and installation, maintenance and repair.
Contact network design
When designing a contact network (CN), the number and brand of wires are selected based on the results of calculations of the traction power supply system, as well as traction calculations; determine the type of contact suspension in accordance with the maximum speeds of movement of the EPS and other current collection conditions; find the span lengths (mainly according to the conditions for ensuring its wind resistance, and at high speeds - and a given level of elasticity unevenness); choose the length of anchor sections, types of supports and supporting devices for hauls and stations; develop CS designs in artificial structures; place supports and draw up plans for the contact network at stations and stages with coordination of zigzags of wires and taking into account the implementation of overhead switches and sectioning elements of the contact network (insulating mates of anchor sections and neutral inserts, sectional insulators and disconnectors).
The main dimensions (geometric indicators) characterizing the placement of the contact network relative to other devices are the height H of hanging the contact wire above the level of the top of the rail head; distance A from live parts to grounded parts of structures and rolling stock; the distance Г from the axis of the outer track to the inner edge of the supports, located at the level of the rail heads, are regulated and largely determine the design of the elements of the contact network (Fig. 8.9).
Improving the design of the contact network is aimed at increasing its reliability while reducing the cost of construction and operation. Reinforced concrete supports and foundations of metal supports are protected from the electrocorrosive effects of stray currents on their reinforcement. Increasing the service life of contact wires is achieved, as a rule, by using inserts on pantographs with high antifriction properties (carbon, including metal-containing, metal-ceramic, etc.), choosing a rational design of pantographs, as well as optimizing current collection modes.
To increase the reliability of the contact network, ice is melted, incl. without interruption of train traffic; wind-resistant contact pendants are used, etc. The efficiency of work on the contact network is facilitated by the use of telecontrol for remote switching of sectional disconnectors.
Wire anchoring
Anchoring of wires is the attachment of catenary wires through the insulators and fittings included in them to the anchor support with the transfer of their tension to it. Anchoring of wires can be uncompensated (rigid) or compensated (Fig. 8.16) through a compensator that changes the length of the wire if its temperature changes while maintaining a given tension.
In the middle of the catenary anchor section, a middle anchorage is performed (Fig. 8.17), which prevents unwanted longitudinal movements towards one of the anchors and allows you to limit the area of damage to the catenary when one of its wires breaks. The middle anchorage cable is attached to the contact wire and the supporting cable with appropriate fittings.
Wire Strain Compensation
Wire tension compensation ( automatic regulation) of the contact network when their length changes as a result of temperature influences, it is carried out by compensators of various designs - block-load, with drums of various diameters, hydraulic, gas-hydraulic, spring, etc.
The simplest is a block-load compensator, consisting of a load and several blocks (pulley hoist), through which the load is connected to the anchored wire. The most widely used is the three-block compensator (Fig. 8.18), in which a fixed block is fixed to a support, and two movable ones are inserted into loops formed by a cable carrying a load and fixed at the other end in the stream of a fixed block. The anchored wire is attached to the movable block through insulators. In this case, the weight of the load is 1/4 of the rated tension (a 1:4 gear ratio is provided), but the movement of the load is twice as large as that of a two-6-lobe compensator (with one moving block).
in compensators with drums of different diameters (Fig. 8.19), cables connected to the anchored wires are wound on a small diameter drum, and a cable connected to a garland of weights is wound on a larger diameter drum. The braking device is used to prevent damage to the catenary when the wire breaks.
Under special operating conditions, especially with limited dimensions in artificial structures, slight differences in heating temperature of wires, etc., other types of compensators are used for catenary wires, fixing cables and rigid crossbars.
Contact wire clamp
Contact wire clamp – a device for fixing the position of the contact wire in a horizontal plane relative to the axis of the pantograph. On curved sections, where the levels of the rail heads are different and the axis of the pantograph does not coincide with the axis of the track, non-articulated and articulated clamps are used. A non-articulated clamp has one rod that pulls the contact wire from the axis of the pantograph to the support (extended clamp) or from the support (compressed clamp) by a zigzag size. On electrified railways non-articulated clamps are used very rarely (in anchored branches of a catenary suspension, on some air switches), since the “hard point” formed with these clamps on the contact wire impairs current collection.
The articulated clamp consists of three elements: the main rod, the stand and an additional rod, at the end of which the contact wire fixing clamp is attached (Fig. 8.20). The weight of the main rod is not transferred to the contact wire, and it only takes part of the weight of the additional rod with a fixing clip. The rods are shaped to ensure reliable passage of the pantographs when they press the contact wire. For high-speed and high-speed lines, lightweight additional rods are used, for example, made of aluminum alloys. With a double contact wire, two additional rods are installed on the stand. On the outer side of curves of small radii, flexible clamps are mounted in the form of a conventional additional rod, which is attached to a bracket, rack or directly to a support through a cable and an insulator. On flexible and rigid crossbars with fixing cables, strip fasteners are usually used (similar to an additional rod), hingedly secured with clamps with an eye mounted on the fixing cable. On rigid crossbars, you can also attach clamps to special racks.
Anchor section
Anchoring section is a section of a catenary suspension, the boundaries of which are anchor supports. Dividing the contact network into anchor sections is necessary to include devices in the wires that maintain the tension of the wires when their temperature changes and to carry out longitudinal sectioning of the contact network. This division reduces the damage area in the event of a break in the catenary wires, facilitates installation, technical. contact network maintenance and repair. The length of the anchor section is limited permissible deviations from set by compensators nominal value tension of catenary wires.
Deviations are caused by changes in the position of strings, clamps and consoles. For example, at speeds up to 160 km/h, the maximum length of the anchor section with bilateral compensation on straight sections does not exceed 1600 m, and at speeds of 200 km/h no more than 1400 m is allowed. In curves, the length of the anchor sections decreases the more, the greater the length curve and its radius is smaller. To transition from one anchor section to the next, non-insulating and insulating connections are made.
Pairing anchor sections
Conjugation of anchor sections is a functional combination of two adjacent anchor sections of a catenary system, ensuring a satisfactory transition of EPS pantographs from one of them to another without disturbing the current collection mode due to the appropriate placement in the same (transition) spans of the contact network of the end of one anchor section and the beginning of the other. A distinction is made between non-insulating (without electrical sectioning of the contact network) and insulating (with sectioning).
Non-insulating connections are made in all cases where it is necessary to include compensators in the catenary wires. In this case, mechanical independence of the anchor sections is achieved. Such connections are installed in three (Fig. 8.21, a) and less often in two spans. On high-speed highways, connections are sometimes carried out in 4-5 spans due to higher requirements for the quality of current collection. Non-insulating interfaces have longitudinal electrical connectors, the cross-sectional area of which must be equivalent to the cross-sectional area of the overhead wires.
Insulating interfaces are used when it is necessary to section the contact network, when, in addition to the mechanical one, it is necessary to ensure the electrical independence of the mating sections. Such connections are arranged with neutral inserts (sections of the catenary where there is normally no voltage) and without them. In the latter case, three or four span connections are usually used, placing the contact wires of the mating sections in the middle span(s) at a distance of 550 mm from one another (Fig. 8.21.6). In this case, an air gap is formed, which, together with the insulators included in the raised contact suspensions at the transition supports, ensures the electrical independence of the anchor sections. The transition of the pantograph skid from the contact wire of one anchor section to another occurs in the same way as with non-insulating coupling. However, when the pantograph is in the middle span, the electrical independence of the anchor sections is compromised. If such a violation is unacceptable, neutral inserts are used different lengths. It is chosen in such a way that when several pantographs of one train are raised, the simultaneous blocking of both air gaps is excluded, which would lead to the short circuit of wires powered from different phases and under different voltages. To avoid burning out the contact wire of the EPS, coupling with the neutral insert takes place on the run-out, for which purpose a signal sign “Turn off the current” is installed 50 m before the start of the insertion, and after the end of the insertion for electric locomotive traction after 50 m and for multiple unit traction after 200 m - the sign “ Turn on the current" (Fig. 8.21c). In areas with high-speed traffic, automatic means of switching off the current to the EPS are required. To make it possible to derail the train when it is forced to stop under the neutral insert, sectional disconnectors are provided to temporarily supply voltage to the neutral insert from the direction of train movement.
Catenary sectioning
Sectioning of a contact network is the division of a contact network into separate sections (sections), electrically separated by insulating connections of anchor sections or sectional insulators. The insulation may be broken during the passage of the EPS pantograph along the section interface; if such a short circuit is unacceptable (when adjacent sections are powered from different phases or they belong to various systems traction power supply), neutral inserts are placed between the sections. Under operating conditions electrical connection individual sections are carried out, including sectional disconnectors installed in appropriate places. Sectioning is also necessary for reliable operation of power supply devices in general, operational Maintenance and repair of contact networks with voltage disconnection. The sectioning scheme provides for such a mutual arrangement of sections in which the disconnection of one of them has the least impact on the organization of train traffic. Sectioning of the contact network can be longitudinal or transverse. With longitudinal sectioning, the contact network of each main track is divided along the electrified line at all traction substations and sectioning posts. The contact network of stages, substations, sidings and passing points is divided into separate longitudinal sections. At large stations with several electrified parks or groups of tracks, the contact network of each park or groups of tracks forms independent longitudinal sections. At very large stations, the contact network of one or both necks is sometimes separated into separate sections. The contact network is also sectioned in long tunnels and on some bridges with traffic below. With transverse sectioning, the contact network of each of the main paths is divided along the entire length of the electrified line. At stations with significant track development, additional transverse sectioning is used. The number of cross sections is determined by the number and purpose separate paths, and in some cases also by EPS starting modes, when it is necessary to use the cross-sectional area of the contact suspensions of adjacent tracks.
Sectioning with mandatory grounding of the disconnected section of the contact network is provided for tracks on which there may be people on the roofs of cars or locomotives, or tracks near which lifting and transport mechanisms operate (loading and unloading, equipment tracks, etc.). To ensure greater safety for those working in these places, the corresponding sections of the contact network are connected to other sections by sectional disconnectors with grounding blades; these knives ground the disconnected sections when the disconnectors are turned off.
In Fig. Figure 8.22 shows an example of a power supply and sectioning circuit for a station located on a double-track section of a line electrified with alternating current. The diagram shows seven sections - four on the hauls and three at the station (one of them with mandatory grounding when it is turned off). The contact network of the tracks of the left section and the station receives power from one phase of the power system, and the tracks of the right section - from the other. Accordingly, sectioning was carried out using insulating mates and neutral inserts. In areas where ice melting is required, two sectional disconnectors with motor drives are installed on the neutral insert. If ice melting is not provided, one manually operated sectional disconnector is sufficient.
To section the contact network of the main and lateral networks at stations, sectional insulators are used. In some cases, sectional insulators are used to form neutral inserts on the AC contact network, which the EPS passes without consuming current, as well as on tracks where the length of the ramps is not sufficient to accommodate insulating connections.
The connection and disconnection of various sections of the contact network, as well as connection to the supply lines, is carried out using sectional disconnectors. On AC lines, as a rule, horizontal-rotating type disconnectors are used, on DC lines - vertical-cutting type. The disconnector is controlled remotely from consoles installed in the duty station of the contact network area, in the premises of station duty officers and in other places. The most critical and frequently switched disconnectors are installed in the dispatch telecontrol network.
There are longitudinal disconnectors (for connecting and disconnecting the longitudinal sections of the contact network), transverse (for connecting and disconnecting its transverse sections), feeder, etc. They are designated by the letters of the Russian alphabet (for example, longitudinal - A, B, V, D; transverse - P ; feeder - F) and numbers corresponding to the numbers of tracks and sections of the contact network (for example, P23).
To ensure the safety of work on the disconnected section of the contact network or near it (in the depot, on the paths for equipping and inspecting the roofing equipment of EPS, on the paths for loading and unloading cars, etc.), disconnectors with one grounding blade are installed.
Frog
Air switch - formed by the intersection of two overhead contacts above the switch; is designed to ensure smooth and reliable passage of the pantograph from the contact wire of one path to the contact wire of another. The crossing of wires is carried out by superimposing one wire (usually an adjacent path) on another (Fig. 8.23). To lift both wires when the pantograph approaches the air needle, a restrictive metal pipe 1-1.5 m long is fixed on the lower wire. The upper wire is placed between the tube and the lower wire. The intersection of contact wires above a single turnout is carried out with each wire shifted to the center from the track axes by 360-400 mm and located where the distance between the inner edges of the heads of the crosspiece connecting rails is 730-800 mm. At cross switches and at the so-called. At blind intersections, the wires cross over the center of the switch or intersection. Air gunners are usually fixed. To do this, clamps are installed on the supports to hold the contact wires in a given position. On station tracks (except for the main ones), switches can be made non-fixed if the wires above the switch are located in the position specified by adjusting the zigzags at intermediate supports. The catenary strings located near the arrows must be double. Electrical contact between the catenary pendants forming the arrow is provided by an electrical connector installed at a distance of 2-2.5 m from the intersection on the arrow side. To increase reliability, switch designs with additional cross connections between the wires of both catenary pendants and sliding supporting double strings are used.
Catenary supports
Contact network supports are structures for fastening the supporting and fixing devices of the contact network, taking the load from its wires and other elements. Depending on the type of supporting device, supports are divided into cantilever (single-track and double-track); racks of rigid crossbars (single or paired); flexible crossbar supports; feeder (with brackets only for supply and suction wires). Supports that do not have supporting devices, but have fixing devices, are called fixing ones. Cantilever supports are divided into intermediate ones - for attaching one catenary suspension; transitional, installed at the junction of anchor sections, - for fastening two contact wires; anchor, absorbing the force from anchoring the wires. As a rule, supports perform several functions simultaneously. For example, the support of a flexible crossbar can be anchored, and consoles can be suspended from the racks of a rigid crossbar. Brackets for reinforcing and other wires can be attached to the support posts.
The supports are made of reinforced concrete, metal (steel) and wood. On domestic trains d. they mainly use supports made of prestressed reinforced concrete (Fig. 8.24), conical centrifuged, standard length 10.8; 13.6; 16.6 m. Metal supports are installed in cases where bearing capacity or in size it is impossible to use reinforced concrete (for example, in flexible crossbars), as well as on lines with high-speed traffic, where increased requirements for reliability are imposed supporting structures. Wooden supports are used only as temporary.
For direct current sections, reinforced concrete supports are made with additional rod reinforcement located in the foundation part of the supports and designed to reduce damage to the support reinforcement by electrocorrosion caused by stray currents. Depending on the installation method, reinforced concrete supports and racks of rigid crossbars can be separated or non-separated, installed directly into the ground. The required stability of undivided supports in the ground is ensured by the upper beam or base plate. In most cases, undivided supports are used; separate ones are used when the stability of non-separated ones is insufficient, as well as in the presence of groundwater, which makes it difficult to install non-separated supports. In reinforced concrete anchor supports, guys are used, which are installed along the track at an angle of 45° and attached to the reinforced concrete anchors. Reinforced concrete foundations in the above-ground part have a glass 1.2 m deep, into which supports are installed and then the cavity of the glass is sealed with cement mortar. To deepen foundations and supports into the ground, the method of vibration immersion is mainly used.
The metal supports of flexible crossbars are usually made of a tetrahedral pyramidal shape, their standard length is 15 and 20 m. Longitudinal vertical posts made of angle bars are connected by a triangular lattice, also made from angle iron. In areas characterized by increased atmospheric corrosion, metal cantilever supports 9.6 and 11 m long are fixed in the ground on reinforced concrete foundations. Cantilever supports are installed on prismatic three-beam foundations, flexible cross beam supports are installed either on separate reinforced concrete blocks or on pile foundations with grillages. The base of the metal supports is connected to the foundations anchor bolts. To secure supports in rocky soils, heaving soils in areas of permafrost and deep seasonal freezing, in weak and swampy soils, etc., foundations of special designs are used.
Console
Console is a supporting device mounted on a support, consisting of a bracket and a rod. Depending on the number of overlapped paths, the console can be single-, double-, or less often multi-path. To eliminate the mechanical connection between catenaries of different tracks and increase reliability, single-track consoles are more often used. Non-insulated or grounded consoles are used, in which the insulators are located between the supporting cable and the bracket, as well as in the clamp rod, and insulated consoles with insulators located in the brackets and rods. Non-insulated consoles (Fig. 8.25) can be curved, inclined or horizontal in shape. For supports installed with increased dimensions, consoles with struts are used. At the junctions of anchor sections when installing two consoles on one support, a special traverse is used. Horizontal consoles are used in cases where the height of the supports is sufficient to secure the inclined rod.
With insulated consoles (Fig. 8.26), it is possible to carry out work on the supporting cable near them without disconnecting the voltage. The absence of insulators on non-insulated consoles ensures greater stability of the position of the supporting cable under various mechanical influences, which has a beneficial effect on the current collection process. The brackets and rods of the consoles are mounted on supports using heels that allow them to rotate along the track axis by 90° in both directions relative to the normal position.
Flexible crossbar
Flexible crossbar - a supporting device for hanging and fixing overhead wires located above several tracks. The flexible crossbar is a system of cables stretched between supports across electrified tracks (Fig. 8.27). Transverse load-bearing cables absorb all vertical loads from the chain suspension wires, the crossbar itself and other wires. The sag of these cables must be at least Vio the span length between the supports: this reduces the influence of temperature on the height of the catenary suspensions. To increase the reliability of the crossbars, at least two transverse load-bearing cables are used.
The fixing cables take up horizontal loads (the upper one is from the supporting cables of the chain hangers and other wires, the lower one is from the contact wires). Electrical insulation of cables from supports allows servicing the contact network without disconnecting the voltage. To regulate their length, all cables are secured to supports using threaded steel rods; in some countries, special dampers are used for this purpose, mainly for fastening contact suspension at stations.
Current collection
Current collection is the process of transferring electrical energy from a contact wire or contact rail to the electrical equipment of a moving or stationary EPS through a pantograph, providing sliding (on highway, industrial and most urban electric transport) or rolling (on some types of EPS of urban electric transport) electrical contact. Violation of contact during current collection leads to the occurrence of non-contact electric arc erosion, which results in intense wear of the contact wire and contact inserts of the current collector. When contact points are overloaded with current during movement, contact electrical explosion erosion (sparking) and increased wear of the contacting elements occur. Long-term overload of the contact with operating current or short-circuit current when the EPS is parked can lead to burnout of the contact wire. In all these cases, it is necessary to limit the lower limit of contact pressure for the given operating conditions. Excessive contact pressure, incl. as a result of the aerodynamic impact on the pantograph, an increase in the dynamic component and the resulting increase in the vertical deflection of the wire, especially at clamps, on air switches, at the junction of anchor sections and in the area of artificial structures, can reduce the reliability of the contact network and pantographs, as well as increase the wear rate wires and contact inserts. Therefore, the upper limit of contact pressure also needs to be normalized. Optimization of current collection modes is ensured by coordinated requirements for contact network devices and current collectors, which guarantees high reliability of their operation at minimal reduced costs.
The quality of current collection can be determined by various indicators (the number and duration of violations of mechanical contact on the calculated section of the track, the degree of stability of contact pressure close to the optimal value, the rate of wear of contact elements, etc.), which largely depend on the design of the interacting systems - the contact network and pantographs, their static, dynamic, aerodynamic, damping and other characteristics. Despite the fact that the current collection process depends on a large number of random factors, research results and operating experience make it possible to identify the fundamental principles for creating current collection systems with the required properties.
Rigid cross member
Rigid crossbar - used for hanging overhead wires located above several (2-8) tracks. The rigid crossbar is made in the form of a block metal structure (crossbar), mounted on two supports (Fig. 8.28). Such cross members are also used for opening spans. The crossbar with the uprights is connected either hingedly or rigidly using struts, allowing it to be unloaded in the middle of the span and reducing steel consumption. When placing lighting fixtures on the crossbar, a flooring with railings is made on it; provide a ladder for climbing to the supports for service personnel. Install rigid crossbars ch. arr. at stations and separate points.
Insulators
Insulators are devices for insulating live contact wires. Insulators are distinguished according to the direction of application of loads and the installation location - suspended, tensioned, retaining and cantilever; by design - disc and rod; by material - glass, porcelain and polymer; insulators also include insulating elements
Suspended insulators - porcelain and glass dish insulators - are usually connected in garlands of 2 on DC lines and 3-5 (depending on air pollution) on AC lines. Tension insulators are installed in wire anchorages, in supporting cables above sectional insulators, in fixing cables of flexible and rigid crossbars. Retaining insulators (Fig. 8.29 and 8.30) differ from all others by the presence of an internal thread in the hole of the metal cap for securing the pipe. On AC lines, rod insulators are usually used, and on DC lines, disc insulators are also used. In the latter case, another disc-shaped insulator with an earring is included in the main rod of the articulated clamp. Cantilever porcelain rod insulators (Fig. 8.31) are installed in the struts and rods of insulated consoles. These insulators must have increased mechanical strength, since they work in bending. In sectional disconnectors and horn arresters, porcelain rod insulators are usually used, less often disc insulators. In sectional insulators on direct current lines, polymer insulating elements are used in the form of rectangular bars made of press material, and on alternating current lines - in the form of cylindrical fiberglass rods, on which electrical protective covers made of fluoroplastic pipes are put on. Polymer rod insulators with fiberglass cores and ribs made of organosilicon elastomer have been developed. They are used as hanging, sectioning and fixing; they are promising for installation in struts and rods of insulated consoles, in cables of flexible cross members, etc. In areas of industrial air pollution and in some artificial structures, periodic cleaning (washing) of porcelain insulators is carried out using special mobile equipment.
Catenary
Catenary - one of the main parts of the contact network, is a system of wires, the relative position of which, the method of mechanical connection, material and cross-section provide required quality current collection The design of the catenary system is determined by economic feasibility and operating conditions ( maximum speed movement of the EPS, the highest current strength removed by pantographs), climatic conditions. The need to ensure reliable current collection at increasing speeds and power of the EPS determined the trends in changes in suspension designs: first simple, then single with simple strings and more complex - spring single, double and special, in which, to ensure the required effect, Ch. arr. to level the vertical elasticity (or rigidity) of the suspension in the span, space-stayed systems with an additional cable or others are used.
At speeds of up to 50 km/h, satisfactory quality of current collection is ensured by a simple contact suspension, consisting only of a contact wire suspended from supports A and B of the contact network (Fig. 8.10a) or transverse cables.
The quality of current collection is largely determined by the sag of the wire, which depends on the resulting load on the wire, which is the sum of the wire’s own weight (in case of icy conditions along with ice) and wind load, as well as on the span length and tension of the wire. On the quality of current collection big influence angle a (the smaller it is, the worse the quality of current collection), the contact pressure changes significantly, shock loads appear in support zone, increased wear of the contact wire and current collector inserts occurs. Current collection in the support zone can be somewhat improved by hanging the wire at two points (Fig. 8.10.6), which under certain conditions ensures reliable current collection at speeds of up to 80 km/h. It is possible to significantly improve current collection with a simple suspension only by significantly reducing the length of the spans in order to reduce the sag, which in most cases is uneconomical, or by using special wires with significant tension. In this regard, chain hangers are used (Fig. 8.11), in which the contact wire is suspended from the supporting cable using strings. A suspension consisting of a support cable and a contact wire is called single; if there is an auxiliary wire between the support cable and the contact wire - double. In a chain suspension, the supporting cable and the auxiliary wire are involved in the transmission of traction current, so they are connected to the contact wire by electrical connectors or conductive strings.
Basic mechanical characteristics Contact suspension is considered to be elasticity - the ratio of the height of the rise of the contact wire to the force applied to it and directed vertically upward. The quality of current collection depends on the nature of the change in elasticity over the span: the more stable it is, the better the current collection. In simple and conventional chain hangers, the elasticity at mid-span is higher than that of the supports. Equalization of elasticity in the span of a single suspension is achieved by installing spring cables 12-20 m long, on which vertical strings are attached, as well as by rational arrangement of ordinary strings in the middle part of the span. Double suspensions have more constant elasticity, but they are more expensive and more complex. To obtain a high index of uniform distribution of elasticity in the span, various methods are used to increase it in the area of the support unit (installation of spring shock absorbers and elastic rods, torsion effect from cable twisting, etc.). In any case, when developing suspensions, it is necessary to take into account their dissipative characteristics, i.e., resistance to external mechanical loads.
The catenary is an oscillating system, therefore, when interacting with pantographs, it can be in a state of resonance caused by the coincidence or multiple frequencies of its own oscillations and forced oscillations, determined by the speed of the pantograph along a span with a given length. If resonance phenomena occur, a noticeable deterioration in current collection is possible. The limit for current collection is the speed of propagation of mechanical waves along the suspension. If this speed is exceeded, the pantograph has to interact as if with a rigid, non-deformable system. Depending on the standardized specific tension of the suspension wires, this speed can be 320-340 km/h.
Simple and chain hangers consist of separate anchor sections. The suspension fastenings at the ends of the anchor sections can be rigid or compensated. On the main railways Mostly compensated and semi-compensated suspensions are used. In semi-compensated suspensions, compensators are present only in the contact wire, in compensated ones - also in the supporting cable. Moreover, in the event of a change in the temperature of the wires (due to the passage of currents through them, changes in the ambient temperature), the sag of the supporting cable, and therefore the vertical position of the contact wires, remain unchanged. Depending on the nature of the change in the elasticity of the suspensions in the span, the sag of the contact wire is taken in the range from 0 to 70 mm. Vertical adjustment semi-compensated suspensions are carried out so that the optimal sag of the contact wire corresponds to the average annual (for a given area) ambient temperature.
The structural height of the suspension - the distance between the supporting cable and the contact wire at the suspension points - is chosen based on technical and economic considerations, namely, taking into account the height of the supports, compliance with the current vertical dimensions of the approach of buildings, insulating distances, especially in the area of artificial structures, etc.; in addition, a minimum inclination of the strings must be ensured at extreme values of ambient temperature, when noticeable longitudinal movements of the contact wire relative to the supporting cable may occur. For compensated suspensions this is possible if the support cable and contact wire are made of various materials.
To increase the service life of the contact inserts of pantographs, the contact wire is placed in a zigzag plan. Various options for hanging the support cable are possible: in the same vertical planes as the contact wire (vertical suspension), along the axis of the track (semi-oblique suspension), with zigzags opposite to the zigzags of the contact wire (oblique suspension). The vertical suspension has less wind resistance, the oblique suspension has the greatest, but it is the most difficult to install and maintain. On straight sections of the track, semi-oblique suspension is mainly used, on curved sections - vertical. In areas with particularly strong wind loads, a diamond-shaped suspension is widely used, in which two contact wires, suspended from a common supporting cable, are located at supports with opposite zigzags. In the middle parts of the spans, the wires are pulled together by rigid strips. In some pendants lateral stability is ensured by the use of two supporting cables, forming a kind of cable-stayed system in the horizontal plane.
Abroad, single chain suspensions are mainly used, including on high-speed sections - with spring wires, simple spaced support strings, as well as with supporting cables and contact wires with increased tension.
Contact wire
The contact wire is the most critical element of the contact suspension, directly making contact with the EPS pantographs during the current collection process. Typically, one or two contact wires are used. Two wires are usually used when collecting currents of more than 1000 A. On domestic railways. d. use contact wires with a cross-sectional area of 75, 100, 120, less often 150 mm2; abroad – from 65 to 194 mm2. The cross-sectional shape of the wire underwent some changes; in the beginning. 20th century the cross-section profile took the form with two longitudinal grooves in the upper part - the head, which serve to secure the contact network fittings to the wire. In domestic practice, the dimensions of the head (Fig. 8.12) are the same for different cross-sectional areas; in other countries, head sizes depend on cross-sectional area. In Russia, the contact wire is marked with letters and numbers indicating the material, profile and cross-sectional area in mm2 (for example, MF-150 - shaped copper, cross-sectional area 150 mm2).
Widespread in last years received low-alloy copper wires with additives of silver and tin, which increase the wear and heat resistance of the wire. Bronze copper-cadmium wires have the best wear resistance (2-2.5 times higher than copper wire), but they are more expensive than copper wires, and their electrical resistance higher. The feasibility of using a particular wire is determined by a technical and economic calculation, taking into account specific operating conditions, in particular when solving issues of ensuring current collection on high-speed highways. Of particular interest is the bimetallic wire (Fig. 8.13), suspended mainly on the receiving and departure tracks of stations, as well as a combined steel-aluminum wire (the contact part is steel, Fig. 8.14).
During operation, contact wires wear out when collecting current. There are electrical and mechanical components of wear. To prevent wire breakage due to increased tensile stresses, the maximum wear value is normalized (for example, for a wire with a cross-sectional area of 100 mm, the permissible wear is 35 mm2); As wear on the wire increases, its tension is periodically reduced.
During operation, rupture of the contact wire can occur as a result of the thermal effect of electric current (arc) in the area of interaction with another device, i.e., as a result of burnout of the wire. Most often, contact wire burnouts occur in the following cases: above the current collectors of a stationary EPS due to a short circuit in its high-voltage circuits; when raising or lowering the pantograph due to the flow of load current or short circuit through an electric arc; with an increase in contact resistance between the wire and the contact inserts of the pantograph; presence of ice; closing the pantograph skid of the different-nopothecial branches of the insulating interface of the anchor sections, etc.
The main measures to prevent wire burnouts are: increasing the sensitivity and speed of protection against short-circuit currents; the use of a lock on the EPS, which prevents the pantograph from rising under load and forcibly turns it off when lowered; equipping the insulating interfaces of the anchor sections with protective devices that help extinguish the arc in the area of its possible occurrence; timely measures to prevent ice deposits on wires, etc.
Support cable
Support cable - a chain suspension wire attached to the supporting devices of the contact network. A contact wire is suspended from the supporting cable using strings - directly or through an auxiliary cable.
On domestic trains on the main tracks of lines electrified with direct current, they are mainly used as a supporting cable copper wire with a cross-sectional area of 120 mm2, and on the side tracks of stations - steel-copper (70 and 95 mm2). Abroad, bronze and steel cables with a cross-section from 50 to 210 mm2 are also used on AC lines. The cable tension in a semi-compensated catenary varies depending on the ambient temperature in the range from 9 to 20 kN, in a compensated suspension depending on the type of wire - in the range of 10-30 kN.
String
A string is an element of a catenary chain, with the help of which one of its wires (usually a contact wire) is suspended from another - the supporting cable.
By design, they are distinguished: link strings, composed of two or more hingedly connected links of rigid wire; flexible strings made of flexible wire or nylon rope; hard - in the form of spacers between the wires, used much less frequently; loop - made of wire or metal strip, freely suspended on the upper wire and rigidly or hingedly fixed in the string clamps of the lower (usually contact); sliding strings attached to one of the wires and sliding along the other.
On domestic trains The most widely used are link strings made of bimetallic steel-copper wire with a diameter of 4 mm. Their disadvantage is electrical and mechanical wear in the joints of individual links. In calculations, these strings are not considered as conductive. Flexible strings made of copper or bronze do not have this drawback. stranded wire, rigidly attached to the string clamps and acting as electrical connectors distributed along the catenary and not forming significant concentrated masses on the contact wire, which is typical for typical transverse electrical connectors used with link and other non-conducting strings. Sometimes non-conductive catenary strings made of nylon rope are used, the fastening of which requires transverse electrical connectors.
Sliding strings, capable of moving along one of the wires, are used in semi-compensated catenary pendants with a low structural height, when installing sectional insulators, in places where the supporting cable is anchored on artificial structures with limited vertical dimensions and in other special conditions.
Rigid strings are usually installed only on the overhead switches of the contact network, where they act as a limiter for the rise of the contact wire of one suspension relative to the wire of the other.
Reinforcing wire
Reinforcing wire is a wire electrically connected to the contact suspension, serving to reduce the overall electrical resistance of the contact network. As a rule, the reinforcing wire is suspended on brackets on the field side of the support, less often - above the supports or on consoles near the supporting cable. The reinforcing wire is used in areas of direct and alternating current. Decline inductive reactance AC contact network depends not only on the characteristics of the wire itself, but also on its placement relative to the overhead wires.
The use of reinforcing wire is provided for at the design stage; Typically, one or more A-185 type stranded wires are used.
Electrical connector
An electrical connector is a piece of wire with conductive fittings intended for the electrical connection of overhead wires. There are transverse, longitudinal and bypass connectors. They are made from bare wires so that they do not interfere with the longitudinal movements of the catenary wires.
Cross connectors are installed for parallel connection all wires of the contact network of the same track (including reinforcing ones) and at overhead contact stations of several parallel tracks included in one section. Transverse connectors are mounted along the track at distances depending on the type of current and the proportion of the cross-section of the contact wires in the general cross-section of the contact wires, as well as on the operating modes of the EPS on specific traction arms. In addition, at stations, connectors are placed in the places where the EPS starts and accelerates.
Longitudinal connectors are installed on the air switches between all the wires of the catenary pendants forming this switch, in the places where the anchor sections are coupled - on both sides for non-insulating joints and on one side for insulating joints and in other places.
Bypass connectors are used in cases where it is necessary to make up for the interrupted or reduced cross-section of the catenary suspension due to the presence of intermediate anchoring of reinforcing wires or when insulators are included in the supporting cable for passage through an artificial structure.
Catenary fittings
Contact network fittings – clamps and parts for connecting overhead contact wires to each other, to supporting devices and supports. The fittings (Fig. 8.15) are divided into tension (butt clamps, end clamps, etc.), suspension (string clamps, saddles, etc.), fixing (fixing clamps, holders, ears, etc.), conductive, mechanically lightly loaded (clamps supply, connecting and transitional - from copper to aluminum wires). The products included in the fittings, in accordance with their purpose and production technology (casting, cold and hot stamping, pressing, etc.), are made of malleable cast iron, steel, copper and aluminum alloys, and plastics. Technical specifications fittings are regulated by regulatory documents.
Electric railway transport is the most productive, economical and environmentally friendly. Therefore, from the middle of the 20th century to the present day, active work has been carried out to convert railway lines to electric traction. Currently, more than 50% of Russian railways are electrified. In addition, even non-electrified sections of railways are in need of electrical energy: it is used to ensure the functioning of signaling systems, centralization, communications, lighting, operation computer technology etc.
Electrical energy in Russia is generated by enterprises in the energy industry. Rail transport consumes about 7% of the electricity produced in our country. It is spent on providing train traction and powering non-traction consumers, which include railway stations with their infrastructure, locomotive, carriage and track facilities, as well as train traffic control devices. Small enterprises and settlements located near it can be connected to the railway power supply system.
According to clause 1 of Appendix No. 4 to the PTE In railway transport, reliable power supply of electric rolling stock, signaling devices, communications and computer equipment must be ensured. consumers of electric energy category I, as well as other consumers in accordance with the category established for them.
comprises external network (power plants, transformer substations, power lines) And internal networks (traction network, power supply lines for signaling and communication devices, lighting network and etc.).
A three-phase alternating current is generated electricity voltage 6...21 kV frequency 50 Hz. To transmit electrical energy to consumers, the voltage is increased to 250...750 kV and transmitted over long distances using ( Power lines). Near the places of electricity consumption, the voltage is reduced to 110 kV with the help of and supplied to regional networks, to which, along with other consumers, electrified railways are connected and supply non-traction consumers, the current of which is supplied at a voltage of 6...10 kV.
Purpose and types of traction networks
designed to provide electrical energy to electric rolling stock. It consists of contact And rail wires, representing respectively feeding And suction line. Sections of the traction network are divided into sections (sectioned) and connect to neighboring ones. This allows substations and contact networks to be loaded more evenly, which generally helps to reduce electricity losses in the traction network.
Russian railways use two traction current systems: permanent And single-phase alternating.
The rules of technical operation are regulated nominal voltage levels on pantographs of electric rolling stock: 3 kV- at constant current and 25 kV- with variable At the same time, the voltage fluctuations that are permissible from the point of view of ensuring motion stability are determined: at constant current from 2,7 before 4 kV, with variable from 21 before 29 kV (Clause 2 of Appendix No. 4 to the PTE).
On railways electrified DC, perform two functions: they reduce the voltage of the supplied three-phase current with help and convert it into direct current with help. From the traction substation electricity through the protective quick release switch supplied to the contact network by - feeder, and from the rails it returns back to the traction substation.
Main disadvantages of the DC power supply system are its constant polarity, relatively low voltage in the contact wire and current leakage due to the inability to ensure complete electrical insulation of the upper track structure from the lower one (“”). The rails, which serve as conductors of current of the same polarity, and the roadbed represent a system in which an electrochemical reaction is possible, leading to metal corrosion. As a result, the service life of rails and metal structures located near the railway track is reduced. To reduce this effect, special protective devices are used - cathode stations And anode grounding conductors.
Due to relatively low voltage in a direct current system to obtain the required power of traction rolling stock ( W=UI) a high current must flow through the traction network. To do this, traction substations are placed close to each other (every 10...20 km) and the cross-sectional area is increased, sometimes using double or even triple contact wire.
With alternating current, the required power is transmitted through the contact network at a higher voltage ( 25 kV) and, accordingly, lower current strength compared to a direct current system. Traction substations in this case are located at a distance of 40...70 km from each other. Their technical equipment is simpler and cheaper than that of DC traction substations (there are no rectifiers). In addition, in a single-phase alternating current system, the cross-sectional area of the contact network wires is approximately two times smaller, which allows significant savings in expensive copper. However, the design of AC locomotives and electric trains is more complex and their cost is higher.
The joining of contact networks of lines electrified with direct and alternating current is carried out at special railway stations -. At such stations there is electrical equipment that allows both direct and alternating current to be supplied to the same sections of station tracks. The operation of such devices is interconnected with the operation of centralization and signaling devices. The installation of docking stations requires large investments. When the creation of such stations seems impractical, two-system ones are used that operate on both types of current. When using such an EPS, a transition from one type of current to another can occur while the train is moving along the stretch.
Contact network device
Contact network- this is a set of wires, supporting structures and other equipment that ensure the transmission of electrical energy from traction substations to electric rolling stock. The main requirement for the design of the contact network is to ensure reliable constant contact of the wire with the pantograph, regardless of the speed of trains, climatic and atmospheric conditions. There are no duplicate elements in the contact network, so its damage can lead to a serious disruption to the established train schedule.
In accordance with the purpose of electrified tracks, they use simple And chain air catenary suspensions. On secondary station and depot tracks at a relatively low speed it can be used (" tram" type), which is a free-hanging taut wire, which is fixed using insulators on supports located at a distance of 50...55 m from each other.
At high speeds, the sagging of the contact wire should be minimal. This is achieved by a design in which the contact wire between the supports is attached to support cable using frequently spaced wires strings. Due to this, the distance between the surface of the rail head and the contact wire remains almost constant. For a chain suspension, in contrast to a simple one, fewer supports are required: they are located at a distance of 65...70 m from each other. On high-speed sections they are used in which they are suspended from the supporting cable on strings. auxiliary wire, to which the contact wire is also attached with strings. In the horizontal plane, the contact wire is located relative to the track axis with a deviation of ±300 mm at each support. This ensures its wind resistance and uniform wear of the contact plates of the pantographs. To reduce the sagging of the contact wire during seasonal temperature changes, it is pulled to supports, which are called, and suspended to them through the system. The greatest length of the section between the anchor supports ( anchor section) is set taking into account the permissible tension of the worn contact wire and on straight sections of the track reaches 800 m.
In accordance with clause 4 of Appendix No. 4 to the PTE overhead wire suspension height above the level of the rail head on hauls and stations there should be not less than 5750 mm, and on crossings - not less than 6000 mm. The maximum permissible hanging height of the contact wire is 6800 mm. The contact wire is made from hard drawn electrolytic copper cross section 85 , 100 or 150 mm 2. For ease of fastening wires using clamps, use MF.
For reliable operation of the contact network and ease of maintenance, it is divided into separate sections - sections by using air gaps And neutral inserts, and.
When the current collector of electric rolling stock passes along it, its skid briefly electrically connects both sections of the contact network. If this is unacceptable due to the power supply conditions of the sections, then they are separated, which consists of several air gaps located in series. The use of neutral inserts is mandatory on lines electrified with alternating current, because adjacent sections of the contact network can be powered by different phases coming from the power plant, the electrical connection of which to each other is unacceptable. The EPS must proceed in the run-down mode and with the auxiliary machines turned off. To fence the sections of the contact network, special signal signs "" are used, installed on the supports of the contact network.
The sections are connected or disconnected using means placed on the supports of the contact network. The disconnectors can be controlled either remotely using a pole-mounted electric drive, connected to the energy dispatcher console, and manually using manual drive, .
The arrangement of station tracks with contact wires depends on their purpose and the type of station. Above the turnouts, the contact network has so-called contact lines formed by the intersection of two contact pendants.
On mainline railways they also use catenary supports. The distance from the axis of the extreme path to the inner edge of the supports on straight sections must be at least 3100 mm. In special cases on electrified lines, it is allowed to reduce the specified distance to 2450 mm- at stations and before 2750 mm- on hauls. Mainly used on hauls individual cantilever suspension of the contact wire. At stations (and in some cases also on stages) it is used group suspension of contact wires on and cross members.
To protect the contact network from short circuit between adjacent traction substations are located, equipped safety switches. All metal structures directly interacting with the elements of the contact network or located within a radius of 5 m from them, ground(connected to rails). On lines electrified with direct current, special diodes and sparks are used. To protect elements and equipment of the contact network from overvoltages (for example, due to lightning strikes), some supports are equipped with arcing horns.
They are used for electrical insulation of live contact network elements (contact wire, support cable, strings, clamps) from grounded elements (supports, consoles, crossbars, etc.). According to the functions they perform, insulators are divided into hanging, tension, fixative, console, by design - disc-shaped And rod, and according to the material from which they are made - , and.
On electrified railways, the rails carry reverse traction current. To reduce electricity losses and ensure normal operation of automation and telemechanics devices on such lines, the following features of the track superstructure are provided:
- Shunts are welded to the rail heads on the outside of the track, reducing the electrical resistance of the rail joints;
- the rails are isolated from the sleepers using rubber gaskets in the case of reinforced concrete sleepers and impregnation of wooden sleepers with creosote;
- use crushed stone ballast, which has good dielectric properties, and provide a gap of at least 3 cm between the base of the rail and the ballast;
- on lines equipped with automatic blocking and electrical centralization, insulating joints are used, and in order to pass traction current bypassing them, or frequency filters.
AC/DC Interconnection Stations
One of the ways to connect lines electrified using different types of current is to section the contact network with switching individual sections to power from DC or AC feeders. The contact network of docking stations has groups of isolated sections: direct current, alternating current and switchable. Electricity is supplied to the switched sections through. The contact network is switched from one type of current to another using special motor drives installed at grouping points. Each point is supplied with two supply lines: AC and DC from the AC traction substation. Feeders of the appropriate type of current of this substation are also connected to the contact network of the necks of the docking station and adjacent sections.
To exclude the possibility of supplying individual sections of the contact network with current that does not correspond to the rolling stock located there, as well as the possibility of EPS leaving sections of the contact network with a different current system, the switches are blocked with each other and with the devices electrical centralization. Switch control is included in a unified route-relay centralization system for controlling switches and station signals. The station duty officer, collecting any route, simultaneously with setting the arrows and signals to the required position, makes the corresponding switches in the contact network.
Route centralization at connecting stations has system for counting the arrival and departure of electric rolling stock to sections of the track of switchable sections of the contact network, which prevents it from being exposed to another type of current. To protect the equipment of power supply devices and DC electric rolling stock when they are exposed to alternating current voltage as a result of any disturbance, special equipment is available.
Requirements for power supply devices
Power supply devices must provide reliable power supply:
- electric rolling stock for the movement of trains with established weight standards, speeds and intervals between them with the required traffic volumes;
- signaling devices, communications and computer technology as consumers of electrical energy of category I;
- all other consumers railway transport in accordance with the established category.
The backup power supply source for automatic and semi-automatic blocking must be in constant readiness and ensure uninterrupted operation of signaling devices and crossing alarms for at least 8 hours, provided that the power has not been turned off in the previous 36 hours. The time of transition from the main power supply system to the backup one or vice versa is not must exceed 1.3 s.
To ensure reliable power supply, periodic monitoring of the condition of structures and power supply devices must be carried out, their parameters must be measured using diagnostic devices, and scheduled repair work must be carried out.
Power supply devices must be protected from short circuit currents, overvoltages and overloads in excess of established standards.
Metal underground structures (pipelines, cables, etc.), as well as metal and reinforced concrete structures located in the area of lines electrified with direct current, must be protected from electrical corrosion.
Within artificial structures, the distance from the current-carrying elements of the pantograph and parts of the contact network that are energized to the grounded parts of structures and rolling stock must be at least 200 mm on lines electrified with direct current, and not less 270 mm- on alternating current.
For the safety of operating personnel and other persons, as well as to improve protection against short circuit currents, they are grounded or equipped with residual current devices. metal supports and elements to which the contact network is suspended, as well as all metal structures located closer than 5 m from parts of the contact network that are energized.
Karelin Denis Igorevich ® Orekhovo-Zuevsky Railway College named after V.I. Bondarenko "2017