Spatial double-wedge auto-compensated  contact mains russionenglish



Т. Demchenko, D-r of Technological Science, Russian State Open Technological University of Communications






Experts in the field are fully aware, that the efficiency of railway traction power supply systems and railway transport in general greatly depends on reliable and economic contact mains.

Nowadays when the speed of movement at the electrified railways is much above 200 km per hour, the issues of the contact mains seem to be already settled. To some extent it is really the state of affairs at the railways in the countries with mild climatic conditions with moderate temperature variations, low wind loads and practical absence of glazed frost conditions. The plan and the profile of the railways in the above countries as a rule cause no problems for arrangement of contact mains system, and the tunnels are not long there. The only exception is the tunnel under La Manche, but its electrification system differs greatly from standard designs The contact mains in the tunnel as well as other devices is unique and their implementation has required corresponding expenses.

High technological level of operating contact mains is a common practice in the industrially developed countries. Nevertheless even under these conditions the cost of construction and contact mains operation with longer inter-repair maintenance terms, service personnel cut down still remain among major factors.

The cost of the contact mains is essential at the electrification of long distance railway lines, working under complicated climatic and geographical conditions. Such a contact mains shall be rated to withstand extreme impacts of temperature drop (sometimes within short time), high wind loads and glazed frost conditions. Specific problems of the electrified long distance railway lines at the East of Russia, in the South-East Asia, India are caused not by the climatic conditions alone5 but also by a lower leva! of power traction systems maintenance and operational technologies, presence of vast and often hard to access territories of servicing.

Drawbacks of the vertical contact suspension system 


A traditional contact suspension system, but for the contact wire zigzags, is designed in vertical plane, thus it is called a vertical suspension. Special devices of longitudinal compensation are applied to eliminate temperature variation in the lengths of the component carrier cables, contact wires, leaf spring suspensions. All the wires of suspension are movable along the axis of the track. In case such a possibility is not envisaged in the design of a contact suspension ( e,g, for the carrier cable of a serni-compensated suspension) the vertical position, i.e. sag of the wire, does change. It's a fact of common knowledge, It is also known that to provide for operability of such a contact mains it is necessary to have sophisticated junking at the anchoring sections, compensating devices, intermediate anchoring, swivel consoles and fixings blocks, a number of articulated joints in some other sections of the mains.

All the above named temperature compensating devices for the wires may play their negative role for breaking of wires. For example several spans of suspension are being damaged when the contact wire is broken, special proliferation preventive blocks are mounted at the compensation units. In case a carrier cable is broken the intensity and the scope of damage may be much more serious.

Vertical contact suspensions among many other factors may have the following drawbacks: difficulty of passing the joints by trolleys, variations in suspension toughness along the length of the span, impact of the ambient temperatures on toughness, necessity of additional devices to increase suspension wind force resistance, much efforts for adjustment and maintenance of the set parameters in the process of operation.

Operational problems deserve special mentioning. The existing contact mains requiring frequent regular inspection and adjustments, which are often rather complicated ones, preclude the development of general maintenance and repair procedures for the electrified sector, oriented at uniform inter-repair periods of all the sector's devices starting with the railway track. Vertical contact system requiring frequent adjustments a year5 demands considerable operational personnel, which at present for a number of reasons is rather difficult to hire and train.

All the above mentioned considerations stimulate searches of new technical solutions of contact mains design. Spatial double-wedge auto-compensated contact mains (SDACM), developed at the Russian State Open Technological University of Communications seems to be an adequate solution of all the above mentioned problems.


Spatial double-wedge contact mains design

Basic feature of the spatial double-wedge suspensions architecture is a novel mutual alignment of contact wires and carrier cables, (See Fig 1), There is quite a number of such suspensions modifications. The basic structure of SDACM includes two carrier cables and two contact wires. The carrier cables are located at both sides of the railway track axis and are either rigidly fixed through insulators at the horizontal console of a single support (See Fig 2) or at a rigid crossbar.

The contact wares top view represents double-wedge figures, symmetrical to the railway track axis.

Two wires are connected in the span with a link bar and in the middle of a sector between the two adjacent bars each wire is fixed to the carrier cable with a fixing element. These elements are the points of the contact wires suspension and at the same time fixing them relative to the axis of the railway track.

The length of a span is selected depending on the operational conditions, At the main lines the spans conform to the presently accepted standards, while in constructed structures they are decreased to match the overall dimensions of the tunnel-. Several sets of double-wedge contact wires are .mounted within a span of a main line depending on the results of calculations.


SDACM specific features 

Automatic wire length compensation feature


 SDACM realizes a new approach to compensation of temperature length variations in suspension wires. Temperature variations in the lengths of carrier cables and contact wires introduce both - alteration of vertical positioning of carrier cables and the distance from the cables to the track axis, i.e. spatial alteration of the wires without longitudinal shift typical for compensated chain suspensions occurs. Alteration in the height of the carrier cables in the spans of 50 to 70 m long at 80° С temperature drop causes difference in height of contact wire suspension height from the level of rail heads up to 100 mm. But it it is very important, that the height of the contact wire position changes evenly along all the points of the span, thus a trolley slide trajectory of movement remains horizontal The height of the contact wire at temperature variations in semi-compensated vertical suspension changes still more: with identical lengths of a span semi-compensated vertical system the height varies 50% more as compared to SDACM system. To keep a constant height of the contact wire along the length of the span a semi-compensated suspension has specially modified design in support area, It is excluded in the compensated suspension due to application of compensating units, but such a suspension practically lose its wind resistance properties.

The calculations of SDACM proved that modification of suspension toughness along the length of a span depending on its length made in average 5 to 7%. Consequently for this parameter SDACM meets the existing requirements to the contact mains of high speed railway lines.

Thus automatic temperature compensation of suspension wire lengths separately in each span by SDACM does not deteriorate its dynamic features.

Length of anchoring sections


The concept of anchoring sections may be excluded as such, due to the fact that compensation of wire temperature elongation with SDACM system happens individually in each span and compensating units are not required. Suspension щау be mounted at a distance of any length with the help of just one anchor cite. Depending on power supply arrangement and sectioning in the areas of contact mains dmsion it is possible either to mount insulating junctions or insulating inserts, which to our opinion has better prospects
Vertical contact suspension is subdivided into anchor sections also for the purpose of limiting the areas of damages at breaking of wires. SDACM system application reduces several times the lengths of damaged sections, caused by breaking contact wires and carrier cables.


Simplicity of design


Absence of wires longitudinal shifts, provided with SDACM system makes completely unnecessary .all numerous devices and units compensating such shifts in vertical contact suspensions, among them rotary consoles and fixing units including all joint connections, intermediate anchoring blocks, compensating units with rollers,.-drums, brakes, loads and various mounting details, sliding strings etc. Thus the problem of servicing these units and blocks also disappears - no lubrication, no checking the rollers running, no load maintenance no regular inspection of these blocks and units.

Let's dwell on the strings alone. SDACM system does not require any strings at all, while in the vertical suspension attention is focused on them. Scores of string clamps designs have been already developed with a lot of non-ferrous metals and high quality steel consumed for there manufacturing. So many troubles and so much time for vertical suspension regulation has been spent. At least at the domestic lines unwinding of pasted bolts and nuts of string clamps is a very painstaking and time consuming process.

Railways in European countries practically have never used bolted connections of ferrous metals in the contact mains, but the scope of adjustment work has not reduced because of that. In a number of countries bolted connections of ferrous metals are widely used at the contact mains of thousands kilometers long.


 SDACM system has eliminated all that. The fixing element consists of a fixing clamp , short bar and regulating link, providing for accurate alignment of contact wires with respect of the track axis. Alignment is performed only once during mounting with no further regulations, which is proved by 20 years of observations of SDACM system in operation.


SDACM system response to wind loads


 Much efforts has been taken to design vertical contact suspensions capable to withstand the wind loads. There is quite a number of alternative designs wTell known in the field. They give positive results only for the winds of moderate speed. Vertical suspensions are not operable at the wind speeds above 25 m/s which is not something rarely happening in some areas.

SDACM system has been mounted in Novorossiisk region as the only possible alternative as far as the wind speed there reaches 40 m/s. Novorossisk is known not for the strong winds but for the wind storms as well. One of the wind storms has thrown vessels to the shore, rained houses, broken all the air communication lines, but SDACM system has remained in operable condition. The reason behind is high wind force resistance inherent to SDACM system as the wires go practically in horizontal plane as opposed to vertical plane in all other conventional contact mains.

Built structures as an application field for SDACMsystems


 SDACM system modification for built structures has small vertical dimension (from fixing point to the vault), which if necessary may be as small as 200 mm (insulation inclusive). Suspension provides for dynamic response for rather high speeds of movement. We checked deflection of suspension caused by several trolleys in tunnels with there limited space from the wires to the vault with minimal permissible clearance. The most complicated operating conditions were reproduced when two locomotives together had all four trolleys lifted with maximum pressure of each trolley. Under these extreme condition the wires of suspension have remained within tolerance limits.


Affected area

Affected area means the length of a damaged section of contact suspension in case of breaking contact wires or carrier cables in various combinations. In vertical suspension systems when a contact wire breaks (when a trolley is burnt or broken) the affected area is equal to half of the anchorage section - from intermediate anchorage to compensating blocks. Major damage occurs in several spans, but at repairs as a rale it is necessary to make adjustment of suspension at several hundred meters lengths.

Should a carrier cable break the scope of damage is incomparably bigger. True, this happens rather rare, at major breakdowns.

With SDACM system applied the affected area reduces several times as the system carrier cables are rigidly fixed at each support and the contact wires are attached to the carrier cables in several points of the span with sufficiently reliable fixing elements.

Special destructive tests showed the following results: when one contact wire is broken the affected area is limited to the length of one rhombus formed by the contact wires in a span. Such length makes 15 - 18 m. After joining the contact wire no additional adjustment is needed. The same scope of restoration will do at breaking of two contact wires. Even in case of carrier cable damage the scope of work is limited to one span.

Operational experience

It is not by chance that vertical system connections between the contact wires and carrier cables are called strings. Just like strings of a musical instrument they need permanent tuning. There are no such connections in SDACM system. The same is true for joint connections. Fixing elements are being mounted and adjusted at assembly and later, for many years of operation, as proved by experience, do not require any suspension adjustment.

Inspection is mainly limited to checking the state of insulators. Special check ups of the contact wire are also done, just like with any other type of suspension. It was revealed that after several years of operation the contact wires had a uniform wear at the section with heavy traffic (130 locomotives and over daily at commuter trains line) with several working trolleys on each locomotive.

For 20 years of operation experience of SDACM system application under various climatic and operational conditions has been accumulated. Operability and reliability of suspension has been proved at the heavy wind regions and in the mountains where tracks have small curve radii (400 m). Suspension had a stable operation even with smaller radii of curves.

The first section of SDACM system was assembled at the Moscow Railway in 1982. In spite of heavy traffic there no adjustments of the contact suspension were made for the whole period of life time. At electrification of bigger test range wit application of SDACM system operational expenses will be considerably minimized as compared to conventional suspension. Servicing technology includes inspections and overhauls.

A considerable experience is gained in the field of introduction and many years operation of SDACM system in the tunnels (See Fig. 3), There the suspension is much superior to others in reliability required dimensions, absence of junctions.

The latter helps to minimize construction works at making a tunnel, when SDACM system is applied. With any other type of suspension special pockets shall be made to house compensation units. As already mentioned any length of a tunnel is passed by SDACM system with one anchor section. This helps to economize money at construction on one hand, and to avoid junctions of anchor sections difficult for trolleys sliding. The first tunnel electrified in 1986 with application of SDACM system was Megradzora tunnel in the Caucasus , it is 6 km long, situated at the mountain pass, and having considerable track gradients. Double traction was used previously for passing through the tunnel. After mounting SDACM system for several years no claims have been filed.

Icing of the vaults and at the points of insulators fixing in winter happens in some tunnels. This is a feature of some regions in Russia and elsewhere. Icicles above the axis of the track in places of carrier cables attachment cause a lot of problems for the operators of vertical suspensions. SDACM system with its insulators at the side away from the axis of the track eliminates the chance of icicle formation in the area of trolley movement.

Electrification of tunnels through Severomuisk mountain range in Siberian Baikal-Amur Mainline (BAM) deserves special mentioning. Electrification projects were jointly developed by Sibgiprotrans and Russian State Open Technological University of Communications. The first bypass tunnel was electrified in 1989. The tunnel has 300 m radius curves and 18% gradient and is situated in a seismically hazardous area, it is permanently «shaken». All these conditions impose additional demands to contact mains design. It's difficult to imagine any other type of suspension but SDACM system that could provide for an adequate current collection in such a tunnel Special contact mains with firm buses could a way out, but in a seismic zone it could hardly provide for proper current collection. So it was decided to apply special purpose modification of SDACM system, which could afford laying the wires in small radii curves, minimize vertical dimensions with consideration of rails elevation in the curves. SDACM system is still in good operating condition there under most severe climatic conditions.

Another tunnel with application of SDACM system was the longest one in Russia Severomuisk tunnel 15 km long. It is situated at a straight section of the same seismically hazardous region. The tunnel has one anchor pass. It is remark able that neither mounting nor adjustment of SDACM system caused any specific problems. Absence of need for pockets that would have been otherwise required for anchoring of vertical contact suspension wires has decreased the amount of rock working by several hundreds of cubic meters.

SDACM system provides for high reliability of locomotive power supply in the area. Adjustment, inspection and revisions, which may be carried out in the tunnel, when the movement is stopped in the tunnel, and artificial lighting is provided, which is not simple, are practically not required. Operational experience of SDACM system application gives grounds to say that technical servicing of the system will be limited to replacement of worn contact wires.

Presently SDACM system besides the above mentioned places, is mounted at the legs and of a number of railways a s well as at a station at rigid crossbars. (See Fig. 4). It is well supported on rigid crossbars, which are often applied at the legs abroad.

Interfaces between SDACM system and existing vertical chain suspensions are developed, trolleys in such connections operate like on ordinary joints.

Various modifications of SDACM system take into account many variations of operation such as vertical and horizontal dimensions, lengths of spans, different mounting and support structures.
Successful design and preparatory work has been performed for utilization of SDACM system at the complicated mountain sections at the South of China, but the work had to be suspended for the lack of financing.

Thus the experience in designing and operation of SDACM system makes it possible to draw a conclusion that the suspension is ready for application under any conditions.

Fig. 1 (page 32) Spatial double-wedge contact mains
Fig, 2 (page 33) Fixing of carrier cables and contact wires of SDACM system at the DC current contact mains support
1-carrier cables-contact wire, 3-reinfor cement wire
Fig. 3 (page 34) Location of SDACM system wiring in tunnel
Fig. 4 (page 35) Location of SDACM system wiring at the rigid crossbar

T. Demchenko


D-r of Technological Science
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