Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
THE UTILISATION OF ELECTRIFICATION IN TUNNELS By Alan O‟Hara BEng (Honours) in Mechanical Engineering, University of Strathclyde, Scotland, UK Associate Member of the Institute of Mechanical Engineers Snowy Mountains Engineering Corporation (SMEC)
SUMMARY This paper broadly analyses the two main types of electrification currently used on heavy rail in Australia, in the context of its application in tunnels. More specifically, this paper compares the differences in adopting each of these systems. Furthermore, this paper also uses cost, design, construction and maintenance specifications from relevant projects, both past and present to offer a suitable system template for future projects. Subject to a more detailed study of the various types of electrification system, it is recommended that forthcoming tunnel projects with associated electrification, adopt the local system for practicality. A fixed conductor rail is only viable on lower speed lines. However, in lieu of Australia rolling out a higher speed system in the nature of Europe or China, alternate electrification systems should be considered for future works. OBJECTIVE The objective of this paper is to analyse current systems of electrification used in tunnels in Australia and around the world. PURPOSE The purpose of this paper is to determine practical and cost effective solutions for future electrification schemes applied within tunnels. INTRODUCTION Overhead electrification has been used in Australia as a means of powering rolling stock for nearly 100 years. W ith Australia currently experiencing a population surge in all major cities, there is an urgent need to upgrade suburban rail networks. The vast majority of these networks are saturated or close to saturation. Therefore, in the quest for more transit corridors for commuters, our state and federal governments have recognised the need to excavate more large scale tunnels, to bolster our networks. Projects are already earmarked or indeed underway such as the Brisbane Cross River Rail. As suburban routes are already electrified, there will have to be investigation into options and solutions for tunnels to be electrified. These can range from conventional overhead line equipment to a fixed conductor rail.
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
NOTATION AC - Alternating Current DC = Direct Current OHW - Overhead Wiring BT = Booster Transformer AT - Auto Transformer V = Volt kV - kiloVolt TSC = Track Sectioning Cabin FS = Feeder Station TBM = Tunnel Boring Machine PTFE – Polytetrafluoroethylene m – Metre mm – millimetre kN – kilonewton km/h – kilometres per hour AT – Auto Tensioned FT – Fixed Tensioned UK – United Kingdom Qld – Queensland VIC – Victoria NSW – New South W ales WA – Western Austrlia SA – South Australia DTEI – Department of Transport Energy & Infrastructure BW A – Balance W eight Anchor
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
1. RAIL TUNNELS AND ELECTRIFICATION
currently use differing overhead electrification systems and variants. For example, the Brisbane suburban network uses a 25,000 V alternating current (AC) Booster transformer system, based on the British Rail example, while Sydney uses a 1500V direct current (DC) system.
1.1 Historical Lessons: The United Kingdom There are a number of inherent engineering issues associated with historical tunnels in the United Kingdom. They were designed for the kinematic envelope of a steam train and not for an electric unit, complete with the pantograph and associated registration arms, brackets and fixings along with the necessary electrical clearance. Moreover, when initial electrification (and periodic maintenance) of these routes were taking place, it was found that the integrity of the fixings for the drop tubes (and registration arms) were very weak. In fact, construction crews often found that a number of bricks would „fall out‟ from the main structure. These bricks would have to be hurriedly packed and replaced in order to reopen a line to „live‟ traffic allowing passage of trains. Subsequently, it is now standard procedure to avoid modifying or replacing any of these „bridge attachments‟, unless absolutely imperative.
From state to state, train gauge does not only differ, but also the means of safely controlling train movements and electrically supplying rail vehicles, both for passenger transit and freight. The time to standardise our different rail systems has long since passed, as capital outlay to recreate one particular system countrywide would be astronomical. However, with the advent of a high speed route around Australia‟s perimeter, this system would undoubtedly be of the one variant. Speculatively, this would be based on a European or Asian high speed system with line speeds in the order of 350km/h. The reality of this system is that it would have to be competitive with airlines not only on price, but also on transit time. A recent study¹ showed the capital outlay to be in the order of $40 billion for the first proposed line from Sydney to Melbourne. Subsequent links would be to Brisbane, Adelaide and eventually Perth and completing the perimeter to Darwin.
Therefore, any new tunnel design, incorporating electrification will not only have to have a large enough envelope to accommodate the rolling stock and electrification equipment but also, the lining should be designed with cast-in-ferrule locations for registration attachments or at the very least a material which can accommodate fixings, without damaging the integrity of the structure.
The Eurostar from London to Paris, being a perfect case study, has now become so widely used that commercial airline carriers on the London to Paris route, are all but extinct. Put simply, the different types of Electrification systems utilised in Australia can be defined by the operating Voltages (see below).
1.2.1 Background: Electrification in Australia
o Overhead electrification has been utilised as a means of powering rolling stock for well over a century. This system was pioneered in central Europe, namely Austria, Switzerland and Germany. The United Kingdom was an early advocate of the system, employing electrification as a means of rebuilding the dense rail network throughout the country in the aftermath of the Second W orld War.
o o o o
Australia derived its electrification systems from European examples. Australian cities
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QLD – 25kV AC (Suburban) & 50kV AC (coal haulage in central Qld and „Mainline‟) & 750V DC (light rail) for the Gold Coast Rapid Transit NSW – 1500V DC (suburban and intercity passenger services) VIC – 1500V DC (suburban) & 600V DC (trams) WA – 25kV BT (suburban) SA – 25kV BT (suburban) and 600V DC (light rail)
Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
However, as the system voltage differs from state to state, so does the associated infrastructure and components. For example, in Perth, pre-stressed concrete masts are used to support the cantilevers and thus conductors, whereas in Brisbane galvanised steel universal columns are preferred. Whilst the design principles may be the same, differences include underground or aerial feeder routes, coming from the substation to tap on to the overhead electrification system itself.
(“System 2”) consisting of two hard drawn copper conductor cables to supply the necessary power to the trains to maintain operations in busy electrical sections. In other areas, one larger contact conductor is used (193mm² with a 270mm² catenary). As such, all fixtures and fittings have to be more robust to accept the higher loading and the mast foundations deeper. This, along with the extra capital outlay costs for more regular substations mean that 25kV AC BT is now considered the standard international option for a basic rail electrification system. The differences between an auto transformer (AT) system and a booster transformer (BT) system are shown in pictures 1 and 2.
In Electrification terms, there are two basic systems in use in Australia: the 25kV AC system and the 1500V DC system. Both have their own characteristics, but are based on the same principles. The DC system is seen in some quarters as archaic and outdated for reasons such as the requirement for higher proportion of substations than the higher voltage AC system. Furthermore, with the nature of DC, there are also stray current issues with lineside equipment and the equipment necessary to carry the required load from the passage of trains. It is also much more expensive by approximately 25%-33%. In Sydney, conductors have to be substantially larger: a twin-contact‟ system (2x137mm² with a 270mm² catenary) is used as standard
Typically, an AT system requires less transformers and is more suited to an electrification system covering a large geographic area, such as the coalfields of Central Queensland. Suburban systems adopt the more common BT system. In essence, an AT system carries a supplementary feeder wire (at 25kV) attached to the associated structures.
Figure 1: Auto Transformer system
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
Figure 2: Booster Transformer system
The existing surface congestion and population surges in Australian major cities are driving a need for new transport routes to be explored and developed beneath city streets. As all major cities now have electrification schemes in place, most recently Adelaide, the methods by which we power trains through subterranean tunnels, has never been more relevant.
Table 1: Comparison of Electrical Clearance System type
Electrical Clearance (mm) 25kV AC (e.g. Qld, 270 Perth, Adelaide, Auckland) 1500V DC (e.g. NSW, 150 Melbourne, Wellington)
The Department of Transport, Energy and Infrastructure (DTEI), in Adelaide, has selected a 25kV BT system to electrify its city suburban network. This is the system used in both the Brisbane and Perth suburban networks and more recently in the Auckland suburban electrification project. The 25kV AC system is now the universal system applied to new standard electrification projects in Australia and New Zealand. However, there are more efficient and advanced systems being used, particularly in Europe, which are arguably better suited to be applied to our new electrification schemes. 1.2.2
Therefore, there is a reduced clearance with the 1500V DC system, and as such a smaller tunnel diameter required to install an electrification system. However, with a DC system as opposed to an AC system, there are increased issues with „stray currents and electrolysis which introduce detrimental long term effects on the surrounding infrastructure. These need to be carefully addressed in any design of a DC electrification system, especially one that is to be deployed in a tunnel which will undoubtedly carry a number of other services.
Electrical Clearance
1.3
In the installation of a tunnel utilising electrification, the defining factor is electrical clearance. A specific value of electrical clearance has to be maintained between the „live parts of the overhead system and the surrounding infrastructure. By its nature, the 25kV AC and 1500V DC systems differ in terms of the required electrical clearance:
Permanent Way
In tunnels, the standard system of supporting the track is by ballast formation. However, with the onus very much on the space requirement within a tunnel, a slabtrack system is used. That is a continuous concrete base which the track is clipped into. This reduces track movement, which is a necessity as the clearances to the walls are usually at a
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels normally applied in Australia for constructing tunnels in an urban environment are: cut and cover, tunnel boring machine, and mechanical mining. Other methods such as drill and blast and immersed tube may also be applied for specific applications.
minimum. As such, there is little deviation in the relative position of the overhead contact wire in relation to the pantograph of the rolling stock. Note, that on open (ballasted) track, there can be large deviations in the superelevated position of the contact wire, from the design and installation setting. This is usually a result of engineering machines performing routine maintenance, such as tampers. Any movement in the track position can have a three to five-fold effect on the relative position of the contact wire, depending on the track gauge. In tunnels, although the exact position of the contact wire at design is absolutely critical not only for its dynamic interaction with the pantograph and power supply to the rolling stock, as well as maintaining electrical and mechanical clearances to surrounding infrastructure, but once defined this is usually set. 1.4
Cut and cover construction is often used at the transitions between surface rail and underground, or where land area can be temporarily occupied to enable construction and subsequently rehabilitated or built over. Various construction methods and sequences are applied to ultimately form a box profile, which forms the shell of the permanent way (for example, the „Stratford box‟ on the Eurostar route, which houses both a station and a stabling facility). The space available within the structure depends on the physical constraints of the construction profile. Usually the construction costs are not excessively dominated by space within the tunnel and therefore adequate space is usually available for tunnel fit-out and overhead electrification.
Power Supply
With electric rolling stock, there is a need to supply power to the vehicles. This is inevitably drawn from substations. For safety, space and maintenance requirements, these are usually located above ground. On design of an electrification system, a power study has to be carried out to determine the loading requirements of the system, based on the operating voltage and the operational requirements of the route.
Tunnel boring machines (TBMs) are one of the exciting developments of the tunnelling industry in the last couple of decades. The most famous examples of TBM driven tunnels include the Gotthard Base Tunnel beneath the Alps in Switzerland and the Channel Tunnel (Eurotunnel) beneath the English Channel. TBM‟s comprise a large drill, operated by internal machinery to mine the ground at the front and leave behind a supported opening as the machine advances. An „Archimedes screw is used to remove the spoil before pre-cast sections of concrete are inserted, bolted together to form the tunnel support and lining.
When we look at a DC versus an AC system in this respect, we realise that the DC system requires a more regular feed of electricity from the provider. Grossly, a DC system requires a substation 4 times as frequently (every 2/3kms for DC system opposed to an AC system every 8km). This means that for extended tunnels, such as the forthcoming North W est Rail Link , in Sydney which has a tunnel section of 14.5km), have to be carefully designed with locations of these substations in mind and the associated feeding arrangements through the length of the tunnel. 1.5 Tunnelling Types and Techniques
TBM’s exist in various configurations suited to different ground types and lining requirements. Rail tunnels generally require structural linings even in rock conditions, to ensure groundwater infiltration is controlled. Often the most efficient application of TBM technology of the TBM drive is largely dependent on the tunnel diameter meaning space within the profile must be optimised and the minimum possible clearance provided above and below the rolling stock profile.
Governments are developing plans for underground rail expansion in Australia‟s largest population centres of Sydney, Melbourne, Brisbane and Perth. The
three
main
contemporary
methods
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
Figure 3: Tunnel Boring Machine (typical example)
Cross River rail, with new urban development planned in Bowen Hills and Wolloongabba, not only as transport hubs, but with shopping precincts and residential apartments, in the airspace above and surrounds. Such developments have been highly successful in South East Asia, not only for the end users but for the owners and operators as further revenue boosting programmes.
Mechanical mining of tunnels is best suited to rock conditions such as Sydney‟sandstone and Brisbane‟s Tuff where the ground can be mined by roadheaders and are relatively easily stabilised. With this method, a suitable mobile plant (roadheader or excavator) excavates the ground and the tunnel advance is temporarily supported by means such as rockbolts and shotcrete prior to construction of a permanent concrete lining. This method when applied in rock, allows for an adaptable cross section and therefore can be created to suit the clearance required by the rail and services. Mechanical mining in soft ground requires greater constructive effort and more strict profile control relative to the rock process described above.
In terms of current and future projects, small scale tunnels (such as South W est Rail Link, Hume Highway “tunnel”, which is 80 metres long) are being built by traditional methods of excavation and concrete lining. The need for a TBM is not financially viable unless a longer drive is required (greater than a kilometre). The TBM method was pioneered in Germany by Herrenkrecht. This technique has been used most recently and locally on Airport Link and the Clem (Jones) 7 tunnel which provides a tunnel for road vehicles from
The proposed tunnels are not only being designed as being passenger transit corridors, but the surface locations are being visualised as satellite urban centres of the greater city. This is displayed in the proposal for Brisbane
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
Woolloongabba, in the south to Bowen Hills, in the north, has drastically reduced cross-city journey times. This method will again be deployed for portions of the North W est Rail Link in Sydney, along with sections of cut and cover.
Bridge. Merivale Bridge is a twin track bridge and is forecast to reach maximum capacity by 2016. To increase capacity to the south, which includes the Gold Coast Lines a new river crossing is required. Along with the Albert Bridge, there is the W illiam Jolly, the Victoria and the Good Will bridges (both road only). There is no physical space available to introduce a new surface bridge spanning the Brisbane River. Therefore, there is a need to develop a new subterranean tunnel route through the city². The proposal is for a tunnel portal on the north side in the Bowen Hills area and on the south side at the existing Yeerongpilly railway station. This project was due to commence in early 2012, but with the reparations required after the devastation of the January 2011 floods, this has been delayed for two years.
2 THE REQUIREMENT: POTENTIAL RAIL TUNNELS IN AUSTRALIA 2.1
The Here and Now
Brisbane is currently undergoing the biggest immigration in the states history. In the last 30 years it has transformed from a city of provincial-like dwelling to a city on a par with most worldwide capitals. As such, the rail network which was designed a hundred years ago is currently undergoing rapid expansions. For example there are new routes, such as the Springfield and Gold Coast lines and proposed branches such as the Moreton Bay Rail Link (MBRL), in the pipeline. The Brisbane River cuts through the city centre. As such, for trains to travel south from the city, they currently pass over the Merivale
Figure 4: Twin TBM Tunnels with Electrification, connected by cross-passage (typical example for Cross River rail)
3 OPTIONS: EXISITNG WIRING EQUIPMENT
OVERHEAD
copper contact wire supported by a copper catenary wire and suspended by intermittent droppers. The tension in this system is regulated by a set of weights (BW A) at either end of the „tension length, which regulate by fluctuations in temperature. Tensions can vary
In general mechanical terms, the standard catenary/contact system deployed in Australia comprises a simple regulated type A
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Alan O’Hara SMEC
The Utilisation of Electrification in Tunnels
from 11kN to 30kN depending on the conductor size and system type. A fixed system (FT) is sometimes used in yard or lower speed areas. A few areas of fixed equipment still exist on the mainlines, however these are being upgraded to regulated systems. Fixed equipment systems do not perform well in higher speed areas or in extremes of temperature. However, most new designs use a regulated system. Moreover this overhead system is supported by a structure approximately every 50m. A tension length is usually between 1200m – 1600m and the contact wire is „staggered‟ at every registration location, to give an even wear of the carbon over the pantograph. The average stagger is usually 230mm – 250mm, either side of the superelevated centreline of the track. In a tunnel, where the ambient temperature is fairly
static, longer wire runs or tension lengths will be achievable. However, with limitations on movement and uplift of the wires, more regular supports will be required. In tunnel designs, a „registration‟ will be required approximately every 25m. The vertical separation or system height is nominally between 600mm-1600mm. Therefore, in a tunnel situation, with electrification, there is a need for a much larger tunnel diameter, when you include not only the conductors, but also the mechanical and electrical clearance for the equipment. Thus there is a need for reduced separation (Encumbrance) equipment, reducing the vertical separation (
