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Powering railby Baset Asaba on Jul 28, 2016
Widespread traffic congestion and concerns over carbon emissions are causing many countries in the GCC to reassess their transportation policies and turn increasingly to commuter rail.
Rapid urbanisation and population growth have given rise to mega metro projects in countries such as United Arab Emirates, Qatar and Saudi Arabia, while other regional governments are right on track to rolling out their own rail projects.
It is an emerging trend that denotes immense opportunities for companies involved in power infrastructure, especially that most of the urban rail projects currently underway in the GCC are designed to run entirely on electricity, right from rolling stocks, metro stations to the centralised control rooms.
Commuter and freight rail projects worth over $350bn are currently ongoing within the Middle East and North African region, according to figures from Terrapin Middle East.
“Rail construction is unlocking prospects in key areas such as traction power supply, propulsion system, communication as well as protection and control systems as regional governments lean more towards modern rail infrastructures,” says Samir Fadda, head of rail, Asia, Middle East and Africa at ABB.
“The expansion of rail networks in the region is already creating an upsurge in power generation to address demand gaps created by the resultant increase in power consumption levels.”
The market for substations in the Middle East is set to register positive growth over the coming years despite uncertain economic conditions, with current and future rail projects in the region expected to be an indispensable contributor to market growth.
ABB and Siemens currently rank among the largest suppliers of substations for rail projects in the GCC with running contracts in UAE, Qatar and Saudi Arabia where governments have allocated huge budgets for rail electrification.
Fadda says that to address the needs of the rail industry, ABB has had to customise its substations to enable the necessary power requirements and also tailor them to the peculiar needs of the GCC region.
“Due to recent changes in social forces, there is a growing need for railway substation systems that are more environmentally friendly, more compact, more efficient and easier to maintain,” says Fadda.
“To address this need, we now see companies developing environmental transformers, switching equipment and rectifiers, as well as protection controllers with enhanced maintainability.”
Fadda says that ABB was responsible for designing and installing Substation Control and Monitoring Systems (SCMS) for three 132/33kV gas- insulated switchgear substations for the Dubai Metro. Two substations supply power to all red line stations, while the third substation supplies power to the entire green line.
ABB has also supplied main distribution panels responsible for the primary power distribution to the low-voltage network, which feeds the power distribution, lighting and HVAC (heating, ventilation, air-conditioning) systems within each metro station.
The Dubai Metro is the first driverless, fully automated rail network in the Middle East whose inauguration in 2009 has inspired several countries in the region to either build new urban commuter trains or electrify their existing rail infrastructure.
At Saudi Arabia’s King Saud University’s rapid transit system, ABB’s scope included the design, engineering, testing, commissioning and installation of three DC traction substations including transformers, rectifiers, uninterruptible power supply systems, switchgears, and low-voltage equipment. ABB also supplied the SCADA control and monitoring system for the RTP system.
For the Haramain high-speed railroad also in Saudi Arabia, ABB will design, supply, install and commission two identical static var compensators (SVCs) so that the power grid remains stable when the HHR service is in operation. Also to power the high-speed trains ABB will supply 72 traction transformer sets and two spares as well as 72 battery chargers to the Spanish train manufacturer Talgo for the Saudi Railways Organization (SRO).
“Electrification projects are really change projects,” says Fadda. “When you electrify a railway, you completely change the service – trains travel faster, carry more passengers and accelerate and brake quicker, so journey times are reduced. That radically changes the way the railway is used by passengers and freight operators.”
Urban massive transportation systems (UMTS), like metro, tramway, light train; requires the supply of electric power with high standards of reliability. An important step in the development of these transportation systems is the electric power supply system planning and design.
Typically, the trains of a UMTS require a DC power supply by means of rectifier AC/DC substations, known as traction substations (TS); that are connected to the electric HV/MV distribution system of a city. The DC system feeds catenaries of tramways or the third rail of metros, for example. The DC voltage is selected according to the system taking into account power demand and length of the railway’s lines. Typically, a 600 Vdc – 750 Vdc is used in tramways; while 1500 Vdc is used in a metro system. Some interurban-urban systems use a 3000 Vdc supply to the trains.
Railway electrification presents a number of tough engineering challenges. Schemes must be energy-efficient and compatible with new trains being procured. At the same time, electrification must comply with an array of rigorous regional and global standards governing everything from safety to on-train energy metering.
Engineers always have to make sure new high-voltage traction supplies will not interfere with critical systems such as signalling and communications. There is also the need to ensure the installation, testing, commissioning and entry into service of the electrification infrastructure, and that electric trains are all delivered with minimum disruption. Upgrades are required to fit within strict operational schedules.
“The first steps include calculating how much electrical energy will be required, identifying where to tap into the National Grid and working out the best locations for transformers, vital if energy losses are to be minimised. Engineers also need to understand how different elements of the overall system – such as timetabling, power supplies and signalling – interact with each other,” says Fadda.
To help deliver these insights, ABB teams have had to work with a number of simulation and modelling tools that allow electrical engineers to delve deep into the physics of electrification to optimise the efficiency and safety of the power system. These tools also allow both train and infrastructure operators to explore scenarios: what happens if you increase the speed and weight of trains? Add a new station? Alter the signalling?
The ability to answer questions like these is important because the power requirements of a railway are enormous. A single freight train, for example, pulls up to 5MW, enough to light up a small town. Even subtle changes, such as altering the position of a signal, can affect the size of the load hitting the grid. Simulation tools not only analyse the impacts of changes, they also help operators to optimise energy consumption, a key element of carbon critical design.
“Simulations tools bring together the best bits that exist in the marketplace and add our own ideas,” says Fadda. “It is now our standard tool.”
But aside the requirement for simulations, modern traction systems present demanding challenges to power grids. Trains taking power from the catenary require stable supply voltages. Voltage and current imbalances need to be confined in magnitude and prevented from spreading throughout the grid, while voltage fluctuations and harmonics need to be controlled and kept within stipulated limits.
Power grids that feed railway systems and rail traction loads benefit enormously from flexible AC transmission system (FACTS) technologies like static var compensators (SVC) and the more recent SVC Light, also known as STATCOM – static synchronous compensator.
“These are technologies pioneered by ABB and provide an extensive range of benefits for rail systems and power grids, including dynamically balancing non-symmetrical loads, mitigating voltage fluctuations, eliminating harmonics, and providing power factor correction and dynamic voltage support,” says Fadda.
Fadda explains that there are two main applications for substations in railways, the first being on high speed, long distance, commuter trains with AC Electrification (15/25kV on catenary. The difference compared with utility substations are mainly the effects of this single phase of the catenary to the system and equipment, compared with 3 phase for utility substations. Secondly, the MV side has an own IEC standards for equipment and systems, meaning special railway type tested equipment need to be used. Thirdly, the unsymmetrical load due can cause voltage unbalance on the HV grid which need to managed by passive or active load balancing measures.
The second application is on metro, tram, trolleybus with DC Electrification (750VDC, 1.5kVDC, 3kVDC on third rail/catenary). In this application, the passenger stations are powered on LV by auxiliary substations and the traction loads are powered by rectifier substation converting the 3-phase MV to DC with the help of MV SWG, rectifier-groups, and LV DC SWG with High Speed circuit breakers. Particularities for the traction feeding system are the overload capabilities of up to 300% of nominal current, all the aspects of DC current to the equipment and environment and the specific standard which are applying.
However, with the increase in the region’s rail electrification, there is widespread concern on whether power generation capacities will increase fast enough to sustain demand from current and future projects.
For example, for the proposed Abu Dhabi Metro, trains would be spaced by approximately 1.3 km apart in each direction with a total power consumption of 135 MW or 4200kw for each train. Yet the maximum power of a 1500 V dc substation is about 12 MW (2 x 6 MW), and therefore thirteen or fourteen substations each rated at 12 MW would be required.
This would give a substation spacing of less than 2 km. This power requirement could be reduced by about 20 % if regenerative braking was installed, as proposed.
Based on available information, it would take one trainset 104 minutes to complete one lap, meaning that to provide a service every 2 minutes in each direction, 104 trains will be required, excluding any out of service. These trains would be spaced by approximately 1.6 km with a total power consumption of 437 MW or 4200kw for each train. With the maximum power of a 1500 V dc substation at about 12 MW (2 x 6 MW), nearly forty substations each rated at 12 MW would be required. This would amount to a total power requirement of 572 MW, or 460 MW with regenerative braking.
“The high dependence on power calls for innovations that are geared towards energy efficiency to lessen the amount of power consumed. It is a trend that most industry players are taking today in order to retain clients and also win over new ones,” says Fadda.
“Cost reduction can also be attained through proper equipment management and maintenance especially in this part of the world that is known for harsh environmental conditions.”
The future of substations for rail will be driven by efficiency, automation, reliability and high availability to guarantee the seamless flow of rolling stocks and uninterrupted operations at each rail stations, says Fadda.
To enable energy efficiency, ABB for examples currently offers ENVILINE DC wayside traction power solutions comprising ENVILINE ESS (energy storage system) and the ERS (energy recuperation system).
ABB’s DC traction substations with energy storage capabilities allow energy to be recovered from braking trains, which would otherwise be dissipated as heat through braking resistors. Storing this energy on the wayside is one way to prevent this energy waste.
Whenever a train brakes, energy is returned to the traction line, but with an ENVILINETM Energy Storage System (ESS), this energy can be saved and re-used for acceleration. ESS is a wayside energy management system that stores and returns the braking energy, which lowers energy costs, reduces peak power demand and penalties, stabilises the voltage for better acceleration, and provides emergency traction power.
Fadda also points out another avenue designed by ABB through an energy recuperation system, which feeds the recovered energy back into the AC grid. ABB’s modular energy recuperation and wayside storage systems are available for standardised traction voltages of 750 V and 1,500 V and can be used in existing and new urban transport systems as well as suburban and mainline railways.
He says that these solutions can increase efficiency by up to 30%, which has led to an increase in the deployment of ENVILINE’s systems.
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