The precept of light rail development is the current trend of modern transport systems that has been embraced in almost all the developed cities in the world. The first system of the kind was invented in 1985 in France. Many variables such as political, economical, security and efficacy have been viewed as underlying factors that have propelled for the incorporate of this modern transit infrastructure. The metro supported light rails have been considered advantageous over the conventional rail as they are easily constructed. The metro buses running on the light rails are relatively smooth, safe and swift in terms of controlling.
This is particularly evident for their interior urban center penetration. This model of transport is actually the greatest success that is so reliable in providing services to most populated cities. William. M (1998) This technology revolves around steel wheels that are grooved to locomote on steel rails while tapping power current by either the third rail or overhead wire. However, overhead wires have not been our preference in Riyadh since they tend to be amorphous in design, and cannot operate in a densely populated city background.
The third rail on the other hand demonstrates versatility by its capacity to operate in densely built surroundings. To facilitate consistence in terms of power supply, the need for constructing substations at reasonable intervals is necessary. The metro operating within a city could use direct current (DC) which requires an impeccable back-up that is feed from the substations. Light rails essentially cover a wide spectrum that is currently serving the transport sector, it boosts with over 350 systems world wide.
The imperatives connote the fact that the new technology is a fundamental leap into the future as far as the transport fraternity is concern. Sakae M (1990) Introduction In our contemporary society electrical and civil engineering has not been left behind by the enormous wave of technological advancements. Light rail systems that support metro buses are being deployed to facilitate rapid transit with minimal frequency in comparison with the heavier mass rapid systems. In this paper we consider designing metro shuttle in Riyadh as an alternative mode of transport.
The paper however, is biased, investigating the power supply, types of rails used and how the metro is controlled. Metro transport systems are powered by light rail systems, a modern variation of transport where trains run separately from the road traffic. On this kind of a system stopovers are normally less and boarding is done over a platform. Sakae M (1990) Types of Rails Light rail systems are the most appropriate architectures suitable for the Riyadh metro service. Light rail infrastructure offers a high platform that is fully separated from roads and pedestrians. This makes the system more convenient in the transport sector.
Many light rail systems should be designed in an embedded way with both on road and off-road sections. William. M (1998) The modest variation of light rails is the dominant form of urban rail development that should be incorporated in Riyadh. By borrowing a leaflet on systems such as the Air Train JFK of New York, we can adopt a driver guided Metro in Riyadh, that is supported by light rails; developed to offer cost effective and easy deployment infrastructure that hinges on modern technology that embraces materials that dramatically reduce the weight of the metro shuttle.
Sakae M (1990) Power sources Overhead lines have been around for quite sometime, they have been supplying electricity to most light rails. This has been embraced ideally based on safety condition unlike the third rail, which endangers passengers that would accidentally step on an electrified third rail. The metro shuttle requires a light rail that is powered by an electric power supply that is accessible full time. However certain variables are considered in determining the viability of the power supply in terms of safety measures and user friendliness. William. M (1998)
Power is supplied in either DC (direct current) or AC (alternating current). Alternating current has been the modest preference since it’s best applicable during long distances and cheaper to integrate. In the case of Riyadh an extra third rail is the most appropriate for supplying power to the metro, since the overhead source is very expensive and is most appropriate in long distances and hence not the medium to implement in Riyadh. William. M (1998) Electric Traction Electric traction is a technology that was invented decades of years ago; however 20 years has witnessed a dramatic evolution of in railway traction development.
This has evolved concurrently with the development of power electronics and microprocessors; this rate of evolution has out-run the conventional rail interims of design and functionality; AC or DC traction. William. M (1998) Both the AC and Dc motors are applicable and can work with an AC or DC supply. The correct control system is required between the source and the motor. AC can be used for long distances while DC could work for short distances; hence transmitting power through overhead lines with AC is much easier.
DC could be our preference in Riyadh to serve for short distances in the urban centre. Since the metro train is so light it requires less power which is powered by a heavy tramission system, a third rail or thick wire is reliable for carrying the power. To avoid the loss of voltage as distance widens between supply connectivity increases, substations are relevant if constructed at intervals of three to four kilometers. Sakae M (1990) The stations should support a 750 volt system. Iron dioxide should also be addressed as one the anathemas bedeviling the supply of power on the DC systems.
This reverts current to wallow away from the running metro into the grounds creating electrolysis with water pipes and other metallic. Power from the central control systems should govern the functions of cooling the passenger’s cabin and the opening and closing of doors including important diagnostic purposes. Third Rail The third rail taps power by the use of a shoe also known as the slipper by its originators. Third rails current designs are multifaceted; top contact is the simplest and is based on the rail where the shoe slides and also acts as a conduct point.
The undoing of the shoe is that it is exposed to anything that might get in contact with. It suffers during bad climatic conditions; the smallest amount of external contact can make the shoe not to function effectively. Sakae M (1990) Separation is effected by the use of wooden paddle between the shoe and the current rail and then trying the shoe up with a strap or rope. Modest systems have their shoes mounted to offer a stable contact via a lever action. Top contact systems have protected covers over them. Side and bottom offer a reliable contact through spring loading.
Sakae M (1990) It should also support completeness of the circuit, right from the energy source to the consuming object and back to the source, this prompts a necessity for the rail return mechanism. To better solve this anomaly steel rails are suitable for this. This also calls for advance precautious measure to prevent the voltage from getting to high above the zero of the ground. Signaling circuits can also be used although special precaution is needed. The circuit is completed by connecting the return to brushes rubbing on the axle ends. William. M (1998)
Most light railways use third rail and DC power, even where overhead lines would otherwise be practical, due to the high cost of retrofitting incurred when installing AC. Every expansion of such system must cope with the problem of compatibility. It usually leads for the choice of already existing technology. Sakae M (1990) Gaps Light rails should contain gaps where the substations feed the line, in most cases the metro should be fed towards the next station. This is important to enhance over supply and also in facilitating continuity in the event that one substation crushes.
The sub station should be labeled by an iconography or light which connotes the presence of current in the sections ahead. The metros are meant to alight before trading on inert territories. In the event where currents are short circuited, it is fundamental for the metro not to connect the inert territory to the live section by passing over the gap hence facilitating the completeness of the gap. To help contain this, complex systems should be integrated to act as a conduit between the traction current status and the signaling. This alters a metro from running over dead territory. Sakae M (1990)
At points where the metro is temporarily isolated from the electrical supply systems, terminal stations are therefore elementary in curtailing this anomaly. The section switches should cushion part of the line for being fed by the substation. This shields the metro from electrical malfunctioning. William. M (1998) A third rail is a strategy of supplying electricity to power a railway by means of constant firm conductor in between or long side the railway track. Many systems have designed an insulating cover above the third rail to protect any electro-cutting those working or moving nearby.
Third rail systems are cheaper to install than over head wires. They are also less prone to whether damages, and can nicely fit into region of reduced vertical clearance, such as tunnels and bridges. Signaling and Communication The system is controlled by numerous color light signals that are networked with the road traffic signals on the street. This features in metro signaling, which gives a driver a reminder of status of the immediate signals. This information clicks on the metro’s central system which relays the information to the central control room by bus links. With the less wiring requirement the reliability is even great.
This diagnostic circuit keeps the driver updated about the functionality of the metro’s engine. Backed up informational data aids in the maintenance aspects since it prompts cost effective and effective maintenances. Sakae M (1990) Bearing in mind the fact most metros convert ac public supply into dc for the feed of the railway traction power supply system. The third rail network should therefore absorb about 600-to-750V dc up through to 1. 5kV for overhead cautionary. Asynchronous ac motors should also be incorporated with complex systems that convert from AC to DC the back to DC. William.
M (1998) Electromagnetic interference which is a health hazard is such a critical issue with using ac traction power supply than for dc. There is lifespan of an electrical system has to be considered adequately. Owing to the fact that electrical systems life lies between 30 to 40 years, it’s therefore definite that it would take 30-40 years to convert the entire systems. Sakae M (1990) While separating electromagnetic and earthen issues Riyadh systems estimates the total cost saving operating an ac metro to range from between 20 and 30% mainly by having a cheaper power supply system.
But considering the high risks and the complexities of electromagnetic and earthing the costs are insufficient to offset. William. M (1998) Station Service Cubicle Section The station service cubicle includes a primary fused interrupter switch and a single phase dry type C transformer that is built on the ANSI specification. The transformer is mounted in the bottom rear of the compartment for easy access and maintenance. To prevent access into the energized equipment the access door is key interlocked with the fuse interrupter switch.
Substations are equipped with AC and DC distribution panel board. Sakae M (1990) Stray Current Monitoring Substations are equipped with systems that monitor stray currents. The negative switch found in the DC switchgear is a shunt and bolted link in series with the DC earth link conductor. Bolting the link in an enclosed position, the DC mat grounds the negative discharge through the diode. In this position, the DC mat acts as a current accumulator where most stray current flow through the shunt. The shunt relays to the chart recorder or voltmeter to monitor stray currents over time.
Emergency Shutdown For security reasons the substation contain emergency shutdown stations, where one button is coated with a stainless steel shutdown mechanism that is mounted on the outer wall and only accessible by key alone. The alternative button is readily available and situated inside the substation by the entrance door. The button trips and locks out the voltage breaker of the substation, transferring trip and locking out the DC breakers at the immediate substations, and thus avoiding the fault. William. M (1998)