The president will have massive problems while trying to electrify the SGR
Cosmas Ronno
Tue 25th Apr 2017 10:54:34am
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The Standard Gauge Railway
After the disappointing news that Kenya's SGR is not going to support high speed rail the government has moved with speed to put in place plans to electrify the Mombasa-Nairobi line.
What is a high speed rail and what are the requirements for its operation? The International Union of Railways (IUC) defines high-speed rail as that capable of 250 km/h or more. To get a train to move at these speeds safely and efficiently is a technological challenge that has been developed, improved and continues to be perfected for close to 110 years now. High-speed rail must be powered by reliable electricity supply if high speeds have to be achieved. In general electric trains can be powered by direct current (DC) ranging from 750 to 3000 volts (V) or alternating current (AC) starting from 15000 to 25000 volts (i.e. 15 kV to 25 kV) and even higher.
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For the Mombasa-Nairobi SGR 25 kV supply would be ideal. Unlike diesel or steam locomotives electric locomotives have better traction (ability to make wheels roll rather than slide on the rails) hence better efficiency in power use. Supplying 25 kV electrical power to a rail network is a complex process requiring a set of separate sophisticated systems.
First there is an overhead supply system that delivers the 25 kV from a special transformer to a single hanging wire called a catenary (from Latin for chain) that acts as a 'live' wire. The return wire (earth) is the steel rail tracks. The catenary is supported by steel pylons spaced every 50 meters or so and is wired in a zigzag manner from pylon to pylon. Because the locomotive draws huge amounts of energy recharge substations are located every 20 km or so. This is because power supply decreases with distance from a recharge station due to loses caused by lengthy wires.
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The locomotive accesses this overhead electricity through a fold-able protruding device known as a pantograph. Contact between pantograph and catenary is made by a graphite rod (like that in a pencil) which is a good conductor of electricity and is also soft and smooth. The catenary moves in a zigzag manner so that the graphite rod is rubbed uniformly, to avoid formation of grooves that would cause sparking and loss of power to the locomotive.
The pantograph delivers the 25 kV power onto a transformer within the locomotive which steps down the voltages and supplies various power requirements to the whole train. The biggest consumers of power are the motors that drive the wheels of the locomotive. Power is also supplied to fans, lights, electronic controls, cooking ranges (yes, food is prepared on a train!) and so forth.
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High-speed trains also have auxiliary or standby diesel powered generators for emergencies at least to keep lights and other systems going on the rare occasion that overhead power fails. Some low speed or short distance electric trains and trams do not require overhead power but are fitted with diesel generators that supply electricity for traction.
Because of the very high voltages involved safety is the number priority of electrified rail systems. Even on low voltage (750 V DC) rail system safety is a big issue since a DC powered train can draw as much as 7000 amperes (A) of current. This is an incredibly large and dangerous current. Your average iron box draws 5 A at 250 V AC while a cooker with oven, grill and 4 plates all turned on draws a mere 30 A. Electrical materials used on these trains must therefor be of the very highest standards with respect to quality, reliability and robustness.
These quality standards must be applied right from the boarding platform, the actual rail line, the overhead power supply and throughout the entire train from the drivers cabin, the passenger section and the utility sections such as washing rooms, dining cabins etc. Electrical safety will be a challenge also in tunnels and overpasses where chances of trespassers being electrocuted is very high. And to prevent theft and pilferage the whole route may have to be fenced in with impenetrable barriers.
For smooth operation of a multi-train network signaling must be synchronized down to the nearest second and above all the overhead power supply must be 100% reliant. Power supply reliability is a product of dedication and work ethic on the part of personnel, and investment in quality technology on the part of government. These are two ingredients that have always been absent on the Kenyan scene. It cannot be achieved in a climate where politicians award themselves tenders while the general citizenry is only too happy to drain off transformer cooling oil and pass it off as cooking oil for cheap profits accompanied by lethal consequences.
Reliability in supply of power is achieved by integrating the generation capacity into one seamless auto-controlled system with adequate dedicated standby plants that kick-in instantly when an outage or interruption occurs anywhere in the network.
On this matter we are not alone. Practically every Sub-Saharan nation has a power system that is either tottering on the edge of collapse or in is such shambles as to be next to useless. Many oil producing nations (Nigeria, South Sudan, Gabon, Angola, Equatorial Guinea etc) have electrical power grids not worth writing home about.
African graduate students doing complex computer calculations requiring weeks of uninterruptible power always head to Europe or South Africa. South Africa has a power supply, admittedly supplemented by nuclear power, that works because African style corruption has not penetrated deep enough to affect efficiency: courtesy of its Apartheid History.
https://www.standardmedia.co.ke/ure...ve-problems-while-trying-to-electrify-the-sgr
MY TAKE
Moreover the infrastructure in place cannot support overheard electrical poles take example across those long brigdes n tunnels!
