Thursday, January 24, 2008

Gautrain doesn't use electricity? Really?

I recently wrote to the Gautrain information centre to find out how much electricity the trains will use. They claim to have no idea. I'm not sure whether they are lying or they really are so incompetent that they don't have any idea. Neither option is reassuring. I wrote:
"Please could you tell me how many MW of electricity the trains will use when they are operational? Also, how much electricity will be used by the stations themselves, and what will happen when there are power outages?"
Their reply was:
"We cannot say for sure what this will during operation as we’re still in the construction phase. This will also depend on various aspects that still need to be finalised from now until the operational phase."
According to the information brochure dated 15 April 2007, page 4, there will be 24 trains of 4 cars each. No mention is made of the power requirements. In fact, the words "power" and "electricity" are entirely absent from the 23 page document. They are also absent from this and this document too. Considering that the Koeberg blackouts had lasted for several weeks a year before, and Eskom had already issued warnings about power shortages for years to come, these documents, coming a year later, are surprisingly short-sighted.
According to Wikipedia, the trains are of the Electrostar family. I found further information on these locomotives, including the following:
Bodywork is aluminium, with steel ends. There are two Adtranz 250kW three-phase traction motors on each motor coach, with IGBT control. The motor bogies are at the trailing end of the driving coaches and at the centre of the unit on the non-driving coach. Bogies are a development of the BREL P3 and T3 design used on class 465/0 and 465/1. Driving coaches have pick up shoes on both bogies. Classes 375 and 377 have a potential maximum speed of 160km/h, but do not normally operate at more than 140 km/h.
Assuming a motor coach on each end, each train will use 1MW of power, so the entire system would consume 24MW, excluding lighting, power consumption at each station, and power loss due to normal transmission. Given the fact that the Kelvin power station produces a maximum of 600MW, this one project will use 4% of the power station's entire output, capacity it simply doesn't have. It already only provides less than a third of the city's power requirements.
Update 30 Jan 2008: I finally got an answer of sorts (see comment below). I under-estimated the power requirements (it's 28.8MW), and the only mention on the web site can be found here.
  • The rail cars are known as Electric Multiple Units (EMUs) and will be powered from overhead electrification wires at a voltage of 25kVAC.
  • An EMU allows distributed power along the train and in the case of the Gautrain, twelve of the sixteen axles of a four car train unit are provided with 200kW electric motors (a motorisation ratio of 75%), leading to a relative high power to weight ratio of approximately 11 kW per ton. This power to weight ratio ensures the high levels of acceleration and deceleration required to achieve the required maximum journey times specified of 42 minutes from Johannesburg Park station to Hatfield station.
  • Having distributed power allows the train to climb gradients significantly steeper than on the national rail network. The direct alignment needed to achieve the shortest distance between the specified stations requires gradients of up to 4% which is significantly steeper than normal railway main line gradients which are normally restricted to 1,5% or occasionally 2% in special instances. The Gautrain has a motorisation ratio of 75% which could allow it to climb gradients in excess of 10%.
  • The use of a high voltage alternating current (AC) system permits the entire Gautrain system to be fed from a single electrical traction substation which will be located at the Gautrain Midrand Depot. The traction substation will be provided with two independent supplies from Eskom to ensure reliability of electrical power supply.
  • All train units will be provided with blended braking systems. Once it is decided to brake a train, the system first goes into regenerative braking mode, thus using its electric motors as brakes. The electrical power is then supplied back into the overhead lines and can then be used by other trains in the system that are accelerating or are otherwise in a power receptive (consuming) mode. Should there be no receptive trains, then the power will be fed back to Eskom supply, thus ensuring efficient electrical usage characteristics throughout the system. Should higher levels of braking be required this can be provided by the motors, the system then automatically applies the disc brakes. Disc brakes are provided on all wheels and the configuration is similar to advanced modern motor vehicle disc braking systems, being fitted with an Anti-skid Braking System (ABS).
There is no mention of what will be done in the event of a power failure. It is obvious that there is no standby power plan, not even one to provide enough power for one train to run, i.e. 2.4MW. Relying on "two independent sources of power from Eskom" does not take into account Eskom's obvious inability to provide power. What a fiasco!


marithapritchard said...

During peak periods, there will be 9 x 4 car train sets travelling on the north/south route between Park Station in Johannesburg and Hatfield Station in Tshwane.

There will be 3 x 4 car train sets travelling on the east/west route between Sandton Station and the OR Tambo International Airport Station.

Each of the 12 train sets will be powered by 12 electric motors, each of 200kW power.

So, 12 train sets x 12 motors x 200kW = 28,8MW absolute maximum demand from all the trains at any one time, assuming that every train set will be simultaneously accelerating, and at maximum power.

In practice it will be somewhat different. It must also be noted that the 25kVac overhead electrification system and the train control systems are so configured that under normal circumstances the trains’ brakes will use regenerative braking. The excess power so generated is then available to other trains wishing to accelerate anywhere within the system. Therefore, the figure of 28,8MW is extremely unlikely to be reached, if ever.

To place this usage into context, the present generation of Eskom power stations each usually comprise 6 x 600MW generating units, or 3600MW per power station. This is less than the power used by a small town. Even large factories use more power than this.

You can also get more info on Gautrain's youth website, MyTrain.


Maritha Pritchard
Gautrain (Gauteng Provincial Support Team)

Donn Edwards said...

Thanks for supplying the facts, but 28MW is hardly a trivial power requirement.

The fact that there is no standby power plan needs to be addressed. I don't plan on living the suburbs left in the dark so that these trains can run.

Colin Alston said...

Donn, that is a *maximum* power rating of the motor which is not at all indicative of typical load. Since the trains will not travel at full speed all the time, with full weight capacity or up huge inclines the real power utilization is unlikely to be greater than half that figure.

Despite that, 28MW is very trivial - Duva generates something along the lines of 4GW alone and the running time of the trains is not going to be that high. Another consideration is that the power factor of the trains will be reasonably good, compared with households which have a terrible power factor that results in a lot of wasted energy.

Donn Edwards said...

28MW may be "trivial" (cough!) when Duvha power station is generating all its 3450MW, but all of that power is already accounted for, hence "Load Shedding".

Buying a 28MW standby generator is definately non-trivial, and Gautrain has announced NO PLANS WHATSOEVER for any standby generation capacity.

The only "standby" is that there will be two connections to Eskom's grid, but since it is the Eskom grid that is the problem, that's not really a solution, is it?

Gautrain needs enough standby power to enable all trains to move to the nearest station or safe point during load shedding. It has no such capability.

electric motor repairs said...

The power requirement is not necessarily stable at all times of the operation.

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