INTRO: Everybody agrees that 25 kV AC is essential on three primary international routes; phased conversion between 2005 and 2017 is the best option for the rest of the trunk network, but who will pay?
BYLINE: Robin Hemelrijk
Senior Project Leader
Railned Innovatie
THE DUTCH national network is 2739route-km of which 1991 km is electrified at 1·5 kV DC. Though small, it is the most intensively used in Europe; while this yields many benefits, there is another side to the coin.
There has for years been a shortage of traction power at the catenary, and this became acute when passenger traffic expanded dramatically in the 1980s. At the present time it is necessary for some trains to run at half power simply because the traction power supply (TEV) is not adequate.
The maximum current that can be drawn from one section of the catenary over one track is 4kA. Each section is about 4 to 7 km long, and may have up to two trains drawing power at the same time. Although sections are shortened according to traffic density, it is obvious that the current capacity at 1·5 kV is inadequate.
In theory, 4kA at 1·5 kV provides 6MW of power, but because there are too many trains attempting to draw current the voltage drops, so the power actually available typically fluctuates between 4 and 5MW. In contrast, power demanded can rise to as much as 9MW. Clearly, the existing TEV has not kept up with the timetable. Sometimes trains cannot depart because the voltage is too low when another heavy train starts at the same time.
Studies of a new train control system with in-cab signalling and moving block assume that the interval between trains can be reduced, raising line capacity. This is obviously impossible when the catenary voltage already falls to 1050V because there are not enough substations. Earlier this year the government approved the construction of an additional 60 substations; these are being built simply to maintain the minimum voltage.
The existing operators, NS Reizigers (Passengers) and NS Cargo (and maybe other operators under our open access regime), want to run more trains which are heavier and accelerate faster to higher speeds. It is just these characteristics that determine the demand for electrical power. We can only conclude that the power problem will get worse.
Strategic study
In 1995, the government commissioned Railned (panel, p520) to undertake a strategic study to which the power shortage and possible solutions were central.
Railned convinced the government that the existing TEV was no longer adequate, and pointed out that one solution was high voltage AC, specifically 25 kV at 50Hz. In collaboration with NS Railinfrabeheer, Railned also studied five possible solutions. An extensive report was presented in March 1996.
The alternatives were based on either 1·5 kV or 25 kV, or a mix of both systems. When determining the best strategy, cost was not the only consideration. The selection was based on a wide multi-criteria assessment including cost benefits, strategic aspects, financing options, price/performance ratios and other factors.
A great deal of attention was paid to quantifying the benefits of the final choice. Through the new TEV, rail travel would become more attractive as a product and there would be opportunities for an improved timetable, so even better utilisation of the infrastructure would be possible. All of these benefits were calculated on the basis of reductions in journey time.
Unsurprisingly, the study confirmed that complete conversion of the network to 25 kV produces the best TEV available. However, universal or even large scale conversion does not appear to be achievable in the short or medium term. Finance constitutes the greatest stumbling block.
So Railned’s advice in March 1996 was, for the time being, only to use the 25 kV system where it was most needed. This is on the three primary international routes: the proposed high-speed line from Amsterdam to Brussels and Paris, the upgraded existing line from Amsterdam and Utrecht to Emmerich (right) and K
