Nederlandse Spoorwegen (Netherlands Railways – NS) runs trains over 2000km of the electrified railway, and conversion of the overhead from 1,500kV DC to 25kV AC is planned to massively improve the quality of service. The changes are needed due to acute, and worsening, capacity problems. Since the 1980s, the drive to increase the number of passenger trains has overloaded the power supply.

Throughout Europe, AC systems have been preferred over DC in recent years because of perceived improvements which are possible in terms of reliability and maintenance costs, as well as the benefits arising from standardisation with the systems of neighbouring countries.

The project

Without major improvements to traction supplies and signalling systems, many trains are having to run at half power because the traction power supply is inadequate. When too many trains attempt to draw current, the voltage drops, preventing trains departing from a station when another heavy train starts at the same time.

This shortcoming greatly reduces the value of new train control systems designed to decrease intervals between trains to raise line capacity.

As 25kV is now standard throughout much of Europe, NS considers it vital that it too adopts this system, so that it can benefit from the ability to run trains across national borders right across mainland Europe. Railned (the nation’s privatised railway planning business) pushed hard for a rapid start to be made on conversion to 25kV, after concluding that it was the best option in terms of a range of criteria, including cost, strategic aspects, financing options, and price/performance ratios.


In 1997, the Dutch government approved construction of an additional 60 substations simply to maintain the minimum voltage. Railned’s advice is therefore to only use 25kV where it is most needed. This is on the three primary international routes: the high-speed line from Amsterdam to Brussels and Paris, the upgraded existing line from Amsterdam and Utrecht to Emmerich and Ksln, and the proposed Betuwe freight line from Rotterdam to Emmerich.

The existing 1.5kV dc system throughout the rest of the country is also expected to be upgraded. Over time, decisions are likely to be taken over whether to extend 25kV to connecting lines.

In February 1997, the government and train operators NS Reizigers (passengers) and NS Cargo (freight), Railned and NS Railinfrabeheer all agreed on the 25kV option. Through the new power system, rail travel is more attractive as a product and there are opportunities for an improved timetable with journey time reductions, and better utilisation of infrastructure.

The government study confirmed that complete conversion of the network to 25kV was the best option, although doubts were expressed whether a large-scale conversion project would be possible under government finance constraints.

Rolling stock

NS Reizigers and NS Cargo (and possibly others in the future) want to run more trains which are heavier and accelerate faster to higher speeds. Unfortunately, it is these characteristics that determine the demand for electrical power, so the logical conclusion is that the power problem will get worse.

Under the cheapest and slowest option, no existing rolling stock would be converted. New trains would be introduced as dual-voltage, and conversion of lines to 25kV would commence as soon as sufficient dual-voltage trains become available.

As many NS routes have seen the introduction of new rolling stock in recent years, this would mean introducing 25kV over the long term.

Conversion would only be possible when existing IC rolling stock and locomotives, in particular, have been phased out. Based on the current view of the lifespan of this rolling stock, conversion of the infrastructure could take place from 2022 to 2032.

The fast scenario would mean the majority of existing rolling stock would need to be converted. New stock would be introduced as dual-voltage or 25kV only, and a line could be converted as soon as the rolling stock using it was suitable. Conversion could then be undertaken between 2005 and 2017.

Signalling and communications

Conversion of the infrastructure involves fitting larger insulators to the catenary and the construction of 25kV substations. If train speeds are no more than 160 km/h, the existing overhead wires can be re-used. With signalling interference, both the track circuits for train detection and the ATP automatic train protection must be adapted for 25 kV, and rolling stock modified to match. Plans centre on the replacement of ATP with a more modern system, such as the European Train Control System, or European Regional Train Management System.

In early 1999, the Dutch government approved the adoption of a transmission-based train control system known as BB21, which uses moving blocks to increase capacity on existing lines. BB21 is also expected to eliminate the need to immunise existing signalling against interference by 25kV power supplies.

The first applications of this system will be on the Betuwe freight route, and HSL Zuid high-speed line between Amsterdam and Antwerp, which are both due to open in 2005.

The future

Fitting of BB21 across the entire Dutch rail network is expected to cost ANG800m in addition to money already allocated, including 300 million guilders for the fitting of on-train equipment. As part of this project, the Ministry of Transport will also be looking to improve safety by eliminating as many level crossings as possible. The Netherlands’ first purpose-built high-speed rail line, between Antwerp and Amsterdam, is expected to be the first to be fitted with BB21, subject to successful trials.

However, as the cost of converting the entire network to 25kV is expected to be around ANG3bn (£1.1bn), the process is likely to be carried out in stages, to tie in with the replacement of existing trains with new equipment. This is also considered desirable in view of the large amount of relatively new rolling stock which could quickly be rendered obsolete if a wholesale re-electrification programme was carried out.