Pieter Kruit et al published paper on "Reducing the Magnetic Fields around DC Light Rail Systems"
DC electrified light rail or tram systems cause low frequency magnetic fields that may disturb scientific and medical instruments in their environment. A concept was developed that significantly reduces these magnetic fields. The overhead contact line is cut into insulated sections.
Each section is powered from a supply cable that runs close to the track. When a pantograph enters such a section, the current to the contact line is supplied from both ends. The system is in operation in Utrecht (NL). It has been built in Lund (Sweden) where it will be tested this year and it is under construction in Delft (NL). Test results in Utrecht show that the horizontal magnetic field at 50 m from the track center line is a factor of 8 to 12 smaller than the field next to a conventional track. The field in the vertical direction shows signs of a net current along the track indicating some stray current.
The whole paper can be read here
