The power collector is mounted underneath the train. A ferromagnetic belt in the conduit allows electricity to flow to the vehicle when contact is made with the power collector. The live area of the line is very short – only 1 meter – to maximize safety. Once the train has passed, gravity causes the magnetic belt to fall back into place, thereby cutting off the power supply.
Power is transferred via contact shoes of copper and graphite. The collector is lifted up and down over the contact line via its own magnets in a tiny pantograph. The EMI of these magnets is small enough to be safe for passengers on the train and does not cause interference with electronic devices onboard. Power is fed at a rate of up to 750vcc.
Moreover, TramWave is adaptable to a variety of different vehicle types, including rubber-wheeled ones. It also is capable of switching between its own power system and a traditional catenary one. In the presence of overhead power, a safety system sets the in-ground power collector to the “off” position. It is therefore possible to install the TramWave system in urban areas and then transfer to a catenary one in the suburbs or rural environments.
The power conduit is easy to install along existing lines and costs about the same as a standard catenary system according to Siciliano. He notes that the maintenance costs of the TramWave are “potentially much lower.”
Because it uses a contact system, TramWave is susceptible to ice, snow or sand on the lines. However, sweepers can be installed to clear lines as the train moves over them, and optional heating elements are available for cold climates where freezing is a concern.
Overall, the system is designed to provide great flexibility for light rail companies. It can be installed on a variety of vehicles, can be integrated with traditional catenary lines and is cost effective for conversion of existing lines or implementation of brand new ones.
“TramWave (has) already been tested and (is) ready to be installed in any city that (needs) an innovative, carbon-free, and efficient mass transit system,” Siciliano says. “TramWave is a product ready to improve urban transit.”
Alstom Transportation Aesthetic Power Supply (APS) System
Like Ansaldo STS’s TramWave, Alstom’s APS system employs an in-ground power source. Power units are buried beneath the track at regular intervals. An electrical conduit is laid between the rails just like the TramWave. The conduit is comprised of 8-meter-long segments with 3-meter insulating joints. Copper/graphite shoes receive the electricity and send it to the power collector.
Like other in-ground systems, APS’s conduit is only “live” when the train rolls over the segment. Antennae in the collector unit send a coded radio signal to the power unit, alerting it to when the tram is present. When the signal is received, power is transferred to the conduit and collected by the train at a rate of 750v DC.
APS is extremely versatile. It can switch from in-ground to traditional catenary power to accommodate hybrid rail solutions. It also carries an onboard backup battery, so the train can continue operating in the event of a power cut.
Alstom makes a special power unit for warm environments, designed to deal with the excessive heat of tropical climates. Although a solution for cold-weather obstacles such as snow and ice hasn’t been developed yet, the company partnered with Systra to implement APS in Bordeaux, France, in 2004. Through April 2010, APS had successfully run over 7 million kilometers of service since becoming operational.
Bombardier Primove System
Bombardier has also developed an in-ground catenary-less power system, but the principle is slightly different than those of TramWave and APS. Like the others, it features a conduit line running parallel to the track between the rails. However, Bombardier’s system features contact-less power transfer using induction principles.
The Primove system features 8-meter cable segments laid beneath the ground. Inverters along the track are connected to a power network at 750v DC. When a segment is energized, a magnetic field is created. Trains are equipped with pickup coils to receive this energy, which they convert into an electrical current that powers the tram. Just like the TramWave and APS, Primove’s conduit segments are only powered when the train is present overhead, making it safe for pedestrians and other vehicles.