Severe weather and other emergencies aside, catenary maintenance is no picnic. Hombach describes the vehicle maintenance shop as “the most dangerous area on the system.” Workers must often work above power lines, and the only efficient way to move vehicles through the shop is via an insulated “hot-stick,” which forces employees to handle exposed contacts. Winches and pulleys are an alternative, but are much slower and less efficient. Eliminating overhead power lines increases safety across the entire system.
Even if safety and expense weren’t problems, catenary lines and their associated equipment do much to interfere with the visual aesthetics of a place. This is particularly true in historic centers of major cities. The view of the architecture is marred by power lines and their poles, creating a less-pleasing urban environment. Siciliano notes that catenary systems can cause a city to look “wrapped in a hank of wires” and observes that overhead wires are often the cause of municipalities choosing other public transportation solutions over light rail.
All of these issues are solved by a catenary-less system. With the power source in the ground rather than above, there are fewer costs to install and maintain an electrically powered train. Safety is less an issue, because catenary-less systems do not supply power when the tram isn’t present (making them safe for pedestrians and other vehicles), and because the lines cannot be brought down by inclement weather or line breaks. Finally, urban centers are visually enhanced by the absence of lines and poles, thereby creating a more pleasing environment.
For all these reasons, a catenary-less system may be the ideal way to implement light rail lines, helping cities solve public transportation problems in ecologically and economically friendly ways.
Types of Catenary-less Systems
Catenary-less power comes in two forms: continuous contact from a ground-based system and onboard power cells. Each has advantages and disadvantages.
Ground-based systems rely on continuous contact with the power source much like a traditional catenary system, with two key differences. The first and most obvious is that the power comes from transformers buried beneath the rails rather than overhead lines. Secondly, electricity is only transmitted when the tram is over the rail.
This is accomplished by means of a segmented electrical system. Each segment is connected to the others, but is only powered when the train rolls over it. The tram moves across it, takes power from it, and thereby receives energy to move to the next segment, where the process is repeated. Tram pickups are insulated so electricity can only be transferred to the train, and, since a segment only gives power in the presence of the tram, pedestrians and other vehicles are not exposed to the discharge.
The downside to this system is that weather can still have an impact on running capabilities. Snow, ice and sand accumulating on the tracks can interfere with the transfer of power. Without some means to clear the track before the train arrives, it could come to a stop on a fouled rail, unable to get power. Thus, not all environments are ideal for this system.
In the second approach, the trains carry giant batteries onboard that feed it power. This makes it possible for them to operate in all environments, since weather or other topographical features cannot inhibit power transfer. The batteries are rechargeable, making the system self-sustaining. Recharge occurs at stations or while the train is running on traditional catenary power in a hybrid system.
However, recharging can take awhile, which can make for long delays at the station. Thus, a battery-powered light rail may not be the most efficient and could suffer during peak hours.
Four manufacturers have developed systems using the above principles. Three (Ansaldo’s TramWave, Alstom’s APS, and Bombardier’s Primove) use the ground-based contact system, while one (Kinkisharyo’s e-Brid) is battery-powered. Each is detailed below.
Ansaldo STS TramWave System
TramWave provides power through a continuous conduit duct embedded in the ground running between the rails on the track. The power “line” is a series of segmented conductor strips that are insulated one against the other. Each segment is between 3 and 5 meters long, with a succession of steel plates that are 50cm each. The tram must be present for the segment to be powered. Presence is detected by simple gravity and electrostatic means.