Trolleys operate by drawing electrical power from an external source to drive an electric motor, propelling the vehicle.
Powering the Trolley
Trolleys are distinct from buses or cars as they do not carry their power source (like a battery or internal combustion engine) on board in the same way. Instead, they connect to a fixed electrical infrastructure to receive the energy they need. The reference states that trolleys use either an overhead cable or 'third rail' to supply power to an electric motor.
Here are the two main methods they utilize to access this power:
- Overhead Cable: This is perhaps the most recognizable method. Trolleys use poles on their roof that connect to overhead wires (often called catenary wires) suspended above the route. These wires carry the electrical current.
- 'Third Rail': In some systems, particularly for larger or interurban trolleys (like trams or light rail), power can be supplied via a third rail running alongside the tracks. A contact shoe on the trolley picks up power from this energized rail.
The Electric Motor
Regardless of whether the power comes from an overhead cable or a third rail, the electricity is directed to an electric motor within the trolley. This motor converts the electrical energy into mechanical energy, turning the wheels and moving the trolley along its route, typically on rails.
Efficiency and Historical Significance
The method of drawing external power directly to an electric motor makes trolleys highly efficient. According to some engineers, this power delivery system is and always has been the most energy efficient form of transportation in human history. This efficiency contributes to lower operating costs and reduced environmental impact compared to vehicles relying on onboard fuel combustion or heavy batteries.
