Trams draw their power from a single overhead wire at about 500 to 750 V DC. Trolleybuses draw from two overhead wires at a similar voltage, and at least one of the trolleybus wires must be insulated from tram wires.
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Arcing flashes happen when the arm that extends from the train, called the pantograph, loses contact with the power cable above, or the catenary. That loss of contact is what causes the loud bang and the sparks, and causes the trains to lose power.
Over the years various refinements have been made, such as replacement of series-parallel controllers with modern solid state control systems, and the substitution of trolley poles with pantographs. However, in the majority of tramways the electricity supply is still between 600 and 750 volts DC [1].
Tram derailments and collisionsTram derailments are often caused by damaged track, collisions with obstacles such as other vehicles or pedestrians, junction failures, or excessive speed at a junction or curve. Additionally, collisions may occur between trams due to faulty junctions or poor driving.
Pedestrians and cyclistsWhile collisions with cars are the most common form of tram accident, cyclists and pedestrians are the group most at risk of death during tram collisions. Cyclists may experience a loss of control if bicycle tires get jammed in tramway tracks.
Train tracks are laid a few inches above the ground while tram tracks are laid at road level to enable cars and other vehicles to drive over them. Trains consist of a series of vehicles or coaches which are coupled together and drawn by a locomotive.
The world's very first tram system was actually a horse train called the Oystermouth Railway, a commercial service which began operation in 1804, in order to transport limestone between the south Wales areas of Mumbles and Swansea.
Trains and trams can turn corners without wheel-slip because the outer horizontal part of the wheels has a slightly tapered rim. The guide flange (ridge) is on the inside to prevent the vehicle from slipping sideways off the rails.
DC motors are used on trains is because of their high torque and good speed control. Compared to AC motors, DC motors can provide industry applications with a fine balance of strong starting torque and controllable speed for seamless yet precise performance.