How does work a Tramway?
In a not very technical way and a bit coloquial way, I will try to explain, not very briefly, how does work an electrical Tramway, beginning with the Classical ones of Buenos Aires and ending with the latest models known until now, the AC driven tramways with computerized controls.
Portenian Classic (1897-1963)
With very few variations along the portenian tramway`s history, the layout and working system of these tramways became something classic, becoming with years technologically obsolete, but not for that reason expensive to run, by the 30`s. Acceleration systems, motors, electricity feeding and distribution became old with time, nevertheless they prove something very true. These cars doesn`t break due to "strange causes", as modern trams do, and also, the bureaucratic system of the Anglo Argentine, and later the Transport`s Corporation, aided on keeping this system alive.
After this unuseful launching of words in the air we`ll arrive to the important thing....
An electrical device with wheels over tracks, the tramway
This diagram, not very well drawn, belongs to the last tramway that run on Buenos Aires, model FM,series TBA 3200-3400. This layout never changed. I am going to explain you (try to ) each part and how it works.
The feeding, made with direct current (as if it were a model railway -märklin users hold your comments-), where the positive pole of an enormous "battery" that lays some kilometres from the car, gives it by it pole or TROLLEY, its voltage, that in our case is of about 550 Volts. The voltage was given by this "battery", that was in fact a direct current generator attached to a steam machine (in the first times), and then was changed by altern current distribution systems, being the Altern current rectificated prior its use by the tramways. The current returned to the power plant by the tracks (the negative pole), closing the circuit.
The current, that comes from the trolley, flows first through the electromagnetical protection switches (1) and (2), which protect the motors from overcurrents, cutting the circuit out if any is detected. The currents flows then through the fuse (3), that offers protection in case of a shortcut. . It passes prior through anti lightning devices. It`s made from two devices, the ruptor`s lightning pole (5) and the sucking coil (4). The huge current of a ray was derived then to the tracks avoiding any threat for the car or the passengers when it rained.
The wires shows that the current was then conducted to the Kontrollers (6) and (7), big mechanical reostatic/combinators. The way of current`s administration and voltaje or these devices could appear risky today, because the motorman was (and is) managing practically all the power just some centimetres from his body. Anyways accidentes with electrocutions hardly could happen, because the devices were very well isolated.
The current, once it was administrated and regulated by means that I will explain on another page, passes through the resistance`s box (8), which were the unforgetable part for the proper work of our tram, and from here it was conducted to the motors, (8) and (9), responsible of moving the car.
The current after all this process returns back to the power plant, power group or emergency electricity`s generating device.
The part where lays our electromechanical comet
The Truck
This little thing with wheels, which actually accomplished many other functions, was the frame on where the car body had its suspension, and where the carīs braking system was housed.
Suspension, and in every rolling machine, had two different suspension parts, being a springīs set the one that kept separate axles from the frame, made with lateral suspension bars and its strenghtenings. The second set of rings separated this frame from the carīs body. In order to give some kind of smoothness to the ride there where placed at each of the truckīs ends suspension stretchers, making posible that the car wouldn`t make a "happy dance" when riding. The suspension was completed with the bodyīs suspension bars, preventing a swivelling movement of the body when braking, besides of giving some cushioning to the unit.
Both motors are placed in a "punctual symetry" layout, something that makes possible to keep balance in the power effort preventing that the wheel would "pull" to one side or the other. The motors, when receinving power from the electrical grid converted the electricity into mechanical power and by means of the gears they acted over the wheels making the unit to move itself. The motors rested by one side over the axle laying on the motorīs bearings, lubricated with oiled burlap, with the motors pivoting around the axle, and they were hold by the other end with the motorīs holding bar, which was suspended by springs in a way that the streetīs shaking wouldn`t be transmitted to the motors.