Piston Pete Posted December 24, 2024 Posted December 24, 2024 I know how to drive the EU07 and ET22 but have no idea what is going on with the electrics. I would like to have some deeper understanding about the physics. Maybe someone can explain ?
Averrnor Posted December 24, 2024 Posted December 24, 2024 Not sure if I can assist you because following web site is in polish, but I hope that with help of some translators you can get all the things you need. It is great source of polish railways knowledge though. The given link is taking you directly to the subject you asked for: https://www.transportszynowy.pl/Kolej/kolnapedoporowy 1 1
Piston Pete Posted December 24, 2024 Author Posted December 24, 2024 (edited) This is the type of information I'm looking for. Thank you for the link (the translation in Dutch is quite good). Edited December 24, 2024 by Piston Pete 1
sTuPid.rar Posted December 26, 2024 Posted December 26, 2024 (edited) What @Averrnor gave to you is really interesting. Generally speaking (some approximations are done here!) electric locomotives of this type have a big rehostat, which is basically a variable resistor. You turn the power controller one notch and you connect the rehostat to the electric motors with the highest resistance available. In this way you have a small voltage across the motors and so the torque generated is small. You can accelerate smootly without burning the motors or the circuits. Now to increase the speed you need more power. Turning the power controller reduces the resistance value step by step, increasing the voltage across motors and so increasing the power and the torque generated. At this point you are still slow (around 40 km/h with EU07) and you can do something that in some way is similar to "shifting up" in cars. You change the electrical combination of the motors. Up until now motors were connect in series. If you connect them in parallel, with the same voltage as before, you get higher values of current. This translate into more power, more torque, thus more speed. This is called Series to parallel transition. Again the rehostat is fully inserted and you reduce the resistance step by step until you reach the end with full voltage across motors connected in parallel. Some locomotives (such as ET22) have more combinations of motors. This locomotive has 6 motors (if I am not wrong) so series S is all 6 motors in series, series-parallel SR is two branches of three motors each, and parallel R is three branches of two motors each. Just to let you know, there is a locomotive in Italy (E656) which has 4 combinations (series S with 1x12 motors, series-parallel SP 2x6, parallel P 3x4, super parallel PP 4x3). There is also another controller, which is the shunt regulator. It permits to gain some more speed. The functioning is a bit more technical. I will try to explain it in a simple way. When the rotor of an electric motor rotates, it generates a "back electric motive force" (or bemf, basically a voltage) which is opposite compared to the voltage you apply to the motor to make it turn. The faster the rotating speed, the higher the bemf generated. Imagine you take a motor. You apply a certain voltage to it. In the exact moment you apply the voltage, the current is maximum (an electric motor standing still is like a short circuit) and so the torque is maximum. The rotor starts to spin. As the speed increases, the back electric motive force increases more and more, balancing the voltage you are applying and reducing the torque available to the rotor. The motor will reach a mechanical equilibrium speed (the torque generate is equal to the friction torque) called "base speed". If you want to increase the speed you can increase the voltage (not possible in electric locomotives), or reduce the bemf. To reduce the bemf you reduce the number of windings electrically connected to the motor. If you have less winding connected to the motor, the magnetic flux has less wires in which the bemf can be generated. In other words, the value of the bemf is lower and so the motor increases the rotating speed. As side note, this is not magic. You are not generating power from the air. From zero speed to base speed the motor is in a region called "constant torque" region. The power increases to it's maximum value at base speed. Beyond this point the motor enters a region called "constant power". The torque decreases as the speed increases. For locomotives this is sufficient and so you gain some more speed. But you will notice that whith the shunt regulator the locomotive is not as powerful as when you use the main power control. Edited December 26, 2024 by sTuPid.rar 1
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