[Weter]

@Darwin:
Hello.

Quote

Notch 1 - Engine 425 rpm - reduced generator excitation

Notch 2 - Engine 425 rpm - full generator excitation

Notch 3 - Engine 600 rpm - reduced generator excitation

Notch 4 - Engine 600 rpm - reduced generator excitation

Notch 5 - Engine 600 rpm - reduced generator excitation

Notch 6 - Engine 600 rpm - reduced generator excitation

Notch 7 - Engine 600 rpm - full generator excitation

Notch 8 - Engine 750 rpm - full generator excitation

Are there excitation steps on 3-6 notches?

@Jean-Paul:
Salut!

@Flo:
What is bemf?

@Phillip:
You've gave me a hope, thanks!

[darwins]

Yes - the generator output is increased in steps - that increases the load on the engine - so increases power output and fuel consumption - without increasing rpm.
bemf = back emf

[Weter]

So, it's governor compensates the load (maintains rpm) by increasing quantity of fuel infected.
Later, joint governors of rpm/excitation were introduced.
Counter-induction?

[FloBarr]

Well, wikipedia would explains it better than me, but Back Emf is a "voltage" created as a DC motor is turning. It "reduces" the voltage used by the motor, and, for a given internal resistance, the current.

That's why, for a given voltage, the current reduces as the motor accelerate, or increase as the motor is slowing down. And when the current reaches an acceptable value, it is possible to increase voltage; the internal resistance is still the same, and the current raises. But, as the voltage is now higher than bemf, the motor accelerates, and so on. For a given voltage, a DC motor could only reach a given speed, we need to supply it with the highest voltage possible, but current would be quickly to high.

The pictures shows the differents torques curves for each notches on a french cc72000. For each notch, 50v are added, raising current and torque. As speed increases, bemf increases too, and current (and torque) decreases.

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[Weter]

Ah, that... so, back electro-motive force... I just spdidnt know that term, so called it counter-current in my posts above.

Again, DC motor works as a generator at the same time, because rotor coil's conductors are moving across stator's magnetic field, as faster, as quicker the rotation.
This generates electro-motive force, having direction, opposite to line voltage, so it works against the later and "compensates" it, being "subtracted.
At some speed, it reaches applied voltage, being a bit lower (some of applied voltage is spent for compensation of active resistance of conductors, inductive losses in core and friction losses in bearings, gear and other mechanical hardware), so all applied voltage is compensated and no more torque is being produced - motor can't accelerate further. Voltage then can be increased, but it's limit is actual line voltage. The (stator's) field weakening reduces "generator effect", hence back-electro-motive force turns lower, and given applied voltage now can produce some extra current, hence torque and rotation speed is increased, by cost of extra losses of power, diccipated by current, being diverged to resistors, inserted in parallel with stator's coil.

[Fablok]

Here is a description of the locomotive I ride on. It's a combustion engine with a bypass, so if anything I have instructions for it. The book has 500 pages, so the diagrams will be found ;) By turning the wheel of the drive controller, the next starting positions are set. In position 2, the main generator is excited with an exciter, as a result of which it starts to generate traction current, which is used to power the traction motors. The locomotive moves. By setting successive positions of the drive controller, we increase the excitation of the main generator and the rotation of the internal combustion engine, which thus increases the appropriate current values. Due to the fact that the combustion engine drives the generator, the power and revolutions of the combustion engine must be synchronized with the power and revolutions of the main generator. The Woodward regulator is responsible for adjusting the rotation of the internal combustion engine to the degree of excitation of the main generator. Woodward regulator

The Woodward's regulator appropriately doses fuel to the cylinders of the internal combustion engine in accordance with the degree of excitation of the main generator, so that the balance between the revolutions and power of the internal combustion engine and the main generator is maintained.

After the travel controller wheel reaches the last 11th position, it is possible to shun the traction motor windings. Shunting consists in excluding a part of the stator winding of traction motors from the main circuit, as a result of which the magnetic flux of the stator windings of traction motors is reduced, which increases the rotational speed of the traction motors' rotors. The locomotive then has low torque but high acceleration.
In order to shun, it is necessary to return the travel controller wheel to position 6. After setting this position, press the "shunting" button on the driver's desk. The shunt indicator light will then turn on. Then, in order to further weaken the excitation, the wheel of the travel controller can be turned up to position 11. The SM42 series locomotive can be driven in two modes: linear and shunting. The "maneuvering" switch located on the driver's control panel is used to set the selected mode.
Switch positions:
0 - shunting is disabled. The locomotive can be started using all the functions described earlier.
1 - shunting is on. It is not possible to attenuate the excitation of traction motors (shunting). However, it is possible to control the locomotive's ride more precisely using the shunting drive excitation potentiometer. This potentiometer is located on the column of the main brake valve and works with the exciter of the main generator. By adjusting the potentiometer knob, the main generator exciter is precisely controlled.

https://upload.wikimedia.org/wikipedia/commons/7/72/SM42-1040_na_stacji_%C5%9Awinouj%C5%9Bcie_Przyt%C3%B3r_-_lipiec_2018_-1.jpg

[Weter]

Hello.
What do You call "bypass"

[Weter]

By the way, that is the reason, why using reverse in kind of "dynamic brakes" is unacceptable: when we reverse polarity of voltage, applied to motor, said counter EMF is then added to voltage, instead of being subtracted. Twice greater voltage can appear, as a result, damaging hardware and even causing fire.

[Fablok]

Translator error. Shunt ;) Its about shunting ;)

[Weter]

I see, thanks. Maneurer(switcher) locomotive. Yes, I remember the video (or photo?) from depot, showing, how it looked.