EU07 Switch off converter

[Bandit]

At the moment I can switch it off while driving and the traction motors still get power, which is not the case in real life.

[Angelo]

Said switch powers two motor+generator units that convert the 3kV from the overhead wires into the 110V for the low voltage circuits - in fact, when you turn it off you can see the battery voltage drops.

[Schyrsivochter]

Yeah, I was about to say that. The air compressor is on that circuit, too, and it doesn’t work when the converter is switched off either.

[Bandit]

vor 56 Minuten schrieb Angelo:

Said switch powers two motor+generator units that convert the 3kV from the overhead wires into the 110V for the low voltage circuits - in fact, when you turn it off you can see the battery voltage drops.

How do the traction motors get their direct current, when the converter is switched off?

 

 

[Schyrsivochter]

Directly from the catenary, more or less. (It goes through a couple breakers and, naturally, the filters and main switch. But it’s still 3 kV on that circuit.)

Edited February 27, 2023 by Schyrsivochter
Add parenthetical

[Schyrsivochter]

Since you’re German, I can link you this (attempt of an) explanation of the EU07/EP07/EP08 traction system I did in German a while ago.

[Bandit]

I already know your explanation. Thank you for that. 
However, I still don't understand where the direct current for the motors or the DC/DC converter comes from.

[Schyrsivochter]

7 hours ago, Bandit said:

I already know your explanation. Thank you for that. 
However, I still don't understand where the direct current for the motors or the DC/DC converter comes from.

From the catenary via the pantograph. Poland has 3 kV DC electrification.

[Bandit]

Ok, now i see the light. I'm always been assumed an AC network. 

[Gazz292]

the over head lines are energised at 3 Kv DC in most of Poland (NOT at 15 or 25 Kv AC as in most of Germany, uk / france etc) 

So the 3Kv DC comes into the loco, a feed is taken off to feed the converter.... this is a motor generator,  a 3Kv DC motor turns a 110 volt DC motor, so that's where you get the output to charge the batteries and run the main air compressor etc. 

The 3Kv then goes to the tap changer, and as you rotate the power wheel, it connects the 3Kv DC to the motors via the resistor bank on the roof of the loco, as you go faster you switch out resistances until notch 28, where the motors are running in series... this is the 3Kv from the overhead line goes straight to one traction motor (via some circuit breakers, overload relays and the tap changer contacts etc) and that 3Kv DC comes out of the first motor and feeds into the second motor (series connection) then the power comes out of the 2nd motor and to earth via the rails.

This means the motors are running on 1.5 Kv each, so they will spin at about half maximum speed. 

Then when you turn the power wheel past notch 28, the motors are connected in parallel, and the resistors switched back into the circuit... this means 3Kv DC goes to both motors, and out of the motors to earth via the rails, so both motors now see 3Kv, and can spin upto their maximum speed once you are in notch 43. 

Then you have the field weakening / shunt lever, which reduces the magnetism of the motors field coils, allowing the motors to spin faster still. 

 

It's a very basic system, but one that has proven to be very reliable. 

The rest of the items on the loco, lights, gauges, control circuits etc run on 110 volts DC, and are connected to the batteries, so they will run if the converter is turned off... until the batteries run down. 
There is an emergency / starting air compressor that runs off the batteries, used to get enough air pressure up to raise the pantograph, where the converter can then be powered up and the main air compressor will run, but this isnt modeled in SimRail yet. 

There is also a big knife switch under the flap to the left of the one with the main battery switch in it, this is to connect the battery charging circuit to external, from the converter feed, used in the shed / depot when you need to recharge the batteries but don't have overhead wires to put the pantograph up to (and other reasons)

[Schyrsivochter]

That explanation is not bad, but I’m taking issue with how it conflates motor speed, motor current, and motor voltage.

Speed, voltage, and current are not the same. The notches change nothing but the voltage across the motors. Notch 28 doesn’t mean that motors are spinning at half their maximum speed, it just means they’ve each got 750 V applied to them (one fourth of 3 kV, since there are four traction motors in total). Similarly, notch 43 just means 1.5 kV at each motor (two motors of each bogie connected in series, two bogies connected in parallel). And field weakening does not, in and of itself, mean that the motors spin faster. It just reduces the motor’s impedance, thus increasing the current.

At a constant speed and constant field weakening, current is directly proportional to voltage. → Turn the wheel and the ammeter needle(s) will go up and down as resistors are switched in and out.

At a constant voltage and constant field weakening, current is roughly inversely proportional to speed. → As you’re accelerating, the ammeter needles will go down (and you have to turn the wheel or use the shunt lever to get them back up).

[Gazz292]

yeah, but there's only so much detail you can go into before it just goes over people's heads, and i get mixed up with terms sometimes so that doesn't help.

Some people thought there were 2 motors in the loco, a slow one and a fast one, and when you go past notch 28 the slow motor is disconnected and the faster one connected. 

But for the topic here, the OP thought the OLE was AC, at 15 or 25 Kv i presume,  so was thinking the converter was changing that AC voltage into DC for the motors, and wondering why the loco would keep on running when the converter was turned off. 

I think converter is the name used for a transformer in some languages too?  as it converts a higher voltage to a lower one (or vice versa) albeit it's AC, then in the older trains a mercury arc rectifier converted the AC to DC :

The one onboard a train would be inside a big metal shield.. and it's no small item either. 
More modern trains use diodes (germanium, silicone etc) to do the AC to DC conversion, and even more modern trains use variable frequency drives with different types of transistor / mosfet to do the switching. 

[Schyrsivochter]

‘transistor / mosfet’? You do know that MOSFET stands for ‘metal-oxide-semiconductor field effect transistor’, right?

Also, I have to disagree there: traction inverters for three-phase motor drives do not generally use MOSFETs, not for the actual switching at least. Older inverters (80s–90s, e.g. German class 120 and 101 locos and ICE 1 and 2 powerheads) use gate turn-off thyristors; newer ones use insulated-gate bipolar transistors.

[Gazz292]

i know what MOSFET stands for.  but i can guess it's just me and you who care about this stuff?

i also have a 'problem' where i mix terms and names for things up at times.. hence why i use '...etc' a lot in my posts, trying to convey that other better explanations are available. 

I know a little bit about electronics but not a great deal, i'm more of a mechanical guy,  but i like to learn how things work,
i know roughly how the VFD works on my milling machine... it takes in 240 volts AC, turns it into DC at about 350 volts (RMS of 240 volts)
Then it chops that DC up (PWM) using IGBT's to produce a pseudo 3 phase output that the 3 phase motor (wired in Delta) can handle. 

The motor needs to be rated for inverter use as it will run hotter on the less than perfect polyphase 'AC'  and boy does it chuck out a lot of RFI... but this is a cheap chinese consumer level inverter rated at just 2.5 Kw, 

the systems in a locomotive are slightly better, and a lot bigger 🙂

[Angelo]

22 hours ago, Gazz292 said:

 

[...] and that 3Kv DC comes out of the first motor and feeds into the second motor (series connection) then the power comes out of the 2nd motor and to earth via the rails.

Just a small correction: the EU07 has 4 motors; when in series, they're powered one after the other, so the voltage is divided by 4; when in "parallel" (which is not a "true" parallel) they're divided in 2 groups, each made of 2 motors in series, and the groups are in parallel, so the voltage is only divided by 2.

This voltage is not actually 3 kV: yes, it comes from the overhead wires which are at ~3000-3500 V DC ca., but two things will reduce the voltage actually measurable at the motors:

- at slow speeds, most of the voltage will be across the resistors;

- at higher speeds, when the resistors are excluded, the rotating motors will generate a voltage opposite to the one that's feeding them, which will "erase" most of it: each motor may be set at, say, 3200V/4= 800V, but at a certain speed it will produce say -750V which will result in only 50V measured across it.

[Gazz292]

yeah, i'm kinda rubbish at explaining things, 
i sort of treated the 2 motors in each bogie as one as they are permanently connected in series (i think... i learn new stuff every day) 

i didn't mean to imply the actual voltage at the motors when in a notch with the resistances in circuit would be 1.5 or 3Kv (or so), but i see now that i implied that there will be that voltage at all times, which isn't true for a DC motor...

a simple AC motor maybe, as the speed for an AC motor is dependant on the frequency of the alternating current  (i notice my mill and lathes VFD's change both the frequency and the voltage output when i measure it with a simple multimeter, but the lower voltage at slow speeds could be the back EMF thing i'm seeing?
i've always chickened out of connecting the oscilloscope to my cheap VFD's (by cheap, the xyz brand 2.5Kw VFD sold for £27.50 on aliexpress when i got my milling machine 3 years ago!)

 

[Angelo]

Correct: the motors in each group are permanently in series - which is why, in case of failure of one of them, you have to exclude two motors.

I don't know if they're coupled 1+2 and 3+4 or, like in some Italian rolling stock that I know, 1+3 and 2+4 - this way, when running with only two of them, you never run with only the front bogie motors, which will have less adhesion due to the pitch moment produced by the acceleration.