gka472l
Member
- Joined
- 29 Apr 2016
- Messages
- 429
769424 was in Liverpool Lime Street a bit earlier this morning, not seen one in before......it was using electric power though
I wonder what the reason is for pulling into the station with the engines almost at full speed?Here we go. 769008 at Aber
It’s no problem, just glad the units are making progress towards entering service hopefully! However, I did notice that the second run only got to Heath High Level again then returned back to the depot again, another engine issue?Thanks for posting Bob and Adlee. These are very smart looking units, the TfW livery is the smartest I think. I hope these four car units are a step up from what went before. The trouble is that it is taking too long all over the country for new, refurbed and cascaded trains to be introduced.
It's the set up, the engines are designed to supply 750v constant supply, to mimic the supply from the third rail; so not like a standard engine which would rev up and down according to power demand.I wonder what the reason is for pulling into the station with the engines almost at full speed?
Can you explain that to an engineering simpleton please - where does all the power go if the motors aren’t drawing it?It's the set up, the engines are designed to supply 750v constant supply, to mimic the supply from the third rail; so not like a standard engine which would rev up and down according to power demand.
On another note, I see the pantograph has been taken off.
But why is the power demand so high when the train is decelerating? The engine speed drops off once it comes to a stand. It's still lower when departing then when it arrived at the station. That's not how other DEMUs behave.It's the set up, the engines are designed to supply 750v constant supply, to mimic the supply from the third rail; so not like a standard engine which would rev up and down according to power demand.
On another note, I see the pantograph has been taken off.
In a conventional diesel electric vehicle the engine generates power which is passed directly to the traction motors to convert into motion through the axles (keeping it simple before anyone says more), a higher moving speed (as an example) requires more power to the traction motors so a higher demand on the engine. On a 769 the diesel engines are generating a constant 750v DC to be passed down the bus line (the high voltage cable) to the transformer, at this point the unit works like a 319 electric unit in that the power is passed through the transformer to be used from there; which is why a 769 still generates the buzzing noise like a 319.Can you explain that to an engineering simpleton please - where does all the power go if the motors aren’t drawing it?
Thanks, but if the engine is running full whack it is creating power which the motors aren’t using - where does that energy go, heat?In a conventional diesel electric vehicle the engine generates power which is passed directly to the traction motors to convert into motion through the axles (keeping it simple before anyone says more), a higher moving speed (as an example) requires more power to the traction motors so a higher demand on the engine. On a 769 the diesel engines are generating a constant 750v DC to be passed down the bus line (the high voltage cable) to the transformer, at this point the unit works like a 319 electric unit in that the power is passed through the transformer to be used from there; which is why a 769 still generates the buzzing noise like a 319.
The voltage output is a constant 750v which is why it should rev at it's maximum speed most of the time, there will be something technical around electric demand on the supply which means it does sometimes rev down and up but that's electrical and I haven't seen the 769 manual
No you're right, I don't wish to sound unkind but AMD's response doesn't answer the question. I suspect it may either be a software defect with the unit, or perhaps some sort of debug mode to have the rear engine operate at full speed continuously while the unit is in motion.Thanks, but if the engine is running full whack it is creating power which the motors aren’t using - where does that energy go, heat?
Apologies to my Physics teacher if I am being a muppet....
Thanks, but if the engine is running full whack it is creating power which the motors aren’t using - where does that energy go, heat?
Apologies to my Physics teacher if I am being a muppet....
If the diesel engine and its generator aren't connected to a load, you're still busy releasing chemical energy from the diesel combustion. If it's not being converted to electrical energy, then it must be converted to other forms (e.g. heat and/or sound); it's not going to disappear anywhere.Doesn't it depend on whether the the generator is connected to a load at the time? If there is no load then current can't flow, so electrical power is not being generated?
Right, but in the video example, doing some quick tonal analysis, the unit arrives (with minimal load as braking) with both engines running at about 1750rpm. Once stationary (with the same minimal load) they are idling at about 1100rpm. Once underway and when power is actually required, that only increases to 1500 at first (a lower power notch for initial acceleration I assume), rising to 1800 shortly thereafter (presumably maximum). The point I'm trying to make here is that arriving at the stations with the engines running at that speed doesn't make any sense.
But only when decelerating, and not when stationary?My best guess and this is only a guess, is that as this is a retrofit rather than clean sheet design, any ancilliary and other high load systems still need supplying when on gen set supply.
On a conventional EMU it is not just traction motors that are supplied, heating is usually 240v and cab air con systems are a high load system, the battery charger I would imagine would also need to be running at all times to supply the remaining 110v supply for the control circuits and lighting as well as charging the batteries. Which may account for the gen packs running under load when braking or at a standstill.
Youtube? It's free and only requires a google account.Engine idle noise did vary a little stopping at Lisvane.My video of the restart(as it’s in a cutting) gives a good idea of sound levels.Happy to post it, but I dont want to get involved with “Photobucket”, any suggestions for another preferably free app?
No problem, looks goodThanks Samual Morris,took a while to get there.769 At Lisvane on the up line (they still call it the up line as it leads to Cardiff and then London)