Homework help needed please

[chloe90]

Studying the electric locomotive:
1) if 25kV, 50HZ AC is from the power grids then what does the transformer reduce it to?
2) whats the DC voltage from the rectifier before turning it into 3 phase?

I've read they're 80-90% energy efficient but is this broken down anywhere to show the calculations and prove it

thanks for any help

 

[D365]

My first thought is that the answers to each of your questions would depend on the class of locomotive that you are investigating.

Modern EMUs are typically designed around a 750V DC busline. The Class 92, being dual voltage, might be similar in that aspect.

90% efficiency sounds right for a modern design, but again it will depend on the technical specifications of the class you are interested in.

 

[43096]

Studying the electric locomotive:
1) if 25kV, 50HZ AC is from the power grids then what does the transformer reduce it to?
2) whats the DC voltage from the rectifier before turning it into 3 phase?

I've read they're 80-90% energy efficient but is this broken down anywhere to show the calculations and prove it

thanks for any help

You may find this helpful from Wikipedia (yes, I know... but it does seem to have a source) about the Belgian Type 13 electric locomotives, which suggests 1520V for the step-down voltage under 25kV supplies.

The key text is:

The electrical system differs from the SNCF BB 36000 Astride locomotives: current collection is via one of two pantographs, one used for AC electrification supply, the other for DC supply. Under 25 kV AC the supply voltage is stepped down by a transformer with four 1375 kW 1520 V secondary windings for traction; the traction supply is actively rectified using a pulse chopper circuit. Under 3 kV DC electrification the supply voltage is regulated by a chopper to 2200 V, producing the same intermediate DC supply voltage as when under 25 kV AC electrification. The intermediate DC link powers four individual three phase GTO-based, heat pipe cooled inverters (one per traction motor); the traction motors are force cooled four pole, three phase asynchronous machines (4FXA4-559B) rated at 1280 kW.[1][4][6] The electrical system allows regenerative braking, except under 1.5 kV DC electrification, under which the locomotives operate at reduced power.[6]

Link here: https://en.wikipedia.org/wiki/Belgian_Railways_Class_13

Link (and Google translate) of the technical information here: https://translate.google.co.uk/tran...tp://www.bfoto.be/docu/hl/e13.php&prev=search

Hope that helps...

 

[Snow1964]

The transformer converts to lower voltage, but depends on the class of loco. Multi system locos often change it to the alternative voltage.

In UK classes 81-85 were are originally dual voltage, could operate off either 6.25Kv or 25Kv (simply switched groups of 4 windings from series or parallel), although the 6.25kv was later isolated

 

[jopsuk]

I'd guess that most British EMUs only transform to 750V (before rectifying to variable frequency for the motors) as that makes dual voltage easy as that's what that's supplied at- so it's convenient to design around it, and convenient even for classes that will never use 3rd rail to do so for commonality of systems across ranges?

And as such, a French dual voltage, AC motored train would likely use 1500V DC?

 

[Domh245]

I'd guess that most British EMUs only transform to 750V (before rectifying to variable frequency for the motors) as that makes dual voltage easy as that's what that's supplied at- so it's convenient to design around it, and convenient even for classes that will never use 3rd rail to do so for commonality of systems across ranges?

And as such, a French dual voltage, AC motored train would likely use 1500V DC?

Yup Modern British EMUs use a 750v DC bus (from 319/Networker on?) excluding the 323s which are a 1500v DC bus rather than 750v off the top of my head.

I suspect given OP's name that they're inquiring about Class 90s?

 

[43096]

I suspect given OP's name that they're inquiring about Class 90s?

Although the second question about the DC link voltage before it goes through the inverter to generate three phase would suggest otherwise?

 

[D365]

I suspect given OP's name that they're inquiring about Class 90s?

Although the second question about the DC link voltage before it goes through the inverter to generate three phase would suggest otherwise?

Indeed; it would have to be a Class 92 or newer.

 

[37057]

Some examples using classes 350 and 390...

Nominal transformer output (traction) is 460Vac on a 350 Desiro and 472Vac on a 390 Pendolino.
Nominal DC Link is 750Vdc on a 350 Desiro and 900Vdc on a 390 Pendolino.

 

[O L Leigh]

Well Cl317s use up to 900V DC for traction, so I think we’re back to “it depends” as an answer.

 

[hobbm013]

Is there more to the question than what you’ve posted? Perhaps you could add a picture of the whole sheet, might help to explain it better

 

[43096]

Whilst the EMU examples are interesting, the question related to AC motored electric locomotives, which in the UK is only Classes 88 and 92 and the Eurotunnel shuttle locos.

 

[hooverboy]

Studying the electric locomotive:
1) if 25kV, 50HZ AC is from the power grids then what does the transformer reduce it to?
2) whats the DC voltage from the rectifier before turning it into 3 phase?

I've read they're 80-90% energy efficient but is this broken down anywhere to show the calculations and prove it

thanks for any help

You should probably be a bit more specific as to which type of locomotive. over the years electric traction has moved from the old fashioned way of DC motors with brushes,then to GTO(gate turnout) and thyristor controlled,then to AC motors power by variable frequency drives(off a DC bus)

Also the DC bus voltage has increased over the years, as you dissipate less power in wiring the higher voltage( and lower current) you have.In the old days 750VDC would have been typical,but on newer locos this busline is perhaps 1500vdc nominal.(dissipated power P= I^2 *R , R= rho*Length /area etc etc)

Same sort of thing for rectifier diodes.a silicon diode junction has around 0.7V voltage drop, so multiply that by the number of amps the train will require(1000 amps at 750v would probably be a nice ballpark figure for an EMU) that will give you dissipated power of 700W (for a drive power of 750KW)
If it has a bridge rectifier then multiply by 2, so 1.4KW lost in rectification from AC to DC.

 

[chloe90]

Thanks everyone, so the homework project was to create a block diagram of an electric train to show the electro-mechanical energy transfers and any losses. Trying to keep it basic, I have attached what I've done so now i'm just filling in some blanks.
I then have to prove the efficiency by calculating it, I've attached the example the teacher gave us

Thanks