Imaginary Locomotives

[Suzie]

I have a 4mm croc kit that will need an interesting livery when I get round to building it...

[Suzie]

A class 77 had about twice the power of a 76 so I think it might be pushing it with only one pantograph per unit for 5000HP. The double unit would be drawing around 4500A which I guess is quite a lot.

 

Not much by 1960s standards when a single class 86 would produce 5000HP on four axles, but would a DC 86 be heavy enough - 80 tons versus 240 tons at the front.

[scots region]

A class 77 had about twice the power of a 76 so I think it might be pushing it with only one pantograph per unit for 5000HP. The double unit would be drawing around 4500A which I guess is quite a lot.

 

Not much by 1960s standards when a single class 86 would produce 5000HP on four axles, but would a DC 86 be heavy enough - 80 tons versus 240 tons at the front.

 

So the trade off, if I'm reading this correctly, is that AC means a more powerful engine, but a heavier one? I.E a DC engine would have wider route availability, but less grunt than a similar AC engine? 

[Suzie]

No, what I am saying is that a class 86 produces 1250HP per axle, while a class 77 produces around 420HP per axle while a class 76 produces around 165HP 330HP per axle. All had around 20 tons axle load and similar route availability in the 6-8 region. Older technology made for much heavier locos to produce a reasonable amount of power 4x 76 = 2x 77 = 1x 86 = 5000HP).

 

AC or DC has little baring, but higher voltage does mean fewer pantographs can be used. A heavier overall loco would make for better braking on an unfitted train, but would not be much advantage on a fitted train.

 

Perhaps we need a 4x76 A-B-B-A lashup American style like the Milwaukee Road EF5... 

 

Corrected miscalculation!

Edited October 27, 2017 by Suzie

[scots region]

No, what I am saying is that a class 86 produces 1250HP per axle, while a class 77 produces around 420HP per axle while a class 76 produces around 165HP per axle. All had around 20 tons axle load and similar route availability in the 6-8 region. Older technology made for much heavier locos to produce a reasonable amount of power 4x 76 = 2x 77 = 1x 86 = 5000HP).

 

AC or DC has little baring, but higher voltage does mean fewer pantographs can be used. A heavier overall loco would make for better braking on an unfitted train, but would not be much advantage on a fitted train.

 

Perhaps we need a 4x76 A-B-B-A lashup American style like the Milwaukee Road EF5... 

 

Ah forgive my ignorance. Electric locos are fascinating to me. 

[Budgie]

Perhaps we need a 4x76 A-B-B-A lashup American style like the Milwaukee Road EF5...

Like this?

 

[Suzie]

Yes, just like that. I drool every time I see your picture. 3000V DC rather than 1500V DC and slightly more powerful than 4x class 76 which would not get away with just two pantographs, but very comparable in many respects.

[DavidB-AU]

AC or DC has little baring, but higher voltage does mean fewer pantographs can be used.

AC or DC has a bearing on the size of the commutator required for any given amount of power. To get the power per axle of the 86 on DC would require traction motors that simply wouldn't fit in the locomotive.

 

Another major advantage of AC over DC is the amount of electrical infrastructure required before the power gets to the overhead and the losses in transmission. You don't need nearly as many substations for AC. Supply efficiency of AC is also about 98% compared to about 92-94% for DC.

 

Cheers

David

Edited October 27, 2017 by DavidB-AU

[Satan's Goldfish]

Well, my work here was easily done....

 

Budgie, I was familiar with the 'Little Joe's' but not familiar with the EF5, thanks for adding that picture.

[Suzie]

 

I think that the LNER might have produced this as their version of the EF5

[Northmoor]

No, what I am saying is that a class 86 produces 1250HP per axle, while a class 77 produces around 420HP per axle while a class 76 produces around 165HP per axle. 

 

Er, wouldn't that mean a Class 76 has a maximum rating of 660hp.  Think you've made a typo.

[Satan's Goldfish]

Class 76; max continuous rating of 1300hp = 325hp per axle, or just shy of 165hp per wheel.

[cheesysmith]

Ok. electric loco 101.

 

A electric loco is limited inn power as to how much electricity it can pass to the motors without overheating/bursting into flames. This is related to how many amps are passing through the electrical systems inside the loco. If the volts increase, the amps decrease. A EM1 has a maximum rail HP of 1868, or 1360 continuous, roughly the same as half a 4REP EMU. But operating at twice the voltage, the amps would have been a quarter. The same applies when you compare 6.25kV AC Vs 25kV AC (1/4 the volts = 4x the amps). To show what this means lets use the old equation of V x A=W. A EM1 has a continuous power output of 1015kW, at a nominal OHL voltage of 1500 volts. So if we have 1.5kV divided by 1015kW we have 677 amp (roughly) just for traction, not including any internal resistance, passing through the small contact patch on the pantograph. So a 4REP has 2388kW at a input voltage of 750 V (or 0.75kV). This give a amps of 1791. So two EM1s on a MGR still draw less than half the amps of a single 4REP. A class 91 has a power output of 6300HP/4830kW from a line voltage of 25kW. This gives a amps of 194. 

 

When you compare electrification systems, remember the amps is the amount of work that can be passed through the various electrical systems, from the substations, conductor (either overhead or 3rd rail), contact between the train and conductor (pantograph rubbing strip/3rd rail shoe), and the trains own electrical systems. The volts are how much distance needed to prevent the electricity passing to earth from the conductor and also the amount of insulation required. In simple terms, the higher the volts the more clearance required.

 

Ps-The most powerful DC loco was the class 71, with a maximum of 3000HP/2239kW (2500HP continuous). The 92 are even more powerful, but have less power on 3rd rail than 25kV due to the lower input voltage and a limit on the amps they can pull from the 3rd rail. The EM2 had a 2400HP/1791kW continuous and a maximum of 2700hp/2015kW. Electric locos have a higher short term rating compared to diesels because the only limit to their power output is how much heat they can handle whilst drawing higher amps than normal, and how much power the input voltage can provide. Good examples of this are when the MGRs were introduced from Wath with 4 electric locos per train, no other train was allowed in the same electrical section as there was only enough power in the substation for one train at a time. Another would be the ban on electric locos on the hertford section of the ECML, for exactly the same reason (only designed for the power consumption of the lower powered EMUs). And this is also why the northern sections of the ECML may require the IEP to operate on diesel power when they replace the HSTs, even when under the wires, due to not enough capacity in the substations for all the services to operate electrically.

 

 

 

Note-Does anyone want to check my maths? Please?

Edited October 27, 2017 by cheesysmith

[Ramblin Rich]

All makes sense to me, just got your units wrong for the statement about 4REPS "4REP has 2388KW at a input voltage of 750 W (or 0.75KW)" - should be V not W! If I'm being really picky, should be a lower case k for kilo - upper case K is Kelvin (temperature) . Only being pedantic for sake of completeness mind you, the explanation is very good. It also illustrates why higher voltage lines can be smaller conductors due to lower current (amps); also I seem to remember the power wastage is lower if the current is lower.

I must say the currents being drawn by the 4REPs look frightening (and the class 71s proportionally higher)! Does anyone know what the maximum current a 3rd rail conductor could support?

As an aside I read that the fast charge stations for a Tesla model S electric car is around 400A, which puts it outside the possibility of domestic supply!

Edited October 27, 2017 by Ramblin Rich

[Suzie]

Yes, I did make a mathematical error! Sorry.

 

Fast chargers for cars typically use something in the region of 21KW from 3-phase. A bit of a pain in the UK where domestic 3-phase is quite rare. Fast charging is around 50V DC between the charger and car hence the 400A.

Edited October 27, 2017 by Suzie

[cheesysmith]

All makes sense to me, just got your units wrong for the statement about 4REPS "4REP has 2388KW at a input voltage of 750 W (or 0.75KW)" - should be V not W! If I'm being really picky, should be a lower case k for kilo - upper case K is Kelvin (temperature) . Only being pedantic for sake of completeness mind you, the explanation is very good. It also illustrates why higher voltage lines can be smaller conductors due to lower current (amps); also I seem to remember the power wastage is lower if the current is lower.

I must say the currents being drawn by the 4REPs look frightening (and the class 71s proportionally higher)! Does anyone know what the maximum current a 3rd rail conductor could support?

As an aside I read that the fast charge stations for a Tesla model S electric car is around 400A, which puts it outside the possibility of domestic supply!

 

My post duly edited. Thanks.

 

Also, to compare power of different locos/units, the conversion factor is 1kw = 1.341 British HP.

 

As a ide note, the 71 electric loco is different, in that the voltage to the motors can be higher than the input volts of 750V due to the fact the 750V input from the 3rd rail actually powered a booster set inside the loco body. This was a big flywheel, with a motor on one end (connected to the 750V 3rd rail supply) and a generator on the other end that supplied the motors (with the electrical switch gear between the motor and generator). If you had 2 generators connected in series, each generator would get 750V from 1500V, so could have been used on the woodhead (although the single pan would have probably exceeded the amps allowed). 

[Coryton]

 Another would be the ban on electric locos on the hertford section of the ECML, for exactly the same reason (only designed for the power consumption of the lower powered EMUs). 

 

Presumably that hasn't been the case for a while, though?

 

Yes, I did make a mathematical error! Sorry.

 

Fast chargers for cars typically use something in the region of 21KW from 3-phase. A bit of a pain in the UK where domestic 3-phase is quite rare. Fast charging is around 50V DC between the charger and car hence the 400A.

 

Never tried it, but I believe it's not too difficult or expensive for most people to get domestic 3 phase if they ask, because all three phases are running past the house anyway even though you normally only have a connection to one.

 

In North America where they use a very different distribution system, it's not so easy.

[cheesysmith]

Also, this talk about V x A=W is also why some DCC decoders cannot work with Heljan motors, as the motors work at the same 12V nominal as other motors, but being more powerful (higher Watts) need more Amps (usually exceeding the 1amp max of most decoders).

 

And UK domestic supplies are 3 phase 415V to the substation, but from there to the house, don`t know. If it is only 240V AC from there to the house, it might be a problem when electric cars take off, as domestic supplies have a big fuse in the supply line with a limit of 100 Amps (IIRC). Most industrial supplies are at 415V 3phase.

[Suzie]

22KW is around 100A at 230V but would be more if mains voltage was lower but still within spec. so a fast charger is really not practical without 3-phase. 3-phase to the home when provided is 415V between phases.

 

I am sure that rather than the government mandating an improvement to the electrical supply infrastructure with all new homes fitted with 3-phase feeds we will all be told to buy an in-house battery that can be trickle charged from the mains when the meagre supply is available and not being used for rush hour electric trains - much like we have to do with the low speed internet!.

[Satan's Goldfish]

in very simples terms, 240v is a single phase of the 415v 3 phase supply. At the low end, the grid moves it around at 11,000v 3 phase, the substation drops it down to 415v 3 phase with a neutral return, the 3 phases are then balanced as close as possible between domestic properties (single phase) being provided for. In commercial applications that use 3 phase, you will find if you look at the circuit breakers that things like lights, domestic sockets, etc, will be allocated to either the Red, Blue, or Yellow phase for the buildings 'domestic' supplies, again with the total load hopefully balanced between all 3 phases.

 

The balancing (or lack thereof) of the phases is why you're told that the neutral wire in a plug isn't necessarily going to equal 0v, as it's the neutral return that helps balance it all out and it can develop 'floating' voltages if things aren't balanced.

 

Standard domestic supply value is 100A which is more than enough for most people, but if you're hooking up to 3 phase though that doesn't have to be set in stone, the limit is the capacity of your cabling and what power networks are able to provide. To put it into context, when I was doing the maths a few months ago for a 100A 3 phase domestic feed over 200m from the substation, the cable with not more than a 5% loss was roughly £14 per meter, and that's before the cost of having it installed.

 

 

 

(As stated at the start, that's all very simplified! I can get more complex with diagrams if you're that bored )

 

 

 

Edit: because I'm being self pedantic: there are many many exceptions to the above, how often have you spotted a transformer on a pole that's just receiving 2 of the phases?!

Edited October 27, 2017 by Satan's Goldfish

[Zero Gravitas]

All makes sense to me, just got your units wrong for the statement about 4REPS "4REP has 2388KW at a input voltage of 750 W (or 0.75KW)" - should be V not W! If I'm being really picky, should be a lower case k for kilo - upper case K is Kelvin (temperature) . Only being pedantic for sake of completeness mind you, the explanation is very good. It also illustrates why higher voltage lines can be smaller conductors due to lower current (amps); also I seem to remember the power wastage is lower if the current is lower.

I must say the currents being drawn by the 4REPs look frightening (and the class 71s proportionally higher)! Does anyone know what the maximum current a 3rd rail conductor could support?

As an aside I read that the fast charge stations for a Tesla model S electric car is around 400A, which puts it outside the possibility of domestic supply!

IIRC, the losses are proportional to (current squared)x(resistance), so as you say, the lower the current, the lower the losses. Which is why the HV National Grid Transmission pylons are at something like 250 kV, with a very small current.

 

Edited for predictive text...

Edited October 27, 2017 by Zero Gravitas

[cheesysmith]

Soory, all this talk on electricity has got us away from imaginary locos. How about these ideas?

 

EM2, but built as a comparison to the BoBos for the WCML? A 25kV EM2 would allow more powerful traction motors.

 

71 but used for passenger servicess on the woodhead (would probably require 2 pantographs).

 

And if the GC had been electrified at 1500V DC, how about EM1 & 2s with 3rd rail pick ups for through freights and passenger services.

 

Or how about when the 309s went to refurb, how about doing what they did with the REPs? Reuse the traction equipment with 156 bodies, with the end powered doors. A 5 coach train of 23m coaches, with the motor mounted 1 under each coach with a drive shaft to a innter bogie and just the gearbox axle mounted for low track forces, with the centre coach having the heavy transformer and disabled bog/access/guards compartment.

Edited October 27, 2017 by cheesysmith

[Satan's Goldfish]

Thanks to your timely reminder, I've stopped writing an essay on how current and Voltage determine the size of the conductor required. I was getting very side tracked!

 

There could have been some merit to a combination of 750v 3rd rail and 1500v overhead combined stock if that had been perused before 25kv took hold. The example of the 71 is good to show the tech was there (just add second pan and switch gear to bypass the booster), but with the bigger 1500V infrastructure, would we now be looking at dual overhead voltage locomotives as 25kv was also introduced to the west and east coasts? Would the GE have remained DC rather than converting to AC instead (EM1 on Norwich passenger?!) Would the new DRS class 88 thus be a combined 25kv AC, 1500V DC, 750V 3rd rail, and last-mile diesel machine? 

[Suzie]

There are plenty of multi-voltage locos in Europe that run on AC and DC - some with four pantographs to keep the systems separate (down to the wire zigzag and loading gauge being different more than anything else).

 

IT is easy to make a DC loco work on AC by adding a transformer and rectifier (in the space vacated by the steam heat boiler perhaps) with some switchgear on the roof, but a twin pan 750/1500 DC 71 sounds like fun - perhaps in a 74 style lengthened body later on to accommodate the transformer for trips on 25KV AC as well when straying from the 'Channel Tunnel' spine route up the GC. Would Settle and Carlisle perhaps be 1500V DC too as a GC extension to Scotland via the Waverley? Edinburgh - Paris 'Scottish Arrow' nameboards on a 71 would be fun too.

[cheesysmith]

The 306 & 307 were DC units, but the DC control equipment and motors were fed from 25kV AC by a transformer that reduced the incoming power to 1500V AC then passed it through a rectifier to make DC. If they had kept the original pantograph as well as the replacement equipment under the trailer coach, you could have a unit able to work on both systems. They would also have been able to work on 3rd rail, but at half power.

 

The 313 is just a DC 750V unit, with a pantograph and transformer/rectifier on the centre coach.

 

The advantage of the 2 DC electrification systems is that if the motors were arranged with both series and parallel switching between pairs of motors, the same train would be able to work off both 1500V and 750V, within the limits of how many amps you can safely draw.