High Voltage Direct Current electrification

 
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I do wonder if cadet Myrtone can supply information on the extra size of, and extra space required for arc suppression that a 30kVdc circuit breaker requires of a 25kVac circuit breaker.
I do wonder if he realises the differences in the breaking arc characteristics of a DC Circuit Breaker compared to an AC one?
Pressman
I know there are differences at hundreds of kilovolts, but as far as I know, these differences don't apply to lower voltage circuit breakers. Let's compare the spaced needed for a 30kV D.C circuit breaker with that for a 25kV AC transformer.

DC supply means corrosion in the wires, slightly greater resistance than AC.
tazzer96
No, D.C means less resistance - no skin effect. Also, neither the inductance nor capacitance of the cables incurs losses.

Here's another rabbit hole to go down. Electrolysis. Specifically the effect of stray DC currents on other infrastructure. 1500 VDC is bad enough. Stray currents from 30,000 VDC would be a nightmare to control. Yes, there are ways to mitigate the risk like insulating the rails as per the Box Hill tram extension, but members of the Victorian Electrolysis Committee would not be happy. A change to 25 kVAC would see a dramatic reduction in stray currents. See Victorian Electrolysis Committee Resource Manual on http://www.esv.vic.gov.au.
RustyRick
A.C electrification does not exist for trams or light rail, as far as I can see, this would mean too many phase breaks relative to the extent of a tramway network.
Does the voltage used affect electrolysis?

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  M636C Minister for Railways

The cadet continues:

"When France's S.N.C.F adopted 25kV A.C between Aix-les-Bains and La Roche-sur-Foron in southern France in 1953, they were in the same position as we would be adopting 30kV D.C. They were using a standard that no one else had at that time. The standard for new electrification projects has changed over time. If the advent of rectifiers on board trains made standard frequency A.C feasible, where previously either D.C with D.C motors or low frequency A.C with universal motors would have been used, then high voltage inverters on board trains should make way for D.C electrification. Only D.C electrification loads phases evenly, and D.C is the only way to deliver constant power with single wire overhead. And we need DC-DC converters to make it work at higher voltages than 3kV, we didn't back then, now we do."
Myrtone
As someone who came through high school when French was compulsory, at least to third year and who has collected technical material regarding French locomotives and infrastructure ever since, I'm not sure that you quite understand what you are saying there...

I'll look up the early test locomotives, for example, but I'm not sure they all had rectifiers...

The big test of AC electrification was in the north east where the French electrified the lines to the coal mines near the German border on the Est region.

At least one class of heavy freight locomotive (CC 14100?) had rotary conversion of 50Hz to DC and even the locomotives with rectifiers had mercury arc rectifiers, big glass balloons that didn't like locomotives much at all. These were progressively replaced by Germanium and Silicon rectifiers as time went on.

The French really went out on a limb with 25kV AC. It worked, but not nearly immediately. They continued to extend 1500 DC south from Lyon to Marseilles and finally adopted AC from there to Nice and on to Italy. They used DC locos on the "Mistral" to Marseilles and dual voltage locos on to Nice. This wasn't a big problem because the train reversed at Marseilles and the train split there anyway.

The DC is still there and was only bypassed by the extension of the LGV for passenger traffic.

The Mistral was a real train with compartments and dining cars and could do 200km/h... and 1500 v DC traction most of the way.

M636C
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I'll look up the early test locomotives, for example, but I'm not sure they all had rectifiers...
M636C
Test locomotives may be, but what about working ones?

At least one class of heavy freight locomotive (CC 14100?) had rotary conversion of 50Hz to DC and even the locomotives with rectifiers had mercury arc rectifiers, big glass balloons that didn't like locomotives much at all. These were progressively replaced by Germanium and Silicon rectifiers as time went on.
M636C
I had no idea that rotary converters existed onboard locomotives. If they did, then standard frequency electrification would have existed earlier. I have heard of mercury arc rectifiers on board trains, and I have heard of grid controlled mercury arc valves elsewhere. First of all, to get it working onboard trains would have involved making them vibration resistant. But if mercury arc valves could work on board a vehicle, and grid controlled mercury arc valves existed back then, one might wonder why chopper control for electric vehicles didn't yet exist. Was it proposed back then?

The French really went out on a limb with 25kV AC. It worked, but not nearly immediately. They continued to extend 1500 DC south from Lyon to Marseilles and finally adopted AC from there to Nice and on to Italy. They used DC locos on the "Mistral" to Marseilles and dual voltage locos on to Nice. This wasn't a big problem because the train reversed at Marseilles and the train split there anyway.
M636C
And they were the first to adopt it.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
I do wonder if cadet Myrtone can supply information on the extra size of, and extra space required for arc suppression that a 30kVdc circuit breaker requires of a 25kVac circuit breaker.
I do wonder if he realises the differences in the breaking arc characteristics of a DC Circuit Breaker compared to an AC one?


I know there are differences at hundreds of kilovolts, but as far as I know, these differences don't apply to lower voltage circuit breakers. Let's compare the spaced needed for a 30kV D.C circuit breaker with that for a 25kV AC transformer.
Myrtone
NO NO NO Don't try and side step the question!
Firstly, Yes there is differences between AC and DC circuit breakers at all voltages. (Extra High, High, Medium, Low and Extra Low)
Even at Extra Low Voltages you can get away with using an AC Circuit Breaker on a DC voltage, but it's life time and reliability are greatly reduced!
{Incidentally, 25kVac and 30kVdc both fall within the Medium Voltage zone}




Secondly, Why do you now side step the original question with a substitute that is akin to comparing Orange Juice with crushed Onion pulp?

Sorry Cadet Myrtone you get an FAIL on this one
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Contrary to that post by @LancedDendrite, I'm not really the cadet here. There is a cadet advocating high voltage D.C, but it's not me. I don't know enough about the details to be a cadet here.
Is it true that even an A.C circuit breaker can form an arc if opened at any of the wrong points in the cycle, and that A.C circuit breakers are thus timed to open at zero crossing points? Do D.C circuit breakers typically have capacitors in parallel with the contacts?

EDIT: Here is my point. While I don't know whether a medium voltage D.C circuit breaker would take up more space that a medium voltage AC circuit breaker, I do know converting onboard to A.C at a higher frequency than the mains means that the transformer will take up less space, even if it's polyphase. My guess is that the difference between the size of even a three-phase 400Hz transformer and a single-phase 50Hz transformer (same power rating) would be greater than the difference between the size of D.C and single phase circuit breakers at medium voltage.
  M636C Minister for Railways

The cadet continues:

"When France's S.N.C.F adopted 25kV A.C between Aix-les-Bains and La Roche-sur-Foron in southern France in 1953, they were in the same position as we would be adopting 30kV D.C. They were using a standard that no one else had at that time. The standard for new electrification projects has changed over time. If the advent of rectifiers on board trains made standard frequency A.C feasible, where previously either D.C with D.C motors or low frequency A.C with universal motors would have been used, then high voltage inverters on board trains should make way for D.C electrification. Only D.C electrification loads phases evenly, and D.C is the only way to deliver constant power with single wire overhead. And we need DC-DC converters to make it work at higher voltages than 3kV, we didn't back then, now we do."
Myrtone

The line opened from Aix-les Bains to Annecy in October 1950 and was extended to La Roche-sur-Foron in May 1951.

There were three locomotives on the line:

CC6051 from Oerlikon, which was basically a Swiss Federal Ae6/6 fitted with motors suitable for 50Hz current.

CC 6052 from Alsthom, which was basically an SNCF CC7101 fitted with a transformer and motors suitable for 50Hz current.

BB8051 from Alsthom which was a BB8100 fitted with transformer and an air cooled rectifier with DC motors.

There was also an electric multiple unit car for passenger service.

The first main line ran between Thionville near Metz to Valciennes south east of Lille.
It hadn't opened at the date of my reference, "Chemins de Fer" of March /April 1953.

Four types of locomotives were puchased:

CC14000 Co Co freight, with three phase motors and a rotary converter from single phase to three phase (20 units)
CC14100 Co Co freight, with DC motors and a rotary converter from single phase to DC (102 units)

BB12000 Bo Bo mixed traffic with transformer and rectifiers (ignitrons) and DC motors (148 units)
BB13000 Bo Bo mixed traffic with transformer and 50Hz motors (53 units)

The prices for these each at the time were:

BB 12000 96 million FF
BB 13000 98 million FF
CC 14100 121 million FF
CC 14000 136 million FF

It is clear why the rectifier locomotives won the day in 1953.
Now with solid state converters, single phase AC converted to three phase AC for the motors is almost universal.

So if Myrtone's statement is true, we might expect some years of testing different technologies and following up blind alleys before 30kV Dc electrification could be made to work...

It might also be borne in mind that the Germans tested 20kV 50Hz on the Hollentalbahn in the Black Forest area in 1936 (so fifteen years before the French)

They had four locomotives:

E244 01 with a Mercury Arc rectifier and DC motors.
E244 11 with a Mercury Arc rectifier and DC motors.

E244 21 with 50Hz AC commutator motors
E244 31 with 50Hz AC aysnchronous single phase motors

A fifth locomotive E244 22 was rebuilt from a dameaged E44 after WWII

The line was converted to standard 15kV 16.66 Hz in 1960.

None of this suggests to me that the adoption of a new system of electrification would be simple or rapid.
The German case suggests that the advantages of the higher frequency were not great enough to justify a change.


M636C
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
There were three locomotives on the line:

CC6051 from Oerlikon, which was basically a Swiss Federal Ae6/6 fitted with motors suitable for 50Hz current.

CC 6052 from Alsthom, which was basically an SNCF CC7101 fitted with a transformer and motors suitable for 50Hz current.

BB8051 from Alsthom which was a BB8100 fitted with transformer and an air cooled rectifier with DC motors.
M636C
See below.


CC14000 Co Co freight, with three phase motors and a rotary converter from single phase to three phase (20 units)
CC14100 Co Co freight, with DC motors and a rotary converter from single phase to DC (102 units)

BB12000 Bo Bo mixed traffic with transformer and rectifiers (ignitrons) and DC motors (148 units)
BB13000 Bo Bo mixed traffic with transformer and 50Hz motors (53 units)
M636C
Firstly, wouldn't converting single phase to three phase need a motor-generator with a flywheel?
Secondly, I wasn't aware of rotary converters being fitted on-board trains until a previous post mentioning them. See below for more.

So if Myrtone's statement is true, we might expect some years of testing different technologies and following up blind alleys before 30kV Dc electrification could be made to work...
M636C
I'm not quite sure what you mean.


It might also be borne in mind that the Germans tested 20kV 50Hz on the Hollentalbahn in the Black Forest area in 1936 (so fifteen years before the French)

They had four locomotives:

E244 01 with a Mercury Arc rectifier and DC motors.
E244 11 with a Mercury Arc rectifier and DC motors.

E244 21 with 50Hz AC commutator motors
E244 31 with 50Hz AC aysnchronous single phase motors
M636C
Firstly, I didn't realise that mercury arc rectifiers could work on board trains back then.
Secondly, I thought traction sized commutator motors could only work with a lower frequency, or with direct current.
Thirdly, I don't see how an induction motor on a fixed frequency supply, let alone single phase, could be suitable from traction purposes, could it have been repulsion-induction, if anyone here knows what that is?

The line was converted to standard 15kV 16.66 Hz in 1960.
M636C
But this was only one line, in a country where other A.C electrified lines had long been electrified at 162/3Hz, so it was most certainly converted to conform with the rest of the network.

None of this suggests to me that the adoption of a new system of electrification would be simple or rapid.
The German case suggests that the advantages of the higher frequency were not great enough to justify a change.
M636C
Germany has a whole separate 162/3 power grid to supply its electrified railway network, and this requires different transformers on board the locomotives and motor coaches to standard frequency, low frequency ones being larger and heavier. Changing over to standard frequency, with a corresponding increase in weighted average line voltage from 15-25kV, increasing the peak voltage by the same amount, would likely require replacing the existing insulators with larger ones, and would certainly require either all the transformers changed or locomotives and motor coaches having oversized transformers during the changeover. And the special traction power grid would need to be cut back while the transition is done.
Much like the reasons that Iarnród Éireann, who operates Ireland's national railways, and uses the same 1600mm track gauge as Victoria and South Australia, won't regauge their tracks, the reasons that the Germans, Austrians' Swiss, Swedes and Norwegians won't change over the line voltage appear to be similar to the reasons that no government would simultaneously replace all water mains in their area at once.
But converting from 15,000 volts D.C to 25kV A.C seems to be pretty trivial by comparison to replacing every water main over a wide area at once. The same power grid would be used as before the changeover, and dual voltage rolling stock would contain transformers and rectifiers which are bypassed under 15,000 volt D.C overhead. The insulators would still need to be replaced and substations redone.
As far as I can see, converting 25kV A.C to 30kV D.C would be pretty trivial even compared to going from 15,000 volts D.C to 25kV A.C. No new insulators needed, pretty much the only thing needing to be changed would be the substations on the wayside and input package on the locomotives and/or motor coaches.
  RustyRick Chief Commissioner

Location: South West Vic
And there it is. Myrtone, please stop throwing out random ideas you've found by Googling. Electrolysis vs voltage? Replacing all water mains in a city at once? Seriously, I'm speechless. Are you looking at a career in politics with your random use of facts and half baked analogies trying to be passed off as reality.

See, you only replace water mains if they no longer meet the intended purpose. An organisation doesn't just decide to replace everything if it still fulfills it's intended purpose. Replacing 100 year old cast iron with pvc because its the latest? Not going to happen.

Dual voltage rolling stock? Keep digging.

Rick
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Imagine being told that all water mains in your town are going to be replaced at once and you will have no running water while they do it. This is not a random idea. Water mains would not be replaced like that in the real world, they must be replaced bit-by-bit, it is to be hoped it doesn't take much thought to see why. Too much disruption. If, for example, you replace the cast iron pipes by P.V.C, you do so bit-by-bit, it doesn't all get replaced at once.
It is given as an analogy and as a basis for comparing how complicated things like changing specifications of a railway network (such as gauge or voltage) can be compared to what such a conversion is worth.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
Imagine being told that all water mains in your town are going to be replaced at once and you will have no running water while they do it. This is not a random idea. Water mains would not be replaced like that in the real world, they must be replaced bit-by-bit, it is to be hoped it doesn't take much thought to see why. Too much disruption. If, for example, you replace the cast iron pipes by P.V.C, you do so bit-by-bit, it doesn't all get replaced at once.
It is given as an analogy and as a basis for comparing how complicated things like changing specifications of a railway network (such as gauge or voltage) can be compared to what such a conversion is worth.
Myrtone
Imagine being the council of an old European city and being told your sewer pipe needed replacing, but you couldn't dig up the heritage listed cobble stone streets to replace the pipes!


Until some smart guy from Adelaide worked out how to reline the old earthenware sewer pipes with PVC without digging anything
up. He made his company millions!
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Until some smart guy from Adelaide worked out how to reline the old earthenware sewer pipes with PVC without digging anything
up. He made his company millions!
Pressman
Did this really happen? Even if it did, water mains would surely still be replaced a little at a time.
  Big J Deputy Commissioner

Location: In Paradise
Until some smart guy from Adelaide worked out how to reline the old earthenware sewer pipes with PVC without digging anything
up. He made his company millions!
Did this really happen? Even if it did, water mains would surely still be replaced a little at a time.
Myrtone
Relining has been in the water industry for years. Pressman was not inferring that they would do the whole water network at once. Asset life is restored in a progressive manner as the original pipes for a city network were laid progressively (over a century plus in some cases) and not at once.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
Until some smart guy from Adelaide worked out how to reline the old earthenware sewer pipes with PVC without digging anything
up. He made his company millions!
Did this really happen? Even if it did, water mains would surely still be replaced a little at a time.
Myrtone
Unlike some 'stories' in the annals of Wikipedia, yes this DID really happen.
The process was invented in Adelaide during the 1980's by Bill Menzel (of Menzel Plastics) who named the method as "Rib Loc" pipe. It is a spiral wound watertight poly pipe made from recycled polyethylene. (Yes that's old plastic milk and soft drink bottles!)
He further developed the rib loc system to enable it to expand once formed.
A special winding machine is lowered down a manhole (less than 450mm diameter) into the pipe to be relined. The rib loc pipe is then wound by the machine into a continuous length inside the existing pipe. then the machine head reverses the direction which expands the pvc pipe to the diameter of the existing pipe.
The rib loc pipe is as strong as concrete pipe, and because the winding machine is small enough to be lowered into manholes, you don't need to dig up any pipes at all.
By 1999 the Rib Loc company was turning sales over $24 million per annum
  justapassenger Minister for Railways

Dual voltage rolling stock?
RustyRick
Where multi-system locos or EMUs are used in Europe on both 15kV 16.7Hz and 25kV 50Hz systems (and possibly also DC) they must have separate transformers for each different AC system and not Myrtone's mythical oversized transformer. On EMUs this will typically result in having separate pantographs (a Velaro e320 unit has eight pantographs) as the transformers will be located under different cars.

Multi-system rolling stock is a pain to operate, not least because maintenance depots need to be capable of testing and diagnosing faults on all of the systems. You would only choose it when there is a need for through services running between two different networks that have grown together from opposite directions.
  M636C Minister for Railways

Dual voltage rolling stock?
Where multi-system locos or EMUs are used in Europe on both 15kV 16.7Hz and 25kV 50Hz systems (and possibly also DC) they must have separate transformers for each different AC system and not Myrtone's mythical oversized transformer. On EMUs this will typically result in having separate pantographs (a Velaro e320 unit has eight pantographs) as the transformers will be located under different cars.

Multi-system rolling stock is a pain to operate, not least because maintenance depots need to be capable of testing and diagnosing faults on all of the systems. You would only choose it when there is a need for through services running between two different networks that have grown together from opposite directions.
justapassenger
My understanding is that a low frequency transformer is suitable for a higher frequency, but that is larger and heavier than would be required for the high frequency alone. It would have to be insulated for the highest voltage and be able to be tapped for the appropriate outputs on each input voltage, but in general only one transformer is needed.

Multiple pantographs are needed because the clearance for pantographs and the stagger of the catenary vary between countries, so in general one pantograph per system per country (so in France 1500 vDC and 25kV AC require different pantographs, in this case because of the different current draw from the overhead).

The number of pantographs on a Velaro will vary with the number of cars. On the Velaro, every second car is powered and the transformer is on a trailer car which should power the cars either side. Alternate trailers do not have transformers or pantographs.

M636C
  M636C Minister for Railways




CC14000 Co Co freight, with three phase motors and a rotary converter from single phase to three phase (20 units)
CC14100 Co Co freight, with DC motors and a rotary converter from single phase to DC (102 units)

BB12000 Bo Bo mixed traffic with transformer and rectifiers (ignitrons) and DC motors (148 units)
BB13000 Bo Bo mixed traffic with transformer and 50Hz motors (53 units)Firstly, wouldn't converting single phase to three phase need a motor-generator with a flywheel?

Secondly, I wasn't aware of rotary converters being fitted on-board trains until a previous post mentioning them. See below for more.

So if Myrtone's statement is true, we might expect some years of testing different technologies and following up blind alleys before 30kV Dc electrification could be made to work...
I'm not quite sure what you mean.


It might also be borne in mind that the Germans tested 20kV 50Hz on the Hollentalbahn in the Black Forest area in 1936 (so fifteen years before the French)

They had four locomotives:

E244 01 with a Mercury Arc rectifier and DC motors.
E244 11 with a Mercury Arc rectifier and DC motors.

E244 21 with 50Hz AC commutator motors
E244 31 with 50Hz AC aysnchronous single phase motors


Firstly, I didn't realise that mercury arc rectifiers could work on board trains back then.
Secondly, I thought traction sized commutator motors could only work with a lower frequency, or with direct current.
Thirdly, I don't see how an induction motor on a fixed frequency supply, let alone single phase, could be suitable from traction purposes, could it have been repulsion-induction, if anyone here knows what that is?

The line was converted to standard 15kV 16.66 Hz in 1960.
But this was only one line, in a country where other A.C electrified lines had long been electrified at 162/3Hz, so it was most certainly converted to conform with the rest of the network.
Myrtone

The good news is that you have learnt a number of new things about railway electrification.

The present 25kV system didn't spring to life fully formed at Aix-les-Bains in 1950
Years of work before and after were required.

The BB 13000 class with 50Hz AC motors were in service for around thirty years. There were only a third as many as the BB12000s but they lasted nearly as long. The CC 14000s were not as successful. The rough diagram I've seen doesn't indicate if there was a flywheel on the converter but there were two single phase to three phase converters, one each side of the central cab. The CC14100 had a single converter which was a single AC motor driving two conventional DC generators, one each end of the shaft. These lasted as long as the two other classes.

But the point I was trying to make regarding your question above which I've italicised was:

If the best railway electrification engineers in France and Germany took around 25 years to come to the best solution for 25kV 50Hz traction, as indicated by the different technologies shown in my earlier posts, how long will it take to get a 30kV DC system to work, and can we be sure it will cost less in the long run?

The main reason to adopt 50Hz was that it could be drawn from the national grid anywhere it was required. The national grid will remain 50Hz (except for the Tasman link which hasn't being doing too well lately). So we would need to convert 50Hz to DC whereever the railway required it.

As regards Germany. There was relatively little electrification in Germany up to 1939. It was concentrated in a few areas. Had the 20kV 50Hz been a success in the Black Forest, the main lines would have been 20kV and the existing systems converted. One difference was that when Austria was incorporated in Germany in 1938, (after the 20kV trials) a lot more 16.66 Hz main line electrification came into Germany. The Germans built new locomotives for Austria to standard German designs (E 18, E94) and post war the additional experience gained from Austria helped to confirm the low frequency as the way to go. German and Austrian locomotives have run across those borders for years.

M636C
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
Where multi-system locos or EMUs are used in Europe on both 15kV 16.7Hz and 25kV 50Hz systems (and possibly also DC) they must have separate transformers for each different AC system and not Myrtone's mythical oversized transformer. On EMUs this will typically result in having separate pantographs (a Velaro e320 unit has eight pantographs) as the transformers will be located under different cars.
justapassenger
I've heard they just de-rate the transformer when running on the non-native frequency.
Multi-system rolling stock is a pain to operate, not least because maintenance depots need to be capable of testing and diagnosing faults on all of the systems. You would only choose it when there is a need for through services running between two different networks that have grown together from opposite directions.
justapassenger
Surely you might also use dual system rolling stock when converting an existing network bit-by-bit to another standard. The pain of operating such rolling stock is in this case a temporary inconvenience for a long term gain.
The present 25kV system didn't spring to life fully formed at Aix-les-Bains in 1950
Years of work before and after were required.
M636C
I have heard of previous standard frequency A.C systems at lower voltages, but these weren't widespread.
The BB 13000 class with 50Hz AC motors were in service for around thirty years. There were only a third as many as the BB12000s but they lasted nearly as long. The CC 14000s were not as successful. The rough diagram I've seen doesn't indicate if there was a flywheel on the converter but there were two single phase to three phase converters, one each side of the central cab. The CC14100 had a single converter which was a single AC motor driving two conventional DC generators, one each end of the shaft. These lasted as long as the two other classes.
M636C
A single phase motor would need a flywheel in that application because of torque pulsations.
If the best railway electrification engineers in France and Germany took around 25 years to come to the best solution for 25kV 50Hz traction, as indicated by the different technologies shown in my earlier posts, how long will it take to get a 30kV DC system to work, and can we be sure it will cost less in the long run?
M636C
25kV was a higher weighted average, let alone peak voltage (35 rounded to the nearest kilovolt) then any previous electrification system, meaning larger insulators. Much of the work involved would be getting mercury arc rectifiers working well on board trains. Transformers, including ones with tap-changers, and rectification filters were most certainly proven. As far as I know, most of the components needed in H.V.D.C electrification are already proven, at least in other applications.
The main reason to adopt 50Hz was that it could be drawn from the national grid anywhere it was required. The national grid will remain 50Hz (except for the Tasman link which hasn't being doing too well lately). So we would need to convert 50Hz to DC whereever the railway required it.
M636C
Two other good reasons were that the transformers on-board would be smaller and lighter for a given power rating, offer better performance per currency unit of price, and that standard frequency A.C, when rectified, would be easier to filter. Splitting three-phase 50/60Hz and then converting it to D.C wherever a railway or tramway requires it is exactly what is done with all D.C electrified systems, this includes all the worlds tram and light rail systems and nearly all metro type rail. Although 50 or 60Hz can be drawn for national power grids of the world where it is required, the national grid is three-phase, something that single wire overhead cannot support, so different sections are supplied different phases with phase breaks in-between them. In order to avoid phase breaks, the national polyphase standard needs to be rectified and reconverted. Doing the reconversion on-board the locomotives/motor coaches would removed the limit of one phase and make it possible for the onboard transformer to work with a higher frequency. The higher frequency polyphase current, when rectified, would be much easier to filter.
As regards Germany. There was relatively little electrification in Germany up to 1939. It was concentrated in a few areas. Had the 20kV 50Hz been a success in the Black Forest, the main lines would have been 20kV and the existing systems converted.
M636C
I didn't realise that German railways were mostly electrified that late.
One difference was that when Austria was incorporated in Germany in 1938, (after the 20kV trials) a lot more 16.66 Hz main line electrification came into Germany. The Germans built new locomotives for Austria to standard German designs (E 18, E94) and post war the additional experience gained from Austria helped to confirm the low frequency as the way to go. German and Austrian locomotives have run across those borders for years.
M636C
Are you saying that Austria already have extensive 162/3Hz electrification earlier?
My understanding is that a low frequency transformer is suitable for a higher frequency, but that is larger and heavier than would be required for the high frequency alone. It would have to be insulated for the highest voltage and be able to be tapped for the appropriate outputs on each input voltage, but in general only one transformer is needed.
M636C
I'm told that transformers on German rolling stock are de-rated under French overhead.
  M636C Minister for Railways

I am reminded of the former US Secretary of State who spoke of "Known unknowns" and "Unknown unknowns"...

It is an assumption that high voltage DC for rail traction will not need any technologies not already proven.

Until we at least test it we won't know....

As to whether the CC 14000 needed flywheels, indeed it may have had them...

But the drawing I saw suggested that both converters were more than 2m in diameter at the armature. The motor and generator would have had enough rotating mass to act as a flywheel itself assuming it turned at a standard speed of 1500 rpm or so... But indeed it may have had a flywheel, or just increasing the mass of the three phase generator armature might have done the trick.

As long as you are reasonably fluent in German, the Austrian National Library (ONB) has scanned copies of "Die Lokomotove" available to read and download (up to five pages at a time). This magazine shows the progress of electrification in Austria at various stages during the 1920s and 1930s. In 1939, the magazine moved from Vienna to Berlin and became a German magazine and I think there was one survey of electrification in Germany before publication ceased at the end of 1944 (forty years).

Because of the more mountainous terrain, the Austrians were trying to electrify main lines more quickly than the Germans. For a much smaller and poorer country they had progressed further in my view.

As to transformers, I understood that for lower frequencies, the transformer structure had to be stronger to resist the lower frequency pulsations and to avoid resonance from the alternating current. This means that lower frequency transformers have to be heavier.

M636C
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
It is an assumption that high voltage DC for rail traction will not need any technologies not already proven.

Until we at least test it we won't know....
M636C
Let's see what it would need. It would need onboard medium voltage inverters. In a way, these are proven as inverters working at higher voltages have long existed in high voltage direct current transmission, as this is in the range of hundreds of kilovolts. Transformers, rectifiers, filters, etc are long proven. Medium voltage D.C circuit breakers are doable, again D.C circuit breakers for higher voltages have existed for a long time.
But the drawing I saw suggested that both converters were more than 2m in diameter at the armature. The motor and generator would have had enough rotating mass to act as a flywheel itself assuming it turned at a standard speed of 1500 rpm or so... But indeed it may have had a flywheel, or just increasing the mass of the three phase generator armature might have done the trick.
M636C
Yes, with a large diameter, the armatures would have doubled as flywheels.
  apw5910 Deputy Commissioner

Location: Location: Location.
As to transformers, I understood that for lower frequencies, the transformer structure had to be stronger to resist the lower frequency pulsations and to avoid resonance from the alternating current. This means that lower frequency transformers have to be heavier.

M636C
M636C
It's the other way around. The equations for transformer magnetisation flux show that the lower the frequency, the larger the transformer has to be to avoid saturating the iron core. The electromechanical considerations you mention are important for high power, but "lower frequency means bigger transformer" is fundamental to transformer design (and why they use 400Hz transformers in aircraft, because they are inherently smaller/lighter).
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
The reason that a lower frequency transformer has a greater size to power rating ratio is basically the same as the reason that any transformer works with alternating and not direct current, at least internally.
400Hz seems to be quite common on A.C electrical systems in buildings or vehicles where the alternating current is generated internally. Larger (jet) planes have that, many ships have that, but apparently not trains. Aside from smaller and lighter transformers, 400Hz also increases the power to weight ratio of A.C motors. Does a 16-pole 400Hz motor produce more torque than a 2-pole 50Hz motor?
Also, fluorescent lights running at this frequency won't (appear to) flicker. Is there anyone here who can see flicker in fluorescent lights on 50Hz?
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
The reason that a lower frequency transformer has a greater size to power rating ratio is basically the same as the reason that any transformer works with alternating and not direct current, at least internally.
400Hz seems to be quite common on A.C electrical systems in buildings or vehicles where the alternating current is generated internally. Larger (jet) planes have that, many ships have that, but apparently not trains. Aside from smaller and lighter transformers, 400Hz also increases the power to weight ratio of A.C motors. Does a 16-pole 400Hz motor produce more torque than a 2-pole 50Hz motor?
Also, fluorescent lights running at this frequency won't (appear to) flicker. Is there anyone here who can see flicker in fluorescent lights on 50Hz?
Myrtone
I spent over 10 years doing electrical repair work on ships (both domestic and international) and never found any with a 400Hz supply. They were either 50Hz 400Volt or 60Hz 220Volt 3 phase systems, obviously except for the few that operated on DC supply.

As to the comparison of a 16 Pole 400Hz motor to a 2 Pole 50Hz motor, Torque is directly related to speed, and given that a motor's power output is the same in both cases the synchronous speed of each motor is equal, therefore Torque would be equal.



I'm afraid my eyes are not quick enough to detect a 100Hz flicker in a fluorescent tube (Yes, that is the rate that lamp on 50Hz will flicker)
  62440 Chief Commissioner

Until some smart guy from Adelaide worked out how to reline the old earthenware sewer pipes with PVC without digging anything
up. He made his company millions!
Did this really happen? Even if it did, water mains would surely still be replaced a little at a time.
Unlike some 'stories' in the annals of Wikipedia, yes this DID really happen.
The process was invented in Adelaide during the 1980's by Bill Menzel (of Menzel Plastics) who named the method as "Rib Loc" pipe. It is a spiral wound watertight poly pipe made from recycled polyethylene. (Yes that's old plastic milk and soft drink bottles!)
He further developed the rib loc system to enable it to expand once formed.
A special winding machine is lowered down a manhole (less than 450mm diameter) into the pipe to be relined. The rib loc pipe is then wound by the machine into a continuous length inside the existing pipe. then the machine head reverses the direction which expands the pvc pipe to the diameter of the existing pipe.
The rib loc pipe is as strong as concrete pipe, and because the winding machine is small enough to be lowered into manholes, you don't need to dig up any pipes at all.
By 1999 the Rib Loc company was turning sales over $24 million per annum
Pressman
There is also the system of inserting a soft lining impregnated and using water pressure to fill the pipe. The water is then heated and the lining sets. The impregnation is the same compound as in fibreglass, so you can join frp bends pretty simply. Unfortunately it doesny go round corners. I've relined 42" water mains using this method
  Myrtone Chief Commissioner

Location: North Carlton, Melbourne, Victoria
I spent over 10 years doing electrical repair work on ships (both domestic and international) and never found any with a 400Hz supply. They were either 50Hz 400Volt or 60Hz 220Volt 3 phase systems, obviously except for the few that operated on DC supply.
Pressman
What sort of ships? Presumably, mains frequency was used so they could be plugged into the mains at the dock.

As to the comparison of a 16 Pole 400Hz motor to a 2 Pole 50Hz motor, Torque is directly related to speed, and given that a motor's power output is the same in both cases the synchronous speed of each motor is equal, therefore Torque would be equal.
Pressman
Torque of an electric motor is related to current draw and to load on the motor. There is a limit to the current that a motor can draw, due to back Electro-motive force.

A.C motors are designed to run at specific frequency-to-voltage ratios, the speed, given a certain pole count, being affected by both the frequency and voltage.

I'm afraid my eyes are not quick enough to detect a 100Hz flicker in a fluorescent tube (Yes, that is the rate that lamp on 50Hz will flicker)
Pressman
But there are people who have significant problems with it.
  Pressman Spirit of the Vine

Location: Wherever the Tin Chook or Qantas takes me
I spent over 10 years doing electrical repair work on ships (both domestic and international) and never found any with a 400Hz supply. They were either 50Hz 400Volt or 60Hz 220Volt 3 phase systems, obviously except for the few that operated on DC supply.
What sort of ships? Presumably, mains frequency was used so they could be plugged into the mains at the dock.

As to the comparison of a 16 Pole 400Hz motor to a 2 Pole 50Hz motor, Torque is directly related to speed, and given that a motor's power output is the same in both cases the synchronous speed of each motor is equal, therefore Torque would be equal.
Torque of an electric motor is related to current draw and to load on the motor. There is a limit to the current that a motor can draw, due to back Electro-motive force.

A.C motors are designed to run at specific frequency-to-voltage ratios, the speed, given a certain pole count, being affected by both the frequency and voltage.

I'm afraid my eyes are not quick enough to detect a 100Hz flicker in a fluorescent tube (Yes, that is the rate that lamp on 50Hz will flicker)
But there are people who have significant problems with it.
Myrtone
What sort of ships????
Bulk carriers, container carriers, oil tankers, roll on/roll off carriers ..... Real ships of the merchant marine. And NO very few of
them have "Shore Supply" facilities.
They use common mains voltage and frequency so that they can purchase "off the shelf" electrical equipment and not need specially made items (This is called Common Sense)

____________________________

I am a fully qualified Special Class Electrician and Armature Winder Myrtone, so I Do know what I am talking about.
AC motor speed IS determined by the number of poles and the frequency, not voltage ratios

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