1500v dc system to a 25 kV AC train system

 
  melbtrip Chief Commissioner

Location: Annoying Orange
How hard would it be for Melbourne train network go from  1500v dc system to a 25 kV AC train system?

The benefits of this:

  • Allows easy country electrification of country lines

  • Lower operating costs of AC versus DC, the more so as DC tension is lower.
    • Better energy efficiency – less current losses.
    • Reduced number of sub-stations, lighter catenary (steel and copper savings)
    • Superiority of AC versus DC well known and universally admited since 1955.
    • Almost all DC electrified networks progressively switched to AC.
    • But no AC network switched to DC since 1927/30 (NS + LBSCR both from 25Hz, but only very short mileage.).
    http://www.rail-electrification-infrastructure-2013.com/media/downloads/32-d2-1616-christophe-keseljevic-rff.pdf

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      dthead Site Admin

    Location: Melbourne, Australia
    Be very hard. but as with any idea, throw enough money at it.....

    Regards,
    David Head
      Myrtone Chief Commissioner

    Location: North Carlton, Melbourne, Victoria
    That's an interresting idea, but DC electrfication loads phases evenly, and transfers constant power and doesn't require phase breaks. Not that I'm firmly against re-electrification, I've had the idea myself for a while, for exactly the benefit mentioned above. But while AC electrification is at a higher voltage than any DC system currently in use, it seems that modern technology does allow HVDC electrification, see this thread.
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    That's an interresting idea, but DC electrfication loads phases evenly, and transfers constant power and doesn't require phase breaks. Not that I'm firmly against re-electrification, I've had the idea myself for a while, for exactly the benefit mentioned above. But while AC electrification is at a higher voltage than any DC system currently in use, it seems that modern technology does allow HVDC electrification, see this thread.
    Myrtone
    There are HVDC transmission lines in Oz and NZ, Bass Link being one and a line in Nth NSW and the NZ N-S trunk line. Is it suitable for rail, probably not. AC would be far better as its alot easier to step down the power once on the train with a basic single phase transformer, you also need far more complicated sub stations and the ability to back feed breaking energy is more difficult.
      melbtrip Chief Commissioner

    Location: Annoying Orange
    The best lines to have done first would be the following:

    • Geelong Line
    • Werribee Line and extend the power lines to the Junction  - having the ability for new Geelong service run via Newport or Sunshine.
    • Pakeham/Cranbourne to Sunbury Lines - with the new metro tunnel
    • Melbourne Airport services
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    How hard would it be for Melbourne train network go from  1500v dc system to a 25 kV AC train system?

    The benefits of this:

    • Allows easy country electrification of country lines

  • Lower operating costs of AC versus DC, the more so as DC tension is lower.
    • Better energy efficiency – less current losses.
    • Reduced number of sub-stations, lighter catenary (steel and copper savings)
    • Superiority of AC versus DC well known and universally admited since 1955.
    • Almost all DC electrified networks progressively switched to AC.
    • But no AC network switched to DC since 1927/30 (NS + LBSCR both from 25Hz, but only very short mileage.).
    http://www.rail-electrification-infrastructure-2013.com/media/downloads/32-d2-1616-christophe-keseljevic-rff.pdf
    melbtrip

    This is mostly true for Greenfield railways, but very few suburban networks have been converted DC to AC and when they have its simply to make life easier with longer distance operations which are at 25kAC or similar. So the statement
    • Almost all DC electrified networks progressively switched to AC.
    is actually incorrect.

    The electrification of country lines in Vic is probably limited to Geelong and the govt has been arguing against this for decades and converting the entire network to 25kVAC doesn't make the argument any stronger.

    Sydney has never been able to justify the conversion, so I doubt Melbourne ever will. The disruption alone would be a nightmare and/or take 30-40 years. Its very expensive for only a marginal return that takes decades.

    http://en.wikipedia.org/wiki/Railway_electrification_in_the_Soviet_Union#DC_vs._AC

    Destroys some of the pro HVAC arguments to convert.

    regards
    Shane
      TheBlacksmith Chief Commissioner

    Location: Ankh Morpork
    In terms of suitability, AC is better for transmission, while DC is better for traction.
      awsgc24 Minister for Railways

    Location: Sydney
    How hard would it be for Melbourne train network go from 1500v DC system to a 25 kV AC train system?
    melbtrip

    Multi-voltage locos and trains are available off the shelf, so you do not have to plan for complete conversion from DC to AC.
    Think France, Czech Republic, USSR, etc, etc.

    Some but not all of India's metro systems are 25kV rather than 1500VDC.

    Melbourne has some difficult overbridges that would be hard to raise to allow for increased clearances for HV AC, such as IIRC, Flinders St overbridge. These bridges are also limiting factors for double deck trains.

    India is now completing the conversion of 1500VDC suburban lines in Bombay to 25kV.

    Holland would like to upgrade its 1500VDC to handle heavier traffic. They are pondering change to 3000VDC, which doubles available power, without having to replace all the insulators, and immunise telephone cables.

    For completely new systems, 25kV is the voltage of choice, except for some metros and light rail.

    Sydney has been strengthening its power supplies by installing additional substations halfway between existing substations, often by converting Sectioning Huts to Substations. More trains and more air-conditioning. Holland has been doing much the same thing.
      Myrtone Chief Commissioner

    Location: North Carlton, Melbourne, Victoria
    There are HVDC transmission lines in Oz and NZ, Bass Link being one and a line in Nth NSW and the NZ N-S trunk line. Is it suitable for rail, probably not. AC would be far better as its alot easier to step down the power once on the train with a basic single phase transformer, you also need far more complicated sub stations and the ability to back feed breaking energy is more difficult.
    RTT_Rules

    But a single phase train only loads one phase at a time, and doesn't get constant instantanious power. Fact is that quite a large transformer is needed to step down 50Hz. In case of single phase transformers, both sides need to be would for full voltage and amperage. Additionally, rectifying and filtering 50Hz single phase is pretty tricky.
    In a three phase transformer, if wye wound, each winding is wound only for the line-ground voltage, and in case of delta wound ones, the current is evenly distributed across each winding.
    If the power were transmitted as DC, and converted to AC on board, one would no longer be limited to one phase, and could thus have constant power transfer. Also the frequency could be higher, probably 400Hz, so the onboard transformer could be smaller and lighter for a given power rating.
    If all else is equal, constant power transfer is more economical than rapidly varying power transfer.
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    In terms of suitability, AC is better for transmission, while DC is better for traction.
    TheBlacksmith
    Yet AC traction is taking over with most bigger locos and EMU's now AC.
      Myrtone Chief Commissioner

    Location: North Carlton, Melbourne, Victoria
    Those locomotives actually have VVVF AC traction motors. These still need a DC source.
      Pressman Spirit of the Vine

    Location: Wherever the Tin Chook or Qantas takes me
    Those locomotives actually have VVVF AC traction motors. These still need a DC source.
    Myrtone
    VVVF ???
      speedemon08 Mary

    Location: I think by now you should have figured it out
    Yet AC traction is taking over with most bigger locos and EMU's now AC.
    RTT_Rules
    Yes, most new locos/emu's have AC traction equipment because it can handle complex traction control equipment and are a lot harder to overload and burn out.
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    But a single phase train only loads one phase at a time, and doesn't get constant instantanious power. Fact is that quite a large transformer is needed to step down 50Hz. In case of single phase transformers, both sides need to be would for full voltage and amperage. Additionally, rectifying and filtering 50Hz single phase is pretty tricky.
    In a three phase transformer, if wye wound, each winding is wound only from the line-ground voltage, and in case of delta wound ones, the current is evenly distributed across each winding.
    If the power were transmitted as DC, and converted to AC on board, one would no longer be limited to one phase, and could thus have constant power transfer. Also the frequncy could be higher, probably 400Hz, so the onboard transformer could be smaller and lighter for a given power rating.
    If all else is equal, constant power transfer is more economical than rapidly varying power transfer.
    Myrtone
    Yes at same max voltage you move more electons but 25kVa your amperage load is tiny and far less of an issue.

    Assume a train has 2000kW of traction and 500kW of Aux load, total of 2500kW

    1500VDC = 1670 amps. Huge losses in moving such amperage. When NSW had 3 EL locos power up there was something like 5000 to 6000 amps in the line

    (I work in Aluminium we have a 450,000 amp bus bar that runs 3.5km, it takes 200V just to push the amps through the aluminium bus bar without the 444 pots in operation).

    25,000VAC = 100amps. that's the size of the battery cable in your car.

    Next thing you have ignored, (if I remember my electronic correctly), the trains no longer operate with a simple resistor to reduce the voltage to start up and control speed, they use a thryister, basically the chop the voltage so it looks similar to AC, just only doesn't go backwards and the lower the energy requirement by the traction motor the longer the gap between the pulses. The pulses are at full power.  

    (pls anyone step in a correct as required)

    The original EMU's in Qld (25kVAC) got the in single phase, stepped down and then converted to DC and then to chopped DC power supply to the traction motors. These trains couldn't regen brake.

    The newer ones covert to DC then to inverter and supply assume 3 phase to the motors using variable frequency drive. These trains can regen brake.

    In NSW which is DC power supply, I could be wrong but I think the newer stuff also converts to AC traction.

    In industry, if I understood an engineer correctly, the 3 phase coming into a Motor Control Center is converted to DC then into 3 phase AC via a Variable Frequency controller so you can control motor speeds where needed.

    The supply transformer for a train isn't that big due to the voltage. Look up a Qld EMU in Google images, middle car is the B car. The transformer sits in the roof between the bogie/door and end of car. Anyone who has sat here as the train goes through a neutral section will remember this.
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    Those locomotives actually have VVVF AC traction motors. These still need a DC source.
    Myrtone
    The locos use alternators these days. Only very old locos have a DC genset.
      dthead Site Admin

    Location: Melbourne, Australia
    To change over one would need new rollingstock, and that is a lot especially as it may have to be duel voltage , present DC and whatever the new system provides. If existing units are capable of conversion, it could be messy.

    Then there is the infrastructure, can the existing wires and insulators etc be used ?

    Next is the power supply, substations and control.

    That is a alot of money.

    David Head
      Pressman Spirit of the Vine

    Location: Wherever the Tin Chook or Qantas takes me
    To change over one would need new rollingstock, and that is a lot especially as it may have to be duel voltage , present DC and whatever the new system provides. If existing units are capable of conversion, it could be messy.

    Then there is the infrastructure, can the existing wires and insulators etc be used ?

    Next is the power supply, substations and control.

    That is a alot of money.

    David Head
    dthead
    Existing Feeders, catenary, insulators, sub stations, power supply lines, switching equipment and control all useless, all need replacing
      dthead Site Admin

    Location: Melbourne, Australia
    Thanks Pressman, some reality in the discussion.

    David Head

    .
      LancedDendrite Chief Commissioner

    Location: Gheringhap Loop Autonomous Zone
    For those wondering, VVVF = Variable Voltage, Variable Frequency. Essentially, a power electronics box is used to synthesise the traction motor's supply voltage waveform instead of 'mains' AC or DC from the third rail or overhead wire. There's very little difference between VVVF and Variable Frequency Drives nowadays, VVVF is just the acronym some Japanese manufacturers use. They're technically AC drives because they use brushless (i.e non-commutating) motors.

    How hard would it be for Melbourne train network go from 1500v dc system to a 25 kV AC train system?
    Melbtrip
    This has been covered on the 'Page before, mostly in relation to Geelong line electrification. In short, suburban conversion really isn't worth it.

    For a conversion, at a minimum you'll need to change the overhead wire insulators to much bigger ones (on account of the 16x greater voltage) and swap out traction power substation rectifiers for mains supply -> 25kV transformers. You can keep the pylons but you'll need to modify it so that the whole thing doesn't go live in a flashover event (higher voltage = larger air gap that current can arc across).

    Wires don't need to be changed over when you're increasing the voltage, but you can get away with smaller cables due to the 'skin effect'. If you're putting in new insulators, you may as well re-string the wire with lighter gauge stuff at the same time though. That's a lot of lineside works for the conversion - you'd better get a big benefit out of it for the number of occupations you'll have to do!

    The technical benefits of 25kV AC over 1500VDC are basically that for a given load you can have greater distance between substations. The more trains you run over a given distance (and hence power you draw), the less relevant this becomes. If you're electrifying country mainlines or building High Speed Rail, 25kV AC is the way to go. For commuter and metro rail networks, it's less relevant because of the service frequencies involved.

    In most cases, as long as you're using overhead wires for supply, you can use any AC or DC legacy electrification system that a suburban system was built with.

    25kV AC substations can be basically pole-mounted - they're basically just a single or 3-phase transformer with a circuit breaker and protection/control relays. A lot less equipment for each substation and fewer substations to boot. That's important when you're electrifying from scratch, which is why Perth, Adelaide and Brisbane chose 25kV AC over 1500V DC.

    These days, multi-voltage EMUs and locos are an off-the-shelf commodity. Japan uses multiple electrification schemes and Europe has a whole bunch of different ones too. Mixing the two different electrification schemes together on the same network is quite a lot less of a problem than, say different rail gauges.

    The likely outcome is that any country electrification would be done with 25kV AC, because you're building from scratch and can pick whatever system works best. In Melbourne's case, the most appropriate examples of this would be future electrification to Melton, Geelong and/or Wallan. Because you'll probably be using new rollingstock to haul the extra suburban/interurban services, you just need to specify dual voltage EMUs or locos.
    For shorter extensions like Mernda or Baxter, sticking with 1500VDC is easier because you're extending existing services and hence want to be able to use existing rollingstock from the get-go.
      RTT_Rules Oliver Bullied, CME

    Location: Dubai UAE
    To change over one would need new rollingstock, and that is a lot especially as it may have to be duel voltage , present DC and whatever the new system provides. If existing units are capable of conversion, it could be messy.

    Then there is the infrastructure, can the existing wires and insulators etc be used ?

    Next is the power supply, substations and control.

    That is a alot of money.

    David Head
    dthead
    I'm thinking you would need to identify a sub part of the network that could operate as an island, including yard.

    Then buy enough rolling stock to operate on this section with dual volatge or accept it will never cross over, however this maybe hard for city sections unless dedicated routes can be made and hence dual voltage is required

    Then upgrade wiring as you and pressman said and install AC supply system read to go.

    Draw a line in the sand and switch over. probably take a few days to test and commission live as I assume after dark with no trains you could do a number of tests.

    You keep adding new section/branches with more rolling stock over 20-30 years (life of rolling). Then when the bulk of the fleet is done, you go through over a long weekend and convert the city/trunk sections.

    Then as each set comes up for major service you progressively remove the DC systems, another 10 years.

    So all in all a 25-35 year project/head ache. At the end, the passengers are no better off and the taxpayer is unlikely to be better off for many many years if ever.

    Hence it will never ever happen.
      Myrtone Chief Commissioner

    Location: North Carlton, Melbourne, Victoria
    For a conversion, at a minimum you'll need to change the overhead wire insulators to much bigger ones (on account of the 16x greater voltage) and swap out traction power substation rectifiers for mains supply -> 25kV transformers. You can keep the pylons but you'll need to modify it so that the whole thing doesn't go live in a flashover event (higher voltage = larger air gap that current can arc across).
    LancedDendrite
    I should note that larger insulators are required for AC of a given RMS value than for DC of approximately the same voltage, becasue for AC, it's the peak voltage that matters.

    Wires don't need to be changed over when you're increasing the voltage, but you can get away with smaller cables due to the 'skin effect'. If you're putting in new insulators, you may as well re-string the wire with lighter gauge stuff at the same time though. That's a lot of lineside works for the conversion - you'd better get a big benefit out of it for the number of occupations you'll have to do!
    LancedDendrite
    The skin effect actually limits the size of the conductor one can use for AC, without the core not conducting.

    The technical benefits of 25kV AC over 1500VDC are basically that for a given load you can have greater distance between substations. The more trains you run over a given distance (and hence power you draw), the less relevant this becomes. If you're electrifying country mainlines or building High Speed Rail, 25kV AC is the way to go. For commuter and metro rail networks, it's less relevant because of the service frequencies involved.
    LancedDendrite

    The technical benefit comes from the higher voltage, not the type of current, and remember that single phase electfricitation requries different sections on each phase1, and phase breaks between them, and also doesn't transfer constant power.

    Metro type heavy rail, as well as light rail, tends not to need to be interoperable with mainline heavy rail and so needn't use the same voltage as mainline railways in the same region. Additionally, they don't need to go over vast distances and can economically have more frequent substations. By converting the AC to DC before suppyling it, they can load the phases evenly and can also filter the recctified current more easily2.

    1Sometimes conveting the three phase to two phase may be able to help with loading phases evenly, while reducing the number and frequency of phase breaks.
    2Three phase is often split into six phases before being rectified, futher cutting down on ripple.

    25kV AC substations can be basically pole-mounted - they're basically just a single or 3-phase transformer with a circuit breaker and protection/control relays. A lot less equipment for each substation and fewer substations to boot. That's important when you're electrifying from scratch, which is why Perth, Adelaide and Brisbane chose 25kV AC over 1500V DC.
    LancedDendrite

    In case of Brisbane, 25kv allowed mainline railways in Queensland to also be electrified, while still maintaining inteoperability without the need for dual voltage rolling stock or complicated switchgear.

    But do note that AC electrification is still confined to non-metro heavy rail electrification, and electrification of other forms of rail (such as light rail) is still DC.

    It seems that single-phase electrification is only economical on very large networks of electrified track, where a very large area can be on each phase.

    The likely outcome is that any country electrification would be done with 25kV AC, because you're building from scratch and can pick whatever system works best. In Melbourne's case, the most appropriate examples of this would be future electrification to Melton, Geelong and/or Wallan. Because you'll probably be using new rollingstock to haul the extra suburban/interurban services, you just need to specify dual voltage EMUs or locos.
    LancedDendrite
    One idea is for all new rolling stock, not just country ones, to have dual voltage capability, so that the suburban system can be converted over time.
      ZH836301 Chief Commissioner

    Location: BleakCity
    Completely pointless.

    Given regional lines will be eventually be totally segregated from suburban lines we can electrify them separately to 25kVAC (same story for standardisation).

    On Metro, obviously the express lines (eg. Sunbury/Airport to Frankston/Dandenong) should run via the viaduct so you can standardise them (you can't send freight trains through a passenger tunnel).

    And no, it does not matter that you can't run your SG 25kVAC regional train to Hurstbridge.

    Oh wait, you're already making that very claim:


    • Werribee Line and extend the power lines to the Junction  - having the ability for new Geelong service run via Newport or Sunshine.
    melbtrip
      LancedDendrite Chief Commissioner

    Location: Gheringhap Loop Autonomous Zone
    I should note that larger insulators are required for AC of a given RMS value than for DC of approximately the same voltage, because for AC, it's the peak voltage that matters.
    Myrtone
    ...Except we're talking about 1500VDC vs 25000V AC, not 1500VDC vs 1500VAC. Peak voltage for AC is a factor of ~1.41 higher than RMS; 25kV vs 1.5kV is a factor of 16⅔ larger - guess which factor makes more of a difference!

    Bigger insulators make the argument for retrofitting even poorer, BTW.

    The skin effect actually limits the size of the conductor one can use for AC, without the core not conducting.
    Myrtone
    You can still use 1500VDC-rated overhead wires for 25kVAC electrification, given that the former handles more current. That was my point. Skin effect means that you can use hollow wire for 50Hz AC, which is even lighter still than an equivalent solid-core 25kVDC-rated wire.

    The technical benefit comes from the higher voltage, not the type of current, and remember that single phase electrification requires different sections on each phase1, and phase breaks between them, and also doesn't transfer constant power.
    Myrtone
    25kV AC is a widely-used railway electrification standard. So is 1500VDC. We are comparing standards as a whole, not AC vs DC in isolation.

    As for 2-phase transformers vs 3-phase, we've gone over that before elsewhere. Put your hobby horse away, please.

    In case of Brisbane, 25kv allowed mainline railways in Queensland to also be electrified, while still maintaining inteoperability without the need for dual voltage rolling stock or complicated switchgear. But do note that AC electrification is still confined to non-metro heavy rail electrification, and electrification of other forms of rail (such as light rail) is still DC. It seems that single-phase electrification is only economical on very large networks of electrified track, where a very large area can be on each phase.
    Myrtone
    Queensland was starting from scratch, having started electrification in the 1970s. Melbourne did not start from scratch  - the VR picked its electrification standard in the 1900s, when 25kV AC didn't exist. 1500VDC has served Melbourne well so far and the benefits of switching to 25kVAC are marginal. Advantages exist, for sure - they just don't stack up for Melbourne's network.

    Light rail and trams use 'low-voltage' DC for several reasons, mostly because 600VDC and 750VDC are legacy standards from more than a century ago:
    • Lower voltages have less safety issues in cluttered street environments
    • Controllers for pure DC drivetrains onboard trams were much simpler, an advantage that is much less of a problem today

    There are no other competing exclusive tramway/light rail electrification standards, although some tram-trains have been designed to also operate on mainline electrification voltages as high as 25kV AC.
      Myrtone Chief Commissioner

    Location: North Carlton, Melbourne, Victoria
    25kV AC is a widely-used railway electrification standard. So is 1500VDC. We are comparing standards as a whole, not AC vs DC in isolation.
    LancedDendrite


    I believe it wasn't back in the 1970s when Brisbane adopted it. I guess that Brisbane, Adelaide and Perth all chose it with rural electrification in mind.

    Queensland was starting from scratch, having started electrification in the 1970s. Melbourne did not start from scratch  - the VR picked its electrification standard in the 1900s, when 25kV AC didn't exist. 1500VDC has served Melbourne well so far and the benefits of switching to 25kVAC are marginal. Advantages exist, for sure - they just don't stack up for Melbourne's network.
    LancedDendrite


    Also, in our case, we haven't needed to be interoperable with mainline electric railways, except for that line to Morwell.

    Light rail and trams use 'low-voltage' DC for several reasons, mostly because 600VDC and 750VDC are legacy standards from more than a century ago:
    • Lower voltages have less safety issues in cluttered street environments
    • Controllers for pure DC drivetrains onboard trams were much simpler, an advantage that is much less of a problem today
    LancedDendrite


    But remeber that 750VDC is more typical of newbuild systems, it's 600V that's the legacy standard.
    Also, remember than metro systems that also don't need to be interoperable with regional/intercity rail also tend to use DC electrification.
      Pressman Spirit of the Vine

    Location: Wherever the Tin Chook or Qantas takes me
    I believe it wasn't back in the 1970s when Brisbane adopted it. I guess that Brisbane, Adelaide and Perth all chose it with rural electrification in mind.



    Also, in our case, we haven't needed to be interoperable with mainline electric railways, except for that line to Morwell.



    But remeber that 750VDC is more typical of newbuild systems, it's 600V that's the legacy standard.
    Also, remember than metro systems that also don't need to be interoperable with regional/intercity rail also tend to use DC electrification.
    Myrtone
    Well when QR looked at electrifying it's lines is chose a well proven system that was 25kV AC (so the technology wasn't new!)
    Perth also chose the 25kV AC system with NO desire to electrify any rural lines
    Adelaide chose the standard 25kV AC system and as the SA Government doesn't own any rural lines they didn't give a rat's smeg about  rural lines.

    Oh and btw Adelaide new tram lines are 600Vdc

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