Just wondering what the maximum permitted current draw per unit is on third rail?
I believe the trains are fitted with 800 amp fuses, so less than that, I presume.
Per shoe or maybe bogie?Would that be per motor?
the 387 line of route states shoe fuses are rated to 1133A, and one shoe fuse will provide propulsion for a 4 car unit. There is no reason for 4 car 377/375's to have any more or less maximum current draw set up, however that's not to say that 1778 is not a valid figure for 5 car 376/377 units? (I know I don't have that detail available to me.I read somewhere that 375/377s can draw a maximum of 1778 amps on 3rd rail
Would that be per motor?
Per shoe or maybe bogie?
I’ve never seen that level of detail I’m afraid. It does seem a bit low to me, in terms of the usual sorts of currents flying around.On 444 and 450s, I think there are two 800 amp fuses on the power bus/train line? (One 800 amp fuse on each driving coach?)
I can’t see full power being available through one shoe though?
that was me, and as part of my training we were informed that a unit could be fully powered and running up off of one shoe, so if it needed to in fault conditions, it could safely.Someone posted a circuit diagram of a 377 a few months back, it shows 8 fuses, ie one for each individual shoe, and 3 x HSCB, so each HSCB should only see a third of the overall current, well within 1200A.
I can’t see full power being available through one shoe though?
You’ve lost a decimal place I think, it should be 1600Athat was me, and as part of my training we were informed that a unit could be fully powered and running up off of one shoe, so if it needed to in fault conditions, it could safely.
That being said, I'm gonna do some simple maths....
Traction motors on an e* are 200KW each... there are six in a four car unit, so that's 1200KW. simple maths makes that 160A at 750V on traction motors, so 1133A might be a correct figure with safety margin included, I can't find any detailed info on the loadings of the auxiliary supplies to support this hypothesis...
(if my maths is wrong, I do apologise!)
that was me, and as part of my training we were informed that a unit could be fully powered and running up off of one shoe, so if it needed to in fault conditions, it could safely.
That being said, I'm gonna do some simple maths....
Traction motors on an e* are 200KW each... there are six in a four car unit, so that's 1200KW. simple maths makes that 160A at 750V on traction motors, so 1133A might be a correct figure with safety margin included, I can't find any detailed info on the loadings of the auxiliary supplies to support this hypothesis...
(if my maths is wrong, I do apologise!)
You’ve lost a decimal place I think, it should be 1600A
Don't assume the voltage is always 750V though...
... and don't assume that an 800A fuse will blow with a little more than 800A running through it. Fuses can carry in excess of their nominal rated current depending on the duration. If say a train was traversing complex pointwork with several condictor rail breaks, there could be short periods where three of the four shoes (on one side of a four car unit) are breifly out of contact with the supply. Thus all of the current for the unit's motors would be passing through that shoe and its wiring connection to the DC bus. A 800A fuse would be able to carry that current for a second or two before the temperature rose enough to blow it, until another shoe was able to share the current.Don't assume the voltage is always 750V though...
Class 92s are rated at 4MW on DC, and their Channel tunnel routes were upgraded to 750V high current specification supplies, so that suggests they might be able to draw up to 5,333 Amps. ISTR the 'high current' work involved doubling the number of substations by converting former so-called 'track paralleling' (TP) huts that previously alternated with substations along the routes into additional full-blown substation feeds with their own 33kV transformers.The OP asked for the maximum current draw per unit. My guess is that the prize would go to either a 12-car Class 700 or the old DC-capable Eurostar. The class 700 packs 5MW which would equate to over 6000A at 750V if it was allowed to pull that much. I can't recall what the maximum DC current is - I have a feeling it might be around 4500A. The Eurostar Class 373 is stated to have a limit of 3.4MW in DC mode, which would be about the same. I know it needed special reinforcement.
That’s a fairly reasonable explanation, I think my issue was with one shoe for a reasonably continuous period.... and don't assume that an 800A fuse will blow with a little more than 800A running through it. Fuses can carry in excess of their nominal rated current depending on the duration. If say a train was traversing complex pointwork with several condictor rail breaks, there could be short periods where three of the four shoes (on one side of a four car unit) are breifly out of contact with the supply. Thus all of the current for the unit's motors would be passing through that shoe and its wiring connection to the DC bus. A 800A fuse would be able to carry that current for a second or two before the temperature rose enough to blow it, until another shoe was able to share the current.
On 444s and 450s, I think there are two 800 amp fuses on the power train line? (One 800 amp fuse on each driving coach?)
When working in multiple, the power train line is not connected (only the 110v supply is connected between units), so would that mean that two units in multiple would draw double and three in triple would draw triple?
(I'm certainly no electrician!)
the 387 line of route states shoe fuses are rated to 1133A, and one shoe fuse will provide propulsion for a 4 car unit. There is no reason for 4 car 377/375's to have any more or less maximum current draw set up, however that's not to say that 1778 is not a valid figure for 5 car 376/377 units? (I know I don't have that detail available to me.
I am slightly confused however, as I know the High Speed Circuit Breakers on electrostars are generally rated to have a tripping current of 1200A, but the relatively slow blow nature of the ribbon fuse probably negates it failing before the HSCB opens, but that does still seem to leave me with more questions than I started with...
Per shoe or maybe bogie?
I was thinking back to the 458/5 fire at Windsor, where the shoe cables were commoned together on or near the bogie, but they had no inline fuse protection for the cables to the circuit breaker anyway. There’s probably as many permutations as possible across the older fleets.Didn't really think of those options
I think that a 3rd rail circuit is rated at a maximum of 10,000A, so limiting trains to around 4000 to 4500A would cover the maximum likely occupancy of a length over which the voltage drop would be acceptable. Any higher current limit would make fault detection unreliable. This is the main weakness of a low voltage traction supply system with modern main line power demands, even if all the human safety issues are ignored.The OP asked for the maximum current draw per unit. My guess is that the prize would go to either a 12-car Class 700 or the old DC-capable Eurostar. The class 700 packs 5MW which would equate to over 6000A at 750V if it was allowed to pull that much. I can't recall what the maximum DC current is - I have a feeling it might be around 4500A. The Eurostar Class 373 is stated to have a limit of 3.4MW in DC mode, which would be about the same. I know it needed special reinforcement.
The RAIB report I was looking at earlier re the Windsor incident, explained that the end of that branch was fed through two 7000A circuit breakers, one for each track, and this meant the pretty massive train earth fault was undetectable for the reasons you give.I think that a 3rd rail circuit is rated at a maximum of 10,000A, so limiting trains to around 4000 to 4500A would cover the maximum likely occupancy of a length over which the voltage drop would be acceptable. Any higher current limit would make fault detection unreliable. This is the main weakness of a low voltage traction supply system with modern main line power demands, even if all the human safety issues are ignored.
The RAIB report I was looking at earlier re the Windsor incident, explained that the end of that branch was fed through two 7000A circuit breakers, one for each track, and this meant the pretty massive train earth fault was undetectable for the reasons you give.