East Coast train delayed by 8 hours (21/10/2013)

[whole diary]

[Chris from Nailsea]

   

[stuving]

Mind you, I did very nearly electrocute myself with a 12V Hornby 00 model railway.

Dangerous things, small boys (especially the ones that go on to become engineers).

[Chris from Nailsea]

Mind you, I did very nearly electrocute myself with a 12V Hornby 00 model railway.

I, too, have done that - many, many years ago. 

[Electric train]

Must admit I did grab the images from google   

A Portal type construction does not always have a span wire as shown in the image I posted, they more often use "stove pipes" as seen on the TTC picture below (Twin Track Cantilever) why TTC you ask ........... because it spans two tracks.  The portals outside Padd use stove pipes (why are they called stove pipes because they look like stove pipes)

[John R]

You do wonder, if NR^» (Network Rail - home page) are serious about reducing delays, whether serious consideration is being given to replacing the more vulnerable sections of headspan (maybe the four track sections?) with one of the more robust designs. Must have been a fair few delay minutes and cancellations yesterday on the ECML^▸ (East Coast Main Line) (and on the few other times a year when it happens.)

Quoting my own post, thinking about it, there will be a golden opportunity to do it relatively quickly and efficiently later in the decade. The fastest way will be to turn the power off in sections (e.g., Hitchin to Peterborough), and replace all the overhead in one hit. That's only possible if there is something to replace the 91/Mk 4 combos. It just so happens that post IEP^▸ (Intercity Express Program / Project.), there will be a surfeit of HST^▸ (High Speed Train)'s for a short period until either a) they find alternative work or b) are scrapped. The local services to Peterborough could utilise IEP's for a period, leaving only the stretch from Finsbury Park to Hitchin difficult to cover with alternative stock. Radical, but probably no more than electrifying Basingstoke to Soton on overhead ac.

[paul7575]

25kV on a OO^▸ ((Double O) - model railway, 4mm to 1 foot scale) layout would be overkill though.

OO scale is roughly 1:76 isn't it?   But the thing your modelling is 3D, so length, width and height are all 1:76, and 76 cubed is around 440000.

So an OO scale 25kV should be about 1/20th of a volt...   

Paul

[grahame]

25kV on a OO^▸ ((Double O) - model railway, 4mm to 1 foot scale) layout would be overkill though.

OO scale is roughly 1:76 isn't it?   But the thing your modelling is 3D, so length, width and height are all 1:76, and 76 cubed is around 440000.

So an OO scale 25kV should be about 1/20th of a volt...   

Paul

Should you be using a cube rule or a square rule, though, bearing in mind that the cable cross-section is 2 dimensional?

25,000 volts becomes
350 volts (simple scaling)
5 volts (square rule)
0.05 of a volt (cube rule)

I suspect the the scaling can't be direct to any of these rules - your OO train's electric has to move 1/72 of the distance of the full sized thing, but has to move only 1/373248 of the mass

[stuving]

Well...

The thorough way to determine scaling of models (I mean scientific ones) is to choose which dimensionless quantities should be kept the same at all scales and deduce it from that. This is an act of choice, not deterministic - there will be other dimensionless quantities that can't be kept the same.

In this case, without doing the dimensional analysis, a good start looks like scaling volts with length (which keeps electric field across the insulators the same) and current with area (so the current density in correct-scale wires is the same). That gives power scaling with volume, hence with mass for the same density of vehicles, which would result from perfect scale modeling using the same materials.

But is that "right"? How would you want to scale time? That tells you how you have scaled velocity and acceleration (distance is already scaled at 1:76). And what about gravity - that's an acceleration, and hard to scale (while still on Earth). Then, the wires at that scale might be too fragile to work...and motors don't scale well at all...and neither does contact resistance...or friction and bearing performance...etc.

Of course this post might be a bit out of scale with the thread, too.