Railway electrification - ongoing (sometimes very!) technical discussion

[whole diary]

[onthecushions]

Think you meant 40MVA .... 10MVA...
 

Quite right. 10kVA would just about drive a bathroom shower.

It's a downside to (slips in using) the metric SI system. You expect your order to come on a low loader and a jiffy bag arrives by post...

Please be patient with the occasional techie post. They do mean something and we have some really valuable insiders here.

Chastened,

OTC

[ellendune]

It's a downside to (slips in using) the metric SI system. You expect your order to come on a low loader and a jiffy bag arrives by post...

There is no problem using the SI system if you use it and not try and translate from some other older system all the time.  If anyone had tried to make me do engineering design in anything else I think I would have gone mad. 

The Americans try and use several systems and they have made some very expensive mistakes as a result (remember the hubble space telescope that would not focus because the lens had been made wrongly?)

I recently tried to look at a design method in an American text book. 

Values in the text were quoted in metric, but quoted in imperial units afterwards in brackets. Equations were then all shown in imperial units (they were not dimensionless).  Fluid flow measurements were quoted in gallons per hour and air flow in cubic feet per second! And we were trying to move two phase flow! The whole thing just made my head hurt reading it.  What chance there was of anyone actually coming out with a correct calculation was quite beyond me.

When I started my career the construction industry had been officially working in metric units for 8 years. All our drawings were metric.  The only problem was that our aged workforce could not or would not take instructions in metric.  They claimed not to be able to understand the drawings.  So I got very used to reading a drawing that said the height of the kerbface should be 125mm and telling a 60 year old craftsman to build a 5" kerbface. Some would say the local authority should have been more forcefull in getting its workers to change, but it was only mildly annoying and far better than the private contractor I had who, although he worked in metric, did not even know what a mitre joint was! 

Those who want a post Brexit Britain to go back to imperial units should be firmly told that UK^▸ (United Kingdom) will only succeed if we have a modern industry and it cannot become a museum.

Please be patient with the occasional techie post. They do mean something and we have some really valuable insiders here.

I am happy to be patient.  I can be techie in my own field but I am not an electrical engineer, but it still interests me.

[IanL]

The Americans try and use several systems and they have made some very expensive mistakes as a result (remember the hubble space telescope that would not focus because the lens had been made wrongly?)

Sorry to correct, it was one of the Mars spacecraft that missed due to mismatch of units. The Hubble Space Telescope suffered spherical aberration due to mis-measurement of a calibration rod used in testing the optical figure of the surface of the primary mirror. The mis-measurement was nothing to do with the units in use but rather due to a defect on the end of the rod. The telescope could focus fine, it was just that there was a different focus for the various parts of the mirror surface!

[ellendune]

Sorry to correct

Thank you facts are important

[Tim]

Sorry to correct

Thank you facts are important

what a refreshingly old-fashioned attitude

[trainer]

Sorry to correct

Thank you facts are important

what a refreshingly old-fashioned attitude

But 'alternative facts' can be wonderfully useful when real ones are annoying. 

[TonyK]

Sorry to correct, it was one of the Mars spacecraft that missed due to mismatch of units.

Don't forget the Gimli Glider. A Boeing 767 had a dicky fuel measuring system, so the pilot asked the engineers to dip the tanks. That gave a result in litres, which they converted to kilograms - but using the multiplier for pounds rather than kilograms. This was the first aircraft they had used that measured things in metric. It ended reasonably happily.

Mods...can we split off the more technical questions and answers of this thread, please ? The last posting was just words to me, with absolutely no level of comprehension whatsoever ! It might have helped if there had been a full stop in there somewhere.

Physics was my best O-Level result, which doesn't make me a scientist! While I appreciate that some of the discussion means nothing to you, and very little to me, I tend to feel that this is the right place for it in the context of the whole electrification project. I have only just got to grips (possibly!) with the Autotransformer concept thanks to patient explanation from our in-house experts and a lot of off-site research.

This forum, IMHO^▸ (in my humble opinion), benefits greatly from the contributions by some of the more learned members, be they couched in technical language or layman's terms. I don't think we will ever get to the point of page after page of swapped equations. Perhaps we could ask for a simple explanation as to what is being explained?

I can still recall the main equations for electricity, which is enough to figure out what fuse an appliance needs, and some of the general principles - an experiment in the laboratory at school using the 12V supply and some basic stuff was enough to convince me that the resistance of a length of wire varied with the cross-sectional area, and how crucial is that on a railway at 25KV?

On metric measurements generally, I was part of the first year at my school to regard the acceleration due to gravity as 9.81 ms^-2 rather than 32 feet per second per second. When you add motion to mass, it is so much easier when everything is based on units that divide by 10, rather than 12, 14, 28, 3, 20, 1760, or whatever. I am occasionally weighed by nurses in hospital. They do it in kilograms, then ask if I want to know the depressing answer in stones and ponds. They are somewhat flummoxed when a man of my age says it would mean absolutely nothing, but they trot it out anyway. How do you work out body mass index in Imperial? Or did we not do that before metrification?

Please bear with the occasional foray into academe, but stick with us chuffed. Your contributions are highly valued too!

[Western Pathfinder]

How many stones does your pond have in it are you perhaps building a water feature ?.

[Red Squirrel]

If anyone had tried to make me do engineering design in anything else I think I would have gone mad. 

You may have hit on something there, with regard to my own mental state: Back in the late seventies when I did Mech Eng at Bristol Poly, we had a lecturer who eschewed SI units in favour of the gravitational fps system, based on the slug. The consequence of this was that we spent our time arguing with him about the relative merits of units systems instead of learning about therodynamics. Turned out that this argument was rehearsed afresh every year, but somehow he kept his job.

[paul7575]

There's a lot of exaggeration about teaching of the metric system, my late mother (b 1929) insisted she was taught metric weights and measures in the 1930s, and she disagreed completely with the argument that older people just couldn't deal with it at all.

I did secondary school science in the CGS system, rather than the MKS system, during the period up until about '71.

Paul

[TonyK]

How many stones does your pond have in it are you perhaps building a water feature ?.

My ounce sometimes drinks from it. I see now why the forged banknotes I printed were quickly spotted. I shall spell my next batch of man-made fivers properly.

(Actually, it was a typo)

[Chris from Nailsea]

This apparently new topic has been created in response to some requests from Coffee Shop forum members, who were understandably concerned that our 'specific discussion' of the electrification of the Great Western Main Line was becoming a bit confused with the rather more technical aspects of railway electrification in general.

I have therefore split off many previous posts and moved them here, into this more general - but often very technical! - discussion topic.

I hope this helps.  CfN. 

[grahame]

This apparently new topic has been created in response to some requests from Coffee Shop forum members, who were understandably concerned that our 'specific discussion' of the electrification of the Great Western Main Line was becoming a bit confused with the rather more technical aspects of railway electrification in general.

I have therefore split off many previous posts and moved them here, into this more general - but often very technical! - discussion topic.

I hope this helps.  CfN. 

Many thanks for doing that ... fearsome ... job of splitting the topics.   Very worthwhile in helping members (and other visitors) finding their way around content that's relevant to them.   Personally, I look forward to reading both threads, with the added joy of being able to do so without having to "context switch" my mind between the technical  and line-specific issues.