Electrical Engineering - Re: "European" catenary on the North-East Corridor (USA)

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Re: "European" catenary on the North-East Corridor (USA)

Hans-Joachim Zierke

2008-03-28, 1:25 pm

Adam H. Kerman schrieb:

> What is a variable weight system and what advantage could it have over a
> simple pulley with a fixed weight?

In theory, a fixed weight works nicely, but in the real world, track
has all kind of curves and obstacles, so that you might not have the
same length, or the same resistance to the pull, whatever.

In order to get done with the job (of setting up catenary) until the end
of the day, you'll simply measure tension, and put up weights as needed.
It's done this way since almost 100 years.

Hans-Joachim

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Adam H. Kerman

2008-03-28, 1:25 pm

Hans-Joachim Zierke <Usenetspam013@Zierke.com> wrote:
>Adam H. Kerman schrieb:

[color=darkred]
>In theory, a fixed weight works nicely, but in the real world, track
>has all kind of curves and obstacles, so that you might not have the
>same length, or the same resistance to the pull, whatever.

>In order to get done with the job (of setting up catenary) until the end
>of the day, you'll simply measure tension, and put up weights as needed.
>It's done this way since almost 100 years.

Now I'm particularly confused. Of course I expected that the weights
hung would be chosen based on observation of conditions, but once the
observations are made, the counterweight is chosen.

When is a variable amount of weight used under daily operating conditions?
I still don't know what the OP was talking about.

Merritt Mullen

2008-03-28, 5:25 pm

In article <5JmdnafIhbB-gXDanZ2dnUVZ_rLinZ2d@comcast.com>,
"Adam H. Kerman" <ahk@chinet.com> wrote:

> Now I'm particularly confused. Of course I expected that the weights
> hung would be chosen based on observation of conditions, but once the
> observations are made, the counterweight is chosen.

Yes, but typically it will not be one solid weight. For practical
reasons, the total weight is divided among smaller more easily handled
weight. Just because you observe a number of weight blocks pulling the
tension, does not mean that, once set, the tension is varied.

> When is a variable amount of weight used under daily operating conditions?
> I still don't know what the OP was talking about.

I don't think the weights are varied once set. I have never heard of a
specifically designed "variable tension" system (other than the ordinary
system where tension is uncontrolled and varies with temperature). The
only reason the tension would change would be if gravity varied, not a
likely occurrence.

Merritt

Don Kelly

2008-03-28, 9:25 pm

----------------------------
"Merritt Mullen" <mmullen8014@mchsi.com> wrote in message
news:mmullen8014-094924.12102328032008@netnews.mchsi.com...
> In article <5JmdnafIhbB-gXDanZ2dnUVZ_rLinZ2d@comcast.com>,
> "Adam H. Kerman" <ahk@chinet.com> wrote:
>
>
> Yes, but typically it will not be one solid weight. For practical
> reasons, the total weight is divided among smaller more easily handled
> weight. Just because you observe a number of weight blocks pulling the
> tension, does not mean that, once set, the tension is varied.
>
>
> I don't think the weights are varied once set. I have never heard of a
> specifically designed "variable tension" system (other than the ordinary
> system where tension is uncontrolled and varies with temperature). The
> only reason the tension would change would be if gravity varied, not a
> likely occurrence.
>
> Merritt
-----------
I could see seasonally variable weights being of use because temperature
changes do have a considerable effect on a catenary -it's "sag" as well as
tension. Cold weather reduces the sag and increases the tension appreciably
due to the change in direction of the forces involved as the conductor
shortens. In hot weather the span may be too loose.

--

Don Kelly dhky@shawcross.ca
remove the X to answer

David Lesher

2008-03-29, 3:25 am

"Don Kelly" <dhky@shaw.ca> writes:

>I could see seasonally variable weights being of use because temperature
>changes do have a considerable effect on a catenary -it's "sag" as well as
>tension. Cold weather reduces the sag and increases the tension appreciably
>due to the change in direction of the forces involved as the conductor
>shortens. In hot weather the span may be too loose.

The wire changes length with temperature. The whole point of the weight
& pulley scheme is to absorb that change; so you won't care about the
temperature..
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