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Portland OR heat delays

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  • Member since
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Portland OR heat delays
Posted by blue streak 1 on Wednesday, August 02, 2017 10:24 PM

Some areas of PDX over 100 F and few spots over 105 F.

WES rail cancelled heat orders. Problems with rail. Trimet MAX slowing to 30 MPH. Other sites say it is due to CAT sagging.  Any one know the actual design of the trolly wire ?  Full  constant tension, just regular trolly wire off hanger or what else?.  Note Seattle is not having these high temp problems.

http://trimet.org/

Temperatures predicted to go to 105 Wednesday. Last time there not too much AC in most homes.  Bet you cannot find portable AC in whole city

http://www.oregonlive.com/commuting/index.ssf/2017/08/free_rides_wednesday_on_trimet.html

 

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Posted by NorthWest on Thursday, August 03, 2017 11:05 AM

It's constant tension catenary on standard masts. Just Portland failing to plan for the weather, again...

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Posted by blue streak 1 on Thursday, August 03, 2017 6:54 PM

Have read that Portland CAT has an unanticipated flaw.  It is constant tension CAT.  However the weight and pulley system has a design flaw where when it gets hot many of the weights hit the ground or stop plate.  Then additional heat causes the CAT to sag.  All that cutting corners to save some tensioning wire and more weights.  Never paid attention to it when there.  Maybe someone can enlighten us if there are any pulleys or weights just attached to tensioning wires ?  Probably different at various points. 

Each pulley on a tensioning cable requires additional weights ~ same weight as just a direct weight.

Brings up a question for Amtrak --- " how hot of a temperature will the NEC constant tension wire remain taunt ?"  Anyone know of any agency CAT subject to same problem ?

Here is a bulletin from TriMetNote fare system down due to heat.  Same old question. When will equipment builders  realize that computers can be heat sensitive ?

Extreme Heat Updated: 5 p.m., Thu. Aug. 3, 2017

Due to extreme heat, MAX is running slower and WES is being served by shuttle buses. Expect delays and stay hydrated. We are not requiring fare today due to network issues. LIFT paratransit is only providing life-sustaining trips.

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Posted by erikem on Thursday, August 03, 2017 10:53 PM

Pulleys and weights gives a more contant tension would be achieved with springs. IIRC, expansion of the wire is directly proportional to temperature change, sounds like TriMet picked too low of a maximum temperature.

FWIW, I remember Portland being stinking hot when visiting there August of 2008. It's cooler here in San Diego - but we're actually on the coast as opposed to quite a few miles inland as is the case for Portland.

RME
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Posted by RME on Friday, August 04, 2017 12:30 AM

blue streak 1
However the weight and pulley system has a design flaw where when it gets hot many of the weights hit the ground or stop plate. Then additional heat causes the CAT to sag. All that cutting corners to save some tensioning wire and more weights.



Now hold on there, son.  Can't you realize that the only thing that would make the tensioning 'stop' early would be too MUCH wire, hanging the stacks down close to the ground?

Fix shouldn't be too much more involved than shortening the cable through the stack, or perhaps using heavier plates in the weight stack to make its adjusted height shorter with the centroid at the same height above ground.

You most emphatically would not use springs in any part of a constant-tension catenary; among other things, springs are temperature-sensitive themselves so no fixed weight system would possibly give you constant tension.  The idea is that the tension, regardless of expansion or contraction in the length of the horizontal wire spans, is imposed strictly by the constant pull of gravity on the large mass 'around the pulley' acting in the vertical plane.  (There are some additional complications in the actual wiring setup, but nothing surprisingly different as far as I know.) 

Everywhere you want constant tensioning, you have to have a weight stack at the end of the span (and a good, stable anchor at the other), and where several tensioned wires join you need to balance all the vector forces so the wires are in equilibrium.  I wonder if at least some of the problems relate to the trolley wire being 'wiggled' from side to side to equalize pan wear -- the pulloffs on the messenger for this won't have their own weight stacks, but simply be cut short for tension and if they loosen with higher temperature the wire might show some unexpected 'set' as it retensions longer.

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Posted by Buslist on Friday, August 04, 2017 9:28 AM

RME

 

 
blue streak 1
However the weight and pulley system has a design flaw where when it gets hot many of the weights hit the ground or stop plate. Then additional heat causes the CAT to sag. All that cutting corners to save some tensioning wire and more weights.

 



 

 

You most emphatically would not use springs in any part of a constant-tension catenary; among other things, springs are temperature-sensitive themselves so no fixed weight system would possibly give you constant tension.  The idea is that the tension, regardless of expansion or contraction in the length of the horizontal wire spans, is imposed strictly by the constant pull of gravity on the large mass 'around the pulley' acting in the vertical plane.  (There are some additional complications in the actual wiring setup, but nothing surprisingly different as far as I know.) 

 

I have observed "spring activated catenary" on a suburban line in Buenos Aries in Argentina. So I guess never say never!

RME
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Posted by RME on Friday, August 04, 2017 10:11 AM

Buslist
I have observed "spring activated catenary" on a suburban line in Buenos Aires in Argentina.

Yes, but don't go calling it 'constant tension' catenary.  Spring 'activation' (presumably a helical spring like a clothesline tensioner providing a longer travel of tension force than that inherently in 'stretched copper') will certainly keep the wire stretched over a longer unmaintained time, or for a wider range of temperature excursion.  But the characteristics of the catenary tension will not be 'constant' over the temperature range, nor will time constants of vibration be reasonably constant, as they are in true constant-tension catenary. 

Let me clarify my original claim a bit: the 'never' applies strictly to a true constant-tension setup, not to a streetcar setup that wants to keep wire reasonably sag-free across a potentially wide temperature swing without manual attention.  I don't want to leave the impression that the only kind of 'active tensioning' in a wire or catenary setup "has" to be orthogonal gravity weighting...

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Posted by CandOforprogress2 on Friday, August 04, 2017 1:43 PM

So how did we do it on old fasioned streetcar wire?

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Posted by Buslist on Friday, August 04, 2017 4:03 PM

RME

 

 
Buslist
I have observed "spring activated catenary" on a suburban line in Buenos Aires in Argentina.

 

Yes, but don't go calling it 'constant tension' catenary. 

I didn't

 

 

RME

Let me clarify my original claim a bit: the 'never' applies strictly to a true constant-tension setup, not to a streetcar setup that wants to keep wire reasonably sag-free across a potentially wide temperature swing without manual attention. 

 

Not a streetcar set up but a suburban railway.

 

RME

I don't want to leave the impression that the only kind of 'active tensioning' in a wire or catenary setup "has" to be orthogonal gravity weighting...

 

 

but you kind of did!

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Posted by blue streak 1 on Friday, August 04, 2017 4:15 PM

RME definitely agree with you about tensioning springs.  What was forgotten is that spring tension can somewhat change due to temperature changes. 

Our point about Portland design is that not enough travel was given for the copper expansion.  Either too long sections from the center point attach to pulley. Or not enough pulleys so weights will not have to travel as far.  Pictures would help from someone there. 

You also touched on how tensioning is attached to contact wire and travelers.  Makes us think that those wires may have been specified with different co-efficients of expansion ?

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Posted by azrail on Friday, August 04, 2017 6:56 PM

How strange, light rail in Phoenix still runs fine in our 110+ weather!

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Posted by blue streak 1 on Friday, August 04, 2017 8:35 PM

 

Well Portland MAX is admittig counterweights are hitting the ground. See this post from MAX

 

Q & A

Why our trains slow down when it heats up

Many of you have asked why our trains slow down when it’s hot outside. We know extra delays can be frustrating, but there are two important reasons why our speeds go down when temperatures go up—science and safety.

Update: How we’re minimizing heat delays on MAX

Like in other cities, the MAX light rail system is designed for the average temperature ranges of our local climate. When temperatures are at the extremes of that range, the materials in the system have a hard time adapting.

Steel and copper expand in the heat

In the case of extreme heat, the rails (made of steel) and the overhead power wires (made of copper) expand.

A one-mile stretch of rail in the MAX system may expand up to a few inches. This rail has to go somewhere, and when it gets too hot it can actually bend or lay over on its side! Our operators and controllers call this a “sun kink.”

Additionally, the overhead power wires may also expand. Because copper expands more than steel, and because we can’t allow the overhead wires to sag, we have a system of pulleys with counterweights that tug on the wires to keep them tight. (But sometimes, it gets so hot that the counterweights touch the ground and the wire starts to sag anyway!)

 

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Posted by ORNHOO on Monday, August 07, 2017 2:06 PM
In spite of the heat restricted speed, a MAX train was involved in a fatal accident yesterday: http://koin.com/2017/08/06/1-dead-after-car-crashes-into-max-train/
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Posted by Travelboy on Monday, August 14, 2017 7:48 PM

We had a long stretch of record-setting temperatures in excess of 100 degrees.  Hottest since 2008.  Definitely not the norm for the Pacific Northwest!   If we have more than one inch of snow, the city shuts down.  Snowfalls occur every three or four years.  We are not prepared for these rare occurrences.

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Posted by BaltACD on Wednesday, August 16, 2017 10:55 AM

azrail
How strange, light rail in Phoenix still runs fine in our 110+ weather!

When temperatures are in the 'normal range' for an area, the track/catenary is adjusted for that norm.  In Portland 100+ temperature are far above the norm.  In Phoenix 110+ is the norm.

Never too old to have a happy childhood!

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