Electrical Engineering - Train collectors

Author

Train collectors - arching in winter

crispin.proctor@gmail.com

2007-12-12, 9:25 am

Hi Folks,

It is now below zero in the mornings. While I wait for my train, a
number of "high speed" trains come past. The light show, as well as
noise, emitting from the collectors is rather spectacular.

My question is why does this only happen when it is cold and frost is
about? The connection, I would imagine, is fairly good and you
generally don't see sparks any other time. It cannot be a buildup of
frost as it happens to two trains on the same line about 5 minutes
apart. I would imagine that both train's collectors have pretty much
the same track so it would not be about it running over a new frosty
section.

TIA for any answers...

2007-12-12, 9:25 am

<crispin.proctor@gmail.com> wrote in message
news:aaeededa-f781-493b-8ea0-f1194e327203@i29g2000prf.googlegroups.com...
> Hi Folks,
>
> It is now below zero in the mornings. While I wait for my train, a
> number of "high speed" trains come past. The light show, as well as
> noise, emitting from the collectors is rather spectacular.
>
> My question is why does this only happen when it is cold and frost is
> about? The connection, I would imagine, is fairly good and you
> generally don't see sparks any other time. It cannot be a buildup of
> frost as it happens to two trains on the same line about 5 minutes
> apart. I would imagine that both train's collectors have pretty much
> the same track so it would not be about it running over a new frosty
> section.
>
> TIA for any answers...

My guess is the lines and their tension springs grow a bit stiff at lower
temps, which can cause an increase in bounce or vibration in the lines. The
struts holding the collectors against the lines may be a little sluggish in
the cold, so that the bounce is amplified.

CS

crispin.proctor@gmail.com

2007-12-13, 3:25 am

I suppose this does make some sense. But still seems weird that it
only happens when there is frost. When it is cold, but no or not much
frost, it's does not happen.
it also stops as the collector goes under the bridge. Although, your
theory would still work because the cables are lower which pushes the
collectors down, tensions the spring which reduces bounce...

Does seem possible... Thanks.

Cheers,
Crispin

crispin.proctor@gmail.com

2007-12-13, 9:25 am

Something else I just thought of which is why it might not be the
spring stiffness idea: it happens as the train starts to pull away.
i.e. As soon as there is a high current draw as a well as movement.
The moment in the first few seconds is so slow that there would now be
any bounce in the collector.

Just thinking out loud...

Tim Perry

2007-12-14, 3:25 am

<crispin.proctor@gmail.com> wrote in message
news:ef282aa3-d620-4ba1-9a9a-1bdb5ad730c5@e10g2000prf.googlegroups.com...
> Something else I just thought of which is why it might not be the
> spring stiffness idea: it happens as the train starts to pull away.
> i.e. As soon as there is a high current draw as a well as movement.
> The moment in the first few seconds is so slow that there would now be
> any bounce in the collector.
>
> Just thinking out loud...

the arcing may be intentional:

from
http://ieeexplore.ieee.org/Xplore/l...48/01454679.pdf

"One of the many problems in high-speed ground transportation is supplying
the necessary power to the vehicle, as on-board power generation is not
attractive due to the rapid increase in the power requirement with speed.
Power collection with a sliding pantograph becomes increasingly difficult as
train speed increases. Alternative methods of contactless power collection
are critically reviewed in this paper. It is concluded that power collection
along the line using an electric arc appears to have the best advantages. A
study of the literature has shown that arcs can be driven magnetically at
speeds higher than 500 km/h without being extinguished, and that electrode
wear at high arc speed is relatively low. The known problems of arc
initiation and reignition at high speeds are not insurmountable in the light
of present day experience and techniques in this area. The results of an
experimental investigation of power collection by an electric arc which is
being carried out at the university of Sheffield are also included. The
electrode geometry plays a significant role in the arc maintenance, and
interelectrode gap changes from 1 to 10 cm can be tolerated without
reduction in arc lifetimes under certain conditions. Experimental results on
electrode wear which is affected by arc current level, arc speed, and the
electrode material, are presented. These show that the damage to the
overhead wire is at an acceptably small level."

contrex

2007-12-15, 1:25 pm

On 12 Dec, 15:03, crispin.proc...@gmail.com wrote:
> Hi Folks,
>
> It is now below zero in the mornings. While I wait for my train, a
> number of "high speed" trains come past. The light show, as well as
> noise, emitting from the collectors is rather spectacular.
>
> My question is why does this only happen when it is cold and frost is
> about? The connection, I would imagine, is fairly good and you
> generally don't see sparks any other time. It cannot be a buildup of
> frost as it happens to two trains on the same line about 5 minutes
> apart. I would imagine that both train's collectors have pretty much
> the same track so it would not be about it running over a new frosty
> section.
>
> TIA for any answers...

A few points...

The "collector" is called a pantograph.

The commonest cause of arcing is icing of contact wire and/or the
renewable carbon (or copper) collector strip on the pantograph.

The contact wire does not exactly parallel the rails, it is zigzagged,
so that it does not touch the same part of the collector strip all the
time. Thus frost can build up on the parts of the strip not recently
in contact.

The pantograph is held against the contact wire by air pressure.

5 minutes is plenty of time for a new frost build up on the wire, but
it sounds as if the pantographs are implicated here.

Arcing is outside design parameters and can cause damage to equipment
and interfere with electronic traction equipment and signalling.

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