All about a contact network
(Spacial thanks to Charlie Bartholomew PE for English
Hi dear visitor! If you read these lines, it means you were lucky. For you, the
perfect opportunity has appeared to expand the outlook, to receive answers to questions,
and also to carry out with me some unforgettable hours. Therefore take seat more
conveniently in a deep armchair, take a cup of coffee with liquor, with beer, at the worst
with cognac, knee-cap of tea with tonic or kvasa with milk, in general, everything, that
it is pleasant to you.
Shortly about himself:
||I do not complain
||senior electrician, Lviv branch
I shall not tell
Like and everything, and now as a matter of fact...
This page is addressed first of all to the one whom already has
ceased to satisfy senseless contemplation infinite trick netting of wires, which can be
seen on the majority of railways, for those readers, who has concept about an electrical
current, property of metals to spend it etc., t .е. Past, as the battle christening is
spoken. I hope, as the professionals can find for themselves some grains of truth here.
The speech here will go mainly about a contact suspension bracket
supporting devices, and about all volume, that is connected to it. Therefore, I want to
warn you beforehand, that a contact network - piece serious and us more than once it is
necessary to be immersed in abysses wise of concepts and terms. Nevertheless, from the
party I promise to make these immersing not too dizzy, having softened, whenever possible,
severe necessity by entertaining examples. Probably, you are confused a little only it is
the read lines, but, good beginning is the half of the battle,
so is recollected by the first steps in an electricity.
So, that the unit on an electrical current could smoothly work a constant
input of electrical current to it is necessary. " Well this is natural " - you
will say - " that here complex - has stretched two wires, and business with the end
". Yes, it so, but only in the event that this device stands on one place, or the
trolley bus moves with small speed, for example. In addition, imagine, snow, rain, wind
reaching 120 kms / hr, and you, in the warm car, penetrate space with speed exceeding a
wind. How do you like it?
So, that it became possible and this web from wires under the name "a
contact network" serves.
With help of contact network an electrical current from substation reaches engines of an
electric locomotive, which pulls you forward. If you were in time to notice, electric
locomotive, moving, it slides, as a toboggan, on tense as a string to a wire, which refers
to as: " a contact wire ", t .е. it provides continuous contact for the passing
of an electrical current between the surface and current by the receiver (toboggan) on
which I drew your attention to.
Above a contact wire, another wire is located by which bottom contact wire
fastens. Due to the functions (to bear on itself mechanical loading), that top wire has
received the name: "carrier cable". But, you will notice, if a contact wire and
carrier cable are connected together, how, the current which has arrived on an electric
locomotive, comes back on substation, may be through ground?
"Is not present!" - I shall answer to you, electrical current,
pass off through engines, and having executed the task, moves on... Rails, yes, yes, on
those rails, on which you so frequently go, and through them comes back to the substation.
But were on the railway you should be afraid of a train, which will strike to you in a
back, instead of current running on rails.
The rails had the best conductivity, on joints (places of connection a
rail) their (joints) shunt (bridge) copper connection (fig. 1)
Contact wire and carrier cable of one party and the rails with another
form two "wires" through which substation transfers energy to rushing
locomotives. Three above named components: contact wire, carrier cable and rails under the
common name: " traction network ", however at once make a reservation,
that in concept " traction network " enters much more than components, but
nevertheless beginning is necessary.
The contact wire fastens to a carrier cable with the help link of strings
(fig. 2), which have received the name because of the design: each string consists of
two-three parts (why and for what it is made find out below).
In addition, here, I feel, at you the question arises:.
- Hа! So if the contact wire is adhered to carrier by means of a usual wire, how then
current receiver rushing with speed 140 kms / hr, does not sweep away on way those
"units", which were imposed by the assemblers during electrification to attach a
contact wire to a string?
The answer here such: the contact wire has the very artful form cross-section (fig. 3)
similar on figure of eight. Due to such form of section, fastening of a contact wire to a
string, through a special clip (fig. 4) business of several seconds, and current the
receiver, passing under this clip, does not touch it. Make a contact wire from special
cold-drawn copper, which depending on the area of cross section is marked so: (МФ) MF
-XXX... Copper, shaped, cross section XXX mm2 (МФО) MFO -YYY... Copper, shaped, oval,
cross-section YYY mm2.
Recently, in connection with shortage of color metals, their high prices, will carry
out development of essentially new types of contact wires: facilitated, with
increased conductivity, less subject to deterioration, in which another theme practically
is not used copper in the pure state. Therefore, having met in the literature other marks
of contact wires, for example: NLoM, BrOM etc. - I shall ask to not throw in me by rotten
What have got tired? I yes, therefore we shall distract from a contact network and we
shall listen we shall read a joke on a railway theme:
On one of stations of Ukraine, the passenger expects a train, but the train is late, and
the passenger goes to the chief of station to learn the reason.
- Now train will be, - the chief calms.
- I already saw at station a dog engine driver. 8-)
Still, whether you know
- If legs from shoulder, the head on them is not necessary;
- It is impossible to resist against the woman, which lays;
- In deep decollete it is difficult to see soul;
- Advice the spouses to the appeal will not lie down.
Have had a rest and again in a way.
Now about a carrier cable. It make from copper or bimetal delays, which in a
consequence braid in burn of the certain section. The cross section of a bearing cable is
shown in figure 5.
How you think, can you make such? To answer this question we shall carry
out an experiment. Take cotton, usual thread, with which sews buttons and try to tear it.
The truth - easily has torn. Now cut twenty such pieces braid them and try again to tear.
See, nothing has happened. The truth you see speak: " One in a field is not a warrior
- iust peasant ".
So, for maintenance of flexibility, durability and economy of metal a bearing cable and
interlace from several tens of thin wire.
Somewhere I already heard such word of "bimetal", you thought, that I should not
remember it. There is nothing easier - bimetal wire - it wire, made not from one, but from
two metals, the steel with copper or steel with aluminum is more often. Inside a wire
there is a steel core, on which the environment from other metal is put to one of possible
ways. Such wire, losing in wiring of unit of percent, gets durability of 100-200 %.
The bearing cable is marked so: PBSM-XX a wire of bimetallic, steel copper, cross
section XX mm2, M -YY copper, cross section YY mm2.
It most frequently used marks, which were in time well themselves to recommend on the
majority of railways of Ukraine.
And end of the first lesson we shall return to a string. I shall try to answer questions:
what is it made for, and what is it made from? Let's begin under the order: " what
for? ". Try for the beginning to fix a piece (about 10 meters) wire and in
points, previously having pulled it. From the party, you will see a picture shown in a
fig. 6. Correctly?
Now take a piece, for example, foam rubber and, concerning wires, stretch
it from a point 1 up to a point 3 (see fig. 6), closely observing for experiment. At any
moment, at an entrance in a zone "B" your foam rubber will come off wires,
and in a zone "C" again will adjoin. Just you imitate movement of a current
receiver on a contact wire, at absence of strings. So, moment come off and the moment of
contact by a current of the receiver with a wire, if such happens, is accompanied by burning arch, that results
in fast deterioration of a wire and its breaking. Therefore, wire is necessary to hang up
zones "B" did not become. Here also there come to the aid of strings. Try
through each meter to tie up the tense wire, and you will see, that it becomes equal -
equal, in which the zones "B" in practically are absent.
The string link is carried out from bimetal wire by a diameter of 4 mm,
less often from kapron ropes.
Well the first lesson of a planned rate " All about a contact network
" also has approached to the end. It has pleased you? Leave the offers and wishes,
do not hesitate, if the questions will appear, ask - we shall answer.
Send your questions, ask - and we shall answer.
To what the carrier cable fastens, as the suspension bracket stretches, why a contact wire
have no above an axis of a way, and much another you find out later in next article.
The author: Andrej Klochko.
Figures: Sergej Kibitkin.
Translation: Charlie Bartholomew PE (special thanks)