OHLE Return Conductor System

[Liamcronin]

Hi,

can anyone help me with explaining exactly how the RC system works from start to finish? Doing a research project for degree on WCML and have come a bit stuck.

Essentially, I know the power is delivered from National Grid / DNO at 132kv, stepped down to 25kv and fed into the OHLE. Power is picked up by pantograph etc etc and anything left is passed back through the wheels to the Traction return rail.

Am I right in assuming the following: the return current is picked up by red Bonds and transferred to the return conductor (which usually hangs on the outside of masts). From this point on how does the power return to source etc?

Many thanks

 

[Philip Phlopp]

It's covered well in a number of places, chiefly the Overhead Line Electrification for Railways PDF from one of Atkins engineers...

Overhead Line Electrification for Railways – An approachable and comprehensive study of OLE for beginners and trainees

www.ocs4rail.com

but also in a lot of NR docs, such as...

https://cdn.networkrail.co.uk/wp-content/uploads/2018/05/EC4T-CP6-DSLFs-Methodology-Assumptions-Report-May-2018.pdf

 

[GRALISTAIR]

I agree with Philip Phlopp - Garry Keenor’s work while not the absolute bible is extremely comprehensive, well illustrated and very readable. It is also free in electronic format.

 

[Liamcronin]

Thanks . I have looked at the OLE for railways book and while I. found it to be very informative, it didn’t provide me with the exact information I was looking for.

How do the red Bonds interact with the traction return circuit?

 

[WAO]

There's a thread under "infrastructure and stations" entitled,

"OLE - Classic Feeding - Return Conductor and Earth",

from way back in 2013/7 that has some informed discussion. You may have to Google the phrase to find it.

You probably need to understand the distinction between the three broad methods of overhead ac supply; Classic, Booster Transfomer (BT) and Auto-transformer (AT). The technology is still developing so expect some changes.

Are you doing a first degree or Masters'?

Good luck, anyway.

WAO

 

[GRALISTAIR]

And you can always look in the pinned thread at the top of the Infrastructure forum with a summary of most threads I could find about electrification.

OLE - Classic Feeding - Return Conductor and Earth

I've been learning about OLE recently, just a quick question in relation to the return conductor; does this also act as the earth wire in classic feeding/ booster transformer arrangement? Or is it the case that the traction return rails act as an earthing point as they are bonded to the OLE...

www.railforums.co.uk

This is thread I am referencing.

 

[Liamcronin]

Thanks again for the help,

Have looked through a lot of these forums/discussions, all very informative.
Would I be right in assuming the following;

The current is transferred, through the train wheels to the traction return rail.
From there, it is carried through red Bonds to the return conductor. Once in the return conductor, the booster transformers force the current back to the feed where it came in originally.?

 

[AM9]

Hi,

can anyone help me with explaining exactly how the RC system works from start to finish? Doing a research project for degree on WCML and have come a bit stuck.

Essentially, I know the power is delivered from National Grid / DNO at 132kv, stepped down to 25kv and fed into the OHLE. Power is picked up by pantograph etc etc and anything left is passed back through the wheels to the Traction return rail.

Am I right in assuming the following: the return current is picked up by red Bonds and transferred to the return conductor (which usually hangs on the outside of masts). From this point on how does the power return to source etc?

Many thanks

Please accept this as a constructive comment, but your words "Power is picked up by pantograph etc etc and anything left is passed back through the wheels to the Traction return rail" is not the best way to describe what happens. A better way would be to say: Current is collected (from the conductor wire by the pantograph and passed through the wheels to the traction current return rail. This hopefully doesn't sound just a pedantic reply but is intended to help.

 

[GRALISTAIR]

Please accept this as a constructive comment, but your words "Power is picked up by pantograph etc etc and anything left is passed back through the wheels to the Traction return rail" is not the best way to describe what happens. A better way would be to say: Current is collected (from the conductor wire by the pantograph and passed through the wheels to the traction current return rail. This hopefully doesn't sound just a pedantic reply but is intended to help.

Indeed and it is good practice to word things well if you come to write a MSc or PhD thesis or even a BSc/B.Eng project. Professors etc do like that and they will give a higher mark imho.

 

[Liamcronin]

Thanks again, and just to calm any worries, I am in the early stages and merely researching facts and procedures, and am a long way off anything remotely near a finished product, but all advi d / information welcome.

So am I right with what I assume about the return path for the current and how this interfaces with red Bonds?

 

[Elecman]

Generally yes, crudely put the effect of the booster transformer where the passage of the traction current through the Primary winding ‘sucks’ the return current from the traction return rail through the Secondary winding into the return conductor

 

[norbitonflyer]

Some confusion between power and current. It is the current which goes round the circuit. Power is generated at the power station and delivered to the train where it is used to drive the train (ultimately dispersed as heat, noise, and other forms of energy. As power is voltage x current, the amount of power in the running rails and the rest of the return circuit should be close to zero, as the rails are at Earth (zero) potential.

 

[Richard Scott]

Some confusion between power and current. It is the current which goes round the circuit. Power is generated at the power station and delivered to the train where it is used to drive the train (ultimately dispersed as heat, noise, and other forms of energy. As power is voltage x current, the amount of power in the running rails and the rest of the return circuit should be close to zero, as the rails are at Earth (zero) potential.

If we get really pedantic then power is energy changed from one form to another per second so really suppose we should say energy dissipated in the running rails and return circuit (as heat) should be close to zero? There will be some as there must be a voltage drop (drop in potential) for the return current to flow as the return circuit will have some resistance?

 

[AM9]

If we get really pedantic then power is energy changed from one form to another per second so really suppose we should say energy dissipated in the running rails and return circuit (as heat) should be close to zero? There will be some as there must be a voltage drop (drop in potential) for the return current to flow as the return circuit will have some resistance?

As will the OLE/3rd rail feed.

 

[norbitonflyer]

If we get really pedantic then power is energy changed from one form to another per second so really suppose we should say energy dissipated in the running rails and return circuit (as heat) should be close to zero? There will be some as there must be a voltage drop (drop in potential) for the return current to flow as the return circuit will have some resistance?

The running rails should be at Earth potential, so the booster transformer would, I assume, provide a small negative potential on the return side of the circuit. Power losses in a conductor are I^2 x R where I is the current.

 

[WAO]

It might be worth while pointing out to the original enquirer that the Booster Transformer system is now out of favour, conversions being made to either Classic or AT. It would be questionable whether he should expend much effort studying such a system.

The earth point at the feeder station is at zero volts but the potential in the rail return must be progressively higher, (steel not being a very good conductor), perhaps a few tens of volts at the most. The BT was at attempt to reduce this. The maximum permitted touch voltage on the railway is I believe 60V.

WAO

 

[Philip Phlopp]

The maximum permitted touch voltage on the railway is I believe 60V.

EN 50122-1 refers and is calculated "as a function of time duration". AC values are 60V for >300s, increasing to a maximum of 865V for 0.02s, touch voltages are limited to 25V for engineering facilities to minimise risk of injury from reaction to higher touch voltages.

DC allows 120V >300s rising to 370V for 0.02s. This obviously doesn't apply to those Scalextric aficionados who can be found licking the third rail and erroneously claiming third rail is the superior traction system...

 

[broadgage]

As an aside, I would urge never treading on the running rails of an electric railway with bare feet. The relatively low voltage is unlikely to be dangerous in MOST circumstances, but could be dangerous in exceptional circumstances.
In general one should be well clear of the line in any case, but considering level crossings and the possibility of going unshod in holiday resorts.

The rails of street tramways likewise.

 

[HSTEd]

As an aside, I would urge never treading on the running rails of an electric railway with bare feet. The relatively low voltage is unlikely to be dangerous in MOST circumstances, but could be dangerous in exceptional circumstances.
In general one should be well clear of the line in any case, but considering level crossings and the possibility of going unshod in holiday resorts.

The rails of street tramways likewise.

Also even if the voltage is not directly dangerous, an uncontrollable muscle contraction might cause you to injure yourself in some other way.
Like reaching into the back of a CRT television and causing a discharge, which causes your arm to thrash around inside the set uncontrollably.