Railway Electric Engine

Because the locomotive body, chassis, etc., is earthed to at least one of the running rails.

Because the return path for the 25 kV source is to the overhead electrified wire that the train connects to.

To receive the shock you refer to would require you to come in contact to both sides of the "circuit". Meaning the grounded train body, as pointed out by Mr. Slack, and the other, overhead, conductor.

The source of the power to the load the motor is isolated from the chassis. The chassis is ground through the track as posted above by PWSlack.

This video demonstrates the above comments:

http://www.ebaumsworld.com/video/watch/80647311/

Definitely a candidate for a Darwin Award.

Hi stager.vasu,

This is an interesting question because although it is fairly obvious that the rails form the return side of the circuit there is the issue of maintaining continuity under all conditions, to avoid a large potential difference occurring between the body of the train and 'terra firma'. Depending on the design of the loco or power cars there are several methods of creating the current return which avoid putting electricity through the axle bearings whilst providing the lowest resistance path back to the track.

As power demands rise the designers of high speed and therefore high energy traction systems (5MVA) are facing a variety of continuity problems and both pantograph dynamics and continuity issues are of paramount importance to the success and reliability of these trains.

Massey.

Rgards.

Let me add:

1.) All the rail-lengths are But-welded to maintain Electrical-continuity.

2.) Material used in Rails is of nearly Zero-Temperature Coefficient to coup the problem of adjusting Rail continuously as seen in under-developed country on none electrified sections, workers loosening bolts to take the way to adjust & then tightening on each joint of rails during day time.

3.) If some further measures are adopted to cope the expansion / ???

Regards.

Hi Haajee,

A good point you make. In the UK the adoption of the 1000 yard continuous (welded) rail section became the standard for main lines from the 1960s. this simplified the continuity bonding intervals.

Another issue that you may be able to advise on is the distance between feeder points as in less developed areas there is the location of available power sources relative to the track to take into consideration when designing the network.

Have you any comments.

Regards,

Massey.

Rgards.

Only a short section is electrified, i.e. Lahore to Khanewal.

I have travelled on this section as this is the part of Main Railway Route from Peshawar to Karachi frequently but have never checked for it.

As this is 1st try of Pak Railways and I think that :

<< the location of available power sources relative to the track >>

The power Transmission Infrastructure in this part of the country is fairly modern & on National-Grid System, so hope it will be quite upto the requirements.

Hope it serves some info.

The outer body connects the rail while the rail connects the general mass of earth,all at zero potential.If powered by Batteries,negative of batteries is connected to body of engine and all connects mass of earth at zero potential thru the rails.At 25kv,yr current is small.

Patrick Whowha

Hi P-W,

I must disagree with you comments. As I pointed out in my first post the energy level is very significant with up to 5MVA being transmitted to the traction system, this would potentially result in a current of 200 Amps being returned to the rails. We are talking about AC and there is then 'on-board' transformer/rectifiers to supply the traction motors.

If any batteries are involved it is only for back-up or train infrastructural requirements,currently they play no part in the motive power layout.

The return from the track to the power source is via the track alone, you should look at the cross-sectional area of the two rails and the current transmitted to determine the voltage differential per mile at the rated power. Therefore it is likely that over a distance of some miles that there will be a small ,but appreciable potential difference between the soil and the track potential, this is not a significant issue. Soil to infrastructure services potential differences occur everywhere and rarely cause a problem.

With Hitachi hybrid technology there is the possibility of carrying a substantial battery capacity,on the train,which when allied to a diesel power unit can allow such a train to run for many miles without the benefit of the overhead line supply.

Massey.

Regards.

I would like to to interfere & point to the :

Railway_electrification_system .

A well described article.

Have a fine day !!!!!

Hi Haajee,

A good 'potted' overview of the principles involved. Clearly there are wide variations and anomalies as the technology has spanned many decades. But the underlying strategy is towards higher powers and longer distances being considered economically viable. On this basis the 25kV single phase arrangement is currently the favoured option.

My chief concern is in the life cycle costs of the overhead line equipment (OLE) and because it is vulnerable to many risks the loss of even one section can disrupt all traffic until repairs are made. Therefore the design and quality of the HV infrastructure plays a vital part in ensuring ,as far as possible, that you get maximum reliability and a long working life.

The French seem to have achieved a fair balance in this respect with their TGV set-up, I imagine the Japanese have a similar quality but I have no direct knowledge of their transport strategy.

The remoter regions with vast distances will always need the 'go anywhere' capability of the diesel powered train either loco hauled for freight or even DMU type configurations for passenger services.

The leading edge technology appears to be focusing on the traction motor efficiency with a change to AC operation via variable frequency drives which exploit the better torque to speed relationship of these motors to that of the traditional DC option.

A lot is being said about the benefits of regenerative braking but in reality it comes down to feeding the on-board power requirements rather than returning power to the supply as there are issues right back to the traction power station to be resolved.

Good chat and best wishes to you.

Massey.

Regards & thanks

When retired some 5 years back VFD was the Hottest of all & lot of develpements have been attained in these years.

So in my view again the ball is in the AC drives, though with the developement of Brush-less DC motors this was the main choice. In Pakistan still it was in use some 10 years back when I got a chance to see the system.

The future ... of a better or the best ...

Have a fine day