Railway Damaged - Cable and Rail Joint

[JHWC]

Hi Everyone,

Would like to consult and seek everyone advise on the kind of damages and what could have causes it.

Please see attached for more information.

Several Observations:
1. There are total of 4 holes drilled onto the railweb for the power cable installation. I have name it A, B C and D for easy referencing. D is in good condition, having a diameter of 21.7 mm (the actual diameter should be around 22 mm). For B and C, the holes were seen melted, with diameter expanding to around 24 mm. For A, the damage could be due to melting but not as severe compared to B and C.

2. The plug which is made of copper has a diameter of 21.5 mm. However, it has difficulties fitting into the hole. What was done was to hammer the plug until it flushed with the railweb (see attached page 2). Therefore, there could already be surface damage induced.

Question:
1. What could have cause the holes to melt because the amount of heat require to melt the rail is relatively high. Why was A, B and C damaged but D still remain intact? If I study the current flow, it wouldn't make sense as well. All 4 should suffer certain damages.

2. Corrosion may have "eaten" the rail externally, producing the air-gap between between the plug and the hole drilled. However, this postulation is not valid since D is still in the good condition.

3. The track and cables in the network are typically low in resistivity. What could have fail first? The plug/cable or IRJ? If the IRJ has suffered deterioration overtime, would the current flow in the IRJ direction instead of returning back to the power station?

4. I have a feeling that the plug/cable is my 1st victim followed by IRJ. Is there any way I would be able to verify?

Appreciate any kind advise and comment. If you require more information, please let me know.

Thanks,
JHWC

 

[dik]

What sort of voltages and current are you looking at? Were the connections pristine and were they tested for resistance when originally installed?

Dik

 

[JHWC]

Voltage drawn from the power rail is 750V DC. Resistance check was also done.

Thanks.

 

[dik]

and amperage... i^2 x r sort of thing...

Dik

 

[kingnero]

Isolating rail joints fail because of burrs or deformed rail ends that contact the adjacent rail, creating a current path.
If the rail lately had surface conditioning done (grinding, milling), could also be because of grinding dust or chips bridging the joint.

Voltage alone doesn't say much, however with a relatively low voltage as yours currect should be easily over 1000 amps, assuming a normal locomotive. Plenty of power to melt rail steel.

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[dik]

Thanks king... Maybe some electrical guy can shed a little more light on this... I was thinking that with the relatively low voltage that the current would have to be high... but, didn't know. Current and pristine connection... I understand that some rails can have a slight magnetism... albeit slight, don't know why... maybe their storage orientation. This may make cleaning a little more difficult with metallic particles clinging a bit and oriented in the correct position for providing an alternative conduction path. I've never seen rail ends blow/burn up the way that the photos depict.

Someone should manufacture a deburring tool that provides a rounded 'chamfer' on bolt holes to eliminate burrs for high current applications.

Dik

 

[kingnero]

Electrical connections (eg. CEMBRE is a trade name) that require core drilled holes, ALWAYS need chamfering both sides. However, in track conditions, this is a step that is widely "forgotten". The sharp edges are a perfect initiation for cracks, this phenomena is even known under a particular name (star cracks) and code (135) in the UIC (Union International de Chemins de fer) book.

However, I was talking about burrs and plastic deformation on the rolling surface of the rail ends, where the wheels cross the gap between both rail ends.

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[dik]

It appears to be a fatigue issue, not an electrical one... important because there is a high incidence of derailments caused by rail end fasteners...

Dik

 

[JHWC]

What are the chances for 2 different materials rubbing against each other resulted from vibration? Would that be able to cause the hole to become bigger and eventually create the air gap?

 

[dik]

I don't know if they still make bearing strip gauges that can be used to determine the clearances with bearings. These were little plastic 'threads' that were compressed in a bearing and from the amount of 'squash' you could determine the clearance with accuracy. You may be able to install shims in the joint with a 'thread' of bearing test material and judge from that if your rails were in contact...I suspect they wouldn't be.

There are means of plastically deforming the hole to increase the size and improve the fatigue resistance; I don't recall what the process is, but, it 'stretches' the hole... I'll try to see if I can find some informaton.

It seems to be a problem with heavily loaded cars and frequent loading...

Dik

 

[berkshire]

Dik,
The plastic strips you mention are made by a company called Plastigauge,

http://plastigauge.co.uk/

And yes they are still available.
B.E.

You are judged not by what you know, but by what you can do.

 

[dik]

Thanks berkshire

Dik

 

[JHWC]

Does the surface looks like there was "rubbing" involved?

 

[MintJulep]

I guess that ground cable has been stolen between this location and the power station.