Railway 25Kv overhead pwr line influence

[robremjer]

Hi everyone,
I'm new on this forum and incidently put this question on an older subject.. anyway..
Regarding the issue of cable separation / influence from powerlines, i have the following question / problem:
In a railway application where 25Kv/50 Hz is used as traction power, datacom cables using ISDN protocols are to be layed in concrete ducts just 2.5 mtr of the track- centreline and covering distances up to 7.5 Km. Does anyone have a proven method of calculating the reductionfactor for these (well-screened)data cables? Also, which specifications / requirements are applicable for data cables in this application? Any suggestions / ideas are welcome,
Rgrds

 

[bobziva]

Everything about installation of communication cables close to the power cables or conductors is standardized.
So open the book before come here for the questions.

 

[alehman]

Telephone line are commonly routed on poles overhead parallel to power lines without excessive difficulty. You may have issues with stray earth current if the rail is the return current path. Consider using optical isolation at the ends. If this is a critical circuit, you may wish to consider using optical fiber instead of copper, which would eliminate any interference concerns. Inexpensive trancievers are available to convert from various types of copper circuits to fiber.

This doesn't really answer your question...

 

[robremjer]

Bobziva,Alehman, thanks for your comments; however i think you may not have missed the point here; if it was that easy i would have taken the "standards" from the (European) book in the first place; apart from the "book standards" (which are different from those in the US i guess you're from), standards do not always provide answers. Old fashion telephone lines are non existing here; we use underground fibers...
The protocol on the datacomm line (must be copper since it's carrying DC for feeding a control device)is ISDN for control purposes so mentioning ISDN does not mean telephone comms, hence using fiber isn't an option at all.
Bear in mind that the equipment on both sides of the line has to withstand voltages induced by a traction shortcircuit current of no less than 17,4 kA during 300 msec. Therefore my question on "reduction factors" for these cables.
Still anyone out there which can contribute?
Thanks.

 

[jghrist]

You might get some guidance from IEEE recommended practice for inductive coordination of electric supply and communication lines, IEEE Std 776-1992. The following abstract indicates that it doesn't apply in your situation (railway signal circuit), but I don't know why.

Abstract:
The inductive environment that exists in the vicinity of electric power and wire-line telecommunications systems and the interfering effects that may be produced are addressed. An interface that permits either party, without need to involve the other, to verify the induction at the interface by use of a probe wire is presented. This recommended practice does not apply to railway signal circuits.

Also try:
Modelling for electromagnetic interference assessment in electric railway traction systems
Brillante, S. Hill, R.J. Pozzobon, A. Pozzobon, P. Sciutto, G.
Bath Univ.;
This paper appears in: Electric Railways in a United Europe, 1995., International Conference on
03/27/1995 -03/30/1995, 27-30 Mar 1995

and:
Electric railway traction. VI. Electromagnetic compatibility disturbance-sources and equipment susceptibility
Hill, R.J.
Sch. of Electron. & Electr. Eng., Bath Univ. ;
This paper appears in: Power Engineering Journal [see also Power Engineer]
On page(s): 31-39
Volume: 11, Issue: 1, Feb 1997