Induced Voltage

[Nick w]

I work on the railway and we juct recently finished a job in london where there are 25KV overheads and weve bonded a hand rail surrounding our equpment which in turn is bonded to all the other eqipment on the platform (columns etc), which is also linked to the taction bonding via a dual link earth bar and were getting a constant voltage of 8-11 Volts it doesnt matter if you disconnet the bonding, separate the earthing systems, even installed a tempoary TT just to test it and still the voltage is constant, the client has said we need to sort it, OLE claim that the voltage sholdn't be there and they claim its not dangerous even though we've not located the source of the problem.

my main concern, Is it possible for the charge to build up some how and become lethal although earthed the voltage is constant, only on the hand rail?

cheers

 

[Technician]

It may look like a silly question but is the 25kV overhead

an alternating (AC) voltage or steady (DC) voltage?

 

[Nick w]

its AC lol sorry should have wrote that in

 

[Technician]

Acknowledged Nick;  no worries;  The reason I asked was

because a lot of rail traction is DC.  There is obviously an

alternating magnetic field all over that kit and it looks like

this is the source of the problem.  As soon as that lot is

de-energised those voltages will disappear but it does not

alter the fact that the other side perceives it as a problem

for you to solve.

Wait for the others to have a look at this and maybe they

will have some ideas.

 

[SPECIAL LOCATION]

were getting a constant voltage of 8-11 Volts

More info needed I think....

8-11 Volts at the hand rail with respect to where?

where is your other meter lead connected to?

and what sort of meter are you using?

8-11 Volts.. AC or DC?

 

[Nick w]

8-11 AC on the hand rail located approximatly 8 meters from the nearest running line, the hand rail its self is hollow galvanised steel 1.5 m high in total 6 meters in length , using a fluke multi tester 1653 summit summit, we tested between the hand rail and the casing of our equipment which is bonded separatly but also disconnected the bonding cable to the hand rail when we were investigating and hand rail remains at constant voltage but bonding cable goes dead when disconnected, we've tested all the bonding cables separtly and everyhting is continuous back to the earth bar but nothing else picks up a voltage except for the hand rail

 

[steptoe]

Can you try to measure it with an analogue meter?

There are loads of threads on here about 'phantom' voltages being induced.

Have you removed the galv where the bond is attached?

 

[Nick w]

yeah mate its drilled and tapped in with a brass bolt??

i dont know...... its bizare, its come to a point that if we can't resolve it by finding whats causing it then we'll have to remove the hand rail and replace it with a GRP hand rail which im considering may be the best option anyway, because if anything were to happen and a charge some how built up someone could die.

 

[binky]

sounds like a good excuse for more work, go for it! LOL.

Think Steps is right in that this maybe a test gear issue. I am assuming rails are bolted to ground, plus you rodded it (steps will be impressed). That should have dissipated any voltage to earth, unless you were really lucky and put rod in a no-conductive bit of ground ie bone dry, but still very unusual.

 

[Nick w]

yeah mate all of the above lol thats why we put another rod in to test in all but the cost to replace the hand rail is out of our pockets, but we tried 3 or 4 various digital voltage indicators and they were all showing somthing but their not reliable enough, and to touch it you fell a tiny sensation or wether we subconcously convinsed ourselves we could but there was 5 or us ther looking at it  

 

[Technician]

The field strength, measured in Teslas, according to

what I have just been looking at is measureable in

microTeslas and is highest when the measurement

is taken directly under the overhead.

 

[steptoe]

I know you have drilled the rail, but have you removed the galv where the lug is in contact?

 

[Nick w]

yeah all the galv is off i check it myself and wire brushed the thread and bolt just to be sure literally the last week in the office weve bin talking about it, starting to get on my wick so i thought id see if there was anyone who may delt with summit like this before, were stuck and on monday were going to have to either have guys onsite to rectify it or remove it and return in two weeks to replace the rail with GRP, its abit W*nky poo pants

 

[steptoe]

Deffo a strange one, especially as its all bonded together. :C

 

[Andy™]

just a thought, but you say its 8-11v between this metallic part and the rail.... are you sure its not the rail thats got 8-11v?

 

[allan moore]

Look up Transient earth voltages and you will probably find an explination there. Its basicaly induction??

 

[Manator]

http://www.hvpd.co.uk/products/sensors/tev-sensor.html