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Bonding of temporary metal fences at a Railway station platform

tattyinengland
HI Chaps


One of the jobs I need to do in the near future is bond some temporary metal fences at a railway station platform.


I would not normally bond metal fences, but I know that this a requirement in this case; metal fences, metal stairways from the platform up to the overhead concourse etc


The overhead train HV lines are probably 5m away from these fences.


Do anyone have any further information for me so that I can understand why we are bonding these fences and what we are trying to achieve? 


I suppose its something to do with the HV side of things..................


Any help would be much appreciated


Kind Regards


Tatty
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  • Former Community Member
    0 Former Community Member
    Hi Harry,

    It is important that accessible voltages are kept to safe levels wherever they can be accessed relative to local earth, e.g. the ground on which a person might stand, so this is 25V w.r.t. local earth.

    Re system volt drop, most of the volt drop is in the Catenary or OHL contact wire, because it's impedance is much higher than that of the traction return circuit, which also has many parallel return paths which keeps its potential low with respect to remote (and local) earth.

    Developments such as the autotransformer (AT) system effectively increase system capacity by transmitting 25kV to the OHL system, and also an antiphase supply via a parallel conductor making 50kV available to autotransformers that cleverly make more power locally available to the train whilst reducing current returning via the rails. Several of the main lines, e.g. the new Great Western electrification use the new AT scheme, which is compatible with both new and old rolling stock, and have the advantage of increasing the length of section that can be supplied from a single supply substation.
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  • Former Community Member
    0 Former Community Member
    Hi Harry,

    It is important that accessible voltages are kept to safe levels wherever they can be accessed relative to local earth, e.g. the ground on which a person might stand, so this is 25V w.r.t. local earth.

    Re system volt drop, most of the volt drop is in the Catenary or OHL contact wire, because it's impedance is much higher than that of the traction return circuit, which also has many parallel return paths which keeps its potential low with respect to remote (and local) earth.

    Developments such as the autotransformer (AT) system effectively increase system capacity by transmitting 25kV to the OHL system, and also an antiphase supply via a parallel conductor making 50kV available to autotransformers that cleverly make more power locally available to the train whilst reducing current returning via the rails. Several of the main lines, e.g. the new Great Western electrification use the new AT scheme, which is compatible with both new and old rolling stock, and have the advantage of increasing the length of section that can be supplied from a single supply substation.
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