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Microshocks from induced voltage

MG
Has anyone ever come across the requirement to earth a section of metallic fence to mitigate micro-shocks that may be induced by an overhead transmission line? I have looked online but there is no methodology or guidance value listed other than just "earth the fence".


Any info would be useful.


Thanks

Mike
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    All thank you for your responses, the guidance in TS 41-24 is a bit similar. I managed to get someone specializing in EMC to model the induced voltage on the fence from the Overhead transmission tower and recommend the maximum continuous metallic section lengths where the standing voltage does not exceed 60V and also earth rods to safely carry that induced current to ground. The continuous section lengths will be separated by 2.5m of non conducting fence.

    Tatty, this is indeed a railway, there is not need to traction bond the fence in this scenario as it is situated far away from the drop zone (OCLZ as specified in 50122-1) therefore the only concern is any induced voltage on the fence parallel to power lines that would likely exceed the 60V limit. Minimum cable size for a 200ms disconnecting system and 12kA Network Rail job is 35mm sq for a XLPE sheathed cable. For a 6kA system a 25mm sq is acceptable although NR prefer bonding rated for a 12kA system. A document No. PAN/E&P-E/EE/ESD/0102 issue 4 is very helpful if you don't have it already. The cable minimum cross sectional area can be calculated with the adiabatic equation in BS 7671 and relevant k from the provided tables. Cable lengths are subject to voltage drop across the specific cable not exceeding 645V in line with the voltage limits specified in 50122-1 for 200ms. Once the voltage limit is exceeded on a cable then use a size up until the criteria are satisfied
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  • 0
    All thank you for your responses, the guidance in TS 41-24 is a bit similar. I managed to get someone specializing in EMC to model the induced voltage on the fence from the Overhead transmission tower and recommend the maximum continuous metallic section lengths where the standing voltage does not exceed 60V and also earth rods to safely carry that induced current to ground. The continuous section lengths will be separated by 2.5m of non conducting fence.

    Tatty, this is indeed a railway, there is not need to traction bond the fence in this scenario as it is situated far away from the drop zone (OCLZ as specified in 50122-1) therefore the only concern is any induced voltage on the fence parallel to power lines that would likely exceed the 60V limit. Minimum cable size for a 200ms disconnecting system and 12kA Network Rail job is 35mm sq for a XLPE sheathed cable. For a 6kA system a 25mm sq is acceptable although NR prefer bonding rated for a 12kA system. A document No. PAN/E&P-E/EE/ESD/0102 issue 4 is very helpful if you don't have it already. The cable minimum cross sectional area can be calculated with the adiabatic equation in BS 7671 and relevant k from the provided tables. Cable lengths are subject to voltage drop across the specific cable not exceeding 645V in line with the voltage limits specified in 50122-1 for 200ms. Once the voltage limit is exceeded on a cable then use a size up until the criteria are satisfied
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