Horse Risk?

Is the HV overhead? If so it's more than likely a "hot" site (in old money) so there'll be separate HV and LV earth electrodes - usually the HV one near the transformer an the LV some distance away (next pole, or even at the consumer's end if it's PNB).

I'd suspect that the HV one is perhaps less of a risk - not because of the voltages involved but because it serves such a small part of the system - i.e. there would have to be a L-PE fault in or right next to the transformer to energise HV electrode to the sort of levels that would cause hazardous step voltages, and the chances of a fault in that small area must be very small.

Much more likely to have a fault somewhere on the LV system - but even that's fairly rare (how many seconds out of a year) unless there's an uncleared L-earth fault somewhere.

DNO electrodes are often a bit more sophisticated than just a 4' rod banged into the ground too - more often tapes or even mesh covering a substantial area and at a reasonable depth - so the step voltages at the surface may well be 'spread more thinly' than we're used to.

So I guess it's a matter of yes there is some risk, but not such a large one I'd loose any sleep over it.

   - Andy.

The cables are overheads. There is no fence around the poles.

Z.

The cables are overheads. There is no fence around the poles.

Z.

It all rather depends on how things are earthed and what the possible fault states are. If the LV side supplies only TT buildings then the ground fault current will be limited by the soil resistance, and the duration will be limited by whatever RCD or earth fault trips those installations are using. An HV fault say from windings to core of the transformer or over an insulator is unlikely, unless damaged by thunderstorm or very poorly maintained, but if it occurs the fault current will be significant. In the UK the 11kV network has earth fault detection (unlike some countries our HV is neutral free, and there is the equivalent of a large RCD at the source end, though made up from discrete current transformers, delays and HV trip units.)

so an HV to ground fault will not go unnoticed for very long.

It also depends on the earthing at the pole - it may be just the HV earth, and if it is recent the earthing wire(s) for the transformer tank and core will be insulated  coming down the pole, and to some way below the surface, so that the surface voltage gradients are to some extent reduced by the fact that the full voltage starts off half a metre or more below the surface, so there is always at least that much earth in the way. An older unit may be bare at the surface.

For a lone pole pig on the end of a long thin line, a 10 ohm electrode impedance and a 50amp HV fault are quite sensible worst case numbers to conjure with, so a 500V electrode rise during fault.
In towns and near the supply end the fault currents are higher and could be in the kA, and so if the rise of earth voltage is to be kept down, the electrode need to be that much better pro-rata.
In some ways, just by sheer force of numbers, a fault on the LV side is more likely, but the LV neutral may well be better earthed - if the HV and LV earth do not share, then there will be LV earthing on another pole, often the next one along from the TX itself, but may be on more than one pole - and on a "PME ready" part. of the  network, there will be several.

But a fence, or gravel around the post base are cheap ways to reduce the risks to livestock - but the risk is small compared to falling, going lame, food poisoning and other ailments.

Mike.

Thanks Mike and all others.

Z.