UK DNO transformer + switch missing HV earth

[UKMeterman]

An interesting sign has appeared on a local DNO distribution transformer, earths missing from Transformer and HV switch. Is this what is meant by a hot site?

 

[davesparks]

As far as I know a hot site is one where the resistance to Earth of the earth electrode system is greater than a specified value (2 ohms springs to mind)

What you have there is, as shown by the handmade sign, an abnormal situation, probably classed as a bit of a problem and they might get around to fixing it one day.

 

[R-fur]

Probably the earthing has been stolen. I would say that missing earthing is fairly serious and should be fixed as soon as possible.
The HV earth connects the transformer and switch gear to the HV earth mat which is usually separate from the LV earth system. As well as providing a fault return path the HV earth normally has a mat shallowly buried in front of the switch gear so that when you are operating the switch gear your hands and feet are at the same potential in the event of a fault. The switch gear will also have earth switches which are closed to connect the cable cores to earth to make them safe to work on.

 

[UKMeterman]

Probably the earthing has been stolen. I would say that missing earthing is fairly serious and should be fixed as soon as possible.
The HV earth connects the transformer and switch gear to the HV earth mat which is usually separate from the LV earth system. As well as providing a fault return path the HV earth normally has a mat shallowly buried in front of the switch gear so that when you are operating the switch gear your hands and feet are at the same potential in the event of a fault. The switch gear will also have earth switches which are closed to connect the cable cores to earth to make them safe to work on.

The site has been subject to severe subsidance which may have damaged an earth mat, either way as it is the transformer that feeds a large school and some of the kids need hoists and so on, the impact of a earth fault could be very nasty...

 

[R-fur]

That is why the LV and HV earths are kept separate. Normally there is eight meters between the two. HV maximum value is 40 ohms, 20 ohms for the LV. However if the combined value is less than one ohm then they can be linked.

 

[davesparks]

The site has been subject to severe subsidance which may have damaged an earth mat, either way as it is the transformer that feeds a large school and some of the kids need hoists and so on, the impact of a earth fault could be very nasty...

If it was the LV earth then they would have done a lot more about it than a handwritten note.

 

[UKMeterman]

After a bit of prompting, they attended today and put the bonds back in.