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DNO temporary generators

AJJewsbury

After an old PILC cable went pop under a pavement outside, myself and a few neighbours are now temporarily supplied by a DNO generator, which has got me wondering...

The generator seems to have no obvious Earth electrode ... how are they Earthing the system? In my case it's spliced into the remaining few 10s of metres of PILC cable so the lead sheath/armour is probably providing fairly decent connection with true Earth, but what would they do in general - e.g. if more modern plastic sheathed cables involved?

The other though is that Zs/PFC from the generator is unlikely to be anything like that from the grid (and what the TN installations would have been designed for) - will the DNO have taken any precautions to ensure that ADS will still operate adequately? Perhaps and RCD on the generator? Or might resilience take priority?

   - Andy.

Parents

  • If the network contains any PME then an RCD is not possible, as it sees it as  an NE fault.

    A genset on skids in the mud may well be its own electrode of 50-100 ohms, and that will be augmented by bonding at the houses that have metallic services.

    The path through the terra-firma ground is not the main fault loop for blowing fuses - that is done via the neutral/ CPC .

    The sort of gensets that DNOs have on 'call-off' with the likes of Agrekko have earth fault relays, because all hire gen-sets do, but when used for network support they are likely to be either off or set to a level rather more than the likely neutral current,  to avoid the PME issue.

    A modest genset for a few houses may not blow a 400A fuse like the substation would, though a house fuse at  60A or 80A should be in reach if a bit slow,  but even  if the fuse does not blow the volts will collapse or the genset will stall, so it is an awkward and flickery problem  rather than a dangerous outcome.

    Mike.

  • in reply to mapj1

    (The new forum? It's ok... plus, it's FREE! Nice!!).

    Hi, I was going to raise a few questions' regarding this. A week ago my neighbour was knocking on my door to say he had no power... turned out that there was a problem with the SWA cable, in the street. For a few days' we had an enormous, (and, haha, noisy), generator. I live in a small close and you could hear it humming away BUT, at least he had power!

    The other thing is, his wife is very disabled and they have 'local service helpers' popping about 4 plus times a day! So, quite a lot of foot traffic! 

    H&S???

    1 - Is this right? They ran an SWA, from the generator, through his letterbox!! I mean... there MUST be some code that this isn't acceptable? 

    2 - See the photo of the TT supply. 

    Any suggestions?

    regards...

    CLICK phots' to enlarge!

    SWA Through the letterbox!

     TT supply to the house.

    OK, you could argue how would you get the required SWA into the house? My answer would be... drill a small hole somewhere... wouldn't that be better??

  • in reply to Tomgunn

    DAMN!! I clicked a wrong sign to report this!!! SORRY!!!! 

  • in reply to Tomgunn

    That letterbox  is indeed a class act. Had they said something to upset the team I wonder ? (shades of the ununlucky Mr Meldrew). Traditional way in would  be a fanlight window and if needed a couple of bits of chipboard one inside one outside screwed together to form a clamp to stop the draught.  I imagine there is no reg broken, apart from the one about good practice, but the earth rods look a bit shallow and rather close to each other to get the low ze  benefit of parallel connections.

    Mike

  • in reply to mapj1

    Thanks Mike... I just laughed, when I noticed this. 

    regards...

  • in reply to Tomgunn

    Cables through letterboxes are in my experience a common approach in this situation. Almost every home has one so it is a simple and quick way of restoring power.

    Drilling holes takes longer and risks damage.

  • in reply to broadgage

    https://www.youtube.com/watch?v=lNEXWITxkmg

    May be of interest, cables through letterboxes for some customers. Others restored by temporary connection of generators into the street mains.

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