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Modern Earthing systems

Legh Richardson
Would somebody care to tell me once the electrical supply to the British isles is fully airborne (70% wind power 2030) where does one stick ones earth electrode?

Legh
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    Legh Richardson:

    Would somebody care to tell me once the electrical supply to the British isles is fully airborne (70% wind power 2030) where does one stick ones earth electrode?

    Legh


    The top of the wind turbine is in the air, but the bottom is still stuck in the ground.  So that should provide a decent Earth path.


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    Legh Richardson:

    Would somebody care to tell me once the electrical supply to the British isles is fully airborne (70% wind power 2030) where does one stick ones earth electrode?

    Legh


    Where the squirrel buries their nuts.


    Jaymack


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    I do not think earthing will a big problem,  as mostly the LV side is already earthed, and the HV side is distributed without neutral or earth anyway, we are used to adding multiple sources to the grid.

    At the point of generation the windings may well be earth free, but that is not important to what happens on the other side of a transformer.  (all those wooden poles with a cross bar and 3 insulators for the 11kV /33kV network carry no earth do they ?)

    The bigger potential problem with wind and solar is the removal of the inertia associated with large spinning chunks of iron and copper synchronously with the grid frequency.

    Most of the grid control and stability comes from the fact that frequency is a very good proxy measure of load, and that conventional generation just dips a bit in speed during short term overloads, and if any one genset is running slow, the phase angles of the current flowing change so that it's load is reduced, and in extremis, the current actually pushes the genset,  motor-like,  to get it back in step.

    Electronic inverter derived AC does not do this naturally, as the voltage and cycle timing are independent, and there is no moment of inertia to borrow from in times of stress - a conventional genset can provide a few hundred percent of rated power for several cycles - electronics has to be designed to withstand that, and the controllers programmed to do it,  and getting that right may well be more of a challenge.

    However once done correctly the grid should function as before, and it opens an interesting possibility..

    While folk are busy designing ever more complex computer networks to meter in small intervals and control smart loads to track prices, a far simpler method seems to have been overlooked (perhaps as there is no money needed for software consultancies). If we charged more when the frequency was below 50Hz, and less when it was above, loads like heaters could contain some frequency detection electronics to wind down the load on a timescale far faster than any computerised system.
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    Thanks for these answers. particularly Mike's clear, consise and well developed one. For some reason I thought the earthing system, or lack of it, might have been an IT system. I think we'll leave the squirrel's nuts in the undergrowth.

    Legh
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    mapj1:

    I do not think earthing will a big problem,  as mostly the LV side is already earthed, and the HV side is distributed without neutral or earth anyway, we are used to adding multiple sources to the grid.

    At the point of generation the windings may well be earth free, but that is not important to what happens on the other side of a transformer.  (all those wooden poles with a cross bar and 3 insulators for the 11kV /33kV network carry no earth do they ?)

    Perhaps pedantry, but I would correct this by saying that in the UK most HV installations don't have a distributed neutral but they are in fact rather well earthed. The fact that there's no earthing conductor for 11/33kV overhead lines belies that fact that there should be a very good electrode at both ends; similar to TT you might say, albeit in many cases potentially with a deliberatlely inserted impedance at the NE "link"(s). There are some HV systems that do run unearthed but they're rare in the UK.


    However it is true that many inverter driven generators that I come across are arranged as IT on the LV windings. But as Mike says this has little or no bearing on the earthing arrangements on the other side of the transformer.

     
    mapj1:

    While folk are busy designing ever more complex computer networks to meter in small intervals and control smart loads to track prices, a far simpler method seems to have been overlooked (perhaps as there is no money needed for software consultancies). If we charged more when the frequency was below 50Hz, and less when it was above, loads like heaters could contain some frequency detection electronics to wind down the load on a timescale far faster than any computerised system.


    This is already being done: Response to (over-)frequency signals is now a requirement for >16A/ph (G99) generators on a linear droop, with more involved arrangements being necessary for larger projets, while frequency response services - controlled entirely based on local frequency measurements - are contracted out by National Grid, with EFR being an extremely fast response. In principle then there is nothing stopping this approach for consumer electronics / equipment, although unless it becomes a mandatory requirement for all new equipment you'd still need smart metering to provide a price signal to encourage take-up.


    Worth noting though that at present NGESO do deliberately run the system at frequencies slightly above/below nominal at times to re-synchronise clocks, so it is not a perfect signal.


    ...Anywho, going back to the OP, Mike is right that once you've gone through several transformers it makes no difference what the earthing system is at the generation end so it'll be business as usual for LV, and at HV the rules are just the same for wind turbines as for steam ones.


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    Just picking up Mikes point on charging more when the frequency is low, do you honestly believe you'd see the frequency above the legal minimum? The deal would have to be that any deviation from the average 50Hz over say 4 hours would have a huge penalty payment, otherwise, we'd have 48Hz for ever more!

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