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National Grid, Low frequency disconnecting system.

broadgage
As is fairly well known, any excessive drop in UK grid frequency results in calls for increased generation from quick starting plant such as OCGT and pumped storage, and for increased output from already running generating capacity.

If this does not relieve matters, then areas are disconnected by frequency sensitive relays in order to preserve the rest of the system. This last happened in August 2019 IIRC.


My question is what will happen during the NEXT low frequency event ?

Will the SAME areas be blacked out via the same (or similar replacement) relays operating the same switchgear as last time.

Or are settings adjusted after a low frequency event, such that next time the burden will fall on different areas.


The first approach sounds simpler, but the second approach is fairer. Or are such low frequency events so rare that "fairness" is not considered important.
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    Not anywhere near as bad as Sir Edward Heath`s "Winter of Discounted Tents"
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    I hope that it does not get as bad as the recent Texas power cuts, with no drinking water, food shortages in supermarkets and no heating in homes.


    Z.
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    I strongly suspect that any widespread and prolonged power cut WOULD result in chaos broadly similar to that in Texas. Very few individuals and businesses are properly prepared for such an event.


    My enquiry was however about a relatively short term outage like the event in August 2019. If/when it happens again, will the SAME areas be blacked out as last time, or will the next low frequency event affect DIFFERENT areas.
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    I think a very reasonable question and, presumably, only one which National Grid could answer. I suppose that the fairest response would be to shut down different regions at random, but I doubt that the engineering would cope.


    Is the "decision" man-made or machine-made?
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    Wasn't there some umming and ahhing after the last incident that resulted in changes being made to some of the parameters? If so it's likely that 'next time' will result in a different outcome anyway.

       - Andy.
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    Chris Pearson:

    I think a very reasonable question and, presumably, only one which National Grid could answer. I suppose that the fairest response would be to shut down different regions at random, but I doubt that the engineering would cope.


    Is the "decision" man-made or machine-made?




    In the short term, the "decision" is machine made since a rapidly falling frequency needs very quick and automatic action to avoid a total collapse.

    Taking the longer term or wider view then the decision is man made, the frequency relays are installed and programmed by men, who must decide which national grid feeders are dissconected in what order and at what frequencies.

    So is this order altered after the event ? or is it the same each time ?


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    These are rare events so the settings arent changed after use. ....that said  there has been a lot of work done in this area including a major programme to change protection settings, new standards etc.  Have a look at TSO-DSO Project Initiation Document (energynetworks.org) for some examples.
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    Low frequency demand disconnection is still quite rare. Blocks of demand are programmed manually to be disconnected automatically at set frequencies. However once these frequencies are reached there is a certain randomness in which blocks actually trip depending on the sensitivity of each relay and the accuracy of it's operation. So the same blocks wouldn't necessarily trip each time. I believe that part of the review.is (was?) to consider what happens now that some 'demand' groups now actually export at least part of the time and tripping these groups (effectively generation) could be the wrong action when trying to contain a falling frequency. The LF relays were originally on the CEGB 132kV to Area Board interface and since most of the 132kV network is now owned by the DNOs then they are maintained and set by the DNOs in accordance with the Grid Code
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    AJJewsbury:

    Wasn't there some umming and ahhing after the last incident that resulted in changes being made to some of the parameters? If so it's likely that 'next time' will result in a different outcome anyway.

       - Andy.


    Yes, IIRC there were adjustments mad to the settings of protection relays for large wind farms and large PV arrays, this should help a bit by allowing such installations to "ride through" grid frequency or voltage disturbances rather than tripping and making the situation worse.

    I think that protection settings for NEW (not yet installed) domestic sized grid tied PV were also altered for the same reasons. I do not believe that settings on EXISTING domestic sized grid tied inverters were altered. Who would do this and at at whose expense ?


    These alterations should tend to reduce the risk of a similar event happening again. OTOH the growth in generating capacity connected via static inverters, and the reduction in classic steam turbine capacity would tend TO INCREASE the risks of instability and a repeat of August 2019.


    So I see some risk of it happening again.


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