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At the slack bus, there is a generator that can change his output instantly. I was wondering if exists in the grid this generator. We use it to study power flow problems but I don't think that there is a generator in the grid (that of the slack) which is able to change his output instantly. Can you give a physical representation of the slack bus?

Samuele Benito Di Gioia
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    I have no idea what or where a slack bus is but if you're looking for instant generation capacity have you considered a battery inverter system? – Transistor Nov 01 '20 at 17:19
  • yes, but I don't think it is a solution because after a few hours the batteries can't supply all the load. – Samuele Benito Di Gioia Nov 01 '20 at 17:26
  • It is not a real machine, it is used to allow solution of power flow equations in load flow. Read [this page](https://en.m.wikipedia.org/wiki/Slack_bus) and see if it helps your understanding. – relayman357 Nov 01 '20 at 17:38
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    http://www.gridwatch.templar.co.uk/ ... at the moment demand is 36.36GW and frequency is 50.021Hz. Add some load and you'll see the frequency fall slightly as all the spinning generators work a little harder. If it falls far enough someone will turn the pumped storage generators up a bit; they are providing about 1.1GW out of 2.5GW capacity. Then the CCGT gas turbines will be the next to react. And so on. –  Nov 01 '20 at 17:48
  • @BrianDrummond so the slack bus is like the representation of all the generators that provide power to compensate for that difference? – Samuele Benito Di Gioia Nov 01 '20 at 17:53
  • I have never come across the term "slack bus" so if that's your actual question I'll have to leave that to someone else. But @relayman357 's comment link suggests slack bus is about power factor, not instant response to demand, so I don't know what you are really asking. –  Nov 01 '20 at 17:59
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    The “slack bus” I am referring to is 1 machine in the system (for which a load flow is being solved) that is used to make up all of the losses not accounted for in the system - to allow a numerical solution. – relayman357 Nov 01 '20 at 18:09
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    There is not a real machine or even a battery system that can change real power output instantly. However there as a wide range of response times for real machines. It may be possible to assign the slack bus role to a real machine with some limitation on what "instantaneous" really means. It would be better to search the technical literature of find a handbook that discusses the subject in depth. –  Nov 01 '20 at 18:15
  • If I change the slack bus the solution will change. So my problem is physically speaking. Ok the theoretical meaning of the slack bus (useful to solve PF computations, compensates losses, etc...) but in real life, if I am the TSO and I want to know the exact value of the power flows flowing in a grid (and voltages, etc...), I should know where is the slack bus. I can't choose it. – Samuele Benito Di Gioia Nov 01 '20 at 18:17
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    You don’t need the slack bus if you are measuring real flows in the system - which is how the system operator gets their data (real transducers). – relayman357 Nov 01 '20 at 18:23
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    Very thanks to all! I really enjoy your answers! – Samuele Benito Di Gioia Nov 01 '20 at 18:25

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