Hi, Ok, quick intro to the frequency steering.
There still remains rules that say that network frequency should be on average 60 Hz on the US grid. (Yes, there is proposals to remove it, but it is still effective.)
Since the generation (let's talk traditional here not to make things more complex than they need to be for the first overview) is from generators, essentially big rotating lumps of iron, the balance between load and generation causes the frequency change. If you have more load than generation, the frequency will lower while if you have more generation than load the frequency will go up. Essentially, if you undergenerate, you would need the rotating energy of the lumps of load to deliver, but that reduces their speed and if you underconsume the energy goes into the rotation of the lumps.
Now, by monitoring the frequency you can steer the balance, askning hydropower to increase or decrease production to balance the shift of load. The operators have a fair clue on how the day will proceed as people wake up, industry starts, workday, industry closes down, people get home etc, so there is a basic pattern there to give a clue, but they monitor it and balance it.
By also balance the phase, you can know how much you lag behind and needs to run up by running the frequency high. This require spending energy by increasing production compared to the load. Now, by being smart you do that when you have low load, so that you don't have to spend as much energy to achieve it, but never the less.
Then you have to manage your reactive energy, the VAr, which is a different matter.
Breakers have several form of catastrophic protections in them, among those if the frequency goes bad. Turns out that the frequency monitoring of breakers gives so diverse readings such that for post mortem analysis, they provide bogus values. They learned this the hard way after the North-Eastern Blackout. When they threw out all the traditional frequency readings, the PMU data that remained painted a consistent picture.
The detailed monitoring of PMU gives much more data, also illustrates forced oscillation, inter-area-oscillations etc. which makes the phase wobble in interesting ways, and when analyzed gives good clues about problems in the network.
An even more "fun" scenario is when the network runs into islanding, since the link between areas is to weak to keep the frequency at the same rate, i.e. the link is to weak to support the load, so one part has overload and goes down in frequency while the other have overproduction and gos high in frequency, which you can see by the way that phase starts to deviate between the networks, and that before you have the de facto islanding.
The islanding illustrates the need of the links to be strong enough so that generators synchronize, or should we say syntonize to be correct with terms, that is, they have the same rate.
The four islands that you identified do their own independent frequency steering, but they exchange power. The generation-load thing still happens, but phase/frequency decoupled. HVDC cables achieve the same thing.
Anyway, phase monitoring has become a very good tool for so many of these measurements, and that requires a common "reference" phase and that is GPS. That helps to monitor the phase and frequency of the grid so that it can be controlled.
A peculiarity of the field is the ROCOF - Rate Of Change OF Frequency. This is what we call linear frequency drift. Looking on those numbers give you a good hint where you are going.
Until recently, photoelectric would not provide any of the rotating iron properties, but the increase popularity of it now requires it to start to have such properties for the stability of the system.
Cheers, Magnus On 04/04/2017 11:28 PM, Thomas D. Erb wrote:
Thanks for the info. So that tells me how data is recorded - but not how the frequency is kept stable ? Is the line frequency now directly tied to GPS clock - with no drift ? Thomas D. Erb t...@electrictime.com<mailto:t...@electrictime.com> / Electric Time Company, Inc. Office: 508-359-4396 x 117 / Fax: 508-359-4482 97 West Street Medfield, MA 02052 USA www.electrictime.com<http://www.electrictime.com> [Facebook]<https://www.facebook.com/pages/Electric-Time-Company-Inc/127918073950854?ref=hl>[Twitter]<https://twitter.com/tower_clocks>[pinterest]<https://www.pinterest.com/electrictime/> [htmlsig.com]<http://www.electrictime.com/> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
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