Generator operating frequencies. 27

[HamburgerHelper]

I have thought about this for awhile and I don't understand it. So, let's say you have generation spread out over a large region and there is a disturbance in the system that causes one of the generators to be at a lower or high frequency than the rest of the generators in the system and the controls don't work to bring that generator back up to normal frequency. What happens? I have a hard time understanding this because in my mind if a generator is operating at a different frequency than the rest of the system, that generator or island around the generator is effectively isolated from the rest of the system from a power flow perspective. The rest of the grid is going to try to motor or add generation to it as the phase angle of the different frequency generation slips around the rest of the grid. I just have a hard time grasping why a generator can operate for example at 59 hz while the rest of the grid is humming along at 60 hz.

 

[KHH1]

CR,

I did not mean to say that the deviation is 0.01 Hz. The frequency deviation is indeed much less than that.

What I meant was that the frequency of gen. speed oscillations around their rated values is ~0.01Hz. It is a slow dynamics between the generator groups from different areas.

And yes, I also think participants in this group have been describing the same elephant from their own viewpoints.

 

[crshears]

Hi KHH1, I never said you said that; I was looking at the Eastern Interconnection frequency display in real time at the link you provided, and noticed that at one point there were three different colors present within the EI, which, based on the legend, would mean a delta of 0.02 Hz as measured between the various locations monitored.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[HamburgerHelper]

KHH1,

Frequency deviation for the generators should be related to their thevenin impedance the grid. Anything near, these generators should be seeing similar frequency excursions, though slightly less. I would be expecting to see more deviation on the edges of an interconnect but it seems like a lot of it is in the midwest in the eastern interconnect.

 

[ScottyUK]

HH,

I find it easier to picture the oscillation as the generator rotor pulling slightly ahead or dropping slightly behind whatever load angle it has adopted relative to the system, gently moving either side of the equilibrium point as the governors and AVR interact with a larger system which is itself dynamic and constantly changing.

Within a power plant containing multiple generators the machines shift load angle slightly relative to each other as their governors and AVR's interact with each other. In a plant with a Bently Nevada vibration monitoring system with keyphasors (index pulses) on the shaft you can actually observe this in real time if you've got a mind to do so. On a larger scale power plants shift in phase relative to each other, and at a macro level entire regions may shift in phase relative to each other.

Dynamically these angular shifts will appear as instantaneous frequency differences if frequency is measured on a sufficiently small time-frame, but in a synchronous system it is much more meaningful to look at how relative phase changes between system elements rather than introducing the idea of 'frequency differences' in a system which is synchronous.

 

[Skogsgurra]

I Think that is worth while to look back at the OP's original question:
"HamburgerHelper (Electrical)
(OP)
5 Apr 18 13:28
I have thought about this for awhile and I don't understand it. So, let's say you have generation spread out over a large region and there is a disturbance in the system that causes one of the generators to be at a lower or high frequency than the rest of the generators in the system and the controls don't work to bring that generator back up to normal frequency. What happens? I have a hard time understanding this because in my mind if a generator is operating at a different frequency than the rest of the system, that generator or island around the generator is effectively isolated from the rest of the system from a power flow perspective. The rest of the grid is going to try to motor or add generation to it as the phase angle of the different frequency generation slips around the rest of the grid. I just have a hard time grasping why a generator can operate for example at 59 hz while the rest of the grid is humming along at 60 hz. "

HH has put a meaningful question, but with the wrong assumptions. Namely that there could be a frequency deviation between different points in a grid. That question has led to a confused philosophical discussion where waveforms, generator slip and pole angles, distorted wave-forms and non-standard (except for what may happen in protections) frequency measurement methods have been mixed into the brew. All that has not served any good. Rather, it has made otherwise perfectly intelligent individuals throw reality over board and introduce etheric and nonsense concepts. The question about frequency is measured has been put several times and there has not been any definitive answer. There is a simple answer, but that has been abandoned, which has not made the thread any clearer.

Some guys has mentioned that this thread is valuable. Yes, perhaps if you leave the original question and introduce a lot of exceptions, like generator speed, islanding, measurement techniques that may be necessary in certain protections and other things. But when it comes to the question if there can be a frequency difference in a connected grid - it has only caused confusion, hypertension and animosity.

ScottyUK did put a good end to the "discussion". Let it stay there.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[HamburgerHelper]

Skog,

You don't have to read this thread if you don't want to. Your comments about people here must be Trump supporters or the threat that you'll leave eng-tips and never comeback was never adding to any discussion that was going on or really in the spirit of things. No one makes you visit this thread. It apparently does nothing for you but you kept coming back to it for two weeks. And twice, told everyone to shut up and shut it down. You contibute a lot to the power threads so this has kind of baffled me.

 

[Skogsgurra]

I understand that.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[HamburgerHelper]

Interesting stuff is going in in the Western Interconnect right now.

http://fnetpublic.utk.edu/frequencymap.html

The whole thing got down to 59.94 or less and was just holding there.
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If you can't explain it to a six year old, you don't understand it yourself.f.

 

[cranky108]

The wild wild west, but the lights are still on.