I am an electrical engineer who worked at a nuclear power plant for 36 years. Since I retired, I have been reading as much as I can about the grid and Energy and of course, “Shorting the Grid”. I’ve also been reading about inverter based resources, and the problems they pose on the grid when there’s a fault. The industry now knows that IBR need to be “grid forming”, instead of “grid following”. There are many YouTube videos available if anyone dares to get into how a grid forming inverter works. Bottom line, if they all become grid forming, they should be able to ride through most Grid voltage andfrequency oscillations. IEEE has issued a standard that NERC can require.
Thank you Meredith for your timely and important article regarding IBRs, particularly for California with its 19,011 MW of solar and 8,120 MW of wind as of 01 April 2024, per CAISO . Californians for Green Nuclear Power provides additional details in their March 4, 2024 GreenNUKE Substack article, "Why is Grid Inertia Important?" https://greennuke.substack.com/p/why-is-grid-inertia-important . Please also note my May 27, 2024 comment to this article which is a glossary entry regarding grid inertia that was published by NARUC. "Area Control Error" is an important concept for IBRs.
Interesting that inverter waves are square or approximations, that gives me an intuitive sense of why some industrial customers need to protect their equipment from the quality of the IRB electricity coming in
That was a mouthful and brainful of technical information, Meredith. I will have to reread it. It’s looks like you are needed again to help your grid allies understand the complexities. Thanks!
I am so embarrassed that I didn't quote Doomberg! I feel terrible about it!
Synchronous condensers are only a partial answer. I wrote about them in Shorting the Grid, on page 31, where Governor Shumlin was angry at ISO-NE for curtailing Kingdom Community Wind. KCW was curtailed because they had not installed synchronous condensers. Later, KCW installed them, but it did not solve all the problems.
I have to write more on this. I WILL quote Doomberg next time. So deeply embarrassed!
Thank you Meredith, good piece. My primary peeve has been the outsized claim by renewable promoters about "synthetic inertia" and how it can replace traditional rotating mass. The issue is it's theory under development, and still a member of the "not ready for prime time players". Here is an article on the subject.
Thanks for that reference. I haven't read through it nor the other references you cite but I expect the major issue isn't simply a matter of matching frequency but also phase. If the phase is off, the grid sees that as a reactive load and as the IBR phase corrects to the grid phase (as it must), other grid generators -- including the many connected IBRs -- will also be adjusting their respective output phase. With time delays due to grid reactive elements and IBR electronics, I imagine the resulting corrections result in a very complex set of harmonic resonances on the grid.
Now I'm not a grid engineer by any means but it seems to me that what's required is a stable reference frequency supplied to each IBR i.e. a frequency reference not from the grid itself. Like the SFTS signal https://en.wikipedia.org/wiki/Standard_frequency_and_time_signal_service Perhaps that's already being done for registered IBRs?
2017, based on information prior to 2017. Modern inverters are fine. I’ve seen batteries installed to improve CCGT reliability and no issues with inertia after the GT trips. It’s 2024 mate.
I am not an electrical engineer, and I don't even play one on TV. But I am a physical chemist and I can usually understand many technical articles. This article about how GFMs affect the Northwest shows that there are indeed some issues with GFMs.
Fast response after a major generator trips off is a very good use for batteries. Batteries provide power to the grid while the gas turbines come up to speed. They allow the gas turbines to come on with a more moderate (and less polluting) ramp rate. Batteries are oversold, but that does not mean they are useless.
This is NOT the same as saying that a grid with mostly GFMs will be a well-behaved grid.
That I can agree with. The argument I have had is with replacing spinning reserve with fast response batteries as some propose. It's unlikely you will ever get the same system inertia out of a battery that you will out of a 200 ton spinning rotor. Inertia comes into play in the energy delivered to the system as 200 tons of mass decelerates as frequently declines. It is that system inertia that slows initial drop, or increase in frequency. The change in frequency is enough that the governors of the dispatchable generation will respond and arrest the frequency decay, and partially restore frequency. The ramping of gas turbines wouldn't ta place until the above actions were complete, and AGC made moves to restore frequency. A fast ramp on a battery could get you back much quicker. I suggest you read this https://www.wecc.org/Reliability/Governor%20Tutorial.pdf
Thank you for this excellent description of inverters and how they fit in to our Bulk Power Supply. I am a retired power engineer and am very well informed regarding the boiler island, balance of plant and steam turbines. However, in my mechanical mind.....I am a strong advocate for spinning reserve of huge magnets turning within the stator at synchronous speeds (1800/3600 RPM) providing the momentum to stabilize the 60 Hz Grid. Your article was great for demystifying inverters. Thank you again. BTW, I did buy a copy of your book for reference.
I suppose if an inverter or series of inverters fails simple cycle natural gas plants fills in? We could probably turn off all solar and wind and and there would hardly be an increase in CO2 emissions and the grid would be more protected.
I had read some time ago that inverters had a 20% failure rate, but had no idea what that failure rate would and could do to the grid, thinking they would just be taken offline and replaced... electricity is just never that simple!!
Thank you for this great and timely post as we gain more and more solar here in Texas.
I can see why Robert Bryce always asks - "ultimately who is in charge?"
Thank you EG! Absolutely correct ! What a short Federal document ! I wish everyone could understand this, or at least Congress, White House and Wall Street, Corporate America, and Union America. K Street already knows but because I don’t have them on retainer so they don’t care about my opinion. I can live with their snubbing me. Go girl, if that’s the right phrase!
I’m just getting to this article, which I enjoyed. No comments on the substance, but thought I’d give a wonky clarification on the “wacky pagination” in the table of contents in the FERC order. The references are not to page numbers but to paragraph numbers-if you look you will see that each paragraph has been given a number. FERC does this because its orders are published in different formats, each with its own pagination. Citing to paragraphs lets everyone look at the same thing regardless of what format is used.
I am an electrical engineer who worked at a nuclear power plant for 36 years. Since I retired, I have been reading as much as I can about the grid and Energy and of course, “Shorting the Grid”. I’ve also been reading about inverter based resources, and the problems they pose on the grid when there’s a fault. The industry now knows that IBR need to be “grid forming”, instead of “grid following”. There are many YouTube videos available if anyone dares to get into how a grid forming inverter works. Bottom line, if they all become grid forming, they should be able to ride through most Grid voltage andfrequency oscillations. IEEE has issued a standard that NERC can require.
https://ieeexplore.ieee.org/document/9762253
Kenneth refer to my comments, those new inverters are causing lots of problems, they still need more development
It is almost as thought solar and wind are not compatible with the grid as designed and constructed, although I'm sure that's not the case
Thank you Meredith for your timely and important article regarding IBRs, particularly for California with its 19,011 MW of solar and 8,120 MW of wind as of 01 April 2024, per CAISO . Californians for Green Nuclear Power provides additional details in their March 4, 2024 GreenNUKE Substack article, "Why is Grid Inertia Important?" https://greennuke.substack.com/p/why-is-grid-inertia-important . Please also note my May 27, 2024 comment to this article which is a glossary entry regarding grid inertia that was published by NARUC. "Area Control Error" is an important concept for IBRs.
See also CAISO's filing in FERC Docket RM22-12, "Reliability Standards to Address Inverter-Based Resources" https://www.caiso.com/Documents/Feb6-2023-Comments_NOPR_ReliabilityStandards_InverterBasedResources-RM22-12.pdf and NERC's April, 2022 "Multiple Solar PV Disturbances in CAISO" https://www.nerc.com/pa/rrm/ea/Documents/NERC_2021_California_Solar_PV_Disturbances_Report.pdf - Both of the reports make multiple mentions of "Blue Cut." The caveats include these are only recommendations and there is no retrofitting requirement.
Interesting that inverter waves are square or approximations, that gives me an intuitive sense of why some industrial customers need to protect their equipment from the quality of the IRB electricity coming in
That was a mouthful and brainful of technical information, Meredith. I will have to reread it. It’s looks like you are needed again to help your grid allies understand the complexities. Thanks!
Great article. Doomberg wrote about this in January
https://substack.com/@doomberg?r=af3i2&utm_medium=ios&utm_source=profile
The answer suggested was synchronous condensers - something that need to be added to the grid as shock absorbers to combat the non-ride-through issue.
Neil....thank you!
I am so embarrassed that I didn't quote Doomberg! I feel terrible about it!
Synchronous condensers are only a partial answer. I wrote about them in Shorting the Grid, on page 31, where Governor Shumlin was angry at ISO-NE for curtailing Kingdom Community Wind. KCW was curtailed because they had not installed synchronous condensers. Later, KCW installed them, but it did not solve all the problems.
I have to write more on this. I WILL quote Doomberg next time. So deeply embarrassed!
Finally a paper on how inverters can cause wide area system occilations
https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-34758.pdf
IBRs have also lead to a re-emergance of subsychronous resonance issues. Here is a IEEE paper
http://ieeexplore.ieee.org/document/9739883
Thank you Meredith, good piece. My primary peeve has been the outsized claim by renewable promoters about "synthetic inertia" and how it can replace traditional rotating mass. The issue is it's theory under development, and still a member of the "not ready for prime time players". Here is an article on the subject.
https://ietresearch.onlinelibrary.wiley.com/doi/10.1049/iet-rpg.2017.0370#:~:text=We%20refer%20to%20synthetic%20inertia,energy%20from%20a%20rotating%20mass.
Thanks for that reference. I haven't read through it nor the other references you cite but I expect the major issue isn't simply a matter of matching frequency but also phase. If the phase is off, the grid sees that as a reactive load and as the IBR phase corrects to the grid phase (as it must), other grid generators -- including the many connected IBRs -- will also be adjusting their respective output phase. With time delays due to grid reactive elements and IBR electronics, I imagine the resulting corrections result in a very complex set of harmonic resonances on the grid.
Now I'm not a grid engineer by any means but it seems to me that what's required is a stable reference frequency supplied to each IBR i.e. a frequency reference not from the grid itself. Like the SFTS signal https://en.wikipedia.org/wiki/Standard_frequency_and_time_signal_service Perhaps that's already being done for registered IBRs?
2017, based on information prior to 2017. Modern inverters are fine. I’ve seen batteries installed to improve CCGT reliability and no issues with inertia after the GT trips. It’s 2024 mate.
I am not an electrical engineer, and I don't even play one on TV. But I am a physical chemist and I can usually understand many technical articles. This article about how GFMs affect the Northwest shows that there are indeed some issues with GFMs.
Fast response after a major generator trips off is a very good use for batteries. Batteries provide power to the grid while the gas turbines come up to speed. They allow the gas turbines to come on with a more moderate (and less polluting) ramp rate. Batteries are oversold, but that does not mean they are useless.
This is NOT the same as saying that a grid with mostly GFMs will be a well-behaved grid.
That I can agree with. The argument I have had is with replacing spinning reserve with fast response batteries as some propose. It's unlikely you will ever get the same system inertia out of a battery that you will out of a 200 ton spinning rotor. Inertia comes into play in the energy delivered to the system as 200 tons of mass decelerates as frequently declines. It is that system inertia that slows initial drop, or increase in frequency. The change in frequency is enough that the governors of the dispatchable generation will respond and arrest the frequency decay, and partially restore frequency. The ramping of gas turbines wouldn't ta place until the above actions were complete, and AGC made moves to restore frequency. A fast ramp on a battery could get you back much quicker. I suggest you read this https://www.wecc.org/Reliability/Governor%20Tutorial.pdf
I believe NERC would disagree, and the erosion in frequency response after an event suggests things are not as rosy as you say.
Thank you for this excellent description of inverters and how they fit in to our Bulk Power Supply. I am a retired power engineer and am very well informed regarding the boiler island, balance of plant and steam turbines. However, in my mechanical mind.....I am a strong advocate for spinning reserve of huge magnets turning within the stator at synchronous speeds (1800/3600 RPM) providing the momentum to stabilize the 60 Hz Grid. Your article was great for demystifying inverters. Thank you again. BTW, I did buy a copy of your book for reference.
Thank you, Steven!
Thank you Dick!
I suppose if an inverter or series of inverters fails simple cycle natural gas plants fills in? We could probably turn off all solar and wind and and there would hardly be an increase in CO2 emissions and the grid would be more protected.
I had read some time ago that inverters had a 20% failure rate, but had no idea what that failure rate would and could do to the grid, thinking they would just be taken offline and replaced... electricity is just never that simple!!
Thank you for this great and timely post as we gain more and more solar here in Texas.
I can see why Robert Bryce always asks - "ultimately who is in charge?"
We are a long way from stable grids.
Thank you EG! Absolutely correct ! What a short Federal document ! I wish everyone could understand this, or at least Congress, White House and Wall Street, Corporate America, and Union America. K Street already knows but because I don’t have them on retainer so they don’t care about my opinion. I can live with their snubbing me. Go girl, if that’s the right phrase!
Always was curious of this. Will read for sure!
I’m just getting to this article, which I enjoyed. No comments on the substance, but thought I’d give a wonky clarification on the “wacky pagination” in the table of contents in the FERC order. The references are not to page numbers but to paragraph numbers-if you look you will see that each paragraph has been given a number. FERC does this because its orders are published in different formats, each with its own pagination. Citing to paragraphs lets everyone look at the same thing regardless of what format is used.
Meredith this paper is really good also https://support.sosintl.com/AvatarHandler.ashx?radfile=%5CDepartments%5C1%5CStudy%20Guides%5CNERC%5CUnderstand%20and%20Calculate%20Frequency%20Response.pdf.pdf