What Happens When You Flip the Light Switch? - Comments

[jim hardy]

I just scanned that fascinating White Paper on frequency response.

So gas turbines droop the wrong way(fig 6)?
And they want to kill coal? That's a dark joke..

Power system stability looks to me like a secure career.
..

btw we had some 3% governors.

 

[anorlunda]

I just scanned that fascinating White Paper on aafrequency response.

Yeah, there is a lot more diversity in frequency regulation than I admitted to in the Insights article. I heard once from a guy in NZ at a hydro plant. They used 1% or 2% droop deliberately so that the nimble fast-responding hydro unit would grab more than its fair share of frequency regulation.

5% governor droop used to be nearly universal. Today it is much less so. I blame the combination of free markets and NERC standards. In the market I know best, frequency regulation was an auxiliary service that we bought by auction and paid hard money for. Once we met the NERC minimum performance standards, what rationale can we give for spending somebody's money to purchase more? Hard money in exchange for soft benefits that are not required sounds like mismanagement to auditors, so we don't do it.

Actually, frequency regulation has been much on my mind for the past year. I view it as our best fallback defense against claims that cyber attacks can black out the country. Think of the wildly irresponsible current book by Ted Koppel for example. The public is all too willing to believe scary stories like Y2K and cyber-grid-Armageddon. I recall that from 1888-1970 something, we operated the grid just fine using mostly flyball governors. Call it the Battlestar Galactica defense if you will. If we eliminated all computers and all electronics, could we (mostly) keep the lights on? I view it as a public relations problem rather than a technical problem. I believe that even if we reverted all the way to the Battlestar Galactica positoin, that the public would believe scary stories from Koppel and others anyhow. The sad fact is that the details of what keeps the lights on is dreadfully boring unless you are depicting disasters. If you try to explain how and why the grid is safe, people get bored and flip channels or flip pages almost instantaneously.

I'd like to have a discussion thread on PF about cybersecurity and the grid. I'm thinking "General Discussion" instead of "Electrical Engineering" because IMO it is a social topic. But I'm working on a couple more Insights articles on AC analysis that I'd like to finish first. I want to make laymen able to understand how we can operate a continent size power grid without any computers or centralized controls.

 

[sophiecentaur]

I want to make laymen able to understand how we can operate a continent size power grid without any computers or centralized controls.

Are you really sure you could do this and keep the system stable with no communications involved?

 

[jim hardy]

A long skinny state like Florida that is fed only from the north requires a steady hand to keep power flow within capability of the lines.
Especially when you get a lot of generating eggs in one basket.
We had some spectacular blackouts in early 70's when two big nukes came on line south of Miami. When they tripped we simply could not move enough power below Palm Beach to make up the shortfall.

A power system is like a bicycle --- there's a learning curve.

Now they have stout power lines from coal plants in south Georgia-Alabama region all the way to Miami . They parallel US 27 for miles and miles, you'll notice them if you take that route to Disneyworld or Miami. . The system is far more stable since they were built.
I'm now retired to the Ozarks. Several coal trains per day pass through my town headed to those plants.

And that's why i think the "Kill Coal" movement is ill advised dilettante tinkering. It adversely affects system inertia.
"Forgive them, Father, they know not what they do. "

old jim

 

[anorlunda]

Are you really sure you could do this and keep the system stable with no communications involved?

Positive. None of our centralized control systems are used to maintain stability. Not now, not historically. Even so-called power system stabilizer devices (which my firm pioneered) use only local information.

We mustn't neglect the fact that power grids evolved from 1888 until the 1960-1970s without the aid of electronics or computers. The analytical basis of power system analysis and system stability was put on a firm footing by Charles Proteus Steinmetz in 1893. The advent of modern controls and computers have allowed us to increase reliability and improve the economics, but they have not displaced the underlying operating principles of AC networks invented by Tesla (before Tesla drifted off into la-la land) and described by Steinmetz, Charles Concordia and others.

If you want an oversight of what the centralized control systems actually do, reread the Insights Article. What Happens When You Flip the Light Switch?

 

[sophiecentaur]

And that's why i think the "Kill Coal" movement is ill advised dilettante tinkering. It adversely affects system inertia.

What is the 'good thing' about coal systems? Isn't it more about steam turbines than the actual heat source? I would have thought that an alternative fuel would not change things but I realize that you couldn't shift enough wood to do the job!

 

[sophiecentaur]

None of our centralized control systems are used to maintain stability.

So they just optimise the profit then? Not a bad thing.

 

[anorlunda]

A long skinny state like Florida that is fed only from the north requires a steady hand to keep power flow within capability of the lines.

That's true Jim. Just 3 weeks ago, I just traversed Florida east coast to west coast crossing Lake Okeechobee on my boat. I was shocked that I only passed under only two major power line corridors on the entire route. Nevertheless, Florida's skinny network pales in comparison to countries like Sweden and Brazil.

In Sweden, much of the generation is way up in Lapland, while the population is 1500 miles away in the south of the country. That was especially true in the decades before they started building nukes in the south. They managed to keep it all flowing for half a century before any modern or centralized controls.

Brazil is similar. Brazil's hydro resources, developed long ago, are 1000 km or more distant from the population centers.

 

[sophiecentaur]

Brazil is similar. Brazil's hydro resources, developed long ago, are 1000 km or more distant from the population centers.

But doesn't the real stability problem arise when the major generating centres are well separated? Doesn't the transmission line length start to affect things? (Unless DC links are used)

 

[anorlunda]

But doesn't the real stability problem arise when the major generating centres are well separated? Doesn't the transmission line length start to affect things? (Unless DC links are used)

I believe what you're thinking about Sophie is the basic transient stability formula. $P=\frac{V_1 V_2}{X}\sin(\theta)$, where X is proportional to line length. But that applies to any two adjacent nodes. It doesn't matter if they are generators or loads or whatever. In actual practice, we keep $\theta$ very much smaller than 90 degrees, so that kind of stability is seldom a problem.

 

[dlgoff]

And that's why i think the "Kill Coal" movement is ill advised dilettante tinkering. It adversely affects system inertia.
"Forgive them, Father, they know not what they do. "

You'll like this photo I just snapped of an ad on the back of a publication from my rural electric utility.

 

[jim hardy]

What is the 'good thing' about coal systems? Isn't it more about steam turbines than the actual heat source?

Coal fired steam plants are being replaced by gas turbines. Different inertia. .

Natural gas is wonderful fuel for steam boilers, doesn't slag them up and there's no flyash to handle.
In my day our fossil units burned oil, natural gas on rare days we could get it, or any mix of the two.
When environmental regulations became unpredictable management contracted to buy power from already permitted coal plants , "Coal by wire", avoiding cost of running trains down the state . Since then there's new pipelines bringing lots more gas.

So you are correct - my objection is not to replacing coal , but to replacing steam with 'high tech' at expense of reliability. old jim

 

[jim hardy]

Even so-called power system stabilizer devices (which my firm pioneered) use only local information.

You understand those things?
We put one in around 1974-ish.I do not know that formula in Anorlunda's post 45

What i do understand is that a line's impedance determines how much power goes down it per degree of displacement between its ends.
So it's a mechanical spring constant for electrical angular displacement between its ends
and there's a rotating inertia at each end of the line
so that rotating spring-mass system has a torsional natural frequency.

So it is possible for torsional harmonic motion to occur between nodes, ie they can swing against each other..
Our power system stabilizers detect minute swings in turbine shaft speed at torsional natural frequency* and change excitation to damp them out .
Prior to the stabilizers we severely overdamped our voltage regulators to keep swings from starting. But that was trial and error and worked some days and not others... i had watched generator shafts swing by shining a Strobotac on them , it was obvious from power angle swings that the voltage regulator was somehow involved but i had not the power systems background to understand .. Placing a voltage regulator to manual stopped the oscillations.

We are speaking of torsional frequencies in the range of 2/3 hz. SCADA systems of 1970's didn't sample often enough to control that from central office.

That's what little i know about system stability. I hope this layman's description helps with the concept.

* that's power system's natural frequency of around a hz, not turbine shaft's natural frequency of closer to 7 hz which is another whole story.

old jim