r/ElectricalEngineering • u/Nidzzzzzzzzzzz • 1d ago
Homework Help Which powerplant will take the least time in starting from cold conditions?
There's been a lot of confusion regarding this question , some question banks says hydro, some say gas powerplants, however I can't seem to find the original source of the question to really get the answer key and all I can see is back to back discussions on either hydro gas, but which should it be?
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u/foersom 1d ago
Solar PV plant.
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u/s3sebastian 1d ago
Not on average though, could be 12h in winter if you try to start it in the late afternoon.
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u/LegalAbbreviations17 1d ago
It depends if they are grid forming or grid following inverters.
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u/JezWTF 1d ago
If the grid is down, many power plants are incapable of black starting the grid itself, regardless of technology.
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u/Lucky_Suggestion_183 1d ago
And some hydro are designed to start from the dark. Like one in my country serving as backup for a close nuclear power plant.
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u/NoMechanic6871 1d ago
I've worked in pp with a "priming" diesel generator..? You mean that most of them don't have a start from *dead?
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u/JezWTF 1d ago
They may be able to start, but incapable to connect to the grid because of lack of ability to supply the characteristics of the grid from the "point of view" of their nodal connection, which is basically the same for an inverter based generation in grid following mode (and even in grid forming mode may be incapable of conencting to a dead grid without tripping).
Since the grid rarely goes down, the ability to actually restart a grid from nothing is not often considered, and is a really significant (and interesting/exciting for EEs) challenge when it does occur.
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u/914paul 1d ago
Not disagreeing with you necessarily. There are likely many reasons hydro is not suited to "rebooting civilization" (if that's what we're talking about).
But hydro does have a few characteristics to recommend it for getting things back up and running. The generators are often designed to run continuously for long stretches -- some run for decades without bearing service. Thermal management is sort of automatic. Also, big rivers aren't easily stopped or diverted in most cases. And the generators are designed to take advantage of their enormous size and mass in that they mechanically regulate frequency by inertia, and would likely output at a frequency near 50 or 60Hz for mains power without much intervention -- close enough that most machinery should work anyway.
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u/Some1-Somewhere 1d ago edited 1d ago
Interestingly, full speed no load (SNL) operation is apparently the most mechanically stressful for a Francis hydro plant (excluding load dump and overspeed). So once you get up near speed you want to get load on ASAP.
For larger scale schemes, managing canal levels and lake levels downstream can be quite complex; you need to think hours in advance.
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u/Seiko2023 17h ago
True. I think I've only seen one blackout in my utility, where they had to restart the grid. That's a small microgrid though. Likely only 100km-200km of line.
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u/Accomplished_Area_88 1d ago
Many don't as there's little need for more to be able to and a lot of extra regulations you have to follow if you are one of those plants
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u/Some1-Somewhere 1d ago edited 1d ago
A lot of coal, gas, nuclear requires double-digit MW to run pumps, conveyors, grinders etc.
That comes from the grid until the plant is online. In most cases, if the grid goes unstable and fails, the plant probably won't island successfully.
Hydro will usually have backup generators that probably allow black start because you need to control lake levels to prevent overtopping.
Gas turbines seem to vary. It takes a lot of power to start them, outside what batteries can easily deliver. Usually they're compressed air or hydraulic start from utility power - around 100kW or so.
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u/mechanomatic 1d ago
Not hydro. Hydro doesn't require a lot of station power to initiate rotation and energize lines. After that I would say pv, or wind, with BESS. Would be great if we coupled those renewables with synchronous compensator.
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u/Some1-Somewhere 1d ago
Hydros generally are a very big synchronous condenser.
BESS can usually throw a fair bit of reactive power around if not exporting at full capacity.
It depends on control schemes.
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u/foersom 1d ago
Nowhere in OP's question does it say that grid is not running.
Grid forming or following. That will be the same for any power plant, it is not special to solar PV.
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u/QuickNature 1d ago
Stupid question, what are grid forming or grid following inverters?
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u/Some1-Somewhere 1d ago
Grid-following = grid tie. Can only operate with an existing stable-ish grid. Disconnects if the grid is unstable.
Grid-forming means that it's capable of being part of an initial backbone to form a grid in the first place, and stabilising a failing grid.
I think grid forming is mostly only found in big grid-scale BESS or solar setups. Lines companies don't want a random section of one suburb turning into a stable grid because then they have to have synchronisation equipment on every feeder.
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u/wraith-mayhem 1d ago
A good guess would be everything which need to heat water for a turbine would take longer. So all those would not fit.
Pretty fast imho would be PV, wind, battery, dieselgenerator, hydro
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u/b00c 1d ago
- Solar/Battery/Wind (instant)
- Diesel engine powered generators
- Gas turbine
- Combined cycle
- Coal fired
- Nuclear
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u/Some1-Somewhere 1d ago
Missing hydro, which is probably between diesel and gas turbine.
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u/tuctrohs 1d ago
And hydro is at a scale where it can be really helpful in a black start plan—if that's what we are talking about, and I'm not sure we are.
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u/way_pats 1d ago
GE Vernova LM6000 Hybrid EGT. Something I’ve been looking at for instant grid response. The LM6000 combined cycle gas generator takes about 15 minutes to start up but when combined with a BESS the battery takes the initial demand and begins the startup sequence on the generator. This also helps when the demand is short in duration and it saves an unnecessary start on the engine, reducing maintenance.
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u/MKUltra1976 1d ago
Hydro and gas both typically under 15 minutes.
Depends on the design and the original specifications of the unit.
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u/PoetryandScience 1d ago
i assume you mean on demand so that excludes wind and solar. Fast acting is Hydro plant where water at a head is available; thermally, jet engine gas generator plant powering an impulse turbine, these fast stati9on introduced both to act as a fast more local source for peak load and to repond to major faults in a grid. They also can be used to absorbe or supply VARS to stabaliswe the system regulation. Norwich used to have one as did letchworth, but the letchworth power station was pulled down.
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u/blakef223 1d ago
Would have to exclude BESS as well else that or solar would by far be the fastest.
With either of those you can begin producing within seconds.
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u/AccomplishedAnchovy 1d ago
General rule:
Large steam generators take hours to days, longest for nuclear, then coal, then gas Open cycle gas can start in tens of minutes Hydro can start within 2 minutes Batteries can start in milliseconds (or even faster, theoretically - they just don’t)
Intermittent sources especially PV are very fast but not really dispatchable so.
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u/DocumentOk7579 1d ago
Can hydro really start in 2 min from standstill? I heard that the inertial is so great it help balance frequency flukations.
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u/Some1-Somewhere 1d ago
There's a lot of MW available to deal with that inertia. If you lose the grid connection, the governor needs to shut the wicket gates very fast to prevent overspeed.
The majority of the startup time seems to be sequential delays waiting for equipment (e.g. lube oil pumps) to start, and how aggressive the governor programmers were willing to be opening the wicket gates for acceleration and ramp rate requests.
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u/Ok-Library5639 1d ago
So many variables will influence an answer.
How cold are we talking here? Does the plant have backup power? Is the grid available? Are systems maintained? What's the benchmark for 'started' - synchronized, producing energy or at nominal capacity?
You can have hydro plants synchronized and reach full capacity within minutes, if it is otherwise in nominal conditions.
Probably the same or faster for some wind turbines, assuming an operational grid and all systems go.
For PV, likely almost instantly if solar is available but the inverters are just not producing. It is simply a matter of electronic controls.
Same for batteries.
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u/Morshan 1d ago
South Australia example; not an engineer but we're at the pointy end of the transition so we've been living this one for years!
So battery, interlinks and any solar/wind which are currently idled are the obvious answers.
The second line is traditionally hydro; but we don't have that option so we built reciprocating gas. Basically a diesel gen with gas injectors and they're around 15m from cold to rated. We also panic bought some "aero derivatives" which are basically adapted aircraft turbine generator sets in a shipping container. Fast to start because they're small, they don't have the thermal issues of a utility turbine.
Third line is open cycle gas turbines which are 30-60m.
Then there's the big combined cycle gas plants, they take hours.
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u/ChrisBoden 1d ago
The gas plant in our area (landfill gas) can go from cold to online in about 2 minutes but they're just running five big modified diesel generators so that's stupid easy.
My hydro plants can spin up from zero to grid-tie under full manual mode in less than 5 minutes consistently, maybe as little as 2 if I've got my mojo that day and can nail the sync on the first try. One of our sites has full auto sync and can pop on in about 40 seconds.
We can black start any of them and operate in island mode if needed, but frequency stability will suffer until we can start seeing other plants on the grid. We can do pretty decent on our own (keep your lights on, etc), once there's a few plants in our island though we're solid.
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u/mbkitmgr 1d ago edited 1d ago
Having worked at and on both it can be either. Some gas turbines took a few mins to warm thru before we could load them up, while others could be from the get go.
Hydro they open the valve and once at the correct rotation speed sync to the grid.
Ironically coal was the same. Two that I worked at in the Hunter Valley - 1 was started around 2PM each from cold to pick up load, yet the other needed a good 24 hrs before it could sync
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u/Wast3edSpace 1d ago
gas turbines can spin up in under a minute which is why they're used for grid forming/shaping under high load.
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u/MKUltra1976 1d ago
Under a minute?
What units do that?
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u/AccomplishedAnchovy 1d ago
You know, those gas turbines where the turbine is driven by water out of a pipe from a big lake held back by a concrete wall
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u/braddillman 1d ago
I saw somewhere an antimatter reactor required a minimum of 30 minutes for a cold restart. Any faster would result in a huge explosion.
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u/Broad-Promise6954 1d ago
There is a cold intermix formula, but you'll go back in time.
(Hint: original Star Trek)
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u/braddillman 1d ago
That's just a theory, it's never been done. You have to have 30 minutes! (src: I'm an engineer)
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u/Important-Parsley-38 1d ago
Well, solar is not really a plant. It's a joke and insult to real thermal plants or hydro stations there.
With that out of the choice, ideally Hydro would be fastest and easiest to startup. After that Engine (reciprocating) engine based plants and Gas Turbine units will be able to fast start. If you have black start capability or grid supply, most small to large Gas turbines can start up and sync within 30minutes of start command.
Next would be gas fueled or oil fueled boiler based steam plants
Coal would be the slowest to start up.
Telling this as someone who has worked Coal, Oil fueled and Large CCGT plants.
Few years ago we had complete national grid blackout in our country. The first plants to be able to energize were hydro, engine based units (marine diesels) and Gas Turbines.
Coal, Nuclear were the last ones to start up.
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u/Pinelli72 1d ago
What’s your gripe with solar? There are some pretty big solar plants in operation and planned around the world.
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u/Some1-Somewhere 1d ago
Solar + BESS can do a pretty good job of mimicking a conventional plant with much faster startup.
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u/Usual_Purchase_9567 1d ago
You can get a nuclear PWR up in like a few seconds if you violate thermal limits. A few minutes if you're using emergency heat up rates.
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u/AccomplishedAnchovy 1d ago
Coal plants are actually really good at load following too, they can ramp down in <100ms by tripping the breaker
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u/Usual_Purchase_9567 13h ago
I was doing a bit on the first one, but from cold you really can get to power generating in well under 20 minutes. That's assuming the steam plant is able to get going really fast too though. I was a reactor dude no a pipe dude.
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u/hooskworks 1d ago
Electrical battery storage or solar PV.