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I tried looking it up but there's no answer for this. This is mainly concerning nuclear power plants or natural gas plants, where they would have other buildings attached on site to operate the plants.

When they run the plants does it go to the grid and then back to the facilities? Or are the building circuits directly powered by the plant electricity, then the remaining electricity goes to the grid?

I also assume wind farms and solar PV farms don't have this concern, but I could be wrong.

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    \$\begingroup\$ Why do you assume wind farms and solar PV farms don't have this concern? \$\endgroup\$ – user253751 Dec 10 '20 at 17:00
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    \$\begingroup\$ Interesting question \$\endgroup\$ – Mitu Raj Dec 10 '20 at 20:04
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When a power station is up and running the power it generates can be used to power its internal operation.

However, many power stations do not have the ability to bring themselves back into service after a major outage. (referred to as a "Black Start").

It may not be worth the capital expenditure to provide adequate backup power (that would only be used very occasionally) to perform start-up; instead, they would use power from the power grid relying on other power stations in the same region. At least one would have to have the ability to bootstrap itself.

Wikkipedia - Power Station Black Start

Hydropower Plants as Black Start Resources

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    \$\begingroup\$ Hydrodams are the typical power plant can boot strap themselves, I believe. Most renewable power in general can bootstrap. \$\endgroup\$ – DKNguyen Dec 10 '20 at 15:41
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    \$\begingroup\$ I've never heard the terms cold start and black start used synonymously. Usually a cold start refers to when a plant has cooled down and all of its mechanisms are at ambient temperature. Black start refers to when there is no grid power available to start rotors spinning, etc. \$\endgroup\$ – Dean MacGregor Dec 10 '20 at 17:09
  • \$\begingroup\$ @DeanMacGregor - OK, thanks for the clarification. \$\endgroup\$ – Kevin White Dec 11 '20 at 1:09
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Nuclear power plants in particular have extremely critical needs for power even when they are not generating, as decay heat requires circulating cooling water through not only the reactor long after shutdown, but also possibly some of the recently spent fuel stored in pools of water outside the reactor.

As a result they are not only able to draw from the grid, but have local diesel backup generators.

One of the fundamental causes of the disaster at Fukushima was that the diesel generators were flooded by the tsunami, leading to loss of power for active cooling.

(The backup generators are sized for emergency cooling only. Very rarely have they been officially sufficient for normal operation in the sense of being able to perform a "Black Start". Some searching will find commentary from plant engineers who think they could get things slowly started if authorized in a dire need by using limited pumping and natural convection, but it would be well outside normal procedures and precautions)

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They are powered off the grid. Power coming out of the plant directly is not suitable for end use, it needs to run through transformers and other conditioning/protection equipment. You also wouldn't want a fault in one of those buildings to take down the plant.

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    \$\begingroup\$ So most power plants aren't able to boostrap themselves? \$\endgroup\$ – Drew Dec 9 '20 at 22:38
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    \$\begingroup\$ See en.wikipedia.org/wiki/Black_start \$\endgroup\$ – Kevin White Dec 9 '20 at 22:39
  • \$\begingroup\$ @Drew How do you come to that from my answer? Bringing up a grid from black is a complicated process, it has nothing to do with the power to the facilities buildings. Of course they can bootstrap, but they have backup systems to provide control power to get there. \$\endgroup\$ – Ron Beyer Dec 9 '20 at 22:42
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    \$\begingroup\$ @RonBeyer I wasn't being sarcastic, it was an honest question. \$\endgroup\$ – Drew Dec 9 '20 at 22:43
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    \$\begingroup\$ I guess this depends on the type and design of a given power plant. The only power plant I'm familiar with in detail (a nuclear one) does power internal consumption from its own output, through a separate set of transformers independent from the grid ones. These transformers can be fed by the generators (normal operation) or back-fed by the grid during shutdown (when the grid is okay). You don't want an issue on the connection to the grid to cause an all-out emergency at the plant. On-site diesels are connected directly, not through these transformers (just in case the transformers blow up). \$\endgroup\$ – TooTea Dec 10 '20 at 15:32
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Allow me to explain with an example, I will be describing a hydraulic generating station, which is the simplest of all generating stations in terms of complexity of equipment. The station in this example does not have black-start capability.

  • Remember that you need some kind of magnets to generate electricity? well, for generators in power plants, we don't have large enough magnets, we need to generate your own magnetic field (excitation system) by running lots of current though coils with large iron cores. After that, we allow the water in to push the turbine to rotate this giant magnetic field (rotor) so that electricity can be generated. You need to supply lots of power to get this magnetic field going. The station has 3 rooms of batteries to serve this "magnetic field" system. "3 rooms of batteries" may sound impressive, they are only enough to get the magnetic field started (field flashing), not to power it forever. After the generator is started (water pushes the turbine) and electricity is flowing, a transformer (unit transformer) will be used to siphon power from the generator to power the generator's magnetic field, taking over the batteries. We don't want to wear off the batteries too fast. (You may have noticed that, this system is is analogous to the relationship between car battery and the car engine)
  • In order to ensure cooling, lubrication and controlling the speed of the turbine properly (governor system, the system in charge of how much water is allowed in from the river to spin the turbine), many aux motors and control systems are installed all over the place. They are fed by a "station bus", it is like a mini-grid within a station with voltage of around hundreds of volts. This bus is fed by designated transformers (station transformers) siphoning some electricity from the generators to feed the station. If None of the generators are running, this mini-grid will be dead and no generator can even be started. That's not good! So, this mini-grid will have an external feed from the real grid as well, thru another designated transformer. Also this "station bus" charges the "3 rooms of battery" mentioned above.
  • In order to ensure safety and regulatory compliance, critical systems like flood control, fire control and drinking water system each has their own diseal backup generators.
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  • \$\begingroup\$ Is that money paying for the batteries and transformers, or the giant turbines and wall of concrete? \$\endgroup\$ – user253751 Dec 10 '20 at 23:35
  • \$\begingroup\$ @user253751 short answer is, everything is expensive. People especially is expensive. \$\endgroup\$ – eliu Dec 10 '20 at 23:58
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When they run the plants does [the power that they generate] go to the grid and then back to the facilities? Or are the building circuits directly powered by the plant electricity, then the remaining electricity goes to the grid?

In theory* it doesn't work that way. There isn't one type of connection that supplies power to the grid, and a different type of connection that takes power from it. Whether or not any given piece of equipment produces power or consumes power depends only on the equimpment itself, and not on how or where it is connected. If you set up a solar power system with a grid tied inverter in your home, the inverter connects to the grid through your circuit breaker panel and your existing electric meter. You don't get a separate wire out to the power line that runs past your home.

It might help to picture one of those old factories in which machines were powered by an overhead shaft that ran the length of the building and was turned by a steam engine. Suppose you owned that factory, and you decided that you needed more power. You could easily remove a machine that was taking power from the shaft, and put a new engine in its place to add more power to the shaft. No need to change anything else. The shaft doesn't know or care which direction the power flows. Neither does the electrical grid.


* I can't speak about things they might do for safety or regulatory reasons.

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  • \$\begingroup\$ Yes, "in theory", electrically there is no reason there couldn't be a single connection. But the safety and regulatory reasons do matter, and so do other practical reasons like being able to meter the electricity coming into the plant so they can be billed for it. \$\endgroup\$ – user253751 Dec 10 '20 at 16:17
  • \$\begingroup\$ @user253751, So, I guess the real heart of the OP's question is, does a major power station have an electric meter? And if so, to whom do they pay? If you told me that they had to pay the local "electric company" because the local P.U.C. said so, then I guess I would be totally prepared to believe that. \$\endgroup\$ – Solomon Slow Dec 10 '20 at 18:17
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During the northeast blackout of 1965, Ravenswood No. 3 in Long Island City, Queens, NY, also known as Big Allis, a 1000 MW steam turbine generating plant, had 14 of its 15 turbine bearings damaged by lack of lubrication. The lube oil pumps were powered by the grid, so when the grid failed, so did the bearings.

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  • \$\begingroup\$ I wonder how long it took and how much it cost to replace those bearings. Also, I wonder what kind of bearings were used, bronze, roller or babbit? \$\endgroup\$ – user148298 Jan 27 at 1:36

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