eli5: what happens to the extra power when a portion of an electrical grid trips offline?

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For example: if a neighbourhood loses power, what happens to the power that the neighbourhood was consuming immediately beforehand?

Is there a sudden excess of power in other places near that neighbourhood?

In: Technology

4 Answers

Anonymous 0 Comments

If the load drops, what happens is that power generation stations will see the frequency of their output power start to increase. In theory, this should then trigger their controls to reduce their output to try to keep it at 60 Hz (for the USA). Likewise if the load increases, the frequency will decrease.

Anonymous 0 Comments

This is a part of the rather complex science of “Grid balancing”.

Grid balancing is the art of making sure that power production matches power consumption. So if a neighbourhood goes offline/loses power that will lead to a power spike elsewhere, especially if the shutdown is unexpected (like a malfunction in a power transformer station or something similar). If this power spike is large enough it can cause other parts of the electrical system to overload or shut down to prevent overload, which can lead to a cascade failure that might knock out the entire power grid.

However, what normally happens is that a power plant that’s able to rapidly change its power output (specialized hydropower or gas turbine powerplants…or these days a battery storage facility. These powerplants can increase or reduce their power output within seconds) will reduce its power output to match the reduced power use.

Anonymous 0 Comments

If the load decreases the result is the load on all generators is reduced a bit. They will spin a bit faster and as a result the frequency of the AC increase. The voltage can change a bit too. A neighborhood is a very small part of a power grid. Here is a map of how large power interconnected power gids are [https://en.wikipedia.org/wiki/Wide_area_synchronous_grid#/media/File:Wide_area_synchronous_grid_(Eurasia,_Mediterranean).png](https://en.wikipedia.org/wiki/Wide_area_synchronous_grid#/media/File:Wide_area_synchronous_grid_(Eurasia,_Mediterranean).png)

The voltage in outlets is typically nominal voltage +- some percentage. US use 120 +-5% which is 114 V to 126V and devices need to handle that. In EU it is 230V +10% -6% which is 253 to 216V, the reason for the odd range is UK nominal voltage was 240V +-5% so when a common standard was set it covered both UK and the rest of Europe’s voltage.

There are frequency standards like that to, often with the requirement that the total error over24-hour periods are very low

The frequency and voltage are controlled by adjusting or even adding and removing power generation resources from the grid. The power source of a generator can be used to change the output in some systems quickly like gas turbines, and hydroelectric but steam-based systems like coal and nuclear change quite slowly. Grid storage with batteries can change the output even faster. So active regulation is used to keep the the power grid at the right voltage and frequency.

Anonymous 0 Comments

So most generators out there are for the most part electric motors in reverse, while motors take in electricity to produce rotation, generators take in mechanical rotation to produce electricity.

A generator connected to the grid will have a load, if you ever play with a motor and try to spin it by hand you will notice it has some resistance. If you connect it to various circuits that have more and less load, the resistance actually changes, same is true of a generator. If there is suddenly some part of the grid that collapses, the mechanical resistance of turning that generator will fall, and whatever is turning that generator will start making it go a little faster since its resisting that force less. Since the frequency the generator outputs (usually 60 Hz) is tied to the rate of rotation, this increases the frequency on the grid too, and the voltage because of Faraday’s law.

This kind of thing happens all across the grid and there are many safeguards and measures in place to prevent it. Most commonly of course, there is an agreement whatever is powering the generators has to reduce its power.