36 votes
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How does turning off electric appliances save energy

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is ...
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19 votes

How does turning off electric appliances save energy

Timescales on the grid Power demand fluctations can be broken into timescales from micro-seconds to decades. On the "decades" end of the scale, the power industry and utility regulators work ...
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18 votes
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Why do electric trains arc at high speeds?

Several factors influence this: at high speed, there's a higher chance of the pantograph losing contact with the catenary wire: at higher speed, bumps in the wire cause a more violent excursion that ...
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10 votes

How does turning off electric appliances save energy

Yes, they monitor demand and due to differences in how different power stations are controlled they can increase or reduce output to match demand. Some power plants like nuclear run at full output as ...
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9 votes
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How to correctly size the blades for a small educational wind turbine?

As it happens, I just recently went through that calculation myself for a different site. Given the following facts from a quick web search, it isn't difficult to work out the numbers. The maximum ...
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9 votes

Why do electric trains arc at high speeds?

It is due to the high voltage still causing a connection when the contacts separate due to an irregularity (bump etc) between the contact and the wire.
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6 votes
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Extracting power from fusion?

This is an excellent question, and one that has not yet been fully answered by people working in this area of research. Let's look at some of the bigger projects and see what their proposals are: ...
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6 votes
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Can large capacitors allow power plants to run at full load and store excess electricity?

Capacitors are currently "rather too costly" for this purpose. I've revised my estimated cost after some more research but you appear to be in the 'well over one hundred thousand dollars" range! ...
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6 votes

Why do electric trains arc at high speeds?

As others have posted, a temporary gap between pantograph and overhead conductor is part of the answer, however that's not the complete story. The other big factor is that the train's motors are an ...
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6 votes

How does turning off electric appliances save energy

Peak Demand One of the biggest issues in the electricity business is managing peak demand. This is the maximum amount of electricity needed at any one time. Typically this will be the middle of the ...
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5 votes
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Advantages/Disadvantages of two-bladed windmill?

A 2-bladed wind turbine is less stable mechanically than 3 (or more) blades. Because the two blades are in line, it is much easier to twist the hub of the turbine in the direction along the line of ...
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5 votes

Working hours of power plant generators

Nuclear power plants are always working, except circa one month/year for maintenance. It's mainly because stopping the nuclear reaction and cooling the reactor down is a very long and difficult ...
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5 votes
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What is the difference between an automatic transmission and an automated manual transmission?

In answering this question I'm assuming you already know the difference between an Automatic Transmission (AT) and a Manual Transmission (MT). Conventional Automatic Transmission (AT) Minimal to no ...
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5 votes

Quantifying inertia on the electricity grid

The Inertial response for a generator is characterised by its Inertia Constant, H, with units of seconds, defined as (Samarakoon, p40): the ratio of kinetic energy stored at synchronous speed $\omega$...
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4 votes

How to calculate hydropower in kW without water head

If you have horizontal water flow (no head) you are extracting its kinetic energy (from its velocity) not its potential energy (from its head). So you need to know the velocity of that flow as well ...
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4 votes
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Why shouldn't we put high voltage cables physically underground?

Your four drawbacks are very good reasons for not laying cables on the ground and just covering them with soil or "stuff". Erosion will be a major issue. Exposed cables would be a safety hazard to ...
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4 votes
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What limits a power plant's load gradient?

A gas turbine plant basically uses jet engines optimized for shaft power instead of exhaust push to drive the generators. These can be controlled quickly because there is little stored energy. You ...
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4 votes
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Efficiency of wireless charging for moving cars

This is not exactly a comprehensive answer, but I found an interesting article on The Institution of Engineering and Technology's website. It is fairly interesting, if not incredibly technically ...
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4 votes
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Question about flow temperature and storage temperature in a cogeneration plant

when the cogeneration plant switches of upon reaching 85°C flow and without another heat source, there's no way to reach 95°C. Are you sure the switch-off happens at 85°C flow, and not at 75°C return ...
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4 votes
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Power systems unclear voltages

Note the problem specifies the load is "delta connected". There is no neutral connection to measure phase voltage ($V_{LN}$) against. Also note the supply frequency is 60 Hz. 208 V is a ...
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3 votes

Working hours of power plant generators

There isn't a single answer that covers large power plants around the world. There's way too much variation in generation plant, and way too much variation in the way that plant is used. Some plants ...
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3 votes
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What theoretical efficiencies can wind / hydro turbines achieve?

The theoretical maximum efficiency of a wind turbine is the Betz Limit, which is $\frac{16}{27}$ ( ~ 59.3%). The result dates back to 1919. The Betz limit is, as you note, speed invariant. To get an ...
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3 votes

Advantages/Disadvantages of two-bladed windmill?

One of the advantages of two blades over three blades is less materials are required to make the blades. The disadvantage of a two bladed rotor compared to a three bladed rotor is due to the ...
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  • 9,517
3 votes

Why do electric trains arc at high speeds?

The upforce on a pantograph is 15-40 pounds, 60 pounds at the outside. (7-18kg, max 30 or so). The trolley (contact) wire is made of solid bronze or copper, typically 4/0 to 400kcmil (107-200mm^2), ...
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3 votes

How does power generation (hydro, wind etc...) account for variable power consumption?

This is more of an addition to the previous answer by blacksmith37. I think it might be more appropriate as a comment, or perhaps an edit to the previous answer. With no ability to comment at this ...
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3 votes

Advantages of hydrogen gas turbine over fuel cell

I've read in one of Smil's books that fuel cells are somehow limited (in what sense I'm not sure anymore but I believe it was power output) by their "active area". I'm having difficulties learning ...
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3 votes

Doubt on a shaft-turbine-generator system

I am not entirely certain about your question but I think, it basically boils down to this equation $$M = I \alpha $$ where: M is the torque applied I is the mass moment inertia of all rotating ...
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2 votes

Can large capacitors allow power plants to run at full load and store excess electricity?

Capacitors typically store power over short periods of time, seconds or minutes. This is too short to be useful for the electrical power grid. Typically peak power demand occurs during the day, ...
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