Tag Info

35

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 constantly adjusted TL;DR 2: Lshaver's excellent post is a suggested reading after reading this, because it expands and explains what happens at timescales ranging from ...

18

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 can exceed the capability of the suspension of the pantograph. Low-speed trains can show arcing too. high-speed trains often use high voltage (15 or 25 kV), ...

18

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 together to plan and fund construction of power plants and the associated transmission and distribution infrastructure. When you turn your air conditioner off ...

10

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 they are slow to change, but others like Dinorwig (in the UK) can go from standby to max output in 12 seconds and reduce to half quickly. Danish researchers did ...

9

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 efficiency of a (large) windmill is about 40%. The density of air is 1.225 kg/m3 You need about 50 mW (10 mA at 5V) to light up an LED First, we'll need about ...

9

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.

6

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: ITER, the tokamak (giant doughnut) being built in France is supposed to be the first reactor to ever beat the break even point, unless someone either beats them to ...

6

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! The dear way: If you were to assemble a 10kF 150 volt capacitor from available smaller capacitors now it would cost around 1 million dollars and store about 30 ...

6

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 inductive load, which seriously complicates what happens when the circuit is interrupted. When there is an interruption of a circuit with an inductive load, ...

6

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 day on the hottest days in the summer, as that combines household usage (everyone is awake), office usage (everyone is at work, or at least before the pandemic...)...

5

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 the blades than to twist it at right angles to the blades. If the turbine is being rotated because the wind direction changes, this will cause an unbalanced ...

5

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 process (a few weeks). So "turning on" and "turning off" a Nuclear Power Plant (NPP) is not as simple as pushing a button. The primary circuit (containing the water ...

5

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 power interruption Automatic moving-off Various gear ratios Efficiency: 90-95% Automated Manual Transmission (AMT) Functionality is the same as a Z-speed ...

5

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 $\omega$ to the generator kVA or MVA rating, $S$. $$H = \frac{0.5J\omega^2}{S}$$ An equivalent Inertia Constant for an entire system can be estimated: (Ekanayake, ...

4

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 as the flow rate to calculate the energy available. (You can calculate it from the flow rate and channel dimensions) You cannot extract all the available ...

4

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 humans and wildlife. It would also increase the risk of cable degradation and failures. Countering the affects of erosion, but covering the cable, will also add ...

4

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 reduce the fuel flow rate, and the turbine pretty much has to slow down quickly, within a few seconds, taking tens of seconds to reach the new steady state. The ...

4

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 detailed, and I encourage you to check it out for projects to learn more about. I'll talk about the most interesting parts here. It has many interesting projects ...

4

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 to the cogernetion plant(this is a typical value for Otto-cycle cogeneration plants for the emergency cooler to kick in)? If you have other heat sources and ...

4

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 common line voltage ($V_{LL}$) in the US (which uses a 60 Hz supply), with corresponding phase voltage of 120 V. You are using a US text (Sarma et al, from another ...

3

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 will operate for just a few minutes occasionally. Some will run 24/7 except when closed for maintenance. And yes, absolutely, the energy is stored before it ...

3

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 interruption to airflow and additional turbulence that the pole, that the wind turbine sits on, produces. This becomes apparent when one of the blades is directly in ...

3

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), with a stranded steel messenger (catenary) wire of 3/8-1/2" (10-13mm) diameter. The messenger wire is supported every 100-200 feet (30-60m) and it supports ...

3

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 time, I'll leave the next step to people smarter than myself. I believe this is a fairly straightforward answer: How they predict the amount to generate How ...

3

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 more about this "active area". Can someone maybe expand on that? I've not worked directly with large-scale fuel cell installations (never heard of one, actually) ...

3

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 masses $\alpha$ is the angular acceleration $(\frac{d \omega}{dt})$ In another form this is written as: $$\Delta M = I \frac{d \omega}{dt}$$ I.e. the turbine has a ...

2

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, often mid-afternoon. Excess power is available at night. To be useful, then, the energy must be stored for many hours. There are many possible technologies for ...

2

Try to cut a few from balsa wood to see what you get. Experimentation is probably the best method on such a small scale, and the math won't get you very far without an extensive knowledge of the materials (i.e. the cheaper the material, the less likely the blade will look like the big ones). I worked summer activities at my university using materials from ...

Only top voted, non community-wiki answers of a minimum length are eligible