Windmill power generation

[jerry1423]

I am a mechanical guy so please forgive my ignorance, but this question has been bugging me:

If a private party has some windmills that are generating more electricity than they need they can sell it to the power company.

How can electricity flow in an opposite direction back into the main power line without being opposed by the electricity in the main power line that has a much greater electric force?

 

[Skogsgurra]

"electricity in the main power line that has a much greater electric force" No, it doesn't have a greater EMF.

The generator is adjusted (the AVR does it, or overspeed if an induction motor) so that the terminal voltage is a little more than grid idle voltage. That forces current (and power) into the grid.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[alehman]

Actually direction of real power flow is determined by the relative phase angles, not voltage. As you apply torque to a generator, it's phase angle will try to lead the grid and result in flow of power in to the grid.

 

[jimgineer]

Jerry,

I think conceptually if you picture two sources in parallel, that might help in understanding what is going on when a power source 'sources' to the grid. Its frequency and voltage will be within a range very close to the existing frequency and voltage on the grid, and with loads that are eventually also in parallel, what you have is that both sources (grid and another) are acting to drive your load.

Also keep in mind that at any one given time, your electrical generating capacity has to equal the power being consumed (including any energy being stored).

 

[cranky108]

While phase angle determines power flow, it's usually dificult to explain.
Basically any source that attempts to speed up the power grid will transfer power onto the grid. Granted a single wind unit won't be able to increase the grid speed a noticable amount. If the grid speed were to increase there are larger generation units that will be backed down to keep the speed (frequency) constant.

 

[alehman]

Jerry is mechanical. A possible analogy - Think of a car on cruise control. As the car starts to climb a hill, more power is required to keep the car moving but the speed is constant. The additional power comes in the form of additional torque driving the wheels, not additional speed.

Now the drive shaft (think power grid) is slightly springy in torsion, so the torque causes the engine crankshaft (think generator) rotation to slightly lead the wheels. More torque means the drive shaft springs more and the angular difference between the engine and wheels increases (increased phase angle).

The power is proportional to the phase angle, which is related to the torque.

Maybe someone can come up with a better analogy.

 

[waross]

The town has a water tower. You have a windmill, a pump and your own very small water tower.
You use connect your water tower to the water main. You connect your pump to your water tower and use water from your water tower. Whenever you use more water than you pump you use a combination of your own water and town water. When you use less water than you pump, the level in your water tower becomes greater than the level in the town water tower and water flows back into the water mains.
Even though we like to use pressure as an analogy for voltage, the generator puts power into the lines by trying to run the grid faster. It usually can not increase the frequency but it just has to try to increase it in order to transfer power. Think of the two elephants pushing a wagon. One is eager and the other is lazy. As the eager elephant pushes harder, the lazy elephant pushes less. The wagon continues at the same speed. A very rough analogy but there are similarities in power transfer. Think an elephant paired with a kitten who is trying as hard as it can. That would be a small generator pushing power into the grid.

Different things happen when the voltage is increased that are beyond the scope of this thread.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Think an elephant paired with a kitten who is trying as hard as it can.

Until the kitten gets stepped on.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Think of it in the simplest sense. 3-phase generators and 3-phase motors are very similar. The big difference is the generators have a prime mover turning the shaft (putting power into the generator) while the motors have a load on the shaft (taking power out of the motor).

We have generating stations all over the continent connected together via the hydro grid. Yet, they all work together to feed power into the grid and run all our electrical loads. A wind mill is much smaller but it will put power into the grid the same way a large coal or nuclear generator does.

 

[cedarbluffranch]

It's real simple.

An electric motor running with no friction is a motor and a generator at the same time. It consumes electricity from the power grid and it generates power that it pushes back into the power grid. It generates no heat since there is no friction (electrical resistance or mechanical). The net power consumption is also zero.

As you apply a load to an electric motor, it generates less power than it consumes. This power is converted into mechanical energy (torque) and heat. It still draws the same amount from the grid but it returns less, so the net power consumption is something more than zero.

If you stall the motor (don't allow the shaft to turn) it generates no electricity but continues to draw electricity. A huge amount of power is consumed and it all it turned into heat, which quickly fries the motor.

On the other hand, if you connect the shaft to an external energy source and cause the shaft to turn faster than it normally would, you generate electricity with the motor and the net consumption is negative since you're generating.

Make sense?

 

[rmw]

Now that many have been so helpful in describing or analogizing how the power is put on the grid, the answer to your question depends on the laws that govern the utility in your area. Depending upon where you are located in the world you may or may not be able to sell this power back to the local utility. You have to research that locally and find out who has jurisdiction and under what conditions you could or could not do so.

That is not a question that can be answered from afar.

rmw