Surplus electric power in grids


by Charles123
Tags: electric, grids, power, surplus
vk6kro
vk6kro is offline
#19
Feb20-12, 08:10 PM
Sci Advisor
P: 4,003
This implies that because power can be generated, it has to go somewhere. This just isn't true.

Take a simple example.

If you have a large car battery capable of delivering 600 amps (that is 7200 watts), is it safe to put a 1000 ohm quarter watt resistor across it?
Would the battery blow up with all that power inside it? Will the resistor be vapourized in an instant?

No, the battery will be fine and so will the resistor.

There will be a current of about 12 mA flowing in the resistor and it will not even get warm with only 144 mW being dissipated in it.

It is the same with the power grid. It only delivers power if the load takes power from it. There is no power "bottled up" in the generators trying to get out.

Each component connected to it is arranged with its own protection so that if there was no load or too much load, the equipment would not be damaged.

For example, a wind generator may tend to spin too fast if it has no load on it. So, it can be turned away from the wind or the blades might be set to present no surface area to the wind.

The equipment is never sacrificed to supply a demand. If there is too much load, power can just be turned off to consumers, possibly only in a few suburbs, preferably the ones that didn't vote for the current government.

Large power stations cannot be just switched off, but they continue to generate the standard voltage whether or not much current is taken from that supply.
As the load increases, it gets harder to turn the generators, so more drive power is used.
Charles123
Charles123 is offline
#20
Feb20-12, 08:46 PM
P: 140
vk6kro, thank you for this answer! The analogy with the battery is great, I wasn`t thinking about that.
Some clarifications:
"It is the same with the power grid. It only delivers power if the load takes power from it. There is no power "bottled up" in the generators trying to get out.

Each component connected to it is arranged with its own protection so that if there was no load or too much load, the equipment would not be damaged."
But and quoting a previous post your yours - "There are circuit breakers which can cut the power if a sudden load is placed on the generators and which they may not be able to react to in time.", and assuming that such circuit breakers were not present, and also assuming that that reaction time was very long, the extra load would act as a brake in the generator? What else would happen, like damages in the system?
The question would also apply for your example of wind turbines, if they were not able to be "turned away from the wind or the blades might be set to present no surface area to the wind".
"The equipment is never sacrificed to supply a demand. If there is too much load, power can just be turned off to consumers", why would the power be turned off to consumers in excess load? It means you would have to switch of all power generators to lower the load? I am confused.
Also, and since you seem so knowledgeable in this matter, I am going to take some more advantage of that, if you don`t mind. I posted in another threat some questions that nobody is answering in a way that enables me be clear about, so here they are for you, if you have the extra patience:
Utility poles have a grounded wire. Is this just for lightening? Is not connected the neither one of the 3 phase wires, is it? Is the static electricity wire always present, and is it grounded (at every pole, or every x poles)? What does the multi-grounded neutral wire do, and has it always have to be present? The 3 phase wires are only grounded at destination when electricity is being consumed?
If domestic consumers receive just one phase current, why there are 3 wires coming from the pole to the house?
Is ground always the return path for electrons? Is there a ground connection at every house directly or at the nearest utility pole?
In power plants the wires in the generator are connected to the ground, to close the circuit (assuming the return path for electrons is the ground?

Thank you very much!
Regards
vk6kro
vk6kro is offline
#21
Feb20-12, 09:40 PM
Sci Advisor
P: 4,003
Quote Quote by charles123 View Post
vk6kro, thank you for this answer! The analogy with the battery is great, i wasn`t thinking about that.
Some clarifications:
"it is the same with the power grid. It only delivers power if the load takes power from it. There is no power "bottled up" in the generators trying to get out.

Each component connected to it is arranged with its own protection so that if there was no load or too much load, the equipment would not be damaged."
but and quoting a previous post your yours - "there are circuit breakers which can cut the power if a sudden load is placed on the generators and which they may not be able to react to in time.", and assuming that such circuit breakers were not present, and also assuming that that reaction time was very long, the extra load would act as a brake in the generator? What else would happen, like damages in the system?
no, you can't have it like that. Each power station is protected locally so that it can't be damaged.
Different types of protection are used depending on the possible type of problem.

the question would also apply for your example of wind turbines, if they were not able to be "turned away from the wind or the blades might be set to present no surface area to the wind".
"the equipment is never sacrificed to supply a demand. If there is too much load, power can just be turned off to consumers", why would the power be turned off to consumers in excess load? It means you would have to switch of all power generators to lower the load? I am confused.

if the maximum current the generators could supply was 50000 amps and the load was creeping above this, rather than have power stations start to protect themselves by shutting down, and making the problem worse, then some of the extra current drain can be eliminated by isolating some areas of the network from any power source, so that they cannot draw current.
This can happen on a hot day when everyone starts turning on air conditioners.

also, and since you seem so knowledgeable in this matter, i am going to take some more advantage of that, if you don`t mind. I posted in another threat some questions that nobody is answering in a way that enables me be clear about, so here they are for you, if you have the extra patience:
Utility poles have a grounded wire. Is this just for lightening? Is not connected the neither one of the 3 phase wires, is it?
this gets down to different power supplies in different countries. It would be normal in some countries to ground the neutral at the power pole.
is the static electricity wire always present, and is it grounded (at every pole, or every x poles)? What does the multi-grounded neutral wire do, and has it always have to be present? The 3 phase wires are only grounded at destination when electricity is being consumed?

multi-point grounding of the neutral is used because it is difficult to make a good ground connection and this is improved if all the imperfect connections are connected in parallel.
if domestic consumers receive just one phase current, why there are 3 wires coming from the pole to the house?

again this varies from country to country. The american system has a 240 volt center tapped transformer on the pole and the three wires from this (the two outside wires and the center tap of the transformer winding) are probably brought into the house although each power outlet only gets one of the active leads and the neutral.
This makes 240 volts available for high powered items like clothes dryers, water heaters etc.


is ground always the return path for electrons?
ground is never the return path for electrons.

is there a ground connection at every house directly or at the nearest utility pole?
you tell me. We have them at every house.
in power plants the wires in the generator are connected to the ground, to close the circuit (assuming the return path for electrons is the ground?

ground is never the return path for electrons.

thank you very much!
Regards
1234
Charles123
Charles123 is offline
#22
Feb20-12, 10:09 PM
P: 140
Thank you again!
vk6kro, thank you for this answer! The analogy with the battery is great, i wasn`t thinking about that.
Some clarifications:
"it is the same with the power grid. It only delivers power if the load takes power from it. There is no power "bottled up" in the generators trying to get out.

Each component connected to it is arranged with its own protection so that if there was no load or too much load, the equipment would not be damaged."
but and quoting a previous post your yours - "there are circuit breakers which can cut the power if a sudden load is placed on the generators and which they may not be able to react to in time.", and assuming that such circuit breakers were not present, and also assuming that that reaction time was very long, the extra load would act as a brake in the generator? What else would happen, like damages in the system?
no, you can't have it like that. Each power station is protected locally so that it can't be damaged. I understand that, but theoretically? Can you ever have a blackout by excess power supply?
Different types of protection are used depending on the possible type of problem.the question would also apply for your example of wind turbines, if they were not able to be "turned away from the wind or the blades might be set to present no surface area to the wind".
"the equipment is never sacrificed to supply a demand. If there is too much load, power can just be turned off to consumers", why would the power be turned off to consumers in excess load? It means you would have to switch of all power generators to lower the load? I am confused.

if the maximum current the generators could supply was 50000 amps and the load was creeping above this, rather than have power stations start to protect themselves by shutting down, and making the problem worse, then some of the extra current drain can be eliminated by isolating some areas of the network from any power source, so that they cannot draw current.
This can happen on a hot day when everyone starts turning on air conditioners.
I got the wrong way, by more load I wanted to say more supply, not more demand. In that case what would happen?

also, and since you seem so knowledgeable in this matter, i am going to take some more advantage of that, if you don`t mind. I posted in another threat some questions that nobody is answering in a way that enables me be clear about, so here they are for you, if you have the extra patience:
Utility poles have a grounded wire. Is this just for lightening? Is not connected the neither one of the 3 phase wires, is it?
this gets down to different power supplies in different countries. It would be normal in some countries to ground the neutral at the power pole. So it`s not for lightning then?is the static electricity wire always present, and is it grounded (at every pole, or every x poles)? What does the multi-grounded neutral wire do, and has it always have to be present? The 3 phase wires are only grounded at destination when electricity is being consumed?

multi-point grounding of the neutral is used because it is difficult to make a good ground connection and this is improved if all the imperfect connections are connected in parallel.
if domestic consumers receive just one phase current, why there are 3 wires coming from the pole to the house?

again this varies from country to country. The american system has a 240 volt center tapped transformer on the pole and the three wires from this (the two outside wires and the center tap of the transformer winding) are probably brought into the house although each power outlet only gets one of the active leads and the neutral.
This makes 240 volts available for high powered items like clothes dryers, water heaters etc.


is ground always the return path for electrons?
ground is never the return path for electrons. From http://science.howstuffworks.com/env...rgy/power3.htm - "The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons." - This is a wrong statement?
is there a ground connection at every house directly or at the nearest utility pole?
you tell me. We have them at every house. I meant the real connection to the earth, if the neutral wire was being grounded only at the nearest pole...
in power plants the wires in the generator are connected to the ground, to close the circuit (assuming the return path for electrons is the ground?

ground is never the return path for electrons. How is the circuit closed? Are theu also conected to neutral, in what way?
thank you very much!
Regards


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