Author Topic: Where does the power go ?  (Read 30116 times)

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Offline DougSpindler

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Re: Where does the power go ?
« Reply #75 on: November 27, 2017, 04:48:08 am »
After the over current situation the power company attempted to shed the load for tens of thousands of customers.  There is no way the power generators could have reacted so quickly.

Of course they could and did react so quickly. The system is designed by engineers to handle such scenarios. A few years ago there was a major blackout in the San Diego area due to a power line fault that took out a whole section of the grid in San Diego county. Millions of consumers were plunged into darkness for hours. The grid handled that, as it had to. There was no alternative. Power plants don't blow up in these situations.

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So again my question is what happens to all of that extra electricity (power) that's on the grid?  It can't be destroyed, so where does it go?

It gets consumed, or wasted. Here's a thought experiment for you: suppose you connect an array of 50 or so 12 V 1 W bulbs to a bench power supply set at 12 V. You will see the power supply indicating a load of about 50 W. Now suppose you simulate turning on a new generator by increasing the voltage to 13 V. The power supply will not indicate something like 55 W. It is pumping an extra 5 W into the "grid". Where is the extra 5 W going?

A similar situation happens in the real power grid, only on a much larger scale. If you pump extra power into the grid it will be dissipated somewhere, somehow, over the millions of square miles that the grid covers.

Now we are getting around to my original question.  What happens to the unused energy?  Where dose it go?

Maybe we have different definitions for the same word.  I was taught an electrical fault is an over current condition.  Since you think it's not an over current condition what's your definition? 
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #76 on: November 27, 2017, 05:15:45 am »
A similar situation happens in the real power grid, only on a much larger scale. If you pump extra power into the grid it will be dissipated somewhere, somehow, over the millions of square miles that the grid covers.

Not to mention that all the spinning generators will see less load, and so less of the mechanical energy being put into them will get converted into electricity and some will go to increasing the rotational speed (and therefore the frequency) of the grid. Control systems will detect this and reduce the amount of mechanical energy being put in to bring this under control on the timescale of, oh I dunno, seconds.

Now we are getting around to my original question.  What happens to the unused energy?  Where dose it go? 

He specifically answered your question with the thought experiment. If the voltage of the grid rises, all the light burns just a teensy bit brighter. All the motors get a teensy bit warmer. And, as I added, any remaining deficit goes into the mechanical rotational inertia of all the generators; which then leads to less steam being let into the turbines and ultimately less coal being burned or less water being let out of the dam.

Look back at my original post.  I said I thought the voltage and frequency would increase.  But now as I think about this I think I have my answer.  Say one has a 12 watt/12 volt light bulb.  At 12 v the current draw would be 1 amp.  But when the same light is connected to 120 volts the  wattage and current draw remains the same, but since the voltage is 10 times higher the light can not dissipate the heat fast enough and the light burns out for excess heat.

And now that I think about it same think happens with the charging circuit of a car.  If the voltage regulator shorts the generator/alternator in the car will continue to generate electricity.  That excess electricity will "cook" the battery due to over voltage.

Same thing must happen on the power grid should breakers fail.  The load on the steam/water turbines decreases so they spin faster.  The voltage and frequency will increase.  This excess energy (from the higher voltage) will be heat the wires and be dissipated as heat energy.  If the heat energy can not be dissipated fast enough it results in an oxidizing chemical reaction, (fire).  This is what's happening in the videos.

Thanks for making me think through this.


 

Offline rs20

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Re: Where does the power go ?
« Reply #77 on: November 27, 2017, 12:11:14 pm »
Same thing must happen on the power grid should breakers fail.  The load on the steam/water turbines decreases so they spin faster.  The voltage and frequency will increase.  This excess energy (from the higher voltage) will be heat the wires and be dissipated as heat energy.  If the heat energy can not be dissipated fast enough it results in an oxidizing chemical reaction, (fire).  This is what's happening in the videos.

Those explosions happen when there are short-circuit/overcurrent conditions (either downstream from the transformer or within the transform complex itself) that aren't caught by circuit breakers, leading to large I^2 R power losses in the windings, excess heat, in turn leading to the insulating/cooling oil boiling, venting, and the resulting vaporised/atomised flammable oil cloud being ignited by the sparks. You can frequently see the puffy white oil cloud, shortly before the explosion. These explosion are not caused by people turning off their lights and there therefore being "excess power that has to go somewhere"; there's no reason why the excess power would be concentrated on a single transformer.

Fast-spinning generators have absolutely nothing to do with the transformer explosions.
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #78 on: November 27, 2017, 07:44:41 pm »
Same thing must happen on the power grid should breakers fail.  The load on the steam/water turbines decreases so they spin faster.  The voltage and frequency will increase.  This excess energy (from the higher voltage) will be heat the wires and be dissipated as heat energy.  If the heat energy can not be dissipated fast enough it results in an oxidizing chemical reaction, (fire).  This is what's happening in the videos.

Those explosions happen when there are short-circuit/overcurrent conditions (either downstream from the transformer or within the transform complex itself) that aren't caught by circuit breakers, leading to large I^2 R power losses in the windings, excess heat, in turn leading to the insulating/cooling oil boiling, venting, and the resulting vaporised/atomised flammable oil cloud being ignited by the sparks. You can frequently see the puffy white oil cloud, shortly before the explosion. These explosion are not caused by people turning off their lights and there therefore being "excess power that has to go somewhere"; there's no reason why the excess power would be concentrated on a single transformer.

Fast-spinning generators have absolutely nothing to do with the transformer explosions.

I really appreciate your replies, but I think we have a language issue which is preventing us from communicating.  There was a post inviting further questions which I responded to with a a very specific question.  While I appreciate all of the answers they were confusing and did not answer the question being asked.  After talking to some other knowledgeable about this topic I found everything you were saying was correct, but was misapplied to the question I asked.  I'm an American so I'm thinking we are having language/cultural differences in our communications.



 

Offline IanB

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Re: Where does the power go ?
« Reply #79 on: November 27, 2017, 08:14:08 pm »
I really appreciate your replies, but I think we have a language issue which is preventing us from communicating.  There was a post inviting further questions which I responded to with a a very specific question.  While I appreciate all of the answers they were confusing and did not answer the question being asked.  After talking to some other knowledgeable about this topic I found everything you were saying was correct, but was misapplied to the question I asked.  I'm an American so I'm thinking we are having language/cultural differences in our communications.

The trouble is, we answered your question but you are not hearing the answer.

I gave you an example with the bench power supply and an array of bulbs. If you make the power supply deliver more power into the grid of bulbs then all the bulbs glow a little bit brighter until the extra power is accounted for.

What you fail to appreciate is that the grid is big. Really big.

When a river flows into the ocean, where does the water go? It spreads out everywhere and the sea level rises imperceptibly.

The grid is like an ocean. If you put more power into the grid the same thing happens. It spreads out throughout the grid and the voltage rises imperceptibly. At the same time all the loads on the grid consume a little more power with the rise in voltage, and all the other generators cut back on their power output a to compensate for the excess power being provided. Before very long everything balances out again.
 

Offline PinheadBETopic starter

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Re: Where does the power go ?
« Reply #80 on: November 27, 2017, 08:21:15 pm »
Don't be messed up  ;)   I'm french-speaking, and sometimes, it's hard for me too to get all the subtilities between British-English, Australian-English, US-english....   :phew:

Anyway, I understand, from an engineering POV what is being said, but I would like to rephrase my original question (the subject of this topic): Considering "the" power mix that feeds my house (some percent of nuclear, some percent of fossils, some percent of renewables), when all those units are producing what they can or what they designed to produce, considering I have, lets' say, a TV-set consuming 1 Wh while in stand-by, what happens if I turn it completely off ?  Will that 1 Wh be registred somewhere else than my own power meter,and be effectively contributing to a lesser consumption of ressources or not ?   
If not, let's just consider that a million people do the same, thus saving 1 Wh times 1 million.  Will it be contributing to a lesser consumption of ressources or not ?     
In any case, where's the threshold, then?

(Mind blowing, isn't it ?  |O)
Please keep our planet clean
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #81 on: November 27, 2017, 08:44:18 pm »
I really appreciate your replies, but I think we have a language issue which is preventing us from communicating.  There was a post inviting further questions which I responded to with a a very specific question.  While I appreciate all of the answers they were confusing and did not answer the question being asked.  After talking to some other knowledgeable about this topic I found everything you were saying was correct, but was misapplied to the question I asked.  I'm an American so I'm thinking we are having language/cultural differences in our communications.

The trouble is, we answered your question but you are not hearing the answer.

I gave you an example with the bench power supply and an array of bulbs. If you make the power supply deliver more power into the grid of bulbs then all the bulbs glow a little bit brighter until the extra power is accounted for.

What you fail to appreciate is that the grid is big. Really big.

When a river flows into the ocean, where does the water go? It spreads out everywhere and the sea level rises imperceptibly.

The grid is like an ocean. If you put more power into the grid the same thing happens. It spreads out throughout the grid and the voltage rises imperceptibly. At the same time all the loads on the grid consume a little more power with the rise in voltage, and all the other generators cut back on their power output a to compensate for the excess power being provided. Before very long everything balances out again.

Again you are not answering my question.  Let me try again.
What happens if the lights are powered by a turbine which spins at twice the normal speed?  Won't the voltage double?  And won't the frequency double as well?
P = I *E    Now that the voltage has doubled it also means the power/wattage has doubled as well.  The current would remain the same, so where's all of that extra power/energy going?

Yes the grid is large.  But again where does all of the energy go in over voltage conditions?   Conservation of energy requires it all be accounted for. 
 

Offline IanB

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Re: Where does the power go ?
« Reply #82 on: November 27, 2017, 08:54:44 pm »
Again you are not answering my question.  Let me try again.
What happens if the lights are powered by a turbine which spins at twice the normal speed?  Won't the voltage double?  And won't the frequency double as well?
P = I *E    Now that the voltage has doubled it also means the power/wattage has doubled as well.  The current would remain the same, so where's all of that extra power/energy going?

If the generator is connected directly to the bulbs, then yes the voltage may go up, and yes the frequency may go up. If the voltage goes up the current goes up too--that's how bulbs and many other things work. Power is voltage x current, so if both voltage and current go up, the power goes up. More power comes out of the generator, and more power goes into the bulbs. So it balances.

Now when the generator is connected to the grid, the generator cannot change speed. It is locked to the grid frequency at 60 Hz. The reasons why need more than a few words to explain. You can study the theory in appropriate textbooks. But regardless, if you push more power into the grid then the consumers will consume more and the other generators will generate less. After a small fluctuation it will balance out.

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Yes the grid is large.  But again where does all of the energy go in over voltage conditions?   Conservation of energy requires it all be accounted for.

As everyone has told you many times it gets consumed by consumers (or absorbed temporarily by other generators). Why is this so hard to understand?
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #83 on: November 27, 2017, 09:14:00 pm »
Don't be messed up  ;)   I'm french-speaking, and sometimes, it's hard for me too to get all the subtilities between British-English, Australian-English, US-english....   :phew:

Anyway, I understand, from an engineering POV what is being said, but I would like to rephrase my original question (the subject of this topic): Considering "the" power mix that feeds my house (some percent of nuclear, some percent of fossils, some percent of renewables), when all those units are producing what they can or what they designed to produce, considering I have, lets' say, a TV-set consuming 1 Wh while in stand-by, what happens if I turn it completely off ?  Will that 1 Wh be registred somewhere else than my own power meter,and be effectively contributing to a lesser consumption of ressources or not ?   
If not, let's just consider that a million people do the same, thus saving 1 Wh times 1 million.  Will it be contributing to a lesser consumption of ressources or not ?     
In any case, where's the threshold, then?

(Mind blowing, isn't it ?  |O)

I understand you completely.  The local power company has an excellent presentation on the power industry.   
https://www.pge.com/includes/docs/pdfs/shared/solar/solareducation/pv_basics.pdf

When you turn of a light, appliance, heather etc. the electricity stops flowing to your device.  The power company is turbines/generators now have slightly less resistance so they will spin a bit faster which will increase the voltage and frequency of the power grid.  The extra power would be dissipated throughout the grid and in your neighbors homes as heat and motors will spin a bit faster.  Now in reality your TV draws so little power compared to the size of the grid it could not be measured.

The way the grid works in the US is there are I think 5.  They are independent of each other and are regional.  West, Texas, south, northeast etc.  The grid on the west coast has 100's of power companies connected to it.  (Consumers)  They buy there power for companies who generate power, producers.  (Coal, nuclear, hydro, wind, biomass, solar etc.)  The power companies place orders for the number of kWhr they will consume minute by minute 24 hrs. in advance so the producers know who much to produce.  Should the orders not cover the demand there's a brown out.  Remember it takes an hour our more to get the grid to open vales to produce more electricity.

I live in California where we have a lot of solar and wind produced electricity.  Since know one knows how windy or if a cloud will cover one of the solar farms we have we can have brown/black-outs on clear summer days.  This has become a real problem for the power companies.

The history of electricity and power companies is quite interesting.  Over 100 years ago thee was no grid and we had local power companies.  As cities grew so did the demand for electricity and larger generation facilities like Hover dam.  To distribute the power grids were created. 

But a grid means a mistake/accident at one power company can domino and bring down and entire grid.  It's interesting if you like this kind of stuff.


 





 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #84 on: November 27, 2017, 09:20:59 pm »
Again you are not answering my question.  Let me try again.
What happens if the lights are powered by a turbine which spins at twice the normal speed?  Won't the voltage double?  And won't the frequency double as well?
P = I *E    Now that the voltage has doubled it also means the power/wattage has doubled as well.  The current would remain the same, so where's all of that extra power/energy going?

If the generator is connected directly to the bulbs, then yes the voltage may go up, and yes the frequency may go up. If the voltage goes up the current goes up too--that's how bulbs and many other things work. Power is voltage x current, so if both voltage and current go up, the power goes up. More power comes out of the generator, and more power goes into the bulbs. So it balances.

Now when the generator is connected to the grid, the generator cannot change speed. It is locked to the grid frequency at 60 Hz. The reasons why need more than a few words to explain. You can study the theory in appropriate textbooks. But regardless, if you push more power into the grid then the consumers will consume more and the other generators will generate less. After a small fluctuation it will balance out.

Quote
Yes the grid is large.  But again where does all of the energy go in over voltage conditions?   Conservation of energy requires it all be accounted for.

As everyone has told you many times it gets consumed by consumers (or absorbed temporarily by other generators). Why is this so hard to understand?

When you say absorbed what exactly do you mean?  In high school physics I learned energy can not be created or destroyed transferred or transformed.

 
 

Offline Ice-Tea

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Re: Where does the power go ?
« Reply #85 on: November 27, 2017, 09:36:44 pm »
I know when gas powered generators are running there RPM is related to load or watts being consumed.  When the load decreases/less watts are being used and the engine RPMs decrease.  But what would happen if the RPMs did not decrease when the load was removed?  That non-consumed energy in the form of electricity has to go somewhere.  I would think the voltage would increase and with the engine RPM increased the hz would also increase.  And now that I think about it a bit more, I would think some of this excess electricity would be converted to heat.

Perhaps this is where you are wrong. RPM does not relate to power. Normally a fixed frequency is chosen, which results in the frequency of the electricity being matched to 50 or 60Hz. The generator will always run at that RPM. After that, the 'throttle' is changed in function of the load while keeping the RPM constant.

Analogy: cruise control. You pick a speed and after that the cruise control manipulates the throttle to keep that speed. If the load is decreased (ie you are going downhill) the throttle will be released a bit and that's it. No drama.

Offline IanB

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Re: Where does the power go ?
« Reply #86 on: November 27, 2017, 09:49:09 pm »
When you say absorbed what exactly do you mean?  In high school physics I learned energy can not be created or destroyed transferred or transformed.

Energy can be stored or accumulated. A grid may have some storage elements, such as large batteries, or pumped storage hydroelectric facilities. Energy can also be stored as the rotational kinetic energy of generators. This may not seem like much, but for small imbalances averaged over many generators it can be enough to smooth out fluctuations and prevent sudden changes.
 

Offline rs20

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Re: Where does the power go ?
« Reply #87 on: November 27, 2017, 09:55:28 pm »
What happens if the lights are powered by a turbine which spins at twice the normal speed?  Won't the voltage double?  And won't the frequency double as well?

A turbine spinning at twice the speed has four times the kinetic energy. Now recall, that power (as measure in Watts or Joules per second) is the flow of energy (measured in Joules) over time. How did this generator, along with all the other generators and AC motors that are virtually mechanically linked, end up with double the energy?

This is why your hypothetical question is silly, it presupposes a situation that will never happen except in the most extreme case of mismanagement. In reality, an excess of power (or the portion thereof that doesn't get dissipated as heat in all the lights in the country as correctly explained by IanB) gets converted to kinetic energy in the turbines. The turbines end up spinning negligibly faster, but not for long because the device metering the steam/water into the turbine (analogy: cruise control as correctly provided by Ice-Tea) notices the slight overspeed and holds back the hydroelectric water flow or steam flow (and, further back down the chain of other control systems, less coal or gas being burned).  So when you turn off your TV, negligibly less coal/gas is burned or less water is let through the dam.

Short term (ms): Lights in your neighborhood burn brighter, with the vast rotational inertia of all motors and generators in the country hold frequency nearly steady
Medium term (100ms - multiple seconds): Turbine flow control in power stations is adjusted
Long term (integrated/infinity): Less coal burned or more water still in dam.
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #88 on: November 27, 2017, 10:28:29 pm »
What happens if the lights are powered by a turbine which spins at twice the normal speed?  Won't the voltage double?  And won't the frequency double as well?

A turbine spinning at twice the speed has four times the kinetic energy. Now recall, that power (as measure in Watts or Joules per second) is the flow of energy (measured in Joules) over time. How did this generator, along with all the other generators and AC motors that are virtually mechanically linked, end up with double the energy?

This is why your hypothetical question is silly, it presupposes a situation that will never happen except in the most extreme case of mismanagement. In reality, an excess of power (or the portion thereof that doesn't get dissipated as heat in all the lights in the country as correctly explained by IanB) gets converted to kinetic energy in the turbines. The turbines end up spinning negligibly faster, but not for long because the device metering the steam/water into the turbine (analogy: cruise control as correctly provided by Ice-Tea) notices the slight overspeed and holds back the hydroelectric water flow or steam flow (and, further back down the chain of other control systems, less coal or gas being burned).  So when you turn off your TV, negligibly less coal/gas is burned or less water is let through the dam.

Short term (ms): Lights in your neighborhood burn brighter, with the vast rotational inertia of all motors and generators in the country hold frequency nearly steady
Medium term (100ms - multiple seconds): Turbine flow control in power stations is adjusted
Long term (integrated/infinity): Less coal burned or more water still in dam.

Your statement, "This is why your hypothetical question is silly, it presupposes a situation that will never happen except in the most extreme case of mismanagement" made me laugh out loud.  So aren't you really saying something that will never happen can happen?  So when what's supposed to never happen, happens, what happens?

So a generator that has more KE than another, as in it's spinning faster, will speed up slower ones and be slowed by the slower ones.  Now if one has 4x the KE as in spinning twice as fast I would suspect the electron flow and magnetic fields would heat things quite a bit with reduced R resistance or I should say reactive resistance.  If the R is low enough that excess energy could result in a massive exothermal oxidative reaction or fire.  Similar to what we are seeing in the transformer fires.
 




 

Offline ruffy91

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Re: Where does the power go ?
« Reply #89 on: November 27, 2017, 10:41:31 pm »
As load increases or power generation decreases the frequency of the grid will decrease.When regulation failsand the frequency decreases more than 1% load shedding occurs (1/3 of all consumers will be shed of the grid, which consumers is rotated on a weekly base, so that it remains fair). On the opposite if load is decreasing or power generation increases generating capacity is shed of the grid and loads are switched on. I know of cases where you would get 700$/MWh of used energy for a few seconds-minutes. Some power companies even have huge resistor arrays which can burn a few MW for a few minutes.
The regulation mechanisms are called primary regulation (simple proportional regulator which uses the difference between the set point (normally 50/60Hz) and the actual frequency to regulate power generation). Then you have secondary regulation which varies the set point so you have exctly 50/60Hz in average on a day. And finally tertiary regulation which is like wall street where energy is sold and bought.

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Offline timb

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Where does the power go ?
« Reply #90 on: November 27, 2017, 11:02:48 pm »
Same thing must happen on the power grid should breakers fail.  The load on the steam/water turbines decreases so they spin faster.  The voltage and frequency will increase.  This excess energy (from the higher voltage) will be heat the wires and be dissipated as heat energy.  If the heat energy can not be dissipated fast enough it results in an oxidizing chemical reaction, (fire).  This is what's happening in the videos.

Those explosions happen when there are short-circuit/overcurrent conditions (either downstream from the transformer or within the transform complex itself) that aren't caught by circuit breakers, leading to large I^2 R power losses in the windings, excess heat, in turn leading to the insulating/cooling oil boiling, venting, and the resulting vaporised/atomised flammable oil cloud being ignited by the sparks. You can frequently see the puffy white oil cloud, shortly before the explosion. These explosion are not caused by people turning off their lights and there therefore being "excess power that has to go somewhere"; there's no reason why the excess power would be concentrated on a single transformer.

Fast-spinning generators have absolutely nothing to do with the transformer explosions.

I really appreciate your replies, but I think we have a language issue which is preventing us from communicating.  There was a post inviting further questions which I responded to with a a very specific question.  While I appreciate all of the answers they were confusing and did not answer the question being asked.  After talking to some other knowledgeable about this topic I found everything you were saying was correct, but was misapplied to the question I asked.  I'm an American so I'm thinking we are having language/cultural differences in our communications.

FWIW, I’m an American and understood the replies to your question perfectly. Honestly, I think the communication problem is on your side; I.e., you’re misunderstanding certain terms or concepts.

A good example of this would be referring to short circuit events as “over current” events. If you touch a live wire and are electrocuted, it’s a short circuit. Over current would imply a specific type of event, with one of the many possible causes being a short circuit; as a result of that event, a breaker would trip or current limiting would kick in. In your example of the linemen being electrocuted in the cherry picker, obviously there wasn’t an over current event, or upstream breakers would have kicked in instantly; the power lines were obviously able to handle the current it took to electrocute them, as it took the power company 20 minutes to shut down that part of the grid.

(Also, I wonder how they were electrocuted to begin with, as the buckets on a cherry picker are generally made from fiberglass or composite plastic and therefor non-conductive. Even if the metal arm of the picker touched the line, the men in the bucket should have been OK as the electricity wouldn’t have a route through them.)

Anyway, your question has been answered repeatedly. Read back through the answers and maybe share what you think some of the terminology means. That way we can all get on the same page. [emoji4]
« Last Edit: November 27, 2017, 11:11:28 pm by timb »
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Offline IanB

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Re: Where does the power go ?
« Reply #91 on: November 28, 2017, 12:09:05 am »
So a generator that has more KE than another, as in it's spinning faster, will speed up slower ones and be slowed by the slower ones.

Yes, good so far.

Quote
Now if one has 4x the KE as in spinning twice as fast I would suspect the electron flow and magnetic fields would heat things quite a bit with reduced R resistance or I should say reactive resistance.  If the R is low enough that excess energy could result in a massive exothermal oxidative reaction or fire.  Similar to what we are seeing in the transformer fires.

But here what you have said does not conform with proper scientific or engineering understanding. It is almost gobbledygook. Therefore there is no way to give any response to this statement.
 

Offline Jr460

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Re: Where does the power go ?
« Reply #92 on: November 28, 2017, 12:34:52 am »

Short term (ms): Lights in your neighborhood burn brighter, with the vast rotational inertia of all motors and generators in the country hold frequency nearly steady
Medium term (100ms - multiple seconds): Turbine flow control in power stations is adjusted
Long term (integrated/infinity): Less coal burned or more water still in dam.

I think you are way off. 
Short term (100 us)
Medium term (ms) Turbine controls are adjusted - and because of feed forward in the control systems, fuel is adjusted.

Myself and others have explained back about 3 pages.  There is no "extra" or excess energy or power that needs to go anywhere.

Let me ask this.

Say I have a lab switching power supply power supply and I set it 12V and connect it to a set of 12V lamps.  The power supply keeps the voltage at 12V as you add or remove load/lamps.  Since it is a switcher you don't have power being dissipated in a large pass transistor.  The current changes and thus the power provided by the supply.

Now I suddenly remove all the lamps, were does all that extra engird from the power supply go?

The answer is nowhere, the control loop sees the voltage start going up because the load is now gone, and reduces the PWM quickly.  Sure you might see on a scope some slight (better supply with better control will have less by amount also time) over/under shoot of the 12V as the load quickly changes, but nothing radical.

Did the supply switch in resistors to handle the loss of the load?   No.
Did your circuit of lamps for a storage element in it?  No.
 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #93 on: November 28, 2017, 02:10:23 am »
Same thing must happen on the power grid should breakers fail.  The load on the steam/water turbines decreases so they spin faster.  The voltage and frequency will increase.  This excess energy (from the higher voltage) will be heat the wires and be dissipated as heat energy.  If the heat energy can not be dissipated fast enough it results in an oxidizing chemical reaction, (fire).  This is what's happening in the videos.

Those explosions happen when there are short-circuit/overcurrent conditions (either downstream from the transformer or within the transform complex itself) that aren't caught by circuit breakers, leading to large I^2 R power losses in the windings, excess heat, in turn leading to the insulating/cooling oil boiling, venting, and the resulting vaporised/atomised flammable oil cloud being ignited by the sparks. You can frequently see the puffy white oil cloud, shortly before the explosion. These explosion are not caused by people turning off their lights and there therefore being "excess power that has to go somewhere"; there's no reason why the excess power would be concentrated on a single transformer.

Fast-spinning generators have absolutely nothing to do with the transformer explosions.

I really appreciate your replies, but I think we have a language issue which is preventing us from communicating.  There was a post inviting further questions which I responded to with a a very specific question.  While I appreciate all of the answers they were confusing and did not answer the question being asked.  After talking to some other knowledgeable about this topic I found everything you were saying was correct, but was misapplied to the question I asked.  I'm an American so I'm thinking we are having language/cultural differences in our communications.

FWIW, I’m an American and understood the replies to your question perfectly. Honestly, I think the communication problem is on your side; I.e., you’re misunderstanding certain terms or concepts.

A good example of this would be referring to short circuit events as “over current” events. If you touch a live wire and are electrocuted, it’s a short circuit. Over current would imply a specific type of event, with one of the many possible causes being a short circuit; as a result of that event, a breaker would trip or current limiting would kick in. In your example of the linemen being electrocuted in the cherry picker, obviously there wasn’t an over current event, or upstream breakers would have kicked in instantly; the power lines were obviously able to handle the current it took to electrocute them, as it took the power company 20 minutes to shut down that part of the grid.

(Also, I wonder how they were electrocuted to begin with, as the buckets on a cherry picker are generally made from fiberglass or composite plastic and therefor non-conductive. Even if the metal arm of the picker touched the line, the men in the bucket should have been OK as the electricity wouldn’t have a route through them.)

Anyway, your question has been answered repeatedly. Read back through the answers and maybe share what you think some of the terminology means. That way we can all get on the same page. [emoji4]

Not sure we agree on the definitions or use of words in the same way.
Are you saying a short does not cause or result in an an over current event?
A short circuit is one where electrons/current flow through an unintended path with very no or very little resistance.
The body is not a perfect conductor, it's a resistive load.  It can be from 1.000 to 100.000 ohms.  At higher voltages after a bit of cooking the skin resistance is about 500 ohms.  Not sure I would consider that a short.   If we were perfect conductors as I think you are implying we could not live.  Your heart could not beat, you could not think or move.  And I guess if you thought hard enough you could get a shock from all of that electrical activity.
I was taught electrocution is what happens when a person becomes a conductor either intentionally or accidentally accompanied with an external flow of electrons/current through the body.  Not sure why you would consider that a short.  There are many medical procedures which use electricity.  The procedure would not work if the body were a perfect conductor.  Intensely there are people who can not get electrocuted if they are on certain drugs and have a sweating disorder.

Not sure what the cherry picker was made out of.  I'm surprised if you understand electricity why you don't understand why the two guys in the cherry picker were being electrocuted.  This is something firemen are taught with live wires.  If a live wire falls on the ground firemen are taught to keep both feet in contact with the ground and shuffle away from the live wire.  If they take a stride the resistance of the ground can be high enough current will flow up one leg and down the other electrocuting the fireman.  I remember hearing of three police horses being killed in Florida because of a live wire in a field.  The resistance of the ground between the legs of the horses was enough that the current flowed through the horses killing them.

This is what I was taught.  Not say I'm right, but then again I've been looking up the definition of the words to make sure I'm using them as properly. 

I do want to thank you for questioning me.  It's required me to do a fair amount of researcher to confirm what I saying is correct.




 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #94 on: November 28, 2017, 02:20:58 am »
So a generator that has more KE than another, as in it's spinning faster, will speed up slower ones and be slowed by the slower ones.

Yes, good so far.

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Now if one has 4x the KE as in spinning twice as fast I would suspect the electron flow and magnetic fields would heat things quite a bit with reduced R resistance or I should say reactive resistance.  If the R is low enough that excess energy could result in a massive exothermal oxidative reaction or fire.  Similar to what we are seeing in the transformer fires.

But here what you have said does not conform with proper scientific or engineering understanding. It is almost gobbledygook. Therefore there is no way to give any response to this statement.

I thought we agreed if the generator is spinning faster voltage would increase.  And if spinning at twice the speed there were by 4 X the kinetic energy.  My question is where is all of that extra energy going?  I'm re-reading what I wrote and it seems very clear to me.  I would suspect the electron flow and magnetic fields would heat things quite a bit with reduced R resistance or I should say reactive resistance.  If the R is low enough that excess energy could result in a massive exothermal oxidative reaction or fire.  Similar to what we are seeing in the transformer fires.

What is it you are not understanding?


 

Offline DougSpindler

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Re: Where does the power go ?
« Reply #95 on: November 28, 2017, 02:49:02 am »

Short term (ms): Lights in your neighborhood burn brighter, with the vast rotational inertia of all motors and generators in the country hold frequency nearly steady
Medium term (100ms - multiple seconds): Turbine flow control in power stations is adjusted
Long term (integrated/infinity): Less coal burned or more water still in dam.

I think you are way off. 
Short term (100 us)
Medium term (ms) Turbine controls are adjusted - and because of feed forward in the control systems, fuel is adjusted.

Myself and others have explained back about 3 pages.  There is no "extra" or excess energy or power that needs to go anywhere.

Let me ask this.

Say I have a lab switching power supply power supply and I set it 12V and connect it to a set of 12V lamps.  The power supply keeps the voltage at 12V as you add or remove load/lamps.  Since it is a switcher you don't have power being dissipated in a large pass transistor.  The current changes and thus the power provided by the supply.

Now I suddenly remove all the lamps, were does all that extra engird from the power supply go?

The answer is nowhere, the control loop sees the voltage start going up because the load is now gone, and reduces the PWM quickly.  Sure you might see on a scope some slight (better supply with better control will have less by amount also time) over/under shoot of the 12V as the load quickly changes, but nothing radical.

Did the supply switch in resistors to handle the loss of the load?   No.
Did your circuit of lamps for a storage element in it?  No.

I agree with everything you have stated.  But that's not the scenario we are taking about.
Let's say you have a generator located at Hover Dam.  You are located 1,000 miles away.  The power lines are directly connected to several motors and light blubs at your location.  All of the motors are running and the lights are lit.  More or less same scenario as your power supply but the distance between ps and load in much greater.

You then turn off half of the motors.  The generator is still spinning at the same speed producing the same amount of energy because it does not know the motors are turned off and you need less energy.  For that split second the wires are conducting far more energy than what you need.  What happens to that excess energy?  Where does it go?  Do we agree the speed of electrons in copper wire is about 1/100 the speed of light?  Same would happen in your power supply example if you added 1,000 miles of wire.

After that split second the load on the generator is less so it will spin faster and the voltage will increase and with the increase in voltage the current should decrease.  (And since the generator is spinning faster the hz will increase.) 

   







 

Offline IanB

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Re: Where does the power go ?
« Reply #96 on: November 28, 2017, 03:14:34 am »
Not sure we agree on the definitions or use of words in the same way.
Are you saying a short does not cause or result in an an over current event?
A short circuit is one where electrons/current flow through an unintended path with very no or very little resistance.

A short circuit is when the current takes a shorter path than it is intended to take. Hence "short" circuit. A short may be high resistance or low resistance, but it is true that a low resistance is commonly assumed in casual speech.

An over current situation is again what the words describe. It is a situation when the current is over what it is intended to be, or over the maximum designed for or allowed for. Hence "over" current. Usually an over current situation will be protected against by tripping a fuse or circuit breaker.

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I was taught electrocution is what happens when a person becomes a conductor either intentionally or accidentally accompanied with an external flow of electrons/current through the body.

Electrocution is to be killed by electricity passing through the body. If you don't die it is not electrocution.

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Not sure what the cherry picker was made out of.  I'm surprised if you understand electricity why you don't understand why the two guys in the cherry picker were being electrocuted.

If the cherry picker was made out of an insulator like GRP, then no current would flow at all and the people riding on it would be safe. This is the case with any cherry pickers that might be used near overhead wires.

If the cherry picker was made out of steel then its resistance would be very low and as soon as it contacted the wires it would cause a short circuit and an over current situation (see above) and the breaker would trip, cutting power to the wires. In the unlikely event that the breaker didn't trip, then the low resistance of the steel would prevent any differential voltage being high enough to cause harm. (Unless the unfortunate person was between the high voltage wires and the cherry picker. In that case they would not only be electrocuted, they would be instantly incinerated.)

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If a live wire falls on the ground firemen are taught to keep both feet in contact with the ground and shuffle away from the live wire.  If they take a stride the resistance of the ground can be high enough current will flow up one leg and down the other electrocuting the fireman.

Just a quick footnote: it is quite unlikely a human can be electrocuted in this way, because the electrical path up one leg and down the other does not pass through a human's heart. In addition to which, the fireman is probably wearing heavy insulated boots. It is sensible to take the proper precautions and avoid unnecessary risks, but the actual risk is not that great.
« Last Edit: November 28, 2017, 03:19:15 am by IanB »
 

Offline IanB

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Re: Where does the power go ?
« Reply #97 on: November 28, 2017, 03:25:08 am »
You then turn off half of the motors.  The generator is still spinning at the same speed producing the same amount of energy because it does not know the motors are turned off and you need less energy.  For that split second the wires are conducting far more energy than what you need.  What happens to that excess energy?  Where does it go?

You have to think of it like this: the generator is "pushing" electricity into the grid.

Imagine you are pushing someone along on a bicycle, but they have the brakes on. You are pushing really hard, but they are only moving slowly. Suddenly they let off the brakes. You are still pushing really hard, but the resistance has suddenly dropped. You are pushing much harder than you really need to. What happens to all your excess energy?
 

Offline rs20

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Re: Where does the power go ?
« Reply #98 on: November 28, 2017, 04:10:31 am »
I thought we agreed if the generator is spinning faster voltage would increase.

Yep.

And if spinning at twice the speed there were by 4 X the kinetic energy.

If the turbine spins at twice the speed, the turbine will have 4x the kinetic energy, yes.

My question is where is all of that extra energy going?

The energy is not going anywhere. A faster spinning turbine has more kinetic energy, just like a fully charged battery has more chemical energy in it. Energy doesn't have to go places, you can just have a system with lots of gravitational potential energy (fully filled dam), lots of chemical potential energy (charged batteries, a pile of coal), or lots of kinetic energy (a rapidly spinning heavy thing), and that's just fine. The energy can stay where it is, it's not a flow (like power) and so it doesn't have to flow, let alone flow to any particular place.

I think you're confusing energy and power? Energy is measured in Joules, and power is measured in Joules per second (also known as Watts). There's a recent EEVBlog video that goes into some detail on this, you really need to have this concept down before you can discuss subtle things like an imbalance in the power going into/out of a turbine leading to a change in the kinetic energy of the turbine (and that being the end of the story and just fine) -- just like an imbalance in the water flow going into/out of a bucket leading to a change in the quantity of water in the bucket with no need to "explain" where all that "extra water" "goes".

 

Online T3sl4co1l

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Re: Where does the power go ?
« Reply #99 on: November 28, 2017, 04:22:29 am »
You then turn off half of the motors.  The generator is still spinning at the same speed producing the same amount of energy because it does not know the motors are turned off and you need less energy.  For that split second the wires are conducting far more energy than what you need.  What happens to that excess energy?  Where does it go?

Directly into the spark(s) that follow switching such a load.

Power is going to ~zero every cycle, too.  It doesn't need to go anywhere at all.  A "lucky" switch can open during the zero crossing.

(This is the case for single phase.  Three phase always has power going somewhere; you'd need an extremely lucky contactor to open two lines in the correct phase so that no current is being switched.)

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Do we agree the speed of electrons in copper wire is about 1/100 the speed of light?  Same would happen in your power supply example if you added 1,000 miles of wire.

Slower than that. But electron drift velocity (which averages zero in mains, BTW) is completely irrelevant to power transmission -- the contactor opening or closing is communicated at light speed [in the conductors], so the force on the rotor changes almost immediately (10s-100s microseconds).

After that, all the mechanical dynamics and control systems play a role.  The instant effect is the generator accelerating incrementally.  Its frequency does not change, in that it makes much less than one full rotation with respect to the grid.  No, its angle change draws power from neighboring generators (others within the plant, and from the grid at large), and that angle oscillates back and forth, like a torsional spring, until the transient energy is dissipated.  Dissipation occurs through losses in the system (generators contain shorting slats*, to reduce harmonic oscillations and dampen these vibrations), transmission losses, and the controller.

*More specifically, synchronous machines do.  Shorting slats are simply shorted turns on the armature, which act to slow any change in its magnetic field (which is an electromagnet, so the field is supposed to be static anyway).  Note: I haven't studied modern generators per se -- their design may vary.  Anyway, even if this isn't the exact solution used, the same effect is required, however it's achieved.


The amount of energy stored in the grid is extremely small.  Only rotating machinery has any inertia at all, and it only accounts for about 10% of the total available power (IIRC).  PFC capacitors might account for 30% of that in turn.

When the grid goes down, whether it's a small neighborhood or the entire northeast, it simply disappears, poof.  Likewise, when it's restarted, the load is there, ~instantaneously, no windup, no springiness.  (In practice, there's a lot of inrush associated with restart.  But they can deal with that, as, of course, they must.)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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