What Happens to Unused Electricity in Distribution Transformers?

[Venkata Satish]

Guy i am so sorry. i tough the initial question is very simple and a Dumb question. It turns out there is lot deeper that I thought

My only question is how Smart Meters are providing profits to utilities. I say this again and again because this is our company has this statement and we sell smart metering solution. All along i have been thinking that we predict load at the consumption point and hence lesser load the utility orders to generation company and Utility save money. But you guys all convinced me that no extra energy is created at all in the first place. So what are the advantages of smart meters for Utilties (Apart from auto disconnect, Usage patterns, Meter statuses etc)

My question when Utility commit(purchase) commit for some Energy say 100MW , Is Utility suppose to pay even thought the 100MW is NOT consumed? Is that we are talking ?

Read the link http://www.powerwise.gov.ae/en/research/programmes-projects/demand-side-management.html

http://etap.com/substation-automation/substation-automation-images/demand-side-management-software-large.jpg

 

[Jeff Rosenbury]

My question when Utility commit(purchase) commit for some Energy say 100MW , Is Utility suppose to pay even thought the 100MW is NOT consumed? Is that we are talking ?

That's a contractual question I don't know the answer though I suspect it depends on which market they buy it from. I'm sure there are penalties involved. They could also recoup some losses by selling some excess on the real time market.

 

[anorlunda]

My question when Utility commit(purchase) commit for some Energy say 100MW , Is Utility suppose to pay even thought the 100MW is NOT consumed? Is that we are talking ?

Now you are wasting our time. You had a direct answer to that question in #7. I'll repeat it.

Actually, that is a very good question. In your first post, you asked about earthing the excess power. Excess power is never generated.

But now you make it clear that you are asking about payment. Yes, if the power plant contracts 100MW in the day-ahead market but only 95MW is needed in real time, he is still paid for 100. But consumers pay only for the energy they use.

Where does the money come from four that 5MW difference? All power plants and all utilities contribute to a fund to pay for someone to run that DAM market. The money comes from that fund.

Suppose the power plant sold 90MW in the DAM market but the next day 95 is needed. The extra 5MW are purchased on the real time RT market where prices may be different than DAM prices. The RT market is calculated every 15 minutes.

The markets are motivated to be as accurate as possible in how much they buy in advance.

Edit: demand response can be thought of as a negative way to balance load and generation. If an extra 10MW is needed, the market can pay a power plant to make 10 more, or it can pay demand response to demand 10 less. Demand response is not normally sold in the DAM but only in the RT market. The prices paid for demand response are much higher than power plant purchases. Therefore demand response is not used unless an emergency is near.

 

[jim hardy]

what is the sort of time involved between increasing the rate of coal feed to an increase in generator output?

ReReading that question i may have mis-answered.

In our plants the heat source, boiler or reactor, follows the turbine. An increase or decrease in generation causes the fuel pumps to inject more oil and/or natural gas , or causes control rods to move in the appropriate direction.

Generation is sensed by pressure drop across turbine , from a sensor just downstream of the throttle valves.
That signal gives feed-forward to combustion controls in the fossil and to rod control in the nuke .
It also gives feed-forward to boiler(called steam generator in nuke) water level controls.
Final control trim of heat generation is by pressure in the fossil or by temperature in the nuke.

So the delay you mention is actually the other way - change in generation precedes change in heat production but only by the time for signals to propagate through the automatic controls and move the final actuators - seconds at most.
Boiler follows turbine.
Remember - we follow the customer not the other way round...

BWR's might be different, and we have some good BWR guys here..

old jim

 

[sophiecentaur]

So the delay you mention is actually the other way - change in generation precedes change in heat production.
Boiler follows turbine.

I understand what you are saying.
It's a bit of a chicken and egg situation but in normal feedback ('loop' is the relevant term) systems, the 'slew rate' of the Amplifier (or equivalent) is the limiting factor to the possible reaction time. In this case, it is the lag in getting fuel to burn, produce steam and to vary the power from the turbine that must be the critical factor. Your feedback signal is the departure of the turbine output from what's required and that can be detected in a few hundred milliseconds but there is a limit to how fast that signal can be used to vary the energy supply to the generator etc.. I guess what I wanted to know is how fast the response is to a step change in fuel input when there is no feedback - the Open Loop performance - which is what determines the possible closed loop performance. (That's just the simple feedback theory I was taught)
Your reply is more to do with the system with the loop closed but the 3-5% per minute is meaningful to me. You would need to dump say ten minute's worth of power if the demand suddenly dried up (a broken single line feeder, for instance).
But you mentioned feed forward, which is the way to deal with high values of lag.

 

[anorlunda]

Response rates aren't just a simple time constant. In many cases, they are restricted to a ramp rate, X %/minute.

Here's a short list of response rates versus generation type. 1 most responsive - 6 least.

1. Batteries/flywheels
2. Hydro
3. Gas Turbines
4. Combined Cycle
5. Gas fired boilers
6. Nukes & Coal
7. Solar and Wind

I put solar & wind last because they don't respond to grid commands at all (Unless you trip their breakers). In fact there is a 50% chance that the gust of wind or passing cloud might increase or decrease their output in opposition to the grid's instantaneous need for incremental changes. They are bad actors regarding grid frequency control.

In theory, some wind generators could change the blade pitch dynamically to be able to respond, but I never heard of them doing that. They like to run at 100% anyhow, leaving zero room to respond to a + change.

 

[jim hardy]

I guess what I wanted to know is how fast the response is to a step change in fuel input when there is no feedback - the Open Loop performance - which is what determines the possible closed loop performance. (That's just the simple feedback theory I was taught)

I'm not quite sure how to approach that. No feedback = no valve motion ,
so i'll venture
A step change in heat production would raise temperature per heat capacity of the boiler system ,
raising pressure hence density hence mass flow rate of steam
hence raising rate of heat removal,
so you'd approach a new equilibrium pressure, exponentially, as heat removal rate approaches new heat input rate.
That'd take probably twenty minutes to quit moving visibly. If that's five time constants then there's a 4-minute-ish time constant.

Point being there's natural feedbacks inherent in the machine. Thermal capacity is high enough it's inherently slow so it needs feedforward as you said...
That's why in our fossil boilers we control fueling rate by pressure and give it feedforward from that turbine first stage pressure signal, which is rate of heat removal.
Bumping the governor so throttle valves go a teeny bit further open causes an almost immediate pressure dip, an upswing in the boiler level as steam bubbles expand, and a near simultaneous increase in firing due to feedforward.
To best of my ancient memories pressure returns in about a minute, with little overshoot as in any well tuned control system.
For the size of the machinery and given its considerable thermal storage it's surprisingly nimble .

The nuke has internal natural feedbacks too
opening throttle valve cools the boiler which cools the water returning to reactor which makes reactor power increase... that takes just a very few seconds.. but the temperature coefficient of reactivity is designed to retain a lot of margin to stability and you'll still have to move rods to settle at the new power.

@anorlunda have you ever done analytical work on control systems that might help Sophie ? I only kept them running , have more of a hands on understanding of them than a theoretical one.
Our fossil gear was pneumatic analog Bailey ... nuke was analog Westinghouse 7100.

Sophie - best i can do is say i think you're looking at several minutes for natural "slew rate"
reduced to somewhat less than a minute by feedforward in the control systems.

old jim

 

[sophiecentaur]

Sophie - best i can do is say i think you're looking at several minutes for natural "slew rate"
reduced to somewhat less than a minute by feedforward in the control systems.

Thanks. That is ball park enough to make me think I have a better grasp than I started with. That could account for a fair few MWh of 'slop'.

 

[jim hardy]

I should know the heat capacity of the plant
but it's one of those numbers that just slipped away with twenty years of non-use.

That could account for a fair few MWh of 'slop'.

Slop ?

A MWh being ~3.4 million BTU... the heat stored by 3.4 degreeF in just 120,000 gallons of water...
Sounds reasonable enough !

 

[sophiecentaur]

I should know the heat capacity of the plant
but it's one of those numbers that just slipped away with twenty years of non-use.
A MWh being ~3.4 million BTU... the heat stored by 3.4 degreeF in just 120,000 gallons of water...
Sounds reasonable enough !

I guess my appreciation of the significance of 'Quantities' in Power Engineering is adrift somewhat! That amount would certainly help me with my Electricity Bill - but I am just an individual.
A point I made, earlier on, about the resulting change in Volts for the other consumers when a load comes or goes, wasn't picked up but that really must be relevant. The system has a vast 'smoothing capacity' hanging on it, in the form of all the other consumers.
My concern was about a single power station problems. But that is not relevant to running a whole network.

 

[anorlunda]

The system has a vast 'smoothing capacity' hanging on it, in the form of all the other consumers.

You can monitor the net effects of smoothing (including voltage effects) and if the ability of power plants to respond in your own home. Just sample and display frequency.

If you don't want to do it at home, there are Web sites that let you do it. I'll bet that Jim could find such a site for us.

I'll give you a magic number 1/8. Take the instantaneous unbalance between grid generation and load (including any effects of voltage), multiply by 1/8 and you get rate of change of frequency. Express power as percent of the total capacity (not current load but rated capacity) of all generators on the grid. Expressed frequency as percent.

Suppose we had a grid with 100GW of capacity online and a base frequency of 50 hertz, then an unbalance of 1GW will cause 1/8 %/second or 1/16 hertz /second rate of change of frequency.

Working backward, watching frequency in real time, differentiate and multiply by 8 and you can observe the real time unbalance in the grid. You should see that typical unbalance is on the order of .005% on a big grid.

On small grids, such as on a self sufficient island, it is much worse. I vacationed once on Grand Canary, and I could hear the refrigerator motor speed changing up and down.

Sophie, is the UK synchronized to Europe?

Watch frequency long enough an you will see a major event like a 1GW plant tripping. Correlate that with news reports, and you can learn which plant tripped.

p.s. The magic number 8 has to do with the inertia of turbine-generators.

 

[sophiecentaur]

Sophie, is the UK synchronized to Europe?

I can answer that one. No. We have a HV DC link with France. I think, in UK, we import more than we export, but I could be wrong.
UK doesn't count as a "self sufficient island" with those sorts of problems. haha

 

[Jeff Rosenbury]

Who's who in European grids.

The UK is connected to Ireland. Parts of North Africa are connected to Europe.

 

[jim hardy]

I'll bet that Jim could find such a site for us.

Here's one, it's part of that fnet link from post #26
i have never watched it before , at first glance it looks a little crude.
http://powerit.utk.edu/worldmap/

The US one i enjoy and watch often.
http://fnetpublic.utk.edu/anglecontour.html

here's their homepage i'll look tonight for more links..
http://powerit.utk.edu/fnet.html

Surely some European universities are doing the same thing.

 

[anorlunda]

Thanks Jim.

I found this video on one of the links you gave. It animates a mega frequency event. Cool.

 

[sophiecentaur]

This made me think. The KE of the rotors can be expressed as a source of instantaneous power, to deal with the changes in load. That could tell you what sort of frequency change to expect before the fuel supply adjustment has time to chase the load change. Or you could work backwards, perhaps.
About 50 years ago, I remember, at a steam rally (traction engines and static ), the commentator referred to the 'instantaneous power' available from the flywheel of a steam ploughing engine. It struck me, at the time as a bit 'vague' but he reckoned he knew what he meant.

 

[jim hardy]

The KE of the rotors can be expressed as a source of instantaneous power, to deal with the changes in load. That could tell you w

That number is a basic machine constant , it enters into Anorlunda's system stability calculations..
Recall from Anorlunda that angular displacement down a wire determines power flow
so we have rotating inertia of a machine coupled by the electrical analogy of a torsional spring to an electrically immovable object(called infinite bus)via the grid...
That rotating inertia through the torsional spring against the grid is a spring-mass system capable of harmonic motion .
A typical natural frequency for it is 1 hz. It's fairly well damped by amortisseur windings on the generator.

The motors in your airconditioner and fridge also have rotating inertia.
So the grid looks stationary, its wires and poles don't move but to me it is a very dynamic living thing. Every wire is transmitting energy in some direction just as if it were a spinning driveshaft on bearings.

Power side of EE is far from boring .

 

[jim hardy]

I found this video on one of the links you gave. It animates a mega frequency event. Cool.

Wow i didnt know about those.

My friends told me about this one. A line near Miami got switched out by accidental relay actuation during maintenance

you can see the adjacent regions speed up when Miami quit accepting power from them
and the transient went clear up to the Great Lakes.We had no such instrumentation in my day - somebody from each plant took our charts to the main office where system guys compared them by hand and magnifying glass.

Cool !

 

[johnbbahm]

There are some economic activities that thrive on cheap power. Making aluminum is an example. I could easily foresee industrial plants designed to take up the slack.

Another option is energy storage. There are several competing technologies being developed, plus some old fashioned hydo projects. Pump the water uphill when power is cheap and generate peaking power when it's expensive. Still, none of these solutions are inexpensive or likely to get that way soon.

I was thinking about refineries using the surplus to make fuel from water, and atmospheric CO2.
Once the energy is stored as fuel, it has a long and very practicable shelve life.

 

[sophiecentaur]

I was thinking about refineries using the surplus to make fuel from water, and atmospheric CO2.
Once the energy is stored as fuel, it has a long and very practicable shelve life.

On the face of it, it sounds like a good idea. What is the conversion efficiency, I wonder?

 

[johnbbahm]

From what I can tell, Audi say about 70%,
http://news.nationalgeographic.com/energy/2015/04/150428-audi-ediesel-made-from-water-air/
"Audi says the efficiency of the overall process is “very high”—about 70 percent"
I think the best and the brightest petroleum engineers might be able to make additional improvements.
From what i have read, the process is very similar Olefin processing.

 

[anorlunda]

From what I can tell, Audi say about 70%,
http://news.nationalgeographic.com/energy/2015/04/150428-audi-ediesel-made-from-water-air/
"Audi says the efficiency of the overall process is “very high”—about 70 percent"
I think the best and the brightest petroleum engineers might be able to make additional improvements.
From what i have read, the process is very similar Olefin processing.

That is what they claim, but color me skeptical. If that was true then they have the solution to climate change. Just run that process with non carbon electricity and remove all excess CO2 from the atmosphere. I don't believe it.

 

[johnbbahm]

The Naval research labs are looking at the same process to make jet fuel for aircraft carriers.
http://www.nrl.navy.mil/media/news-releases/2012/fueling-the-fleet-navy-looks-to-the-seas
I think they hit a snag about the fuel was not flight certified.
Then they were saying 60%.
I think it would be a good way to store surplus alternative energy.

 

[sophiecentaur]

I think it would be a good way to store surplus alternative energy.

If it could be done on a small scale (shoebox size) then it could be an addition to the Hybrid Vehicle.
[Edit - actually that's a bit daft, isn't it? Except for regen braking. Change that to 'in the home' and it could make sense.]

 

[johnbbahm]

One of the first articles I saw on this, was from Germany,
they were thinking of an outdoor air conditioner size unit,
to convert summer surplus photovoltaic electricity to natural gas, for winter heating.
The gas would be stored in the
natural gas grid. The is not really a price performer at the current price of natural gas.
At roughly 55 Kwh per gallon of gasoline, I am thinking it is something that needs a bigger scale.