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Mains frequency in different locations of the country?

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Hi, I am looking at a circuit for monitoring the frequency of the mains electricity grid in the UK - 220V 50Hz. I've read that if the grid is under load, the frequency will decrease as the generators effectively slow down. Then they will speed up when there is less load on the grid. My question is will this be a local effect near the load (or generator) or will this be 'seen' on the whole grid (instantaneously?)

My basic idea is to charge batteries / use electricity to air condition (heat/cool) when the frequency is above 50Hz (indicating a surplus) and either stop charging or push electricity back onto the grid when the frequency is below 50Hz. Is this the basis of 'smart appliances' - they monitor the frequency and adjust their consumption accordingly?

Thanks,

Jules
 

alec_t

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Welcome to ETO.
My question is will this be a local effect near the load (or generator) or will this be 'seen' on the whole grid (instantaneously?)
It's grid-wide. If it weren't, one part of the grid would be severely out of phase with another part and effectively short-circuit it. BANG!
Is this the basis of 'smart appliances' - they monitor the frequency and adjust their consumption accordingly?
No. Most appliances don't care a fig what the exact frequency is, providing it's within a few Hz of the nominal 50/60Hz.
 

MikeMl

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Thanks Mike, That was lots of info :)

Alec - I understand most appliances are 'dumb' in that most modern goods have a SMPS which immediately converts to 350V DC anyway. What I meant was the newer 'smart' appliances which are designed to talk to a smart meter or some kind of interface to 'know' when electricity will cost more. Electric companies charge more at peak times and less at off-peak times (currently economy 7 or 10 tariffs) but these tariffs are time of day related. I think with smart metering / monitoring of the grid, eventually consumers would be charged more for the 10 minutes everyone puts the kettle on during the adverts between TV shows for instance. If smart appliances 'knew' when the grid is under strain and not turn on it would be easier to balance consumption and generation.
 

kinarfi

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I'm from the USA, our houses are fed with 220 - 240 and grounded at the mid point to give us 120. My question is, in the the UK and other place that use 220, are the mains grounded some where?
 

Nigel Goodwin

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Is this the basis of 'smart appliances' - they monitor the frequency and adjust their consumption accordingly?
No, the electrical system in the UK is excellent, and frequency changes are only very minor - and corrected every night to ensure synchronous clocks stay accurate (or at least it was, I presume it still is?).
 
In that case Nigel, would there be issues with trying to balance the grid based on frequency alone? Or National Grid purposely adjust the frequency overnight to compensate for the slightly below 50Hz during the day, irrespective of actual load / generation?

Is there an easy way to know when the grid is under strain and when it is not?

Simply, at <49.9Hz push power onto the grid from batteries connected to a grid-tie-inverter, do nothing between 49.91Hz and 50.09Hz, then charge the batteries when the frequency is above 50.1Hz.

Ultimately, does anyone know how National Grid know when to increase generation or its just a guess?

Thanks,
 

alec_t

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This link may be of interest re frequency deviation.
 

MikeMl

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Thanks Mike, That was lots of info :)

Alec - I understand most appliances are 'dumb' in that most modern goods have a SMPS which immediately converts to 350V DC anyway. What I meant was the newer 'smart' appliances which are designed to talk to a smart meter or some kind of interface to 'know' when electricity will cost more. Electric companies charge more at peak times and less at off-peak times (currently economy 7 or 10 tariffs) but these tariffs are time of day related. I think with smart metering / monitoring of the grid, eventually consumers would be charged more for the 10 minutes everyone puts the kettle on during the adverts between TV shows for instance. If smart appliances 'knew' when the grid is under strain and not turn on it would be easier to balance consumption and generation.
They have been doing this in the US for years, but only for items that produce a large draw. For example, deep-well irrigation pumps (several hundred HP) and house and industrial AC units have radio-remote-control-receivers (pre-internet-tied-devices) where the power company can send out a command to drop these off-line for up to several tens of minutes to level peak demand. As a homeowner, you can get a slight reduction in your electric rate if you allow the power company to install said box. Nowadays, the idea is expanded to include internet-controlled smart devices, like electric water heaters, heating, airconditioning. I would think it is not worth screwing with things that draw a few hundred Watts or less...
 

audioguru

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This is a big world with many differences. I think there are places where AC electricity is produced by donkeys or elephants walking in a circle and turning the alternator without much care for frequency, or an alternator on a paddle wheel in a river.
 

tcmtech

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Simply, at <49.9Hz push power onto the grid from batteries connected to a grid-tie-inverter, do nothing between 49.91Hz and 50.09Hz, then charge the batteries when the frequency is above 50.1Hz.
And you figure you gain what from doing this?

Are you getting paid to do it?

Is your few hundred watts going back really helping stabilize the terawatt plus European electrical network regarding the few hundredths of a Hertz down drift that happens at peak loads? o_O
 
I realise it's a drop in the ocean, but I'm thinking proof of concept. I think we need more renewable energy sources which I know are intermittent and that's an argument against them. But if we can get a hell of a lot of renewable, all we need to do is store it for the dips and even it out.
 

tcmtech

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all we need to do is store it for the dips and even it out.
...........:facepalm:

There is so very much more to how a electrical grid system works than that.

That and obviously if your line voltage is not dropping severely below the standard spec the system is working just as it is suposed to.
Simply put, a tew hundredths of a HZ frequency drift up of down during the day is not a major issue. Losing 20+% or substantially more of your line voltage or having outright rolling blackouts for extended periods is. If you are not experiencing the second effect on a regular basic obviously the utility power people have their stuff working well within in its limits.

Theres nothing wrong with AE though. I've played around with it all my life and still do. I have no intention of trying to use it to fix a probe that not the though. The only problem I put it towards is cutting my own purchased energy bill down. The rest of the world can fend for itself until they start paying me to solve their perceived problems.

If you haven't already, check out this sites Renewable and AE section. I've put a lot of my personal experiences on working with it there including DIY Grid Tie Inverter design. ;)
 

kinarfi

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Thanks Nigel, I thought it would be, now I know, how do they do 3 phase, Y connected with 220 per phase I would guess.
 

Nigel Goodwin

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Thanks Nigel, I thought it would be, now I know, how do they do 3 phase, Y connected with 220 per phase I would guess.
Yes, except the UK is 240V, not 22oV.

Essentially everything is three phase here, with three phase down every street - it's how it's connected that makes it single phase.

Each house receives a connection from the neutral, and a connection from one of the lives - giving 240V single phase. Alternate houses are connected to different phases, so as to balance the load evenly - this allows the use of a thinner neutral wire, as most of the current goes down the three live wires. So in the case of a single live failure every third house would lose power :D
 

tcmtech

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Each house receives a connection from the neutral, and a connection from one of the lives - giving 240V single phase. Alternate houses are connected to different phases, so as to balance the load evenly - this allows the use of a thinner neutral wire, as most of the current goes down the three live wires. So in the case of a single live failure every third house would lose power :D
Sounds efficient but when someone rips the neutral line off a pole someplace nearby for that feeder set everyone's lights and electronics go POP shortly after! :oops:
 

MikeMl

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Sounds efficient but when someone rips the neutral line off a pole someplace nearby for that feeder set everyone's lights and electronics go POP shortly after! :oops:
Not much different if you lose the Neutral connection in your own panel on the US or CAN 240V center-tapped system...
 

Diver300

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I've seen instances of every 3rd house loosing power, and I've heard of overvoltage from loss of neutral, but that is very rare.

On the frequency issue, the whole of the UK is synchronised, but not with mainland Europe. The links between the two are DC. I understand that the grid in mainland USA is in three sections.

The frequency does slow in times of high demand, and it is increased overnight to catch up. That is for synchronous motor clocks, of which there are millions, even if fewer than there used to be. For most of those, loosing a minute or so during the day doesn't matter if they catch up at night.

I did some work on this http://www.ast.cam.ac.uk/about/36-inch.telescope a few years ago.

It has an 80 W synchronous motor to hold it pointing at the same star as the earth rotates. Unfortunately, the mains frequency is often high at night when the speed control is needed. Also there is a lens effect of the atmosphere, so the desired speed is slightly lower than 50 Hz, about 49.98 Hz, so a frequency adjustment is needed.
 

tcmtech

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On the frequency issue, the whole of the UK is synchronised, but not with mainland Europe. The links between the two are DC. I understand that the grid in mainland USA is in three sections.
Yep.
Surprisingly I didn't know that until just a few years ago. I thought we were all one system from coast to coast. :oops:
 
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