Is the "Smart" meter role out being done ready for another Winter of discontent.

[ericmark]

How does a micro-generator tell whether the incoming power is from the real mains or from another micro-generator. ?

Maybe ( I don't know ) the real mains has a high frequency marker signal added to it and if this marker is not there then the micro-generator will shut down,

This is the big problem, any coil of wire will turn simulated sine wave into a more conventional sine wave, so if the output supplies a transformer it knocks off the corners, so there are three methods to switch off the grid tie inverter, under voltage, over voltage or not 50 Hz.

But there must be a delay between switching off and switching back on again, or a street with 30 grid tie inverters could keep each other going.

This in the main means a manual reset, the same with EV chargers, often a manual reset is required, so a short brown out can have a knock on effect, which can go either way, reducing or increasing load.

It is rare to have power cuts two days on the run, at least where I live, so as long as the EV has enough capacity for 2 days running there is not a problem.

However the milkman across the road to where I use to live had a Renault kangoo van, which had a charging rate of 3.5 kW later versions were 7 kW, and a range of 120 miles, his mile round I think he said was 64 miles, so he expected no problems, and due to carrying milk the heater was rarely used, only used to demist, so there should have been no problems, however there was, if there was a brown out he was unaware of the charging being stopped, so would get up to a vehicle not fully charged.

I thought charge points like the one at work would charge an EV at 22 kW, but it seems many can't use 3 phase or DC and even on single phase some are only 3.5 kW clearly designed for Europe with 16 amp outlets, and some granny leads only 2 kW.

The early versions had a 22 kWh battery, even that small at 3.5 kW it takes around 7 hours to fully charge, which normally should be enough, but since we sleep for around 8 hours, very easy not to realise the charger needs resetting.

 

[Adam_151]

How does a micro-generator tell whether the incoming power is from the real mains or from another micro-generator. ?

A lot of the time its done on frequency change. An islanded network of micrognerators will be more volitile in terms of frequency than the public supply as loading changed, looking at the rate of change of frequency against time can be telling, and the ROCOF relay is configured to pre-decided limits, theres also vector shift as well as a few other systems that appear to have been proposed but not adopted

 

[Mike13]

There are autochanging taps on the distribution transformers to allow for changes of load, and hence can change the direction of net current on the grid.

 

[ericmark]

There are autochanging taps on the distribution transformers to allow for changes of load, and hence can change the direction of net current on the grid.

Showing my age, never worked with high voltage in the UK, have worked with 10 kV and 11 kV in Hong Kong, and 3.3 kV on the Falklands, but not auto tapping on what I worked on, so was unaware it existed.

 

[JohnW2]

Showing my age, never worked with high voltage in the UK, have worked with 10 kV and 11 kV in Hong Kong, and 3.3 kV on the Falklands, but not auto tapping on what I worked on, so was unaware it existed.

I don't know what happens in practice, but I would have thought that there has to be some such tap changing since, without it, it would presumably be impossible to supply a significant number of installations without the nearest going above 253V or the furthest under 216.2V at some times?

Kind Regards, John

 

[Harry Bloomfield]

I don't know what happens in practice, but I would have thought that there has to be some such tap changing since, without it, it would presumably be impossible to supply a significant number of installations without the nearest going above 253V or the furthest under 216.2V at some times?

Some are manual, some are voltage sensing and automatic. I remember one job I was involved with, where a tractor factory close to the source was fed first, then my pumping station 3/4 of a mile further beyond, with four very large motors installed in it. As the factory fired up, it would pull the voltage way down my motors. It remained low during the working day, so a tap changing compromise had to be arranged as a short term fix. Long term, they agreed to a new separate feed.

 

[JohnW2]

Some are manual, some are voltage sensing and automatic.

What do you mean by 'manual'? I presume you must be talking about 'remotely operable', since there's no way they could send human being out, probably at least twice every day, to change the taps on every transformer in the country?

Kind regards, John

 

[Harry Bloomfield]

What do you mean by 'manual'? I presume you must be talking about 'remotely operable', since there's no way they could send human being out, probably at least twice every day, to change the taps on every transformer in the country?

Kind regards, John

Fixed tappings, where they set and forget, unless they need further tweaking later.

 

[AdrianUK]

As far as I'm aware there are no auto-tap changes on the 11kV transformers in the UK. Its 33kV and above.

Most distribution transformers are set (using manual off load changes) to have a secondary voltage of 433V off load

 

[JohnW2]

Fixed tappings, where they set and forget, unless they need further tweaking later.

That used to be my understanding. However, as I recently wrote, when I thought about it, I found it hard to see how, without tap changing (somewhere, not necessarily at the HV->LV transformer) they can maintain supply voltages within the 'permitted range' throughout the day/night, if there is an appreciable number of installations fed by the same cable. Am I missing something?

Kind Regards, John

 

[SimonH2]

However, as I said, I would not think that we are yet anywhere near the point at which the amount of microgeneration represents a problem for the current distribution network, would you/

We reached that point many years ago.
Historically, the DNO would set the taps to run the network at the highest voltage they could while staying in spec - higher voltage, lower current, lower I²R losses. That's fine when you have a unidirectional power flow and a general understanding of the loads.
As embedded generation has increased, it's changed the assumptions about voltage drops. If you think about it, it doesn't take many houses with (say) 4kW PV installs to completely reverse the power flow in part of the network during sunny weather.

Take the case where the micro-generation in an area is producing just enough to supply all the local requirement with no power flowing in or out of the local substation / transformer. Then ( in theory at least ) that local supply network could be disconnected from the zero loaded substation / transformer without any affect on the micro-generators in the area. Each micro-generator would continue to "see" a 50Hz supply of the correct voltage and hence continue to micro-generate,

In reality, the chances of getting load to match supply is nil. Any imbalance will cause a rapid change in voltage and a variation in frequency that will trip the mandatory anti-islanding protection in all the inverters. The scenario you describe is a serious concern, which is why it's not permitted to happen.
There are many ways to detect islanded operation, ROCOF (rate of change of frequency) is one, but not all that reliable I believe. I've seen, but not understood, papers describing some fancy maths that some units use.

There are autochanging taps on the distribution transformers to allow for changes of load, and hence can change the direction of net current on the grid.

I was under the impression that the DNOs don't change taps more than they have to - and it's a manual (even if remotely performed) operation. I do however know that our local DNO has been running some trials a few years back on sensing end-user voltages at points in the network and feeding that back into network ops - a relative working for then once asked if anything showed up on my logs (I was graphing, amongst other things, voltage from our UPS at work), and I could see a period when the voltage had changed as though a tap had been changed. I think in part this research was looking into ways of temporarily changing demand by altering supply voltage.


But back to the original question.
Yes, as already stated, the isolation switch is a mandatory part of ever smart meter - so yes they could implement a more finely grained version of the 1970s rolling blackouts. I was at school then, and I recall noting the schedule posted up in the local electricity board showroom window.
In practice though, the idea is that such action would be a last resort - having applied price pressure first. Basically, the IHD (in home display) will turn red to indicate that temporary price increases are being applied - and then users can go round turning off stuff to save themselves money. But since the average TTD (time to drawer, yes that's a real thing !) for IHDs is apparently only a few weeks, I don't see that working very well.

 

[ericmark]

In my last home, the voltage was always around the 245 mark, and the old 65 watt fluorescent fitting worked fine with a 58 watt thin tube, then we saw a load of solar panels being fitted, and the voltage over night seemed to drop to 230 volt, not much of a drop, but enough for the old fluorescent light to regularly fail to start. I changed it for a LED tube and removed the ballast.

In this home, I have not got a smart meter, and I only have a 60 amp supply, there is no mains gas, central heating is oil fired, I have got an open grate, so could burn wood, clearly not coal, as can't get coal any more, our local train service is trying to use compressed coal dust briskets, but they are not working out very well, the carriages are covered with dust from the new fuel, and the trains are often late where they have had to stop to build up the fire and get more steam pressure.

I well remember the Winter of discontent, as our new house had gas hot air central heating which needed electric to work, so no electric meant no heating, but at that time most people still had coke fires, cheap coke was sold off by the steel works, as they could only use big lumps, so most homes has coke fires, however the steel works no longer has open hearth, so no coke ovens, and the replacement smokeless fuel is very expensive, there are some who use wood, but to use wood or coal without particular emissions needs a rather expensive set up, so many have capped their chimneys and blocked up their fire places, ours still can be used, but I have very little stock of wood, the chimney is used for the AC in the summer, and it is capped off in winter.

So the open fire is really only any good for emergency use, if everyone started using their fires to burn wood, we would get smog again, and a massive shortage of wood.

So only real option if we got power cuts would be a generator to run the oil boiler, hard luck if anyone has a heat pump.

 

[JohnW2]

We reached that point many years ago. ....
Historically, the DNO would set the taps to run the network at the highest voltage they could while staying in spec - higher voltage, lower current, lower I²R losses. That's fine when you have a unidirectional power flow and a general understanding of the loads.
As embedded generation has increased, it's changed the assumptions about voltage drops. If you think about it, it doesn't take many houses with (say) 4kW PV installs to completely reverse the power flow in part of the network during sunny weather.

That's a good and valid point, but rather different from what I was responding to with my comment which was a suggestion that "the National Grid did not have the capacity to handle lots of local microgeneration'.

In terms of your point, I don't think it's quite as bad as you suggest, since an appreciable proportion of locally-generated power will not 'go back to the transformer' (and hence into the HV network), creating a 'negative VD' on its way, but, rather, will go to those consumers in the local LV network who do not have their own generation - and ('on average') something like half of that proportion will travel 'downstream', not 'upstream', and hence will result in VD 'in the same direction' as that deriving from grid-supplied power.

Kind Regards, John

 

[Diver Fred]

TTD (time to drawer, yes that's a real thing !) for IHDs is apparently only a few weeks,

TTD - time to Dustbin! In my household - under 30 seconds, in fact before the fitter had left the premises!

 

[ericmark]

Well looking at the adverts once I get a smart meter I will be able to turn lights on and off by clapping my hands, at the moment I have to say hey google turn on landing lights, but can't see how clapping hands is an improvement, how does it know which to turn on/off?

OK I know Freddy Boswell look alike is just a daft advert, and we will not turn lights on and off by clapping hands, but really can't see how smart meters help the consumer? Will find out soon, was to be completed by 2022 so not long left before they force me to have one fitted.

My father-in-law had one, and we tried to get it so we could seen what was going on, as to see 3 kW used for 3 minutes likely means he is making a cup of coffee so is OK, but the attempt failed, we never were able to monitor his use of electric.