EV Charging Article in E&T Lack of Joined Up Thinking

Thanks for the heads up - very interesting article. He didn't even mention heat pumps, another load to add to the local LV network. The whole smartmeter thing has been a costly disaster so far and as pointed out, useless to the DNO. The aims are good but implementation has been very poor. I thought the units would be able to provide the house with a price for the electric in real time and you could choose what you were prepared to pay e.g. for your car pay anything up to 50% charge, pay up to ££ for rest of charge, pay lowest price possible for charge etc. This could be pre-programmed into the car or the "charger" on the wall (there is an app for that). Presumably other smart devices could be treated accordingly e.g. freezer, heat pump etc.

I can and do meter my electric (not got a company smartmeter) but on it's own it doesn't make one jot of difference to how much power I use. I can schedule a charge period in advance, but have no way of varying the tarrif yet. Hopefully version 3 of these devices will be a bit more advanced, and useful.

I don't know the answer to your question about fuse sizes, but 300A seems more likely based on the size of cables you can see down the average trench (not big).

Unbalance is also an issue with earthing of course, a whole other topic!

I was under the impression that the standard single-phase charging rates for an EV were 7.2kW/32A, 3.6kW/16A, with 2kW/10A for "granny leads" on a 13A socket.

In the long term, with EVs and heat pumps, the solution is to uprate the infrastructure, not getting people to compete as to who is allowed to charge their EV each evening.

This is quite amusing as those of us who have some idea how the network holds together have been saying more or less the same thing (there be trouble ahead) for some time, usually to be described as luddite or naysaying, and referred to such technical gurus as the directors of National Grid saying reassuring things like they are aware of no issue. It is a welcome change to see an article with some numbers in that look about right (round here SSE land, the typical suburban substation is half megawatt with perhaps 70 houses per phase,  so 400A fuses are common.) We may soon be at the stage where some substations and street mains get tested for real. Of course the substation fuse is not the real limiting factor, but the heating of the transformer itself - and with an unbalanced load the two may not coincide.
Longer term it will probably need streets re-wiring, ideally to 3 phase,  or the voltage changing to something higher to retain the same cables.

Demand management is probably not best done over an internet that can be blocked by foreign hackers. A frequency based load shed may be better.
Mike.

Interesting - a lot of goods points there.

Do many DNO cables really have a reduced N? I thought that in modern concentric cables the copper 'armour' would have pretty much the same resistance as one of the line cores - it might have a smaller c.s.a. in some cases but that just balances out the increased resistance of the aluminium cores. All the old PILC cables I've seen looked to have a same-sized core for N, and the sheath/armour originally for PE only - even when converted to PME the original N core is retained in parallel. Were there lots of CONSAC cables with smaller Ns?

The phase imbalance issue/knowing which phase a customer is on ... I wonder if there might be some natural compensation where multicore/ABC cables are used - i.e. if one core is nominally overloaded but other cores are running cool, then heat from the overloaded core would find it easier to escape than if all the other cores were at a similar temperature, so overall temperatures might be still acceptable. e.g. a 185mm2 SWA might be rated at 243A 3-phase, but that goes up to 292A for a similar cable with only 2 loaded cores - so there may be some margins there.

In some ways the EV issue isn't entirely new - we've had areas with lots of electric storage heating for instance - and seem to have managed in the past without a 'booking system'. Overall there will be a considerable amount of natural diversity - not everyone will need to fully charge theor car every night, just like not everyone fills up with petrol every day. On average EVs will need charging less often or for far shorter durations. The actual numbers are still a bit of an unknown though, so certainly still worth keeping in mind until the evidence becomes available.

   - Andy.

Roger B said:

Is the unbalanced phase problem realistic?

Does the 'car to grid' feeding in to the cable and potentially causing an unmonitored overload also apply with other local generation such as solar PV? 

Potentially, if one phase is relatively heavily loaded with little generation, the second phase has little load and no generation, and the third phase is lightly loaded with export exceeding the loading, this will increase the supply Neutral current to a value above the largest line current.

The National Grid are happy with their capacity.  With the decline in heavy industry in the UK, their big HV cables are now running well within their limits.

It's the stuff owned by the DNOs that's the problem.  The street-level transformers feeding the housing estates.

I have a feeling the problem will be a temporary one, EVs being nothing other than a brief flurry before hydrogen takes over.