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70sbudgie

The total network was designed to have generation connected at the transmission level. As it is rotating generators that contribute the most inertia, the transmission system was designed to operate with high levels of inertia. Transformers (and to a lesser extent cables and switchgear) absorb that inertia, so the distribution network was designed to operate with relatively low inertia. 

With smaller proportions of the total generation capacity connected to the transmission network, the low levels of inertia are causing the network to not operate as it was designed to. Inversely, at the distribution level, the higher levels of inertia are having an impact - but in a different way. Network operators are required to limit the impact of inertia on end users (the socket in your lounge for example) to within specified limits - for safety. But with fewer transformers between the end user and where the inertia is input into the electricity network, this becomes increasingly difficult. 

Artificial inertia at the transmission level just increases the total inertia of the system without taking into account how much is already in the system, downstream.

ABrass

70sbudgie said:

The total network was designed to have generation connected at the transmission level. As it is rotating generators that contribute the most inertia, the transmission system was designed to operate with high levels of inertia. Transformers (and to a lesser extent cables and switchgear) absorb that inertia, so the distribution network was designed to operate with relatively low inertia. 

With smaller proportions of the total generation capacity connected to the transmission network, the low levels of inertia are causing the network to not operate as it was designed to. Inversely, at the distribution level, the higher levels of inertia are having an impact - but in a different way. Network operators are required to limit the impact of inertia on end users (the socket in your lounge for example) to within specified limits - for safety. But with fewer transformers between the end user and where the inertia is input into the electricity network, this becomes increasingly difficult. 

Artificial inertia at the transmission level just increases the total inertia of the system without taking into account how much is already in the system, downstream.

It's always hard to tell the difference between someone who knows what they're talking about but communicating badly and someone who doesn't understand the topic.

You seem to be saying that MCS systems have significant inertia, which afaik they don't. They're designed to conform to the current frequency, never to work against it.

Inertia has always historically been a byproduct of the mass of generation equipment. Literal inertia of spinning turbines minimising out fluctuations in frequency as the changes try to accelerate or decelerate the spinning mass, which in turn stabilises the frequency. It was never a design feature because before things were connected to the grid by HVDC there was nothing else.

zeupater

ABrass said:

[...]

You seem to be saying that MCS systems have significant inertia, which afaik they don't. They're designed to conform to the current frequency, never to work against it.

Inertia has always historically been a byproduct of the mass of generation equipment. Literal inertia of spinning turbines minimising out fluctuations in frequency as the changes try to accelerate or decelerate the spinning mass, which in turn stabilises the frequency. It was never a design feature because before things were connected to the grid by HVDC there was nothing else.

Hi

Pretty much sums up what I was just about to post ..

... grid connected microgeneration follows & matches frequency (whatever it is) and when it moves outside set criteria the inverter is mandated to disconnect. 

... grid wasn't 'designed' to have frequency inertia (inertia=resistance to change!), it's simply a historical 'given' based on available generating technologies, almost exclusively based on mechanical rotation.

HTH - Z

70sbudgie

I'm not talking about micro generation. I don't disagree with either of the statements above. 

I am talking about the wind and solar farms (and more significantly CCGT generators) that connect ~20MW to the electricity network at distribution voltages - 132kV to 11kV that have replaced the 1GW power stations connected at 400kV.

Apologies for not being more clear.

70sbudgie

QrizB said:

To my mind, zeupdater is correct.

@70sbudgie please provide a link to a relaible source that supports your contention that:

70sbudgie said:

Wow, I don't know where to start. But in brief, no it doesn't work like that.

Thank you.

I did miss this, but now I've seen it, I'm not avoiding responding. Just thinking what a suitable link might be...

70sbudgie

Appreciate it doesn't cover everything, but does this link explain it better than me?
https://www.nationalgrideso.com/electricity-explained/how-do-we-balance-grid/what-inertia

Also, this is a capacity map from one of the DNOs showing where it is still possible to connect power stations to their distribution network... (You might need to click a couple times to view the image)
https://www.westernpower.co.uk/our-network/network-capacity-map/

zeupater

70sbudgie said:

Appreciate it doesn't cover everything, but does this link explain it better than me?
https://www.nationalgrideso.com/electricity-explained/how-do-we-balance-grid/what-inertia

Also, this is a capacity map from one of the DNOs showing where it is still possible to connect power stations to their distribution network... (You might need to click a couple times to view the image)
https://www.westernpower.co.uk/our-network/network-capacity-map/

Hi

1 - Inertia Link ... pretty much sums up what I and others posted then ...

2 - Capacity Map ... Looks to portray both supply & demand balance by substation/area highlighting not only where new generating capacity opportunities currently exist (without network upgrades), but also where housing/industrial/commercial development could be targetted within current network capacity ... it's probably based on the data resource that DNOs utilise to check for domestic >16A (~3.6kWp) microgeneration installation pre-approval & commercial >16A/phase installation pre-approval ... of course, some of the larger substations close to demand sources would be suitable to connect solar farms etc with little modification expense, but in context the 5-10MWp generation at full tilt is just about 1500-3000 kettles, however, a couple of the PV farms within walking distance from where I'm sitting now have battery capacity to shift supply timing & enhance investment returns ... it's likely that this capacity will also be made available as a resource to reinforce supply stability at some time in the future ... nothing really to do with inertia services then ...      

Considering comments made, it's probably beneficial to next research the effect of transformers on frequency as this is the subject at hand (re:inertia)  >> hint, there isn't any, they just maintain frequency at differing voltages & add to network losses (heat/noise) and therefore act as a a background load .... however, don't just accept the ramblings of some random profile on a forum, spend some time on a trusted source & check for yourself!

HTH - Z

70sbudgie

zeupater said:

70sbudgie said:

Appreciate it doesn't cover everything, but does this link explain it better than me?
https://www.nationalgrideso.com/electricity-explained/how-do-we-balance-grid/what-inertia

Also, this is a capacity map from one of the DNOs showing where it is still possible to connect power stations to their distribution network... (You might need to click a couple times to view the image)
https://www.westernpower.co.uk/our-network/network-capacity

Considering comments made, it's probably beneficial to next research the effect of transformers on frequency as this is the subject at hand (re:inertia)  >> hint, there isn't any, they just maintain frequency at differing voltages & add to network losses (heat/noise) and therefore act as a a background load .... however, don't just accept the ramblings of some random profile on a forum, spend some time on a trusted source & check for yourself!

HTH - Z

I'm not sure if this is aimed at me or others!

Inertia impacts on the network in more ways than just the frequency. I am not disagreeing with any of your comments, but they seem to be viewing inertia from a fairly narrow perspective. And that's kind of the point of my original comment - if inertia is viewed only as affecting one aspect of the transmission network, the repercussions of fixing that issue rather than looking at the system as a whole could be very widespread (and disastrous, though that is possibly too strong a word).

Martyn1981

70sbudgie said:

Martyn1981 said:

Not my area of expertise (like most others), but I believe this is important news. If battery storage can offer frequency services, then the fear of losing steam turbines (whose enormous mass provides inertia) may wane a bit. So another positive step in the direction of 100% viable RE generation in the future.

World 1st: Tesla Batteries Providing Inertia Services At Scale

I’ll let the UK’s National Grid ESO explain:

“Many generators producing electricity for the grid have spinning parts — they rotate at the right frequency to help balance supply and demand and can spin faster or slower if needed.

“The kinetic energy ‘stored’ in these spinning parts is our system inertia. If there’s a sudden change in system frequency, these parts will carry on spinning — even if the generator itself has lost power — and slow down that change (what we call the rate of change of frequency) while our control room restores balance.

“Inertia behaves a bit like the shock absorbers in your car’s suspension, which dampen the effect of a sudden bump in the road and keep your car stable and moving forward.”

Tesla’s “Big Battery” in South Australia got approval from the Australian Energy Market Operator to provide inertia services for the National Electricity Market in Australia. Neoen, which owns and operates the 150 MW/193.5MWh Hornsdale battery (aka Hornsdale Power Reserve), claims that this is the first large-scale battery providing inertia services in the world. The Big Battery is able to provide ~2,000 “megawatt seconds” (MWs) of an inertia equivalency to help keep the grid stable. It does so via Tesla’s Virtual Machine Mode service.

Most of us don’t know anything about megawatt seconds. How much is this Big Battery helping by getting into the inertia services business in South Australia? According to Neoen, it will be able to provide ~15% of South Australia’s inertia shortfall.

Imho, we have a completely different problem in the UK. We haven't just got rid of the large power stations, we've replaced them with smaller power stations connected to a different section of the network. So the transmission network may be struggling with low inertia, but the distribution network is also struggling with excessive inertia. Fixing the problem of low inertia at transmission level by adding "artificial" inertia, will severely exacerbate the issue of excess at distribution level. The whole network needs a holistic approach to finding a solution.  In my opinion.

There is only so much that can be squeezed out of the 1960s design.

Hiya, I've been pondering this last night and this morning, and had some thoughts, though I now see others have raised similar.

Can I just point out that the inertia is needed to stop the frequency dropping too fast when additional demand is added, or some supply unexpectedly drops out.

The batteries, as I understand it, (and I'm sorry if I've got it wrong, I'm just a fun follower of these issues) don't add inertia to the network, but they can 'fake' it by adding additional supply (or removing some) in milliseconds, thus acting like steam turbine inertia, in that they prevent a rapid fluctuation in frequency.

If that's close to correct, then I assume (sorry, I know that's risky) that batteries can also do the same on the distribution network, which includes reducing too much inertia, if you are correct that more is being added.


This may be related, or complete nonsense, but hopefully a pleasant coincidence - I had a chat with an engineer 10days ago at the Ripple windfarm open day. They explained that their WT doesn't use mechanical parts, such as a gearbox, but instead is electrically controlled. So the WT creates AC via the spinning magnet mounted on the hub behind the blades, to the nacelle. This travels down the tower to a rectifier (I think that was the term) where it's changed to DC, then inverters change it back to AC at the required voltage and frequency.

Based on that I asked if they could offer frequency services, since the inverter tracks to the network. He said that theirs doesn't, but for electrically controlled WT's on a larger windfarm (no mechanical gearboxes), then it is a potential service.

If it's relevant, then about 30m away from the WT was a small DNO substation, perhaps 4mx3mx2.5m.

thevilla

I suppose what 70sbudgie could be suggesting is if a 'remote' bit of grid has higher inertia than the whole and a failure occurs then it could achieve frequency separation from the grid?  A breach in the space time compendium

Or not.