Quelle: eandt.theiet.org
Today’s electricity infrastructure, driven by commercial forces, will find it hard to cope when things go seriously wrong.
Even in industrialised nations in the 21st century, the sort of electricity-grid system failure that’s been seen in parts of Australia in recent years is not uncommon. In the UK, the risk of total blackout or significant partial shutdown of the transmission network is increasing.
The rise in renewables is making failure more probable. Wind farm growth creates frequency-management issues arising from reduced system inertia, while declining network strength can cause longer, stability-risking, fault-clearance times. Then there are the challenges to match supply to demand following sudden variations in wind generation and the reduced one-hour notice of input variations from European interconnectors. Other risk factors include grid substation failure, lightning or overhead line faults and cyber attack.
For grid recovery following widespread collapse, a process known as ‘black starting’ is deployed where the UK is split into different areas. Being able to rapidly black-start the country is a public health priority and, rightly, a public expectation, but in Scotland, and probably London, it is unrealisable; it would take several days to re-establish networks. So serious has the issue become that I understand it has attracted the attention of the government’s Cobra civil contingencies committee.
Professional expectation for Scotland to black-start has now, I’ve been told, risen to five days, largely as a result of large-scale, dispatchable, on-demand generation being replaced with intermittent distributed renewables. London has experienced a similar progressive local reduction and will also take longer to recharge since much of its high-voltage grid uses cable and not overhead line transmission.
The Scottish Black Start Restoration Working Group reviewed its procedures in September 2018. These are based on local joint restoration plans that would see transmission operators powering up and stabilising local transmission islands, which would then have to be synchronised and progressively interconnected.
The group’s report warns that, following the 2016 closure of the Longannet coal-fired power station in Fife, there would be ‘severe delays’ to restoration. Peterhead gas-fired station, now Scotland’s only high-powered and high-inertia (essential to stabilise frequency) dispatchable power station, is seeking planning permission to install 31 diesel generators, capable of full power for seven days, to secure its restart. However, it has only half the capacity of Longannet and couldn’t restart all of Scotland without input from the pumped-storage capacity at Cruachan and Foyers and, crucially, from England, which arrangement is untested.
Nor would wind farms be able to black-start the grid. Main generator types in use need external power to start generating; some more recent designs are self-starting, but connecting to a dead grid via long offshore AC cable interconnections remains an unsolved problem as the turbines cannot provide enough reactive power to recharge what are, in effect, large capacitors. In any case, they wouldn’t be able to meet National Grid requirements for block loading, grid voltage or frequency control.
The first local joint grid-restoration activity is to disconnect all offshore generation. Onshore wind farms can be progressively reintroduced once the grid has been re-established, but only providing they are not frozen and there is wind. As with all nuclear stations, Scotland’s Hunterston and Torness could only be reconnected into a stable grid, this taking several days.
The new £2.4bn HVDC interlinks from Wales to the Hunterston area and from Moray Firth to Spittal have not been engineered to support black start as they do not include the latest voltage source converter (VSC) technology and cannot commutate into a dead network. Scotland is now literally at the end of the line and critical restart power would arrive only once the north of England grid had been re-established. Similarly, for London, the two HVDC interconnector links to France and the Netherlands cannot support black start.
National Grid confirmed in 2016 that the restoration strategy “must be adjusted” as “system strength and the number of black-start providers declines” and that black-start costs are “anticipated to increase by a 7-10 factor” over the next 10 years. While, like Ofgem, it favours the provision of up to seven new VSC interconnectors between Britain and the European mainland, these are not yet built and power availability from them would depend on market conditions. The UK is a net importer of electricity. And then there is Brexit…
The situation is clearly untenable. It exemplifies the need for proper governance of the UK electricity system to replace the present disparate, profit-driven weakening of the grid that ‘the market’ has caused.
Several of the engineering institutions are advocating change, including the IET, the IMechE and the Institution of Engineers in Scotland. We need to be heard.
David Watson is a chartered electrical engineer who before retirement was manager of projects at Foster Wheeler Energy, based in Glasgow.
Kommentar
Siehe hierzu auch den Beitrag Großbritannien kämpft gegen den Blackout. Das GB-Netz ist zwar mit dem kontinentaleuropäischen Netz per Gleichstromleitungen vernetzt, aber ein Blackout würde sich darüber wahrscheinlich nicht ausbreiten, da dies automatisch nur im Wechselstromnetz passiert. Wobei sich natürlich die Frage stellt, ob der möglicherweise gerade stattfindende Import ausgeglichen werden kann, oder ob es dann auch in GB zu einen Dominoeffekt kommt. Umgekehrt ist die Gefahr geringer, das das europäische Netz deutlich größer ist und die Störung wahrscheinlich kompensieren kann. Zum anderen solle es aber zum Nachdenken anregen, wenn man im deutlich kleineren Netz bereits mit mehreren Tagen Wiederherstellungszeit rechnet. Wobei hier wahrscheinlich im europäischen Verbundsystem aufgrund der noch vorhandenen Großkraftwerke und Netze ein gewisser Vorteil beim Netzwiederaufbau vorhanden ist, wenn einmal wieder eine gewisse Größer des Inselnetzes vorhanden ist. Alles in allem aber leider wenig
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