Fragile grids
Over a million people customers lost power in the UK yesterday thanks to the sudden outage of a gas and a wind plant. Some of the country’s biggest railway stations were inoperable. Passengers were stuck on trains for up to seven hours. Others stayed in hotels, walked miles or paid “hundreds” for taxis. The outpatient sections of Ipswich Hospital were blacked out for 15 minutes when backup generators failed. “At the height of the Friday rush hour, all trains out of King’s Cross were suspended and remained so for most of the evening.” — BBC. Commuters resorted to using their phones as torches to get out of tunnels in the dark.
Urgent Investigation called for into “fiasco”
According to headlines, at this early stage before the investigation all we know for sure is that wind power is definitely not to blame, but Boris might be. (Seriously, it’s the no-deal Brexit that hasn’t happened).
Officially, people are saying in solemn knowing tones that it is “extremely rare” for two generators to go out at once. But the odd thing about this is how small the loss was. Barfield Gas power is only a 730 MW generator, and Hornsea Wind “Farm” is, at most, 1.2 GW. The whole UK grid is more in the order of 60-80GW. The word on twitter was that this was only a 1.4MW loss. If so — wow. For some reason this small loss meant the grid frequency fell from the usual 50 Hz to a heartache 48.889 Hz (disastrous in grid terms). At that point, pre-programmed emergency “load shedding” kicked in.
“One source at a local energy network said: “I’ve never heard of anything like this in 20 years.”…” – Financial Times
Hmm. This could be a clue – a storm was sweeping through and wind farms were running full tilt just before things fell apart. Half an hour before the crash the National Grid was bragging about a new wind power record:
At 16 minutes past four on Friday a press officer at National Grid put out a tweet which seemed to signal Britain’s progress towards its much-vaunted zero-carbon economy. The proportion of UK electricity generated by wind power, ‘it boasted, had just reached a record high of 47.6 per cent.
–Ross Clark, Spectator.
With such a high proportion of wind power the system inertia would have been very low, which would mean the system was much less able to adapt to any disruption. (And if that is the case then this is a renewables problem. Too many intermittent generators, not enough spinning reserve). Large baseload turbines have spinning weights in the order of 200 – 600 tons, and they turn at 3,000 rpm. Solar and wind power just can’t provide that stability. Wait and see, but there are similarities with the South Australian blackout of 2016.
UK power cut: National Grid promises to learn lessons from blackout
National Grid has said it will “learn the lessons” after nearly one million people across England and Wales lost power on Friday.
Industry experts said that a gas-fired power station at Little Barford, Bedfordshire, failed at 16:58, followed, two minutes later, by the Hornsea offshore wind farm disconnecting from the grid.
This energy expert is hinting that renewables were to blame:
David Hunter, energy analyst at Schneider Electric, told the BBC … the transition to clean energy may be creating “greater stresses” on the system because energy such as wind power is less effective as a “shock absorber” to shifts in supply and demand.
At Tallblokes, commenter: It doesn’t add up... has the best analysis I’ve seen so far. As far as I can tell, he knows the finer details down to the sixth significant figure plus all the generators, capacities and cables. He blames the wind turbines going out then triggering the gas plant, and is suspicious of the official timings given, pointing out some details were only filed 20 minutes after the event. He makes a good case that it was the lack of grid inertia that meant the small outages were too much for the system. There is simply not enough synchronous generators working (coal, hydro, nuclear and gas).
It doesn’t add up: The extremely rapid initial drop in frequency to below the statutory minimum of 49.5Hz is compatible with the drop in wind generation of about 850MW recorded in grid 5 minute data (although there appear to be timing discrepancies between the frequency and power data – but I would regard the frequency data as conclusive, especially with wind). That is followed by a small bounce as the gird starts to try to recover, before a further smaller collapse in frequency to the nadir at around 48.8Hz, which is entirely consistent with the smaller drop in CCGT output recorded in grid data that suggest that Little Barford was probably operating at about 50% of its 727MW capacity. There is a major grid transmission line that runs from Keadby near Killingholme past Little Barford at St. Neots and on to the transmission ring around the North of London. It is almost certain that this power line was delivering power from the wind farm towards London. When that failed, there would have been a sudden extra demand on Little Barford, which would have caused its frequency to drop and that (if not the already rapid drop in grid frequency) would have tripped it out of operation.
That these disturbances caused such a rapid and severe frequency drop that triggered load shedding is entirely due to the lack of grid inertia caused by the high proportion of generation from wind and solar, which had been running at over 40% most of the day. A 2016 presentation from National Grid has a chart that shows the relationship between the rate of change of frequency that can be expected for different amounts of load loss at different levels of grid inertia: it suggests that they were sailing far too close to the wind. You can think of grid inertia as the flywheel energy stored in the rotating heavy generator turbines.
h/t Tomomason at Tallblokes for the frequency info. h/t Pat for the story. Thanks to “It doesn’t add up” and Tallbloke.