Ratcliffe Power Station

[Killingworth]

I suspect that the latest batch of coal is being unloaded from the bulk carrier SIVOTA which arrived at Immingham on the 15th, and had departed Newcastle, Australia, on the 26th September, with a call at Rotterdam.

What irony. We used to talk of carrying coals to Newcastle in the days when ship loads of coal sailed from the Tyne to Thames power stations every day - originally carried down to the river on tramways that developed into railways.

 

[dangie]

As you say as the first generation nuclear plants became end-of-life new should have been built with a higher capacity. Hinkley Point C is still years from completion. Are any others actually being constructed?

There is a potential problem with higher output generating units. Nuclear power stations tend to run ‘base load’ meaning they are at full output 24/7 (maintenance shutdowns excepted).

Take for example 4am on a summer morning. National Grid system demand is very low. A major fault occurs on at a nuclear station. A generating unit or even the whole station trips off line. That would cause a massive drop in grid system frequency. This could initiate automatic trips for areas of the country to protect the system. Bigger is not always better.

 

[JamesT]

There is a potential problem with higher output generating units. Nuclear power stations tend to run ‘base load’ meaning they are at full output 24/7 (maintenance shutdowns excepted).

Take for example 4am on a summer morning. National Grid system demand is very low. A major fault occurs on at a nuclear station. A generating unit or even the whole station trips off line. That would cause a massive drop in grid system frequency. This could initiate automatic trips for areas of the country to protect the system. Bigger is not always better.

Even at the low points, demand is of the order of 20-25GW. National Grid is currently setup to handle a whole power plant going offline, the issues we've seen in the past have been when multiple plants went offline at the same time.
But we already have very large plants, Ratcliffe is 2GW in total, Drax is 3.9GW. Those values are for the whole plant, but this is the situation you're postulating. Thermal plants are generally better in these situations as the turbines spin down gradually and still provide power which covers the backup spinning up. (e.g. Dinorwig can start providing 1800MW in 16 seconds)

 

[dangie]

Thermal plants are generally better in these situations as the turbines spin down gradually and still provide power which covers the backup spinning up. (e.g. Dinorwig can start providing 1800MW in 16 seconds)

No they don’t. Most power station turbine generators are 2 pole machines spinning at 3000rpm. This gives us a system frequency of 50htz. This turbine speed is the same whether the unit is generating 1 megawatt or 500 megawatt, it’s the amount of steam ‘pushing’ the turbine that’s different. When the unit trips off the grid it trips. Whatever load it was doing at the time that load goes to zero.

Yes Dinorwig can in theory go from Zero to approx 1800mw but that is assuming non of the units are already running, and that all units are available to run.

 

[edwin_m]

No they don’t. Most power station turbine generators are 2 pole machines spinning at 3000rpm. This gives us a system frequency of 50htz. This turbine speed is the same whether the unit is generating 1 megawatt or 500 megawatt, it’s the amount of steam ‘pushing’ the turbine that’s different. When the unit trips off the grid it trips. Whatever load it was doing at the time that load goes to zero.

I think the point here is that if a big generator goes offline, all the other spinning generators act as flywheels to keep the frequency from changing suddenly. Solar and windfarms must employ power electronics to feed their output into the grid in phase with what's there already (as a train does when regenerating on an AC supply), so they just track the frequency as it changes until it goes out of the range they can cope with, when they will go instantly offline too. I speculate that it might be possible for those systems to be programmed to advance their phase a fraction when the frequency is low, to provide an element of correction.

 

[dangie]

I think the point here is that if a big generator goes offline, all the other spinning generators act as flywheels to keep the frequency from changing suddenly...

Yes that is basically correct. Grid will have some generating units on ‘Frequency Response’ mode, meaning that if the system frequency should fall, the turbine speeds will also fall (a synchronised unit is locked onto the grid frequency. What will happen is that the turbine governor valves will open to let more steam into the turbine to try and get the speed back up to 3000 rpm. Because of this locked on effect the result is that the generators output load increases.

Up till now this has worked pretty good with a few scary bits! Increasing the generator capacity as suggested whilst ok in theory, in practice may be a bit risky.

I Know my initial example quoted a summer low demand scenario, but for quite a few years now we have been lucky with the winter weather. At times there had been very little spare capacity. A loss of a large unit/station would not have been good.

 

[stuving]

I think the point here is that if a big generator goes offline, all the other spinning generators act as flywheels to keep the frequency from changing suddenly. Solar and windfarms must employ power electronics to feed their output into the grid in phase with what's there already (as a train does when regenerating on an AC supply), so they just track the frequency as it changes until it goes out of the range they can cope with, when they will go instantly offline too. I speculate that it might be possible for those systems to be programmed to advance their phase a fraction when the frequency is low, to provide an element of correction.

No need to speculate - if you look for "virtual inertia" you'll find a lot of work being done already, here in the UK and elsewhere, and mostly small-scale projects. One of the biggest is at Horndale in Australia (see Neoen). For VI purposes the inverter feeding power from a battery or other source (e.g. wind farm) needs to be "grid-forming" not "grid-following".

 

[edwin_m]

No need to speculate - if you look for "virtual inertia" you'll find a lot of work being done already, here in the UK and elsewhere, and mostly small-scale projects. One of the biggest is at Horndale in Australia (see Neoen). For VI purposes the inverter feeding power from a battery or other source (e.g. wind farm) needs to be "grid-forming" not "grid-following".

Thanks - good to know. I only said "speculating" because I think I suggested it on a previous thread. possibly the one on the Class 700 mains frequency shutdowns, and the responses seemed to suggest it wasn't possible.

 

[david1212]

There is a potential problem with higher output generating units. Nuclear power stations tend to run ‘base load’ meaning they are at full output 24/7 (maintenance shutdowns excepted).

Take for example 4am on a summer morning. National Grid system demand is very low. A major fault occurs on at a nuclear station. A generating unit or even the whole station trips off line. That would cause a massive drop in grid system frequency. This could initiate automatic trips for areas of the country to protect the system. Bigger is not always better.

While I suggested the sites having a higher output it could be more reactors than larger reactors. While I understand output can not be changed quickly can reactors be throttled back during spring, run at low output during summer and ramped up again during autumn?

Another factor is that EV's are going to significantly increase the 0:00 - 6:00 demand both cars, minibuses and small commercials charging at 7kW and buses plus larger commercials for overall low daily mileage or the opportunity for boosts during the day charging at 30kW. There will be rail too but within the big picture a small proportion.

I Know my initial example quoted a summer low demand scenario, but for quite a few years now we have been lucky with the winter weather. At times there had been very little spare capacity. A loss of a large unit/station would not have been good.

Indeed. Back on this forum the schedule for cuts if demand exceeded supply was discussed a while ago. Aside from the physical limits of our import sources they may well not have spare capacity to sell but rather throttle back or even cut their exports.

Back around 40 years ago it was normal to have a period during the winter of low temperatures daytime as well as night after snowfall. As to 1947 and 1963 when too cold for snow to melt for weeks and rivers not just static water froze over ......

 

[dangie]

Back in the days of the Nationalised Central Electricity Generating Board (CEGB) there was a Merit Order. The cheapest (usually largest) generating units were at the top, along with Nuclear. These units were known as base load, running 24/7. Following those, units were listed in cost/megawatt. Some would run morning to night, others ran peak times. Those towards the bottom of the list may not run at all during the summer months.

But as it was a nationalised industry, it was run for security of supply not for making money. Therefore all units which were available to run, whether they ran or not, received a payment.

Move forward to privatisation. Basically a unit only got a payment if it ran. The accountants would think this good practice, but for security of supply it isn’t. What happened was that older infrequently used units were shutdown & decommissioned. To attempt to counter this some companies offered their units to the National Grid at low cost, often below cost/megawatt to generate. Obviously this couldn’t carry on.

The electricity supply industry is a strange one in matching demand to available generation. After privatisation when for summer months on end, some generating units would be sitting there but not getting paid, but for winter security they need to be kept open. Those days are gone.

 

[edwin_m]

Back in the days of the Nationalised Central Electricity Generating Board (CEGB) there was a Merit Order. The cheapest (usually largest) generating units were at the top, along with Nuclear. These units were known as base load, running 24/7. Following those, units were listed in cost/megawatt. Some would run morning to night, others ran peak times. Those towards the bottom of the list may not run at all during the summer months.

But as it was a nationalised industry, it was run for security of supply not for making money. Therefore all units which were available to run, whether they ran or not, received a payment.

Move forward to privatisation. Basically a unit only got a payment if it ran. The accountants would think this good practice, but for security of supply it isn’t. What happened was that older infrequently used units were shutdown & decommissioned. To attempt to counter this some companies offered their units to the National Grid at low cost, often below cost/megawatt to generate. Obviously this couldn’t carry on.

The electricity supply industry is a strange one in matching demand to available generation. After privatisation when for summer months on end, some generating units would be sitting there but not getting paid, but for winter security they need to be kept open. Those days are gone.

Don't they now pay some generators (possibly including Ratcliffe) to keep their facilities available for this very reason, even if they don't actually get used?

 

[dangie]

Don't they now pay some generators (possibly including Ratcliffe) to keep their facilities available for this very reason, even if they don't actually get used?

Yes they do now. The danger of blackouts forced the government’s hand. It's certainly a good earner for the companies involved. I would imagine Ratcliffe’s owners, Uniper I think, a German company, are doing quite well.