Tesla Big Battery Outsmarts Lumbering Coal Units After Loy Yang Trips (reneweconomy.com.au)

The Tesla big battery is having a crucial impact on Australia's electricity market, far beyond the South Australia grid where it was expected to time shift a small amount of wind energy and provide network services and emergency back-up in case of a major problem. From a report: Last Thursday, one of the biggest coal units in Australia, Loy Yang A 3, tripped without warning at 1.59am, with the sudden loss of 560MW and causing a slump in frequency on the network. What happened next has stunned electricity industry insiders and given food for thought over the near to medium term future of the grid, such was the rapid response of the Tesla big battery to an event that happened nearly 1,000km away. Even before the Loy Yang A unit had finished tripping, the 100MW/129MWh had responded, injecting 7.3MW into the network to help arrest a slump in frequency that had fallen below 49.80Hertz.

Comments

AC frequency

[ebcdic]

For the benefit of Americans reading: the nominal AC frequency in Australia is 50Hz, not 60Hz.

Re:AC frequency

[Thelasko]

For those that don't know. The frequency of AC power is an indicator of the supply and demand status of the grid. The frequency is determined by the speed of the generators at the power station. If there is too much load on the generators, they slow down, and the grid frequency drops.

The Australian grid is targeting 50Hz, and had dropped to 49.8Hz.

Re:AC frequency

[Anonymous Coward]

More demand / less supply > generators have to work harder > greater force needed to spin them > turbines slow down > frequency drops.

There's not really anywhere on an electricity grid where one can connect a meter and say "we need more power" so they monitor frequency instead.

Re:AC frequency

[xvan]

Synchronous Generators are fed by a torque sources, if you have a generator outage, and the other generators don't have enough power reserve there are 2 consequences that balance the power consumption. A drop in voltage and a drop in the network frequency (P=T* w, so with the same torque available, less frequency means less power injected to the network )

Re:AC frequency

[Orne]

Not quite. The original coal plant tripped, so the power that it was injecting ceased to be. In the very short term (tens of cycles), the energy demand on the system outweighs the supply, and frequency begins to drop. The remaining synchronized generating resources next engage "primary frequency response", which is an automated (governor) response that temporarily increases the output of the generators. By governor, there is a device in the generator controller that regulates the steam pressure to keep the rotation constant, so the energy imbalance creates mechanical drag that the governor attempts to correct. Each generator twitches up a tiny amount, the frequency decline is arrested, and the system stabilizes. You then have secondary systems that engage that drive the system back to a pre-loss state.

The battery in this contributed primary frequency response, as a direct response to the observed low frequency. In the United States, Energy Storage devices are not required to provide primary frequency response, since almost all frequency response is provided by steam units. As more coal plants are retired and replaced by Wind and Solar (inverter-based units), the US grid will need to adapt and modify its requirements.

Re:AC frequency

[mspohr]

First of all, OP isn't talking about injecting frequency.

I didn't say he did. The summary talks about injecting 7.3MW to "arrest a slump in frequency".

When the system is overdrawn on power the high load slows down the turbine generators and the frequency drops. The solution is to add power to the system. The battery added 7.3 MW of power to the system which helped to bring the frequency back up to nominal 50 Hz.

Re:AC frequency

[Thelasko]

Read up on generators and how demand influences frequency.

When you're done, go read some man pages.

It astounds me that someone will take the time to write a post, but not take the time to actually answer the question that was asked. How that is that insightful?

Re:AC frequency

[Pseudonym]

I've worked a little bit with data from the AEMO. I'm not a power distribution engineer, but I did to learn enough to be able to explain it badly. So here goes...

One way to think of it is that all of the equipment on a given segment of the network synchronises to the frequency of the network, but tries to nudge it ever so slightly closer to 50Hz. If every piece of equipment on the network does this, the network as a whole trends towards the correct frequency. The system can tolerate some drift, so each piece of equipment acting independently can force the network as a whole to keep to 50Hz as long as it isn't overloaded.

A typical alternator that you may find in a generation plant is designed so that it will produce 50Hz when fully loaded, that is, whenever the amount of power that it's designed to generate is being drawn. When none of the power is being drawn, it physically turns around 4-5% faster, so it might run at 52 Hz if you did nothing. So if the full power output of the generator is not being used, you need to physically slow it down.

That's easy, but of course the specific technique depends on how the alternator is being physically turned. If you can turn down the amount of fuel (trivial for hydro, almost as easy for a gas turbine), you do that, or you might use a mechanical or electromechanical governor on a coal plant.

The problem happens when the network is overloaded. When you draw more power from an alternator than it is rated to produce, this acts like an electromechanical brake, and it will run slower than 50Hz. You can't force an overloaded alternator to run faster, so any attempt to increase the frequency won't work. The only fix is to not overload it by adding more power to the system or reducing demand.

One of the key reasons why the South Australian government wanted to build the Tesla battery was because the AEMO couldn't get a generator turned on in time and so had to shed load by deliberately causing blackouts in South Australia. The amusing thing about TFA is that we may have just discovered that the Tesla big battery may be designed to protect the SA grid from the AEMO.

Just for completeness, I'm using the word "network" here to refer to a region for which the frequency is synchronised. I believe this is true for most of the NEM; TFA seems to indicate that Hornsdale (SA) and Gladstone (QLD) are synchronised. However, I seem to recall from the data that Tasmania's connection is via a HVDC link which can work in either direction, so presumably Tasmania's frequency doesn't need to be synchronised to that of the mainland.

The AEMO, by the way, is essentially a big integer linear program plus some human intervention in the case of emergencies. The ILP represents the network constraints (e.g. the capability of every generator, the maximum current of every distribution line, a squillion contract clauses) and tries to minimise dollars per kWh.

Re:A slump in what?

[HornWumpus]

They are both affected. But power companies will let the voltage drop while holding frequency as close to theoretical as they can. They even run 0.1 Hz high or low at the end of the day to get the correct number of cycles for the period.

If you've ever designed a power supply, you'd see that you must accept low/high voltages, but should expect the frequency to be fairly steady.

Re:A slump in what?

[RobinH]

Good question. A simple way to view it is that the grid is powered by generators. The generators are built to run at a fixed speed, and are wound so that the fixed speed outputs (in this case) 50Hz at a fixed voltage. The voltage output of the generator is a sine wave and it will lead (since it's generating) the grid voltage by a small amount (lead means same frequency, slightly ahead of phase). The amount it leads determines the load, and the generator has a limit to how much load it can handle, so if you tried to speed it up by turning it faster, it would start to lead slightly more and the load would increase (more current, but more resistance to the prime mover turning the generator) so the speed stays close to 50 Hz and it only speeds up a very small amount very briefly. When you drop a bunch of generation offline, the rest of the generators see a bunch more load suddenly, which is felt as a physical torque, so the generator gets harder to turn. The prime movers (turbines typically) can't produce more power instantaneously so the generators start to decelerate slightly. That's why you see the grid frequency drop slightly until the turbines increase power to take up the load. That's assuming the remaining generation can handle it. What they're saying here is that the Tesla system, since it uses inverters, can respond faster than the turbines generating power (duh). I'm not sure why it's described as shocking. Near where I live, in Canada, they installed a few MW of magnetic bearing sealed-vacuum flywheel energy storage specifically for frequency regulation due to all the new windmills they installed. The flywheels are spinning at synchronous speed and can absorb and deliver energy to the grid as needed, similar to the Tesla battery system.

Re:na

[Mr D from 63]

...where it was expected to time shift a small amount of wind energy and provide network services and emergency back-up in case of a major problem.

No, the primary purpose of the battery was to help the grid ride through transients just as the one described, not for time shifting. Who is writing this stuff?

Frequency drop indicates overload

[raymorris]

The drop in frequency itself isn't the big problem, it's a gauge, an indicator.

The frequency tells you how fast the generators are turning. They are automatically throttled to try to spin at the right speed to produce 50Hz. If they aren't producing 50Hz, that means they are full wide open throttle and still can't keep up. It means they can't produce enough power.

Re:na

[Rei]

Actually, no, it wasnt engineered to back up a power plant in Victoria, it was engineered to back up power in South Australia. There was an entirely different coal power plant that was supposed to back up Loy Yang (which is one of Australia's largest) - a plant that ratepayers have to pay to keep running on standby, which is supposed to hold the grid up until downed power plants can be brought back up and/or more baseload elsewhere ramped up. But from nearly 1000km away, the Tesla battery did the standby plant's job for it during its 4-second wakeup time - stopping and reversing the decline in grid frequency so that there wasn't even a meaningful blink in power quality.

This is not what the Tesla battery was designed to do. It was designed to deal with situations with downed lines / plants in South Australia, to keep the lights on there. It wasn't supposed to take over the work from standby plants halfway across the country. That it technically can should surprise nobody. But that's not what it was purchased to do.

Re:na

[ChumpusRex2003]

It is likely a linear power response to frequency with a small dead band.

In the UK, battery backed frequency response is an important contributor to frequency stability, and is operated with a dead band of 0.015 Hz. The power injection is required to be proportional to the frequency deviation from outside the dead band, reaching 100% rated power at 0.5 Hz deviation from nominal. Response time is a maximum of 1 s.

Additionally, in the UK, the requirement is that the frequency response is symmetrical. If frequency rises, then the system must absorb power - up to 100% of maximum rated power at 50.5 Hz, for a minimum of 15 minutes.