September 28, 2016 / Miscellaneous/
Currently, there’s a massive problem unfolding in South Australia – the ENTIRE STATE is without power. There’s a huge storm, and the state’s power grid has been shutdown. Aside from those with emergency power contingencies, such as hospitals and emergency services, no one has had power for a number of hours. There’s still connectivity via mobile phone towers – they apparently have around four hours of UPS power, and because this isn’t just a localised outage there isn’t exactly enough generators to supplement that.
This state-wide outage was confirmed by the local network provider just before 5pm AEST (4.30pm local time).
No upstream supply from the transmission network. State currently w/out power. Do not report outages. We will provide updates when avail.
— SA Power Networks (@SAPowerNetworks) September 28, 2016
There’s a been a bit of speculation as to how this can happen. After all, leaving 1.7 million people without power raises a few questions.
Around 40% of local SA power generation is from renewable sources – particularly Wind Turbines. Wind Turbines don’t do well in storm conditions, and have a maximum speed at which they can still produce power. Many turbines are designed to shut down when they exceed a certain speed (25 metres per second is a commonly cited maximum speed for a wind turbine). In South Australia, it’s likely a large number of wind turbines stopped producing power over the course of the day as the storm picked up speed.
There’s been speculation that the high quantity of renewable sources has left the state without enough baseload power generation – that is, consistent reliable power that isn’t dependant on environmental conditions like wind or sunshine.
However, a lot of power still comes from elsewhere. South Australia is a part of the National Electricity Market.
Queensland, New South Wales, Australian Capital Territory, Victoria and South Australia all participate in this network. There is a demand-based pricing mechanism where electricity generators all compete to provide power at the lowest wholesale price.
Even without the wind turbine power, surely they could just draw power from the national market?
According to the ABC, there’s been storm-related transmission tower damage in the state’s north and lightning damage to another of the state’s power plants (possibly reducing generation further).
Premier Jay Weatherill revealed two very important details about what caused the network to shut down:
We have baseload power which kicks in in these circumstances. What happened is there was a break in the electricity line which caused a dramatic drop in frequency, which means the system trips. This would happen in any circumstance, even if we had the Northern Power Station up and running. For people to be saying those things [the lack of baseload power] without being properly appraised of all the facts demonstrates people are using this to play politics.
Source: ABC News 24
The two emphasised phrases are the key pieces of the puzzle here.
Alternating Current (AC) Electricity Grids require consistent frequency across all generation sources (in Australia, this is typically 50Hz – meaning 50 cycles per second). The process of creating this consistent frequency is called Frequency Synchronisation. Every generator must have a way of synchronising it’s generation with the rest of the power in the network. This is why solar power panels needs an expensive inverter, and why they should shut down altogether if they loose sync with the grid source.
Let’s put together the required information, and speculate a little. I must emphasise here… the conclusions I’m arriving at here are based on the available information and a bit of guessing. I’m not an expert in power transmission networks, but just have a basic working knowledge of electricity systems (from my background in broadcast and the need to have continuity in those facilities).
The problem in South Australia today probably came about by a significant drop in supply, which wasn’t matched by a drop in demand. A mis-match in supply and demand is bad. It’s like having a car on cruise-control while going up a big hill – if the motor isn’t big enough, it can’t maintain the speed. In simple terms, if demand exceeds supply then the frequency will drop. A big enough frequency drop will damage equipment. There’s some very interesting explanations of this on the Physics Stack Exchange.
If an interconnect with the National Electricity Market (which would’ve been supplying a significant portion of generation capacity in the network at the time) fails – or even drops for a moment – at the same time as a significant potion of the state’s own generation (wind power) is down, failure detection systems are going to sense a frequency drop and very quickly shut down portions of the network. If you can’t maintain the frequency, you need to shut down demand so it can be met by the available supply.
Hence, we have a massive outage affecting an entire state.
For fun, let’s take a look at the current generation output:
And here’s the current market price in SA:
Wow! That’s expensive! Let’s hope that price drops very quickly as they get customers back online :)
An variant on this explanation is that there was a surge in a large feeder to the network, and that feeder was isolated to prevent the surge from damaging anything. As a result, the rest of the network was unable to take the load and the same frequency drop occurred.
How can this be prevented in the future? Probably via diversification of supply. There were clearly multiple events leading to this outage, with one or two generation sources (or transmission lines) providing the majority of the power to the state. By diversifying the sources and transmission, it means you can immediately isolate one or two sources and still maintain the load.
Getting the power back up now is obviously a slow process, requiring each generator and segment of the network to be brought back online one by one. This ensures everything is correctly synchronised and the load is managed.
We are in the process of restoring power to parts of the metro area as transmission supplies become avail. More updates to follow.
— SA Power Networks (@SAPowerNetworks) September 28, 2016
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