We always hear about the elusive ‘grid’ - in the media, when there’s a blackout, in politics! But what exactly is the grid?
The grid refers to electricity infrastructure - the generators that produce power, and the various poles, wires, and transformers that electricity flows through as it makes its way into homes, businesses, and everywhere else we use electricity!
Once electricity is generated, either in coal- or gas-fired power stations or via rooftop solar panels, or larger wind and solar farms, it is fed into wires that carry high-voltage electricity to bulk supply substations.
At the substation, transformers reduce the voltage and the electricity is transmitted to distribution substations, where the voltage is stepped down again. From there, the electricity travels along wires to smaller-scale transformers, which reduce the voltage again before the electricity reaches homes and businesses.
Some big users like industrial smelters or large businesses tap into the grid at a higher voltage than households do.
Who runs the grid?
The electricity supply for most states in Australia is linked in one massive grid connecting Queensland, New South Wales, Victoria, South Australia, and Tasmania, forming the National Electricity Market (NEM). The NEM comprises around 40,000 km of transmission lines and cables and supplies over 10 million customers. Western Australia and the Northern Territory each have their own separate electricity infrastructure.
Then there are the distributors and the retailers. Electricity distributors own and maintain the distribution network. That includes poles, wires, and electricity meters. You can’t choose your electricity distributor – it’s assigned based on where you live.
You can choose your electricity retailer – the company that sells you your electricity. Retailers buy the electricity created by generators at a wholesale price on the NEM, and then sell this electricity to individual customers.
In essence, distributors own and operate the infrastructure for the grid, while retailers buy and sell the electricity itself. An organisation called the Australian Energy Market Operator (AEMO), is responsible for managing wholesale electricity (and gas) markets and maintaining a secure energy supply.
What causes blackouts?
‘Grid stability’ essentially means keeping electricity flowing through this network at a particular voltage and frequency.
It’s a delicate balance between supply and demand because the network is very complex and can only operate within a fairly narrow range of both voltages and frequencies.
Equipment that uses electricity is designed to function at a specific frequency and voltage and can be damaged if these values aren’t kept within a certain range. At a larger scale, problems with either voltage changes or frequency instability can trigger safety mechanisms that take parts of the grid offline, leading to blackouts.
Increased demand for electricity causes the voltage to drop; decreased demand causes it to spike. For example, if a rooftop solar system is producing more electricity than the building it’s on is consuming at a given time, the excess is fed into the grid, pushing up the voltage in local distribution lines.
Frequency refers to the number of oscillations per second of the alternating current (AC) – the dominant form in which electricity is transmitted. In Australia, electricity is supplied to end users like you and me as AC at a frequency of 50 cycles per second, or 50 hertz. Frequency doesn’t have to shift very far away from 50 hertz, say 49.8 before things stop working properly. Large-scale instabilities in frequency can be caused by generators failing or going offline.
The power that’s coming down the line is essentially a sine wave that goes up and down. When these waves collide in the wrong way, the frequency becomes unstable.
When most electricity was generated by large fossil-fuel power stations, slowly rotating turbines that connected to the generators were used to stabilise electricity at the desired frequency. With the increasingly diverse mix of electricity sources feeding into the grid, maintaining stability requires new approaches.