By Phil Kreveld
The Crows almost beat the Pies in the AFL qualifiers on the date of filing this report on the CIGRE Australia meetings in Adelaide (September 2-5), South Australia. Very disappointing as they were doing so well the first three quarters. However, the state is definitely a clear winner in the renewable race, exporting 200MW on a lovely bright day last year, and beating its own export forecast of that figure it had set as target for 2029. The export of power is confidently expected to triple in the next decade. South Australia is the testbed for renewables in distribution grids, and therefore the appropriate venue for the CIGRE Australia, three-day conference, focussed on renewable energy source integration.
Vehicle-to-grid requirements per the draft standard AS5438, and South Australian Standard SA TS 5573:2025 for smart inverter communication in modern distribution grids were major topics of discussion. The electric vehicle standard applies to charging rates of 19kW for a single-phase supply and up to 30kW for three-phase. The V2G aspect of the standard is affected by the availability of bi-directional charging in electric vehicles. The new Australian standard, AS/NZS4777.1:2024 also has relevance to this application.
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Dynamic envelope operation in distribution grids was a hot topic. The technology relies on smart communication with inverters. The above-mentioned South Australian standard, now being adopted in Victoria and New South Wales, referred to as the Common Smart Inverter Profile (CSIP), is based on IEEE 2030.5. Dynamic envelope operation, actively being trialled in South Australia, can instruct complying inverters to reduce power, and also to provide reactive power support for additional voltage control.
Voltage control was also a big topic within the category of DMS (distribution management systems). Several presentations focussed on excessive temperature in transformers and in their voltage-buck restrictions. Traditionally transformer tap settings were appropriate for inductive loads, for example motors. Voltage buck limitations therefore constrict the flow of permissible reverse current due to high solar energy production. Dynamic operating envelopes have to take account of this, as was mentioned in one presentation which also made the point that lack of detail in distribution grids—some may find this hard to believe, but it attests to documentation lagging implementation—required a conservative DOE control strategy, thus affecting the economic advantages for solar panel owners.
Interesting panel conversations took place discussing the relative merits of DMS versus DOE, security of operation being more important, it could be argued, than economic return on solar systems. One presentation focussed on SICAM, a self-healing program for distribution networks comprising of overload reduction, area voltage regulation, automatic generator source transfer and load management.
The dominant question on transmission and renewable generation emerged on day one of the conference—with all manner of possible answers but not one dominant one. In short, how will declining grid strength affect the renewable transition. There were other considerations; required increases in ramping rates for generators, whether synchronous or asynchronous, and shortages in new generation capacity estimated to necessitate an increase of 10GW capacity annually.
Presentations on system power and voltage oscillation in transmission grids underscored the electrical engineering challenges already being faced. Inter-area modal frequencies (around 0.5Hz in 2008, and doubled by 2022) are a headache and may not as yet result in a migraine, but decline in system strength may well bring them on. Forced oscillations due to inverter-based resources, as distinct from natural modes, are much higher, around 20Hz. These forced oscillations are exacerbated by reductions in system strength as measured by short circuit ratios.
Several presentations were on the subject of impedance-based stability analysis as a tool for predicting forced oscillations caused by inverter-based resources. Presentations outlined the methodology to determine the Thevenin impedance of inverters as a function of frequency so as to provide a prediction of stability when connected to grids of varying system strengths based on short circuit ratios.
An important point to emerge from at least two presentations was that impedance-scan based analyses provided more reliable stability predictions than electromagnetic transient analyses based on black box models of inverters. The SCR ratios are not an absolute indicator of likely instability, a British study found, indicating a SCR value of 2.3 as marginal condition. It is serious stuff as a National Electricity Rules change now require disconnection of generating systems causing instability. The responsibility for monitoring and decision-making regarding disconnection is the responsibility of the transmission line operator with one important indicator being that when the reactive power component is more than 90 degrees out of phase with voltage phasor, the oscillation is not likely to have originated from the particular generator.
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A rather frightening presentation slide plotted the stability criterion of a grid following inverter connected to a grid forming inverter as a function of the transmission line distance separating them, with the capacity of the grid forming inverter requiring an increased capacity rating as a ratio to the short circuit MVA at the grid forming inverter bus; at 350km, the grid forming inverter requiring an over-capacity of 300%.
The general tone of the IBR stability presentations, were best described as academic including one from AEMO on inter area oscillations, of itself not news as these are a general feature of interconnected AC systems. What would happen in a 100% IBR grid? In the plenary session, the blackout in Spain was mentioned. It was noteworthy for the absence of specific detail. Your correspondent posed the question to one speaker as to how he would find it if the renewable transition were taken out of the hands of politicians and economists, in favour of a national engineering authority, in charge of the whole process. “Nirvana” was the response.
