By Phil Kreveld for Energy Source & Distribution
Held in Cairns from September 4-8, the international CIGRE meeting was significant in its choice of an Australian venue in that the focus on electrical energy systems transitioning to virtually 100% renewable generation fits neatly with our national aspirations.
There were important contributions on the transition theme by leading researchers from around the world and institutions including the USA-based National Renewable Energy Laboratory (NREL) and the Electric Power Research Institute (EPRI). Some 1400 engineers and researchers attended the Cairns Convention Centre and technologies exhibition during four, very busy days.
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The technological consequences of Europe’s renewable energy transition were highlighted at the plenary session. The mantra of ‘no transition without transmission’, as espoused by Alan Middleton, European Vice President of CIGRE, has particular relevance for Western Europe. The accent in the European Union countries is on wind power and the North Sea is regarded as the prime energy source for Europe’s continuing economic development. Some 300 gigawatts of offshore wind power are foreseen as necessary in the next decade, to be delivered by 20,000 wind generators, each of 15 megawatts capacity. Delivering this huge power source onshore will be via an extensive network of bi-polar DC transmission lines.
The commercial pull of the Europeans may well get in the way of delivery schedules for our own projects such as Victoria’s ‘Star of the South’ marine wind generator project. It is a painful reflection on Australia’s unique status: on the one hand, we are the world’s most enthusiastic adopters of green energy per capita and on the other hand, we represent a puny market against the USA with its Inflation Reduction Act investment attraction and Europe with its massive green expansion plans.
AEMO was a significant contributor to CIGRE, focusing on the stability challenges posed by distributed energy resources in medium and low voltage networks. The operator of our national electricity infrastructure ‘intervenes’ on behalf of network stability maintenance by ‘shaking off’ ‘mum and dad’ solar inverters when stability limits fall below minimum standards. At its most sophisticated level solar inverter disconnection (shaking off) takes place remotely via communication protocols such as IEC 2030.5. The bulk of Australia’s suburban solar inverters cannot be remotely controlled so that ‘shaking off’ is achieved by the rather crude means of raising voltage—and that is obviously not a good thing for much electrical equipment.
The foregoing is a convenient segue to the subject choice of many papers dealing with the technology issues facing distribution networks. The focal point ‘de jour’ at the CIGRE meeting was on Dynamic Operating Envelopes (DOE), a means of restricting net power outflow from inverters so as to avoid taxing distribution assets beyond their permissible ratings. Proposed solutions included gathering power, reactive power and voltage measurements from household and enterprise smart meters and the use of artificial intelligence in ‘parsing’ network topologies permitting inverter control.
Community batteries were an obvious topic because they can relieve the pressure on restrictive DOE envelopes. An interesting German paper presented a solution in which a single community battery, energising a grid forming inverter created a micro-grid, hiving the distribution network off its sub-transmission connection. Australian presenters mentioned matters to be resolved including poor network data, lack of telemetry, and insufficient transformer and conductor power ratings. Although community batteries appear to be more for the convenience of network operators rather than energy consuming and generating clients, they fulfil a useful role in lowering voltage rise in feeders by absorbing excess energy. In due course, larger capacities providing energy arbitrage could become of benefit to ‘prosumers’.
There were technical issues aplenty in distribution networks discussions resulting from distributed energy resources (DER), but inadequacy of transformer ratings rated at the top of the list. Other problems included phase imbalance resulting from virtually uncontrolled installations, not only spread unequally in numbers in the individual phases of 3-phase wiring but also in the variation of ratings of solar systems. A Queensland-based company, Eco-Joule, presented a paper on the technology of a phase balancing device, essentially based on dynamic filtering.
The operation of the high-voltage grids and connected generators made for intensely technical discussions. Emerging clearly is that the shutting down of traditional synchronous generator sources of energy and replacing them with inverters is fine in theory. The change from synchronous to asynchronous sources inspired a rich field for academic investigations and a large number of presentations by researchers and engineers. However, it is also leading to worrying conclusion that experimentation in vital infrastructure is not desirable and it is safe to assume, that it will not be allowed to occur.
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The subject of grid-forming inverters attracted particular attention as they are likely to become replacements for traditional synchronous generators. Emerging from the many presentations, it is evident that the practical incorporation of grid forming inverters in electricity systems is some time off even if there are already some of limited capacity in service. In the meantime, much work is being done in grid monitoring apparatus because this is seen as essential in the operation of the newer forms of generation.
PMUs (synchrophasor monitoring units), capable of simultaneous measurement of voltage, current, frequency, and phase angles in multiple locations of geographically extensive grids were the subject of many presentations and discussions. Brisbane-based company NOJA Power has incorporated PMUs in its reclosers and made a significant presentation of its technology in a section of the CIGRE meetings devoted to PMUs and their incorporation in wide area monitoring protection and control (WAMPAC) systems. There were also similar presentations by PowerLink and AEMO.
