Managing System Strength During the Transition to Renewables

Managing system strength during the transition to renewables GHD ADVISORY i GHD Report for ARENA - Managing system strength during the transition to renewables Acknowledgement This project received funding from ARENA as part of ARENA's Advancing Renewables Program. Disclaimer The funding for this report was secured from the Australia Renewable Energy Agency (ARENA) by Powerlink Queensland along with its project partners, GHD, Pacific Hydro and Sun Metals. While the comments of the project partners were taken into consideration in the preparation of this report, the final report is independently authored by GHD. GHD disclaims responsibility to any person in connection with this report. GHD also excludes implied warranties and conditions, to the extent legally permissible. The services undertaken by GHD in connection with preparing this report were limited to those specifically detailed in the report and are subject to the scope limitations set out in the report. The opinions, conclusions and any recommendations in this report are based on conditions encountered and information reviewed at the date of preparation of the report. GHD has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared. The opinions, conclusions and any recommendations in this report are based on assumptions GHD has made in this report. GHD disclaims liability arising from any of the assumptions being incorrect. GHD has prepared this report on the basis of information provided by various parties, which GHD has not independently verified or checked beyond the agreed scope of work. GHD does not accept liability in connection with such unverified information, including errors and omissions in the report caused by errors or omissions in that information. GHD ADVISORY ii GHD Report for ARENA – Managing system strength during the transition to renewables Executive summary In this report we focus on explaining system location and configuration for renewable energy strength, outlining the range of remedial options projects as well as placement of system strength available and the circumstances in which they provision infrastructure. This will help prevent might be applicable. We also explore the unanticipated expenditure and protracted project economic merit and commercial/regulatory issues delays. of a shared and scale-efficient model for implementing system strength provision by use of Our collective understanding of system synchronous condensers. strength is evolving over time. Initially system strength was understood in terms This report is intended to promote a broader of the fault level required for individual generators understanding of system strength. to be able to operate stably and to ride-through As Australia’s power system transitions toward system faults. renewable forms of power generation, system Subsequently the potential for multiple generators strength has emerged as a prominent issue and to interact in an unstable fashion became the has led to difficulties in developing and operating dominant concern. renewable generation projects. More recently, it has become apparent that the System strength is a technical subject and an “system strength issues” we are observing are area in which Australia is on the “bleeding edge” also influenced by other factors including system of international experience. Generally, there is a inertia. limited understanding of the topic and it is often There is every likelihood that we will uncover confused with other related power system issues additional aspects of system strength over time. such as inertia, adequacy or resilience. Our expanding understanding of system This report has been developed to promote a strength creates challenges for how we speak better understanding of system strength and its about it. implications, and the range of remedial options There are (at least) two options: that may be available. It is targeted at a broad audience, including readers from non-engineering 1. To progressively expand our definition of backgrounds. The goal is to establish a base level system strength to include these additional of understanding between all stakeholders aspects. In this case, system strength is involved in the power system and serve as a basis effectively becoming a synonym for power for dialogue, and informing the ongoing system stability. development of regulatory frameworks. 2. To preserve a more focussed definition of The report includes a “deep dive” on synchronous system strength as a subset of power system condensers, including the potential for a stability, but recognise that system strength is centralised approach to implementing them. interactive with other aspects of power system Although the report uses North Queensland as a stability, and that these aspects are equally worked example, the implications are expressed relevant to the connection of new generation in a way that should enable readers to consider and the secure operation of the power system. how they might apply in other regions. Whilst this distinction may seem pedantic, it has A clear and common understanding of the topic a significant bearing on how system strength is will allow utilities and generator proponents to described. This report has been written in terms work together in identifying the most optimal of the latter option. GHD ADVISORY iii GHD Report for ARENA – Managing system strength during the transition to renewables What is system strength? System strength is a way of describing how resilient the voltage waveform is to disturbances. Having a pliable voltage waveform is a precondition in which other problems are much more likely to emerge. System strength is a way of describing how process to the way in which the physical inertia of resilient the voltage waveform is to the synchronous generators resist changes in the disturbances. power system frequency. If a transmission network location is said to be In order to provide system strength, the “strong” in terms of system strength, the change in generators merely need to be online and voltage at that location will be relatively unaffected synchronised to the grid – they don’t have to be by a nearby disturbance. However, if a location is producing any real power. said to be “weak” in system strength the voltage at that location will be relatively sensitive to a system The progressive displacement of conventional, disturbance, resulting in a voltage dip that is fossil fuel powered, synchronous generators with deeper and more widespread. non-synchronous generation is reducing the overall level of system strength in the power Having a pliable voltage waveform is a system. precondition in which other problems are much System strength naturally diminishes with more likely to emerge. This includes longstanding electrical distance from synchronous issues such as power quality and voltage stability, generators. and emerging issues such as unstable Given the scale and topology of Australia’s power interactions between inverter-based generators. system, there are many locations in the network Conventional generators inherently provide where the system strength is naturally low and system strength. has always been this way. Whilst this has given System strength is created by conventional forms rise to some challenges, these have largely been of generation, not because of their fuel source managed internally within network service (e.g. coal, gas and hydro) but because of their use providers (NSPs). of synchronous generators which are electro- However, such locations are often attractive for magnetically coupled with the power system. the connection of renewable generators because Such generators inherently respond to voltage of good resource availability, low land costs, and disturbances on the power system in a manner the expectation of a straightforward connection to which resists the disturbance and limits its size, the power network. The high penetration of thereby automatically helping to stabilise network inverter-based renewable generators in areas with voltages arising from a network disturbance. The low system strength have led to new and complex ability to resist sudden changes in voltage issues that also impact upon generation magnitude comes from the magnetic flux in the proponents. generator’s core (i.e. flowing in and between the generator’s stator and rotor as a consequence of excitation (electrical energisation) of the generator’s stator windings), and is a distinct GHD ADVISORY iv GHD Report for ARENA - Managing system strength during the transition to renewables Currently, solar and wind technologies do not The problem is complex because it is not inherently provide system provide system necessarily a consequence of a single ‘rogue’ strength. inverter, but rather a mutually-incompatible Inverters transform the power produced by these combination of inverters and network conditions. sources into a form which is compatible with the Analysing the potential for unstable interactions grid. They are not driven by the physics between multiple inverters requires extremely associated with magnetic fields in the same way detailed models of each inverter and the network, as synchronous generators are, but rather rely on e.g. with a full representation of each inverter’s algorithms to sense and appropriately respond to control system. any fluctuations on the power network. Detailed modelling is now typically required If the system strength is low there is a risk that the for

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