The dynamic behaviour of power systems changes as the share of non-synchronous Inverter Based resources (IBRs) increases. These changes are typically characterised by a reduction in
the inertia and fault levels on the system, which, in turn, alter the sensitivity of the system’s frequency and voltages to changes in operating conditions. This Thesis investigates the changing dynamic behaviour of the power system in response to network faults, focussing on the interaction between voltage dips and the system frequency. Traditionally, these phenomena are studied separately, but their coupling has the potential to increase in IBR dominated power systems. A new dynamic power system model is introduced, called the ‘North-GB Test System’ (NGBTS), which incorporates the long-term electricity system infrastructure plans in GB required to operate a zero-carbon system by 2035. It is demonstrated that disturbances in the IBR-dense locations of the network can lead to transients of the system’s centre of inertia frequency nearing the statutory limits of 49.5 Hz, with high initial rates of change exceeding 2 Hz/s. Regional frequency deviations in the fault region are found to be more severe than at the centre of inertia, posing risks of generation tripping and load shedding. The work assess several solutions to mitigate these risks and proposes grid code modifications aimed at improving the performance of IBRs during faults. It is shown that increased active power injection from IBRs can mitigate frequency transients, improve rotor angle stability of synchronous machines (SMs), and maintain voltage stability. This Thesis also presents a quantitative assessment of fault level changes in the Scottish network from 2022 to 2032. Contrary to common assumptions of declining fault levels, the analysis reveals a significant increase in fault levels across the region by 2032, largely driven by IBRs, that can be leveraged for dynamic voltage support in future grids. It is recommended that issues related to elevated fault levels, such as exceeding equipment ratings or misconfigured protection systems, be identified and addressed to avoid unnecessary costs and delays in connecting new renewable generation and transmission infrastructure. This work highlights the growing need to accurately define the system’s needs relating to fault level requirements, converter stability and quasi-steady-state voltage sensitivity as it transitions to low-carbon operation.
| Date of Award | 19 Sept 2024 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | EPSRC (Engineering and Physical Sciences Research Council) |
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| Supervisor | Keith Bell (Supervisor) & Qiteng Hong (Supervisor) |
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