Application of synchronous compensators in the GB transmission network to address protection challenges from increasing renewable generation

Nedd, M. and Hong, Q. and Bell, K. and Booth, C. and Mohapatra, P. (2017) Application of synchronous compensators in the GB transmission network to address protection challenges from increasing renewable generation. In: 2017 CIGRE B5 Colloquium, 2017-09-11 - 2017-09-15. (In Press)

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The GB transmission network is experiencing significant changes in its generation mix, with increasing volume of renewables and the decommissioning of large-scale thermal power plants. One of the main challenges resulting from these changes in the generation portfolio is the potential impact on the reliable operation of the existing protection schemes. Specifically, the likely decrease in the fault level may result in conventional protection schemes being slow/failing in detection faults, and the decrease of the system inertia would lead to a power system being more sensitive to disturbances, which may subsequently lead to undesired operation of Rate of Change of Frequency (RoCoF) – based Loss-of-Main (LOM) relays. Synchronous compensators are considered to have the potential to offer, among other benefits, a boost to system inertia and an increase of system fault level, which could facilitate the operation of protection systems in future energy scenarios. This paper presents the initial studies conducted under a project that has been initiated by a number of utility companies in the UK, focusing on the demonstration and deployment of the first synchronous compensator at a strategic point in the GB transmission system. The studies investigate the potential impacts of a GB transmission system with high penetration of non-synchronous generation on fault levels and system inertia, while contrasting the results with that of a system reinforced by synchronous compensation. The results of the inertia studies show that synchronous compensation could be used as a potential solution to limit system RoCoF following a disturbance, thereby reducing the risk of a cascading event as a result of the tripping of RoCoF relays. In the fault level studies, it was observed that while increasing the synchronous compensator rating, fault current and short circuit ratio increased, with a faster rate of increase the closer the synchronous compensator is to the fault. This observation suggests that synchronous compensators can also be used to minimise the risk of commutation failure of HVDC links, with the added likelihood of ensuring that the network protection operates correctly in low fault level scenarios.