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The A1 Wind Farm: An investigation into the voltage control, network support capability and stability of the A1 distribution network

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The wind energy generation investigated by this thesis is the A1 Wind Farm. This thesis aims to investigate the voltage control capabilities of the wind farm and how the wind farm is able to provide network voltage support through the generation and absorption of reactive power. The thesis also aims to investigate how the voltage control capabilities and reactive power support affect the voltage stability of the network. These aims will be referred to as voltage control, network support capability and stability of the network. The A1 Wind Farm consists of twelve 1800kW wind turbine generators, manufactured by ENERCON. These wind turbines are variable speed, pitch controlled, using synchronous generators with a full scale power converter which is coupled to the SWIS. Specifically, the role of the A1 Wind Farms power converter and its control has been investigated. The power converter has proven to be vital to the voltage control, network support capability and stability of the A1 Distribution Network. The thesis analyses the A1 Wind Farm (AWF) by using PowerFactory Version 14. This is used to construct a model that represents the A1 distribution network and A1 Wind Farm. These simulations are conducted using steady state and transient conditions. The findings of the steady state investigation was that operating the AWF at a limited active power output of 15MW and a power factor of 0.95 leading would result in the least impact on the voltage of the Western Power customers. By using limited active power and power factor control (PQ) it resulted in the least amount of tap changers with a changing load and AWF generation. In turn this resulted in reduced maintenance of the tap changer and a decrease in voltage fluctuations at the 22kV busbar of the A1 zone substation. The power factor of 0.95 leading (absorbing reactive power) also compensated for the voltage rise in the capacitive transmission and distribution network during low load conditions. When using a fixed PQ control for the “constructed” AWF model, it acts like a negative load model. Thus, all the synchronous generator reactive power capabilities had no influence on the voltage at steady state. This is because the reactive power flow of the generator is decoupled by the power converter. From the transient investigation, it was concluded that the AWF must have under voltage ride through (UVRT) capabilities. UVRT is important to the voltage control, network support capability and stability of the A1 network, because this specific capability allows the AWF to remain online and to generate reactive power output even if its voltage is under the required limits. If the AWF was required to disconnect after a fault then the voltage levels and stability would be worse than if it remained connected. Also, using the same PQ control used for the steady state investigation for transient analysis caused problematic results. This is because PQ control makes the power converter absorb reactive power after the fault has been cleared when in fact the power converter control should support the voltage by generating reactive power. Therefore, by reverting to voltage control from constant PQ control, the AWF has also reverted from absorbing reactive power to generating reactive power. In doing this the AWF has provided reactive power support following the fault. Thus, the AWF should utilise V control instead of PQ control under transient conditions and this voltage control and UVRT should be triggered by the under voltage of 0.8 per unit. In conclusion, under transient conditions, the under voltage ride through capabilities of the A1 Wind Farm were essential to the voltage control, network support capability and stability of the A1 distribution network.

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