Energization of windfarm infrastructure as part of microgrid based restoration

Abstract

Studies on windfarms have focussed on their integration under normal and short duration weak grid conditions. With their increasing penetration at the same time that there is increasing disaster related blackouts, there is need to investigate their role during restorative conditions assuming a bottom-up approach in which local generation is used to re-energize the network. This is commonly referred to as microgrid based restoration. Wind Energy Conversion Systems (WECSs) are not blackstart units thus they require cranking from designated blackstart units in order to play a role in re-energizing the network. Prior to the WECSs being cranked up, the windfarm infrastructure, which includes underground cables, reactors (applicable to long HV cables), WECS transformers and yaw-pitch motor system, needs to be re-energized. This paper investigates the energization of different components within the windfarm considering availability of a single medium sized (5 MVA) blackstart synchronous source. Firstly, diesel based generation (DBG) will be used to study the different challenges associated with the energization of the different components considering different re-energization sequences after which thermal (TBG) and hydro (HBG) based generation will be used for comparison. High frequency modelling has been considered for static network components such as transformers, cables and reactors while dynamic models have been considered for rotating network components such as generators and motors. Excitation limiters have been included in the generation systems in order to obtain a near accurate response on energization of the different components. Discussion is provided on the different factors that influence the success of energization. Analysis is also provided on the effect of size of the excitation source and influence of the synchronous condenser which has been considered as part of the windfarm. Resonance, using a simple empirical formula, is briefly discussed as a factor in influencing and determining the energization sequence. A typical windfarm layout has been considered in this study with MATLAB/Simulink being used as the simulation platform due its flexibility in modelling.