Various technical impacts are associated to the interconnection of wind turbine generators to the grid. Among them, the increase of short-circuit levels along with its effect on the settings of protecting relays has long acted as an important inhibiting factor for the interconnection of new wind power plants to the grid. This is especially true at the medium voltage level where networks operate close to their short-circuit design value . As renewable energies are progressively replacing traditional power generation sources, short-circuit studies need to adequately assess the impact of newly interconnected wind power plants on the fault level of the network. For planning and design purposes, short-circuit studies are usually performed using steady-state short-circuit programs. Unfortunately, very few have developed models of wind turbine generators that accurately estimate their fault contribution in the phase domain. In particular, no commercial fault-flow analysis program specifically addresses the modeling of inverter-based wind turbine generators which behavior is based on the inverter's characteristics rather than the generator's. The main contribution of this research work is the development of a simplified and yet accurate model of full-scale converter based wind turbine generator, also called Type 4 wind turbine generator, for steady-state short-circuit calculations. The model reproduces the real behavior of the Type 4 wind turbine generator under fault conditions by correctly accounting for the effect of the full-scale converter. The data used for the model is easily accessible to planning engineers. An additional contribution of this research work is the development of a short-circuit algorithm adapted to support the proposed model of Type 4 wind-turbine generator. Short-circuit algorithm based on modified-augmented-nodal analysis (MANA) is solved iteratively to accommodate the proposed model. The algorithm is successfully implemented in CYME 7.0, a commercial distribution system analysis program, to perform short-circuit calculations in multiphase complex unbalanced systems. Detailed study of the behavior of Type 4 wind turbine generator using electromagnetic type programs like EMTP-RV has assessed that the proposed model closely reproduces the real behavior of the wind turbine generator under steady-state fault conditions. The proposed model is then implemented in CYME 7.0 and validated for different fault scenarios using the Fortis Alberta 25 kV distribution system as benchmark. The fault contribution obtained from the proposed model is compared against the one obtained from the previous model implemented in CYME 7.0. The validation test cases show that the proposed model estimates the fault contribution of the wind turbine generator with better precision than the former models. Besides, the performance and robustness of the short-circuit algorithm developed allow handling unbalanced networks with inverter interfaced wind turbine generators as it is based on the MANA formulation.
- Pub Date:
- Engineering, Electronics and Electrical;Energy