Safety And Stability Control Strategy Of Isolated Grid For Aluminium Smelting Powered By Thermal Power Plants

The aluminium smelting process powered by thermal power plant operates in a typical isolated grid mode.Because of its low load level and small installed capacity,even a small power disturbance will cause a big impact on the system.In order to improve its safety and stability,this thesis studied method of safety and stability control of isolated grid for thermal power plants power supply for electrolytic aluminium plants,under a steel enterprise group.As the first step,it analyzed the basic theory of power grid safety and stability control and the algorithm of probabilistic load flow;and developed the calculation steps of safety and stability levels and probabilistic load flow.Afterwards,it studied the calculation of static safety and stability of electrolytic aluminium process in the thermal power plant;improved the N-1 check based on fault ranking method;made the comprehensive sequencing behavior index considering random factors;and then put forward the static security sensitivity analysis method based on probabilistic load flow.Finally,a transient stability control system and control strategy was designed for this thermal power plant.A detailed design on the transient stability control strategy of small generator unit tripping,large generator unit tripping and electrolytic aluminium load out of operation were carried out.And this formed three detailed transient state safety and stability control strategies.Taking the electrolytic aluminium factories isolated grid powered by thermal power plants of a steel enterprise group as the object of calculation,its full load operation mode was calculated by the static stability analysis.The calculation results proved this method in the calculation accuracy and the validity of the calculation time.The bus voltage characteristic and system frequency characteristic were carried on simulated analysis under four different conditions including small generator units tripped in the maintenance mode,one large generator uni t tripped in both normal and maintenance modes,one electrolytic aluminium load out of operation and all electrolytic aluminium load out of operations.The simulation results showed that the proposed control strategy was effective in maintaining the stabil ity of the voltage and frequency of the system,and it can provide guidance for the safe and stable operation of electrolytic aluminium factory isolated grid powered by thermal power plant.