Impact Of Load Models On The Grid Transient Stability And Transmission Capability

With the advance of large power grid interconnected progress, the grid scale is unceasingly expanding and its complexity is increasingly rising. Now the grid uses the conventional load model to guide the electricity production, and it’s found that the level of the stability of the interconnected power system fails to achieve the expected goal, resulting in electricity transmission bottlenecks. Therefore, enhancing the study on the impact of the load models on the grid transient stability and transmission capacity has important theoretical and practical significance to improve the accuracy of the power grid simulation and the safety and economy of the grid operation.On the basis of fully discussing the theory of the power system load modeling and using the statistical synthesis load modeling method, the paper carries on an investigation and classification to the220KV transformer substations of a region according to their load composition. As a result, two types of substation are obtained and the typical transformer substations are selected. Using the typical static device model parameters from the EPRI simulation experiments, the paper comes to the ZIP static load model parameters by using the mathematical formula. What’s more, the paper use the IEEE recommended typical induction motor parameters to obtain the dynamic load model parameters by using average weighting for capacity. What’s more, this paper takes into account the impact of the power distribution network impedance on load modeling. Through using the theory equivalent method, we get the equivalent impedance of the power distribution network. And then the synthesis load model concerning with the distribution network is established.Secondly, using the IEEE standard node system, by setting the most serious three-phase short-circuit fault, the impact on the grid transient stability caused by the conventional load model, synthesis load model and the actual load model is analyzed. Due to the same fault of the fixed-line and under the condition of increasing the send-side output and reducing the by-side output, the line maximum transmission power of different models considering the transient stability is obtained. And then the paper compares the transient stability and the transmission capacity when the grid uses the conventional load model, synthesis load model and the actual load model. Besides that the adaptability of the synthesis load model based on the statistical synthesis load modeling method is analyzed.Finally, three types of load models are added to the actual power system and the paper analyzes the impact of different load models on voltage stability. From the simulation, it’s found that the voltage recovery after the fault using the traditional load model spends less time than using the actual load model. Besides, the voltage change using the synthesis model is more close to that using the actual load model. At the same time, the paper calculates the critical clearing time when setting faults in several lines. Through comparing the stability limit of the lines, it’s found that the critical clearing time when using the traditional model is longer than the real situation. This proves that the traditional load model is more optimistic than the actual system.In short, the simulation illustrates that the load model established by using the statistical method is more realistic than the conventional load model, which verifying that the method is effective and feasible. This provides new methods and ideas for the power system planning, operation and decision-making.