Impact Study Of A Group Of Induction Motors For 110kV Substation Main Transformer High Reserve Gap Protection

With the rapid development of economy, the grid scale expands unceasingly.Meanwhile, because of the failure and the number of damaged transformer are growing, the quality of power supply declined rapidly. Ineffective ground connection of neutrality points in the transformers with 110kV or higher voltage levels will result in transformer insulation abrasion or force transformers to exit the system operation. In order to ensure the safety of the power grid, it is necessary to ensure substation main transformer neutral point grounding directly, because it can reduce the impact of the over-voltage caused by fault on the insulation of transformer.Taking certain 110kV transformer station gap protection malfunction event as the example, the process of malfunction is analyzed in this thesis, concluding the problems exited in the transformer station and impacts on main transformer insulation and operation. According to llOkV system typical structure, this thesis observes main transformer high-backup gap protection operation process and constructs corresponding simulation model. The model of triple-phase asynchronous motor is established in line with the voltage equation, magnetic linkage equation,torque equation and motion equation in asynchronous motor. After aggregating a group of induction motors cluster pursuant to the static aggregation approach in non-load and locked-rotor conditions, this thesis further puts forward an improved static aggregation approach which not only considers the influences of rotation inertia, inertia constant and stead-state slip on the dynamic performance of asynchronous motor, but also utilizes inertia time constant,motor rotor transient reactance, and critical slip and other motor properties to classify the asynchronous motor cluster. This improved approach is able to effectively elevate the aggregation accuracy of the asynchronous motor cluster. While observing the influences of the asynchronous motor cluster on gap protection,this thesis also sets up single-phase ground connection malfunction and makes a comparative simulation to conclude corresponding simulation waveform and back electromotive force in three conditions when the terminal line is non-loaded or when the terminal line is large-scale asynchronous motor or when the terminal line is asynchronous motor cluster. Finally, targeted at different operation conditions, this thesis probes into the zero-sequence voltage in case of single-phase ground connection malfunction, and draws the conclusion that when there exist enough asynchronous motor clusters, the resulting back electromotive force will trigger main transformer high-backup gap protection malfunction and force the transformer to exit the system. In order to prevent the main transformer high-backup gap protection malfunction, this thesis raises effective improvement measures and makes simulation test and verification in MATLAB...