Research on calculation model of voltage sags due to high voltage and great power motor starting

High voltage and great power motors´ starting cause big impacts to power grids and introduce voltage sags. In severe cases, it will affect the normal operation of other devices. Voltage sags have been the most prominent problems of the power quality, and both sides of the power supply pay close attention to them. This paper mainly focuses on the starting process of the high voltage and great power induction motors which are widely used in industries. It´s key to model the motor starting process, including selections of the equivalent circuit of motors with different structures, collections and checking of stators and rotors´ impedance. Normally, lacking the delivery test materials, they should be obtained by experience. The key point to improve the simulation accuracy is to model mathematical expressions of motor stators and rotors´ impedance in the starting process to get more accurate curve of motors´ electromagnetic torque, including the collection and evaluation of motors´ rotation inertia. It is directly related to the duration of the starting process. The collection and evaluation of load torque curve are related to acceleration torques. Finally, it determines the duration of the starting process. This paper also introduces techniques to reduce the starting current, to reduce the impact to the power grid, to control voltage sags levels in limits. The research has been successfully used in power quality evaluation for the integration of Shanghai Qingcaosha Raw Water Project, Shanghai Zizhuyuan Refrigeration Units project.