Research on Harmonic Characteristics of Transformer Operation under Frequent Switching of High-proportion New Energy Access Trend

With the distributed access of a high proportion of new energy, the coordinated operation mode of traditional power grids has been greatly changed, making the feeder voltage no longer have the characteristic of gradually decreasing, resulting in the operation of step-down transformers under frequent power flow switching conditions, which brings voltage control difficulties. Meanwhile, due to the presence of a large number of power electronic devices in the power grid, harmonics are inevitably generated during the power flow switching process, which may also cause abnormal temperature rise of structural components, accelerated aging of insulation, and distortion of iron core excitation. Therefore, this article analyzes and calculates the changes in voltage and current of step-down transformers after large-scale integration of wind power and photovoltaic power. Through analysis, it was found that when wind turbines and photovoltaics are separately connected, the range of current harmonic content is greater than the fluctuation range of voltage. When wind and photovoltaic power are connected in a 1:1 ratio, the harmonic content range of the low-voltage side current of the transformer is 5.11% -36.59%, which is smaller than the fluctuation range when wind turbines and photovoltaics are connected separately; The voltage harmonic range is 1.53% -3.91%, which is lower than the value when the photovoltaic is connected separately but higher than the value when the wind turbine is connected separately.