Numerical Research on Space Charge inside Solid Dielectrics under Unipolar and Bipolar Voltage Conditions

This paper focuses on the effect of unipolar and bipolar square, sine and triangle voltages on space charge characteristics inside solid insulation based on the bipolar charge transport model. According to the model solution process and the polarization characteristics, it is found the algorithms for the model should be chosen with regard to the direction of the electric field at each subdivision inside the calculation sample. Further comparison shows that the charge amount under different conditions is mainly determined by the input power of the imposed voltage, while the migration depth of the injected charge is less than 20 μm from the sample surface. Correlation between the current injection and the charge amount indicates that the variation trends of them follow basically the same. The results under unipolar conditions are not affected by the frequency provided it is larger than 10 Hz, while the charge amount under bipolar ones is negatively correlated to the frequency. Meanwhile, the impact of the initial phase of bipolar polarization decreases rapidly with the increased simulation time. Hence, for space charge measurement inside dielectrics under such conditions, a reliable system should be established according to the polarity and waveforms of the polarization.