Purpose/Aim
The converter transformer plays a key role in the UHVDC transmission system. Accurately computation of the electric field distribution under polarity reversal voltage is helpful to evaluate the operation status of the bushing.
Experimental/Modeling methods
The electric field of the bushing during polarity reversal is investigated by using Ansys Electric Transient Solver. The permittivity and conductivity of the various insulation of the bushing are determined. A finite element model of the transient electric field is established to compute the electric field variation during the polarity reversal. Finally, the factors that affect the electric field during the polarity reversal are studied.
Results/discussion
Under the excitation of DC voltage, due to the accumulation of charges at the interface, the electric field in insulation with high resistivity gradually increases, and the electric field in insulation with low resistivity gradually decreases. During the polarity reversal, the electric field in insulation with small resistivity increases, and the electric field of insulator with large resistivity tend to decrease.
Conclusions
The accumulated charge is a key factor which affects the electric field distribution during polarity reversal. The amount of accumulated charge is time dependent. The reason for the charge accumulation is that insulation materials have different conductivities.
 

bushing,Polarity Reversal Voltage,electric field,ANSYS