290 / 2018-09-25 19:39:34

Effect of Pre-Field on the dielectric properties of BaTiO3-based equalizing ceramics Capacitors of Surge arrester

Pre-Field,dielectric properties,BaTiO3,ceramics Capacitors,Surge arrester

Arrester is the main equipment for limiting overvoltage, and is the basis for insulation coordination and the reliable operation of the power system. Since the UHV gapless metal oxide arrester is more than 10 meters, the stray capacitance between the earth and the grounding body around the mounting point will cause the axial voltage distribution of the resistor to be extremely uneven during continuous operation. The resistors near the high voltage end has a much higher charge rate than the remote resistor, thus it will accelerate the deterioration due to excessively high sustained voltage, resulting in damage to the arrester and shortening the expected operating life. Therefore, the equalization is often performed by adding a parallel equalizing capacitor.
At present, the capacitors used in domestic UHV projects are BaTiO3-based ceramics. BaTiO3-based materials are ferroelectric phases at room temperature, and the dielectric constant is high. However, due to the alternating electric field, the direction of the domain changes with the electric field direction often result in large losses. If the loss is too large under the long-term electric field, heat will be generated and the equalizing capacitor will be destroyed. Moreover, in order to miniaturize the capacitors would increase electric field strength , thus the dielectric constant and loss of the BaTiO3-based grading capacitor will increased greatly.
BaTiO3-based ceramics have a significant aging effect as a ferroelectric ceramic. That is, as the standing time increases, the domains gradually become stable, exhibiting a small dielectric loss. In previous studies, it was found that the pre-applied electric field realigns the domains and changes the domain stability of the sample. For the actual high-voltage ceramic capacitor, after the completion of the production, it must pass the large electric field AC withstand voltage test, which can not be ignored for the influence of the domain state of the BaTiO3 ceramic. However, there is no report on this pre-field effect on the dielectric properties of the capacitor.
In this paper, high-voltage ceramic capacitors for lightning arrester are used as research objects, and the changes of dielectric constant and loss after pre-applied electric field in different aging stages are studied. The results show that for the unaged sample (new firing), the pre-applied electric field increases the loss value of the sample under the electric field of 0.35kV/mm from 0.05 to 0.08, and the average rate of change of the loss with the electric field increases from 14.4% to 22.7. %; For short-time aging samples, the pre-applied electric field reduces the loss value of the sample at 0.35kV/mm electric field strength from 0.046 to 0.007, and the average rate of change with electric field increases from 13% to 0.4%; The long time aging sample, the pre-applied electric field increases the loss value of the sample at 0.35kV/mm electric field strength from 0.036 to 0.065, and the average rate of change of the electric field with the increase of electric field increases from 9% to 17%. This result indicates that in the short-term aging phase, the pre-applied electric field can greatly reduce the loss of the high-voltage ceramic capacitor, which has important engineering significance.