复杂波形作用下的直流ZnO电阻片缺陷结构及老化机理研究

It is an effective way to further reduce the insulation level of UHV DC power equipment and improve the economic performance of UHV DC project by making full use of the aging resistance of the existing lightning arrester and reasonably selecting the charge rate of the lightning arrester. But due to the short of aging device, it is difficult to determine the optimal charge rate of the arrester in converter station which was endured complex voltage waveform. In order to improve the converter arrester charge rate, reduce the protected equipment over-voltage level, the project with the help of converter typical waveform generator, to carry out the research as follows: 1) complex waveform aging effect on macro electric arrester performance are investigated through the variation of volt ampere characteristic and power loss characteristics in low current region; 2)the aging model of ZnO resistor under different voltage waveforms was built through the study of defect structure, respectively; 3) establish the equivalent relation between DC and AC aging with complex waveform aging based on the defect structure analysis. This project can not only theoretically reveal the ZnO resistance defect structure and aging mechanism under the converter station complex wave, and provide experimental support and theoretical basis for optimizing the protection level of converter equipment.

充分利用现有避雷器的耐老化能力，合理选择避雷器荷电率，是进一步降低特高压直流电力设备绝缘水平，提高特高压直流工程经济性的有效途径。但受限于老化装置，要确定换流站复杂波形位置避雷器的最优荷电率难度较大。为了全面提高换流站避雷器荷电率，降低被保护设备过电压水平，本项目借助换流站典型波形发生器，开展如下研究:1)通过小电流区伏安特性及功率损耗特性，研究复杂波形老化对避雷器宏观电性能影响；2）针对不同电压波形老化对ZnO电阻片缺陷结构的影响，分别建立不同电压波形下ZnO电阻片的老化模型；3）基于不同电压波形老化的缺陷结构分析，建立直流、交流老化与复杂波形老化之间的等效关系。本项目的开展不仅能从理论上揭示ZnO电阻片在换流站复杂波形下的缺陷结构及老化机理，同时为换流站设备保护水平优化提供了实验支持和理论依据。

为了全面提高换流站避雷器荷电率，降低被保护设备过电压水平，本项目基于自行研制开发的换流站典型波形发生器，研究了复杂波形作用下的直流ZnO电阻片缺陷结构及老化机理。首先，在特高压工程所用新一代电阻片配方体系下研究了典型添加剂Bi、Sb、Co、Mn、Ni等5种掺杂元素对电阻片宏观电性能及微观缺陷结构的影响。其次，开展了直流、交流电压应力作用对电阻片缺陷结构及宏观电性能的影响，获得了各种电压下的老化机理。通过对电阻片加速老化试验研究，发现目前国内特高压所用电阻片功耗特性不同于早期电阻片，功耗随老化时间不断下降后趋于稳定，按现行试验标准，电阻片均能通过老化试验，但宏观电性能参数变化率较大，不利于ZnO电阻片的安全稳定运行。研究发现由于新一代电阻片配方优化，使得Zn填隙数量减少，从而改善了电阻片直流老化特性；交直流劣化过程均由氧离子在电场作用下的迁移主导。最后，开展了阀电压、6脉动、12脉动等换流站复杂波形作用下ZnO电阻片缺陷结构及宏观电性能变化，获得了复杂波形作用下的老化机理。复杂波形老化过程中，直流分量起主导作用，其老化机理同样适用于复杂波形老化，不同之处在于还需要同时考虑交变电场作用下离子位移极化产生的损耗，脉动电压频率越高，功耗越大。