基于微带环谐振器的油纸绝缘介电响应特性与受潮评估

Dielectric Response Properties and Moisture Assessment of Oil-Paper Insulation Based on Micro-Strip Ring Resonator

该文介绍了微带环谐振器介电响应分析的原理,分析了微带环谐振器表征上层介质材料介电特性的计算模型,运用HFSS电磁仿真软件研究了上层介质材料、基底厚度、圆环半径对微带环谐振测试结果的影响。设计了谐振基频在1.16GHz左右的微带环谐振器,制备了从干燥(含水量低于0.5%)到含水量6.87%之间七种不同含水量的纸板样品。将微带环谐振方法的测试结果与标准谐振腔方法的测试结果进行了交互对比和验证,运用传统的1mHz~5kHz频域介电谱(FDS)测试进行了辅助分析。研究了水分对绝缘纸板1~6GHz频段介电特性的影响,分析了均匀受潮和不均匀受潮绝缘纸板在1~6GHz频段的介电特性。微带环谐振测试能够明显区分均匀受潮下不同含水量的纸板样品。对于不均匀受潮的纸板样品,在1~6GHz频段下,其与均匀受潮样品的曲线存在一定差距,且差距随着不均匀程度增加而增大。根据均匀受潮单层纸板的含水量与谐振频率平均值■的对应关系,建立了所选1.1mm厚绝缘纸板的水分评估曲线,并利用受潮样品进行了验证。研究表明,微带环谐振测试方法在绝缘纸板受潮快速评估中有着较好的应用前景。

In the condition assessment of oil-paper insulation, the dielectric response is a widely used characterization method. Both time domain spectroscopy(TDS) and frequency domain spectroscopy(FDS) test at lower frequencies require long time and cannot reflect damp state of insulation pressboard in time. In order to improve the speed of dielectric characterization and the convenience of experiment, the GHz-band dielectric response technology based on the resonant measurement method gradually has the feasibility of research and the possibility of application in the detection of damp state in oil-paper insulation. The resonant method is to measure the scatter parameters by designing a resonator with some weak couplers. The dielectric characterization of resonant method is carried out at the resonant frequencies, which can indirectly calculate dielectric properties of the upper medium at the GHz frequencies, which has the advantages of convenient experiment, fast characterization, and high testing frequency. Resonators usually have a fixed geometry, and the micro-strip ring is a commonly used resonator.In the physical structure of the micro-strip ring resonator, the selected substrate is Nelco’s NX9320 highfrequency plate, whose thickness is 0.762mm, εr is 3.2±0.4, and tanδ is 0.002 4. Two copper micro-strip lines and a copper ring are attached to the high-frequency sheet base. The characteristic impedance is 50?, the copper thickness is 0.5oz, the width of the copper ring and microstrip line is 1.85mm, the inner radius of the copper ring is 25mm, the outer radius is 26.85mm, and the coupling gap is 0.4mm. Above the substrate is a layer of experimental material with known thickness. Two high-frequency SMA interfaces are designed at both ends of the micro-strip lines, which are used to connect the network analyzer. The network analyzer Pico VNA 106 produced by Pico company is used, and the test bandwidth is 1~6GHz. By testing the S21 parameter of the whole resonant device, that is, the insertion loss characteristic, the resonant point is found and its dielectric parameter is deduced.By analyzing the test results of the micro-strip ring resonant dielectric response, it can be concluded that the dielectric parameter response curve of GHz insulating pressboard is relatively flat with weaker frequency dependence. The dielectric characteristic curves show an obvious gradient with water content, indicating that εr and tanδ of the insulation pressboard at GHz band also increase significantly with the gradual aggravation of damp state. In the obtained dielectric characteristics of 1~6GHz, the dielectric response curves with different degrees of damp conditions show weak polarization peaks and loss peaks between 1GHz and 3GHz. It’s pointed out that the polarization process in oil-paper insulation is dominated by dipole steering polarization at higher frequencies, and the dominant charges involved in polarization mainly come from cellulose molecules and water molecules with polarity. According to the Debye model, the real part of the complex permittivity of pure water at 0℃ and 1~100GHz shows a monotonically decreasing process, and the imaginary part shows an obvious polarization peak,indicating that pure water has a certain polarization process at GHz frequencies. Therefore, the dielectric properties of the insulating board obtained in this paper in the GHz frequency band are of great significance to the study of the polarization process in this frequency band, especially the dipole polarization process. As for dielectric response curves of three kinds of pressboard stacks with equivalent water content at 1~6GHz, the uneven damped samples also show a certain polarization peak and loss peak between 1GHz to 3GHz. In addition, in the sample groups with the same equivalent water content, the fluctuation trend of dielectric response curves is the same, but the intensity of fluctuation increases with the increase of the degree of inhomogeneity. There is an obvious gap between the curves of the uneven and even damped samples, especially at the peak, and the gap increases with the increase of the degree of unevenness.