Measurement Sensitivity Assessment of Space Charge Electro-Optical Detection System
Qi Tianrun1, Wang Wei1, Ren Hanwen1,2, Gao Haoyu3, Li Qingmin1,2
1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China; 2. Beijing Key Lab of HV and EMC North China Electric Power University Beijing 102206 China; 3. China Electric Power Research Institute Beijing 100192 China
Abstract：Space charge distribution has become a key indicator for reliably evaluating the properties and states of insulation materials at the micro-mechanical level. A short- and long-term charge injection process will accompany the insulation material under the complex stress environment. Meanwhile, the space charge evolution under high-frequency stress is characterized by fast migration rate and small distribution range. Therefore, the spatial resolution and measurement speed of measurement instruments need to be further improved in order to meet the demand for space charge measurements in high-frequency stress environments. For high temporal and spatial resolution measurements of solid insulation space charge in complex transient stress environments, the sensitivity of the space charge electro-optical detection system is a key factor affecting the reliability and accuracy of the measurement for weak charge perturbation electric fields. In view of this, this paper carries out an analytical study on the factors affecting the detection sensitivity based on the space charge electro-optical detection method. The transmission-based and reflection-based topology are proposed for space charge electro-optical measurement. Moreover, the optical-mechanical-electrical signal transmission model of the reflection-based and transmission-based topology is constructed. Meanwhile, the analytical platform of detection sensitivity in the corresponding topology is established. Further, the key factors affecting the measurement sensitivity are analyzed for the core electro-optical detection system. The feasibility of achieving nanoscale spatial resolution is verified from both simulation and experimental perspectives. Theoretical analysis shows that the difference in measurement sensitivity between transmission-based and reflection-based topologies is mainly determined by the following two factors: (1) Difference between incidence coefficient α and light transmission coefficient β. (2) The difference in the effective optical distance of the detection laser in the transmission/reflection topology. Further, the experiment results demonstrate that the reflection-based topology exhibits a higher measurement sensitivity. Excellent output linearity under high-frequency and narrow pulse-width charge signals is also ensured. In addition, both sensing and detection parameters have a large impact on the measurement sensitivity. An increase in the electro-optical coefficient of the sensor can effectively improve the measurement sensitivity. On the other hand, as the incident angle approaches Brewster angle, the detection system will obtain better measurement sensitivity. Relatively optimal measurement sensitivity is obtained by using LiNbO3 crystals as electro-optical sensors in conjunction with the angle incidence of 65°. For detection parameters, the detector bandwidth is the central factor limiting the performance of the detection system. To obtain nanoscale spatial resolution, the bandwidth of the detection system has to achieve sub-THz level. Finally, the optoelectronic coupling model of the full-size electro-optical detection system is developed. The nanoscale spatial resolution performance of the space charge electro-optical detection system is analyzed and verified. From the perspective of sensitivity enhancement, the optimized design of electro-optical detection system is proposed, which is combined with the optical sampling principle to form a highly sensitive electro-optical detection system. Optical sampling measurements attenuate the detector bandwidth limitations associated with direct measurements. Each sample is equivalent to the acquisition of a DC signal, effectively reducing the noise level. Measurement sensitivity is further improved. The experimental results show that the proposed detection system has the capability to achieve tracking of picosecond pulse-width electric field signal. The optimized electro-optical detection system achieves measurement sensitivity and bandwidth in the mV/mm and THz levels, respectively. It has the potential to realize nanoscale resolution measurement of space charge. The related work can provide strong support for the development of high temporal and spatial resolution detection technology for space charge.
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2026, Vol. 41 
