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Based on the three-phase detection method, a three-phase combined transformer error verification platform is designed and the error properties of three-phase two-element combined instrument transformers, including the interaction between voltage transformer unit and current transformer unit are studied systematically. The experimental results show that the error characteristics of CT and PT are greatly influenced by rated current percentage of CT and rated voltage percentage of PT, the size of secondary load and whether the CT unit and PT unit are excited at the same time. Especially when the current transformer unit and the voltage transformer unit are excited at the same time, due to the strong electromagnetic interaction between them, even the test point of the current transformer below 20% of the rated current is out of tolerance.

The Brillouin-scattering fiber-optic gyroscope (BFOG) is a new-generation miniaturized high-precision fiber-optic gyroscope. By focusing on the light characteristics of the BFOG resonator, we derive a recursive relationship for the intensity of light of different orders by using the coupled equations for stimulated Brillouin scattering. We then establish mathematical models of the light characteristics, threshold power analysis, and optimum resonance condition analysis. Based on these models, we derive a functional relationship between the incident pump light intensity, light intensity in the cavity, the intensity of each Stokes wave order, and emitted light intensity. Finally, we simulate and quantify the threshold power and resonance critical condition influenced by several main factors including the insertion loss, coupling coefficient, and transmission loss.

Every optical state polarization in Sagnac fiber optic current sensor (S-FOCS) is restricted in specific stage theoretically. However, complex transforming processes of optical state polarization induce illegal linear optical state polarization and illegal circular optical state polarization in Sagnac fiber optic current sensor, then, decrease performance of S-FOCS. According to the parameters of the optical components, we built Jones matrixes and the mathematical model of optical transmission in S-FOCS. Based on polarization state error models of Sagnac fiber optic current sensor, we made experiments to evaluate performances of several key components, including polarizer, quarter-wave retarder and sensing head, then, investigate the influence of several main polarization error factors on S-FOCS's performance practically. The result shows that the changing degree of polarization state causes bias instability, nonlinear of scale ratio, and random noises of S-FOCS, and influents S-FOCS's performance.