A hybrid optical current transducer based on adaptive Kalman filter theory

The benefits of optical current transducers (OCT) have been intensively investigated in recent years. However, temperature and stress-induced linear birefringence in sensing materials cause error and instability, which limits severely the practical application of OCTs. In order to take advantages of both the conventional CT and OCT, the paper presents a new kind of hybrid optical CT formed by the conventional CT with high accuracy in the steady state and the optical CT with no saturation under fault current conditions. By means of the adaptive Kalman filter algorithm derived in this paper, the hybrid optical CT is adjusted adaptively to improve the accuracy to satisfy the need of measurement and protection in the power systems. In addition, applying the noise estimation with unknown prior statistics to the basic Kalman adaptive filter equations, the adaptive Kalman filter algorithm with noise estimation is derived in the paper. The test results show the validity of the hybrid optical CT and the adaptive Kalman filter algorithm.