UBC Theses and Dissertations
Integrated optics pockels cell high voltage sensor Rahmatian, Farnoosh
In this thesis an integrated optics version of the Pockels cell, to be used for the measurement of high voltage in power transmission systems, is described. The operation of the sensor is based on the electro-optic effect in lithium niobate. The sensing head consists of a waveguide formed by diffusing a strip of titanium in a y-cut lithium niobate substrate. This waveguide (z-propagating) supports two orthogonal modes. An electric field, in which the sensor is immersed, alters the difference in the phase velocities of the two modes and, in turn, alters the polarization state at the output of the waveguide. Polarization maintain ingoptical fibres transmit light to the sensor head and interrogate its output. The electric field in which the sensor head is immersed can be detected by measuring the change in the polarization state at the output of the sensor. Also, some of the technological problems encountered in realizing an integrated optics Pockels cell (IOPC) have been addressed and overcome. The photolithographic fabrication of the waveguides, waveguide end preparation, permanent fibre to waveguide butt-coupling, and other fabrication steps have been successfully completed. Fully connectorized systems have been fabricated and tested to characterize the performance of the IOPC. Various device parameters such as intrinsic phase, half-waveelectric field, and extinction ratio have been measured for several devices. The effects of waveguide width and length on the performance of the sensor have been studied. Test results indicate that useful devices, well biased, need to be at least 5 mm long. The linearity of sensor response and noise in the measurements have been investigated. The test results show that the sensor is capable of metering high voltage AC signals with less than 0.3% error and,therefore, is likely to meet the power industry standards, such as those proposed by Erickson in 1992, for optical high voltage transducers. The stability of the sensor under various conditions has been explored. The piezoelectric resonances of the sensor heads and their effects on the bandwidths of the sensors have been examined. Sensors with large enough bandwidths have been fabricated which have successfully measured the IEC (InternationalElectrotechnical Commission) standard lightning impulses with 1.2 As front time and 50 Astail time. The results indicate that one IOPC can be used as a high voltage sensor in several applications such as metering high voltage AC signals, protection, and time-resolved-fault-location.
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