The proposed research is a GOALI industry-university collaborative project between MIT and EPRI for the continued analytical, computational, and experimental study using optical tomography measurements of high voltage insulation, conduction, prebreakdown and breakdown characteristics in dielectrics. The methodology uses electric field induced birefringence (Kerr effect) with an improved sensitive optical measurement system and a new advanced mathematical formulation that allows calculation of electric field magnitude and direction in any electrode geometry from optical intensity measurements. Because the physics of high voltage charge injection and transport, prebreakdown and electrical breakdown are not known for most metal/dielectric systems, the electric field distribution cannot be calculated from knowledge of system geometries alone. Optical measurements provide a direct approach to determining electrical constitutive laws and learning the physics of the electrical breakdown process and so offers a research methodology for major advances in increasing the breakdown strength of dielectric systems.
The proposed continuing research program involves both graduate and undergraduate students together with EPRI personnel to try to further understand charge injection, conduction, aging, degradation, prebreakdown and breakdown mechanisms in high field stressed gaseous, liquid, and solid dielectrics using new modern optical, electronic, and computer instrumentation to give "eyes" inside materials to see prebreakdown and breakdown field and charge distributions that could not be measured before. Specific proposed work tasks are 1) Extend and complete the mathematical formulation of the Kerr effect where the applied electric field magnitude and direction change along the light path for any three dimensional geometry; develop computational algorithms to convert measured optical signals to electric field distributions; and to verify analysis with experiments; 2) Develop a computer interfaced camera system with an optical array detector distributed over an area to automate sensitive Kerr measurement data acquisition and processing without mechanical motion; 3) Perform sensitive Kerr electro-optic field and charge mapping measurements in a well controlled and monitored test cell for various liquid/solid material combinations in the volume and within the electrical double layer near interfaces as a function of DC voltage amplitude and polarity, AC voltage amplitude and frequency, direction of interface with respect to applied electric field, temperature, moisture, conductivity, and concentration of moisture and trace additives; 4) Extend the sensitive Kerr effect technique and perform measurements for weakly birefringent dielectrics in pulsed, ramped, and other time varying applied electric fields; 5) Relate the results of the modelling, optical measurements, and dielectrometry measurements to a better understanding of high voltage conduction, prebreakdown and breakdown phenomena in dielectrics in order to reliably extend the operation of high voltage apparatus to higher voltages; and 6) Construct a compact optical sensor measurement system that with the help of EPRI personnel and contractors will be applied to electric field and space charge measurements in an operating transformer. ***
