Dielectric Materials for Advanced Applications Progress Report (Oct – Feb. 2011) Xuewei Zhang and Prof. Markus Zahn Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science Research Laboratory of Electronics Laboratory for Electromagnetic and Electronic Systems High Voltage Research Laboratory Mar. 2,

I. Introduction Problem Setting 2

I. Introduction Possible Space Charge Configurations 3

I. Introduction Kerr Electro-Optic Measurement (Pre-Semi Polariscope) 4

I. Introduction From Light Intensity to Electric Field (Simple Case 1) 5

I. Introduction From Light Intensity to Electric Field (Simple Case 2) 6

I. Introduction From Light Intensity to Electric Field (Complex Example) There are 4 possibilities for E in total 7

I. Introduction From Light Intensity to Electric Field (General Method): Suppose there are N sections in the light intensity profile and M monotonic sections of the sine function, the total number of possibilities is ; Then, enumerate all these possibilities, and find solution to the following optimization problem: 8

I. Introduction Detect Light Intensity by CCD Camera 9

I. Introduction Synchronization of waveforms 10

I. Introduction Experimental Procedures: Before the application of the high voltage, the CCD camera is set to be in the internal-triggering kinetic mode. Take 50 subsequent images, in which each pixel corresponds to an electron count indicating the brightness. Compute the average of them as background. Then switch the CCD camera to external-triggering image mode and press the manual trigger button of the delay generator. High voltage pulse is generated; the waveform measured by the divider is recorded by the oscilloscope. After being triggered the CCD camera takes the signal. Cut off the high voltage supply, use the real-time mode of the CCD to monitor the liquid stabilization, wait about 10 minutes and start the next measurement. 11

An example: Narrow lines and small fluctuations may not be seen by naked eyes. The old “counting fringes” method is inaccurate:“counting fringes” method a)Spatial resolution b)Number of fringes c)Contrast of light intensity d)Diffusivity of pixels e)Time synchronization 2. Results 12

2. Results More electrode combinations (heterocharge distribution) 13

2. Results More electrode combinations (homocharge distribution) 14

2. Results 15

3. Results 16

2. Results Up to now, we have shown the results of: 1). For various pairs of electrodes and the same peak HV value (25 kV), measuring the distributions of electric field and space charge density in the gap at the same instant (peak HV); 2). For the same pair of electrodes (S-S #21) and various peak HV values (both polarities), measuring the distributions of electric field and space charge density in the gap at the same instant (peak HV); Stainless steel electrodes can realize homocharge distribution in propylene carbonate. It seems that only when a stainless steel electrode is stressed by a positive polarity high voltage, the “injection” at the anode supersedes the heterocharge distribution due to bulk dissociation, which, however, is not exactly an injection, since propylene carbonate is reactive with stainless steel generating particle layers on the anode. We also did the following work: For the same pair of electrodes and the same peak HV value, we video recorded the dynamics of the charge injection and transport. 17

2. Results Practical difficulties and solutions: The shortest exposure time of the CCD camera is 10 μs. Due to its high spatial resolution and sensitivity, the transfer of an image to memory is relatively slow, resulting in a frame rate of < 100 fps. The high voltage pulse duration is ~ 10 ms, requiring the frame rate >> 100 fps. Directly recording the dynamics seems impossible at the current stage. The solution is to repetitively apply the high-voltage pulses and take images with different delays at different times. In principle we can take images every 10 μs; however, the jitter of the Marx generator brings about uncertainties in the starting time of the HV pulse, causing variations in the waveform. At t=0, the 15 V trigger pulse is applied to the Marx generator, but the time it takes to initiate a HV pulse may vary from 1 to 50 μs. There are fluctuations in the HV pulse starting time during the first 0.1 ms after trigger, which makes the measurement on the rising-edge of the HV pulse inaccurate and inconclusive. In all cases, the peak appears at about t=0.1 ms, and images were taken every 0.5 ms from t=0.1 ms to t=10.1 ms. 18

2. Results Stainless Steel (#21) electrodes, peak HV ~25 kV Light intensity evolution: 19

2. Results Stainless Steel (#21) electrodes, peak HV ~25 kV Electric field distribution: 20

2. Results Stainless Steel (#21) electrodes, peak HV ~25 kV Space charge dynamics: 21

Plan for Continuing Work Transformer oil electric field and charge density measurements for various electrode combinations and high voltages (March-May) Breakdown experiments to determine if there is a correlation between charge density magnitude and polarity near the electrodes and the breakdown voltage (June-August) 22

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