98_Mijuno_ELF_PE_impulse - I EEE Transactions on...

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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 5 No. 2, April 1998 211 Electroluminescence in Polyethylene Subjected to Impulse Voltages T. Mizuno, Y. S. Liu, W. Shionoya, S. Matsushima, K. Yasuoka, S. lshii Dept. of Electrical and Electronic Engineering, Tokyo Institute of Technology, Tokyo, Japan A. Yokoyama and H. Miyata Polymer & Chemicals Department, Materials Research Laboratory, Fujikura Ltd., Tokyo, Japan ABSTRACT Electroluminescence (EL) from HDPE (high-density polyethylene) films subjected to repetitive rectangular-shaped impulse voltages has been investigated at electric fields <BO kVlmm in or- der to clarify the temporal behavior of carriers injected into the polymer. EL emission was dis- tinctly observed during the voltage rise and fall phases. During the voltage plateau and the zero voltage phases, the intensity did not instantly decrease to zero but a very weak emission lasted for at least 3 ms. The number of pulses was determined by the amplitude of the im- pulse voltage, whereas the intensity strongly depended on the temporal variation rate of the voltage. The total number of pulses during both phases of the voltage rise and fall was al- most equal. The spectra did not depend on the phase and the amplitude of the impulse volt- age. The above behavior of emission can be explained qualitatively by the electron-hole recombination in the metal-polymer interface region and showed the picture of temporal be- havior of carriers, carrier injection and transport, in the interface region for the field relaxation at the interface. 1 INTRODUCTION LECTRICAL degradation, such as electrical treeing, in polymeric in- E sulating materials is a serious problem under high electric field. To overcome such a problem, we have to understand the behavior of charge carriers injected into polymers. It has been reported [l-31 that the occur- rence of electrical trees in PE (polyethylene) is strongly affected by the temporall variation of the applied voltage under impulse and/or dc volt- age, because of the time required for space charge formation to reduce the local electric field at the injecting electrode. Based on such obser- vations of electrical trees, it has been estimated that the time required for the Jormation of space charges near the electrode is in the order of 300 ps 111 or 30 to 80 [2], and that the time required for their dissi- pation is in the order of 10 ms [l] or 30 min [2]. From these reports, we need to visualize the temporal behavior of carriers in polymers near the electrode, especially at the pre-stage of the degradation such as at the occurrence of an electrical tree. (electroluminescence) associated with carrier injection and trans- port has been observed in various insulating polymers at the pre-stage of the degradation under ac [&SI, dc [9,10] or impulse voltages [ll-151.
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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98_Mijuno_ELF_PE_impulse - I EEE Transactions on...

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