No abstract

No abstract

No abstract

No abstract

Much progress had been made during the last two decades in acoustic and optical methods for measuring charge distributions in dielectrics. A review on this topic is given, which mainly covers the past research activities associated with that at our laboratory. For acoustic methods, we will discuss and compare the pulsed electroacoustic (PEA) and pressure wave propagation (pwP) methods and present some of the results that enabled us to gain physical insights into the charge dynamics within solid plate samples and coaxial cables. For optical methods, we will discuss the Pockels effect technique that is used for the dynamic measurement of surface charge distributions, and the Kerr effect technique that is developed for measuring electric field distributions within liquid dielectrics. 1 INTRODUCTION T HE Poynting vector represents a flow of electric power equivalent to EXH [W 1m2], where E [V 1m] represents electric field inten sity and H [Aim] the magnetic field intensity. To facilitate the transmission of large amounts of electric energy, which has its equivalent in a large Poynting vector, researchers must strive to increase either the magnetic field jj or the electric field E. An increase of H can be ac complished by using superconducting transmission lines, while that of if can be achieved by increasing the transmission voltage. However, at present, the development of a practical, usable superconducting trans mission system has not been fully realized. Therefore, we have to con tinue our efforts in obtaining high E through a HV transmission system.. To this end, much research on the properties of dielectric and insulating materials will have to be conducted. This is one of the goals of the present workThe advancement of excellent electric insulating materials, in which electric power flows in the form of a Poynting vector, has made a sig nificant contribution to the development of electric power engineer ing, electronics engineering and electronic communication systems in present everyday life, Many researches have been conducted on de voltage-current characteristics by electric conductivity (r; [S/m]) mea surement, and on ac voltage�current characteristics by permittivity (c [F/m]) measurement in the past years. However, that research con sidered only the case where the current flowing through the materials had reached the steady state and the electric field across thematerial was uniform and independent of time.During the last 20 years, because electric power apparatus has be· come more compact, and electronic devices have become much smaller, the insulating materials used are highly stressed to > 1 MV I cm, which is near the breakdown strength of the insulating materials. Under such high electric field application, electric charges may be injected fromelec trodes or be dissociated from impurities that occur in the material. These electric charges accumulated in the insulating material distort the orig· inal internal electric field distribution. The process may cause the insu lating material to degrade and som...

This paper reports on an investigation into the space charge formation and decay at different material interfaces. In particular, the influence of the interface between electrode and polymer or polymer and polymer on the space charge dynamics has been studied. Planar samples were subjected to high dc electric stresses for extended periods of time and space charge measurements taken using the pulsed ( ) electroacoustic PEA technique. It has been found that the types of interface between electrode and polymer play a significant role in determining the charge distribution in the insulation and that the interface between polymer and polymer acts as a potential barrier to electrons while allowing positive charge carriers through easily.Index Terms -LDPE insulation, insulation interface, space charge dynamics, PEA technique, effect of electrode materials, charge formation, charge decay, potential barrier.

We studied the trapping of positive and negative charges in the chemical structures of polymers under a high electric field using a space charge measurement system. Positive charges accumulated in low-density polyethylene (LDPE), whereas positive and negative charges accumulated in polyimide (Kapton ® ) and also in ethylene tetrafluoroethylene (ETFE) subjected to electron beam irradiation. To determine the charge-trapping sites in the chemical structures, a quantum chemical calculation was carried out using Density Function Theory (DFT) with Gaussian 09. The relationship between the energy band and the isosurface of orbital electrons at various energy levels was obtained. A threedimensional (3D) electrostatic potential distribution map was obtained for positively and negatively charged polymers to determine the relationship between a trapping site and the charge accumulation center in the 3D potential distribution map. Positive and negative charges in Kapton and ETFE films are trapped in trapping sites in chemical structures and the positive charges in an LDPE film are trapped in physical defects.

Since the beginning of the 20th century, surface discharge phenomena have been investigated from a viewpoint of scientific interest.