IEEE Transactions on Dielectrics and Electrical Insulation

In the time domain characterization of dielectrics a fundamental measure is the dielectric response function Φ(t). This function permits the relaxation time and the complex permittivity of the dielectric under test to be determined, allowing the complete characterization of the dielectric properties. To calculate the Φ(t) function a time domain deconvolution algorithm (TDD), developed in a... View full abstract»

A model of partial discharge development in electrical tree structures is presented. The model considers channel conductivity, charge transport, and electric field redistribution during propagation of the discharge along the channels. It has been used for numerical investigation of temporal-spatial and electric characteristics of the partial discharges in capillaries and electrical trees exposed t... View full abstract»

It is important to investigate electrostatic charging phenomena in insulating oil pressboard (PB) composite system in electrical insulation design of oil-immersed power transformers. Our research aim was to clarify the charge accumulation mechanism at the oil/PB interface under static and flowing oil. In this paper, we directly measured the time variation of the electric field in the insulation sy... View full abstract»

In the past two decades, significant advances in space charge measurements in polymers have resulted in a better understanding of charge dynamics and their effect on material selection and processing. However, little attention has been given to the effect of semiconducting screens on space charge formation in the bulk insulation. This paper reports on space charge measurements on ∼ 1.5 mm thic... View full abstract»

A dynamic model for predicting DC arc behavior and critical flashover voltage of ice-covered insulating surfaces is presented. The model takes into consideration insulating geometry, pre-contamination level, and characteristics of ice layers. Assuming arc behavior as a time dependant impedance, it is possible to determine various arc characteristics such as time histories of leakage currents, pote... View full abstract»

When a spherical conducting particle exists in an electrode system where electrical gradient force acts along the electrode surface, the particle tends to move towards the high field region. The possibility of appearance of this phenomenon is experimentally investigated with wire particles, which can easily produce the corona discharge on their ends resulting the action of a reactive force on the ... View full abstract»

AC corona pulses have been measured using a computer-based commercial partial discharge detector. The pulse height distribution was measured in air as a function of phase angle and pulse height for a range of voltages using a point/cup electrode system. An earlier paper discussed the effect of space charge on the onset voltages for both positive and negative half-cycles and on the patterns obtaine... View full abstract»

This paper investigates the dielectric properties of various N2/SF6 gas mixtures based upon a cylindrical spacer model with adhering particle on the surface tinder homogeneous field conditions. The investigation involves a comparison with pure SF6. The flashover field strength for clean and particle contaminated spacer surface under AC and LI stress is determined. ... View full abstract»

A study is presented on changes in the structure and the chemical composition of antimony-doped semiconducting glazes before and after exposure to AC and DC electric fields in outdoor conditions and in the laboratory using the rotating-wheel-dip (RWD) test. Surface sensitive techniques such as scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX), X-ray photoelectron... View full abstract»

This paper deals with free-conducting particle motion and particle-triggered breakdown in AC electric fields between nonparallel plane electrodes in atmospheric air. Spherical particle motion was investigated theoretically and experimentally under AC voltages with various frequencies, considering the effect of the electrical gradient force and the dependence of the Coulomb force magnitude on the d... View full abstract»

Extruded films prepared from blends of low-density polyethylene (LDPE) and random copolymer of ethylene and propylene (EP) with the T-die method were studied with respect to electrical properties and morphology. Comparisons with data on blown films are made. These blends are of interest as improved LDPE for making XLPE for insulated power cable. In the high temperature region (90°C), a specime... View full abstract»

This paper deals with the experimental measurements and analysis of the formative time lags to breakdown and an estimation of the Toepler's constant for gas gaps, under the application of 50 Hz AC voltage. The experiments were carried out in a 145 kV gas insulated system (GIS) bus duct with pure N2, pure SF6 and SF6-N2 mixture as insulating media. The fo... View full abstract»

The step-up method is used to estimate the impulse breakdown voltages when the electrical insulation is not usable after it is broken. This paper analyses the reliability of the estimates of the underlying breakdown probability distribution in the step-up method, when (1) the observed breakdown voltage itself is available and (2) it is not available. The former case has many advantages compared to... View full abstract»

This paper presents investigations concerning the variations and significance of PD measurements in mineral oil, when detectors with different frequency response are used. Typical durations of discharge phenomena in liquids are much longer than in other media, and the measurement technique must be adapted accordingly. However, depending on the application concerned, this is not always possible. In... View full abstract»

The aim of the European project "ARTEMIS" is to develop a diagnostic system for assessing aging in power cable insulation. Its first task was to make a thorough characterisation of the cable insulation before aging. This is intended to provide a background against which any changes introduced by thermo-electric aging can be identified. The aging markers derived from this initial characterisation w... View full abstract»

Results of investigations performed to evaluate the effectiveness of a new inference method for the diagnosis of solid insulation systems, based on partial discharge (PD) measurements, are reported in this paper. Signal separation, noise recognition, and PD source identification are the main features of the proposed inference method. Techniques for signal separation and automatic noise rejection a... View full abstract»

This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under DC voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move later... View full abstract»

The velocity of ultrasonic waves, which were launched using the pulse-echo method and propagated in a stator insulation, was measured to assess the insulation condition of the stator bars. A statistical minimum velocity (Vmin) and a statistical average velocity (Vav) were computed for a new and three sets of stator bars which were in operation for 16, 18 and 23 years. After v... View full abstract»

Internal space charge measurement has been mainly applied to investigate insulating materials used in RV apparatus, such as HVDC cables. We have observed the space charge profiles to monitor copper ion migration occurring in an insulation layer of a metal-base printed circuit board and found that the space charge distribution along the thickness direction corresponds to the progress of ion migrati... View full abstract»