AC Dissipation Current Waveforms Research Articles

Nonlinear distortion of AC dissipation current waveform and space charge in EVA film

AC dissipation current waveform shows nonlinear distortion at AC high field, and this nonlinear distortion is supposed to be related to the behavior of space charge under AC field (AC space charge). We investigated the relationship between the nonlinear distortion of AC dissipation current waveform and AC space charge formation in ethylene–vinyl acetate copolymer film (EVA film). At low field, the capacitive current component was subtracted from the output signal of AC current, and then, the AC dissipation current waveform was obtained with the increase of applied AC field. As the result, the AC dissipation current waveform of EVA film showed nonlinear distortion at high field. In addition, the AC dissipation current waveform has a phase advanced from the phase of the applied AC field. The phase advance is considered to be caused by the increase of the capacitive current component due to space charge injection. We suggested that the nonlinear distortion and the phase advance of AC dissipation current waveform of EVA film were affected by the space charge injection. In addition, we developed a new evaluation method of the AC space charge injection layer based on the phase advance and the nonlinear deformation of the AC dissipation current waveform. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Space charge behavior in polymer film based on increment of capacitance under AC high field

AbstractPolymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high‐field AC dissipation current waveform of polymer materials 1. AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high‐field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement.We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high‐field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high‐temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10018

High-field dissipation current waveform in e-beam-irradiated XLPE film at high temperature

We developed a detection method of ac dissipation current waveforms combined with a fast rising ac ramp voltage application as a new technique to evaluate the high-field dielectric properties and the dissipation current waveform over a very short time range. This measurement was carried out on electron beam irradiated crosslinked polyethylene film. At high temperature the high field tan /spl delta/ and ac dissipation current show nonlinear electric field dependence and the dissipation current during decreasing field becomes larger than that during increasing field, suggesting the contribution of carrier injection from electrodes. The dissipation current waveforms in the high temperature region show the peak in the first part of each half cycle of a full waveform, and fast decrease in the latter part. This result is probably due to the hetero and home space charge formation caused by the injected carriers from the electrode.

High-field dielectric properties and AC dissipation current waveforms of polyethylene film

The authors have developed a new method for the detection of AC dissipation in dielectric materials under high AC field. Using this technique, high-field dielectric loss properties and their relation to AC dissipation current of low-density polyethylene (LDPE) films are measured. Near room temperature, tan delta of a LDPE film has small electric field dependence. In this temperature region, the dissipation current shows saturation around the voltage peaks in phase even with high-field application. At higher temperatures, however, the high-field tan delta tends to have a strong field dependence, and the AC dissipation current deforms and is nonlinear near the voltage peaks. The nonlinearity of the AC dissipation current decreases under the decrease of tan delta with the voltage application period. These results show that the large increase of tan delta in the high-field and high-temperature region is related to the loss due to DC-like carrier motion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-field dielectric properties of polyethylene in the high-temperature region

Nonpolar polymers such as polyethylene or polypropylene are widely used as insulation materials, often under conditions involving strong electric fields and high temperatures. Under these conditions, the conduction loss due to DC-like carrier transport may give rise to a high-field AC dissipation factor (tan δ). This paper describes the high-field dielectric properties of polyethylene films at frequencies from 50 to 400 Hz and temperatures from room temperature to 100°C, as measured with a new type electrode design developed by the authors. In the high-temperature region, the AC dissipation current waveform at 50 Hz was also measured. At room temperature, the electric-field dependence of tan δ is almost unaffected by the frequency of the applied field. But at high temperatures and strong electric fields, tan δ tends to have a large field dependence and to be almost inversely proportional to the frequency. Thus the AC conductivity becomes independent of the frequency of the applied field in the region of strong fields and high temperatures. A theoretical analysis shows that the high-field dielectric loss is governed by two processes, namely, the dielectric relaxation loss inherent to the AC field and the DC-like carrier transport loss that becomes prominent in the high-temperature region, where AC dissipation current waveform becomes significantly nonsinusoidal.

Measurement of AC dissipation current in oil-film composite insulating system

The electric field dependence of tanδ in oil-film composite insulating system sometimes has a peak and then decreases. This is known as the Garton effect. It is caused by the fact that at high voltages, the contribution of carriers in oil to the conduction loss does not last through an entire alternating field cycle. Since the separation of the loss current from the extremely large capacitive current is usually very difficult, the nonlinear ac dissipation current waveform caused by the Garton effect has not been measured. The authors developed a new method for the measurement of high-field ac dissipation current in polymeric insulating materials. This technique was applied to the detection of nonlinear dissipation current and its waveform in oil-film composite insulating system associated with the Garton effect. We measured the variation of dissipation current with applied field and its frequency.