Aramid Paper Research Articles

新アラミド絶縁紙による変圧器巻線絶縁の高耐電圧化

新アラミド絶縁紙による変圧器巻線絶縁の高耐電圧化

Thermally stimulated discharge currents in corona-charged aramid paper

Thermally stimulated discharge (TSD) currents were measured in corona-charged aramid paper to study the mechanisms of charge storage and its subsequent release from the bulk of the material. Studies were carried out on paper thicknesses of 76 and 127 μm using a point-plane gap in air at atmospheric pressure. TSD currents were measured over a temperature range of 0–200 °C and the influence of various parameters, such as the poling voltage, rate of heating and effect of electrode materials, were investigated. Corona-charged aramid paper with positive polarity voltage showed that the TSD current is of either polarity depending upon the temperature range. Three distinct peaks were observed, one in the low-temperature range, 20–25 °C, and the other two peaks at higher temperatures. The low-temperature peak was considered to be due to an abnormal TSD current, whereas the currents at higher temperatures were normal TSD currents. Activation energies were determined using the low-temperature tail of the TSD curves and were found to be dependent on extrinsic parameters such as the thickness of the sample. The activation energy for aluminium electrodes was observed to be in the range of 0.5–2.0 eV. The TSD currents for the low-temperature peak was considered to be electronic. It is postulated that the charge carriers are generated within the material by the intense electric field due to corona.

Dielectric and thermoanalytic behavior of moisture and water in aromatic polyamide paper

Specimens of an aromatic polyamide (Aramid) paper, which were subjected to various degrees of moisture adsorption as well as water immersion, were investigated in order to estimate how much the adsorbed moisture and the stored water affect the dielectric and thermoanalytical behavior. In the humid specimens the dielectric properties did not change much and there were no endothermic and exothermic peaks. In the soaked specimens the dielectric properties changed remarkably and there were endothermic and exothermic peaks due to free water recognized at approximately 0 degrees C. It is concluded that the dielectric properties of Aramid paper are rather stable to moisture adsorption because its polyamide linkage bonds tightly with the adsorbed water which is in the shape of nonfreezing bound water, but when the total water content increases over the saturated moisture value of 6.8%wt, increases in the dielectric properties take place due to the free water in the fiber structure. In the bound water region, Aramid paper has higher DC resistivity values compared with other synthetic papers such as polyester paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Conduction and thermally stimulated discharge currents in aramid paper

Conduction currents and thermally stimulated discharge (TSD) currents were studied in aramid paper at various field strengths and temperatures. At low field strengths the conductivity is ohmic, and at higher field strengths (up to 30 MV/m), ionic conduction is a possible mechanism. The activation energy of low field conduction is determined and at high electric fields the hopping distance for ions is in the range of 4.4 to 8.0 nm. TSD currents are also measured at various poling fields, formation and storage times, and rates of heating. The TSD current shows a peak at 135 degrees C for a rate of heating of 1 K/min and shifts to a higher value when the rate of heating is increased. The peak current and the charge released to the external circuit is proportional to the poling field. The observed peak is attributed to the depolarization of permanent dipoles with a room temperature relaxation time of 5.3*10/sup 5/ s. >

Conductor insulation tests in oil: aramid vs. kraft

Developments in transformer insulation, leading to increased use of aramid insulation in oil-filled transformers, are briefly summarized. A series of tests designed to gather data on the dielectric strength of aramid paper in oil used as turn-to-turn insulation is presented. The test setup, sample configuration and preparation, and test procedures are described. Turn-to-turn and coil-to-coil results are presented and discussed. It is shown that, turn-to-turn, the aramid paper is stronger dielectrically than the kraft paper by 25% using a full-wave impulse and 20% using a 1 mu s chopped wave. There is little or no difference in the dielectric coil-to-coil strength between the aramid and kraft papers. Thus, it is possible to improve the turn-to-turn impulse strength of liquid-filled power transformers by using aramid paper in place of kraft paper. The aramid also has improved mechanical strength and thermal aging characteristics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phenyl Methyl Silicone Fluid and Its Application to High-Voltage Stationary Apparatus

Phenyl methyl silicone fluids of low phenyl radical concentrations and low viscosities are characterized by their extraordinary gasabsorbing property in high electric fields. Their physical, chemical and electrical properties were investigated and compared with those of dimethyl silicone fluids. The corona resistant characteristics and applied voltage vs. life expectancy relationships were studied, using model capacitors consisting of the silicone fluid and polypropylene film capacitor paper insulation system, and heatresistant transformer models consisting of the silicone fluid and Nomex Aramid paper. It was found that the phenyl methyl silicone fluids greatly improve the corona resistance property and the life expectancy in high voltage fields over the dimethyl silicone fluids, although both fluids are similar in their general characteristics. As a result, it is suggested that the phenyl methyl silicone fluids can be used to construct reliable high voltage stationary apparatus which is small in size.