High Voltage Ratio Research Articles

The Effects of Valence States of Manganese on Electrical Properties of ZnO Varistors

The electrical characteristics of ZnO varistors with various valence states of manganese were studied. The composition containing low valence state of manganese exhibits low donor concentration, trap density and barrier height. The compositions with lower trap density have the characteristics of higher nonlinear coefficient, higher voltage ratio and lower leakage current. The electrical properties were improved by increasing the sintering temperature and time. It is also found that the depression angle decreases as a function of the increasing sintering time and temperature. The relaxation time for τ3 decreases with increasing sintering time. It indicates an enhancement in the degree of uniformity in trapping conductance and the trap emission/capture rate when sintering time increases. The dependence of the depression angle and relaxation time on the composition have been also presented. On the other hand, the dependence between the electrical properties and wetting behavior of intergranular phase is investigated.

Grain Growth and Electrical Properties in ZnO Varistors with Various Valence States of Additions

Grain growth and electrical properties in ZnO system with various valence states of manganese and cobalt were studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: Gn=Dtexp (-E/RT). In this work, the grain growth kinetic exponent n was 6 and activation energy was 230±21 kJ/mol. The grain size increased with the valence states of manganese and cobalt. The compositions with lower trap density have higher nonlinear coefficient, higher voltage ratio and lower leakage current. The varistor properties were improved by increasing the sintering temperature and time because of the more obvious tunneling effect.

Determination of Voltage Transformer Errors by Means of a Parallel-Series Step-Up Method

Improvements in the accuracy of determining standard voltage transformer errors by the utilization of specially developed amplifiers are described. Results of recently evaluated measurements in the fundamental parallel-series step-up method of the Physikalisch-Technische Bundesanstalt (PTB) are reported. The overall limit of uncertainty in the calibration of high voltage ratios has been improved by a factor of ten as compared with previous results at power frequencies.

A Self-Balancing High-Voltage Capacitance Bridge

A self-balancing high-voltage capacitance ratio bridge, especially designed for continuous measurement of corona losses on experimental transmission lines, is described. The instrument is derived by combining a negative-feedback amplifier with a high-voltage capacitance bridge based on the current comparator principle. Manual control is provided for the four most significant decades of the bridge, thus permitting the function of the feedback amplifier to be limited to the balancing of small deviations. In this manner the errors originating in the amplifier and the associated indicating or recording instruments are made insignificant in the overall measurement. The accuracy of the built-in current comparator is 0.001 per cent, of the circuitry associated with the amplifier, 1 per cent. The output of the automatic balancing circuit is instrumented to produce a readout which is proportional to the power loss and reactive volt-amperes. Both components are in the form of small dc voltages and thus are suitable for recording.

A transformer-ratio-arm bridge for high-voltage capacitance measurements

A high-voltage capacitance ratio bridge based on the current comparator principle is described. The inherent advantages of this bridge are high sensitivity and high accuracy without the necessity of a secondary balance. By suitable design the bridge is made direct reading in capacitance ratio and dissipation factor. It has a resolution of 1 ppm (part per million) and an accuracy of approximately 10 ppm. The highest capacitance ratio internally available with full resolution is 1,000/1. Design considerations and construction details are given. Possible applications are discussed.

Fabrication of a Fused Silicon Diode

Fabrication of a commercial type of fused silicon diode from an n-type material of resistivity 10 ohm cm. is described. The design is such that it will give about 150 mA. at 1 volt and will have a high breakdown voltage and high rectification ratio. For P-type doping of n-type silicon, results of several alloys are discussed. The complete details of fabricating the diode, i.e. slicing, etching, alloying and of testing the diode characteristics are presented.

The focusing properties of the electrostatic field between two cylinders

A general survey of the focusing properties of an electron mirror formed by two cylinders has been made. Photographs of the images formed are shown, and the relation between object and image distances for different voltage ratios on the cylinders are obtained. A special case of multiple reflections is described. Some qualitative results relating to the behaviour of the two-cylinder lens at very high voltage ratios are given, and the formation of intermediate images in both lenses and mirrors is discussed. Finally, a qualitative description of the focusing properties of two cylinders for voltage ratios from -∞ to +∞ is given.