摘要:

This paper gives the results of conduction-current measurements on air-saturated transformer oil using direct voltages and both bare and coated aluminium electrodes. The coated electrodes were covered with a thin plastic insulating film and the variations studied were: (a) both electrodes bare, (b) both electrodes coated, (c) the cathode coated and the anode bare and (d) the anode coated and the cathode bare. It was noted that the magnitude of the conduction current was considerably reduced by coating either one of the electrodes or both.With bare electrodes, a region of rapid current increase with increasing voltage was always present. When only one of the electrodes was coated, the magnitude of the current was reduced by two orders of magnitude and the current/voltage characteristics showed different trends dependent on whether the cathode or the anode was the coated electrode. With a coated anode, provided that sufficient voltage was applied across the gap, the current showed a region of rapid rise with voltage, but, with a coated cathode, the current increase with voltage remained small up to the highest voltages used. An unexpected result was that, with both the electrodes coated, the region of rapid current increase reappeared. These results indicate the importance of the conditions at the electrode-liquid interfaces on the processes of generation and neutralisation of charge carriers and should contribute towards a better understanding of the conduction and breakdown mechanisms in liquid insulants.The paper concludes with a discussion observations of a mechanism which could be responsible for the experimental observations.

DOI:10.1049/piee.1965.0098

出版商:IEE    

年代:1965

数据来源: IET

摘要:

Increasing demands on electriciiy supply systems are focusing attention on the future requirements of insulating materials. Their performance, when subjected to operating temperatures and stresses higher than those currently in use, is of interest,1and development work has been carried out to improve the correlation between laboratory tests and service performance.This paper describes investigations into the life,of insulating oils in transformers operating at top-oil temperatures of 100–105°C. The results obtained indicate that an inhibited oil will give approximately twice the life of an uninhibited oil when operating under severe temperature conditions.

DOI:10.1049/piee.1965.0099

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The arbitrary conditions of electrical stress and temperature adopted by the electrical industry when assessing the gassing tendencies of insulating oils have been examined closely. This had led to the important conclusion that oils commonly accepted as ‘gas-absorbing’ can evolve gas if suitable conditions exist. With the possibility of increasing temperatures and stresses in transformer insulation in the future, investigations have been carried out on their influence on the gassing characteristics of oil. It is clearly evident on the basis of this work that, in defining an oil as ‘gas-absorbing’ or ’gas-evolving’, the parameters of the gassing test must be fully defined, not only with regard to the gas phase but also in respect of the temperature stress applied.

DOI:10.1049/piee.1965.0100

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The conduction currents innhexane, carbon tetrachioride and transformer oil have been found to be dependent on field strength, temperature and impurity content, but independent of hydrostatic pressure up to a gauge pressure of 150lbf/in2for field strengths up to 90% of the normal breakdown stress. It is suggested that the decrease of conduction current with time is associated with the decrease of concentration and drift velocity of charge carriers, and that the linear portion of conduction-current/field-strength characteristics is attributable to ionic conduction, while the nonlinear portion is attributable to Schottky-type electron emission from the cathode. The strong pressure dependence of electric strength indicates that breakdown is initiated by bubbles formed in the liquid.

DOI:10.1049/piee.1965.0101

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The main properties required of paper for use in high-voltage dielectrics are concerned with its electric strength and dielectric losses. The effect of such physical properties as thickness, apparent density and air impermeability upon the impulse strength of impregnated paper are studied by both flat-sheet and model test methods, not only for types used in cables and transformers, but also for those used in capacitors.The incorporation of synthetic and other types of fibre into softwood pulp is discussed, and the electric strength is shown to be dependent upon the associated physical properties.Factors affecting dielectric losses, on the other hand, are the chemical constitution and purity of the pulp and water from which the paper is made, as well as its apparent density. The effect on the electrical properties of changes in the pulp and washing treatment is demonstrated, and the importance is shown in the case of capacitor tissues of the presence of conducting particles and other impurities. Methods of assessment of quality are described in detail.

DOI:10.1049/piee.1965.0102

出版商:IEE    

年代:1965

数据来源: IET

摘要:

An investigation has been carried out into the effect of ionic and other additives on the power factor of oil-impregnated paper, with the object of relating the power factor of the impregnated paper to the power factor of the impregnant. For power-factor measurements, an improved test cell was used which was designed to operate at high stresses over a wide temperature range. it was observed that there was a variable relationship between the power factor and the volume resistivity of oils depending upon the type of additive. There was no correlation between the power factor of impregnated paper and the power factor of the impregnant, but a definite relationship was found between the power factor of impregnated paper and the volume resistivity of the impregnant, this relationship being independent of the type of additive.

DOI:10.1049/piee.1965.0104

出版商:IEE    

年代:1965

数据来源: IET

摘要:

The limitations of any accelerated oxidation test carried out under a single set of conditions are such that it may give a good rating to insulating oils known to have a poor performance in service. The BS 148 and IEC oxidation tests have these limitations.The service limits of the three factors materially affecting oil oxidation have been determined and used to design a test procedure which will not misrate oils in this way.An oxidation-stability-assessment procedure designed at CERL uses four sets of conditions: one basic, and three designed to show the susceptibility of oils to oxygen, copper and temperature, respectively. Test criteria and limits are proposed which eliminate oils showing adverse susceptibilities to these factors. When an oil formulation has been accepted by this assessment procedure, further supplies can be checked using the basic conditions only.Comparison of the results, on a series of oils, from the BS 148 and IEC oxidation tests and the CERL procedure and examination of the effect of adding aromatics to two base oils have shown that the CERL procedure selects only those oils which are expected to have a good service performance.

DOI:10.1049/piee.1965.0105

出版商:IEE    

年代:1965

数据来源: IET

DOI:10.1049/piee.1965.0107

出版商:IEE    

年代:1965

数据来源: IET