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This paper is concerned with the aspects of conditioning pertinent to electrical resistance measurements as covered by the scope of Standard Methods of Test for Electrical Resistance of Insulating Materials (ASTM Designation: D-257). Attention is therefore directed to d-c testing of electrical insulation. Further, the primary interest will be in general engineering practice with solid insulations...
Experience has shown that an analysis of test results based on a simple comparison of calculated averages can be misleading. The thermal evaluation literature shows that the insulation systems are compared by a linear relationship between the logarithm of life versus the reciprocal of the absolute temperatures. AIEE #1F describes method to obtain the most probable values of the constants in the equation...
The thought has been expressed that the manufacturer and user of insulating materials, who may use electrical resistance measured in accordance with ASTM D-257(1) as one means of evaluation and control, may not be familiar with the d-c tests that these materials are subjected to after assembly into insulation systems in apparatus. One of the purposes of this paper is to review d-c tests as they are...
The most accepted method for the thermal evaluation of insulation systems(1) is based on the Arrhenius(2) equation. The Arrhenius equation, which describes the temperature dependence of the "velocity coefficient" of chemical reactions, is being used to approximate the relationship between insulation life and temperature. This equation indicates that the logarithm of insulation life should...
The paper-and-oil insulation system of distribution transformers, which has served the industry well for many decades, is now being challenged by resin encapsulation. It is not yet clear whether encapsulated transformers will eventually supersede oil-filled pole-type designs, or will be limited to specialty applications such as installations in or adjacent to buildings. A field trial of encapsulated...
The application of electrical insulation by means of a dip coat process provides switchgear manufacturers with an economical method of applying insulation to both regular and irregular configurations. It is the purpose of this paper to discuss the application of dippable insulation, the range in properties available in these materials and typical applications of current use.
Asbestos-reinforced plastics, rigid shapes and pre-pregs, are widely accepted for high temperature service. These materials are being used, for example, as missile parts because they have good ablation characteristics at burn-out temperatures, and good physical strength and stability up to the thermal decomposition temperatures. On the other hand, rigid asbestos laminates have traditionally been held...
Recent years have seen the advent and application of many new and valuable insulating materials. We have seen new applications for older materials and increased emphasis on certain insulating properties such as surface track resistance and operation at higher temperatures. These new materials and new applications should provide the users of high voltage equipment with electrical apparatus which is...
I am not saying anything new when I say that d-c electrical conductance or conductivity (reciprocal resistance or resistivity) of electrical insulating materials is not generally a property of major concern to the user of these materials. In fact, the conductance of an insulating unit is usually several orders of magnitude smaller than is required for efficient use. Only in those cases where extremely...
Many engineers are familiar with the early ratings of materials as defined in A.I.E.E. #1, the present emphasis on systems, and the determination of system life by approved test procedures. The material definitions were found wanting in transformers, since the life of oil insulated transformers operated under full load continuously was found to be very short as long ago as 1925. At the same time,...
The Navy has been performing spot checks of solenoid coil insulation systems in accordance with a modification of a test(1) consisting of dielectric strength, insulation resistance, heat and moisture resistance. These tests have usually been performed at one temperature. The results were then compared with the results obtained with a typical Class A motorette system. However, these tests were limited...
Ever since 1935, when their development was announced by Westinghouse, dry-type power transformers have become increasingly important in the distribution of electric power. From the common beginning of ventilated dry-type transformers, there has evolved a wide variety of related lines of equipment. The best known of these is the open dry-type transformer, which uses class B and C solid insulations...
Since the announcements in mid 1961 that certain electrical equipment manufacturers had succeeded in encapsulating distribution transformers with an epoxy resin system, it has become a well known and widely discussed fact that a major breakthrough has been achieved in the field of power distribution equipment. After many years of searching for high quality insulating resins and unit designs to replace...
Glass reinforced polyester laminate has enabled important advances in medium voltage switchgear construction in the past few years and has become the workhorse of the industry. The recent advent of this material in channel and angle form greatly adds to its versatility and will increase the safety, reliability, and economy of this switchgear.
For almost half a century temperature classification of electrical insulation has been a primary basis for the rating of electrical equipment and apparatus. In 1913, Lamme of Westinghouse and Steinmetz(l) of General Electric, recognized in a joint AIEE paper that electrical insulation is expendable at a rate which is variable with operating temperature. Their work laid the basis for the establishment...
The importance of polymeric insulation in the electrical industry is shown by the many hundreds of published papers concerning the AC electrical conduction (or dielectric loss) of such materials. In contrast, not much attention has been given to the study of DC conduction with which we shall be exclusively concerned in this paper. Difficulty in the interpretation of the DC measurements is primarily...
It is common in all specifications for insulated electrical components to require that the components be 100% subjected to a high test voltage before accepting them for use. The idea behind this is that any weak points in the insulation will fail when subjected to the high voltage stress and the surviving components will contain good sound insulation, improved in quality by eliminating the poor ones.
I welcome this opportunity to participate in the Fourth Electrical Insulation Conference, and especially in this meeting devoted to the interest of marketers.
Insulation resistance is defined as the ratio of the direct voltage applied to two electrodes in contact with or embedded in a specimen to the total current between the electrodes. Test values, therefore, are highly dependent on the geometry of the electrode-specimen system and the volume and surface resistances of the material under test. Also, the numerical results obtained are extremely sensitive...
In an earlier article(1) the relationship between the Electrical Research Association (E.R.A.) and the British Standards Institution (B.S.I.) regarding the production of standards for insulating materials was outlined. Briefly the arrangement is that preparatory research work on methods of test, and the acceptable level of performance required, are done by the E.R.A. and the resulting proposals are...
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