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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...
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...
Over the years there has been a continual increase in the rating requirements for metal-clad switchgear. Both the continuous ratings and the interrupting values have been pushed upwards in order to keep pace with the growing needs of industrial and utility electric power systems. Each rating increase has generally led to the need for better insulation for one or more of the following reasons: higher...
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...
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.
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.
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...
HT-1 is the designation for an experimental high temperature resistant polymeric material under development by the Du Pont Company. It is being developed to fulfill the need for a product which combines durability under high temperature conditions with those mechanical and electrical properties required for acceptable performance in a wide range of industrial end uses. HT-1 can be produced as filament...
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...
A group of insulation products based on a polyimide polymer have been introduced to the electrical industry gradually since late 1959. This group of products, sold under the trade name of "Pyre-M.L.®," includes wire enamels, coated glass fabrics, and an insulating varnish. The polyimides were selected for commercialization as the most thermally stable type of polymer yet characterized in...
A great deal of work has been done, and standards have been developed for the testing of enameled magnet wire in air(1), and for the evaluation of complete insulation systems(2) for induction motors, transformers, and similar electrical equipment. These techniques apparently give excellent correlation with field results when applied to equipment having stationary windings and operating at temperatures...
One of the major factors governing the selection of magnet wires for rotating machinery designed for higher temperature operation is thermal stability of the insulation.
Traction motors for diesel electric locomotives are subjected to perhaps the most severe environment imposed on any rotating electrical equipment. Heat, moisture, dirt, chemical contamination and mechanical shock and vibration combine and subject insulation to far greater abuse than found in most industrial applications. And traction motors must give long and reliable service under these demanding...
The demand for higher reliability in electrical and electronic components, coupled with the advent of many new magnet wire insulations and epoxy formulations, has made it advisable to look at epoxy encapsulated coils used in the electro-mechanical, electrical and electronic fields in terms of the complete systems. (The term "system" is used here to mean a specific insulated magnet wire encapsulated...
Full scale production conversion to a new Class B field coil insulation system for industrial d-c motors and generators was completed at General Electric Company in Erie, Pennsylvania, during the summer of 1960. This system provides a heavy epoxy coil coating applied by a closely monitored and controlled dipping process. The encapsulated coil is then molded to the pole piece to provide a rigidly tight...
Over twenty one hundred years ago the famous Greek philosopher, Archimedes, made the following statement in reference to a simple lever "Give me where to stand and I will move the earth." Were Archimedes amongst us today he could develop a similar statement with respect to fractional horsepower motors. For truly, the world of the average American, his home is moved by fractional horsepower...
An armature varnish is a special type of impregnating varnish. It gives outstanding bond strength to the windings of the wire around the iron core as the armature rotates at speeds of 20,000 to 30,000 revolutions per minute. This paper suggests how this type of varnish can be formulated, tested and applied to armatures that are used for small, high speed motors, such as vacuum cleaners and hand tools...
Research and development in synthetic fiber papers, started by the authors' company in 1955, has been directed for the past four years toward flexible sheet insulation for use in electrical equipment. This paper is a progress report on the work done to date.
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