Transformer Engineering : Principles, Designs & Applications (Sachan Book 29) by Dr. Vibhav Kumar Sachan

Author:Dr. Vibhav Kumar Sachan [Sachan, Dr. Vibhav Kumar]
Language: eng
Format: azw3, pdf
Publisher: Smt. Jay Devi Sachan Memorial Publication House
Published: 2019-09-27T16:00:00+00:00

According to Insulation inside Bushing

Still another classification relates to the insulating material used inside the bushing. In general, these materials can be used in either the solid- or capacitance-graded construction, and in several types, more than one of these insulating materials can be used in conjunction. The following text gives a brief description of these types:

1. Air-Insulated Bushings: Air-insulated bushings generally are used only with air-insulated apparatus and are of the solid construction that employs air at atmospheric pressure between the conductor and the insulators.

2. Oil-Insulated or Oil-Filled Bushings: Oil-insulated or oil-filled bushings have electrical-grade mineral oil between the conductor and the insulators in solid-type bushings. This oil can be contained within the bushing, or it can be shared with the apparatus in which the bushing is used. Capacitance-graded bushings also use mineral oil, usually contained within the bushing, between the insulating material and the insulators for the purposes of impregnating the kraft paper and transferring heat from the conducting lead.

3. Oil-Impregnated Paper-Insulated Bushings: Oil-impregnated paper-insulated bushings use the dielectric synergy of mineral oil and electric grades of Kraft paper to produce a composite material with superior dielectric-withstand characteristics. This material has been used extensively as the insulating material in capacitance-graded cores for approximately the last 50 years.

4. Resin-Bonded or -Impregnated Paper-Insulated Bushings: Resin-bonded paper-insulated bushings use a resin-coated kraft paper to fabricate the capacitance-graded core, whereas resin-impregnated paper-insulated bushings use papers impregnated with resin, which are then used to fabricate the capacitance-graded core. The latter type of bushing has superior dielectric characteristics, comparable with oil-impregnated paper-insulated bushings.

5. Cast-Insulation Bushings: Cast-insulation bushings are constructed of a solid-cast material with or without an inorganic filler. These bushings can be either of the solid or capacitance-graded types, although the former type is more representative of present technology.

6. Gas-Insulated Bushings: Gas-insulated bushings use pressurized gas, such as SF6 gas, to insulate between the central conductor and the flange. It uses the same pressurized gas as the circuit breaker, has no capacitance grading, and uses the dimensions and placement of the ground shield to control the electric fields.

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