Bushing insulator: types and types

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

This article will contain information about bushings, their types and types. The design of various types, the types themselves, their scope and purpose will be analyzed in detail. Their advantages in comparison with similar devices will also be considered. After reading the article, you will not only learn general information about bushings, but you will also be able to decipher the markings and be able to distinguish one type from another.

Scope of application of bushings

What is a bushing insulator? This is a special device, the main function of which is to ensure the isolation of conductive elements from the inner or outer wall of the shell through which they pass. They are also used when installing switchgears at transformer substations, they also play the role of conclusions on complete switchgears.

Post insulators are designed to fix overhead power lines to current-carrying busbarsswitchgears and other electrical installations. It is worth adding that the bushing-type porcelain insulators, which were popular earlier, are still used today with many modifications.

The bushings are very convenient to use to connect the outputs of substations, from which residential buildings are powered.

Types of insulators

Bushings are divided into two types. The first type is insulators that are designed for indoor installation. They are used as high-voltage or vacuum outputs from transformers of high-voltage circuit breakers. The bushing insulator of the presented type is made of porcelain, and a metal rod is located inside the product. It is secured with flanges made of metal, attached with a porcelain cap and adhesive sand.

The second view has been reassigned for both outdoor and indoor installation. Such devices have intermediate ribs, which are located at a small distance from each other. These devices are designed for isolation from current-carrying parts of enclosed switchgears. This type of bushing insulator is used at mains operating voltage of 10, 25, 35, 110 kV and operating current from 630 to 11,000 A.

There are also other types of insulators, but they are designed for a specific purpose. Through-type devices are necessary for isolating the conductive parts of switchgear and for connecting consumers with tires to overhead power lines. These products are manufacturedfrom materials of increased strength, so that their design is resistant to dynamic current loads.

The benefits of insulators

The bushing should have a long service life, so it has the following characteristics:

• high resistance to aggressive operating conditions;
• relatively small mass;
• UV resistant;
• high strength;
• long service life;
• relatively small overall dimensions.

IP construction

IP bushings must have maximum mechanical and electrical strength, so the material from which they are made can be as follows:

• polymer;
• porcelain;
• tempered glass.

The insulator is designed to have a breakdown voltage higher than the flashover voltage. External insulators are constantly under the influence of external environmental factors, so their surface is ribbed. This is done specifically to improve the performance of the product.

Insulators according to their purpose are divided into bushings, support and suspension, there are also types of installation for placement in buildings and structures or for outdoor installation.

The IP-10 checkpoint is most often made of porcelain. The design of such an insulator is determined based on the rated voltage and power frequency of the network. The item itself is made of porcelain.cylindrical shape, on the axes of which ribs are installed, tightly fastened with a cement-sand mortar.

Assignment of bushings

The main purpose of bushings is the insulation of current-carrying conductors that pass through the walls and coatings of buildings or structures. Such insulators are made of dielectric porcelain. The housing is made in the form of a cylinder, on the upper part of which there is a current-carrying rod. Metal flanges are installed on the middle level of the case, which, as mentioned above, are designed to fasten the insulators to the surface.

The SP bushing insulator at an operating voltage of up to 10 kV is made of porcelain, and at an operating voltage of more than 35 kV, the device case is made as a complex insulating structure, which, in turn, consists of a porcelain case, cardboard plates, dielectric paper and transformer oil.

Installation of bushings

During installation, outdoor bushings are inspected for cracks and other defects, since the surface of the insulators could be damaged during transportation. They also inspect whether the surface glaze, which serves for additional protection and insulation of the product, has worn off.

Insulators must be placed on any metal structures to securely fasten products, as well as the durability of busbars or overhead power lines.

The installation of bushing insulators begins with the placement of a bushing plate, which is fixed onstructures or any fittings. Further, the insulators are closed on both sides with cast-iron caps with metal partitions having rectangular holes resembling a railway rail. Their size depends on the size of the fixed tires. Spacers are installed on the product busbar leads between the fixed busbars.

Marking bushings

Marking has been reassigned to highlight all product features. For example, a bushing insulator IP-10 630 7, 5 UHL1, where:

• I - insulator;
• P - checkpoint;
• 10 is the normal operating voltage of the product (kV);
• 630 - normal operating current of the product (A);
• 7, 5 - breaking force (kN);
• UHL - climatic condition of performance;
• 1 - accommodation category.

SP breakdown voltage

The breakdown voltage of porcelain PIs can vary depending on the thickness of the porcelain layer. Despite this, the design of insulators is determined by the required mechanical strength, the design flash stress and additional corona removal measures.

When the 10 kV bushing is in operation, no measures are taken to remove the corona. At rated voltages above 35 kV, measures are taken to install the crown near the rod opposite the flange, just in the place where the highest tension in the air.

In order to prevent corona, insulators are made without an air cavity around a metal rod installed inside the insulator. During thisthe surface of the IP is metallized with the rod. And in order to eliminate the appearance of discharges at the bottom of the power supply, the surface under it is also metallized and additionally grounded.

Conclusion

Probably everyone has ever seen a transformer whose overhead lines are attached to the IP. These devices are also necessary for connecting wires to fixed installations, since high-voltage wires cannot be connected without insulators.