Classification of high-voltage casing pipe
 

Concept of high-voltage casing pipe

High-voltage casing pipe refer to devices that provide insulation and support for one or several conductors to pass through partitions such as walls or boxes. They are important equipment in power systems. During the manufacturing, transportation and maintenance of high-voltage casing pipe, latent defects may remain due to various reasons; during long-term operation, defects will gradually occur due to the effects of electric fields and conductor heating, mechanical damage and chemical corrosion, and atmospheric conditions.

High-voltage casing pipes are mainly used for ground insulation of power equipment such as transformers, reactors, and circuit breakers, and high-voltage circuits passing through walls. There are three types of high-voltage casing pipes: single dielectric casing pipes, composite dielectric casing pipes, and capacitor casing pipes. The main insulation of the capacitor casing pipe is composed of a coaxial cylindrical series capacitor group formed by alternately winding layered insulating materials and foil-like metal electrodes on conductive rods. According to different insulating materials, it is divided into adhesive paper and oil paper capacitor casing pipes.

During the operation of high-voltage bushings, the main insulation must withstand the action of high voltage, and the conductive part must bear large current. The main faults include poor connection of internal and external electrical joints, dampness and deterioration of casing pipe insulation, lack of oil in bushing, partial discharge of capacitor core and discharge of end screen to ground.
 

Classification of high-voltage casing pipe

High-voltage casing pipe can be divided into oil-filled casing pipe and capacitor bushing.

The cable paper in oil-filled bushing is similar to the voltage-equalizing plate in capacitor casing pipe. The capacitor core in capacitor casing pipe is a string of coaxial cylindrical capacitors, while in oil-filled casing pipe, the dielectric constant of insulating paper is higher than that of oil, which can reduce the field strength at this location.

Oil-filled casing pipe can be divided into single oil gap and multi-oil gap casing pipe, and capacitor casing pipe can be divided into adhesive paper and oil paper casing pipe.

When the current-carrying conductor needs to pass through a metal box or wall with a different potential from it, a casing pipe is required. According to the applicable occasion, the casing pipe can be divided into transformer casing pipe, casing pipe for switch or combination appliance, and wall casing pipe. For this "insertion-type" electrode arrangement, the electric field at the edge of the outer electrode (such as the middle flange of the casing pipe) is very concentrated, and discharge often starts from here.