CS260783B1 - A method of producing radial inserts - Google Patents

Abstract

The solution falls into the field of power transformer construction and concerns a method of manufacturing radial inserts from soft cardboard for windings with increased short circuit resistance. Inserts cut from soft cardboard are stacked into columns and these columns of inserts are compressed with a pressure of 60 to 140 MPa with a pressure ramp of 1 to 50 MPa per second, while the total compression time including ramp is 60 to 300 seconds.

Description

The invention relates to a process for the manufacture of radial liners of poppy cardboard having a compressibility of 10 to 30 ° / o at a pressure of 40 MPa, in particular for winding power transformers with increased short-circuit resistance.

At present, for power transformers requiring increased short-circuit resistance, the radial inserts are made of hard cardboard having a compressibility of 1 to 4% at 40 MPa, or made of hardened paper. However, the manufacture of cured paper inserts is relatively costly since these inserts can only be cut to a depth of 1 millimeter and when a thickness greater than 1 mm is used, these inserts must already be milled. Moreover, the cured paper is also relatively expensive, which greatly increases production costs.

The manufacture of hardboard inserts requires first cutting the cardboard strips to the width of the insert and then cutting the inserts with the dovetail groove, but this can only be done with cardboard to a depth of 2 mm. For a cardboard thickness of 3 mm and more, cutting the board is problematic. The production of hardboard is quite demanding and is introduced only in some foreign companies, so it has to be imported for foreign exchange from capitalist states and at relatively high monopoly prices.

Said disadvantages of manufacturing radial inserts for winding power transformers with increased short-circuit resistance are substantially eliminated by the production method of the present invention. It is an object of the invention that the inserts cut from soft cardboard are laminated into columns and the columns of inserts are compressed at a pressure of 60 to 140 MPa with a rise time of 1 to 50 MPa per second, the total compression time even with a rise time of 60 to 300 seconds.

The method according to the invention makes it possible to manufacture radial inserts of poppy cardboard with a compressibility of 10 to 30% for windings of power transformers with increased short-circuit resistance. Radial inserts made according to the invention have a compressibility below 3%, independent of how compressible the paperboard was based, which achieves a one and a half times less compressibility interval than that of hard paperboard, where the compressibility of the paperboard is below 3% at 40 MPa in between the elastic deformations of this material, the short-winding takes the original dimension, which is important in terms of maintaining the reliability of the transformer function at further shorts.

To further explain the nature of the method of the invention, one example of its use is given. Depending on the size of the hydraulic press, it is possible to simultaneously compress multiple columns of the same height. In a particular case, it was compressed at one time to stick the columns of cardboard inserts B according to GOST 4194-68 with thicknesses of 1.2 and 3 mm. The inserts are cut from cardboard in the condition in which they were delivered, thus without any modification. The floatability of the board was 40 MPa according to ČSN 50 3175 28 θ / ο.

Compression of the stacked inserts was performed at a pressure of 100 MPa with a pressure rise of 10 MPa per second for a total of 180 seconds. In the case of the inserts on which the method according to the above example was used, the compressibility at 40 MPa according to CSN 50 3175 was measured to be 2.5 to 3%.

The inserts produced according to the invention were used in the windings of the new construction of 2.5 and 6.3 MVA power transformers. These transformers were short-circuited. The windings after the short-circuit test remained without any sign of damage.

Claims (1)

SUBJECT A method for producing radial carton cartridges, having a compressibility of 10 to 30 percent at a pressure of 40 MPa, especially for power transformer windings with increased short-circuit resistance, characterized in that the inserts cut out of the carton are LOADED in pillars and these piles of inserts are with a pressure of 60 to 140 MPa, with a pressure rise of 1 to 50 MPa per second, with a total compression time of 60 to 300 seconds.