RU2138899C1 - Process of impregnation and drying of electrical engineering articles - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: invention is related to impregnation and drying of such electrical engineering articles as windings of stators and rotors of electric motors, of transformers, of magnetic cores, etc. Proposed process provides for heating of articles, for their vacuum treatment before impregnation, for impregnation of given articles and their drying. In agreement with invention impregnation material is heated before impregnation and is subjected to degassing under condition of pulse vacuum treatment, articles are vacuum-treated before impregnation, impregnation and drying of impregnated articles are conducted under condition of pulse vacuum treatment too. For all mentioned operations of process conditions of pulse vacuum treatment are reached under residual pressure of 0.1-13.3 kPa and time for its achievement equal to 0.07-1.0 s. Technical result of this process consists in provision for high uniformity of impregnation of electrical engineering articles without entrapped gas with filling coefficient equal to 1.0, in high-quality drying of articles, including large-sized ones, in shorter time and in 3-5 times shortened technological cycle. EFFECT: enhanced operational efficiency of process. 3 cl, 1 dwg

Description

 The invention relates to electrical engineering, in particular, to methods for manufacturing electrical products, for example, windings of stators, rotors of electric motors, transformers and magnetic circuits, based on vacuum impregnation of their polymer compositions and drying in vacuum. There are various methods of impregnation of electrical products (dipping, vacuum), see, for example, Japanese patents NN 1-39310 publ. 09/09/02; 1-50736 publ. 02/02/27, EPO N 0489962 publ. 1992, RF patents NN 1820453, 1820981, 1819367; German patent N 3916619; Hungarian line ABB for vacuum impregnation, etc.

 Existing methods of impregnation are not effective enough. They allow you to achieve filling the inter-turn space with a coefficient of 0.5 - 0.8; and products with high intra-diffusion resistance (magnetic cores of various types) are practically not impregnated with these methods. Poor impregnation and drying are the causes of the formation of air (gas) inclusions in the insulation, electric discharges occur under the influence of an electric field.

 This causes sound interference, vibration, overheating, the gradual destruction of insulation, which leads to inter-turn circuit. With uneven impregnation of transformers, dielectric losses increase, which leads to their overheating.

 The closest in technical essence and the achieved effect is taken as a prototype method for the manufacture of electrical products in accordance with the invention as. USSR N 1376181.

The method includes pre-heating the products, followed by drying them in a vacuum, impregnating the products at a residual pressure of 0.1 - 13.3 kPa and drying the impregnated products with pulsed vacuum. In this case, a residual pressure of 0.1 - 13.3 kPa and a time to reach this pressure of 0.1 - 10 s are used. Being more advanced in comparison with previously known methods (more productive, it provides a saturation coefficient K _n = 0.876), this method is also not efficient enough, leads to incomplete impregnation of products, which negatively affects their performance. This is due to the fact that the windings (in their dense inter-turn space) contain in their pores, as well as on the surface, adsorbed molecules of gases and vapors, which impede a sufficiently deep penetration of the impregnating composition into them. All operations of the method are carried out in one device. Prepared for impregnation (evacuated) products are poured with an impregnating composition, in which, in addition to moisture, various gases are in a dissolved state.

 In contact with evacuated products, the reverse process occurs - these gases and moisture rush into the inter-turn space and fill the pores released during the vacuuming, which interferes with the subsequent operation - impregnation - of the deep penetration of the impregnating material into the winding. In addition, the applied vacuum mode both in the preparation of products and in the impregnation operation does not allow to achieve the desired degree of saturation of the windings.

 The objective of the present invention is to develop a method of impregnation and drying of electrical products, which will increase the degree of saturation of their impregnating material (thereby improving their quality) by creating conditions that allow more efficient to remove gases and vapors from the surface and inter-turn space of the products.

 To solve the problem, the proposed method provides for impregnation of the impregnating material and the products in isolation from each other, degassing in a vacuum-pulse mode, then impregnating and then drying in the same mode. Pulse evacuation is carried out at a residual pressure of 0.1 - 13.3 kPa and a time of its achievement of 0.07 - 1.0 s. The above modes on existing equipment ensure the optimal flow of all stages of the technological process and allow to achieve 100% impregnation of electrical products with high diffusion resistance, such as magnetic cores, electric motors and transformers with a dense winding from wires of small cross section.

 The proposed method is presented below with a more detailed description of the operations and their modes.

 The first operation is the degassing of the impregnating material.

 The impregnating material is gradually warmed up to a viscosity having sufficient opportunity for degassing. For various impregnating materials, the heating temperature is individual. So for the varnishes ML-92 and KO that are most often used for these purposes, they are 70–75 degrees C and 85–95 degrees C, respectively. Heated impregnating material (which, when it is pumped under vacuum into a degassing apparatus, is evacuated and simultaneously warmed up) is continuously evacuated at a residual pressure of 0.1 - 13.3 kPa for 5 to 20 minutes. During degassing of the impregnating material, a gradual increase in temperature and vacuum is necessary, since when they rise sharply, intense foaming will occur. After exposure to vacuum, the pressure is increased to atmospheric pressure and at this temperature pulsed evacuation is carried out at a residual pressure of 0.1 - 13.3 kPa with a time to reach it in 0.07 - 1.0 s, again give an exposure of 5 - 10 minutes. then the vacuum is released to atmospheric pressure. The cycle of heating the impregnating material, pulse dialing and vacuum dropping is repeated 3-5 times. In this mode, the maximum removal of gases from the impregnating material is achieved, which cannot be achieved by conventional evacuation even for a long time.

 The second operation is the preparation (degassing) of the product for impregnation.

 Products at atmospheric pressure are heated to the same temperature to which the impregnating material is heated. After heating, the product is subjected to pulsed evacuation to a residual pressure of 0.1 - 13.3 kPa and the time it reaches 0.07 - 1.0 s. They withstand this pressure for 1-10 minutes, then increase the pressure to atmospheric pressure, then warm up the products again and produce 3-5 cycles of pulse dialing and vacuum reset, depending on the sizes of the products.

 In this mode, the maximum removal of adsorbed gases from the surface of the product is achieved.

 The third operation is the impregnation of products. An evacuated impregnating material is supplied to the products prepared for impregnation, and the impregnation is carried out in a pulsed vacuum mode and under conditions similar to preparing the products for impregnation, i.e., at the same temperature, residual pressure of 0.1 - 13.3 kPa and the time it reaches 0.07 - 1.0 s, followed by exposure at this pressure and increasing it to atmospheric pressure. In the impregnation operation, the flowing material comes already free from the gases dissolved in it. The removal of air from inter-turn voids, adsorbed gases from the surface of the windings creates the conditions for the deep penetration of the impregnating material without gas inclusions into the inter-turn space with better adsorption on the surface of the windings.

 Repetition of pulsed evacuation cycles enhances this effect.

 After impregnation, the excess of impregnating material is removed.

 The fourth operation is the drying of products and baking of the impregnating material. The impregnated products, depending on the impregnating material used, are heated at atmospheric pressure (for 1.5 - 2.0 hours when using varnish ML-92 to 110 - 130 degrees C, for 1.5 - 3.0 hours when using varnish KO up to 180 - 220 deg. C) followed by a 3 - 5-fold cycle of pulsed evacuation at a residual pressure of 0.1 - 13.3 kPa and time to reach it in 0.07 - 1.0 s, holding for 5 - 10 minutes . Drying is carried out to remove the solvent from the impregnating material (varnish). The end of the solvent removal process is accompanied by polymerization (baking) of the varnish in the products. The dried products are cooled.

 When implementing the proposed method for the maximum removal of adsorbed gases and vapors from the surface of electrical products and dissolved gases and vapors from impregnating varnishes, it is necessary at each stage of the method after heating to carry out a sharp pressure relief in a short time and maintain the achieved residual pressure (carry out evacuation) for a certain time . The combination of the claimed parameters - the value of the residual pressure of 0.1 - 13.3 kPa and the time of its achievement of 0.07 - 1.0 s provide the required desorption of gases and vapors on existing equipment and contribute to the complete (almost 100%) impregnation of electrical products.

 Increasing the vacuum depth is impractical because at the same time, the volatilization of the solvent from the varnish increases both during its preparation (degassing) and during the impregnation of products, while the composition of the varnish can change, which can lead to accelerated coagulation and ultimately to poor-quality impregnation. With a smaller vacuum depth, the effect of removing adsorption and dissolved gases and vapors is reduced. The time to reach a residual pressure of 0.07 - 1.0 s ensures optimal process performance. A decrease in time of less than 0.07 s is associated with a complication of the hardware design and is therefore technically impractical, and its increase reduces the efficiency of the method, because the amount of gases and vapors removed from the adsorption layers is reduced.

 The evacuation parameters used in the method are achieved using a vacuum receiver. Currently, no vacuum pump achieves vacuum set-up time in less than 1.5 - 3.0 minutes.

 An indispensable condition for the process is heating at all stages before performing pulsed evacuation.

 At the stages of varnish degassing, evacuation of products and impregnation, the heating temperature is associated with the properties of the impregnating varnish. Heating is carried out to a temperature at which the viscosity of the varnish has sufficient opportunity for degassing.

 For various impregnating materials, it is different and is selected experimentally. An increase in temperature is impractical because the solvent will evaporate and the composition of the varnish will change before impregnation.

 At the drying stage, the heating temperature is higher than at the previous stages. In this case, its increase no longer affects the quality of impregnation and is necessary for intensive evaporation of the solvent and baking varnish. This temperature is also individual for various varnishes, and is also selected experimentally. The rate of solvent removal from varnish increases with pulsed evacuation with the claimed modes: the value of the residual pressure of 0.1 - 13.3 kPa and the time it reaches 0.07 - 1.0 s., T. the higher the vacuum set-up time, the greater the non-relaxable pressure gradient is created inside the product and the more intensive is the removal of solvent from the varnish in the impregnated products during the drying process.

 The proposed method was tested for the impregnation and drying of a large number of electrical products in various combinations of residual pressure and time to reach it. In all cases, the filling ratio - Kn was higher than in the prototype, and amounted to 0.98 - 1.0.

The following is information about products that have been impregnated and dried by the proposed method:
1. Stators of electric motors by 0.5; 1.5; 4,5; 38; 220 kW

- Kn was 1.0;
- breakdown voltage - 9.0 - 10 kW.

 For impregnation, varnish ML-92 was used.

 2. 40 kW electric motor designed for mining and coal industry.

- The filling factor Kn was 0.99 - 1.0;
- breakdown voltage of 9.8 kW;
- insulation resistance - infinity.

 For impregnation, KO varnish was used.

 3. The transformer windings with a size of 160 x 270 from a wire with a diameter of 0.38 mm and the transformer with a size of 500 x 500 x 280 mm in the assembly were impregnated with KO varnish. Saturation coefficient - Kn was 1.0.

 4. Magnetic cores - Шл-25; Shl-50; Shl-75; Шл-100 was impregnated with a compound based on epoxy resin (SG-2).

 The drawing shows a graph of the dependence of the filling coefficient (KN) on the vacuum-pulse effect (N) only on the impregnating compound (curve - 1), only on the magnetic circuit (curve - 2) and according to the proposed method (curve - 3), as well as on the quantity cycles of vacuum exposure (marked by dots on the curves). As can be seen from the graph, the maximum filling ratio is achieved when carrying out the proposed method of impregnation with fewer cycles (heating and vacuum-pulse exposure was carried out four times).

 The high quality of the magnetic cores impregnated with the proposed method is confirmed by sawing them into 2 parts.

 SHL magnetic cores impregnated according to the existing technology with the help of a compound pencil are stratified during sawing and up to 30% of SHL made of expensive special metal goes into marriage. Of the 1000 pieces of HL impregnated by the proposed method, when cutting into marriage, not a single product was left. Analysis of the cut magnetic cores showed 100% product continuity. Peeling of the windings was absent. The method provides impregnation of the magnetic cores over the entire surface with reliable bonding of the coils to each other.

 Tests of magnetic cores in accordance with the requirements of GOST were carried out according to two parameters: the dielectric loss tangent and the leakage current. The test results showed that these values during the impregnation and drying of products by the proposed method are reduced by an order of magnitude or more, i.e. the resistance of electrical insulation materials increases sharply, which confirms the high quality of the manufactured magnetic cores.

 5. On the instructions of one of the plants, approximately 400 electric motors were processed (power 0.2 - 20 and 220 kW, voltage - 380 volts). High quality of impregnation (Kn = 1.0) of products was noted. These electric motors did not arrive for secondary repair after 3 years of operation, but earlier they returned for repair every 3 months.

 Comparison of the proposed method with the prototype shows that they have in common the operations of preparing the products for impregnation and impregnating them using vacuum, as well as the drying operation using vacuum in a pulsed mode.

 The difference from the prototype is that before the impregnation operation, the impregnating material is degassed, all operations of the method are carried out using vacuum in a pulsed mode with a residual pressure of 0.1 - 13.3 kPa and a time of its achievement of 0.07 - 1.0, t .e. the operation of preliminary degassing of the impregnating material using pulsed evacuation was introduced, and the evacuation mode was changed in the operations of preparing the products for impregnation and their subsequent impregnation.

 Thus, the proposal is new.

 The use of vacuum in various technological processes, including and in the manufacture of electrical products. The originality of the proposed method lies in the above differences from the prototype method, and even more so from other methods of similar purpose, which allowed us to solve the problem. Such a combination of operations and modes does not follow directly from the prior art and was not obvious to specialists. To date, with all the variety of methods using vacuum in the manufacture of electrical products, such modes have not been applied.

 A technique is known in the art for vacuum impregnation of electrical products, in which the so-called "training process" is used, when the varnish is alternately under atmospheric pressure and a pressure of 7-8 ati for 3 to 5 minutes (K.N. Barembo and L.M. Bernstein " Drying, impregnation and compounding of the windings of electric machines ", Gosenergoizdat, Moscow, Leningrad, 1961; p. 84). However, this technique is not effective enough and does not allow to achieve a high degree of impregnation.

 During evacuation, moisture and air are removed from the pores, which facilitates the penetration of the impregnating varnish into the winding.

 The creation of pressure after normal vacuuming contributes to the fact that the gases and vapors remaining in the inter-turn space are driven even deeper inward, forming conditions for uneven and incomplete impregnation of the products.

 The changes in technology proposed in this application provided the conditions that would allow to get rid of moisture, adsorbed gases and vapors from the inter-turn space of the products and from the impregnating material as much as possible before impregnation and to impregnate more efficiently, reaching a saturation coefficient of up to 1.0.

 Such impregnation improves the quality of electrical products.

So, for electric motors:
- breakdown voltage increases by more than 5 times against normalized by current technologies;
- the power of the current affecting the thermal decomposition of insulation increases by more than 5 times;
- the insulation resistance of low-voltage (380V) electric motors increases (with the current test method) to infinity;
- mechanical strength increases, vibration of the windings is suppressed.

 These indicators dramatically increase the duration of continuous operation of electric motors, including in harsh operating conditions, in a humid environment, in chemical vapor.

For magnetic cores:
- high rates of electrical parameters - the tangent of the angle of electrical losses is so small that it is within the limits of the errors of the testing devices;
- the degree of cementation of the impregnating material exceeded the requirements of TU.

For transformers:
- implements transformer impregnation in the assembly, with a fill factor of inter-turn space close to unity;
- simplification of the design of transformers is achieved, because there is no need for inter-turn gaskets, painting transformers, etc .;
- electrophysical indicators are improved in the same way as for electric motors.

 The proposed method, in addition to high quality impregnation of products, allows to reduce the duration of the technological cycle by 3-5 times, it becomes possible to use the method in the manufacture or repair of large-sized electric motors and transformers of high power.

 The method allows to reduce the cost of electric motors during their repair by 40%, and the quality of repaired motors becomes higher than new ones manufactured at factories using traditional technologies.

 The proposed method will not cause difficulties when implementing it in a production environment. Applied devices, means of creating a vacuum in the art are known. Devices depending on the type of product can be used with some adjustment of their design. The appearance in the technique of a method to improve the quality of electrical products is always relevant.

 The greatest effect can be obtained when using the method at manufacturers of electric motors, transformers, starters, television and radio equipment, household appliances.

Claims (4)

 1. The method of impregnation and drying of electrical products, according to which conduct heating of electrical products, their impregnation with an impregnating material, evacuation, drying of impregnated electrical products, characterized in that the evacuation of electrical products is carried out before they are impregnated, drying of impregnated electrical products is carried out in a pulsed vacuum mode residual pressure of 0.1-13.3 kPa and the time it takes to reach 0.07-1.0 s, while the impregnating material is heated before impregnation, rgayut degassing it in a mode of pulsed vacuum and evacuating the electrical products directly before impregnation and also their impregnation is carried out in pulsed mode, and wherein the vacuum use the same value of residual pressure and at the same time to achieve it, as in the drying operation.  2. The method according to claim 1, characterized in that before performing pulsed evacuation of the impregnating material, it is heated and continuously evacuated at a residual pressure of 0.1-13.3 kPa, an exposure time of 5-30 minutes is provided, while the impregnation material is heated to a viscosity, providing the possibility of degassing.  3. The method according to p. 2, characterized in that when using ML-92 varnish as an impregnating material, heating is carried out to 70-75 ° C.  4. The method according to p. 2, characterized in that when using KO varnish as an impregnating material, heating is carried out to 85-95 ° C.