DE2215206C3 - Wrapping tape for the insulation of electrical machines - Google Patents

Description

Table II

Temperature Mixture without Mixture Mixture + Binder-Accelerator

Accelerator + 0.25% benzyl- starting from diethylamine

dimethylamine _{Q 25% Q 5% 1%}

130 ⁰ C not measurable 60mm 46 Min 28 Min 18 mins 160°C 4 to 5 hours 35 mins 16 Min 9 Mmm 5 mins Table II (Continuation) temperature Mixture + binder Accelerator outgoing from Mixture + Binder additive outgoing

35 mins 28 mins >3hrs >3hrs >3hrs HV ₂ mm 7 ^l /2 min >2hrs >2hrs >2hrs

Dipropvlamin of dusobutylamine or dibenzylamine

(for comparison)

0.25% 0.5% 1% 0.25% 0.5% 1%

130 ⁰ C 54 Min

160 ⁰ C 17'/2 Min

\from Table II it can be seen that the new binder has a significantly stronger accelerating effect than an accelerator frequently recommended in practice for such resin-hardener systems

From both Tables I and II it is clear that the resins with tertiary amine groups, as used as binding agents for the tape according to the invention, are not dissolved out of the tape by the solvent-free impregnating resin, but on the other hand have a strong accelerating effect on the impregnating resin remaining in the winding at the temperature at which windings are pressed in practice. A correspondingly constructed binding agent based on dialkylamines with branched alkyl radicals, on the other hand, shows practically no accelerating effect.
The invention therefore represents a significant technical advance

1 With the new wrapping tape, the impregnation process can be carried out without additional treatment of the tape to apply an accelerator, since the binder and accelerator are now one and the same

2 The hardening of the solvent-free resin used for impregnation is greatly accelerated by the binder >o of the tape

3 Since the binding agent of the tape is hardly soluble in the solvent-free impregnating resin during the impregnation time, slowly hardening resin systems can be used as impregnating resins, which hardly change when stored in the cold and also only show a slight increase in viscosity at the impregnation temperature.

Claims (3)

Patent claims: 1. A winding tape for insulating electrical machines by the impregnation process, consisting of a porous carrier, mica paper and a binder derived from an epoxy resin and a secondary amine, which is also the accelerator for the hardening of the subsequently added impregnating resin, characterized in that an oxyamine resin of the formula R, /
-CH-CH ₂ -N (I) I\ OH R ₂ in which R| and R ₂ each represent a straight-chain alkyl group with up to 4 carbon atoms or together represent a lower alkylene group which may be interrupted by a heteroatom, which is obtained by quantitatively reacting an epoxy resin with a melting point above 50 ⁰ C (according to ASTM E 28) and at least two oxirane groups per molecule, and a secondary amine of the formula Ri NH (&Igr;&Pgr;) _R2 in which R ₁ and R ₂ have the above meaning, so that no oxirane groups are present in the oxyamine resin obtained. 2. Wrapping tape according to claim 1, characterized in that the porous carrier material is a glass silk fabric or a felt made of glass or synthetic fibers. Jn 3. Wrapping tape according to claim 1 or 2, characterized in that the oxyamine resin used as a binder and accelerator originates from an epoxy resin of the novolak type or from one based on bisphenol or heterocycles. 4. Wrapping tape according to one of claims 1, 2 and 3, characterized in that in the formula of the oxyamine resin R 1 and R ₂ each represent an ethyl group. 5. A process for producing a winding tape according to claim 1, characterized in that the porous carrier material and the mica paper are bonded together using an oxyamine resin of the above formula I in just sufficient quantity and the resulting material is cut into tapes. 6. Process according to claim 5, characterized in that the oxyamine resin is dissolved in an organic solvent, such as a ketone or an aromatic hydrocarbon, in such a concentration that, when the solution is subsequently applied to the carrier material, approximately 2 to 20 g of oxyamine resin are applied per m of surface. 7. Agent for carrying out the process according to claim 5 or 6, characterized in that it consists of an oxyamine resin of the above formula I. In electric motors and generators for medium and high voltage and power, the conductors are insulated with mica products. In high-voltage windings, the conductor is insulated with a mica product using the molding process or by re-treatment before being installed in the slots. For windings with operating voltages of up to about 6 kV, the so-called full impregnation process is also used today, i.e. the entire winding is insulated with porous mica strips, and after being inserted into the slots, the finished winding is impregnated with a solvent-free impregnating resin. Whether in the manufacture of high-voltage conductors, which are only inserted into the slot in the fully insulated state or in the full impregnation process with the winding already in the slot, the mica insulation must be completely impregnated with a solvent-free synthetic resin for both processes. If the resin is only applied after the tape has been wound onto a conductor made up of insulated individual conductors and If the glued conductor rod is brought into the winding by impregnation, a prerequisite for the success of the process is that the gasket insulation is completely saturated with the resin in a vacuum pressure process. The winding tape used must therefore be porous so that it can absorb the resin, especially when the layer thickness is several millimeters. The wrapping tapes consist of a carrier material, such as a glass silk fabric with a surface weight of about g/m ² or a fleece made of glass or synthetic fibers, as well as a layer of mica. The carrier material must give the composite material the necessary mechanical strength. But in order for the material to be handled at all, the carrier and mica must be bonded together by a binding agent. The following requirements for the starting materials are essential to this process: The winding tape must be mechanically resistant and able to withstand the stresses of machine winding On the other hand, it must be practically free of binding agents so that the winding can be completely penetrated by the resin As you can see, both requirements contradict each other A wrapping tape is in fact mechanically stronger the more the carrier and mica are bound by a flexible binding agent The binding agent, however, prevents the subsequent impregnation Therefore, the aim is to bond the carrier and mica as point by point as possible In the case of winding tapes, which are made of mica paper and a tensile and heat-resistant fabric (glass fabric or synthetic fibers) due to the weak tensile strength of the mica paper, the following requirements must be met by the binding agent: 1 With a minimal amount of binding agent, it should produce the best possible bond between mica paper and carrier, so that machine winding is guaranteed, 2 For the required good bonding, the binding agent should penetrate as little as possible into the mica paper and serve mainly or only to bond the mica paper and the carrier (so that the subsequent impregnation can take place unhindered), ij 3 The binding agent must be compatible with the resin to be used later The impregnating resin must have all the required dielectric properties and be so low-viscosity that it can penetrate the porous insulation and, after curing, bond it to the conductor bundle to form a compact, inclusion-free insulation. A number of requirements must also be placed on the impregnating resin. 1 The resin should wet the glow insulation well, 2 its viscosity should be low and preferably below 300 cP at the impregnation temperature, 3 In order to be able to be stored in a tank without any change, its viscosity must remain constant over time, even if it is frequently heated to 50 to 60 ⁰ C during operation, 4 during curing, the viscosity should increase as quickly as possible so that little resin drips off and curing occurs quickly, which means that the oven is occupied for a short time, 5 the resin should be so heat-resistant that the winding can be operated at the operating temperatures commonly used today (class F, 155°C). It must therefore not soften significantly at this temperature, and it must also suffer little or no weight loss at this temperature during continuous operation Low dielectric losses are required from high-voltage insulation, ie a small increase in tg f5 as a function of voltage and temperature The insulation must not soften up to the peak temperatures during operation These two requirements rule out resins mixed with large amounts of reactive thinner Reactive thinners are monofunctional, low-viscosity epoxy compounds which act as chain stoppers due to their monofunctionality and thus prevent the formation of long polymer chains In the hardened state, this shifts the Martens point (according to DIN 53 462) or the dimensional stability (according to ISO R 75) to lower temperatures compared to the mixture containing no thinner If the diluted resins already discussed are excluded, there are few suitable impregnating resin systems with viscosities below 1000 cP at 20 ⁰ C Since the resin penetrates the winding more easily at low viscosity, attempts are made to increase the temperature. This causes the impregnating resin to react, which increases the viscosity. If the throughput is not high, so that new resin can always be added, the mixture will soon become unusable for the intended purpose. So you want a resin system that reacts as little as possible at the impregnation temperature, L B an epoxy resin and a liquid anhydride. However, these systems have the disadvantage of taking a long time to drip off, as they react slowly even at higher temperatures. This is why the idea of adding an accelerator to the winding tape came up. Common accelerator types for such systems include mj Metal naphthenates and octoates, &zgr; B Cobalt or zinc naphthenate or octoate,
tertiary amines such as &zgr; B benzyldimethylamine, dimethylaminomethylphenol,
2,4,6-Tn(dimethylaminoethyl)phenol or tri(methoxycarbonylethyl)amine, and
Boron fluoride amine complexes, &zgr; B Borontrifluond-ethylamine, -piperidine or Pyndin 5s For example, German publications No. 1162 898 and No. 12 19 554 describe a process of submerging the tape rolls in an accelerator solution and drying them before winding. After winding, the impregnating resin in the tape comes into contact with the accelerator and the reaction acceleration should take place practically locally in the winding. Since these are low-molecular substances, they are partially dissolved out by the impregnating resin and thus end up in the resin supply. This means that the accelerating effect also takes effect in the impregnating resin supply, especially because the resin is 50 to 60 ^° C warm during impregnation. The invention is based on a wrapping tape according to the preamble of claim 1. Its task is to provide a binding agent for bonding the hammer paper to the carrier, which optimally meets the requirements formulated above and at the same time has a catalytic effect on the stable resin hardener systems mentioned. This object is achieved according to the invention by the features specified in the characterizing part of claim 1 Features solved. The new binder therefore consists of an oxyamine resin of formula I, which has been prepared by quantitatively reacting an epoxy resin of formula II with a melting point above 50 ⁰ C (according to ASTM E 28) and at least two oxirane groups per molecule with a secondary amine of formula III: ^R1 -CH -CH ₂ + HN O
(&Pgr;) -CH-CH ₂ -N OH (D In the above formulas, R ₁ and R ₂ each represent a straight-chain alkyl group with up to 4 carbon atoms or together represent a lower alkylene group which may be interrupted by a heteroatom. The described reaction leads to a new class of tertiary amines, namely oxyamine resins of partial formula I, which are very suitable as binders for carriers and mica and at the same time as accelerators of the curing of the epoxy resin systems subsequently added for impregnation. It is necessary that the reaction takes place quantitatively, because if it were incomplete, the tertiary amine groups formed would initiate the reaction of the oxirane groups remaining in the molecule and the binder would not be stable. Of the epoxy resins, novolak types and those based on bisphenol or heterocycles are particularly suitable; cycloaliphatic resins, on the other hand, are less suitable. Epoxy novolaks have the following basic structure: 0- _CH3 -CH -CH, These are therefore chain-shaped phenol-formaldehyde novolaks, where the phenolic hydroxyl groups are substituted by glycidyl groups. Since the resulting oxyamines usually have a lower melting point than the starting resins, the starting resins chosen will be those with a higher melting point. Examples of suitable amines with straight-chain alkyl groups or of suitable cyclic amines are dimethylamine, diethylamine, di-n-propylamine, pyrrolidine, piperidine, morpholine, thiomorpholine, etc. With branched chains, the accelerating effect apparently does not occur or only occurs to a limited extent due to steric effects. For practical reasons, the reaction with diethylamine is preferred. The reaction with the amine is advantageously carried out in a solvent, the amine being used in an amount of 1 to 3 equivalents, based on the epoxy resin. So that the oxyamine formed can be freed from the excess amine and the solvent easily and without damage, ketones boiling below 150 ^° C, aromatic hydrocarbons or mixtures thereof are preferably used as solvents. A glass silk fabric or a felt made of glass or synthetic fibers is particularly suitable as a porous carrier material. To produce the binder and accelerator, you can proceed as follows: 1) 260 g of an epoxy novolac resin with an epoxy equivalent of about 200 and a melting point of 80 ⁰ C are dissolved in the same amount of toluene at 100 ⁰ C. After cooling to about 50 ⁰ C, 280 g of diethylamine are added with vigorous stirring. After 5 hours of reaction at reflux at 60 to 70 ⁰ C, the temperature is gradually increased and the excess diethylamine and toluene are distilled. A resin with a melting point of 75°C is obtained. It is not necessary to use an epoxy novolac resin. You can just as well start with a bisphenol resin, as described below. 2) 175 g of a bisphenol-based epoxy resin with melting point 80 ⁰ C and epoxy equivalent 555 are dissolved in 120 g of toluene at 80 ⁰ C. After cooling to 50 ⁰ C, 70 g of diethylamine are added and the mixture is refluxed at 60 ⁰ C for 4 hours. The temperature is then slowly increased to distill off the excess diethylamine and the toluene; the last residues are removed at 150 ⁰ C under vacuum. A resin with a melting point of 78°C is obtained, with an undetectable epoxy equivalent and a hydroxyl number of 230. The product obtained can be dissolved in acetone or, better, in methyl ethyl ketone, dissolves in xylene in the heat, but precipitates again in the cold. Alcohols and aqueous solvents do not dissolve it. 3) 560 g of a mixture of two epoxy resins (a bisphenol and a novolak type) with a melting point of 70 ⁰ C and an epoxy equivalent of 580 are dissolved in 500 g of toluene at 100 ⁰ C. After cooling to 60 ⁰ C, 102 g of diethylamine are added and the solution is allowed to react for 3 hours under reflux without heating. A distillation head is then connected and the temperature is slowly increased to 150 ⁰ C, during which excess diethylamine and toluene distill off. The mixture is then kept at the same temperature under vacuum until distillation stops. No epoxy groups can be detected in the product obtained; the melting point is 70 ⁰ C. 4) 575 g of a bisphenol-based epoxy resin mixture with an epoxy equivalent of 560 are dissolved in 500 g of toluene at 100 ⁰ C. After cooling to about 60 ⁰ C, 140 g of diproylamine are added and the solution is stirred for 3 hours at 60 ⁰ C. The temperature is then slowly increased to 150 ⁰ C and the excess amine and toluene are distilled off. The reaction mixture is kept at the same temperature under vacuum until distillation stops. The product obtained softens at 70 ⁰ C and is soluble in methyl ethyl ketone. In the thin-liquid epoxy hardener mixtures used to impregnate the finished windings, the binding agent does not dissolve in the cold, but is increasingly soluble at temperatures above 60 ^° C. The binder produced in this way can now be used to bond mica paper and the carrier. To do this, the resin is dissolved in a suitable solvent, e.g. a ketone or an aromatic hydrocarbon or mixtures thereof, and applied to the carrier material, e.g. a thin glass fabric. The concentration of the solution is selected depending on the coating device chosen so that about 2 to 20 g of resin are applied per ^m2 of surface. The glass fabric treated in this way is bonded to the mica paper in machine width. The winding tapes can be cut from the material, which is wound up in roll form, on tape cutting machines. The amount of resin should be kept to a minimum that is just sufficient to firmly bond the two layers so that the cutting of the tapes and their mechanical winding is possible without difficulty. The smaller this amount, the easier it is to subsequently impregnate the finished winding. Since the tape and the winding produced with it also contain the accelerator for the impregnating resin, the resin itself can be kept in the impregnation tank without an accelerator; the impregnating resin will therefore last much longer. Nevertheless, the hardening of the impregnated winding in the oven is rapid, since the accelerator of the binding agent in the tape takes effect. Since the accelerator is also resinous, it is not washed out during impregnation, even at 50 to 60 ^° C, whereas metal salts, for example, get into the impregnating resin under these conditions and impair its durability. The following figures are intended to illustrate these relationships: A liquid epoxy resin with an epoxy equivalent of approximately 180 was mixed with an equivalent amount of hexahydrophthalic anhydride. The freshly prepared mixture has a viscosity of 900 to 1000 cps at 20 ⁰ C. The following tests were carried out: a) The mixture was kept in a glass vessel at 50 ⁰ C in a thermostat and samples were taken over time and their viscosity was determined at 20 ⁰ C. b) The mixture was brought into contact with a tape according to the invention and left in contact with it for 2 hours at 50 ⁰ C. The tape was then removed and the mixture was kept at 50 ⁰ C. The viscosity of the mixture was again checked at 20 ⁰ C. c) A similar procedure to b) was used with a tape that had previously been soaked in a 1% cobalt naphthenate solution (accelerator). After removing the tape, the viscosity of the mixture was determined at 20 ⁰ C. Table I shows the results:
Table I Test viscosity of Viscosity, measured at 20 ⁰ C after Mixture, 3 days Initial value after after at 50 ⁰ C 2 hours. 24 hrs. at 50 ⁰ C at 50 ⁰ C Blind test (a) Test with tape according to the invention (b) Test with tape previously immersed in cobalt naphthenate solution (c) 930cps 930cps 930cps 1112 cps
1022 cps
1068 cps 1573 cps
1731 cps
1806 cps 2004 cps 1960 cps 4065 cps 60 65 The following conclusions can be drawn from this The tape according to the invention does not affect the resin-hardener system of the mixture used in the test, i.e. no accelerator is dissolved out of the tape. In contrast, the low molecular weight accelerator is dissolved out of the tape pretreated with cobalt naphthenate, which is reflected in the considerable increase in viscosity. On the other hand, it can be demonstrated that the binder contained in the tape according to the invention significantly shortens the gelling time of the same resin-hardener mixture as was used in the previous tests at higher temperatures. The gelling time was determined at 130 ⁰ C and 160 ⁰ C in a thermostat. The rising time is the time between the moment the resin-hardener-accelerator mixture is brought to the reaction temperature in the thermostat until the moment the mixture no longer flows freely but becomes a jelly. This can be determined using a fine glass rod that is dipped into the mixture and pulled out every few seconds. As long as drops form, gelation has not occurred. Finally, as the viscosity increases, threads form that break off at the moment of gelation.