Patent Application
20150017410
The invention relates generally to stator winding assembly of an electric machine, and more particularly to resin compositions free of formaldehyde emission that may be applied to a stator winding assembly of an electric machine.
In today's manufacturing environment, there has been an increasing trend of environmental awareness. For instance, due to recent environmental regulatory law, lead paint and asbestos containing buildings have been phased out. Further, formaldehyde has been a focus of more recent trends in legal restrictions. Current restrictions on formaldehyde and formaldehyde emissions vary by area, however typical restrictions are in the range of 0.5 ppm to 4.5 ppm in some European countries and the United States.
These restrictions can pose a challenge for some current electric turbo generators. In some current generators, mica-based ground wall insulation may be utilized for insulation of some parts of the generator. However, mica-based resin, and other currently utilized insulation systems, often contains stand-alone phenolic/novolac resin component. This un-epoxidized phenolic resin component, made from the reaction of phenol and its derivatives with formaldehyde, typically contains approximately 0.001%-0.01% wt. (100 ppm to 1,000 ppm) of formaldehyde residue, which equates to approximately 0.00008%-0.0008% residue in the resin system used in generator stators or large motors, or 0.8 ppm-8 ppm of formaldehyde within the system. While this is more than some current restrictions, it could be assumed that some level, or potentially all, of the formaldehyde is depleted during the high temperature vacuum and curing cycles, as well as stator windings baking cycles. Nevertheless, thermal and electrical aging of insulation systems are known to occur during generator operation. Formaldehyde volatile emission may be produced due to the degradation of those CH2 linkages formed from those compounds made using formaldehyde as a component. Stator windings and stator cores are the potential main source of the emission. The produced volatiles, if any, are contained within generators during the operation if the machines are cooled with hydrogen. For hydrogen-cooled generators, the procedure to tackle formaldehyde emission, and other volatiles produced during the operation, if there could be any, are typically to discharge them safely out of roof stacks of the building before the opening of the generators. The procedure often coincides with hydrogen discharging steps. A similar discharge of the potential volatiles is often used for air-cooled generators. Formaldehyde volatile emission of hydro generators often pose a higher environmental safety and health challenge to workers than other electric machines thanks to their un-sealed winding constructions. Due to the growing trend of formaldehyde restrictions and the fact that all types of current generators may contain components made using formaldehyde as an ingredient, the conventional method of discharging potential formaldehyde emission out of the building demands an innovative thinking for its improvement.
Embodiments of the invention disclosed herein may include a resin binder for use in formaldehyde emission-free stator insulation, the resin binder comprising: an epoxy; a catalyst; and a polymer material, wherein the polymer material is hydroxyl-terminated.
Embodiments of the invention may also include a method of making a resin binder for use in formaldehyde emission-free stator insulation, the method comprising: mixing an epoxy; dissolving a polymer material into the epoxy, wherein the polymer material is hydroxyl-terminated; and adding a catalyst.
Embodiments of the invention may also include an insulation tape for a stator ground wall, the insulation tape comprising: a mica tape; and at least approximately 25% weight or less than 12% weight of a resin binder incorporated into the mica tape.
Embodiments of the invention may also include some motors where a wrapper of mica insulation is used on the stator slot area.
Embodiments of the invention do not exclude construction of the coating based on the spirit of the invention to coat the stator laminates.
These and other features of the invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various aspects of the invention.
a shows an illustrative stator coil wrapped in insulation tape according to some embodiments of the invention.
b shows a cross section view of a stator bar.
It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Disclosed herein is a resin binder for use in a stator insulation structure. The inventors have discovered that a resin binder can be formulated that may be formaldehyde free and create a stator insulation material that is formaldehyde emission-free. According to one embodiment, the disclosed resin binder may include at least one epoxy material. The epoxy material may include any now known or later developed epoxy or epoxy resins. These epoxies may include, for example, DEN 438 epoxy and/or DEN 439 epoxy, which are trademarks of The Dow Chemical Company and are available commercially, and Epon 828 epoxy and/or EPON 826 epoxy, which are Momentive Specialty Chemicals trademarks that are available commercially. Further, the resin binder may also include a catalyst in the resin binder. The catalyst can allow the epoxy to set or harden at a desired curing temperature. Many catalysts are known in the art, however as a non-limiting example, the catalyst may include aluminum acetylacetonate, available from most chemical suppliers.
The resin binder may also include a polymer material. The polymer material, according to some embodiments, may include a polymer, a pre-polymer, an oligomer, a low molecular weight compound, or some combination therein, which is hydroxyl-terminated. Some effective examples of hydroxyl-terminated polymers include polyphenylene ether (PPE) polymers and copolymers, Noryl SA90, nonylphenol, Bisphenol-A, Bisphenol-A's dimer, trimer, and tetramer derivatives, and pyrocatechol or 1,2-dihydroxybenzene (catechol), all of which are available from chemical suppliers and epoxy vendors. Turning to
In any case, the polymer material used, including that illustrated in
The resin binder may further include a solvent or other above-disclosed liquid low molecular weight hydroxyl-terminated or hydroxyl-containing compounds in order to (1) reduce the viscosity of the resin or resin component for convenience of a resin-making process, or (2) to tailor the curing kinetics, mainly the onset curing temperature to any desired temperature range to fit in various curing profiles. In some embodiments, the solvent may include methyl ethyl ketone (MEK), butanone, and xylene, as some non-limiting examples. In some embodiments, the solvent may contain the polymer material dissolved in a solution.
Turning to
At step 120, a polymer material, which may include any of the above disclosed polymer materials, may be dissolved into the epoxy that was mixed at step 110 at a temperature between 100° C. and approximately 130° C. This may, in some embodiments, be done shortly after or during the mixing of the epoxy in step 110. In an alternative embodiment, this may be done in the presence of the solvent and/or liquid low molecular weight hydroxyl-terminated or hydroxyl-containing compounds disclosed above to reduce the viscosity. In some cases, the solvent and the polymer material are combined at a ratio of approximately 1:1 prior to dissolving into the epoxy. In some cases, when the liquid nonylphenol is present, a smaller amount of solvent may be used. In some other cases, when solid Bisphenol-A or catechol is present, the ratio of solvent to hydroxyl-terminated polymer may be increased up to 60 to 40. 100% liquid low molecular weight hydroxyl-containing compounds are not designed or desired to replace phenolic resin component as (1) the resultant mica tape made may be “sticky” when taping onto Roebelled bars; or (2) they may be vacuumed out of the wound stator bar during vacuum cycle thus losing the accelerating factor in the curing kinetics. The liquid low molecular weight hydroxyl-containing compounds may be always applied in the presence of the hydroxyl-terminated/capped polymer material for tailoring cure kinetics or adjusting the resin viscosity. The un-dissolved polymer material may affect the epoxy curing properties of the resin binder. For instance, the resin binder may not cure properly or have the same heat resistance if un-dissolved polymer is present. The dissolving of step 120 may be done at a temperature between approximately 50° C. and approximately 70° C. The dissolution of phenolic resin into a solvent requires no or slight heat overnight.
At step 130, the catalyst may be added to the epoxy and polymer material mixture. The catalyst may be added into one of the epoxies, for instance, to Epon 828 in desired ratios to make a homogeneous solution in bulk for multiple uses at the temperature of approximately 100° C. In one embodiment, the catalyst-Epon solution with the calculated ratio and amount is added into a viscous solution of epoxies and hydroxyl-terminated material in a final step at a temperature between approximately 70° C. and approximately 130° C. In one embodiment, the addition at step 130 may be done at approximately 100° C. It should be understood that each of the materials disclosed in the method steps may comprise any of the materials described above in reference to the resin binder.
While step 130 step of making the resin binder is suitable for the application of an autoclave process for making stator components, it is known to those skilled in the art that, at step 130, the catalyst or accelerator can be withheld, so as not to add a catalyst into the bulk resin. For instance, in a vacuum pressure impregnation process, the catalyst or accelerator can be added onto the mica tape, which may contain a minimal amount of resin in order to bind the mica paper together. The bulk resin stored in a tank can be introduced into the slots of stators for curing at certain high temperature when the resin flow is in contact with catalyst-rich mica tape wound on the stator winding coils of a large motor or generator. The storage life of the bulk resin binder is prolonged in the tank.
In one embodiment, the formaldehyde containing phenolic resin has been completely replaced with a hydroxyl-terminated polymer material or in combination with a hydroxyl-terminated organic compound. The concentrations of each component may be varied to achieve the final resin binder that fits varying cure profiles and processes.
In other embodiment, phenolic resin is replaced with a combination of hydroxyl-terminated polymeric material or resin or oligomer and organic compounds, such as, but not limited to, catechol and its derivative (for instance, dihydroxy-α-methylstilbene), nonylphenol, XIAMETER PMX-0156, and Tris(2-hydroxyethyl)isocyanurate
In yet another embodiment, diorganopolysiloxane prepolymer may be used for replacement of the phenolic resin component frequently used for generator insulation systems. They are obtainable from Dow Corning. XIAMETER PMX-0156 is one of such examples. Diorganopolysiloxane is a fluid or gum having a viscosity of at least 10 Pa·s at 25° C., which is terminated with silanol (i.e., —SiOH) groups. The silicon-bonded organic groups of the component can be independently selected from hydrocarbon groups. These may be specifically exemplified by alkyl groups having 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl and hexyl; cycloalkyl groups, such as cyclohexyl and cycloheptyl; alkenyl groups having 2 to 20 carbon atoms, such as vinyl, allyl and hexenyl; aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl and xylyl; aralkyl groups having 7 to 20 carbon atoms, such as benzyl and phenethyl; and halogenated alkyl groups having 1 to 20 carbon atoms. These groups are selected such that the diorganopolysiloxane has a glass transition temperature (or melt point) below room temperature and forms an elastomer when cured. Methyl may make up at least 85, or even at least 90, mole percent of the silicon-bonded organic groups. The hydroxyl-terminated polymer material may also include hydroxyl-terminated polyester, and hydroxyl-terminated polyisobutylene, as taught by U.S. Pat. No. 4,429,099.
Table 1 illustrates a comparison between one example of the polymer material of the present invention, compared to the phenolic and novolac resins of previous materials.
500-7,000
100-1,000
As is clear from Table 1, the polymer material according to current embodiments can have a much higher hydroxyl equivalent weight relative to previous resins. Further, when there is a need to match the hydroxyl equivalent weight of the new component to that of phenolic resin if fitting existing cure profiles or processes is so desired, one may achieve this by mixing the polymer material with other low hydroxyl equivalent weight material such as catechol or Bisphenol A, or nonylphenol, etc. For instance, a 1:1 ratio of catechol to the polymer material in MEK or xylene results in 432 hydroxyl equivalent weight which is in the range of phenolic resin. In some embodiments, more polymer material may still be used despite this, as it can enhance the mechanical and thermal properties. Additional polymer material may increase the heat resistance, increasing the thermal properties, and decrease the loss of material under heating, as well as create a stronger resin, increasing the mechanical properties. These enhance mechanical and thermal properties can be due to more crosslinking between polymer molecules by increasing the polymer material. It can also be seen from Table 1 that the glass transition temperature, and thus the heat resistance, is higher in the polymer material. In practice, the polymer material is added to its dissolvable quantity in the designed ratio of DEN epoxy and EPON epoxy.
When applied as a resin binder for resin-rich mica tape for stator winding, the autoclave cure method of the composition in either resin form or tape form is achieved by heating to approximately 80° C.-140° C. at the rate between approximately 0.14° C./min to approximately 0.24° C./minute for prolonged period of time, such as about 8-10 hours, during the vacuum cycle. The temperature is then raised quickly to approximately 160° C. to approximately 175° C. for approximately 10 hours to allow the tape binder to flow and its cure to take place. The resultant cured resin binder or tape has a hardness of approximately 80 to approximately 94, as measured by Shore D harness in accordance with ASTM D2244. The glass transition temperature (Tg) of the resultant cued resin binder or tape, a measure of degree of resin cure and its heat resistance, may be in the range of approximately 135° C. to approximately 165° C.
Tg of the resin binder or tape is further increased to approximately 180° C. when higher temperatures are practiced in both vacuum and cure cycles. The ultimate Tg of the composition can reach approximately 190° C. in curing tests.
It is known that dielectric properties such as a dissipation factor (Df) of stator winding is associated with inner local Joule heating in the insulation winding matrix. The higher Df results in the higher local heating and the higher propensity of local degradation and micro-defect formation, thus the higher the local electrical stress concentration. Df determined at high temperatures, such as 100° C. or 155° C. (hot Df) is a measure of such a dielectric property. When T, is below a certain value, for instance, below 110° C.-120° C., the lower T, is correlated inversely with high hot Df. Therefore, Tg may preferably be kept above 110° C.-120° C. from dielectric standpoint alone. Nevertheless, mechanical and thermal properties demand for relatively high Tg, for instance, it is preferred that T, is greater than 130° C.
A few examples are given below to illustrate the invention, showing that a stator winding ground wall insulation resin binder may be made without formaldehyde residue carrying from phenolic resin and that is thermally stable.
Control: 98.5 grams of DEN 439, 46.1 grams of Epon 828 and 36 grams of 50% wt phenolic resin-MEK solution were mixed in a glass container, sealed, power-magnet stirred and heated to 100° C. to 130° C. for 2-4 hours. The homogeneous solution is then cooled to 25° C.-50° C. The solution is then mixed at 100° C.-130° C. for 1-3 hours with 20 grams of Epon 828 solution containing dissolved 0.5 gram of catalyst aluminum acetoacetate. The solution is allowed to cool in a vacuum oven at 25° C.-50° C. overnight. The Epon 828-catalyst solution was made in bulk for multiple uses at 100° C. for 2 hours. The 50% wt phenolic resin and 50% wt MEK or 50% wt phenolic resin and 50% wt xylene solution was made in bulk for multiple uses at approximately room temperature or slightly higher than room temperature overnight. The resultant uncured resin has Tg between −6° C. and 6° C., more specifically 3.8° C. determined by DSC (differential scanning calorimetry) in accordance with ASTM E1356. The viscosity simulated at 110° C., a typical vacuum cycle temperature for autoclave cure, is approximately 7991 cps using WLF equation. The onset curing temperature (OCT) measured by DSC of the resultant resin, a measure of cure-triggering temperature, is between 185° C. and 200° C. The OCT is very important and varies with pre-cure time-temperature profile. The prolonged pre-cure cycle reduces OCT, so does a vacuum cycle whose temperature is higher than 110° C. In addition, in practice, the cure is often triggered at the temperature 10-20° C. below the measured OCT. The Tg of the resultant cured resin is between 150° C. to 190° C. when the cure temperature may be raised to more than 190° C.
92.5 grams of DEN 439, 40.7 grams of Epon 828, and 120 grams of 50% wt SA90-MEK solution were mixed in a glass container, sealed, power-magnet stirred and heated to 100° C. to 130° C. for 2-4 hours. The homogeneous solution is then cooled to 25° C.-50° C. The solution is then mixed at 70° C.-130° C. for 1-3 hours with 20 grams of Epon 828 solution containing dissolved 1.0 gram of catalyst aluminum acetoacetate. The solution is allowed to cool in a vacuum at 25° C.-50° C. overnight. The Epon 828-catalyst solution was made in bulk for multiple uses at 100° C. for 2 hours. The 50% wt Noryl SA90 and 50% wt MEK or 50% wt Noryl SA90 and 50% wt xylene solution was made in bulk for multiple uses at approximately 50° C.-70° C. for a few hours in a sealed condition. The resultant uncured resin has Tg=−16.6° C., determined by DSC in accordance with ASTM E1356. The viscosity simulated at 110° C., a typical vacuum cycle temperature for autoclave cure, is approximately 4160 cps using WLF equation. The onset curing temperature (OCT) measured by DSC of the resultant resin, is approximately 214° C. The OCT varies with pre-cure time-temperature profile. The Tg of the resultant cured resin is 159° C.
92.5 grams of DEN 439, 40.7 grams of Epon 828, and 60 grams of 50% wt SA90-MEK solution were mixed in a glass container, sealed, power-magnet stirred and heated to 100° C. to 130° C. for 2-4 hours. The homogeneous solution is then cooled to 25° C.-50° C. The solution is then mixed at 70° C.-130° C. for 1-3 hours with 20 grams of Epon 828 solution containing dissolved 1.0 gram of catalyst aluminum acetoacetate. The solution is allowed to cool in a vacuum at 25° C.-50° C. overnight. The Epon 828-catalyst solution was made in bulk for multiple uses at 100° C. for 2 hours. The resultant uncured resin has Tg=−12° C., determined by DSC in accordance with ASTM E1356. The viscosity simulated at 110° C., a typical vacuum cycle temperature for autoclave cure, is approximately 4755 cps using WLF equation. The onset curing temperature (OCT) measured by DSC of the resultant resin, is approximately 230° C. The OCT varies with pre-cure time-temperature profile. The Tg of the resultant cured resin is 164° C.
105.1 grams of DEN 439, 14.9 grams of Epon 828, and 120 grams of 50% wt SA90-MEK solution were mixed in a glass container, sealed, power-magnet stirred and heated to 100° C. to 130° C. for 2-4 hours. The homogeneous solution is then cooled to 25° C.-50° C. The solution is then mixed at 70° C.-130° C. for 1-3 hours with 20 grams of Epon 828 solution containing dissolved 0.05 gram of catalyst aluminum acetoacetate. The solution is allowed to cool in a vacuum at 25° C.-50° C. overnight. The Epon 828-catalyst solution was made in bulk for multiple uses at 100° C. for 2 hours. The resultant uncured resin has Tg=−6.7° C., determined by DSC in accordance with ASTM E1356. The viscosity simulated at 110° C., a typical vacuum cycle temperature for autoclave cure, is approximately 5599 cps using WLF equation. The onset curing temperature (OCT) measured by DSC of the resultant resin is approximately 250° C. The OCT varies with pre-cure time-temperature profile. The Tg of the resultant cured resin is 158° C.
98.5 grams of DEN 439, 46.1 grams of Epon 828, 30 grams of THEIC (tris(2-hydroxyethyl)isocyanurate) and 72 grams of 50% wt SA90-MEK solution were mixed in a glass container, sealed, power-magnet stirred and heated to 100° C. to 130° C. for 2-4 hours. The homogeneous solution is then cooled to 25° C.-50° C. The solution is then mixed at 70° C.-130° C. for 1-3 hours with 20 grams of Epon 828 solution containing dissolved 0.1 gram of catalyst aluminum acetoacetate. The solution is allowed to cool in a vacuum at 25° C.-50° C. overnight. The Epon 828-catalyst solution was made in bulk for multiple uses at 100° C. for 2 hours. The resultant uncured resin has Tg=−13° C., determined by DSC in accordance with ASTM E1356. The viscosity simulated at 110° C., a typical vacuum cycle temperature for autoclave cure, is approximately 4603 cps using WLF equation. The onset curing temperature (OCT) measured by DSC of the resultant resin is approximately 250° C. The Tg of the resultant cured resin is 150° C.
The thermal capability of groundwall insulation for stator winding is important. The temperature at which the resin loses its 5% weight is 321° C., which is comparable to the control resin whose average thermal stability temperature at 5% wt loss is 322° C. The projected life of control resin and formaldehyde-free composition is compared after an accelerated dynamic life testing using Thermogravimetric Analyzer in reference to ASTM E1461 and E1877. The end of life criterion is not the failure of micaeous groundwall insulation of 100-150 mil (1 mil=25 microns), but the neat resin when losing 5% wt for purpose of comparison of the resin binders. The new resin binder has typical thermal life of 20 years at 140° C., compared with an average thermal life of the control resin binder which is 20 years at approximately 135° C. The slight increase in the projected thermal life of new resin binder may mean that it may be at least the same as that of the control in terms of thermal capability, which is expected.
Turning to
Still referring to
Still referring to
Turning to
The curing process may require modification from known autoclave curing processes. In some embodiments, the stator bar 310 may be held in a vacuum cycle, in some instances in a range of approximately 80° C. to approximately 140° C. This temperature may be held for approximately 8 hours up to approximately 12 hours. In a further embodiment, following the vacuum cycle, stator bar 310 may then undergo a curing cycle. The curing cycle may be done at approximately 160° C. to approximately 175° C. The curing cycle may be held for anywhere from about 12 hours to about 20 hours. In some embodiments, the temperature will be gradually lowered following the curing cycle. This may allow the thermal stress of stator bar 310 with insulation tape 200, now cured, to be lowered or even eliminated. The stored thermal stress in stator bars encourages the potential crack and delamination of the ground wall insulation during the process and services.
In another embodiment, stator bar 310 with resin-poor insulation tape 200 may be cured using a vacuum pressure impregnated (VPI) process. In these embodiments, stator bars 310, stator coils 300, or wound stators may be heated to a low temperature prior to being placed in the VPI tank. The VPI tank may then be sealed and a vacuum applied in order to remove air and any volatiles. While stator bars 310 or stator coils 300, or entire wound stators are still under vacuum, the resin may be introduced from a resin storage tank. After atmosphere pressure is arrived in the tank, the VPI tank may then be pressurized with inert gas to drive the resin into the insulated bars or coils in the tank. Individual bars are generally clamped in a fixture to consolidate the insulation either prior to or after impregnation. After the VPI process is complete the bars or coils or wound stators are generally put into an oven to cure the resin. The thermal relaxation process follows the cure in order to encourage the elimination of potentially stored thermal stress. It is often achieved with a gradually lowering temperature profile.
Referring to autoclave curing, once stator bar 310 has been cured, insulation tape 200 including the resin binder is properly cured and set. Stator bars 310 may be inserted into stator core 400. Now a plethora of stator bars 310 may be paired with a second stator bar 310 to make a stator coil 300 while they are placed in slots of the stator core 400. Without the inclusion of any formaldehyde residue in the stator winding assembly, not only is stator coil 300 free of formaldehyde at the beginning of operation, but there may be no formaldehyde emissions at the generator operating temperatures, including stator core 400, from the stator coils 300. As a result, a stator winding free of formaldehyde emission may be achieved.
In a further embodiment, referring to the above stator coil winding, the stator cores that bars are wound into and then coiled by brazing and connecting together are typically made up by stacking hundreds of thousands of stator punching laminations. Each of the laminations has a thin coating to insulate them from each other to reduce the loss due to an Eddy current. These lamination coatings may potentially be susceptible to release formaldehyde due to degradation during generator operation, especially under abnormally high temperature operation.
While use of the resin binder has been described with regard to insulation around stator bars 310, it should be understood that stator core 400 may also have the resin binder incorporated into the material used to coat the punching laminations of stator core 400. In such an embodiment, rather than including the resin binder in insulation tape 200, stator core 400 may have the resin binder cured to part of the material, insulating the whole stator assembly. As a result, a stator assembly free of formaldehyde emission may be achieved.
Still referring to laminations of stator core 400, formaldehyde-free materials for coating the laminations are not limited to the epoxy-based solution provided above. Any non-formaldehyde-containing coatings that meet thermal, electrical, mechanical, and chemical requirements of laminations specified by OEM are not excluded, such as, but not limited to, filler-containing acrylate coating systems, filler-containing high temperature polyester coating systems, filler-containing polyamideimide coating systems, and any further inorganic particulate material filled coating systems.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
