SMALL-FRACTION NANOPARTICLE RESIN FOR ELECTRIC MACHINE INSULATION SYSTEMS

Abstract

An insulation system of a current-carrying conductor of an electric machine. The insulation system comprises a thermally curable resin including a polymer resin matrix and a nanoparticulate filler. A mica paper or mica tape is impregnated with the thermally curable resin. The thermally curable resin comprises nanoparticulate filler, the total quantity of nanoparticulate filler being at least 0.1 wt % and not more than 0.5 wt %.

Claims

1. An insulation system of a current-carrying conductor of an electric machine, the insulation system comprising: a thermally curable resin including a polymer resin matrix and a nanoparticulate filler; and a mica paper or mica tape impregnated with the thermally curable resin, wherein the thermally curable resin comprises nanoparticulate filler, the total quantity of nanoparticulate filler being at least 0.1 wt % and not more than 0.5 wt %.

2. The insulation system of claim 1, wherein the polymer resin matrix comprises epoxy resin.

3. The insulation system of claim 2, wherein the nanoparticulate filler consists of Al.sub.2O.sub.3.

4. The insulation system of claim 3, wherein the nanoparticulate filler consists of Al.sub.2O.sub.3 spheres.

5. The insulation system of claim 4, wherein the thermally curable resin further comprises microparticulate pigment for coloration.

6. The insulation system of claim 5, wherein the insulation system is a stator coil insulation system.

7. The insulation system of claim 1, wherein the nanoparticulate filler consists of Al.sub.2O.sub.3.

8. The insulation system of claim 7, wherein the nanoparticulate filler consists of Al.sub.2O.sub.3 spheres.

9. The insulation system of claim 1, wherein the thermally curable resin further comprises microparticulate pigment for coloration.

10. The insulation system of claim 1, wherein the insulation system is a stator coil insulation system.

11. A method for producing an insulation system on a current-carrying conductor within an electric machine, the method comprising: providing a mica paper or mica tape; wrapping the current-carrying conductor with the mica paper or mica tape; providing a polymer resin comprising nanoparticulate filler thoroughly mixed therein, the total quantity of nanoparticulate filler being at least 0.1 wt % and not more than 0.5 wt %; fully impregnating the mica paper or mica tape with the polymer resin; and thermally curing the polymer resin that impregnates the mica paper or mica tape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawing is a schematic view of an exemplary insulation system on a current-carrying conductor of an electric machine.

[0010] Other aspects of the embodiments described herein will become apparent by consideration of the detailed description.

DETAILED DESCRIPTION

[0011] Mica tape is known in the art as a tape made of mica paper, natural phlogopite, calcined muscovite or synthetic mica, glued with resin to the substrate of glass fiber or polyethylene as the basis for the insulation system of an electric machine. Epoxy, polyester or silicone polymer resins are most commonly used to bond mica paper to the tape substrate. Vacuum Pressure Impregnated (VPI), high dielectric tapes are used for the main insulation of low and high voltage electric machine current-carrying conductors, sometimes referred to as the main wall insulation. According to one aspect of the present disclosure, mica paper or mica tape of a main insulation 26 is placed around the current-carrying conductors 24 (e.g., wire windings, coils, bars) of the electric machine 20 to provide a covering that insulates the conductors 24 against each other and/or against other electrically conductive parts of the machine 20. Beyond the main insulation 26 additional separate layers may be provided as part of the overall insulation system. The mica tape is fixed to the conductors 24 by a matrix resin system, which is cured to provide a solid polymer mass interpenetrating the mica tape that surrounds the conductors 24. As such, the mica tape along with the cured resin provides the finished main insulation 26 that goes into service with the electric machine 20. As one example, the resin-impregnated mica tape can insulate a stator coil. According to the present disclosure, the resin can be a polymer resin such as epoxy, silicone, or polyester. The resin can, in some constructions, take the form of a unique blend of epoxy resins, novolac epoxy and epoxy diluents catalyzed using Lewis Acid

[0012] Latent technology blended with specific nanoparticles to offer improved mechanical, electrical and environmental protection. Examples of commercially available resins that can be used in accordance with the present disclosure include, but are not limited to those in the following table.

TABLE-US-00001 Supplier Resin Name Resin Type VonRoll USA, Inc. Permafil ® 74038 Epoxy Schenectady, NY Permafil ® 74041 Thixotropic epoxy Permafil ® 74050T Thixotropic epoxy Elantas PDG, Inc. Pedigree ® 4000F VTC Epoxy copolymer Olean, NY Pedigree ® 433-75 VTC Polyester Epoxylite ® 006-0841 Epoxy Epoxylite ® E 477 Epoxy Epoxylite ® E 478 Thixo Thixotropic epoxy ELAN-Volt ® EX 51302 Epoxy copolymer RanVar ™ R2003 VTC Epoxy copolymer AEV, Ltd. ULTIMEG ™ U2050L Epoxy Birkenhead, Wirral (UK) ULTIMEG ™ U2020 Epoxy ULTIMEG ™ U2002HVR Epoxy ULTIMEG ™ U2220 Epoxy

[0013] By using nanoparticles inside the insulation system, particularly in the resin that impregnates the mica tape to form the main insulation 26, the mechanical strength of the main insulation 26 can be improved without any increase in physical size and an insignificant reduction in thermal transfer capabilities. These technical factors allow the electric machine 20 having the insulation system to achieve higher rating potential, longer expected lifespan, or both. In particular, thermal conductivity should remain high so that heat transfers easily from the current-carrying conductors 24 to the environment to enable high current flow without inducing undue thermal stress of the main insulation 26, which is known to result in decomposition and destruction of the insulation material. The main insulation 26 according to the present disclosure also exhibits a low dielectric dissipation factor at operating temperatures, such that heating of the insulation material is limited to reduce the corresponding thermal stress.

[0014] The figure of the present disclosure schematically illustrates a portion of an electric machine 20 including a stator core 22 along with a current-carrying conductor 24. The conductor 24 can be in the form of a bar or coil and can be built-up of numerous internal strands, each of which has its own strand insulation (not shown), which is separate from the main insulation. The main insulation layer 26, and particularly the thermally curable polymer resin used in the manufacture thereof, is the subject of the present disclosure. The main insulation 26 is applied directly to the (insulated) current-carrying conductor 24. One or more additional layers may be provided on the conductor 24, outside the primary layer of the main insulation 26. For example, the figure schematically illustrates a corona armor tape layer 28, along with a stress grading tape layer 30.

[0015] As prefaced above, the main insulation 26 is manufactured by providing a mica tape, wrapping the conductor 24 with the mica tape, placing the wrapped conductor 24 in an impregnation cavity, applying internal vacuum to the wrapped conductor 24 within the cavity, inserting a curable polymer resin into the evacuated impregnation cavity containing the wrapped conductor, and thermally curing the resin to form the main insulation. The curing can include the application of heat and optionally positive pressure. Prior to inserting the curable polymer resin into the impregnation cavity, the curable polymer resin is formulated, which includes thoroughly mixing nanoparticulate filler into the base polymer resin. The amount of nanoparticulate filler is kept small, further protecting against poor mixing or settling within the base polymer resin. The total quantity of nanoparticulate filler in the thermally curable resin is at least 0.1 wt % and not more than 0.5 wt %. Yet, even with this small quantity of the nanoparticulate filler, the resin has shown an increase of over 25% in bond strength (e.g., 28.4% increase in bond strength).

[0016] Suitable nanoparticles for the nanoparticulate filler to the polymer resin matrix can include a metal-oxide or semi-metal oxide particle type. For example, the nanoparticles can be aluminum oxide (Al.sub.2O.sub.3), also known commonly as “alumina,” or alternately silicon dioxide. Both of these may be relatively erosion resistant for the cured main insulation 26. Nanoparticles are defined as those having at least one dimension (e.g., diameter in the case of spheres) that is less than More particularly, the nanoparticles can have an average particle size in the range of 1 nm up to 100 nm, in some cases 20 nm or less or 10 nm or less. In one example, the polymer resin matrix is epoxy resin and the nanoparticulate filler therein consists of alumina nanoparticles of an average particle size of 6 nm, in a quantity of 0.5 wt %. Nanoparticles, according to their particle size, have a particularly high surface area-to-volume ratio, which helps these particles demonstrate markedly different characteristics than the same material would exhibit on a particle scale one or more orders of magnitude larger.

[0017] Along with the polymer resin matrix and the nanoparticulate filler, one or more additional additives and/or fillers can be included in the thermally curable resin that is provided to impregnate the mica paper or mica tape. For example, the thermally curable resin can include any one or more of: one or more hardeners, one or more adhesion promoters, one or more wetting agents, one or more curing initiators, one or more tougheners, and one or more microparticulate thermal conductivity aides. Microparticles are defined as those having an average particle size of 1 μm or more and less than 1000 μm. Microparticles, if present in the resin formulation for the main insulation layer 26, can be present in an amount of 1 wt % to 40 wt%. In some embodiments, the resin includes microparticulate pigment (e.g., under 250 μm, under 200 μm, or under 180 μm). The pigment makes it easier for the operators of the VPI process to identify the height of the resin in the tank during the process. The pigment enables easy visual inspection for the operators of the VPI process to identify the height of the resin in the tank during the process and thus other more complicated means of measuring the resin height, for instance Hydrostatic devices, Magnetostrictive Level Transmitters, Magnetic Level Gauges, Capacitance Transmitters, Ultrasonic Level Transmitters, Laser Level Transmitters, Radar Level Transmitters, are not needed and may be dispensed with.

[0018] The insulation systems according to the invention are particularly suitable for use in the manufacture of rotors or stators of electrical generators or motors, in particular of large generators or motors.

[0019] Various features and advantages of the embodiments are set forth in the following claims.