Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
2002-02-12
2004-05-11
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S11000P
Reexamination Certificate
active
06734361
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an insulated wire preferable to be used in a coil for, for example, a motor and a transformer, which insulated wire has good insulating property and excellent resistance to working.
BACKGROUND ART
Insulated wires coated with an electrical insulator are used in a large amount in many applications as coils incorporated into a variety of electric machinery and tools. Many insulated wires are used especially in electric machinery and tools, represented by motors and transformers. In recent years, progress has been made in both miniaturization and the level of performance characteristics of these machinery and tools, and now such insulated wires are often used by bundling them into a very narrow space. Specifically, it is no exaggeration to say that the performance of a rotator, such as a motor, is determined by how many wires are held in a cross section of a stator slot. As a result of this, the ratio (space factor) of the total sectional area of each conductor (the total sectional area of conductor in each wire) to the sectional area of the stator slot has been highly increased in recent years.
When insulated wires whose cross section has a round shape are closely packed inside of a stator slot, voids forming dead space, or the large sectional area of an insulating film, may be a barrier to increase the space factor. For avoiding this, when insulated wires are subjected to coil-winding, in order to improve the space factor as much as possible, the wires are pushed into the stator slot to such an extent that the wires having a cross section of a round shape are deformed. However, as expected, remarkable reduction in the sectional area of the insulating film has not been made, because it may sacrifice electrical performance (e.g. dielectric breakdown property).
In view of the above, as means for improving the space factor, an attempt has been made, very recently, to use an insulated wire of a rectangular wire with a conductor having a sectional shape similar toga quadrangle (a regular square or a rectangle). Use of the rectangular wire brings about a dramatic improvement in the space factor. However, it is difficult to apply an insulating film uniformly on a rectangular conductor, and it is particularly difficult to control the thickness of the insulating film in the case of insulated wire having a small sectional area. Therefore, the rectangular wire has not been widely used so much.
With regard to rectangular windings, there are several proposals concerning the method of manufacturing the windings and insulating materials of the windings. For example, a method of adhering a polyesterimide film uniformly onto a rectangular conductor is described in JP-A-2000-260233 (“JP-A” means unexamined published Japanese patent application), proposing an approach from the material side.
As to conventional insulated wires using a round a conductor, many attempts are being made to improve the insulating performance of the film. For example, the use of resins, such as polytetrafluoroethylene, having a low dielectric constant, as the insulating film, is already known. However, these resins having a low dielectric constant have not been used in the field of enameled wires, because these resins having a low dielectric constant are thermoplastic, and also it is difficult to form such a thin film, as in the case of enameled wires.
Similarly, a method in which fine particles of metal oxides (e.g. titanium oxide and silica) are added in a varnish, to form an insulating film, is conventionally adopted. As a result, although an improvement in dielectric breakdown voltage is not observed, the occurrence of a corona in a high frequency region (for example, 1 kHz or more) is reduced, as is known. It is estimated that the reason dielectric breakdown voltage is not improved, though the occurrence of a corona is suppressed, is that, when the fine particle of the metal oxide is added to the varnish, air components, such as oxygen, are caught in the surface of the fine particle of the metal oxide, and the involved parts of the surface are converted into dielectrics, and therefore no improvement in dielectric breakdown voltage is observed.
The characteristics of the insulating film that are required when the coiling of a motor or transformer is conducted, include resistance to working of the insulating film. This is because, in the aforementioned coiling, the electrical insulating property is reduced if the wire film is damaged.
Various methods are proposed to provide the wire film with resistance to working. For example, these methods include one in which lubricity is imparted to an insulating film, to lower the friction coefficient, thereby decreasing external damage during coiling, and a method in which adhesion between an insulating film and an electric conductor is improved, to prevent the film from peeling from the conductor, thereby maintaining the electrical insulating property that the insulating film originally has.
As the former method of imparting lubricating ability, a method in which the surface of a wire is coated with a lubricant, such as wax, or a method in which a lubricant is added in an insulating film and then is allowed to breed out on the wire surface when a wire is produced, thereby imparting lubricating ability, is conventionally adopted and practically used in many examples. However, this method of providing lubricating ability does not improve the mechanical strength of the wire film itself, in any sense. Therefore, this method appears to have an effect on factors of external damage; however, there is a limitation on these effects, in actuality.
Various methods have been hitherto proposed concerning improving the adhesion between the conductor and the insulating film. As specific examples of an insulating coating to be used for this purpose, 1) a heat-resistant coating, composed of a polyamideimide resin, an alkoxy-modified amino resin, and benzotriazole (JP-A-3-37283), and 2) a coating composed of a polyamideimide resin and trialkylamine (JP-A-6-111632), are proposed. Wires produced by these measures are found to have an effect to pass the reciprocating abrasion test (test in which a relatively low load is applied to the wire to be tested and the film is rubbed by a bead-needle). However, in the one-way abrasion test (the test prescribed in JIS C 3003; the film is scratched by a piano wire while applying a load gradually to the wire), a satisfactory effect is not observed. In recent years, the latter test method is regarded as important in testing for film damage. Further, many wires produced using only means of improving adhesion are decreased in the reciprocating abrasion value with a decrease in the thickness of the film, and the adhesion of these wires is eventually decreased to the same level as that of the conventional wire in which no means of improving adhesion is utilized.
On the other hand, a method is proposed in which many rigid structures are introduced into a molecule, in light of the molecular structure of the resin, to improve the film strength, thereby decreasing working damage to the film. JP-A-6-196025 describes such an insulated wire having an insulating film having a prescribed tensile strength and tensile elasticity modulus. Such an insulated wire is found to have an outstanding effect in the one-way abrasion test, and it ensures that damage to the film when coiling can be prevented, even if the film is decreased in thickness. However, such an insulated wire is more reduced in the level of flexibility after it is elongated or is subjected to thermal history, compared with the conventional wire, and it might crack and break down in the film because of insufficient flexibility when it is subjected to bending under particularly severe conditions.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have found, as a result of studying the reasons to cause dielectric breakdown in an insulating film of conventional insulated wires, that a material that is resistant against dielectric breakdown, that is, an i
Mesaki Masakazu
Tatematsu Yoshinori
Nguyen Chau N.
The Furukawa Electric Co. Ltd.
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