JP2001518775A - Electrical insulator and insulation method - Google Patents

Abstract

(57) [Problem] To provide an insulator and a method of insulating a conductor having a plurality of turns for generating a magnetic field. The electrical insulation of a plurality of winding-shaped conductors (2, 3, 8) for generating a magnetic field, comprising an insulating material (6) of a solid material. The insulator is cylindrical and has an internal semiconductor layer (5) and an external semiconductor layer. The two semiconductor layers are formed so as to include an electric field between them. The joint between one semiconductor layer and the insulating material (6) exerts an adhesive force so as to maintain a mechanical connection when a changing stress is applied to the structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a conductor insulator having a plurality of turns for generating a magnetic field, and an insulating method thereof. In particular, the present invention relates to an insulator for an electric circuit of a rotating electric machine.

[0002]

[Prior art]

The rotating electric machine means a device that converts electric energy into mechanical energy or vice versa. Such a device consists of an electrical circuit, a magnetic circuit, and a mechanical circuit. The mechanical circuit has two bodies that can move with respect to each other.
When a mechanical movement is applied, a magnetic field is generated, which is converted by a circuit into electrical energy. When supplied with electrical energy, a magnetic field is generated, which is converted mechanically by a mechanical circuit. The rotating electric machine used in the following description means both a generator and an electric motor.

[0003] The present invention is preferably intended to be applied to a rotating electric machine that operates under a high current and a high voltage, such as a generator that generates electric power. The mechanical circuit includes a stator and a rotor, and the rotor can rotate with a certain degree of freedom with respect to the stator. The electrical circuit is arranged as a winding on one or both of the rotor and the stator. When a current is applied to the winding, a magnetic field is generated between the rotor and the stator. The magnetic field is controlled or amplified by the magnetic core in the stator and rotor,
The magnetic core consists, for example, of a stack of magnetically oriented strips. However, the present invention is not limited to the application of the rotating electric machine alone, but can also be used for electric machines or devices having conductors that are insulated so that high voltages can be handled.

[0004] In order to describe the meritorious characteristics of the invention, a rotating machine in the form of a generator will be briefly described here. The most often used effective generator type is the so-called synchronous machine. Such a machine comprises a rotatably supported rotor surrounded by a stator having a stator winding and having a rotor winding. Both the rotor and the stator are made of a magnetized material, which preferably consists of a stack of strips. By applying a mechanical force to the rotor shaft, the rotor starts a constant rotational movement. When current begins to flow through the rotor windings, a rotating magnetic field is generated, which generates current in the stator windings.

[0005] The stator windings are mounted in slots embedded radially in the stator. The slots are oriented axially and are arranged rotationally symmetrically along the stator. The stator winding is made up of one or more series-connected conductors arranged in a coil shape, and two coils are inserted in each slot. In an AC machine, a change in inductance occurs between the cross sections of the winding conductor. Maximum reactance is obtained at the bottom of the conductor, and the main part of the current tends to flow at the top of the conductor. In order to prevent such a displacement of the current, the conductor is divided into a plurality of wires insulated from each other. Splitting into strands keeps the inductance unchanged for different strands, but they must be transposed or repositioned. Such dislocations are usually performed outside the stack of strips, but are also loaded into the slots by performing a so-called Roebel transposition. The choice of strand size is determined by a compromise between electrical and mechanical requirements. From an electrical point of view, it is preferable to use a large number of strands to reduce the displacement of the current, but from a mechanical point of view such coils are associated with many difficulties in manufacturing and installation. With small strands of large dimensions, problems arise, for example, when bending conductors.

When insulating high voltage windings, thermal, electrical, environmental and mechanical stress must be taken into account, among others. These are commonly referred to as TEAMs (thermal, electrical, ambient, mechanical) and have a considerable effect on the life of the insulator. From a thermal standpoint, the insulator can tolerate a temperature rise from 0 ° C. to 180 ° C. within one hour. From an electrical point of view, insulators provide satisfactory electrical insulation without electric field concentration. From a surrounding or environmental point of view, insulation can be dust, ozone,
It is not affected by condensation. Further, from an environmental point of view, the insulator must be capable of being recycled during scrap, without necessarily causing harmful emissions to the environment during manufacture or operation. Eventually, from a mechanical point of view, the insulator allows the coil to be fixed to the stator, but can move during thermal expansion of the conductor and the insulating material.

[0007] Although the voltage between conductors is higher than between wires, the conductor voltage and the wire voltage are relatively low. Therefore, wire and conductor insulation can usually be easily implemented. However, the coil itself must be able to withstand all-phase voltages up to several KV. As a result, the coil is insulated from the stator by the main insulation. Due to the high potential difference, partial discharges or PDs readily occur due to deformation of the electric field at high electric field strengths, and such partial discharges are commonly called coronas. When corona is generated, ozone (O ₃ ), which has a particularly strong impact on organic substances, is generated. In this way, corona degrades the organic insulating material, so that the main insulation contains a corona-compatible material. One such material is an inorganic compound, mica that can resist the impact of ozone.

[0008] The most commonly used insulating materials contain mica as a major component. Mica is often embedded in a binder disposed on a tape-forming carrier. The material of the carrier and the binder can be changed. A common embodiment of the main insulator is a resin-saturated tape containing mica flakes, which is wrapped around a conductor and cured in a furnace treatment. At the top of the main insulator is provided a corona protector which blocks external corona between the side of the coil and the slot wall.

Mica is a very fragile material with low shear strength. The thermal expansion of mica is, for example, 1/5 that of copper. When a load is applied to electrical equipment, the temperature of the windings increases.
Copper conductors usually tend to expand more than insulators. Due to the different thermal properties of the materials, a potential difference occurs between the conductor and the insulator. Since mica has low shear strength, crushing will occur and voids will form in the insulator. In fact, the cavity will be filled with air, causing a considerable deformation of the electric field. Corona is generated due to the concentration of the electric field.

Although generator insulators are known from the description of US Pat. No. 5,066,881, their primary function is to provide a layer capable of dissipating charge to reduce corona in contact with the outside of the main insulation. That is. The end result is that the insulator is surrounded by a hardenable glass fiber coated semiconductor layer. Such coatings can replace conventional ground tapes that can dissipate charge to prevent corona. The new coatings conform well to the contours of the insulator and maintain good semiconductor properties after curing of the main insulator. In one embodiment, the semiconductor layer is applied to the upper and lower end regions of the coil inside the main insulator. In this embodiment, the periphery of both ends can be made to have an equal potential uniformly. Known insulators did not add anything new to the prior art. It is well known that electric charges can be diverged by providing a semiconductor layer outside an insulator in this manner.

For example, a significant problem during the insulation operation of a rotating electric machine such as a generator or a motor has been that the insulating material and the conductor have different thermal expansions. In the case of a temperature change, it means that the insulator and the conductor are displaced from each other to generate a cavity. The electric field is greatest where it is closest to the conductor. Cavities occur where the risk of corona is greatest. In known generators, some corona is acceptable and contains mica instead of an insulator that can resist discharge. As mentioned above, mica has poor mechanical properties. When the discharge occurs, ozone is generated which impacts the insulator carrier and the binder, and the insulator is gradually destroyed. In this way, after a certain time, the stator winding with the insulator must be replaced.

A further problem with known electric machines that accept a corona is that the discharge can cause electromagnetic disturbances, delicate electrical devices and even stop functioning.

[0013]

[Problems to be solved by the invention]

An object of the present invention is to provide a conductor insulator composed of a plurality of windings for generating a magnetic field. In particular, the present invention relates to an insulator that eliminates the occurrence of partial discharge (PD) and is applied to a rotating electric machine having a long operating life. In addition, insulators can reduce maintenance and are more reliable than known insulation systems. From an environmental standpoint, insulators do not necessarily involve environmentally harmful emissions during manufacture, use and scrapping. Another object of the present invention is to provide a method for insulating a rotating electric machine while achieving the above-mentioned objects. Insulators are particularly effective when replacing windings in existing electrical equipment.

[0014]

[Means for Solving the Problems]

This object is achieved according to the invention by an insulator based on the features of the independent claims 1 and 8, and by a method according to the features of the independent claim 9 relating to the method. Advantageous embodiments are described in the features of the dependent claims.

[0015] An electrical insulator is a medium or material that, when placed between conductors of different potentials, causes very little or insignificant current to flow therebetween. Further, as the potential between the conductors increases, the electric field strength between the insulators also increases. This also increases the risk of destruction because the insulation strength of the material is exceeded. Dielectric s
trength) is defined as the maximum voltage gradient a material can withstand without breaking.

[0016] Dielectric breakdown of the gas results from the multiplication of the power index of the free electrons induced by the applied electric field. For a constant electric field, breakdown occurs at a voltage that is a function of the product of pressure and distance. Here, whether this product is small or large, the gas has a high breaking stress. In the case of a small amount and high pressure, electrons accelerated by the electric field cannot be accelerated enough to start destruction due to collision with other electrons. For large volumes and low pressures, the number of electrons is too small for a sufficient number of collisions to occur. Under appropriate conditions, the electrons collide with other electrons and are similarly accelerated, resulting in an avalanche-like destruction. Practically, the magnitude of the gas insulation strength is about 0.5 KV / mm. Therefore, at low electric field strengths, no corona is generated in the insulating material or in the gas-filled cavity between the conductor and the insulator.

Thus, in high voltage engineering, when the electric field strength exceeds the insulation strength of the gas, the danger of corona is obvious. Cavities containing gas in the insulation necessarily begin to discharge spontaneously. Therefore, the need to set the electric field so that cavities in the insulator between the conductor and the insulator can be reduced or completely eliminated and electric field concentration is avoided should be considered.

The insulator according to the present invention comprises an elongated tubular insulator for surrounding the conductor. The insulator has one internal and one external semiconductor layer disposed to include an electric field therebetween. The semiconductor layer covers the inside and the outside of the insulating material, respectively, and is joined to the adhesive insulating material such that the materials accompany each other when the structure changes due to, for example, heat or mechanical stress. In this way, the joint must not contain cavities, not only during manufacturing, but also when the materials to be joined together are stressed. Such adhesion between the insulating material and the two semiconductor layers can be achieved by manufacturing them from the same material. In the case of temperature changes, the material expands equally, so that the force acting between the joints is zero or very little. However, joints with the desired cohesion are achieved by heat treatment of the materials such that they flow at each other into a uniform structure. The mechanical and thermal changes between the insulation and the two semiconductor layers are absorbed as elastic or plastic changes in the material of the closest joint.

Since the inner layer is galvanically or capacitively coupled to the conductor and the outer layer is connected to, for example, ground or other controllable potentials, the electric field created between the conductor and ground is an insulator semiconductor. Surrounded between layers. Due to changes in temperature and mechanical influences, cavities created inside the insulator have no adverse effect on the occurrence of PD. There is no potential difference between the conductor and the internal semiconductor layer.

As mentioned above, by ensuring that no corona is generated, the insulation consists of an organic material without the addition of mica. The overall insulation capacity of the material is utilized. Since no ozone is formed which weakens the material, the thickness of the insulator is reduced. Therefore,
The insulator is composed of a homogeneous material such as, for example, a thermoplastic resin or a rubber mixture. One such suitable material is cross-linked polyethylene. The semiconductor material is of the same material and contains conductive dust such as, for example, carbon black or powdered coal. An insulating material having two semiconductor layers is applied to the conductor in a simple manner, for example by extrusion.

The insulation system of the present invention is intended especially for a coil having a plurality of conductors divided into strands. The conductor and strand insulation consist of a suitable material having a higher dielectric constant than the main insulation. With this arrangement, the insulator inside the internal semiconductor layer of the main insulation can change the electric field such that the concentration over the internal insulation is very small. By extruding the equipotential lines of the electric field instead of the internal insulation, a large concentration occurs in the main insulation. Due to such a change in the electric field, the large concentration spreads over a wide range, and thus the electric field concentration becomes sparse.

For example, in the case of a lightning shock, the rotating electric machine receives an electric shock. For one or a few microseconds, the voltage rises in the winding. The potential difference between the conductors of the coil increases to tens of thousands of volts. Each conductor strand is surrounded by a thin strand insulation provided to insulate the conductor strands from each other. Wire insulation usually exhibits good short-term strength to electroflash. The two conductor strands are insulated from each other with an insulation thickness corresponding to the two strand insulations. Similarly, between the conductor strands associated with the different conductors in the coil there is a two layer thickness of such insulation. Thus, in the event of a shock between them, flashovers are very rare.

Since the insulator according to the invention surrounds a plurality of conductors, the insulator between the semiconductor layer and the conductor strands in contact with them forms the thickness of the actual strand only. The semiconductor layer is appropriately connected to one of the conductor strands belonging to one of the conductors. The potential difference between the semiconductor layer and the closest conductor strand is only a few hundred volts during normal operation. Wire insulation provides sufficient insulation to prevent flashover. When shocked, the voltage increases momentarily to several thousand volts. However, such a change in voltage will not have time to propagate to the entire structure of the semiconductor layer, so in either case flashing will probably not occur in either case.

The insulator of the present invention provides a corona-free environment during normal operation. This means that organic insulating materials can also be used for strand insulation. This gives the insulator a new possibility to be a rather elegant solution than the environment in which coronas occur. An organic insulator with improved properties is selected and the insulating layer is thinner. To manage the insulation between the conductor strands and the internal semiconductor layers, each conductor, including all conductor strands, is coated with an additional layer of high quality insulating material.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention described with reference to the accompanying drawings. FIG. 1 shows a cross section of a normal winding coil of a rotating electric machine. The winding includes a first conductor having a plurality of strands 2 and a second conductor similarly having a plurality of strands 3. The strands belonging to each conductor are surrounded by a strand insulator 4, thus forming an insulating layer surrounding the stack of conductor strands. The insulator 1 surrounding the wire insulator 4 includes an intermediate insulating layer 6 having an internal semiconductor layer 5 and an external semiconductor layer 7.

FIG. 2 shows a first conductor 11 composed of a plurality of conductor strands 2 and a plurality of conductor strands 3
2 shows a cross section of an insulator 1 surrounding a second conductor 12 made of the same. The first conductor is surrounded by an insulating layer 9 and the second conductor is surrounded by an insulating layer 10. Surrounding insulator 1
Comprises an insulating intermediate layer 6, an internal semiconductor layer 5 and an external semiconductor layer 7. In the figures, the different layers are intentionally thickened for emphasis. In fact, the semiconductor layers are thin and the insulating layers surrounding the conductors and the conductor strands are very thin. When insulating the conductors and conductor strands according to the invention, the insulation layer is compressed to a homogeneous insulator surrounding the conductors and conductor strands.

Since one conductor strand 8 is galvanically or capacitively coupled to the internal semiconductor layer 5, this layer is considered to be at the same potential as the conductor strand 8. The external semiconductor layer 7 is grounded. With this arrangement, the insulator 1
It includes an electric field formed between the conductor and the ground. What is particularly important for the insulating function is that no cavity is formed between the internal semiconductor layer and the external semiconductor layer.
The insulating layer and the two semiconductor layers are homogeneous and completely mechanically connected to each other. The mechanical connection must also be maintained in case of changes caused by temperature changes or mechanical effects.

The outer semiconductor layer serves to distribute ground potential between the outer limiting surfaces of the outer insulator. The outer semiconductor layer must thus cover the entire jacket surface. Similarly, the internal semiconductor layer acts to distribute the phase voltage connected to the conductor via the internal limits of the insulator. The internal semiconductor layer must cover the entire internal critical plane of the insulator. As used herein, the term semiconductor material is considered to be an insulating material, having a significantly lower conductivity than a conductor. For example, the material contained in the two layers have a resistivity of between 10 ^-4 [Omega] m to 10 ⁴ [Omega] m, in particular has a resistivity between 1Ωm to 100 [Omega] m.

The insulating intermediate layer is selected from an insulating material having a high electric field strength of, for example, 7 KV / mm or more. By including a total potential difference between ground and phase in both semiconductor layers, and since there are no cavities between them, no partial discharge occurs. Thus, the insulating intermediate layer is selected from organic materials, for example thermoplastic resins or rubber mixtures. Advantageously, the two insulating layers are made of the same material as the insulating intermediate layer, in which case conductive fines such as, for example, carbon black or finely divided coal are mixed therewith.
A suitable material is, for example, a cross linkable polymer.

According to the invention, there is a considerable advantage over the prior art, as the insulating material is no longer supplied by the windings. Advantageously, the polymer material is supplied by an extrusion process, in which case the two semiconductor layers are also supplied in a similar process. It is not always necessary that the insulating material and the semiconductor layer be made of the same material. The important point is that there are no cavities between the materials. Eventually, the two separate materials are joined together in such a way that an adhesion therebetween is obtained under thermal or mechanical influence. For materials having different properties, stress occurs in the area around the joint as one material expands more than the other. Therefore, the bond must be fairly strong so that the joint can absorb the stresses. This is achieved by elastic or plastic deformation of the material on either side of the joint.
An important advantage of the polymeric material is that it is deformable and can withstand repeated mechanical deformation without any danger to the adhesion between the layers during operation. Such materials easily melt together during heating so that they float together and form a void-free uniform bond.

It is effective that the wire insulator 4 has a larger dielectric constant than the main insulator. Due to these conditions of the material, the wire insulation changes the electric field such that the equipotential lines are arranged radially. The area closest to the conductor has the highest electric field concentration, which is displaced from the center and occurs in the main insulation between the two semiconductor layers. The further away from the center means that the electric field is distributed over a wider area and less concentrated.

For example, an insulating layer is disposed around each conductor to overcome a load due to an electric shock such as a lightning shock. The potential difference between conductor wires combined with different conductors is on the order of tens of thousands of volts when subjected to an impact. Flashove of a simple layer of wire insulation
The short-time strength for r) is usually insufficient to prevent flashover between the conductor strand and the semiconductor layer. To safely maintain sufficient resistance to such flashover, the conductor is surrounded by additional insulating layers 9,10. Further, by providing the internal semiconductor layer with a resistor capable of transmitting a potential that does not cause harm when subjected to an impact, sufficient safety against flashover can be obtained.

[0033]

【The invention's effect】

ADVANTAGE OF THE INVENTION According to this invention, in order to generate | occur | produce a magnetic field, the improved insulator of the conductor which consists of multiple winding can be provided. In particular, the present invention can provide an insulator that eliminates the occurrence of partial discharge (PD) and is applied to a rotating electric machine having a long operating life. In addition, insulators can reduce maintenance and are more reliable than known insulation systems.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of a coil of a stator winding provided with an insulator according to the present invention.

FIG. 2 is a cross-sectional view of the insulator of the present invention, which is made of an insulator surrounding two conductors and has a circular cross section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulator 2 Element wire 3 Element wire 4 Element insulator 5 Internal semiconductor layer 6 Insulating material 7 External semiconductor layer 8 One conductor element wire 9 Insulating layer 10 Insulating layer 11 First conductor 12 Second conductor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) H01F 27/34 H01F 27/34 (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM ), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, G E, GH, GM, HR, HU, ID, IL, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN , MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW F term (reference) 5E043 BA03 5E044 AC01 5E058 BB17 5H604 AA01 BB03 BB10 CC05 DA17 DB03 DB16 DB18 PB01 PB02 PB03 PD01 PD06 PD07 PD09 PD10

Claims (13)

[Claims] 1. An electrical insulator (1) of a conductor (2, 3, 8) comprising a solid material insulator (6) and having a plurality of turns for generating a magnetic field, wherein the insulator is It is cylindrical and has an internal semiconductor layer (5) and an external semiconductor layer (7), both of which are arranged so as to include an electric field therebetween, and one of the semiconductor layers and the insulating material (6). An electrical insulator of a conductor, characterized in that it exhibits adhesiveness to maintain mechanical contact when structural change stress is applied to a joint between the conductors. 2. The electrical insulator according to claim 1, wherein the internal semiconductor layer is electrically connected to a conductor strand. 3. The electrical insulator according to claim 1, wherein the external semiconductor layer is connected to a controllable potential, preferably a ground potential. 4. An electrical insulator according to claim 1, wherein the insulator (6) and the two semiconductor layers (5, 7) have the same thermal expansion characteristics. 5. The electrical insulator according to claim 1, wherein said semiconductor layer is made of a material having a resistance between 1 Ωcm and 100 Ωm. 6. An electrical insulator according to claim 1, wherein said insulator is provided so as to surround a conductor having a substantially rectangular cross section. 7. An electrical insulator according to claim 1, wherein at least one of said insulating material (6) and said semiconductor layer (5, 7) is in the form of cross-linked polyethylene. 8. An electrical insulator (1) of a conductor (2, 3, 8) comprising a solid material insulator (6) and having a plurality of turns rotated in a magnetic field, wherein the insulator is It is cylindrical and comprises an internal semiconductor layer (5) and an external semiconductor layer (7), both layers being arranged so as to contain an electric field between them, between one of said semiconductor layers and said insulating material (6). An electrical insulator for a conductor, characterized by exhibiting adhesiveness to maintain mechanical contact when structural change stress is applied to the joint. 9. A method for insulating a conductor (2, 3, 8) having a plurality of turns to generate a magnetic field, wherein the insulator comprises a solid material surrounding the conductor, and the insulator comprises a cylindrical material. And an inner semiconductor layer (5) and an outer semiconductor layer (7), both of which are arranged so as to contain an electric field therebetween, so that between one of the semiconductor layers and the insulator (6) A method of insulating a conductor, characterized by exhibiting adhesiveness to maintain mechanical contact when a structural change stress is applied to a joint of the conductor. 10. The method for insulating an electrical insulator according to claim 7, wherein said insulating material (6) and said two semiconductor layers (5, 7) are made of a material having similar thermal expansion characteristics. Insulation method. 11. The method for insulating an electrical insulator according to claim 7, wherein the insulator surrounds a conductor having a substantially rectangular cross section. 12. The method for insulating an electrical insulator according to claim 7, 8 or 9, wherein the insulating material and the two semiconductor layers are attached to the conductor by extruding a cross-linked polymer. And insulation method. 13. The electric insulator according to any one of claims 1 to 7, or the electric insulator according to any one of claims 8 to 11, in repairing a rotating electric machine, particularly when replacing a winding. An insulating method characterized by using an insulating method.