JPH0454961B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a molded transformer in which a shield layer is formed that is safe even if the human body touches the surface of the molded coil during energization, and in particular, This invention relates to a shield layer structure that alleviates the electric field between the layers.

[Prior art]

The surface of the molded coil is covered with an insulating resin layer, but because of the capacitance that exists between the resin layer and the ground, generally when a molded transformer is energized, the surface of the molded coil will have a considerable high voltage. It has a potential and there is a risk of electric shock if the body touches it. As a countermeasure, a shield layer made of a sprayed metal coating of aluminum, zinc, etc., which has good adhesion to the resin layer and is chemically stable, is provided on the surface of the resin layer except for the area around the terminals of the molded coil. It is conceivable to ground the

Figures 1 to 3 are diagrams showing this surface shield type molded transformer, where 1 is an iron core, 2 is a molded coil combined with this, 2' is its terminal, 3 is a coil conductor, and 4 is an insulating resin. Layers 5 and 6 are coil terminals provided in the terminal portion 2', 7 is a shield layer made of a metal spray coating coated on the surface of the insulating resin layer 4 except for the periphery of these terminal portions, and 8 is a grounding terminal. A metal fitting 9 is a grounding wire connected to the metal fitting 9, and the other end of the grounding wire 9 is connected to an iron core fastener 10 or the like which is at earth potential, thereby grounding the shield layer 7.

Such a surface shield type transformer is constructed so that the shield layer 7 has high conductivity throughout and is equal to the ground potential in order to prevent electric shock.

However, in this structure, one shield layer 7 is at ground potential, and the surfaces 2' and 4 of the other insulating resin layer are at high potential, and furthermore, the edge 7 of the shield layer 7 is at a high potential. Since ' has a sharp shape, the potential between the resin layer and the shield layer changes rapidly and the electric field is concentrated. Therefore, there is a possibility that discharge may occur between the two through the air, and in particular, since high voltage is applied to the terminals 5 and 6 of the terminal portion 2', discharge is likely to occur between the terminal and the shield layer. If discharge actually occurs, not only will the resin layer deteriorate, but this discharge current will flow to the ground via the ground terminal 8, causing problems with other equipment and equipment, such as communication problems due to corrosion and noise. There is a fear.

Further, since the molded coil has a large ground capacitance, the current for charging this capacitance also flows to the ground, which may also cause the above-mentioned trouble.

[Purpose of the invention]

An object of the present invention is to provide a surface shield type molded transformer in which the electric field strength between the resin layer and the shield layer is reduced and the potential difference within the shield layer is set to a potential difference that does not cause electric shock to the human body.

[Summary of the invention]

To achieve the above object, the present invention provides a coil wound with a conductor, an insulating resin layer covering the coil, a coil terminal connected to the coil, and a coil terminal formed on the surface of the insulating resin layer on the outer circumferential side of the coil. In a surface-shielded molded transformer comprising a shield layer, a molded coil having a ground terminal connected to the shield layer, and an iron core that is inserted into the molded coil, the molded coil has the coil terminal arranged thereon and the molded coil having the ground terminal connected to the shield layer. A discontinuous portion for preventing the formation of one turn of the shield layer is provided on a part of the outer peripheral surface of the insulating resin layer, and the shield layer is disposed at the edge thereof and adjacent to the discontinuous portion.
It has a high conductivity part having a volume resistivity of about 2.75 to 5.9 μΩcm surrounded by the low conductivity part having a volume resistivity of about 118 μΩcm, and the high conductivity part and the low conductivity part are The thickness of the shield layers is kept constant by overlapping each other so that as the thickness of one layer increases, the thickness of the other layer decreases at the boundary between the shield layers.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 4 to 6, parts that are the same as those of the conventional example are designated by the same reference numerals. Various methods can be considered for forming the shield layer 7 on the surface of the resin layer of the molded coil, such as applying a conductive paint, plating, thermal spraying, etc. Here, conductive thermal spraying will be described as an example.

In the figure, masking tape is pasted on the surface of the resin layer of the molded coil where the molded coil is not provided. Specifically, these are the end surface 13 of the molded coil 11 in FIG. 4, the terminal portion 12, and the edge of the outer circumferential surface of the coil adjacent thereto (portion 7b, which will be described later). In this state, metal is sprayed using a metal spraying device to form a highly conductive metal film with a thickness of about 20 to 200 μm on the outer surface of the coil, thereby forming the central portion 7a of the shield layer 7. After this central portion 7a has hardened, the masking tape at a portion 7b, which will be described later, adjacent to the central portion 7a is peeled off, and the masking tape is pasted on the surface of the central portion 7a. In this state, a low conductivity metal is sprayed using a metal spraying device to form a metal film with a thickness of about 20 to 200 μm on the resin surface in the same manner as described above, thereby forming the edge 7b of the shield layer. After this edge 7b has hardened, remove all the masking tape. Conductors with high conductivity include aluminum and zinc, and conductors with low conductivity include nichrome, tungsten, conductive varnish, iron, and the like. Note that the volume resistivity (μΩcm) of aluminum, zinc, tungsten, and iron is
℃ 2.75, 5.9, 5.5, and 9.8 (Compiled by Tokyo Tenmondai, "Science Chronology 1968," published by Maruzen on December 25, 1961), and the volume resistivity (μΩcm) of nichrome is 108 at a temperature of 20℃. ±6 to 112±6 (JIS
C 2520 Heating wires and bands).

If the central part 7a and edge part 7b of the shield layer are thermally sprayed so that their boundaries overlap, they can be electrically connected. Reference numeral 8b is a grounding terminal, which may be provided on either the center portion 7a or the edge portion 7b, but in this embodiment, it is embedded in the resin surface that will become the edge portion 7b before metal spraying, and a low conductivity terminal is placed on top of it. It is electrically connected to the edge 7b by thermal spraying metal.

The surface-shielded molded coil constructed as described above is combined with the iron core 1 to form a molded transformer in the same manner as shown in FIG. In this state of use, a considerably high voltage is induced on the surface of the molded resin layer as described above. According to the configuration of the above embodiment, since the edge 7b at the circumferential edge of the shield layer is formed of a low conductivity metal, the potential difference between the ground terminal 8b and the surface of the resin layer is as follows: ground terminal 8b - edge 7b
The potential difference between the edges 7b and the surface of the resin layer becomes small.

Note that the ground terminal 8b is made of a highly conductive metal.
This is the same even if the ground terminal 8b is connected to the central portion 7a.

Therefore, the potential gradient between the latter, that is, the edge 7b of the shield layer and the resin surface becomes gentle, and even if these are exposed to air with relatively low insulation strength, discharge between them is unlikely to occur. Also between the terminals 5, 6 and the shield layer 7, electric field concentration does not occur for the same reason as described above, making it difficult for discharge to occur.

In the above embodiment, since the ground terminal 8b is electrically connected to the edge 7b of the shield layer, the current flowing from the shield layer to the ground terminal due to the large capacitance of the molded resin coil is caused by this edge 7b. As a result, the current is limited and there is less interference with other facilities and equipment.
In addition, in the area of the edge 7b, the farther the area is from the ground terminal, the higher the resistance becomes and the potential gradient can be shared between the areas.For example, when the terminal 5 is used as a high potential terminal, the ground terminal 8b should not be placed too close to the terminal 5. In this case, the discharge between the terminal 5 and the shield layer can be reduced.

If the above embodiment is illustrated as an electric circuit, it will be as shown in FIG. That is, the capacitance formed by the coil wire 3 connected to the terminals 5 and 6 and the central part 7a of the shield layer is defined as the capacitor C1, and the capacitance formed by the coil wire and the edge 7b is defined as the capacitor. C
Set it to 2. A mold resin layer 4 is interposed between the electrodes of these capacitors. It can be seen from this figure that the edge 7b of the shield layer makes the potential gradient between the shield layer and the surfaces 12 and 14 of the mold resin layer gentle, and limits the charging current of the capacitor. In addition, the parts 7a and 7b are actually touched by the human body, and the conductivity of 7b should be determined so that there is a potential difference between these parts and the ground terminal that will prevent people from getting electrocuted. .

FIG. 8 shows a second embodiment of the present invention. In this embodiment, the edge of the shield layer of the previous embodiment is composed of a first edge 7b' and a second edge 7c having different conductivities,
The first edge 7b' is set to have higher conductivity than the second edge 7c. The center portion 7a, the first edge portion 7b', and the second edge portion 7c are adhered to the surface of the resin layer by conductive thermal spraying using masking tape in the same manner as in the previous embodiment so that the boundaries of each portion overlap slightly. In this case, since the absolute amount of thermal deformation due to the thermal expansion coefficient of the outermost edge 7c is large, it is preferable to select a conductor that has a thermal expansion coefficient close to that of the resin layer. Also, each part 7a, 7
b', 7c are ground terminals 8a, 8b, 8c, respectively.
are electrically connected, and any terminal therein is grounded.

Let us consider a case where the terminal 8a of the central portion 7a is grounded. In this case, large electric field concentration occurs at three locations: between the center portion 7a and the edge portion 7b', and between the edge portions 7b', 7c and the resin layer. Therefore, compared to the previous embodiments, the electric field burden at each concentration point is reduced, the potential gradient between the shield layer and the resin layer becomes gentler, and the suppression of discharge caused by both is more effective. Decide which grounding terminal to ground by taking into account the characteristics of the transformer, such as the ease with which discharge occurs, the magnitude of the charging current for the capacitance, and the voltage applied to the human body when it touches the shield layer. It will be done. Note that the ground terminal is connected to two terminals at the same time.
It is also possible to configure more than one of them to be grounded.

If each overlapping part becomes thicker than the other and its heat capacity increases, heat generation and radiation due to heat cycles during use will not be uniform, and the expansion and contraction of the entire conductor will become unbalanced, resulting in peeling.

A configuration for improving this will be explained with reference to FIGS. 9 to 11. That is, each overlapping portion is configured to have a mutually thinner thickness. During manufacturing, the amount of thermal spray is reduced when spraying each overlapped part, but specifically, the outlet of the thermal spray nozzle is narrowed down, or a mask or the like is placed between the thermal spray nozzle and the resin surface to control the amount of thermal spray. intervene. Furthermore, it is also possible to raise the spraying temperature to make the spray particles finer. With the above configuration, since the thickness does not change in the overlapping portions of different types of conductors, the heat capacity becomes almost uniform throughout the shield layer, and peeling between the conductors due to heat cycles is prevented. With this configuration, considering that the electric field is concentrated in the overlapping portion of the conductors, since there is no stepped corner (detail at the tip) in this portion, it is possible to reduce the discharge during this portion.

Further, FIG. 10 shows a first modification of this embodiment in which each conductor overlaps and each part is formed in a step shape.
The effect is almost the same as that shown in FIG. As a second modification of this embodiment, the spraying order of each conductor may be reversed as shown in FIG. 11, and the conductors may also be sprayed in any order.

When constructing each conductor by thermal spraying, it is necessary to apply masking tape, and the work may become troublesome if the number of types of conductors increases. As a countermeasure for this, it is easy to apply conductive varnish or conductive paint, and it is also easy to apply conductive tape. When attaching the conductive tape, it is important to avoid creating a space on the attachment surface between the conductive tape and the resin layer that would induce electrical discharge.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, it is possible to moderate the voltage gradient between the shield layer and the surface of the insulating resin layer, and the thickness of the shield layer is constant and the thickness is maintained at the boundary between the low conductivity part and the high conductivity part. Since there are no steps, it is possible to reduce electrical discharge, reduce the electrical resistance from a point in the shield layer to the point where the ground terminal is provided, and further reduce the potential difference between the high conductivity part and the low conductivity part in the shield layer. Since it is possible to prevent electric shock even if the shield layer comes into contact with the shield layer, it is also possible to suppress the discharge during this time, which prevents deterioration of the molded coil resin layer and damage to other equipment due to noise and corrosion. Damage to equipment can be prevented.

[Brief explanation of drawings]

Figures 1a and b are front and side views of a surface-shielded molded transformer, Figure 2 is a perspective view of a shielded molded coil according to the prior art, Figure 3 is its A-A' sectional view, and Figure 4. is a perspective view of a molded coil according to the present invention, and FIG. 5 is a sectional view taken along line B-B'.
Fig. 6 is a plan view thereof, Fig. 7 is an electrical equivalent circuit diagram thereof, Fig. 8 is a side view of the molded coil of the second embodiment, Fig. 9 is a sectional view of the present embodiment, and Fig. 10 is the main body. FIG. 11 is a sectional view of a first modification of the embodiment, and FIG. 11 is a sectional view of a second modification of the embodiment. 12: Coil terminal part, 12, 13: Insulating resin layer surface, 7: Shield layer, 7a: High conductivity part (center part), 7b, 7b', 7c: Low conductivity part (edge part), 8
a, 8b, 8c: ground terminal.

Claims (1)

[Scope of Claims] 1. A coil wound with a conductor, an insulating resin layer covering the coil, a coil terminal connected to the coil, a shield layer formed on the surface of the insulating resin layer on the outer circumferential side of the coil, and In a surface shield type molded transformer comprising a molded coil having a ground terminal connected to a shield layer, and an iron core fitted into the molded coil, the molded coil has the coil terminal arranged thereon and a ground terminal connected to the shield layer. A discontinuous portion that prevents the formation of one turn is provided on a part of the outer peripheral surface of the insulating resin layer, and the shield layer is disposed at the edge thereof and has a volume resistivity of about 9.8 to 118 μΩcm adjacent to the discontinuous portion. and a high conductivity part located in the center thereof and surrounded by the low conductivity part and having a volume resistivity of about 2.75 to 5.9 μΩcm. A surface shield type mold transformer characterized in that the conductive parts are overlapped at the boundary part such that as the thickness of one increases, the thickness of the other decreases, and the thickness of the shield layer is kept constant. vessel. 2. The surface shield type molded transformer according to claim 1, wherein the ground terminal is electrically connected to the low conductivity portion. 3. The surface shield type molded transformer according to claim 1, wherein the low conductivity section is composed of a plurality of sections having different conductivities, and the sections are arranged in descending order of conductivity from the edge to the center. 4. Claim 3, wherein the grounding terminal is electrically connected to any conductivity portion of the low conductivity portion.
Surface shield type molded transformer as described in .