Current transformers and zero-phase current transformers

Abstract

A current transformer and a zero-phase current transformer are obtained that can prevent a decrease in electrical characteristics caused by the pressure exerted on the coil housed in the outer case by pressure molding of heated and fluidized molding resin. [Solution] By lowering the height of the outer cylinder 3 in the outer case 1 and providing a molded resin filling section 7 on the outer circumference, the inflow of molded resin between the side of the coil 9 and the outer cylinder 3 is prevented, thereby suppressing the pressure applied to the coil.

Description

Technical Field

[0001] The present invention relates to a current transformer and a zero-phase current transformer for measuring an alternating current or an alternating current with a superimposed direct current, such as a half-wave sinusoidal alternating current or their leakage current.

Background Art

[0002] As shown in FIG. 6 of Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2021-064772), for example, a conventional general current transformer has a secondary winding W2 wound around a closed magnetic circuit composed of an annular core, and a primary winding W1 through which the current to be measured flows penetrates the central opening of the closed magnetic circuit. Its operation is that when a current I1 flows through the primary winding W1, a current I2 corresponding to, preferably proportional to, the magnitude of the current I1 is generated in the secondary winding W2 by electromagnetic induction. At this time, by connecting a burden resistor to the secondary winding W2, a voltage is generated across the burden resistor, and as a result, it becomes possible to measure the current I1 flowing through the primary winding W1 as a voltage signal.

[0003] Also, as a method for manufacturing a conventional current transformer, as shown in FIG. 7 of Patent Document 1, for example, a metal upper mold and a lower mold are prepared, and a core having at least one winding, that is, a coil, is inserted into the lower mold in a state where it is incorporated into an outer case, the lower mold is closed with the upper mold, and a heat-fluidized molding resin is filled into the mold under pressure to perform pressure molding and integrally seal and mold.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional current transformers can seal the coil 12 housed in an outer case 1 by pressure molding, as shown in Figure 7 of Patent Document 1. However, as shown in Figure 1(a) of Patent Document 1, if the gate 20 for filling the molding resin is located near the outer circumference of the outer case 1, the molding resin 10 poured directly below the gate 20 will enter between the outer circumference of the coil 12 and the outer cylinder 3 of the outer case 1, applying a pressure of at least several hundred N to the outer surface of the coil 12. As a result, the case 14 (for example, made of PP (polypropylene) or PBT (polybutylene terephthalate) material, with a thickness of about 0.5 mm and a structure that covers the entire thing) that houses the magnetic core inside the coil 12, as shown in Figure 1(b) of Patent Document 1, will deform, and stress will be applied to the internal magnetic core 15. This will cause a decrease in magnetic flux density due to a decrease in the permeability of the magnetic core 15, resulting in a decrease in the output voltage signal and thus a decrease in sensitivity.

[0006] Regarding the pressure exerted by the molded resin 10, the coil 12 is in contact with the molded resin 10 on the top surface, which is the opening side of the outer case 1, as shown in Figures 1(b) and 1(e) of Patent Document 1, and is therefore subjected to pressure. However, the case 14 housing the magnetic core does not have a fitting portion on its top surface like the outer peripheral side surface, and is narrower and has a smaller area compared to the outer peripheral side surface, making it less susceptible to the effects of pressure. Therefore, it is relatively durable against forces from the top surface towards the bottom surface (downward direction as shown in Figure 1(e)) and is less prone to deformation.

[0007] Furthermore, while molded resin 10 may also seep between the coil 12 and the inner cylinder 2 of the outer case 1, the distance from the gate 20 is greater compared to the outer cylinder 3, making it difficult for enough pressure to be applied to the inner circumferential surface of the coil 12 to deform the case 14 that houses the magnetic core. Therefore, the present invention addresses the effect caused by the pressure applied to the outer circumferential surface of the coil 12 when the gate 20 is located near the outer circumference of the outer case 1.

[0008] Furthermore, while increasing the thickness and strength of the case 14 that houses the magnetic core can reduce the stress on the magnetic core 15 caused by pressure molding, this creates the problem that the size of the coil 12 will increase by the amount of the increased thickness. [Means for solving the problem]

[0009] The current transformer or zero-phase current transformer in this invention comprises a coil having a winding on an annular magnetic core having high relative permeability characteristics, a case having a bottom surface and a double cylindrical wall for housing the coil, and a molded resin poured into the case from a molding die injection port and pressure-molded integrally with the coil, wherein the height of the outer cylindrical wall of the double cylindrical wall of the case is lower than the height of the inner cylindrical wall of the double cylindrical wall, and the outside of the outer cylindrical wall is provided with a molded resin filling section made of the molded resin. [Effects of the Invention]

[0010] As described above, this invention can accommodate a coil, and by providing an outer cylindrical wall that is lower than the inner cylindrical wall, and a molding resin filling section on the outside of the outer cylindrical wall, the molding resin poured in during pressure molding can flow out into the outer molding resin filling section, preventing the molding resin from flowing between the coil and the outer cylindrical wall and having the effect of suppressing the pressure applied to the coil. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a current transformer or zero-phase current transformer according to Embodiment 1 of the present invention. [Figure 2] This is a perspective view showing a coil and lead pins used in a current transformer or zero-phase current transformer in Embodiment 1 of the present invention. [Figure 3] This figure shows an outer case used for a current transformer or zero-phase current transformer in Embodiment 1 of the present invention. [Figure 4] This is an explanatory diagram of a pressure molding method for a current transformer or zero-phase current transformer according to Embodiment 1 of the present invention. [Modes for carrying out the invention]

[0012] Embodiment 1. Figure 1 shows a current transformer or zero-phase current transformer 100 in Embodiment 1 of the present invention, where Figure 1(a) is a plan view, Figure 1(b) is a cross-sectional view along line AA in Figure 1(a), Figure 1(c) is a front view, Figure 1(d) is an enlarged view of part B in Figure 1(b), Figure 1(e) is a cross-sectional view along line CC in Figure 1(c), and Figure 1(f) is a cross-sectional view along line DD in Figure 1(a).

[0013] Figure 2 is a perspective view of the coil 9 and lead pin 5 used in the current transformer or zero-phase current transformer 100 in Embodiment 1 of this invention.

[0014] In Figure 1(a), 1 is an outer case made of, for example, PP (polypropylene) or PBT (polybutylene terephthalate) resin, and the through-hole 24 corresponds to the central opening of a typical current transformer and is a through-hole for passing through the primary winding through which the current to be measured flows.

[0015] In Figures 1(b) and 1(d), the coil 9 is housed in an outer case 1. An annular magnetic core 12, made by rolling a magnetic material such as nanocrystalline alloy, amorphous material, or permalloy into a strip and then winding it, is housed in a hollow annular magnetic core housing case 11 made of, for example, PP (polypropylene) or PBT (polybutylene terephthalate) resin with a thickness of 0.5 mm. A secondary winding 10, made of, for example, a 0.1 mm diameter copper wire with an insulating coating, is wound around the magnetic core housing case 11. The top surface of the magnetic core 12 (the end surface in the upward direction shown in Figure 1(d)) is located at a predetermined height t1 from the coil support bottom surface 19, which will be described later. In this embodiment, unless otherwise specified, the upward direction shown in Figure 1(b) is referred to as the top surface direction, and the downward direction shown is referred to as the bottom surface direction.

[0016] As shown in Fig. 1(e), for example, the lead pin 5 made of brass, hard copper wire, etc. is electrically connected to the terminal wire 16 of the coil 9, a part of which is housed in the outer case 1 and sealed together with the coil 9 by the molding resin 6. The molding resin 6 is a thermoplastic resin and is injected by the pressure molding described later. 23 shown in Fig. 1(a) is a gate mark remaining after separating the runner generated when injecting the molding resin 6 at the gate part, and is located near the outer periphery of the outer case 1. As shown in Fig. 2, the coil 9 and the lead pin 5 are electrically connected by soldering in a state where the terminal wire 16 of the secondary winding 10 of the coil 9 is wound around the lead pin 5. The voltage signal generated in the coil 9 by electromagnetic induction due to the current flowing through the primary winding passing through the through-hole 24 is output by the lead pin 5. As shown in Fig. 1(d), the molding resin 6 is also filled on the outer periphery of the outer case 1 to form the outer peripheral filling part 7.

[0017] Fig. 3 shows the outer case 1 used for the current transformer or zero-phase current transformer 100 in the first embodiment of this invention. Fig. 3(a) is a plan view of the outer case 1, Fig. 3(b) is a side view, Fig. 3(c) is a cross-sectional view taken along the E-E line of Fig. 3(a), Fig. 3(d) is a cross-sectional view taken along the F-F line of Fig. 3(a), and Fig. 3(e) is a cross-sectional view taken along the G-G line of Fig. 3(a).

[0018] In Fig. 3(a), 24 is a through-hole, 3 is an outer cylinder for holding the outer peripheral side of the coil 9, 2 is an inner cylinder for holding the inner peripheral side of the coil 9, and in Fig. 3(c), 19 is a coil support bottom surface for supporting the coil 9.

[0019] In Fig. 3(c), it is desirable that the height t2 of the outer cylinder 3 from the coil support bottom surface 19 is not less than the height t1 (see Fig. 1(d)) of the magnetic core 12 from the coil support bottom surface 19 and not more than the height t4 (see Fig. 1(d)) of the coil 9 from the coil support bottom surface 19.

[0020] The inner wall surface of the outer cylinder 3 is at a position in contact with the outer peripheral surface of the coil 9, and it is desirable that the coil 9 is press-fitted into the outer cylinder 3 (it can be pushed in only by the force of a human finger, and the coil 9 does not fall by its own weight even when the orientation of the outer case 1 is reversed).

[0021] In FIG. 3(c), the height t3 from the coil support bottom surface 19 of the inner cylinder 2 is higher than the height t4 (see FIG. 1(d)) from the coil support bottom surface 19 of the coil 9 by a predetermined height t5 (for example, 1 mm or more, and a height that does not hinder the filling of the molding resin 6 during the pressure molding described later is desirable).

[0022] In FIG. 3(d), 4 is a through-hole-shaped lead pin holding portion for fixing the lead pin 5. The lead pin 5 is attached by being press-fitted from the top surface to the bottom surface so that the tip protrudes from the outer case 1 as shown in FIG. 1(e). The portion where the terminal wire 16 of the secondary winding 10 is wound and soldered is housed in the outer case 1.

[0023] In FIG. 3(a), 21 is an enclosure for protecting the lead pin provided so as to cover the lead pin holding portion 4 from the outside of the outer case 1, and is provided between the terminal 21a and the terminal 21b on the outside of a part of the outer cylinder 3 (near the portion connected to the lead pin holding portion 4). As shown in FIG. 3(d), the height of the lead pin protection enclosure 21 from the support bottom surface 19 is higher than the height t2 from the support bottom surface 19 of the outer cylinder 3, and it is desirable to be equal to the height t3 from the support bottom surface 19 of the inner cylinder 2. The enclosure 21 contacts the outer peripheral filling portion 7 (see FIG. 1(d)) at the terminals 21a and 21b.

[0024] In FIG. 3(b), 8 is a protruding portion on the outer periphery of the outer cylinder 3 of the outer case 1. The molding resin 6 filled in the upward direction from the protruding portion 8 forms the outer peripheral filling portion 7 (see FIG. 1(d)), and is a portion that supports the outer peripheral filling portion 7 as described later. The protruding portion 8 protrudes from the outer periphery of the outer cylinder 3 by a length t8. The length t8 is, for example, 1 mm or more. The position where the protruding portion 8 supports the outer peripheral filling portion 7 has a bottom surface direction depth of h2 based on the height t2 from the support bottom surface 19 of the outer cylinder 3, and has a depth greater than or equal to the bottom surface direction depth h of the recess 18 described later. The length t8 and the depth h2 are such that the molding resin 6 can be filled in the entire portion corresponding to the outer peripheral filling portion 7 by the pressure molding described later.

[0025] In Figure 3(e), 18 is a recess with a depth h in the bottom direction relative to a height t2 from the support bottom surface 19 of the outer cylinder 3, and a width t6 (for example, width t6 is 0.5 mm or more, depth h is 4 mm or more), provided between the outer cylinder 3 and the enclosure 21. The recess 18 is also open in the circumferential direction of the outer cylinder 3 at the ends 21a and 21b of the enclosure 21 (see Figure 1(f)), and the molding resin 6 is filled from both this circumferential and bottom directions. As shown in Figure 1(f), the recess 18 has a depth h and a width t6 such that the molding resin 6 can fill up to the bottom surface of the recess 18 by pressure molding. Also, the width from the inner circumferential side surface of the outer cylinder 3 to the outer circumferential side surface of the enclosure 21 for protecting the lead pins is t7.

[0026] This section describes a method for pressure molding (sealing) the coil 9 of the current transformer or zero-phase current transformer 100 using molding resin 6 in Embodiment 1.

[0027] Figure 4 is an explanatory diagram of a general pressure molding method (sealing method) for current transformers, with a cross-sectional view to show the ejector pin added to Figure 7 of Patent Document 1. Figure 4(a) is a perspective view, Figure 4(b) is a top view, and Figure 4(c) is a cross-sectional view of the HH line in Figure 4(b).

[0028] In Figures 4(a), (b), and (c), 14 is the upper mold, which has a gate 13 for injecting the molding resin 6. The gate 13 is positioned 180° opposite to the lead pin 5, relative to the central axis of the through hole 24 in the outer case 1, thereby reducing the stress on the lead pin 5 and terminal wire 16 caused by the flow of the molding resin 6. 15 is the lower mold, which has a storage section 20 for housing the coil 9 and lead pin 5 assembled in the outer case 1 during pressure molding. 17 is an ejector pin for pushing out the current transformer or zero-phase current transformer 100 from outside the lower mold 15 after pressure molding.

[0029] As shown in Figures 4(a), (b), and (c), the outer case 1 with the coil 9 and lead pins 5 assembled is set in the storage section 20 of the mold (lower mold) 15, the mold (upper mold) 14 is closed, and heated and fluidized molding resin 6 is poured in through the gate 13 of the mold (upper mold) 14 and pressure molded to seal a portion of the coil 9 and lead pins 5. After that, the mold (upper mold) 14 is opened, and the current transformer or zero-phase current transformer 100 is released from the mold by pushing up the outer case 1 with the ejector pins 17.

[0030] In Figure 4(c), a space with a width t8 is formed in the storage section 20 of the mold (lower mold) 15 by the protruding portion 8 of the outer case 1 and the outer peripheral side surface of the outer cylinder 3. The outer peripheral filling portion 7 is formed by the molding resin 6 poured into this space. In conventional current transformers such as those shown in Patent Document 1, the outer cylinder 3 becomes the outer shell of the product, but in the current transformer or zero-phase current transformer 100 of Embodiment 1, the outer peripheral filling portion 7 becomes the outer shell of the product.

[0031] In a current transformer or zero-phase current transformer 100 using the outer case 1 configured as described above, when the molded resin 6 is injected during pressure molding from the gate 13 at a position where a gate mark 23 is created near the outer circumference of the outer case 1, the space corresponding to the outer circumference filling portion 7 is wider than the space between the outer cylinder 3 and the outer circumference side surface of the coil 9. Therefore, the molded resin 6 flows into the space corresponding to the outer circumference filling portion 7 and does not enter the space between the outer cylinder 3 and the coil 9 as in the conventional method. As a result, the stress applied to the outer circumference side surface of the magnetic core 12 inside the coil 9 can be reduced compared to the conventional method, and the decrease in sensitivity of the current transformer can be suppressed.

[0032] Furthermore, the pressure from the outer circumference towards the center generated by the flow of the molded resin 6 into the space corresponding to the outer circumference filling portion 7 can be absorbed by the outer cylinder 3 by making the height t2 of the outer cylinder 3 greater than or equal to the height t1 of the iron core 12. As a result, the stress applied to the outer circumference side surface of the magnetic core 12 inside the coil 9 located inside the outer cylinder 3 can be reduced compared to conventional methods, thereby suppressing a decrease in the sensitivity of the current transformer.

[0033] Furthermore, by setting the height t2 of the outer cylinder 3 to be less than or equal to the height t4 of the coil 9, the molding resin 6 can be injected without obstructing the flow of the molding resin 6 near the top surface of the coil 9 during pressure molding.

[0034] Furthermore, by providing a protective enclosure 21 for the lead pins 5, it is possible to prevent the terminal wires 16 of the coil 9 from being carried away by the molding resin 6 during pressure molding and exposed to the outside, while extending the creepage distance from the outside to the lead pins 5 at the interface between the outer case 1 and the molding resin 6. By setting the height of the enclosure 21 from the coil support bottom surface 19 to the same height t3 as the height of the inner cylinder 2, which is the maximum outer diameter height of the current transformer or zero-phase current transformer 100, the aforementioned creepage distance can be extended to the maximum extent.

[0035] Furthermore, the shortest creepage distance from the outside to the coil 9 at the interface between the outer case 1 and the molded resin 6 is along the DD cross-sectional line passing between the lead pin protection enclosure 21 and the molded resin 6, as shown in Figure 1(a), and follows the path 22 indicated by the arrow in Figure 1(f) (the section from the top surface to the bottom surface of the recess 18 is not added to the creepage distance because the lead pin protection enclosure 21 is interrupted). The shortest creepage distance without the recess 18 is t7, so by providing the recess 18, the creepage distance is extended by a depth h to t7+h, which improves the withstand voltage characteristics.

[0036] Furthermore, the demolding of the current transformer or zero-phase current transformer 100 is performed by pushing up the outer case 1 with the ejector pin 17. However, as shown in Figure 4(c), the molded resin 6 is in broad contact with the outer surface of the housing section 20 of the mold (lower mold) 15 in the outer peripheral filling section 7, so deformation occurs due to friction. In this case, as shown in Figures 4(c) and 1(d), the deformation of the molded resin 6 in the outer peripheral filling section 7 can be prevented by providing a support structure, which is a protrusion 8, on the bottom side of the outer case 1 so as to counteract the frictional force. Until now, the protrusion length t8 of the protrusion 8 of the case 1 has been the same as the width of the outer peripheral filling section 7, but t8 may be made smaller as long as deformation of the molded resin 6 does not cause problems.

[0037] Furthermore, by making the bottom-direction depth h2 of the position supporting the outer peripheral filling portion 7 of the protruding portion 8 equal to or greater than the bottom-direction depth h of the recessed portion 18, the creepage distance from the outside to the coil 9 becomes t7+h or greater, thereby further improving the voltage withstand characteristics.

[0038] Furthermore, the current transformer or zero-phase current transformer 100 of this invention can be used without issue even if the structure of the lead pin holding part 4 is replaced with a structure for holding lead wires as shown in Patent Document 1. [Explanation of Symbols]

[0039] 1 Outer case 2. Inner cylinder 3. Outer cylinder 4 Lead pin holding section 5 Lead pins 6. Molding resin 7. Outer periphery filling section 8. Protruding portion (outer circumference of outer cylinder 3) 9 coils 10 windings 11 Magnetic core storage case 12 magnetic core 13 Gate (for filling with molding resin) 14. Mold (upper mold) 15. Mold (lower mold) 16 Terminal lines 17 Ejector Pins 18 recesses 19 Coil support base 20. Storage compartment (a place to house the combined outer case and coil) 21. Enclosure for protecting lead pins 21a, 21b Lead pin protective enclosure termination 22 Shortest creepage distance from the outside to the coil 23 Gate marks 24 through holes 100 Current transformers and zero-phase current transformers

Claims

1. A coil formed by winding a wire around a ring-shaped magnetic core having high relative permeability characteristics, A case having a bottom surface and a double cylindrical wall for housing the coil, A current transformer or zero-phase current transformer having a molded resin that is poured into the case from the injection port of a molding die and pressure-molded integrally with the coil, A current transformer or zero-phase current transformer characterized in that the height of the outer cylindrical wall of the double cylindrical wall of the case is lower than the height of the inner cylindrical wall of the double cylindrical wall, and the outer surface of the outer cylindrical wall is provided with a molded resin filling portion made of the molded resin.

2. The current transformer or zero-phase current transformer according to claim 1, characterized in that the height of the outer cylindrical wall of the case is higher than the height of the annular iron core of the coil and lower than the height of the coil.

3. The current transformer or zero-phase current transformer according to claim 1, characterized in that the case has a projection of a predetermined length on the outside of the outer cylindrical wall that contacts the end face in the bottom direction of the molded resin-filled portion.

4. The current transformer or zero-phase current transformer according to claim 1, characterized in that the case has an enclosure outside a part of the outer cylindrical wall, the height of the enclosure is a predetermined length higher than the height of the outer cylindrical wall, the case has a recess between the enclosure and the outer cylindrical wall, the depth of the recess is a predetermined depth excavated from the height of the outer cylindrical wall, and the recess is open in the circumferential direction of the outer cylindrical wall.

5. The case is provided with a projection on the outside of the outer cylindrical wall that contacts the bottom end face of the molded resin-filled portion, and the contact position of the projection with the bottom end face of the molded resin-filled portion is located deeper in the bottom direction than the depth of the recess of the enclosure, as described in claim 4.

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