Current transformer

Abstract

To provide a current transformer that can accommodate different pin pitches with a minor component change even when various pin pitches are required.SOLUTION: A current transformer 100 is manufactured by housing a coil 5, which is wound around an annular magnetic core, in a resin case 3 with an open top, a case bottom and outer and inner case walls, and injecting heated and fluidized molding resin 1 into the case 3 and pressurizing it, and is provided with a resin output portion 2 which holds a metal terminal 4 connected to an end of the winding. The output portion 2 is housed in the case 3 and is disposed between the coil 5 and the outer case wall, and has a terminal insertion hole for inserting the terminal 4, and a resin inflow portion, which is a space that is open towards the coil 5 and towards the top.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a current transformer for measuring an AC current or an AC current superimposed with a DC current, for example a half-sine wave AC current, and to a zero-phase current transformer for measuring a leakage current. [Background technology]

[0002] A conventional current transformer has a coil with a secondary winding wound around a closed magnetic circuit made of a ring-shaped magnetic core, and two leads connected to both ends of the secondary winding of the coil, with the primary winding through which the current to be measured flows passing through the central opening of the closed magnetic circuit. When a primary current flows through the primary winding, a secondary current corresponding to the magnitude of the primary current is generated in the secondary winding by electromagnetic induction. At this time, a voltage signal is output by connecting a burden resistor between the outputs of the two leads connected to both ends of the secondary winding, and as a result, it becomes possible to measure the primary current flowing through the primary winding as a voltage signal. (See, for example, Fig. 1 of Patent Document 1)

[0003] Furthermore, in conventional current transformers, rather than using lead wires as described above for the output of the secondary winding, L-shaped metal terminals may be used so that the current transformer can be mounted by soldering directly onto a printed circuit board. In this case, the mounting portion of the metal terminal is provided with multiple terminal mounting structures in advance so that the spacing between the metal terminals (hereinafter referred to as pin pitch) can be changed (see, for example, Fig. 1 of Patent Document 2).

[0004] Also, a conventional method for manufacturing a current transformer is to prepare an upper metal die and a lower metal mold, insert the coil into the lower mold with the outer case attached, close the upper and lower metal molds, and inject heated and fluidized molding resin into the mold from the injection gate under pressure, thereby molding the molded product under pressure and sealing it together (hereinafter referred to as a low-pressure injection molding method) (see, for example, Fig. 7 of Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-064772 [Patent Document 2] Application No. 05-057815 Summary of the Invention [Problem to be solved by the invention]

[0006] In conventional current transformers, when an L-shaped metal terminal is used as the output of the secondary winding for direct soldering mounting on a printed circuit board, the metal terminal is inserted and fixed into the through hole of the lead wire outlet of the outer case of Patent Document 1. In this case, since the pin pitch, which is the distance between the metal terminals, depends on the shape of the outer case (the position of the through hole of the lead wire outlet), the pin pitch cannot be changed later, and if a different pin pitch is required, a new outer case must be prepared. There was a problem in that a large amount of resources were required to design and manufacture a new mold to prepare a new outer case.

[0007] Furthermore, when the mounting portion of the metal terminal is provided with multiple terminal mounting structures in advance, as in Patent Document 2, the types of pin pitch that can be changed are limited to about two or three, and the degree of change is also small, making it difficult to obtain an arbitrary pin pitch.

[0008] The present invention has been made to solve the above-mentioned problems, and has as its object to provide a current transformer that can accommodate different pin pitches with minor component changes, even when various pin pitches are required. [Means for solving the problem]

[0009] In the current transformer of this invention, a coil wound around an annular magnetic core is housed in a resin case with an open top and a bottom, outer case wall, and inner case wall, and heated and fluidized molding resin is injected into the case and pressure-molded, and a resin output section is provided which holds metal terminals connected to the ends of the windings, the output section being housed in the case and positioned between the coil and the outer case wall, and having a terminal insertion hole for inserting the terminal, and a resin inflow section which is a space which is open towards the coil and towards the top. Effect of the Invention

[0010] According to this invention, even if the pin pitch is different, it is possible to accommodate the difference in pin pitch by replacing small parts that hold the output terminals of the outer case. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a current transformer 100 according to a first embodiment of the present invention. [Diagram 2] 1 is a diagram showing a first output section 2 of a current transformer 100 in accordance with the first embodiment of the present invention. [Diagram 3] 2 is a front view showing a second output section 20 of the current transformer 100 in the first embodiment of the present invention. FIG. [Figure 4] 1 is a diagram showing a storage case 3 of a current transformer 100 according to a first embodiment of the present invention. [Diagram 5] 1 is a front view showing an output terminal 4 of a current transformer 100 according to a first embodiment of the present invention. [Figure 6] 2 is a diagram showing a coil 5 of the current transformer 100 according to the first embodiment of the present invention. FIG. [Figure 7] 1 is a diagram showing a pre-molding product 7 of a current transformer 100 according to the first embodiment of the present invention. [Figure 8] 3A to 3C are diagrams illustrating a low-pressure injection molding procedure for the current transformer 100 according to the first embodiment of the present invention. [Figure 9] 1 is a diagram showing a mold 8 used for assembling a current transformer 100 in accordance with the first embodiment of the present invention. [Figure 10] 2 is a contact surface diagram of an upper and lower die showing an upper die 9 used in assembling a current transformer 100 in accordance with the first embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiment 1 FIG. 1 is a diagram showing a current transformer 100 according to a first embodiment of the present invention, where (a) is a front view, (b) is a cross-sectional view along AA, and (c) is a cross-sectional view along BB. FIG. 2 is a diagram showing a first output section 2 of the current transformer 100 according to a first embodiment of the present invention, where (a) is a front view, (b) is a side view, and (c) is an isometric view. FIG. 3 is a front view showing a second output section 20 of the current transformer 100 according to a first embodiment of the present invention. FIG. 4 is a diagram showing a storage case 3 of the current transformer 100 according to a first embodiment of the present invention, where (a) is a front view, and (b) is an isometric view. FIG. 5 is a front view showing an output terminal 4 of the current transformer 100 according to a first embodiment of the present invention. FIG. 6 is a diagram showing a coil 5 of the current transformer 100 according to a first embodiment of the present invention, where (a) is a front view, and (b) is a cross-sectional view along CC.

[0013] In FIG. 1, current transformer 100 comprises a storage case 3 formed of an insulating synthetic resin such as polypropylene, a first output section 2 formed of the same resin, output terminals 4 made of hard copper wire plated with tin or the like, a coil 5 in which copper wire is wound around an annular magnetic core to form a secondary winding, and molded resin 1 made of a thermoplastic resin such as an elastomer injected into storage case 3 from the outer surface (hereinafter referred to as the top surface) side of current transformer 100, which is in front of the figure, by a low-pressure injection molding machine.

[0014] 2(a), (b), and (c), the first output section 2 has two terminal insertion holes 2c for inserting output terminals 4 that output the outputs (two) of the coils 5 to the outside of the current transformer 100, and has two terminal holding grooves 2d for holding the portions of the output terminals 4 extending downward in the figure. The distance (pin pitch) between the two terminal holding grooves 2d is P1. In addition, the upper side as shown in FIG. 2(c) has an arc shape 2f that follows the outer diameter of the coil 5 so as not to interfere with the coil 5, and as shown in FIGS. 2(a) and 2(b), it has a bottom surface 2g, a side surface 2h, and a back surface 2i that are perpendicular to each other, and has a predetermined thickness T1. 2(a) is a space of a predetermined depth T2 that is open upward (toward the coil 5 of the current transformer 100) and forward (toward the top surface) in Fig. 2(a), and is a resin inflow section into which the molding resin 1 flows during low-pressure injection molding. Here, four resin inflow sections 2a are provided, two at both the left and right ends in Fig. 2(a) and two between the pin pitches P1, but the number, positions and sizes are not particularly important as long as there are spaces into which a predetermined amount or more of the molding resin 1 flows at both the left and right ends in Fig. 2(a) and between the pin pitches.

[0015] Also, 2b is a slit opened in the direction of the arc shape 2f from the terminal insertion hole 2c, and accommodates a part of the winding start 5c and winding end 5d (see FIG. 6) of the coil winding 5a when assembling the current transformer 100. The slit 2b also serves to allow the molding resin 1 to flow into the terminal insertion hole 2c when the molding resin 1 is poured in by low-pressure injection molding.

[0016] Further, a protrusion 2e is provided so that the output terminal 4 held in the terminal holding groove 2d can extend to the outside without interfering with the storage case 3.

[0017] 3, the second output section 20 has a configuration similar to that of the first output section 2 except that the pin pitch dimension is P2, and the first output section 2 of the current transformer 100 can be replaced with the second output section 20. In that case, a current transformer 100 having a pin pitch dimension of P2 is obtained.

[0018] As shown in FIG. 4, the storage case 3 is open on the front side (top side) of the figure and has a coil storage section 3a that stores the coil 5 from the top side. The coil storage section 3a is surrounded by a circular inner wall 3b and outer wall 3c, as well as a bottom surface between them, in order to store the annular coil 5.

[0019] The storage case 3 has an output section storage section 3d for storing the first output section 2, and the output section storage section 3d has a platform 3e for storing the first output section 2 and positioning it in the depth direction in the figure, a first holding wall 3f for positioning it in the downward direction in the figure, and a second holding wall 3g for positioning it in the left-right direction in the figure. The first holding wall 3f is provided with a notch 3h for engaging with the protrusion 2e (see FIG. 2) of the first output section 2. The storage case 3 also has a through hole 3i for passing through the primary winding through which the current to be measured flows.

[0020] The output terminal 4 has an approximately L-shaped cylindrical shape as shown in Figure 5, one end 4a is soldered to one end of the winding end of the coil 5 and inserted into the terminal insertion hole 2c (see Figure 2) of the first output section 2, the other end 4b is held in the terminal holding groove 2d (see Figure 2) of the first output section 2, and the terminal portion of the other end 4b extends outside the storage case 3.

[0021] As shown in FIG. 6, coil 5 has a secondary winding 5a wound a predetermined number of times (for example, 1,000 turns) around an annular magnetic core 5b, and has a start point 5c and an end point 5d of winding 5a.

[0022] Next, a procedure for assembling the current transformer 100 in the first embodiment will be described. FIG. 7 is a diagram of a pre-molding product (assembly immediately before low-pressure injection molding) 7 of the current transformer 100 in the first embodiment, where (a) is an exploded isometric view and (b) is an isometric view. FIG. 8 is an explanatory diagram of a low-pressure injection molding procedure for the current transformer 100 according to the first embodiment.

[0023] As shown in Fig. 7(a), first, the start 5c (see Fig. 6) of the winding 5a of the coil 5 is wrapped around one end 4a (see Fig. 5) of the output terminal 4 on the right side of the figure as shown in 7a, and soldered. Similarly, the end 5d (see Fig. 6) of the winding 5a of the coil 5 is wrapped around one end 4a of the other output terminal 4 on the left side of the figure as shown in 7a, and soldered. The product assembled up to this point is called the coil section 6.

[0024] Next, the first output portion 2 is engaged with the output portion storage portion 3d (see FIG. 4) of the storage case 3 as follows. The first output unit 2 is installed so that the back surface 2i (see FIG. 2) of the first output unit 2 contacts the mounting base 3e (see FIG. 4), the bottom surface 2g (see FIG. 2) of the first output unit 2 contacts the first holding wall 3f (see FIG. 4), and the side surface 2h (see FIG. 2) of the first output unit 2 contacts the second holding wall 3g (see FIG. 4). At this time, the protrusion 2e (see FIG. 2) of the first output unit 2 engages with the notch 3h (see FIG. 4) of the storage case 3. In this description, the first output unit 2 with a pin pitch dimension of P1 (see FIG. 2) is used here, but if the pin pitch dimension is set to P2, the second output unit 20 (see FIG. 3) will be used instead of the first output unit 2.

[0025] Next, the coil section 6 is stored in the coil storage section 3a (see FIG. 4) of the storage case 3, and one end 4a of the two output terminals 4 of the coil section 6 is inserted into the two terminal insertion holes 2c (see FIG. 2) of the first output section 2 with the ends 4a tied together and soldered 7a, and the other end 4b (see FIG. 5) is engaged with the terminal holding groove 2d. At this time, a part of the winding start 5c and winding end 5d of the coil winding 5a is stored in the slit 2b of the first output section 2 (see FIG. 2). The assembly up to this point is the assembly immediately prior to low pressure injection molding and is referred to as a pre-molding product 7.

[0026] Next, the low pressure injection molding procedure will be described with reference to FIG. 8. Before describing the procedure, however, the mold used in the low pressure injection molding will be described. 9A and 9B are diagrams of the lower mold 8 used in low-pressure injection molding, in which (a) is a diagram of the contact surface between the upper and lower molds, and (b) is an isometric diagram. FIG. 10 is a diagram of the contact surface between the upper and lower molds 9.

[0027] The lower die 8 is made to store, for example, two pre-molded products 7 as shown in FIG. 9, and has two storage sections 8a carved into the outer shape of the storage case 3 based on the upper and lower die contact surface 8e, which is the contact surface between the lower die 8 and the upper die 9, so that the pre-molded products 7 can be stored exactly. The storage sections 8a are arranged so that the output terminals 4 of the pre-molded products 7 face the outside of the lower die 8. 8b is a space carved to a predetermined depth from the upper and lower die contact surface 8e, which is a space to prevent the output terminals 4 from being pinched between the upper and lower dies 9 and 8 as shown in FIG. 8, and 8c is a positioning pin provided at the four corners. 8d is the end position of the runner 9b (see FIG. 10) of the upper die 9 described later, and corresponds to the approximately midpoint between the inner wall 3b and the outer wall 3c (see FIG. 4) of the storage case 3 of the pre-molded products 7 stored in the storage sections 8a.

[0028] As shown in Fig. 10, the upper die 9 has a resin inlet hole 9a in the center through which the molding resin 1 flows from the low-pressure injection molding machine into the die, and has a runner 9b which serves as a passage for the flow of the flowing molding resin 1 to the pre-molded product 7. The runner 9b has a semicircular shape at the top and bottom ends in the figure, a predetermined taper on the side, and is shaped to be carved out to a predetermined depth from the top and bottom die contact surface 9d which is the contact surface between the lower die 8 and the upper die 9, and the top and bottom end portions in the figure reach the end position 8d shown in Fig. 9. 9c is a positioning hole which is arranged at a position corresponding to the positioning pin 8c of the lower die 8.

[0029] As shown in Fig. 8, the low-pressure injection molding procedure involves first storing the pre-molded product 7 in the storage section 8a (see Fig. 9) of the lower mold 8 with the output terminals 4 facing outward from the lower mold 8. The output terminals 4 are then stored in the space 8b (see Fig. 9).

[0030] Next, the positioning pins 8c provided at the four corners of the lower die 8 and the positioning holes 9c provided at the four corners of the upper die 9 are aligned, and the upper die 9 and the lower die 8 are brought into contact and closed. At this time, both ends of the runner 9b (see FIG. 10) are located at the end positions 8d (see FIG. 9).

[0031] Finally, low pressure injection molding is performed as follows. The resin injection nozzle of the low pressure injection molding machine is installed in the resin inlet hole 9a during molding. From this resin injection nozzle, molding resin 1, which is a viscous liquid thermoplastic resin, is poured from the resin inlet hole 9a into the upper mold 9, passes through a passage formed by the runner 9b (see Fig. 10) and the upper and lower mold contact surfaces 8e of the lower mold 8, flows in the directions of the arrows S1 and S2, and is poured into the storage case 3 of the pre-molded product 7 from the outer wall 3c (see Fig. 4) side, branches off to the left and right as shown in Fig. 4(a) at the inner wall 3b, flows into the gap between the storage case 3 and the coil 5, into the resin inlet part 2a, and into the slit 2b (see Fig. 2), and fills up to the gap between the output terminal 4 and the terminal insertion hole 2c. Through the above steps, assembly of the current transformer 100 is completed.

[0032] In the current transformer 100 configured in this manner, during low-pressure injection molding, the first output section 2 is pressed against the first retaining wall 3f and the second retaining wall 3g of the storage case 3 by the molding resin 1 pressurized in the directions of arrows S1 and S2 in Fig. 8. At this time, the first retaining wall 3f and the second retaining wall 3g are positioned by the side walls of the storage section 8a of the lower mold 8. Moreover, since the first output portion 2 is positioned by the upper and lower die contact surface 9d of the upper die 9, the first output portion 2 does not rise up.

[0033] In addition, the molded resin 1 hardens after low-pressure injection molding, and the molded resin 1 that flows into the resin inlet portion 2a of the first output portion 2 and hardens holds the first output portion 2 to the left and downward as shown in Figure 1(b) , making it possible to fix the position of the first output portion 2 in the storage case 3, as shown in Figure 1(b) .

[0034] Moreover, the molded resin 1 that flows from the slit 2b around the output terminal 4 and hardens can fix the position of the output terminal 4 to the first output section 2. Moreover, as shown in Fig. 1(c), the molded resin 1 that flows around and above the coil 5 in Fig. 1(c) and hardens can seal the coil 5.

[0035] The first output section 2 can be replaced with the second output section 20 at the stage of assembling the pre-molded product 7. This makes it possible to easily change the pin pitch of the current transformer 100 from P1 (see FIG. 2) to a pin pitch P2 (see FIG. 3) different from the pin pitch P1. By preparing output sections with different pin pitches such as the second output section 20 in this way, it is possible to accommodate a variety of pin pitches. In addition, the first output section 2 and the second output section 20 have smaller external dimensions and capacity than a conventional outer case (corresponding to the storage case 3 of the present invention), so they can be manufactured using a small mold. This makes it possible to reduce resources such as the mold manufacturing costs when dealing with various pin pitches. [Explanation of symbols]

[0036] 1 Molding resin 2 First output section 2a Resin inlet 2b Slit 2c Terminal insertion hole 2d terminal retaining groove 2e Protrusion 2f Arc shape 2g bottom side 2h side 2i back 20 Second output section 3 Storage case 3a Coil storage section 3b Inner wall 3c Exterior wall 3d Output section storage section 3e Stand 3f First retaining wall 3g Second retaining wall 3h Notch 3i through hole 4 Output terminals 4a one end 4b Other end 5 Coil 5a winding 5b magnetic core 5c Start of winding 5d End of roll 6 Coil section 7 Pre-molded product 7a Soldering 8 Lower mold 8a Case storage section 8b Output terminal space 8c Locating pin 8d End position 8e Upper and lower die contact surfaces 9 Upper mold 9a Resin inflow hole 9b Runner 9c Positioning hole 9d Upper and lower die contact surfaces 100 Current Transformer

Claims

1. A current transformer in which a coil wound around a toroidal magnetic core is housed in a resin case having an open top and a bottom, an outer wall, and an inner wall, and heated and fluidized molding resin is injected into the case and pressure-molded, a resin output section that holds a metal terminal connected to an end of the winding, the output unit is housed in the case and disposed between the coil and an outer wall of the case, A current transformer comprising: a terminal insertion hole into which the terminal is inserted; and a resin inlet portion which is a space open toward the coil and toward the top surface.

2. 2. The current transformer according to claim 1, wherein the terminal insertion hole has a slit which is a space open toward the coil.

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