Current transformer and zero-phase current transformer

Abstract

To provide a current transformer and a zero-phase current transformer that make it easy to assemble such that the short side of a U-shaped lead pin passes through the central opening of an outer case.SOLUTION: Low portions 7a and 7b are provided at respective positions of an inner cylindrical part 2 and an outer cylindrical part 3 of an outer case 1 to facilitate assembly of a U-shaped lead pin 10 that also functions as a molded-resin injection inlet.SELECTED DRAWING: Figure 2-1

Description

[Technical Field]

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

[0002] Figure 4 is a schematic diagram of a typical conventional current transformer. A conventional current transformer has a secondary winding W2 wound around a closed magnetic circuit made of a ring-shaped magnetic core, and a primary winding W1, through which the current to be measured flows, passes through a central opening in the closed magnetic circuit. When a current I1 flows through the primary winding W1, a current I2 corresponding to, or preferably proportional to, the magnitude of the current I1 is generated in the secondary winding W2 by electromagnetic induction. By connecting a burden resistor to the secondary winding W2, a voltage signal is output to the secondary winding W2, making it possible to measure the current I1 flowing through the primary winding W1 as a voltage signal.

[0003] Another conventional method for manufacturing a current transformer involves preparing a metal mold, inserting a magnetic core with at least one winding, i.e., a coil, into an outer case, closing the mold, and filling the mold with heated and fluidized molding resin under pressure to form a pressure-molded, integrally sealed mold (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-183145 Summary of the Invention [Problem to be solved by the invention]

[0005] Fig. 5 shows an example of the structure of a conventional current transformer 101. As shown in Figs. 5(a) and 5(b), a U-shaped lead pin 10 is used as a primary winding and passes through the central opening of the current transformer 101. When the height L1 of the outer case 17 of the current transformer 101 and the short-side length L2 of the U-shaped lead pin 10 are approximately equal and the diameter N of the central opening of the outer case 17 is smaller than the short-side length L2 and the long-side length L3 of the U-shaped lead pin 10, it is difficult to assemble the U-shaped lead pin 10 so that its short side passes through the central opening. After passing a straight pin through the central opening, it must be bent to form a U-shape as shown by the imaginary line in Fig. 5(c), which increases the number of steps. [Means for solving the problem]

[0006] The current transformer or zero-phase current transformer of this invention has a structure in which a coil wound around a toroidal magnetic core with high relative magnetic permeability characteristics is housed in a case with a bottom and double cylindrical walls, and heated and fluidized molding resin is poured into the case through the injection port of a molding die to pressure-molde the coil and the case together, and the double cylindrical walls of the case have a low section for easily assembling a U-shaped lead pin which also serves as the molding resin injection port. [Effects of the Invention]

[0007] As described above, this invention has the effect of enabling a change in direction when one end of the U-shaped lead pin is passed through a central opening at a location on the double cylindrical wall of the case that is lower than the periphery by a specified amount, thereby making it easier to assemble the U-shaped lead pin in a direction that allows the short end of the pin to pass through the central opening and to inject molding resin from outside the case. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a current transformer or a zero-phase current transformer according to a first embodiment of the present invention. [Figure 2] 1 is a diagram showing an outer case used in a current transformer or a zero-phase current transformer according to a first embodiment of the present invention. [Figure 3]10 is a diagram showing an outer case used in a current transformer or a zero-phase current transformer according to a second embodiment of the present invention. FIG. [Figure 4] FIG. 1 is a schematic diagram showing a typical current transformer. [Figure 5] FIG. 1 is a diagram showing an example of the structure of a general current transformer. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiment 1 FIG. 1 shows a current transformer or zero-phase current transformer 100 according to a first embodiment of the present invention, in which FIG. 1(a) is a plan view, FIG. 1(b) is a cross-sectional view taken along line AA, FIG. 1(c) is a front view, FIG. 1(d) is an isometric view, FIG. 1(e) is a front view of a U-shaped lead pin 10, and FIG. 1(f) is an isometric view of a coil 13.

[0010] In FIG. 1(e), reference numeral 10 denotes a U-shaped lead pin for carrying a primary current, 11 denotes a long side, and 12 denotes a short side.

[0011] Reference numeral 13 shown in Figure 1(f) denotes a coil composed of a toroidal-shaped magnetic core 16 (shown in Figure 1(b)) for collecting magnetic flux, a toroidal-shaped case 15 (shown in Figure 1(b)) for housing the magnetic core 16, and a winding 14 (shown in Figure 1(b)) wound around the case 15 housing the magnetic core 16 for converting changes in magnetic flux within the magnetic core 16 into current, and reference numeral 9 denotes an L-shaped lead pin for drawing out the secondary output, which is electrically connected to the coil 13.

[0012] 1(a) and 1(b), the U-shaped lead pin 10 is positioned so that its short side 12 passes through the central opening of the coil 13. Reference numeral 8 denotes a thermoplastic molding resin that seals the coil 13, L-shaped lead pin 9, and U-shaped lead pin 10 housed in the outer case 1.

[0013] FIG. 2 shows the outer case 1 used in the current transformer or zero-phase current transformer 100 according to embodiment 1 of the present invention, where FIG. 2(a) is a plan view of the outer case 1, FIG. 2(b) is a cross-sectional view taken along line BB, FIG. 2(c) is a front view, FIG. 2(d) is an isometric view, and FIGS. 2(e) to 2(l) are plan views and isometric views showing the steps for assembling the U-shaped lead pin 10 in sequence.

[0014] In FIG. 2(a), 4 is a lead pin holding portion for accommodating a part of the L-shaped lead pin 9, 5 is a holding portion for the short side 12 of the U-shaped lead pin, and 6 is a holding portion for the long side 11 of the U-shaped lead pin.

[0015] 2(a) and 2(b), outer case 1 has low points 7a and 7b on the top surfaces of inner cylinder 2 and outer cylinder 3, respectively, which are provided at a distance from L-shaped lead pin holder 4 (for example, on the opposite side of the side wall having L-shaped lead pin holder 4), and height K is set to a depth (for example, 0.7 times or less the height L1 of outer case 1) that does not interfere with the assembly of U-shaped lead pins 10 and the injection of molding resin 8. Low points 7a and 7b are provided so as to overlap when outer cylinder 3 is observed from the outer periphery in the direction of inner cylinder 2.

[0016] The U-shaped lead pin 10 is assembled by orienting the terminals toward the bottom as shown in Figures 2(e) and (f), aligning the U-shaped lead pin's shorter side 12 along the lower points 7a and 7b so that one terminal passes inside the inner cylinder 2 and the other passes outside the outer cylinder 3, then rotating it 90° so that the U-shaped lead pin's shorter side 12 fits inside the inner cylinder 2 and the U-shaped lead pin's longer side 11 is perpendicular to the outer cylinder 3 as shown in Figures 2(g) and (h), then translating the U-shaped lead pin's shorter side 12 so that it fits into the U-shaped lead pin's shorter side holding part 5 as shown in Figures 2(i) and (j), and then rotating it around the U-shaped lead pin's shorter side 12 as an axis so that the U-shaped lead pin's longer side 11 fits into the U-shaped lead pin's longer side holding part 6 as shown in Figures 2(k) and (l). The outer case 1 configured as described above can be assembled even when the length L2 of the U-shaped short side 12 of the lead pin is equal to the height L1 of the outer case 1 and the width M of the central opening is smaller than the length L3 of the U-shaped long side 11 of the lead pin and the length L2 of the U-shaped short side 12 of the lead pin.

[0017] In addition, the low points 7a and 7b can also function as injection ports when injecting heated and liquefied thermoplastic molding resin 8 into the interior of the outer case 1 and the interior of the outer case inner cylinder 2, the entire circumference of which is fixed by a mold.

[0018] Embodiment 2 In this embodiment, we will explain the differences from embodiment 1. Figure 3 shows an outer case 1 used in a current transformer or zero-phase current transformer 100 in embodiment 2 of the present invention, where Figure 3(a) is a plan view of the outer case 1, Figure 3(b) is a cross-sectional view taken along line BB, Figure 3(c) is a front view, and Figure 3(d) is an isometric view.

[0019] 3(a), 3(b), and 3(d), the low portions 7a and 7b are extended to a range (for example, just before the U-shaped lead pin short-end holding portion 5) that does not interfere with holding the coil 13, L-shaped lead pin 9, and U-shaped lead pin 10. The low portions 7a and 7b are provided so that they overlap by at least a width that does not interfere with assembling the U-shaped lead pin 10 when observing the outer cylinder 3 from the outer periphery toward the inner cylinder 2. With this configuration, the U-shaped lead pin 10 can be changed direction near the U-shaped lead pin short-end holding portion 5, and the number of steps can be reduced compared to the first embodiment. [Explanation of symbols]

[0020] 1 outer case 2. Inner cylinder 3 outer cylinder 4 L-shaped lead pin holder 5 U-shaped short lead pin holding section 6 U-shaped lead pin longitudinal holding section 7a, 7b Low spots 8 Molding Resin 9 L-shaped lead pin (for secondary voltage output) 10 U-shaped lead pin (for carrying primary current) 11 U-shaped lead pin length 12 U-shaped short lead pin 13 Coil 14 windings 15 cases 16 magnetic core 17 Outer case (conventional current transformer and zero-phase current transformer) 100 Current transformers and zero-phase current transformers 101 (Conventional) Current Transformer (Example)

Claims

1. A current transformer or zero-phase current transformer in which a coil wound around a toroidal magnetic core having high relative magnetic permeability characteristics is housed in a case having a bottom and a double cylindrical wall, and a heated and fluidized molding resin is poured into the case through an injection port of a molding die to pressure-molde the coil and the case together, A current transformer or zero-phase current transformer, wherein the case has low points on both the inner and outer cylinders of the double cylindrical wall.

2. 2. A current transformer or zero-phase current transformer according to claim 1, wherein the low points on the inner and outer cylinders of the double cylindrical wall overlap at least partially when the outer cylinder is observed from the outer periphery toward the inner cylinder.

3. 3. A current transformer or zero-phase current transformer according to claim 1 or 2, wherein the low point provided in the double cylindrical wall is lower than the top surface of the case by a predetermined amount.

4. A current transformer or zero-phase current transformer characterized in that the low point provided in the double cylindrical wall is provided within a predetermined range based on the injection port of the molding die.

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