Patent Application
20220277892
This invention relates to a current transformer used in various AC equipment and adapted to detect electric currents flowing in the equipment to provide output control and overcurrent protection operation of the equipment and a method of manufacturing the same.
A current transformer is used to detect electric currents in high-power electric instruments such as air conditioners and IH devices that operate on household power supplies. A current transformer comprises a primary coil, a secondary coil, and a core for forming a magnetic path common to these coils (see, for example, Patent Document 1). In the current transformer, a current-sensing resistor is connected to the secondary coil, and the power supply commercial frequency of the instruments is energized to the primary coil. When the current in the primary coil changes, the magnetic field in the secondary coil changes through a magnetic circuit, creating a potential difference at both ends of the current-sensing resistor in the secondary coil. The difference is detected as a voltage at the current-sensing termination resistor. The instrument inputs the voltage into the microcomputer to control the inverter circuit, etc., to thereby controlling the input to or output from the instrument.
The core of a current transformer is composed of laminated iron cores made of electromagnetic steel sheets. For example, Patent Document 1 discloses in FIG. 6 that E-shaped iron cores (E-type cores) and I-shaped iron cores (I-type cores) are alternately stacked to form a magnetic path. The leakage flux is reduced and the magnetic efficiency is increased by alternately stacking E-type cores and I-type cores, i.e., stacking them in different directions. And the decrease in secondary output voltage due to the increase in primary current is suppressed. However, a gap that is formed between the junction surfaces of E-type core and I-type core varies. Therefore, there was a problem of variation in the secondary output voltage. On the other hand, it is necessary to use resin or varnish to fix E-type core and I-type core with one another. Still, the resin or varnish expands or contracts thermally depending on temperature change, resulting in that variation of the secondary output voltage increases. Thus, the current transformer does not have sufficient temperature characteristics.
Patent Document 1 discloses a coil shown in FIGS. 1 and 2 wherein E-type cores are alternately stacked such that tips of each leg overlap, without alternately interposing I-type cores between E-type cores. Such a current transformer has no gap between E-type and I-type cores and is not affected by thermal expansion and contraction, thus having good temperature characteristics.
The circuit breaker regulates the amount of electric current that can be used for electrical devices by a household power supply. Therefore, for operating such electrical appliances at their maximum output, it is necessary to detect the current values and control them so that the sum of the current values of these devices does not exceed the maximum current value of the circuit breaker. At this time, if there is an error in the current value detected by the current transformer, the electrical devices are required to operate at a lower total current value in anticipation of safety. For this reason, there is a need for a current transformer that can detect the current value accurately and increase the output of electrical equipment to the maximum within the range that does not exceed the maximum current value of the breaker.
However, the current transformer shown in FIGS. 1 and 2 of Patent Document 1 has no I-type core, and the leg tips of the E-type core are open, thus increasing the leakage flux between the legs, causing faster magnetic saturation. As a result, as the primary current increases, the drop in the secondary output voltage becomes larger. Therefore, the core had to be sized up.
The output voltage can be adjusted also by changing the gap spacing between E-type and I-type cores. However, the current transformer disclosed in Patent Document 1 does not have a gap, so it is impossible to adjust the output voltage. In addition, considering variations in the material magnetic properties of the core and variations in temperatures during the heat treatment process to anneal the core, it was necessary to set larger tolerances for the secondary output voltage (e.g., ±3% to 5% of the actual measured value).
An object of the present invention is to provide a current transformer having excellent temperature characteristics and realizing high-precision adjustment of the output voltage via gap adjustment and small tolerance, and a method for manufacturing the same.
In accordance with the present invention, a core component for current transformers comprises,
an E-type core formed of an electromagnetic steel sheet and having three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and
an I-type core formed of an electromagnetic steel sheet and having the same length as the connecting portion,
the I-type core being placed on and bonded to the connecting part of the E-type core to form a single-piece core component.
In accordance with the present invention, a current transformer comprises,
a resin-made bobbin with a through hollow section, the bobbin having a primary coil and a wire-wound secondary coil,
a core consisting of E-type cores and I-type cores provided in the hollow section of the bobbin, wherein each E-type core is formed of an electromagnetic steel sheet and has three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and each I-type core is formed of an electromagnetic steel sheet and has the same length as the connecting portion, and wherein E-type cores are stacked with its central leg alternately in opposite directions, and I-type cores are placed between the connecting parts of the stacked E-type cores, wherein
the core is a stack structure of the core components mentioned above, and each of the core components is inserted into the hollow section alternately from a first direction and a second direction opposite to the first direction.
In the current transformer as mentioned above, the core is a stack structure of core components inserted into the hollow section alternately from a first direction and a second direction opposite to the first direction,
wherein each of the core components comprises E-type core formed of an electromagnetic steel sheet made by press-punching process and having three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and I-type core formed of an electromagnetic steel sheet made by press-punching process and having the same length as the connecting portion, wherein the I-type core is placed on and bonded to the connecting part of the E-type core to form a single-piece structure of the E-type core and the I-type core,
wherein each of the core components is inserted into the hollow section from a first direction and a second direction opposite to the first direction alternately while interchanging the top and bottom of the core component to form a single core component block, and
the E-type core and the I-type core opposed to the E-type core are preferably arranged such that press-punched directions are in the opposite direction.
In the present current transformer, end faces of the E-type core and the I-type core that were prepared by the press-punching process have a rounded, slope shaped, sheared surface on their corners, a sheared surface with striations formed in the thickness direction, a fractured surface with unevenness as if the steel sheet was plucked, and a jagged burrs protruding from the end face in the punching direction,
the E-type core and the I-type core of each core component are arranged such that the sheared surface and the fractured surface are opposed to each other.
The core components stacked in the hollow section of the bobbin can be combined in a single core component block.
Core components inserted into the hollow section of the bobbin from the first direction can be combined into a single core component block. Core components inserted into the hollow section of the bobbin from the second direction can be combined into a single core component block.
A method of manufacturing a current transformer according to the present invention comprises:
a core component preparing step of preparing core components consisting of a combination of E-type cores and I-type cores wherein each E-type core is formed of an electromagnetic steel sheet and has three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and each I-type core is formed of an electromagnetic steel sheet and has the same length as the connecting portion, and the I-type core is placed on and bonded to the connecting part of the E-type core to form a single-piece core component;
a bobbin preparing step of preparing a resin-made bobbin with a through hollow section, the bobbin having a primary coil and a wire-wound secondary coil;
a stacking step of inserting central legs of the E-type core into the hollow section of the bobbin alternately from a first direction and a second direction opposite the first direction to form a stack of the core components; and
a block forming step of combining the stacked core components into a single core component block.
The foregoing method of manufacturing a current transformer preferably comprises
a core component preparing step of preparing a single-piece core component consisting of E-type core and I-type core wherein the E-type core is formed by press-punching an electromagnetic steel sheet and has three legs extending substantially parallel to each other and a connecting part connected at each end of the legs, and the I-type core is formed by press-punching an electromagnetic steel sheet and has the same length as the connecting portion, the I-type core being placed on and bonded to the connecting part of the E-type core;
a bobbin preparing step of preparing a resin-made bobbin with a through hollow section, the bobbin having a primary coil and a wire-wound secondary coil; and
a stacking step of stacking the core component by inserting central legs of the E-type core of the single-piece core component into the hollow section of the bobbin alternately from a first direction and a second direction opposite the first direction while interchanging the top and bottom of the core component alternately, such that the E-type core and the I-type core are stacked in the opposite direction of the respective press-punched directions.
The foregoing method of manufacturing a current transformer preferably comprises a gap adjusting step after the stacking step and before the block forming step,
the gap adjusting step comprising adjusting a spacing of the gap formed between distal ends of legs of the E-type core inserted from the first direction and end edges of the I-type core inserted from the second direction and the gap formed between distal ends of legs of the E-type core inserted from the second direction and end edges of the I-type core inserted from the first direction, by pressing the stacked core components from the first direction and/or the second direction.
The gap adjusting step preferably adjusts the gap while referring to the output voltage characteristics.
In accordance with the present invention, the E-type core and I-type core of the core component are bonded to form a single-piece component so that the core component can be easily handled and easily inserted into the bobbin of the current transformer.
In accordance with the present invention, the current transformer is adapted to adjust a gap formed between distal ends of legs of the E-type core of the core component inserted from a first direction and end edges of the I-type core of the core component inserted from a second direction, and a gap formed between the distal ends of legs of the E-type core of the core component inserted from the second direction and end edges of the I-type core of the core component inserted from the first direction. This adjustable gap structure realizes the high-precision adjustment of the output voltage and the possible minor tolerance.
In accordance with the present invention, the method of manufacturing the current transformer includes a step that the E-type core and the I-type core are bonded to form a single-piece core component. Therefore, the single-piece core components can be inserted into the hollow section of the bobbin from the first direction and the second direction and then combined into a single core component block to thereby achieving the increased efficiency of manufacturing the current transformer.
In accordance with the present invention, the current transformer is configured to adjust a spacing of the gap formed between distal ends of legs of the E-type core of the core component inserted from a first direction and end edges of the I-type core of the core component inserted from a second direction, and a spacing of the gap formed between the distal ends of legs of the E-type core of the core component inserted from the second direction and end edges of the I-type core of the core component inserted from the first direction. This adjustable gap structure realizes the high-precision adjustment of the output voltage and the possible small tolerance.
Core components 31 used for current transformers (hereinafter referred to as “core components”), current transformer 10, and current transformer module 12 of one embodiment of the present invention will be explained below with reference to the drawings.
The core 30 is composed of a plurality of core components 31 that were stacked together.
E-type core 40 comprises three rectangular-shaped legs 41, 42, 41 extending substantially parallel to each other, and a rectangular-shaped connecting part 43 connected at proximal ends the legs 41, 42, 41. The width dimension 43a of the connecting part 43 is preferably longer than the width dimension 41a of the leg 41 to suppress magnetic flux leakage. The I-type core 50 may be a rectangular shape with the same size as the connecting part 43. E-type core 40 and I-type core 50 preferably have pilot holes 44, 51 for positioning them. Furthermore, the longitudinal dimension of I-type core 50 is preferred to be 0.1 mm to 0.3 mm smaller than the longitudinal dimension of the connecting part 43 of E-type core 40 to make positioning and stacking of I-type 50 on E-type core 40 easier.
I-type core 50 is placed on and bonded to the connecting part 43 of E-type core 40 to form a single-piece core component 31. E-type core and I-type core are bonded, for example, by crimping 34 shown in
In one embodiment, crimping 34 is used to combine E-type core 40 and I-type core 50 into a single-piece core component. In this case, crimp holes 45 are formed in one of E-type core 40 or I-type core 50, and dowels 52 are provided on the other of E-type core 40 or I-type core 50, as shown in
In another embodiment, welding 35 is used to combine E-type core 40 and I-type core 50 into a single-piece core component. In this case, welding is performed between the outer edge of the connecting part 43 of E-type core 40 and the outer edge of I-type core, as shown in
When E-type core 40 and I-type core 50 are interconnected by weld 35, the magnetic properties of the welded area and its vicinity may deteriorate. For this reason, as shown in
As shown in
As shown in
In this state, however, the first core components 31a and the second core components 31b have not been fixed yet and remain inserted in the hollow section 21. Therefore, as shown in
In the current transformer 10 including a block of the first core components 31a and a block of the second core components 31b, a gap 60 is formed between distal ends of legs 41, 42, 41 of the first core component 31a and an inner-side end edge of I-type core 50 of the second core component 31b. A gap 60 is also formed between distal ends of legs 41, 42, 41 of the second core component 31b and an inner-side end edge of I-type core 50 of the first core component 31a. A spacing of the gap 60 can be adjusted by pushing the first core component 31a from the first direction and the second core component 31b from the second direction (gap adjusting step).
Adjusting the gap 60 can be performed, as shown by the arrows in
After the adjustment of gap 60 is completed, the first core component 31a and the second core component 31b are joined by weld 37 or other means at the overlapped legs 41, 41 on the outside position (joining step). Since the first and second core components 31a and 31b are joined, the gap 60, once adjusted, can be prevented from changing the determined distance. Each of the first and second core components 31a and 31b is combined into a single core component block before this joining step. Therefore, welding 37 for joining the first and second core components 31a and 31b may be a spot welding only at one or more places. Therefore, the magnetic properties of the core components 31a and 31b are not substantially affected by welding 37.
In the current transformer 10 of the present invention, the first core component 31a and the second core component 31b can be made into single core component blocks without using varnish, glue, or resin. Therefore, the current transformers are not affected by thermal expansion and contraction and provide excellent temperature characteristics.
In the above explanation, after a stack of the first core component 31a and a stack of the second core component 31b are formed, the spacing of gap 60 is adjusted, and then the stacks of the first and second core components 31a and 31b are joined to each other. However, for example, a spacing of the gap 60 may be adjusted without applying weld 36 to the stacks of the first and second core components 31a and 31b, as shown in
In accordance with the present invention, the first core components 31a and the second core component 31b are welded 37, 38 at substantial central part of the legs 41 of E-type core 40, as shown in
In the embodiment mentioned above, all the first core components 31a are stacked with I-type core 50 facing up, and all the second core components 31b are stacked with I-type core 50 facing down. However, if the first core component 31a and the second core component 31b are paired, as shown in
In the above embodiment, the first core component 31a and the second core component 31b are inserted into the hollow section 21 one by one. However, in another embodiment as shown in
The current transformer 10 obtained by the above can be accommodated in a casing 80, for example, and used as a current transformer module 12.
The lower case 85 has insertion holes 86a, 86b, through which the terminal wires 26a, 26a of the primary coil 26 and the terminal wires 27a, 27a of the secondary coil 27 extend out, respectively. As shown in
After the current transformer module 12 is made, the output voltage characteristics are individually measured, and the obtained characteristic data can be printed or sealed on the upper case as a data matrix 89, as shown in
As for a combination of the current transformer 10 and the casing 80 mentioned above, there is a demand for downsizing the current transformer module 12. To downsize the current transformer module 12, the current transformer 10 must be smaller. As shown in
In accordance with the present invention, as shown in
When the current transformer 10 is housed in the upper case 81, the upper side protrusion 83 of the upper case 81 fits into the upper side recess 23 of the bobbin 20. This makes up an insulating wall and provides a longer creepage distance of insulation between the primary coil 26 and the secondary coil 27. Since the upper side protrusion 83 fits into the upper side recess 23, the bobbin 20 can be adequately positioned in the upper case 81.
The upper case 81 is formed on the inner side of the upper surface with a recess along the outer shape of the primary coil 26 as a contact area 82 that restrains the primary coil 26 from coming loose. This contact area 82 prevents the primary side coil 26 from being lifted when the current transformer module 12 is mounted on a printed circuit board or the like.
As shown in
When the current transformer 10 is placed on the lower case 85, the lower side protrusion 87 fits into the lower side recess 25 of the bobbin 20. This makes up an insulating wall and provides a longer creepage distance of insulation between the primary coil 26 and the secondary coil 27.
Thus, the current transformer 10 and the current transformer module 12 can be downsized by lowering the heights of the upper and lower insulating walls 22 and 24 of the bobbin 20 while keeping the creepage distance between the primary coil 26 and the secondary coil 27. In addition, since the lower side protrusion 87 fits into the lower side recess 25, the bobbin 20 can be adequately positioned in the lower case 85.
The lower case 85 is preferably provided with a step portion 88 to support the lower surface of the bobbin 20. When the bottom surface of the bobbin 20 contacts the step portion 88 of the lower case 85, the bobbin 20 can be held in the casing 80 without tilting.
Concerning the current transformer 10 of the present invention, the gap 60 can be adjusted while referring to the output voltage characteristics. Hence, the core 30 has some play against the bobbin 20 in the longitudinal direction of the legs 41, depending on the width of the gap 60. This may cause the core 30 to slide in the passage direction of the hollow section 21, resulting in the rattling in the current transformer module 12. Therefore, the current transformer module 12 is preferably required to determine the position of core 30 relative to the bobbin 20 to avoid this rattling.
As described above, the position of bobbin 20 in the casing 80 is determined by the engagement between the upper side recess 23 and the upper side protrusion 83 and between the lower side recess 25 and the lower side protrusion 87. In this case, if the position of the core 30 can be determined relative to the casing 80, the positions of the core 30 and the bobbin 20 can also be determined relative to the casing 80. In accordance with this embodiment, the structure to determine the position of the core 30 relative to the casing 80 is employed, as shown in
The above description is intended to explain the invention and should not be construed as limiting or reducing the scope of the invention as described in the claims. The present invention is not limited to the above examples, and of course various variations are possible within the technical scope of the claims.
The output voltage characteristics were measured by incorporating the current transformer 10 into the output voltage measurement circuit 90 shown in
For comparison, Comparative Examples 1-3 were prepared. Comparative Example 1 is a current transformer 100 with E-type core 40 and without I-type core that is shown in FIG. 1 of Patent Document 1 (
For the current transformer of Inventive Example, the output voltage (V) was measured by varying the input current (A) under temperature atmosphere at −25° C., 25° C., and 80° C. The results are shown in
For the current transformer 10 (
For the current transformer 102 (
The above EXAMPLES 1 to 3 show that the current transformer of the Inventive Example has excellent temperature characteristics than Comparative Examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-140979 | Jul 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/024549 | 6/23/2020 | WO |
