Current sensor and electric energy meter

Abstract

To provide a current sensor and a watt-hour meter with which it is possible to detect the measured current of a current bar with good accuracy even when a current sensor is close to the current bar.SOLUTION: Provided is a current sensor 2 for detecting a magnetic field formed around a current bar 1 that flows a current and detecting a current signal flowing in the current bar 1, the current sensor 2 comprising: magnetism collecting cores 11a, 11b formed so as to enclose the current bar 1 that flows a current; and a printed board 4 provided with a first coil 2a and a second coil 2b for detecting magnetism, which are interposed in a gap g of the magnetism collecting cores 11a, 11b, with one end connected to the ground. A solid ground layer 3a is located at least on the surface on the current bar 1 side of the printed board 4, to which are connected one end of the first coil 2a and one end of the second coil 2b.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a current sensor and a wattmeter that can accurately detect the measured current of a current bar even when the current sensor is close to the current bar.

Background Art

[0002] Conventionally, as current sensors that have been used, there are a current transformer (CT), a configuration in which a magnetoelectric conversion element such as a Hall element is arranged in a gap portion of a magnetic flux concentrating core, and a configuration in which a coil pattern is formed on a winding coil or a dielectric substrate in the gap portion of the magnetic flux concentrating core. In particular, the method of arranging a magnetoelectric conversion element such as a Hall element or an element having a coil pattern formed on a substrate in the gap portion of the magnetic flux concentrating core is electrically separated from the circuit in which the primary current to be measured flows. Therefore, it is excellent in that it can accurately measure the current without affecting the circuit on the primary current side. Furthermore, the method of arranging an element having a coil pattern has characteristics of excellent linearity and temperature characteristics, and few component parts, making manufacturing easy (see Patent Document 1).

[0003] The current sensor described in Patent Document 1 passes a current bar through a central opening of an annular magnetic flux concentrating core and arranges a substrate having a coil pattern in a gap portion of the magnetic flux concentrating core. When a current flows through the current bar, a magnetic flux proportional to the magnitude of the current flowing through the current bar is generated around the current path. The generated magnetic flux is concentrated by the magnetic flux concentrating core. When the current is a periodic current, the magnetic flux generated according to the period also changes periodically. As a result, an induced voltage corresponding to the magnitude and frequency of the current is generated in the detection coil having the coil pattern, and this induced voltage is used as a detection signal of the current flowing through the current bar.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, since the current sensor and the current bar are arranged close to each other, electrostatic coupling occurs between the current sensor and the current bar, and a minute leakage current flows through the current sensor via the capacitance, which may cause an error in the detected voltage. This error is an unnecessary current detection signal that has nothing to do with the measured current because it is caused by the potential difference between the current bar and the current sensor even when no measured current is flowing through the current bar. Therefore, ideally, in a no-load state where no current flows through the measured current, the detection voltage of the current sensor does not occur and the detection power becomes zero. However, via the capacitance generated between the current bar and the current sensor, an output that has no correlation with the energization current of the current bar is generated in the detection signal of the current sensor, resulting in an issue of mismeasuring the power.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a current sensor and a wattmeter that can accurately detect the measured current of a current bar even when the current sensor is close to the current bar.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, the present invention is a current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar, including a magnetic flux collecting core formed so as to surround the current bar through which a current flows, and a printed circuit board provided with a magnetic detection coil that is interposed in a gap of the magnetic flux collecting core and has one end connected to ground for magnetic detection, and is characterized in that a solid ground layer to which one end of the magnetic detection coil is connected is disposed at least on a surface of the printed circuit board on the current bar side.

[0008] Further, the present invention is characterized in that, in the above invention, a solid ground layer to which one end of the magnetic detection coil is connected is disposed on both side surfaces of the printed circuit board.

[0009] Further, in the present invention, in the above invention, the printed circuit board is provided with two magnetic detection coils for detecting magnetic fluxes in different directions generated by the magnetic core, one end of each magnetic detection coil is connected to the solid ground layer, and the magnetic detection coils are connected in series.

[0010] Further, in the present invention, in the above invention, the printed circuit board is a multilayer printed circuit board, and the magnetic detection coils are characterized in that coil patterns formed in each layer are connected in series.

[0011] Further, the present invention is characterized in that the amount of electric power flowing through the current bar is calculated based on the current signal detected by the current sensor according to any one of the above inventions and the voltage signal detected by the voltage sensor.

Advantages of the Invention

[0012] According to the present invention, even when the current sensor is close to the current bar, the measured current of the current bar can be accurately detected without being affected by electrostatic coupling.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 8

Figure 9

Embodiment for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

[0015] FIG. 1 is a perspective view showing the schematic configuration of a current sensor 2 which is an embodiment of the present invention. Further, FIG. 2 is a diagram showing the cross-sectional configuration of the current sensor 2. As shown in FIGS. 1 and 2, the current sensor 2 is disposed in a gap g between linear magnetic cores 11a and 11b formed so as to surround a current bar 1 through which a current flows. At both ends on the printed circuit board 4, a first coil 2a and a second coil 2b are disposed.

[0016] When a current flows through the current bar 1, a magnetic flux Φ is generated, and this magnetic flux is magnetically concentrated by the magnetic cores 11a and 11b. When this magnetic flux links with the first coil 2a and the second coil 2b, an induced voltage is generated in the first coil 2a and the second coil 2b. The arithmetic unit 3 detects the current signal flowing through the current bar 1 by detecting and processing this induced voltage.

[0017] Here, as shown in FIG. 2, on the front and back surfaces of the printed circuit board 4, there are disposed solid ground layers 3a and 3b that cover the first coil 2a and the second coil 2b as magnetic detection coils, and one end of the first coil 2a and one end of the second coil 2b are connected.

[0018] FIG. 3 is a cross-sectional view showing the detailed configuration of the current sensor 2. As shown in FIG. 3, the current sensor 2 uses a multilayer printed circuit board 4 to form the first coil 2a and the second coil 2b in four layers L1 to L4, respectively. The external connection terminals 22a and 22b are terminals for connecting to a signal processing circuit such as the arithmetic unit 3. FIG. 4 is an explanatory diagram for explaining each layer structure. As shown in FIG. 4, in each of the layers L1 to L4, a via a1 connecting between the layers L1 and L2 and a via c1 connecting between the layers L3 and L4 are formed at the center of the first coil 2a, and a via b1 connecting between the layers L2 and L3 is formed on the outer periphery of the first coil 2a. Similarly, a via a2 connecting between the layers L1 and L2 and a via c2 connecting between the layers L3 and L4 are formed at the center of the second coil 2b, and a via b2 connecting between the layers L2 and L3 is formed on the outer periphery of the second coil 2b. Further, between the first coil 2a and the second coil 2b, a via d is formed which connects one end of the first coil 2a, one end of the second coil 2b, and the solid ground layer 3a and also connects between the solid ground layers 3a and 3b. By making it multilayer, a small and highly accurate current sensor can be achieved.

[0019] FIG. 5 is an explanatory diagram for explaining prevention of generation of unnecessary leakage current due to electrostatic coupling between the current sensor 2 and the current bar 1. As shown in FIG. 5(a), when the solid ground layers 3a and 3b are not provided, leakage current flows from the current bar 1 side to the current sensor 2 side due to electrostatic coupling between the current bar 1 and the coil substrate (current sensor 2). Here, as shown in FIG. 5(b), when the solid ground layers 3a and 3b are provided in the current sensor, the leakage current from the current bar 1 does not flow to the current sensor 2 side, and the current sensor 2 can reduce the detection of leakage current.

[0020] Note that, as shown in FIG. 6, since the solid ground layers 3a and 3b only need to reduce the electrostatic coupling with the current bar 1, the current sensor 2' provided with only the solid ground layer 3a on the current bar 1 side may be used.

[0021] In addition, the materials of the solid ground layers 3a and 3b do not use iron with a large relative permeability so as not to interfere with the magnetic detection function of the current sensor 2, and use aluminum or copper with a relative permeability close to 1.

[0022] FIG. 7 is a diagram showing the measured results of the no-load power measurement value with respect to the conventional power supply voltage and the no-load power measurement value with respect to the power supply voltage in the case where the solid ground layers 3a and 3b of the present embodiment are provided. As shown in FIG. 7, in the current sensor 2 of the present embodiment, the error of the no-load power with respect to the power supply voltage can be significantly reduced as compared with the conventional case.

[0023] Note that the current sensor 2 has a multilayer structure, but is not limited thereto, and may have a single-layer structure.

[0024] <Electric energy meter> FIG. 8 is a block diagram showing an example of an electric energy meter 200 using the current sensor shown in the embodiment. This electric energy meter 200 measures the three-phase electric energy between a power supply SP and a load LD, and obtains it by a two-wattmeter method. Note that FIG. 9 shows a vector diagram between three-phase currents IR, IS, IT and three-phase voltages VR, VS, VT.

[0025] As shown in FIG. 8, the electric energy meter 200 includes current sensors 20a and 20b corresponding to the current sensor 2 shown in the embodiment and the modification example, voltage sensors 201a and 201b, an electric energy calculation unit 202, and an output unit 203. The current sensor 20a detects the current signal of the R phase. The current sensor 20b detects the current signal of the T phase. The voltage sensor 201a detects the voltage signal between the R phase and the S phase. The voltage sensor 201b detects the voltage signal between the T phase and the S phase.

[0026] The electric energy calculation unit 202 multiplies the current signal of the current sensor 20a and the voltage signal of the voltage sensor 201a to generate an instantaneous power signal, obtains the active power obtained by smoothing this with a low-pass filter, multiplies the current signal of the current sensor 20b and the voltage signal of the voltage sensor 201b to generate an instantaneous power signal, obtains the active power obtained by smoothing this with a low-pass filter, and calculates the active power obtained by adding the respective active powers as the electric energy. The output unit 203 displays or externally outputs the calculated electric energy.

[0027] Note that the three-phase power P obtained by the two-wattmeter method is P = VRS·IR + VTS·IT = (VR - VS)·IR + (VT - VS)·IT = VR·IR + VS·(-IR - IT) + VT·IT = VR·IR + VS·IS + VT·IT This is the same as obtaining the power obtained by summing the power of each phase.

[0028] Also, each configuration illustrated in the above embodiment is functionally schematic, and it is not necessarily physically configured as illustrated. That is, the form of distribution and integration of each device and component is not limited to that illustrated, and all or part of it can be functionally or physically distributed and integrated in any unit according to various usage situations and the like.

Explanation of Reference Numerals

[0029] 1 Current bar 2, 2´ Current sensors 2a First coil 2b Second coil 3 Calculation unit 3a, 3b Beta ground layer 4 Printed circuit board 11a, 11b Magnetic flux concentration cores 22a, 22b External connection terminals 200 Electric energy meter 201a, 201b Voltage sensors 202 Electric energy calculation unit 203 Output unit Via a1, a2, b1, b2, c1, c2, d Three-phase currents IR, IS, IT Layers L1, L2, L3, L4 Load LD Three-phase power P Power supply SP Three-phase voltages VR, VS, VT Magnetic flux Φ

Claims

1. A current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar, comprising: A magnetic flux collecting core having a linear portion formed so as to surround the current bar through which a current flows; A printed circuit board provided with a magnetic detection coil that is interposed in a gap of the magnetic flux collecting core and has one end connected to ground for magnetic detection; And comprising: A current sensor characterized in that a solid ground layer provided integrally with the printed circuit board is arranged on both side surfaces of the printed circuit board and one end of the magnetic detection coil is connected thereto.

2. The current sensor according to claim 1, further comprising external connection terminals provided on a surface opposite to the current bar.

3. The printed circuit board is provided with two magnetic detection coils for detecting magnetic fluxes in different directions generated by the magnetic flux collecting core, one end of each magnetic detection coil is connected to the solid ground layer, and each magnetic detection coil is connected in series. The current sensor according to claim 1 or 2.

4. The printed circuit board is a multilayer printed circuit board, The current sensor according to any one of claims 1 to 3, wherein the magnetic detection coils are characterized in that coil patterns formed in each layer are connected in series.

5. An electric energy meter characterized by calculating the amount of electric energy flowing through the current bar based on the current signal detected by the current sensor according to any one of claims 1 to 4 and the voltage signal detected by the voltage sensor.

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