JP7706281B2 - Current Sensors and Power Meters - Google Patents

Description

The present invention relates to a current sensor and a watt-hour meter that can accurately detect the measured current of a current bar even when the current sensor is close to the current bar.

Current sensors that have been used to date include a current transformer (CT), a configuration in which a magnetoelectric conversion element such as a Hall element is placed in the gap of a magnetic core, and a configuration in which an element with a wound coil or a coil pattern formed on a dielectric substrate is placed in the gap of a magnetic core. In particular, the method of placing a magnetoelectric conversion element such as a Hall element or an element with a coil pattern formed on a substrate in the gap of a magnetic core is excellent in that it is electrically separated from the circuit through which the primary current to be measured flows, and therefore can measure the current with high accuracy without affecting the circuit on the primary current side. Furthermore, the method of placing an element with a coil pattern has the characteristics of excellent linearity and temperature characteristics, a small number of parts, and easy manufacturing (see Patent Document 1).

The current sensor described in Patent Document 1 has a current bar passing through the central opening of a ring-shaped magnetic collector core, and a substrate with a coil pattern placed in the gap of the magnetic collector 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 collected by the magnetic collector core. If the current is periodic, the magnetic flux generated according to the period also changes periodically. As a result, an induced voltage according to the magnitude and frequency of the current is generated in a detection coil with a coil pattern, and this induced voltage is used as a detection signal for the current flowing through the current bar.

JP 2010-48755 A

However, since the current sensor and the current bar are placed in close proximity, electrostatic coupling occurs between the current sensor and the current bar, and a small leakage current flows through the current sensor via the electrostatic capacitance, which can cause an error in the detection voltage. This error occurs due to the potential difference between the current bar and the current sensor even when no measurement current flows through the current bar, so it is an unnecessary current detection signal that is unrelated to the measurement current. For this reason, ideally, in a no-load state where no current flows through the measurement current, no detection voltage is generated in the current sensor, so the detected power is zero. However, due to the electrostatic capacitance generated between the current bar and the current sensor, an output that is uncorrelated with the current flowing through the current bar is generated in the detection signal of the current sensor, resulting in an erroneous measurement of power.

The present invention has been made in consideration of the above, and aims to provide a current sensor and a watt-hour meter that can accurately detect the measured current of a current bar even when the current sensor is close to the current bar.

In order to solve the above problems and achieve the object, the present invention provides a current sensor that detects a magnetic field formed around a current bar that carries a current and detects a current signal that flows through the current bar, and is characterized in that it comprises a magnetic flux collector core formed to surround the current bar that carries a current, and a printed circuit board on which a magnetic detection coil is provided that is interposed in the gap of the magnetic flux collector core and has one end connected to ground to perform magnetic detection, and a solid ground layer to which one end of the magnetic detection coil is connected is disposed on at least the surface of the printed circuit board on the current bar side.

The present invention is also characterized in that, in the above invention, a solid ground layer is arranged on both sides of the printed circuit board, to which one end of the magnetic detection coil is connected.

In addition, in the above invention, the printed circuit board is provided with two magnetic detection coils that detect magnetic flux in different directions generated by the magnetic 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 present invention is also characterized in that, in the above invention, the printed circuit board is a multi-layer printed circuit board, and the magnetic detection coil has coil patterns formed on each layer connected in series.

The present invention is also characterized in that the amount of power flowing through the current bar is calculated based on a current signal detected by a current sensor and a voltage signal detected by a voltage sensor described in any one of the above inventions.

According to the present invention, even if the current sensor is close to the current bar, the measured current of the current bar can be detected with high accuracy without being affected by electrostatic coupling.

FIG. 1 is a perspective view showing a schematic configuration of a current sensor according to an embodiment of the present invention. FIG. 2 is a diagram showing a cross-sectional configuration of the current sensor. FIG. 3 is a cross-sectional view showing a detailed configuration of the current sensor. FIG. 4 is an explanatory diagram illustrating the layer structure of the current sensor. FIG. 5 is an explanatory diagram for explaining prevention of unnecessary leakage current caused by electrostatic coupling between the current sensor and the current bar. FIG. 6 is a diagram showing a modified example of the current sensor. FIG. 7 is a diagram showing the results of actual measurement of no-load power metered values for a conventional power supply voltage and a power supply voltage when a solid ground layer according to this embodiment is provided. FIG. 8 is a block diagram showing an example of a watt-hour meter using the current sensor shown in the embodiment. FIG. 9 is a vector diagram between three-phase currents and three-phase voltages.

The following describes the embodiment of the invention with reference to the attached drawings.

Figure 1 is a perspective view showing the general configuration of a current sensor 2 according to an embodiment of the present invention. Also, Figure 2 is a diagram showing the cross-sectional configuration of the current sensor 2. As shown in Figures 1 and 2, the current sensor 2 is placed in the gap g between linear magnetic cores 11a and 11b formed to surround a current bar 1 through which a current flows. The current sensor 2 has a first coil 2a and a second coil 2b placed at both ends on a printed circuit board 4.

When a current flows through the current bar 1, a magnetic flux Φ is generated, and this magnetic flux is collected by the magnetic collecting cores 11a and 11b. When this magnetic flux interlinks 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 calculation unit 3 detects and processes this induced voltage to detect the current signal flowing through the current bar 1.

As shown in FIG. 2, solid ground layers 3a, 3b are arranged on the front and back surfaces of the printed circuit board 4 to cover the first coil 2a and the second coil 2b as magnetic detection coils and to which one end of the first coil 2a and one end of the second coil 2b are connected.

Figure 3 is a cross-sectional view showing the detailed configuration of the current sensor 2. As shown in Figure 3, the current sensor 2 uses a multi-layer printed circuit board 4 to form the first coil 2a and the second coil 2b with four layers L1 to L4. The external connection terminals 22a and 22b are terminals for connecting to a signal processing circuit such as the calculation unit 3. Figure 4 is an explanatory diagram explaining the structure of each layer. As shown in Figure 4, in each layer 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 in 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 in 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. In addition, between the first coil 2a and the second coil 2b, a via d is formed that connects one end of the first coil 2a and one end of the second coil 2b to the solid ground layer 3a, and also connects the solid ground layers 3a and 3b. By making it multi-layered, it is possible to make a small, highly accurate current sensor.

Figure 5 is an explanatory diagram explaining the prevention of unnecessary leakage current caused by electrostatic bonding between the current sensor 2 and the current bar 1. As shown in Figure 5(a), if solid ground layers 3a, 3b are not provided, leakage current flows from the current bar 1 side to the current sensor 2 side due to electrostatic bonding between the current bar 1 and the coil substrate (current sensor 2). Here, as shown in Figure 5(b), if solid ground layers 3a, 3b are provided on the current sensor, leakage current from the current bar 1 does not flow to the current sensor 2 side, and the current sensor 2 can reduce detection of leakage current.

As shown in FIG. 6, the solid ground layers 3a and 3b only need to reduce the electrostatic coupling with the current bar 1, so the current sensor 2' may be provided with only the solid ground layer 3a on the current bar 1 side.

In addition, the material of the solid ground layers 3a and 3b is not iron, which has a high relative permeability, but aluminum or copper, which has a relative permeability close to 1, so as not to interfere with the magnetic detection function of the current sensor 2.

Figure 7 shows the actual measurement results of the no-load power measurement value for the conventional power supply voltage and the no-load power measurement value for the power supply voltage when the solid ground layers 3a and 3b of this embodiment are provided. As shown in Figure 7, the current sensor 2 of this embodiment can greatly reduce the erroneous measurement of the no-load power measurement for the power supply voltage compared to the conventional case.

Although the current sensor 2 has a multi-layer structure, it is not limited to this and may have a single-layer structure.

<Power meter>
Fig. 8 is a block diagram showing an example of a watt-hour meter 200 using the current sensor shown in the embodiment. This watt-hour meter 200 measures the three-phase power between a power source SP and a load LD, and obtains the power by the two-wattmeter method. Fig. 9 shows a vector diagram between the three-phase currents IR, IS, and IT and the three-phase voltages VR, VS, and VT.

As shown in FIG. 8, the electricity meter 200 has current sensors 20a and 20b corresponding to the current sensor 2 shown in the embodiment and the modified example, voltage sensors 201a and 201b, an electricity calculation unit 202, and an output unit 203. The current sensor 20a detects a current signal of the R phase. The current sensor 20b detects a current signal of the T phase. The voltage sensor 201a detects a voltage signal between the R phase and the S phase. The voltage sensor 201b detects a voltage signal between the T phase and the S phase.

The power calculation unit 202 multiplies the current signal of the current sensor 20a by the voltage signal of the voltage sensor 201a to generate an instantaneous power signal, smooths this signal using a low-pass filter to obtain active power, and multiplies the current signal of the current sensor 20b by the voltage signal of the voltage sensor 201b to generate an instantaneous power signal, smooths this signal using a low-pass filter to obtain active power, and calculates the active power by adding up each active power as the amount of power. The output unit 203 displays or outputs the calculated amount of power to the outside.

The three-phase power P calculated using 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 calculating the total power of each phase.

In addition, each configuration illustrated in the above embodiment is a functional schematic, and does not necessarily have to be physically configured as illustrated. In other words, the form of distribution and integration of each device and component is not limited to that illustrated, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage conditions, etc.

REFERENCE SIGNS LIST 1 Current bar 2, 2' Current sensor 2a First coil 2b Second coil 3 Calculation unit 3a, 3b Solid ground layer 4 Printed circuit board 11a, 11b Magnetic flux collecting core 22a, 22b External connection terminal 200 Power meter 201a, 201b Voltage sensor 202 Power calculation unit 203 Output unit a1, a2, b1, b2, c1, c2, d Vias IR, IS, IT Three-phase current L1, L2, L3, L4 Layer LD Load P Three-phase power SP Power supply VR, VS, VT Three-phase voltage Φ Magnetic flux

Claims (5)

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,
a magnetic flux collecting core having a linear portion formed so as to surround a current bar through which a current flows;
a printed circuit board having a magnetic detection coil disposed in the gap of the magnetic flux collecting core and having one end connected to ground for magnetic detection;
Equipped with
A current sensor comprising: a solid ground layer disposed on both sides of said printed circuit board as an integral part of said printed circuit board, said solid ground layer having one end connected to said magnetic detection coil. 2. The current sensor according to claim 1, further comprising an external connection terminal provided on a surface opposite to the current bar. The current sensor according to claim 1 or 2, characterized in that the printed circuit board is provided with two magnetic detection coils that detect magnetic flux 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 printed circuit board is a multi-layer printed circuit board,
4. The current sensor according to claim 1, wherein the magnetic detection coil has coil patterns formed on each layer and connected in series. A watt-hour meter that calculates the amount of power flowing through the current bar based on a current signal detected by a current sensor and a voltage signal detected by a voltage sensor according to any one of claims 1 to 4.

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