JP2006214855A - Electric current sensor and watthour meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a working cost by dispensing with complicated work while achieving the widening of a measurement allowing range. <P>SOLUTION: Conventionally, hall ICs are used for many electric current sensors, but sensors of this type are expensive on the whole. This electric current sensor 3 is mounted with three or more magnetic impedance (MI) elements. The current sensor 3 is disposed in an illustrated positional relation with respect to current bars 2 through which a measuring object electric current flows, thereby giving a simple shape to the current bars 2 to reduce the cost while achieving range widening. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a current sensor that detects a current flowing through a conductor to be measured in a non-contact manner, and a watt hour meter using the current sensor.

FIG. 9 shows a basic configuration example of this type of small watt hour meter disclosed in Non-Patent Document 1, for example. 2A is a plan view, FIG. 2B is a sectional view taken along line XX, and FIG. 2C is a side view in a direction orthogonal to the X axis. Reference numeral 51 in (c) denotes a housing.
This is a structure directly connected to a breaking means such as a breaker. For example, the attachment shown in (b) is such that the A-side terminal 521 is the three-phase power breaker side and the B-side terminal 522 is the load side. Wiring is performed with screws 54. Then, the current and voltage flowing through each phase on the load side from the A side to the B side are detected, and the power is calculated. Further, the amount of electric power can be monitored from the outside by a liquid crystal display 58 and a metering pulse LED (light emitting diode) 59 that emits light at a period proportional to the amount of electric power. In order to calculate the amount of power from a three-phase signal, at least a two-phase current signal and a voltage signal are required. Therefore, at least two current sensors are required per watt-hour meter.

FIG. 10 shows a main part from which the casing 51 and the electronic circuit are removed from FIG. 9 and only the current bar which is a current bar and a current detection sensor is extracted.
A current transformer is usually used as a current sensor for a watt-hour meter. In FIG. 10, a hollow hole 55 is formed at the center of the current transformers 561 and 562, and a magnetic field generated from a current flowing through the current bar 53 disposed through the hollow hole 55 is detected, and the strength of the magnetic field is determined. It is processed as a current value. In this watt-hour meter, current sensors are arranged only in the A phase and the C phase so that the electric energy can be calculated. Reference numeral 52 denotes a terminal.

FIG. 11 shows a basic configuration example of a general electronic watt-hour meter disclosed in Patent Document 1, for example.
That is, the electronic watt-hour meter basically calculates the current signal I and the voltage signal V obtained from the current transformers 561 and 562 and the voltage sensors 611 and 612, which are not specifically described here. The data is taken into a microcomputer (microcomputer) 60 or the like as a means and calculated in the microcomputer 60 to obtain the electric energy. Further, the microcomputer 60 controls a metering pulse LED (light emitting diode) 59 that generates a pulse corresponding to the amount of electric power and a liquid crystal display 58 that displays the amount of electric power.

Osaki Electric Industry Co., Ltd .: Product Information Index “Compact EM” [Searched on December 1, 2003] Internet <URL: http: // www. osaki. co. jp / product / denryoku / cem_tan3san3. html> Japanese Patent Laying-Open No. 2003-149276 (second page, FIG. 13)

(1) The current transformer is generally expensive, which is a factor of increasing the cost of the watt-hour meter.
(2) Since the hole of the current transformer is arranged at the center of the main body of the current transformer, it is necessary to devise the shape and assembly of the current bar. As a result, the watt-hour meter is a high cost factor.
(3) The current transformer needs to change the configuration of the main body and the peripheral circuit according to the electric energy specification (for example, 5A specification, 30A specification, etc.) of the watt hour meter. In other words, since parts cannot be shared by each specification, the watt-hour meter costs due to inventory management costs and the incidence of defective products increase due to assembly errors.

(4) In the case of a current transformer with a large current specification, even a small current cannot be detected (the detection range is small).
There are problems such as.
Accordingly, an object of the present invention is to reduce costs by eliminating complicated processing and to achieve a wide range.

In order to solve such a problem, in the invention of claim 1, n (natural number of 3 or more) current measuring devices, positioning means for positioning these current measuring devices, and the n current measuring devices A current sensor including n detection circuits that convert the signal of into a voltage signal proportional to the external magnetic field,
The n current measuring devices are arranged at different distances from a conductor to be measured, and each signal output difference from the n detection circuits is used as an output signal of a current sensor.

  In the first aspect of the invention, the n current measuring devices are arranged at different distance positions on the same line on the same plane with respect to the current flowing through the conductor to be measured, respectively, With any one of the detection circuits corresponding to the current measuring device as a reference, each signal output difference from the other detection circuits can be used as an output signal of the current sensor (invention of claim 2). In the invention of claim 2, at least one of the current measurement devices not serving as the reference can be arranged on a different line on the same plane as the current measurement device serving as the reference (the invention of claim 3). ) Or at least one of the non-reference current measurement devices can be arranged on a different plane from the reference current measurement device (invention of claim 4).

  In the invention according to any one of claims 1 to 4, the current measuring device includes a magnetic impedance element, a negative feedback magnetic field applying means for applying a magnetic field proportional to an external magnetic field to the magnetic impedance element, and the magnetic And a bias applying means for applying a bias magnetic field to the impedance element. (Invention of claim 5) In the invention of claim 5, the bias applying means can be a permanent magnet. Invention of Claim 6). Moreover, a watt-hour meter can be comprised using at least 1 of the current sensor of Claims 1-6 (Invention of Claim 7).

  According to the present invention, since the MI element is used and the arrangement thereof is devised, the structure of the current bar can be simplified, and as a result, the cost of the current sensor and the watt-hour meter can be reduced.

FIG. 1 is a block diagram showing an embodiment of the present invention.
As is apparent from FIG. 1, this is arranged at a certain distance from each of the three concave current bars 2 attached to the lower housing 1, its A-phase and C-phase current bars 2. The current sensor 3, the current sensor board 4 on which the current sensor 3 is mounted, the signal processing board 5 that is disposed perpendicularly to the current sensor board 4 and electrically connected thereto, and is parallel to the signal processing board 5. It is comprised from the electric energy calculation board | substrate 6 etc. which are arrange | positioned in the position away only by fixed distance. Here, the current bars 2 have the same simple structure as shown in FIG. The upper casing is not shown.

FIG. 2 is a perspective view showing the configuration of the current sensor and the current bar.
That is, the current sensor 3 is installed with respect to the current bar 2 as illustrated. Here, when a current flows through the current bar 2, the currents on the α, β, and γ planes are indicated by arrows. Since the rotating magnetic field (magnetic field) Φ generated by the current flowing in the α plane is indicated by an arrow, in order to effectively detect the magnetic field Φ by the current sensor 3, the current sensor 3 is connected to the current bar as shown in the figure. It is necessary to install perpendicularly to the α plane of 2. In this way, the current sensor 3 disposed at a position that is separated from the current bar 2 by a predetermined distance R in the vertical direction is inversely proportional to the distance R and proportional to the current I flowing through the current bar 6 as follows: Such a magnetic field Φ is applied.
Φ = αI / R ………… (1)

FIG. 3 shows an enlarged configuration diagram of the current sensor.
That is, as shown in FIG. 3A, the current sensor is configured as a permanent magnet 30 and MI elements 31, 32, and 33, which are current measuring devices, molded with resin. Here, the MI element 31 is disposed at a distance R from the current bar 2 (see FIG. 2) to be measured, the MI element 32 is disposed at a position ΔR1 from the MI element 31, and the MI element 33 is disposed at the MI element 33. 31 to ΔR2.

  As shown in FIG. 3B, the MI element includes a magnetic material 34 formed by sputtering a magnetic film formed on a glass 36 by a photo process and the like, and a negative feedback coil wound around the MI element. 35. In general, MI elements have been reported to be more sensitive to magnetic fields than Hall elements and magnetoresistive elements (for example, Higa et al., “Sputtered thin-film micro-MI sensor by pulse current”, Journal of Japan Society of Applied Magnetics) , Vol. 21, No. 4-2, 1997).

FIG. 4 shows an example of impedance characteristics due to a magnetic field applied to the MI element.
The horizontal axis represents the magnetic field strength, and the vertical axis represents the impedance (Ω). When the magnetic field applied to the MI element changes, the impedance of the MI element changes as shown. In general, the relationship between the impedance of the MI element and the magnetic field is not stable near zero magnetic field. Therefore, in the present invention, for example, as shown in FIG. 3, the permanent magnet 30 is arranged on the surface facing the MI element, and thereby the magnetic field when the bias magnetic field Φ0 [A / m] is applied is used as a reference (hereinafter, the operating magnetic field Φ0). In other words, the impedance change of the MI element is detected by the change of the external magnetic field. Here, the external magnetic field corresponds to, for example, a magnetic field generated by a current flowing through the electric wire.

When using the MI element as a current sensor,
1) Improvement of rangeability 2) For the purpose of improving temperature characteristics, etc., a magnetic field (negative feedback magnetic field) proportional to the external magnetic field and in the opposite direction to the external magnetic field is applied to the MI element. The negative feedback coil 35 shown in FIG. 3B applies this negative feedback magnetic field.

Next, the operation of the current sensor arranged on the current bar and the power calculation method will be described.
Now, when a current flows through the current bar, a magnetic field as shown in FIG. 5 is generated around the current bar. For example, when a current corresponding to 50 A is passed through the current bar, magnetic fields of 780 A / m, 420 A / m, and 720 A / m are applied to the MI elements 31, 32, and 33, respectively. The impedance changes proportionally.

FIG. 6 shows a circuit block diagram of the current sensor and the power calculation unit. 411, 412 and 413 are oscillation circuits, 421, 422 and 423 are fixed resistors, 431, 432 and 433 are rectifier circuits, 441, 442 and 443 are amplifier circuits, 461, 462 and 463 are negative feedback magnetic field generation circuits, 48 is a microcomputer, 481 is a liquid crystal display, 482 is a metering pulse LED, 31, 32 and 33 are MI elements, 35 is a negative feedback coil, and V ₁ and V ₂ are signals from voltage sensors (not shown).

  Now, when a high frequency signal of several MHz to several tens of MHz is applied from the oscillation circuits 411, 412, and 413 to the MI elements 31, 32, and 33 in FIG. 6, each MI element is proportional to the external magnetic field as shown in FIG. Impedance changes. Therefore, the signals at the input parts of the rectifier circuits 431, 432 and 433 become high-frequency signals having an amplitude proportional to the external magnetic field, and this signal passes through the rectifier circuits 431, 432, 433 and the amplifier circuits 441, 442, 443, and the current signal A , B and C are taken into the microcomputer 48.

The outputs of the amplifier circuits 441, 442 and 443 are output from the negative feedback magnetic field generation circuits 461, 462 and 463 for generating a negative feedback magnetic field for the purpose of improving the rangeability and temperature characteristics of the current sensor. A predetermined current is supplied to the negative feedback coil 35 provided in the elements 31, 32, 33, and a negative feedback magnetic field is applied to the MI elements 31, 32, 33.
The current signals A, B, and C captured by the microcomputer 48 are detected as impedance changes from the MI elements 31, 32, and 33 disposed at distances R, R + ΔR1, and R + ΔR2 from the current bar, respectively. Therefore, the current signals A, B, C are
Current signal A = αI / R (2)
Current signal B = αI / (R + ΔR1) (3)
Current signal C = αI / (R + ΔR2) (4)
It becomes.

Here, since R <R + ΔR2 <R + ΔR1, the output signal of each current sensor is
Current signal A> Current signal C> Current signal B
It is. Therefore, in the watt-hour meter of the present invention, in order to eliminate the influence of disturbance noise, the output difference of each current sensor is used as the difference between the current signals. Therefore, as a current sensor signal used in the watt-hour meter,
Current signal S = current signal A−current signal B
Current signal L = current signal A−current signal C
These two signals are used.

Here, since the difference in the magnetic field appears larger than that in FIG. 5, the current signal S can be sufficiently detected even with a magnetic field generated with a small current. Therefore, it is effective for use for detecting a small current. On the other hand, the current signal L is effective in detecting a magnetic field generated with a large current because the difference in magnetic field appears smaller than that in FIG.
By calculating the current signals S and L and the voltage signal from the voltage sensor by the microcomputer 48, the electric energy can be calculated. Further, by switching the current signals S and L, it is possible to measure with high current measurement accuracy from a large current to a small current. The above processing is performed for all current sensors attached to the current bar.

With the above configuration,
1) By using an inexpensive MI element, the cost can be reduced.
2) Since it is possible to measure a wide range of current from large current to small current, it is not necessary to prepare a current sensor for each current specification, and it is possible to share components for each specification.
Advantages such as are obtained.

In order to detect even a larger current, it is necessary to further reduce the distance between the MI element 31 and the MI element 33.
FIG. 7 corresponds to such an example, in which the MI element 33 is disposed on the same plane as the MI element 31 at a distance of ΔR3 (ΔR3 <ΔR2). This makes it possible to detect a larger current than in the case of FIG.
FIG. 8 also has the same concept as above, but the MI element 33 is arranged on a different plane from the MI element 31 and at a horizontal distance of ΔR4 (ΔR4 <ΔR3). This makes it possible to detect a larger current than in the case of FIG.

  In the above, an example in which three MI elements are used has been described. However, the present invention can be applied to the case of four or more elements in the same manner as described above. That is, using any one of the MI elements as a reference and using each signal output difference from the other MI elements, it is possible to expect an improvement in accuracy as compared with the case of three.

Configuration diagram showing an embodiment of the present invention The perspective view which shows the installation structure of the current bar and current sensor of FIG. Configuration diagram showing a specific example of the current sensor of FIG. Characteristic diagram showing magnetic field impedance characteristics of MI element Illustration of magnetic field distribution example generated by current applied to current bar FIG. 1 is a block diagram showing an example of a current sensor and an electric energy calculation circuit for FIG. Configuration diagram showing another example of current sensor Configuration diagram showing still another example of a current sensor Configuration diagram showing a conventional example of a watt-hour meter The perspective view which shows the example of the electric current detection part of FIG. Configuration diagram showing another conventional example of watt-hour meter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lower casing, 2 ... Current bar, 3 ... Current sensor, 4 ... Current sensor board, 5 ... Signal processing board, 6 ... Power calculation board, 30 ... Permanent magnet, 31, 32, 33 ... MI (magnetic impedance) Element 34... Magnetic body 35. Negative feedback coil 36 Glass substrate 411 to 413 Oscillator circuit 421 to 423 Fixed resistor 431 to 433 Rectifier circuit 441 to 443 Amplifier circuit 461 to 463 Negative feedback magnetic field generation circuit, 48... Microcomputer (microcomputer), 481... Liquid crystal display, 482.

Claims (7)

n (natural number of 3 or more) current measuring devices, positioning means for positioning these current measuring devices, and n pieces of signals for converting signals from the n current measuring devices into voltage signals proportional to an external magnetic field In a current sensor equipped with a detection circuit,
The n current measuring devices are arranged at different distances from a conductor to be measured, and each signal output difference from the n detecting circuits is used as an output signal of the current sensor.   The n current measuring devices are respectively arranged at different distance positions on the same line on the same plane with respect to the current flowing through the conductor to be measured, and any of the detection circuits corresponding to the n current measuring devices. 2. The current sensor according to claim 1, wherein each of the signal output differences from the other detection circuits is used as an output signal of the current sensor with one of them as a reference.   The current sensor according to claim 2, wherein at least one of the non-reference current measurement devices is arranged on a different line on the same plane as the reference current measurement device.   The current sensor according to claim 2, wherein at least one of the non-reference current measurement devices is arranged on a different plane from the reference current measurement device.   The current measuring device includes a magneto-impedance element, a negative feedback magnetic field applying means for applying a magnetic field proportional to an external magnetic field to the magneto-impedance element, and a bias applying means for applying a bias magnetic field to the magneto-impedance element. The current sensor according to claim 1, comprising:   The current sensor according to claim 5, wherein the bias applying unit is a permanent magnet. A watt hour meter comprising at least one of the current sensors according to claim 1.

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