JPH11237411A - Dc current sensor and dc current measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for a large annular core magnet-field guiding path by arranging an odd number of magnetoelectric conveyers at an equal interval while the direction of a detection axis is directed toward the same orbital direction and adding each output. SOLUTION: In a DC current sensor 100 for measuring a large DC current, at least four, preferably 6-24, magnetic resistance effect type magnetoelectric converters 2 are arranged at an equal interval, while each detection axis is directed toward the same orbital direction on a circumference that is at an equal distance from the axial center of a bussbar 6 in the groove of a yoke 1 consisting of an annular nonmagnetic body. Each magnetoelectric converter 2 is connected to a circuit part 4 by a lead wire 3, and for example is converted into current and then is outputted. Accordingly, even if the position of a current conductor to be measured such as the bussbar becomes eccentric, the influence is canceled out and is reduced, thus eliminating the need for using a large core and similarly reducing the influence of earth magnetism and external magnetism. A magnetoelectric converter utilizing a Hall effect element or the like can also be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC current sensor for measuring a large DC current and a DC current measurement system.

[0002]

2. Description of the Related Art For example, in a DC substation for electric railways, high-voltage AC power received from a power transmission network is converted into 600 to 300 by a transformer.
The voltage is reduced to about 0 V, converted to DC by a silicon rectifier, a mercury rectifier, and supplied to the line. The DC supply line is provided with a DC current sensor for measuring the amount of load and indication recording instruments.

[0003] There are many types of DC current sensors used for the above applications. Among them, a current sensor using a Kramer type DC current transformer and a magnetoelectric converter such as a Hall effect element has been widely used. Have been. In both cases, the magnitude of the static current is detected by detecting the magnetic flux density of a static magnetic field generated concentrically around a direct current, but the principles of the respective magnetic field detection are different.

In a Kramer type DC current transformer, a pair of annular magnetic cores having a rectangular magnetic characteristic are provided around a DC conductor, windings of the same number of turns are wound around each magnetic core, and they are connected to each other in an inverse series. Excite. By exciting each of the magnetic cores, which are polarized and saturated by the current to be measured, with AC, the saturation state of each magnetic core is canceled and reset every half-wave, and during that time, the windings are wound on the windings according to the law of equal ampere-turn. A detection current proportional to the measurement current flows. This detected current is full-wave rectified to obtain a DC current or voltage as a current transformation output.

[0005] In a conventional DC current sensor using a Hall effect element or the like, a magnetic path composed of a large annular magnetic core is provided around a DC conductor, a gap is provided in a part of the magnetic path, and a Hall effect element or Put the magnetoresistive effect element. Since the magnetization of the magnetic path due to the current to be measured is kept within the unsaturated range, the strength of the magnetic field in the air gap is proportional to the current to be measured. The magnetic field is converted into a voltage or a resistance value by a Hall element or the like.

In the above-mentioned claimer type DC current transformer, the direction of the current to be measured is limited to one direction, and when the current rises sharply from 0, a high voltage is generated in the exciting winding and dielectric breakdown may occur. There is a structural weakness that there is. Further, the response time is as slow as 0.5 to 1 second, and the measurement accuracy is as low as about ± 2.5% of the rated value, which may not be sufficient for recent demands for high accuracy.

In a conventional DC current sensor using a Hall effect element or the like, the magnetic core becomes large because the magnetization of the magnetic path is limited to an unsaturated range, and the structure is complicated because the Hall effect element or the like is embedded in the magnetic core. Further, since semiconductor devices such as Hall effect devices do not have a high endurance temperature, the upper limit of the operating temperature is limited to about 50 ° C.

That is, these conventional DC current sensors are:
All have large magnetic cores, so they are heavy and large in size.The positional relationship between the DC conductor and the sensor window affects the measurement accuracy, and the effects of external magnetic fields such as terrestrial magnetism cannot be ignored. Various considerations are required and handling is inconvenient. In general, it is undeniable that these conventional DC current sensors have been left out of the trend of microelectronics in recent years, and because they have a structure in which miniaturization and high functionality are delayed, and it is difficult to increase productivity, It has not been able to meet the demand for lower prices.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light-weight and easy-to-handle DC current sensor that does not require a large annular magnetic core magnetic path.

[0010]

An object of the present invention is to provide an even number of magneto-electric sensors for detecting the strength and direction of a local static magnetic field in a space on a circumference equidistant from the center axis of a conductor through which a current to be measured flows. The DC current according to the present invention, wherein the converters are arranged at equal intervals with the detection axis direction of each magneto-electric converter facing the same circumferential direction, and the output signals of each magneto-electric converter are added by an adder and taken out. This can be achieved by a sensor (hereinafter, referred to as “the present sensor”).

Consider any closed path that goes around the DC conductor. Assuming that the strength of the magnetic field measured at each point on the path is H and the angle between the magnetic field vector and the tangent direction of the path is θ, the circuit integral value of Hcos θdl (dl is a differential path) calculated over the path is the path It is equal to the algebraic sum I of the current interlinking.
This is Ampere's orbital integration law that is the operating principle of this sensor. However, this rule is based on Hcos at each point on the route.
While it is assumed that the value of θ is measured sequentially and continuously, this sensor uses Hcos observed at a finite number of measurement points.
The difference is that the linkage current I is obtained based on the value of θ. The magnetoelectric converter for measuring the value of Hcos θ will be described later.

Due to the difference between the Ampere's law and the configuration of the present sensor, the orbital integration path in the present sensor is not an arbitrary path, and a specific path on which the magnitude of the magnetic field H is as constant as possible is selected. I have to. The specific path is a circle equidistant from the central axis of the conductor. When the cross-sectional shape of the conductor is a circle, the shape of the lines of magnetic force around the circumference is also a circle, and the magnetic field strength H is constant on the circumference and θ = 0.
It is. Therefore, in this case, the linkage current I can be accurately obtained even by the present sensor using a finite number of magnetic field measurement values.

In the case of a conductor having an irregular cross section other than a circle,
The shape of the lines of magnetic force around the periphery is not always a circle. For example, in the case of a strip-shaped bus bar having a rectangular cross section, the shape of the line of magnetic force becomes elliptical near the conductor. In this case, the circle as the orbital integration path in the present sensor intersects the ellipse of the line of magnetic force, and the value of Hcos θ on the circumference does not become constant. Therefore, interpolation is required in the middle of the measurement points. In this sensor, the number of magnetoelectric transducers arranged on the circumference is increased as much as possible, and the algebraic sum of the measured values at each measurement point is replaced with the interpolation calculation. The diameter of the circle is made as large as possible in order to take advantage of the fact that the shape of the magnetic field lines approaches the circle as the distance from the circle increases.

In the present sensor, in principle, each magnetoelectric converter is arranged so as to coincide with a circular line of magnetic force around the conductor.
However, an installation error may occur when the present sensor is installed, and the center axis of the present sensor may not coincide with the center axis of the conductor. In order to cope with such a case, in the present sensor, a pair of magneto-electric converters are arranged axially symmetric with respect to the center axis of the sensor (therefore, the number of magneto-electric converters used in the present sensor is an even number). (Actually, all the magneto-electric converters) are added and calculated. As a result, the detected values of the individual magnetoelectric converters with errors are averaged to cancel the errors, and as a result, the influence of the installation errors is reduced. Thus, in the present sensor, the tolerance for the installation error can be increased.

Further, this type of DC current sensor needs to have a structure that is hardly affected by geomagnetism or external magnetism generated by a device or a wiring that handles a large external current.
Since these external magnetisms are caused by currents existing outside the circle as the circuit integration path in the present sensor, it can be said that they do not affect the circuit integration value from the Ampere's law. However, in this sensor, as described above, the value of the magnetic field that should be continuously measured along the orbital integration path is substituted by a finite number of measured values, so it is necessary to consider the influence of external magnetism resulting from this. is there.

In this case as well, a countermeasure is to arrange the magnetoelectric converter at an axially symmetric position with respect to the central axis of the present sensor. When the magnetic field lines of the external magnet penetrate through the sensor, the external magnetic field detected by a certain magneto-electric converter is the other magneto-electric converter located at a position substantially symmetrical with respect to the diameter of the circle where the magnetic field lines intersect at right angles. Since the magnetic field acts as a magnetic field having almost the same magnitude and being almost opposite to each other, the output signals of the pair of magnetoelectric converters are additively taken out so that the two cancel each other out, and the influence of external magnetism is not removed. Can be reduced. The above-described cancellation effect is expected to increase as the number of magnetoelectric converters arranged on the circumference increases.

It is necessary to be able to cope with the installation error and the external magnetism in any direction of 360 ° with respect to the present sensor. In order to meet this demand, in the present sensor, the magnetoelectric converters are arranged at equal intervals on the circumference.

As described above, in the present sensor, the influence of external magnetism is substantially reduced by arranging an even number of magnetoelectric converters on the circumference at an equal distance from the center axis of the conductor and at equal intervals. And the effect of installation errors can be reduced, so a large annular core used in conventional DC current sensors for such a purpose can be omitted, making it lightweight and easy to handle. A simple direct current sensor can be realized.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (a) As a preferred embodiment of the present invention, a magnetoelectric converter used in the present sensor will be described.

The magnetoelectric converter used in the present sensor is capable of detecting Hcos θ from the magnitude H of the static magnetic field at the place where the sensor is arranged and the angle θ between the magnetic field vector and the axial direction (direction of maximum sensitivity). Any principle and format are possible. There are many magnetoelectric converters having such characteristics, and examples thereof include a magnetoresistance effect element, a Hall effect element, and a saturable core type magnetic field detector.

Among these, a direct current sensor using a saturable core type magnetic field detector was filed by the present inventors as an inventor and filed as a patent application (1997 Patent Application No. 118832).
, The description is omitted in this specification.

The magnetoresistive effect element utilizes a phenomenon (magnetoresistive effect) that when a current is applied to a ferromagnetic material and a magnetic field is applied simultaneously, the electric resistance of the ferromagnetic material increases with the magnetic field. The magnetoresistance effect is maximum when the current and the magnetic field are parallel and minimum when the current and the magnetic field are orthogonal. The responsivity of a magnetoresistive element using a ferromagnetic thin film is high enough to be used in a read head of a storage device for a computer, but does not itself have a function of determining the polarity of a magnetic field. However, as shown in FIG. 2A, a bridge is formed by arranging magnetoresistive elements on four sides a to d, and a bias magnetic field is applied by a permanent magnet in a diagonal direction of the bridge as shown in FIG. 2B. By doing
The polarity of the measured magnetic field applied in the other diagonal direction of the bridge can be determined.

That is, when the magnetic field to be measured 1 is directed downward from above in FIG. 2B, the combined magnetic field 1 with the bias magnetic field points diagonally downward and to the right, and intersects sides a and c of the bridge to each of these sides. The resistance value of. Conversely, when the magnetic field to be measured 2 is directed upward from the bottom in the figure, the combined magnetic field 2 with the bias magnetic field points diagonally to the upper right and crosses the b and d sides of the bridge to reduce the resistance values of these sides. Therefore, the bridge a,
It can be seen that the potential difference between the middle point of the b side and the middle point of the c and d sides is reversed depending on the direction of the magnetic field to be measured. As a result, the relationship between the direction of the magnetic field to be measured based on the direction of the bias magnetic field and the output terminal voltage of the magnetoelectric converter has a relationship as shown in FIG. In this sensor, the direction of 90 ° along the plane of the bridge with respect to the bias magnetic field is defined as the detection axis direction of the magnetoelectric converter.

By configuring the bridge in this way, not only can the polarity of the magnetic field to be measured be determined,
The effect of the temperature change of the magnetoresistive element and the fluctuation of the bridge power supply voltage can be reduced, and the magnetic field detection sensitivity can be increased. Since a magnetic-electric converter commercialized with such a configuration is easily available on the market, the present sensor can be assembled using this.

The Hall effect element utilizes a phenomenon (Hall effect) that, when a current flows in a semiconductor and a magnetic field is applied simultaneously, an electric field proportional to the magnitude of the current and the magnetic field is generated in a direction perpendicular to both the current and the magnetic field. I do. The Hall effect element has a high-speed response, and is used as a control element of a brushless DC motor by utilizing its characteristics. Since the Hall effect element itself has a function of detecting the direction of the magnetic field vector, it can be used as it is as a magnetoelectric converter in the present sensor. It should be noted that the Hall effect of a semiconductor generally has a relatively large temperature coefficient, and that a change in current flowing through the semiconductor directly appears in an output signal.

Since magnetic sensors are evolving, there is a possibility that magneto-electric converters that can be used for the present sensor may appear in the future, but since this sensor is mainly used in unmanned DC substations, etc. It is a particularly important condition that the structure is simple and the reliability is high. In addition, in this sensor, the output signal of each magneto-electric converter is taken out additively.At this time, the input impedance of the adder is adjusted so that the taking out of the signal does not cause interference of each magneto-electric converter or adversely affect the performance. It needs to be high enough.

Further, other preferred embodiments of the present invention include the following (b) to (f).

(B) The number of magnetic field detectors constituting the present sensor is at least 4, more preferably 6 or more and 24 or less.

As described above, the principle of operation of the present sensor is the circuit-integral law of amperes. However, the sensor differs from amper's law in that the interlinkage current I is obtained based on a finite number of measured values. Due to this difference, the installation error (eccentricity) and the effect of external magnetism, which should not be affected, cannot be ignored. In order to reduce this weak point as much as possible, it is necessary to provide an even number of magnetoelectric converters arranged on the circumference, which is a circular integration path of the present sensor, and to increase the number as much as possible. From that point of view, at least four, four, and six are more desirable. On the other hand, since the magnetoelectric converter has a fixed size, there is a limit to the number that can be accommodated on the circumference. Considering that the diameter of the circle of the present sensor is actually about 20 to 40 cm, the upper limit is considered to be about 20 to 24.

(C) A test magnetic field generating coil provided coaxially with the detection axis in contact with the tip of each magnetoelectric converter constituting the sensor.

It is desirable to be able to test occasionally in order to ensure that the magnetoelectric converters making up the sensor are always functioning satisfactorily. For this purpose, in the present embodiment, a test magnetic field generating coil is installed coaxially with each magneto-electric converter, and a predetermined current is simultaneously applied to each test coil at regular time intervals to check the output voltage of the present sensor.

(D) Each magneto-electric converter is fixed to a regular polygonal or annular non-magnetic yoke having a number of sides equal to the number of magneto-electric conversion fields constituting the sensor.
Cover the whole with an insulating material.

As described above, the present sensor does not have a large magnetic core, and each magnetoelectric converter is arranged in the space on the circumference.
Each magneto-electric converter is fixed to an annular yoke made of a non-magnetic material so as to be supported in this space, and the whole is covered with an insulating material to protect each magneto-electric converter from a high DC voltage. For example, aluminum is used as the non-magnetic material, and AB is used as the insulating material.
Resins such as S or various rubbers are exemplified.

(E) The entirety of the present sensor can be divided into two symmetrical parts with respect to the diameter.

When installing the present sensor, it is necessary to penetrate the conductor for the current to be measured through the center hole of the present sensor. However, if the present sensor has a split structure as in the present embodiment, the work is omitted. It can be done easily.

(F) Two sets of the DC current sensors are arranged close to each other around the conductor, and the output values of the two sets of DC current sensors are constantly or intermittently compared, and a difference between the output values is a predetermined value. Output an alarm signal when exceeding.

According to the present embodiment, a DC current measurement system is provided in which two sets of the present sensor are compared with their output values constantly or intermittently and a comparison alarm device which issues an alarm when a problem occurs. Will do. As a result, the reliability of the value measured by the present sensor can be improved. FIG. 4 shows an example of the configuration of such a DC current measurement system.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present sensor using a magnetoelectric converter comprising a magnetoresistive element will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view showing the external shape and installation state of a DC current sensor (reference numeral 100) having a rated current of 20 KA according to the present embodiment. FIG. 2A is an internal connection of a magnetoresistive effect type magnetoelectric converter used in the sensor 100. FIG. 2B is a diagram showing the relationship between the bias magnetic field and the magnetic field to be measured, and FIG. 2C is a diagram showing the relationship between the direction of the magnetic field to be measured and the output voltage of the magnetoelectric converter.

In FIG. 1, reference numeral 1 denotes a yoke, 2 denotes a magnetoresistive magnetoelectric converter, 3 denotes a lead wire, 4 denotes a circuit unit, 5 denotes a dividing line for dividing the sensor 100 into two symmetrical parts, 6 Denotes a bus bar as a conductor through which a current to be measured flows (indicated by a dotted line because it is outside the present invention). The sensor 1
The casing made of an insulating material covering the entire 00 is not shown. Since the contents of FIG. 2 have already been described above, the description will not be repeated.

As shown in FIG. 1, an even number (six in this embodiment) of magnetoresistive effect type magnetoelectric converters 2 are equidistant from the axis of the bus bar 6 in the groove of the yoke 1 forming an annular shape. They are supported in a space on the circumference and are arranged at equal intervals with the detection axes directed in the same circumferential direction. The DC current flowing through the bus bar 6 forms an elliptical static magnetic field in the vicinity thereof and a substantially concentric static magnetic field in a slightly distant place, and each magnetoelectric converter 2 outputs an output signal proportional to the strength of the static magnetic field. Since the yoke 1 can be divided into two parts symmetrical with respect to the dividing line 5 passing through the diameter, the operation of passing the bus bar 6 through the center hole of the yoke 1 can be easily performed. Each magnetic-electric converter 2 may be provided with a test magnetic field generating coil shown in FIG.

Each magnetoelectric converter 2 is connected to a circuit section 4 by a lead wire 3, and the circuit section 4 is provided with an addition operation circuit (not shown), a voltage-current conversion circuit, and a power supply circuit.
The addition operation circuit algebraically adds the output signals of the six magnetoelectric converters 2, and the voltage-current conversion circuit generates a current proportional to the added output voltage. The power supply circuit supplies a necessary power supply voltage to the addition operation circuit, the voltage-current conversion circuit, and each of the magneto-electric converters 2.

FIG. 3 shows a test magnetic field generating coil 7 provided at the tip of each magnetoelectric converter 2. A required power supply voltage is supplied to the coil 7 from an external power supply 8 via a switch 9. When the switch 9 is closed, the coil 7 generates a test magnetic field. The output of each of the magnetoelectric converters 2 that has detected the test magnetic field is processed by the circuit unit 4 and inspected for normality. Note that the switch 9 can be manual or automatic. When the switch 9 is an automatic switch, the above-described inspection of whether or not the switch 9 is normal may be automated, and this and the automatic switch may be linked.

In the above-described embodiment, an example using a magnetoelectric converter made of a magnetoresistive effect element has been described. However, the present invention is not limited to this, and a magnetoelectric converter using a Hall effect element or other elements may be used. However, it goes without saying that the DC current sensor of the present invention can be similarly configured.

[0044]

According to the first to third aspects of the present invention, in the present sensor, even if the position of the current conductor to be measured is eccentric from the center of the circle where the magnetoelectric converter is disposed, the effect is canceled out and reduced. In addition, the influence of geomagnetism and external magnetism crossing the circle is also reduced, eliminating the need for a large magnetic core found in conventional semiconductor element type current sensors, and providing a highly accurate, lightweight, and easy-to-handle DC current sensor. Provided. In addition, the response time is much faster than that of the conventional Kramer type current sensor, and even if the direction of the current in the conductor is different from the expected one, it can be dealt with only by reversing the connection polarity of the output terminal.

According to the fourth aspect of the present invention, when the number of magneto-electric converters in the present sensor is four or more, the effect of canceling the eccentricity of the conductor for current to be measured is smaller than when the number is less than four. The effect of canceling out the effects of magnetism becomes more certain,
Moreover, the larger the number, the more advantageous. However, considering that there is a limit to the number of magnetoelectric converters that can be accommodated on the circumference, a value of 6 to 24 gives a practical range of the number of magnetoelectric converters in the present sensor.

According to the fifth aspect of the present invention, a test magnetic field generating coil is installed in each of the magneto-electric converters in the present sensor, and a short-time test is performed at regular time intervals. Functioning can be guaranteed.

According to the sixth aspect of the present invention, the magnetoelectric converter in the present sensor is supported by the annular yoke made of a nonmagnetic material, so that each magnetoelectric converter is equidistant from the axis of the current conductor to be measured. It can be fixed in a space on a certain circumference. In addition, by covering the whole with an insulating material, each magnetoelectric converter can be protected from high DC voltage.

According to the seventh aspect of the present invention, since the present sensor has a split structure, it is easy to penetrate the conductor for current to be measured through the center hole of the present sensor when installing the present sensor. be able to.

According to the eighth aspect of the present invention, if there is a problem by comparing the output values of the two sets of present sensors constantly or intermittently and an alarm is issued, the reliability of the measurement result of the DC current by the present sensors is improved. Can be improved.

In summary, according to the present invention, there is provided a DC current sensor having a new structure, which is lightweight, inexpensive, has high accuracy and high responsiveness, and is hardly affected by an external magnetic field and an installation error. Many problems of the conventional current sensor can be solved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an external shape and an installation state of a DC current sensor as an embodiment.

FIG. 2 is a diagram showing an internal connection diagram of a magnetoresistive effect type magnetoelectric converter and a diagram showing a relationship between a bias magnetic field and a magnetic field to be measured.

FIG. 3 is a diagram showing an installation state of a test magnetic field generating coil.

FIG. 4 is a block diagram showing a configuration example of a DC current measurement system based on the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Yoke 2 ... Magnetoelectric converter 3 ... Lead wire 4 ... Circuit part 5 ... Division line 6 ... Bus bar (outside the present invention) 7 ... Test magnetic field generating coil 8 ... Power supply of test magnetic field generating coil 9 ... Switch

Continued on the front page (72) Inventor Tsuyoshi Nagata 7-32-6 Nishikamata, Ota-ku, Tokyo Inside the Makome Laboratory Co., Ltd.

Claims (8)

[Claims] An even number of magnetoelectric converters for detecting the intensity and direction of a local static magnetic field are provided in a space on a circumference equidistant from a central axis of a conductor through which a current to be measured flows. A DC current sensor wherein the detection axis directions are arranged at equal intervals in the same circumferential direction, and the output signals from the respective magneto-electric converters are added by an adder and taken out. 2. The direct current sensor according to claim 1, wherein said magnetoelectric converter comprises a magnetoresistance effect element. 3. The DC current sensor according to claim 1, wherein said magnetoelectric converter comprises a Hall effect element. 4. The method according to claim 1, wherein the number of the magnetoelectric converters is at least four,
The direct current sensor according to any one of claims 1 to 3, wherein the number is more preferably 6 or more and 24 or less. 5. The DC current sensor according to claim 1, further comprising a test magnetic field generating coil provided in contact with a tip of each of the magnetoelectric converters and coaxial with an axis of the magnetoelectric converter. 6. Each of the magnetic field detecting elements is fixed to a regular polygonal annular or annular yoke made of a nonmagnetic material having the number of sides equal to the number of the magnetoelectric converters, and the whole is covered with an insulating material. The direct current sensor according to any one of claims 1 to 5, comprising: 7. The direct current sensor according to claim 6, wherein the entirety of the sensor can be divided into two symmetrical portions with respect to a diameter. 8. Two sets of DC current sensors according to claim 1 are arranged close to each other around said conductor, and the output values of these two sets of DC current sensors are constantly or intermittently output. A DC current measurement system that outputs an alarm signal when the difference exceeds a predetermined value.