JP3326737B2 - DC current sensor - Google Patents

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 of a static magnetic field detection type, and more particularly to a light and small DC current sensor for measuring a large DC current.

[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, Kramer type DC current transformers and current sensors using magnetoelectric converters such as Hall elements have been widely used. ing. 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 rectangular magnetic characteristics are provided around a DC conductor, windings having the same number of windings are wound around each magnetic core, and connected in anti-series with each other. 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 detection current is full-wave rectified to obtain a DC current or voltage as a current transformation output.

In a current sensor using a Hall element or the like, a magnetic path of an annular magnetic core is provided around a DC conductor, a gap is provided in a part of the magnetic path, and a Hall element or a magnetoresistive element is placed therein. Since the magnetization of the magnetic path due to the current to be measured is kept in the unsaturated region, 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 Kramer-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 current sensor using a Hall element or the like, the magnetic core becomes large because the magnetization of the magnetic path is limited to an unsaturated region.
The structure is complicated because a Hall element or the like is embedded in the magnetic core.
Further, since the durability temperature of a semiconductor element such as a Hall element is not high, there is a weak point such that the upper limit of the operating temperature is limited to about 50 ° C.

That is, these conventional DC current sensors are:
Since both have large magnetic cores, they are heavy and large in size, and the positional relationship between the DC conductor and the sensor window affects the measurement accuracy, and it is necessary to consider external magnetic fields such as geomagnetism.
Inconvenient handling during installation work. In general, it cannot be denied that these conventional DC current sensors have been left out of the trend of microelectronics in recent years.
Because of its structure that has been delayed in enhancing its functions and it is difficult to increase its productivity, it has not been able to meet the demand for lower prices.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional current sensor, so that it has a small size, light weight, low cost, high accuracy and high response, and is hardly affected by an external magnetic field. Another object of the present invention is to provide a DC current sensor having a new structure that can be used stably in a wide temperature range.

[0010]

The object of the present invention is to detect an even number of local static magnetic fields in the sensor axis direction in a space on the circumference equidistant from the axis of a conductor through which a current to be measured flows. This is achieved by arranging the saturable core type magnetic field detectors at equal intervals with the detector axes directed in the same circumferential direction, and adding and outputting the output voltages of the respective magnetic field detectors in series.

One of the features of the direct current sensor (hereinafter referred to as the present sensor) of the present invention is that a large magnetic core is not required. Therefore, it is small and lightweight and easy to handle. The key to enabling such a basic structure lies in the adoption of a saturable core type magnetic field detector that detects a local static magnetic field. This magnetic field detector was originally developed and used as a non-contact position sensor combined with a magnet.
No. 24269 and Japanese Patent Publication No. 7-21536). The present inventors have paid attention to the static magnetic field detection performance, have made further improvements for use in the present sensor, and have completed the present invention.

The structure and operating principle of the saturable core type magnetic field detector will be described with reference to FIG. FIG. 2A is a simplified internal connection diagram of a saturable core type magnetic field detector, and FIG. 2B is a BH curve of the core.

In FIG. 2A, each pair of saturable cores having the same shape, the same size, and magnetically shielded from each other has dimensions of, for example, about 3 mm wide × 5 mm long × 0.1 mm thick. . Coils L1 and L2 are wound in the long side direction of each core, and are excited by pulse currents I1 and I2 of about 1 MHz. The directions of excitation of the respective cores are opposite to each other, and the magnitude of the excitation magnetic field is set to a level immediately before saturation in the absence of the detected magnetic field Hex. Magnetic field H to be detected going from right to left in the figure
ex in the direction of the long side of each core shown in the upper and lower positions in the figure, the magnetic field by excitation and the detected magnetic field He
Since x and x act in the same direction, they are added, and in the core on the lower side, the addition is subtracted.

This state will be described with reference to the BH curve in FIG. The upper core becomes the saturation magnetization by adding the excitation magnetic field and the magnetic field to be detected Hex, and the peak of the magnetization pulse by the excitation is cut by an amount corresponding to the DC magnetization by the magnetic field to be detected Hex. Conversely, in the lower core, the magnetization pulse due to excitation oscillates in the negative direction in the range of non-saturation starting from the portion corresponding to the DC magnetization due to the detected magnetic field Hex. Such a difference in the magnetization state in each core causes a difference in the inductance of the exciting coils L1 and L2. In the state described, the inductance of the coil L1 is smaller than the inductance of the coil L2, and the difference is proportional to the magnitude of the detected magnetic field Hex. Therefore, as shown in FIG. 2A, currents I1 and I2 flowing through L1 and L2 are detected by detection rectifiers D1 and D2, respectively.
By terminating the load capacitors C1 and C2 and the resistors R1 and R2 having the same value, the difference between the two DC voltages V1 and V2 respectively generated is proportional to the magnitude of the detected magnetic field Hex.

When a high-frequency pulse of about 1 MHz is used as the excitation pulse to increase the response speed, a large excitation current must be applied to excite each core to a state just before saturation as described above. Instead, a large-capacity high-frequency pulse oscillator is required. In order to improve this point, it is conceivable to arrange a permanent magnet in contact with the short side of each core, and to apply a bias magnetic field in the direction of each exciting magnetic field in advance. Japanese Patent Publication No. 21536/1995 relates to such an improvement.

As can be seen from the above description, the saturable core type magnetic field detector has sensitivity to only the magnetic field to be detected in this direction, with the long side direction of each core wound with the exciting coil as the axial direction of the detector. And the circuit is configured in a symmetrical bridge type, so that a response voltage of the opposite polarity is applied to the detected magnetic field in the opposite direction. Further, since this magnetic field detector uses an excitation pulse of about 1 MHz, the response time is as fast as about 5 milliseconds. In this sensor, an even number of magnetic field detectors having such characteristics are placed at equal intervals in a space on the circumference that is equidistant from the axis of the conductor through which the measured current flows, with the detector axes oriented in the same orbit. And the output voltages of the respective magnetic field detectors are added in series to form an overall output signal.

The present sensor configured as described above has the following features in addition to the feature that a large magnetic core is not required as described above. In other words, even if the position of the current conductor to be measured is eccentric from the center of the circle, an even number of magnetic field detectors are arranged at equal intervals on the circumference, and their outputs are added, so that the effects are offset. That the influence of geomagnetism and external magnetic fields crossing the circle is also reduced for the same reason, and that the current measurement accuracy is less than ± 1% of the rated value, which is higher than the conventional one. The response time is much faster than that of the conventional one. Even if the direction of the current on the conductor is different from the expected one, it can be handled only by reversing the connection polarity of the output terminal. -10 ° C ~ +
About 60 ° C., which is wider than conventional ones.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention include the following (a) to (d). (A) The number of magnetic field detectors constituting the present sensor is at least 4, more preferably 6 or more and 12 or less.

(B) A test magnetic field generating coil provided coaxially with the detector axis in contact with the tip of each magnetic field detector constituting the present sensor.

(C) fixing each magnetic field detector to a regular polygonal annular or annular yoke made of a nonmagnetic material having the same number of sides as the number of magnetic field detectors constituting the present sensor;
Cover the whole with an insulating material.

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

Embodiment (A) relates to the number of magnetic field detectors constituting the present sensor. As described above, in order to reduce the influence of the case where the position of the current conductor to be measured is decentered from the center of the circle and the influence of the external magnetic field by canceling the output voltages of the respective magnetic field detectors, the magnetic field must be reduced. It is desirable that the number of detectors is four or more. In the case of two, the canceling effect works effectively only on the eccentricity on the diameter connecting the magnetic field detectors, but has little effect on other eccentricities. The influence of the external magnetic field can be effectively canceled even in the case of two magnetic fields since the external magnetic fields in the respective magnetic field detectors are substantially opposite in direction and have substantially the same magnitude.

In the case where the number of magnetic field detectors is four or more as compared with the case where the number of magnetic field detectors is two, the number of reference diameters increases, so that the effect of offsetting the displacement of the conductor position becomes more reliable. The same applies to the cancellation of the influence of external magnetism. From this viewpoint, the number of magnetic field detectors is better as long as it is an even number, and it can be said that at least four magnetic field detectors are more preferable than four. On the other hand, the number of magnetic field detectors that can be accommodated on the circumference is limited because of its size. Considering that the diameter of the circle of the actual sensor is about 10 to 20 cm, the upper limit is considered to be about 12 pieces.

Embodiment (b) relates to the installation of a test magnetic field generating coil. It is desirable to be able to test occasionally to ensure that the magnetic field detectors that make up the sensor are always functioning satisfactorily. For this purpose, a test magnetic field generating coil is individually installed in each magnetic field detector, and a predetermined current is simultaneously applied to each test coil at regular time intervals.
It is conceivable to check the output voltage of this sensor.

Embodiment (c) relates to the external structure of the present sensor. As described above, this sensor does not have a large magnetic core, and each magnetic field detector is arranged in the space on the circumference, but is made of a non-magnetic material in order to support each magnetic field detector in this space. It is fixed to an annular yoke, and the whole is covered with an insulating material to protect each magnetic field detector from a high DC voltage. The non-magnetic material includes, for example, aluminum, and the insulating material includes, for example, rubber.

Embodiment (d) relates to making the present sensor into a split structure. 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, the operation can be easily performed.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present sensor 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. 2 is a simplified internal connection diagram of a saturable core type magnetic field detector used in the sensor 100. (A) and FIG. (B) showing a BH curve of the saturable core.

In FIG. 1, reference numeral 1 denotes a yoke, 2 denotes a saturable core type magnetic field detector, 3 denotes a lead wire, 4 denotes a circuit unit, 5 denotes a dividing line for dividing the sensor 100 into two symmetrical portions, 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 saturable core type magnetic field detectors 2 are equidistant from the axis of the bus bar 6 in the groove of the hexagonal yoke 1. It is supported in a space on a certain circumference, and is arranged at equal intervals with the detector axes directed in the same circumferential direction. The DC current flowing through the bus bar 6 creates a concentric static magnetic field around the bus bar 6, and the respective magnetic field detectors 2
Outputs a voltage 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 field detector 2 may be provided with a test magnetic field generating coil shown in FIG.

Each magnetic field detector 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, a voltage-current conversion circuit, and a power supply circuit (not shown).
The addition operation circuit adds the output voltages of the six magnetic field detectors 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 magnetic field detector 2.

FIG. 3 shows a test magnetic field generating coil 7 provided at the tip of each magnetic field detector 2. A desired 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 magnetic field detector 2 that has detected the test magnetic field is processed by the circuit unit 4 and then checked 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.

[0032]

According to the first aspect of the present invention, since the present sensor does not require a large magnetic core, it is small and lightweight and easy to handle. In addition, even if the position of the current conductor to be measured is eccentric from the center of the circle where the saturable core type magnetic field detector is arranged, the influence is offset and reduced, and terrestrial magnetism or external magnetic field crossing the circle The effect is also reduced, so the accuracy is high, the response time is much faster than the conventional one, and even if the direction of the current in the conductor is different from the plan, the connection polarity of the output terminal is changed. It has features that it can be dealt with simply by reversing it and that the service temperature can be broadened to about -10 ° C to + 60 ° C.

According to the second aspect of the present invention, when the number of saturable core type magnetic field detectors in the present sensor is four or more,
The effect of canceling out the eccentricity of the measured current conductor and the effect of the influence of the external magnetism are more reliable as compared with the case where the number is smaller, and the larger the number, the more advantageous. However, considering that there is a limit to the number of magnetic field detectors that can be accommodated on the circumference, a value of 6 to 12 provides a practical range of the number of magnetic field detectors in the present sensor. .

According to the third aspect of the present invention, a test magnetic field generating coil is installed in each of the saturable core type magnetic field detectors in the present sensor, and a short-time test is performed at regular time intervals. It can be ensured that the detector is always functioning satisfactorily.

According to the fourth aspect of the present invention, the saturable core type magnetic field detector in the present sensor is supported by the annular yoke made of a non-magnetic material, so that each magnetic field detector has the axis of the current conductor to be measured. Can be fixed in a space on the circumference that is equidistant from. Further, by covering the whole with an insulating material, each magnetic field detector can be protected from a high DC voltage.

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

In summary, according to the present invention, a new structure having a small structure, light weight, low cost, high accuracy, high responsiveness, less susceptible to an external magnetic field, and stable use over a wide temperature range. A DC current sensor is provided, which overcomes many of the problems with conventional current sensors.

[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 a simplified internal connection diagram of a saturable core type magnetic field detector and a BH curve of a saturable core.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Yoke 2 ... Saturable core type magnetic field detector 3 ... Lead wire 4 ... Circuit part 5 ... Division line 6 ... Bus bar (outside the present invention) 7 ... Test magnetic field generating coil 8 ... Test magnetic field generating coil power supply 9 ... Switch L1, L2 ... Coil I1, I2 ... Exciting current D1, D2 ... Detection rectifier R1, R2 ... Terminating resistor C1, C2 ... Capacitor V1, V2 ... Detection rectifier output voltage P ... Excitation pulse current source A ... Differential voltage amplifier

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Uegaki 2-9-9 Kitasato, Sagamihara City, Kanagawa Prefecture Showa Electronics Co., Ltd. (72) Inventor Tsuyoshi Nagata 7-32-6 Nishikamata, Ota-ku, Tokyo Co., Ltd. Inside the Makome Laboratory (56) References JP-A-54-115174 (JP, A) JP-A-3-18765 (JP, A) JP-A-7-333263 (JP, A) JP-A-52-101419 (JP, A) A) Japanese Utility Model Showa 51-24269 (JP, U) Japanese Utility Model Hei 7-20572 (JP, U) Japanese Patent Publication 7-21536 (JP, B2) Japanese Utility Model Showa 40-16820 (JP, Y1) (58) Survey Field (Int.Cl. ⁷ , DB name) G01R 15/20 G01R 19/00

Claims (5)

(57) [Claims] An even number of saturable core type magnetic field detectors for detecting an even number of local static magnetic fields in the axial direction of a detector in a space on a circumference equidistant from an axis of a conductor through which a current to be measured flows. A DC current sensor, wherein detector axes are arranged at equal intervals in the same circumferential direction, and output voltages of the magnetic field detectors are added in series and output. 2. The method according to claim 1, wherein the number of the magnetic field detectors is at least four,
More preferably an even number of 12 or less 6 or more, the DC current sensor of claim 1, wherein. 3. 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 said magnetic field detectors and coaxial with a detector axis. 4. Each of the magnetic field detectors is fixed to a regular polygonal or annular non-magnetic yoke having a number of sides equal to the number of the magnetic field detectors, and the whole is covered with an insulating material. The direct current sensor according to any one of claims 1 to 3, comprising: 5. The direct current sensor according to claim 1, wherein the entirety of the sensor is dividable into two symmetrical portions with a diameter as a boundary.