JPH02203279A - Detector for minute current - Google Patents

Abstract

PURPOSE:To detect sensitively and accurately with a small and lightweight device by setting an exciting current based on a high frequency excitation part in the neighborhood of a residual magnetic flux density of magnetic hysteresis curve for an iron core and utilizing the change of incremental permeability caused by the magnetic field. CONSTITUTION:The high frequency excitation part 12 in which a high frequency excitation coil 7 is connected to a high frequency power supply 11 through e.g. a half-wave rectifying circuit with a rectifier 8 and a detection resistor 9 matched with a reactance of the iron core part, is provided in the iron core 1a. An output part 15 connected with a low-pass filter 13 and a DC removing device 14 in order is formed with the resistor 9. When the magnetic field generated from a current i0 to be detected which is made to flow in a conductor 2a passing through a center hole of the iron core 1a is applied, the change of reactance for the coil 7 according to the change of magnetic flux is abundantly appeared. So, with the condition that the magnetic field generating from the excitation part 12 is always being applied, the change of reactance according to the whole fluxes at the time when a minus hysteresis is moved thereto by the magnetic field generated from the current i0, is detected. Further by means of removing 13, 14 high frequency and DC parts, an output voltage having the correct current waveform to be detected can be taken out from the output part terminal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is used in zero-phase current detectors, various leakage current detectors, etc., and uses the magnetic phenomenon of the iron core to electrically contactless and small The present invention relates to a device for detecting current.

[Conventional technology]

2. Description of the Related Art Zero-phase current transformers used in earth leakage circuit breakers, earth leakage protection II/IJ circuits, etc. are known as devices that electrically and non-contact detect small currents. FIG. 12 is a schematic diagram for explaining the principle of a zero-phase current transformer. As shown in Fig. 12, the zero-phase current transformer consists of two conductors 2 passing through the center hole of an annular iron core 1 with high magnetic permeability, and a resistor 4 connected to both ends of a detection coil 3 wound around the iron core. and both ends of the conductor 2 are connected to an AC power source 5.
, is connected to the load 6. Under normal conditions, the current flowing through the two conductors 2 is a round trip current 11.112 whose direction is indicated by the arrow.
Since the values of are the same and the directions are opposite, the iron core 1 is not magnetized and no voltage is induced in the detection coil 3. When a leakage occurs on the load 6 side, the value of the current 11 + I2 changes and the difference current magnetizes the iron core 1. This induced voltage causes current to flow through the small resistor 4, and the voltage drop across the small resistor 4 is converted into a control signal. It can be done. Although Fig. 12 shows a single-phase case, in the case of a three-phase case, the conductor 2 can be expressed as three.
The principle is the same as single phase.

Since the detection current of this zero-phase current transformer is small, Fe-
Even if a high magnetic permeability material such as N metallurgy (trade name Permalloy) is used, the detected magnetic field is small as shown in the magnetization curve shown in Figure 13, so the obtained magnetic flux is also low (and the voltage induced in the detection coil 3 is very low). Therefore, it is preferable that such a zero-phase current transformer has even higher sensitivity, and depending on the equipment used, there is a strong desire for miniaturization.

[Problem to be solved by the invention]

However, in order to increase the sensitivity of a zero-phase current transformer having one or more structures and to detect even lower currents, there are the following problems. To increase the output voltage, for example, you can increase the magnetic path cross-sectional area of iron core 1 as shown in Fig. 12, or replace conductor 2 with iron core 1.
There is a method of increasing the magnetic field applied to the iron core 1 by winding the conductor 2 a large number of times, but increasing the magnetic path cross-sectional area of the iron core 1 naturally leads to an increase in the size of the device.
The reason for increasing the number of turns around iron core 1 is that the wire diameter is increased because [fi of the main circuit flows through this conductor 2, and similarly, the size of iron core l is thick (unavoidable). .

Therefore, the usual method is to pass the conductor 2 through the center hole of a small iron core 1, increase the number of turns of the detection coil 3, and amplify the induced voltage using an electronic circuit.

As mentioned above, increasing the core cross-sectional area and the number of windings of the detection coil will also increase the size of the detection part, l1m, but in recent years (i141 girder placement, protection g&placement, measuring devices, etc.) have become smaller due to advanced electronicization, Along with this, it is strongly desired that the current detectors used in these devices be made smaller as well.

The present invention has been made in response to the above-mentioned points, and its purpose is to provide a small current detection device that can detect small currents with high sensitivity and precision by reducing the weight of the iron core and the number of windings of the detection coil. It's about doing.

[Means to solve the problem]

The present invention utilizes the fact that the variational magnetic permeability near the t-retention magnetic flux density of the magnetic hysteresis curve of the iron core changes depending on the magnetic field. A high-frequency excitation coil is wound around the iron core, and minor hysteresis is drawn by exciting it with high frequency near the final magnetic flux density of the hysteresis curve. When a small magnetic field due to the current to be detected is added to this state, the minor hysteresis becomes [1
The magnetic flux density range changes, the core actance changes, and the high-frequency excitation current changes, and the small current in the main circuit is determined from the change in the high-frequency excitation current. Note that an appropriate resistor is connected in series to the high-frequency excitation coil so that the output is proportional to the current to be detected.

[Effect]

As described above, the small current detection device of the present invention sets the excitation current (magnetic field) by the high-frequency excitation section near the penetrating magnetic flux density of the magnetic hysteresis curve of the iron core, and utilizes changes in variational magnetic permeability. Even when a small magnetic field is applied due to the current to be detected in the conductor, it is excited at a high frequency, so the reactance changes greatly due to changes in magnetic flux. Therefore, in the device of the present invention, a magnetic field is constantly applied by the high-frequency excitation part, and when the minor hysteresis is moved by the magnetic field caused by the current to be detected in the conductor, the reactance change due to the total magnetic flux is detected. By removing this, it is possible to extract an output voltage with a correct liquid detection current waveform from the output end, and from the above, it is possible to detect small currents with high sensitivity and precision.

〔Example〕

The present invention will be explained below based on Examples.

FIG. 1 is a schematic diagram illustrating the main part configuration of a small current detection device according to the present invention, and this diagram will be explained first. The iron core 1a is made of a material having high magnetic permeability and is formed into a closed magnetic path, for example, in the shape of a ring.

The center of this iron core 1a? The conductor 2a is connected to the power supply of the detected device and the load 1 through h, but illustration of these is omitted. In addition, to detect zero-sequence current, there are two or three conductors 2a, and the difference current between each conductor is used, but the principle is the same as detecting a small current in a single wire, so here In the following, the conductor 2a is represented by one conductor, and the current to be detected whose direction is indicated by an arrow is set to 30, and the following explanation will be made. In FIG. 1, a high-frequency excitation coil 7 is connected to a high-frequency power source 11 in a thick part of the iron core 1a through a half-wave rectifier circuit using a rectifier 8 and an appropriate detection resistor 9 matched with the flux actance of the iron core. An excitation section 12 is provided, and the detection resistor 9 forms an output section 15 to which a low-frequency F wave generator 13 and a DC remover 14 are connected in this order. The DC remover 14 can be easily constructed with a capacitor or an isolation transformer. As described above, the device of the present invention includes a high frequency excitation section 12 having an excitation coil 7 on the iron core 1a, and an output section 15 having a detection resistor 9.
When used, the small current to flowing through the conductor 2a of the device to be detected is passed through the center hole of the iron core 1a.

Next, Figure 2 shows the overall shape of the magnetic hysteresis curve of the iron core 1a, and Figures 3 and 4 are enlarged views of the vicinity of the residual magnetic flux density in Figure 2 for the convenience of the following explanation. Minor hysteresis due to high frequency excitation is added by 11F.

The operation of the apparatus of the present invention will be described below with reference to the apparatus configuration shown in FIG. 1, the magnetic hysteresis curves shown in FIGS. 3 and 4, and other necessary drawings. The iron core 1a is normally excited by the high frequency half-wave rectified current shown in FIG. 5 by the high frequency power supply 11 shown in FIG. 1, the rectifier 8, and the resistor 9.

The relationship between the voltage applied to the iron core 1a, the magnetic flux density, and the excitation current is expressed by the following equation, where the second term is the actance component.

dB Ex = IHR + NHACrt ・・・・・・・・・
・・・・・・・・・・・・ (1) However, El: High-frequency applied voltage IH: High-frequency excitation current R: Value of detection resistor 9 NH: Number of turns of high-frequency excitation coil 7 Ac: Magnetic path cross-sectional area of iron core 1a B :Magnetic flux density t of iron core 11 :Time Here, dB IHR<Island Acrt ・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・(
Under the condition of 2), I) E in 1,,'xc...
... (3).

However, Xc is the reactance of the high frequency excitation coil 7 including the iron core 1a. Note that E+ is kept at a constant value. The magnetization curve shown in FIG. 3 is obtained by excitation under the above conditions. In Figure 3, iron core 1a
The magnetic field draws a minor hysteresis between H and Hl, the magnetic field range is △Ha, and the a flux density range is △Bo. The variational magnetic permeability becomes ΔBo/ΔHa. Conductor 2a here
When a magnetic field of 10Hi is applied, the magnetic field of minor hysteresis moves to H2 and H3 as shown in Figure 3, and the magnetic field range is Δ
H1, the magnetic flux density range becomes Heda. When -Hi is applied to conductor 2a, the magnetic field of minor hysteresis moves to the negative side,
At that time, the magnetic field range is ΔH2 and the magnetic flux density range is ΔB2. The magnetic field of minor hysteresis is △H2<ΔHa<ΔHt ・・・・・・・・・・・・
・・・・・・・・・・・・ ・・・・・・ ・・・(4
). On the other hand, as shown in Figure 3, the change in the magnetic flux density of the minor hysteresis curve becomes smaller as the magnetic field strength increases in the positive direction, so ΔBg>ΔBo>ΔB1・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...(5). Since the high frequency excitation current changes according to ΔB, the current in the conductor 2a can be determined from this change. However, under this condition, the detected current io
and the change in high-frequency excitation current do not have a linear relationship.

A method of establishing a linear relationship between the detected current i0 and the change in the high-frequency excitation current will be described below. In equation (1), (2
) is set to a circuit condition such as an inverse l-square equation.

IHR＞NHACdB・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(6) i When the applied voltage El is kept constant, the excitation current In is expressed by the following equation and becomes a substantially constant value.

XH*E1/R・・・・・・・・・・・・・・・・・・
··········river··············
・・・・・・・・・・・・(V) Figure 4 shows the magnetization curve when excited under these conditions, and the current in the conductor 2a! Magnetic field with minor hysteresis due to 0,
The six values of magnetic flux density are as follows.

ΔHs=Δ1Hs=ΔH4・・・・・・・・・・・・・
・・Moe・・・・・・・・・・・・・・・・・・・
...(8) ΔBe>ΔBs>ΔB4 ...
・・・・・・・・・・・・・・・・・・・・・・・・
(9) Here, Fig. 6 shows a relationship diagram between △) and Hi.

The relationship between ΔH and Hi under the conditions of equation (2) and FIG. 3 is the curve (a) in FIG. 6, and the relationship between ΔH and Hi in the case of equation (6) and the conditions of FIG. It becomes like (b). Figure 6 shows the relationship between the magnetic field Hi due to the current to be detected 1o and △H which corresponds to the output voltage.Since the current to be detected is determined from the change in ΔH with △Ho as the base point, With the characteristic (a), the output is large, but the output characteristic is curved, and with the characteristic (b), although it is a straight line, the output does not change, so it cannot be used. Therefore, by setting HR in equation (1) to an appropriate value, the relationship between △H and Hi is approximated to a straight line as shown in (c) in Figure 6, and the output characteristics are adjusted to a level that does not cause any practical problems. can do. FIG. 7 shows the magnetization state under this condition.

Although it is not easy to calculate the value of R in equation (1), that is, the value of the detection resistor 9 shown in FIG. 1, so as to obtain the characteristic line shown in FIG. can be easily found.

Next, the magnetic field Hi due to the conductor current and the high frequency excitation current II will be described. Note that the above-mentioned ΔH is proportional to IH. The high frequency excitation current when the detected current i6 is O is shown in Fig. 8(a).
The waveform will be as shown in . When a magnetic field H1 due to the current i0 to be detected as shown in Fig. 8(b) is added here, the minor hysteresis becomes HIO and H in Fig. 7 in the case of a positive magnetic field + Hi.
Moves to the range of tn, the magnetic field change increases, and ΔH?
, the high-frequency excitation current increases, and in the case of negative magnetic field -Hi, it moves to the range of H + z and 1 (is in Figure 7), and the magnetic field change decreases to ΔHs, and the high-frequency excitation current decreases, and these Figure 8 (C) shows the inverse frequency excitation @ current waveform.
The waveform is a superimposition of a high frequency wave such as , and a low frequency waveform of the current to be detected. Note that the horizontal axis in FIG. 8 is a common time axis.

The change over time in the maximum value of the waveform in FIG. 8(, c) is proportional to each instantaneous value of the waveform of the detected current i0. By removing the high frequency component from this waveform using the low-frequency wave filter 13 of the output section 15 and the DC component using the ILI current remover 14, the current waveform to be detected can be accurately reproduced and determined. Therefore, according to the present invention, as is clear from the above operating principle, it is possible to detect a small current having any waveform such as a distorted waveform or a rectangular wave.

The current detection range of this device uses the change in variational magnetic permeability near the residual magnetic flux density of the hysteresis curve, so it is up to just before the point where the magnetic flux density on the negative side sharply decreases (coercive force). By selecting core materials with different magnetic hysteresis characteristics, the detected current can be set over a wide range. Note that it is necessary to use a core material that has low loss due to high frequency excitation and good high frequency characteristics.

The waveform of the high-frequency excitation current is not limited to a sine wave, and other waveforms may be used. For example, a full sine wave or a waveform obtained by making a direct current into a rectangular shape using a timer IC may be used, and if a timer IC is used, the number of electronic circuit components can be reduced. However, if a full-wave waveform is used, the input side of the low-frequency door waver 13 in Figure 1! It is necessary to install an I-flow device.

In principle, the higher the frequency of the high-frequency excitation current, the better.
In practice, it must be determined by taking into consideration the frequency of the current to be detected, its harmonic components, the required detection accuracy, the frequency characteristics of the iron core material, etc.

Although the case where the detected current i0 is AC has been described so far, it is also possible to detect DC by changing the circuit of the output section 15 shown in FIG. FIG. 9 shows a circuit configuration diagram of the main parts, and the parts common to those in FIG. 1 are indicated by the same symbols, including the iron core.

Since the conductor and the high frequency excitation part are the same as in FIG. 1, their illustration is omitted. The bottom of the circuit groove will be described with reference to FIG. 9 along with its function. With no current to be detected flowing through a conductor (not shown), the voltage across the detection resistor 9 by a high-frequency excitation section (not shown) is filtered by a low-pass filter 13 to remove high-frequency components, and then the differential amplifier 16 The output of the differential amplifier 16 becomes O by inputting a reference voltage having the same value as this heavy voltage to one terminal of the differential amplifier 16 via the DC power supply 17. Next, when a positive current flows through a conductor (not shown), the high-frequency excitation current becomes thick (and the difference from the reference voltage becomes positive), so the output side of the differential amplifier 16 has a voltage proportional to the detected current. A positive voltage can be obtained.Even when the current to be detected is negative, a negative voltage proportional to the current can be obtained using the same principle.Thus, according to the device of the present invention, when the small current to be detected is only direct current, it is possible to obtain a negative voltage proportional to the current. When an alternating current overlaps with an alternating current, it can be detected in any case where only an alternating current is detected.In addition, when detecting only a direct current, the low-pass P-wave device 13 in FIG. 9 may be replaced with a smoothing circuit.

The basic matters regarding the configuration and operation of the small current detection device of the present invention have been explained above. Next, a specific example using the device of the present invention will be described with reference to FIGS. 1 and 10. In Fig. 10, parts common to Fig. 1 are represented by the same symbols.
As a component corresponding to the high frequency power source 11 in FIG.
It consists of a DC power supply 18 and a timer IC1.
9 makes the high frequency 100! (It generates a square wave whose voltage changes to the positive side at z, and uses this as a high-frequency excitation power source.The output section is the same as in Fig. 1, so it is not shown in Fig. 10. This part will be explained with reference to Fig. 1. In Fig. 10, the iron core is a cylindrical wound core made of Co-based amorphous alloy ribbon. This amorphous alloy has magnetic properties. In addition to being excellent, it has a small magnetostriction, so the influence of stress on magnetic properties is small, and it is easy to handle, making it suitable for use in the iron core 1a.The dimensions of the iron core 1a are an outer diameter of 3911 m, an inner diameter of 35 mm,
The height (width of the thin strip) is 21. As the conductor 2a in FIG. 1, a twisted copper wire with a diameter of five fins was used. The high frequency excitation coil 7 has a diameter Q
, 1111 formal copper wire was wound 100 times around the thick part of the iron core A. Since the current of the high frequency excitation coil 7 is small, it is sufficient to use this amount of copper wire.

The voltage across the detection resistor 90 in Figure 1 has a cutoff frequency of 11c.
High frequency components and direct current components were removed using a Hz low-pass filter 13 and a direct current remover 14 using a capacitor.

Next, FIG. 11 shows a diagram showing the relationship between the detected current value and the output voltage obtained when an AC 50 Hz sinusoidal current is detected as described above.

For comparison, Fig. 11 shows, for example, that the iron core 1 in Fig. 12 is made of Permalloy (product name), has the same inner diameter as the iron core 1a, and has a cross-sectional area about 10 times larger, and the number of turns of the detection coil is 1000. The output when the dimensions of the conductor 2 in FIG. 12 are the same as in the case of the present invention is also shown. 1st
In FIG. 1, a solid characteristic line A represents the device of the present invention, and a dotted characteristic line represents the conventional device. As can be seen from Fig. 11, both 410 characteristic lines show very good linearity, but the present invention provides higher output and the core weight is lower than IA.
O. Even though the number of coil turns is 1/10, the output is about twice as high.

Next, Table 1 shows an example of a comparison of the iron core and the number of turns when the output of the inventive device and the conventional device are the same.

Compared to conventional devices, this device has 1/10 the iron core weight and 1/10 the number of coils, making it possible to reduce the outer diameter, height, and weight of the detection section, making it possible to downsize the entire device. I know what will happen.

Table 1 As mentioned above, the small current detection device of the present invention has been explained as using one conductor, but as mentioned above, good linearity can be obtained between the detected current and the output voltage. Therefore, it is of course possible to apply the device of the present invention to a zero-sequence current detector that uses a differential current between two or three conductors, and it can also be used in a wide range of other applications as required.

〔Effect of the invention〕

Conventionally, small current detection devices, such as zero-phase current detectors, have a weak magnetizing force due to the detected current and a small induced voltage, so small 11! In order to detect current, it is unavoidable to increase the cross-sectional area of the iron core and the number of turns of the detection coil.

On the other hand, according to the present invention, as explained in the embodiment,
The area near the residual magnetic flux density of the iron core with good high-frequency characteristics is magnetized at high frequency by connecting a resistor with an appropriate value in series to a high-frequency excitation coil to cause magnetic flux changes at high speed. Therefore, the waveform of the output voltage obtained by removing the high frequency component and DC component and the detected fi current are the same, so it is not limited to AC sine wave current, but can have any waveform such as distorted wave, DC, etc. For the current to be detected, the J iron core weight is set to 1/10, and the number of coil turns is set to 1.
/10, making it possible to reduce the size and weight of the detection unit. In addition, since this device requires only the positive voltage of the high frequency power supply, it is possible to use an inexpensive timer IC, and the high frequency excitation section can be made into a shed, which is advantageous in terms of economy.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the main part configuration of the device of the present invention,
Figure 2 is a conceptual diagram showing the shape of the magnetic hysteresis curve of the iron core material, and Figures 3, 4, and 7 represent changes in the magnetic field and magnetic flux density of minor hysteresis near the residual magnetic flux density in Figure 2. Enlarged view, Figure 5 is a waveform diagram of high frequency excitation current, Figure 6
The figure is a relationship diagram between the magnetic field of the detected current and the magnetic field of minor hysteresis.
A waveform diagram of the high-frequency excitation current when high-frequency excitation is performed, a waveform diagram of the current to be detected, a waveform diagram of the high-frequency excitation current when the current to be detected is applied, and Figure 9 is a circuit configuration diagram of the output section that is different from Figure 1. , Fig. 10 is a circuit configuration diagram of the high-frequency excitation section that is different from Fig. 1, Fig. 11 is a relationship diagram between detected current and output voltage, and Fig. 10 is a diagram for explaining the operation of a zero-phase current transformer. FIG. 13 is a schematic diagram showing the configuration of main parts, and is a conceptual diagram showing the shape of the magnetization curve of the iron core material in FIG. 11. 1, la: iron core, 2, 2a: conductor, 7: high frequency excitation 1
11 = r coil, 8: rectifier, 9: detection resistor, 11: high frequency power supply, 12.12a: high frequency excitation section, 13: low frequency filter, 14: DC remover, fence: output section, 16: operational amplifier , Figure 1 Figure 3 Figure 2 Figure 5 Figure 4 Figure ■ Hirohiro Figure 10 Figure 11! ! 1 Figure 72 Output Magnetic Field 1. Display of the case is π/-2172 daq. 3. Name of the address of the person making the amendment in relation to the case.

Claims (1)

[Claims] 1) The strength of the magnetic field generated in the core by a small current flowing through a conductor passing through the center hole of a cylindrical core in which a closed magnetic path is formed using a high magnetic permeability material whose magnetic hysteresis curve exhibits rectangular characteristics. A device for detecting the small current from a change in magnetic flux generated in the iron core, the device comprising: i) a high-frequency excitation coil wound around a thick part of the iron core through a central hole, and this high-frequency excitation coil; A high-frequency power source includes a means for controlling a magnetic minor hysteresis magnetic field generated in the iron core to a predetermined magnitude by a current, and a detection resistor for detecting a change in a high-frequency excitation current due to the small current magnetic field, connected in series. a high-frequency excitation section; ii) an output section connected to the detection resistor and having a circuit that separates the small current from the high-frequency excitation current that changes when the small current is applied. Device.