JPH01285866A - Small current detector - Google Patents

Abstract

PURPOSE:To enhance sensitivity and accuracy, by a method wherein a conductor is provided so as to pass through the center hole of a cylindrical iron core magnetized by a high frequency exciting part and the change of the high frequency current based on the total magnetic flux, wherein the magnetic flux generated by the small current of the conductor is superposed is detected. CONSTITUTION:The conductor 2a connected to the power supply of device to be detected and load is inserted through the center hole of an iron core 1a having high magnetic permeability and a high frequency exciting coil 7 is connected to the iron core 1a and also connected to a high frequency power supply 11 through a control circuit 10. Next, the exciting current by a high frequency exciting part 12 is set to the linear part of the magnetic histeresis curve of the iron core 1a and, when a magnetic field is applied to the conductor 2a, a large change is given to magnetic flux to change a high frequency exciting current. This change is taken out by a detection resistor 13 and output voltage is detected through a rectifier 8c, a low-band filter 14 and a DC removing device 15. Therefore, a small current can be detected with high sensitivity and high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a small current detection device that is used in earth leakage circuit breakers and the like and utilizes the magnetic phenomenon of an iron core.

[Conventional technology]

2. Description of the Related Art Zero-phase current transformers such as earth leakage circuit breakers are known as a main use of small current detection devices. FIG. 8 is a schematic diagram showing the main structure of a zero-phase current transformer in order to explain its operating principle. In FIG. 8, two conductors 2. It consists of a resistor 4 connected near both ends of a detection coil 3 wound around an iron core 1, and both ends of the conductor 2 are connected to an AC power source 5 and a load 6, respectively. Under normal conditions, current 11 flows through the two conductors 2 and reciprocates, the direction of which is indicated by an arrow. ! Since the value of t is the same (7) 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 1,,I changes, and the difference current magnetizes the iron core 1.The induced voltage generated at this time causes current to flow through the small resistor 4, and the current flows across the small resistor 4. The voltage drop can be taken out as control number 58.

Note that Figure 8 shows the case of single phase, but in the case of three phases, conductor 2
can be expressed as three lines, and in principle it is the same as a single phase.

Since the detected current of the zero-phase current transformer is as small as 5 to 30 mA, the iron core is made of Fe-Ni alloy (for example, the product name is Permalloy F7).
J, Unataka i! Even if an iI index material is used, the detection magnetic field is small as shown in the magnetization curve shown in FIG. 9, so the obtained magnetic flux is also low, and the voltage induced in the detection coil 3 is very small. Therefore, it is preferable that such a zero-phase current transformer has even higher sensitivity, and it is strongly desired that the zero-phase current transformer be made smaller.

Although a zero-phase current transformer has been described above, the basic operating principle, high sensitivity, and miniaturization are also desired for small current detection devices used for other purposes.

[Problem to be solved by the invention] However, in order to increase the sensitivity of the zero-phase current transformer with the above structure and detect even lower currents, the following steps must be taken:
There is a problem. To increase the output sensing pressure in order to increase sensitivity, for example, increase the magnetic path cross-sectional area of iron core 1 as shown in Figure 8, or wind the conductor 2 around iron core I in large numbers to increase the magnetic field applied to iron core I. There are many ways to do this, but increasing the magnetic path cross-sectional area of iron core 1 naturally leads to an increase in the number of devices, and increasing the number of turns of conductor 2 around iron core 1 is this method. Since the current of the main circuit flows through the conductor 2, the wire diameter is made large, and it is also unavoidable that the dimensions of the iron core l become large. Therefore, a method is usually adopted in which the conductor 2 is passed through the center hole of a small iron core J, the number of turns of the detection coil 3 is increased, and the induced voltage is amplified by an electronic circuit. However, this method reduces the detection coil 7) to 100
It is very difficult to detect a current of 5 mA or more even after 0.4 years of testing. Furthermore, when the detection coil 3 is wound about 1000 times, even if a thin wire is used, the diameter (Aj method) of the 21st coil section including the iron core 1 becomes larger.The diameter of the coated copper wire used for the detection coil 3 is However, since the strength of the wire itself is required during winding work, it is not possible to use a wire that is too thin.From the following, detection':
] without increasing the number of turns of the coil 3, that is, without increasing the outer diameter of the detection coil portion including the iron core 1, 1) IIA
It is desirable that the following small currents can be detected.

The present invention has been made in view of the points mentioned above, and its object is to provide a small current detection device that can detect small currents with high sensitivity and precision without using a detection coil. It is in.

[! l! [Failure to solve the problem]

In order to detect a small current flowing through a conductor passing through the center 7L of a cylindrical core in a closed magnetic circuit, the present invention provides a control circuit that controls a high frequency excitation coil wound around this core to set both positive and negative magnetic fields generated in the core to predetermined magnitudes. High-frequency excitation M! is caused by the total magnetic flux in which the rising magnetic flux and the magnetic flux due to the detected current of the conductor are superimposed on the high-frequency excitation section connected to the high-frequency ii source via the high-frequency excitation section and the high-frequency excitation section. 1 is a small current detection device equipped with a detection resistor for detecting flow rate and an output section having a circuit for separating a conductor current component from the detected high frequency excitation current.

(Function J) By configuring the small current detection device of the present invention as described above, the excitation current (1 field) from the high frequency excitation section is controlled by the slope of the straight line near the coercive force of the magnetic hysterin curve of the iron core, that is, by the differential permeability. Since the magnetic flux can be set at a large point, even when a small magnetic field due to the current to be detected in the conductor is applied, the magnetic flux shows a significant change, the iron core actance changes greatly, and the high frequency excitation current also changes significantly. Since the magnetization is performed using a high-frequency current by an excitation coil, the time required for the magnetic flux to change is fast.Therefore, in the device of the present invention, a magnetic field is always applied by the high-frequency excitation section, and a magnetic field due to the detected II current of the conductor is superimposed on this. By detecting the change in the high-frequency excitation current when the high-frequency excitation current is applied and further removing the high-frequency DC component, it is possible to extract an output voltage with the correct detection current waveform from the output end. It has high sensitivity and high precision, making it possible to detect smaller currents.

〔Example〕

The present invention will now be explained based on Examples.

FIG. 1 is a schematic diagram for explaining the main part configuration of the small current detection device of the present invention. In FIG. It is formed into a closed magnetic circuit, for example, in the shape of a ring.

A conductor 2a is connected to the t source and the negative end of the detected device through the center hole of the iron core 1a, but these are not shown. In addition, to detect zero-sequence current, there are two or three conductors 2a, and the difference in current between each conductor is used, but in principle it is the same as detecting a small current in a single wire.
Here, the conductor 2a is represented by one conductor, and the following description will be made assuming that the direction of the object to be detected whose direction is indicated by an arrow is io.

In addition, the iron core 1a has a high frequency excitation coil wound around its thick part: r
- rectifier 8a and resistor 9 connected in series, for example
a. A high frequency excitation section 12 is provided which is connected to a high frequency type 1I111 via a control circuit 10 in which a rectifier 8b and a resistor 9b are connected in parallel. An output section 1G is formed in which a low-pass filter 14 and a direct current remover 15 are connected in this order with a rectifier 8c interposed from both ends of the detection resistor 13 connected in series with Lua.

The DC remover 15 can be easily constructed with a capacitor or an isolation transformer. As described above, the device of the present invention has a high frequency excitation section 12. which has an excitation coil 7 on the iron core 1a. It is equipped with two elements, an output section 16 having a detection resistor 13, and in use, it is used to detect a small current flowing through the conductor 2a of the device to be detected through the center hole of the iron core 1a. .

Next, Figures 2 and 3 show the magnetic hysteresis curve of the iron core 1a, and Figure 2 shows the relationship between the magnetic field strength (■ ()) and the magnetic flux density (B). Although this is a conceptual diagram simply illustrating the squareness, in Fig. 3, Fig. 2 is enlarged for the convenience of the following explanation, and the slope of the straight line near the coercive force is increased.B4 in Fig. 3 ~
- In the straight line part of B4, a slight change in H causes a large change in B,
This change in magnetic flux causes a change in the reactance of the iron core 1a, and this change becomes larger as the frequency becomes higher. The device of the present invention is characterized in that it makes effective use of these points, and the operation thereof will be described below with the device configuration shown in FIG. 1, the magnetic hysteresis curve shown in FIG. 3, and other necessary drawings. This will be explained using them together.

Normally, the iron core 1a receives a high-frequency current from the high-frequency excitation section 12 shown in FIG. 1, and the magnetic field is H&+ on the positive side and -1(
, has been added. As shown in FIG. 4, the waveform has a higher high frequency excitation current 1 on the positive side than on the negative side. 8. Magnetic field. , -)(, are set by appropriately selecting the rectifiers 8a, 8b and resistors 9a, 9b of the control circuit 10. Note that this resistor 9a can be omitted if each component of the high frequency excitation section 12 is appropriately set. can.

At this time, the magnetic flux 1Mi field applied to the iron core 1aL is represented by B 6 (Hl, ), B 1 (-Hl), B in Fig. 3.
6 (H6) A high frequency excitation section that draws a hysteresis tune IA that changes in the direction of the arrow? 1 is determined by the reactance Yoshizume resistors 9a, 9b and the detection resistor 13 due to changes in the magnetic flux of the iron core 1a, and the current waveform is shown in Figure 5 (al).Next, when an AC sinusoidal current flows through the conductor 2a, 1, A magnetic field is generated on the positive side by the second current 1o, and a magnetic field -ΔI (is generated on the h side, and the magnetic field waveform is shown in Fig. 5 fb. Then -CΔ)1. −
Corresponding to ΔH, the magnetic flux changes by ΔB in both positive and negative directions, and the positive side Δ11 of the magnetic hysteresis curve is a loop of C (Bt → B, →St
), and the negative side -ΔH is D indicated by the dashed-dotted arrow.
A loop of (B s - B z - B a) is drawn, and the high-frequency excitation VAii current i is large when ΔH is positive and small when ΔH is negative, and its current waveform becomes a modulated wave as shown in Figure 5 (tel). Become. Note that the horizontal axis in Figure 5 is ta+
(This is the common time axis for bl tc+.

The waveform of FIG. 5 fcl can be extracted as a voltage from the voltage drop F of the detection resistor 13, and from this waveform,
rectifier 8c, low pass filter 14. By removing the high frequency component and the DC component using the DC remover 15, the detected current waveform can be accurately reproduced and determined. Therefore, as is clear from the above operating principle, the device of the present invention is capable of detecting small currents having any waveforms such as distorted waveforms and rectangular waves.

Although the waveform of the high-frequency excitation current i has been described as a sine wave as shown in FIG. 4, other waveforms may be used.

The frequency of the high-frequency excitation current i may be high in principle, but in practice it must be determined by taking into account the frequency of the current to be detected, its harmonic components, the required detection accuracy, the frequency characteristics of the iron core material, etc. It won't happen. As is clear from Fig. 3 already mentioned, the magnetic properties of the iron core 1a are such that the hysteresis curve has good squareness with respect to the magnetization of high-frequency current, the absolute value of the magnetic flux density is large, and the coercive force is small. It is necessary.

Although the case where the detected current Eo is AC has been described so far, it is also possible to detect DC by changing the circuit of the output section 16. FIG. 6 shows a circuit diagram of the main part of the iron core 1a.

Since the conductor 2a and the high-frequency excitation section 12 are the same as those shown in FIG. 1, their illustration is omitted, and the circuit configuration and operation will be described with reference to FIG. When the current to be detected is not flowing through the conductor 2a (not shown), the current 1 caused by the high frequency excitation section 12 (not shown)
The voltage detected by the detection resistor 13 is rectified by a8c, the positive component is expressed by the low-pass filter 14a, and the positive component is inputted to the O terminal of the differential amplifier 17.
By inputting the signal to the ■ terminal of the differential amplifier 17, the output of the differential amplifier 17 becomes O. Next, when a positive current flows through the conductor 2d (not shown), the voltage across the detection resistor 13 increases, and the difference from the reference voltage is output from the differential amplifier 17, resulting in a positive voltage proportional to the detected current. is obtained. Even when the current to be detected is negative, a yellow voltage proportional to the t current can be obtained using the same principle. Note that when detecting DC current, it is only necessary to compensate so that the output becomes O when the current to be detected is O, so there are other methods than using the differential amplifier F, but they are basically the same, so they will be omitted.9 Thus, according to the device of the present invention, it is possible to detect whether the current to be detected is only a direct current, a combination of a direct current and an alternating current, or only an alternating current.

The basic matters regarding the configuration and operation of the small current detection device of the present invention have been explained above, and next, a specific example using the device of the present invention will be described with reference to FIGS. 1 and 3 again. The iron core 1a is formed as a cylindrical wound core using a Co-based amorphous alloy ribbon.

Ta. This amorphous alloy has superior magnetic properties.
- Also, because the magnetostriction is very small, the influence of stress that increases the magnetic properties is always small, and it is easy to handle.
It is suitable for use as the iron core 1a.

-1 method of iron core 1a has an outer diameter of 39N and an inner diameter of 35f1. Height (width of yl band) is 2 mm. Conductor 2a has a diameter of 31φ
copper wire was used. The high frequency excitation coil 7 has a diameter of 0. lfl
Using formal insulated copper wire of φ, connect
It was manufactured by turning the bag 00 times. Since the high-frequency current of the high-frequency excitation coil 7 is small, even if such a thin wire is used, it takes only one minute. The high frequency excitation current is a sine wave of 100 kHz. The voltage across the detection resistor 13 is made into only positive components by a rectifier 8c, passed through a low-pass filter 14 with a cutoff frequency of 1 kHz to remove high frequency components, and then removed by a DC remover 15 to remove the DC component. . Note that condenser 4J was used for the DC remover 15.

Next, as described above, the device of the present invention is used to
FIG. 7 shows the output characteristics when a sine wave current of H is detected. Figure 7 shows the detected voltage'/#L value,
It is a diagram showing the relationship of 1-. Figure 7 shows a comparison
For this reason, output characteristics are also shown in the case where the conventional iron core 1 shown in FIG. 8 is made of Permalloy (trade name) and a detection section that provides the necessary characteristics is constructed. The conventional one for comparison has iron core dimensions of an outer diameter of 43 mm, an inner diameter of 35 fins, and a width of 10 fi, and the number of windings of the detection coil 3 is 1000 turns. In FIG. 7, a solid characteristic line A represents the device of the present invention, and a dotted characteristic line represents the conventional device. As shown in Figure 7,
460. Both characteristic lines show very good linearity, but the present invention provides a higher output voltage and has a core cross-sectional area of 1/10.
゜Even though the number of turns of the coil is 1710, the output is about 1
It will increase five times. In this way, the device of the present invention can reduce both the core cross-sectional area and the number of coil turns to 1/10 compared to conventional devices, so the size and weight of the core including the coil can be significantly reduced. be.

For example, the case of a closed magnetic circuit iron core as shown in FIG. 1 has been described above, but it goes without saying that the apparatus of the present invention can also be applied to a cut-core type detection section such as a detection section of a clamp ammeter.

〔Effect of the invention〕

Conventionally, small current detection devices have been used to detect small currents with high sensitivity, for example in zero-phase current transformers, because the magnetizing force due to the current to be detected (B, 2) is weak and the induced voltage in the detection coil is small. In order to
- Since it is necessary to reduce the weight of the winding part and the iron core part, -1 & 2d L,
According to the present invention, as described in the embodiment, without using the L The change in the high-frequency excitation current caused by this change in magnetic flux is detected by a detection resistor connected to the high-frequency excitation part, and then the output current 5 ( Because the current is separated, the current to be detected can be detected with high sensitivity, and the dimensions of the iron core can be easily detected.

This made it possible to significantly reduce the weight.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the configuration of the main parts of the device of the present invention, and Fig. 2 shows the shape of the magnetic hiskerinus curve of the iron core material;
Fig. 13 is an enlarged view of Fig. 2, Fig. 4 is a waveform diagram of the high-frequency excitation current, and Fig. 5 is a waveform diagram of the high-frequency excitation current when high-frequency excitation is performed. Magnetic field waveform diagram (1)) and a high-frequency current waveform diagram (C1) in which both are superimposed, Figure 6 is a circuit configuration diagram of an output section different from Figure 1, and Figure 7 is a diagram of the present invention shown in comparison with a conventional device. A diagram showing the relationship between detected current and output voltage in the device, Figure 8 is a schematic diagram showing the main configuration to explain the operation of a conventional zero-phase current transformer, and Figure 9 shows the iron core material in Figure 8. It is a conceptual diagram showing the shape of the magnetization curve. 1, la: iron core, 2.2a: conductor, 7: high frequency excitation coil, 8a, 8b, 8c + rectifier, 9a, 9b + resistor, 10: control circuit, 11: High frequency power supply, 12; High frequency excitation section, 13: Detection resistor, 14, 14a: Low pass filter,
15: DC remover, 16: Output section, 17: Differential amplifier,
18: Chosenju01 Figure 7 Figure 9

Claims (1)

[Scope of Claims] 1) Strength of 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 permeability material whose magnetic hysteresis curve exhibits rectangular characteristics. The device detects the small current from the change in magnetic flux generated in the iron core by changing the magnetic field, the device comprising: i) applying both positive and negative magnetic fields generated in the iron core to a high-frequency excitation coil wound around a thick portion through a center hole of the iron core; ii) a high-frequency excitation section connected to a high-frequency power source via a control circuit that sets the magnetic flux to a predetermined size; A small current comprising: a detection resistor for detecting a change in high-frequency excitation current based on the superimposed total magnetic flux; and an output section having a circuit that separates a small current of the conductor from the detected high-frequency excitation current. Detection device.