JPH0464068A - Method for detecting dc current - Google Patents

Abstract

PURPOSE:To detect a DC current with high accuracy without scaling up an apparatus by subjecting an iron core having a gap to AC excitation and detecting the change of induced voltage accompanied by the movement of the magnetic flux density range generated by a current to be detected. CONSTITUTION:A cylindrical body formed using a material having a square magnetic histeresis curve and small coercive force is divided to obtain iron cores 12a, 12b having a gap in a magnetic circuit. These iron cores 12a, 12b become linear in a magnetic characteristic by the magnetic resistance of the gap. When the iron cores 12a, 12b are excited by an AC magnetic field of the same waveform and a constant current due to an AC electromagnetic power supply 17, a control resistor 16 and an AC exciting coil 13, a magnetic flux density range moves on a histeresis curve by the magnetic field generated by the current I to be detected flowing to the conductor 15 passed through the inside space parts of the iron cores 12a, 12b. The change component of induced voltage based on this movement is detected by a detection coil 14 to be returned to a magnetic flux waveform through an integrator 18 and this waveform is converted to DC voltage by a positive and negative amplitude converter 19 to calculate the current to be detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in overcurrent detectors, various current detectors, etc., and utilizes the magnetic phenomenon of the iron core to make electrical contact with the main circuit non-contact. This paper relates to a method for detecting small direct currents.

[Conventional technology]

To detect direct current without electrical contact with the main circuit,
A DC transformer and a device that provides a gap in the iron core and inserts a Hall element into this gap are used.

FIG. 20 is a schematic diagram showing the circuit of the DC transformer together with the main part configuration. In Fig. 20, the detected DC current I
The conductor 3 through which the current flows is passed through the center hole of the iron cores 1a and lb in a closed magnetic circuit, and the excitation coils 2a and 2 wound around the iron cores 1a and lb are connected.
b is connected to the AC power source 5 in the opposite direction. Iron core 1a
, lb uses a material with rectangular magnetic properties and low coercive force. When the detected current I in the conductor 3 is O, only the excitation current of the iron cores 1a and lb flows in the AC current i, but when the DC current ■ flows in the conductor 3, the magnetic flux density range of the iron cores la and lb changes and the AC Since the current i increases, by reading the change with the AC ammeter 4, the DC current, that is, the detected current ■ can be determined. Note that 6 is the t source of the main circuit, and 7
also represents the load.

FIG. 21 is a schematic diagram showing the configuration of a device using an iron core and a Hall element. In FIG. When the current to be detected flows through the conductor 3 passing through the center hole of the iron core 8, the iron core 8 is magnetized, and the magnetic flux generated at this time generates a voltage in the Hall element 9, and this voltage is measured with a DC voltmeter 11. The detected current ■ can be determined.

[Problem to be solved by the invention]

In recent years, preventive maintenance of equipment has become important, and overcurrent circuit breakers and relays for DC have become necessary, and for this purpose, a highly accurate DC current detection method is desired.

However, DC current transformers require the use of two iron cores, and there are problems such as the size of the detection section being thick (and the excitation current of the iron core flowing even when the current to be detected is 0, which tends to cause errors). The device for attaching the Hall element to the gear part of the iron core has problems such as being greatly affected by ambient temperature, causing errors, and the Hall element part being structurally weak and easily broken.

The present invention has been made in view of the above points, and an object of the present invention is to provide a current detection method capable of detecting a direct current with high accuracy without increasing the size of the device.

[Means to solve the problem]

In order to solve the above problems, the method of the present invention forms a gap in a part of the magnetic circuit of an iron core made of a material with a rectangular magnetic hysteresis curve and a small coercive force, and an excitation coil wound around this iron core. Connect a resistor larger than the reactance of the iron core in series,
The iron core is magnetized with a constant AC double-wave or half-wave current, a conductor through which the current to be detected flows is passed through the center of the inner space of the iron core, and the magnetic flux density range of the iron core is determined by the magnetic field of the current flowing through this conductor. The DC current flowing through the conductor is detected without electrical contact with the main circuit from changes in the induced voltage of a detection coil wound around an iron core separately from the excitation coil, or from changes in the voltage across the excitation coil. be.

[Effect]

As described above, the method of the present invention forms a gap in a part of the core made of a material that has high magnetic permeability, low coercive force, and exhibits a rectangular magnetic hysteresis curve. Since it is excited by an alternating magnetic field with a constant current,
The magnetic field range of the core moves due to the magnetic field generated by the detected current flowing through the conductor passing through the inner space of the core, and the magnetic flux density range is changed. It becomes possible to ask for it.

〔Example〕

The method of the present invention will be explained below based on Examples.

First, the first method of the present invention will be explained. FIG. 1 is a schematic diagram showing an example of the main part configuration of an apparatus to which this method is applied.

In FIG. 1, iron cores 12a and 12b are made of a material with rectangular magnetic hysteresis curves and low coercive force, and are, for example, a cylindrical integral piece that is divided to form gears in the magnetic circuit. These iron cores 12a, 12b
A conductor 15 is connected to the power source and load of the detected device through the center of the inner space, but these are not shown. The iron core 12a has an AC excitation coil 13 in its thick part.
, the control resistance 16 is larger than the iron core glue actance.
is connected to the AC excitation power supply 17 via the iron core 12b.
The detection coil 14 is wound around the integrator 18. Positive/negative amplitude converter 19. Il! Connect in the order of true device 20, summer reducer 2
0 is connected to a DC reference power source 21.

Next, FIGS. 2 and 3 are magnetic hysteresis curves of the iron cores 12a and 12b, FIGS. 4 and 5 are magnetic flux waveform diagrams, and FIG.
FIG. 7 shows a relationship diagram between detected current and output.

Hereinafter, the operation of the method of the present invention will be explained with reference to FIGS. 1 to 7. Before being divided, the iron cores 12a and 12b have the characteristics shown by the solid line (A) in FIG. 2, but after being divided, they have linear characteristics as shown by the dotted line (-) due to the magnetic resistance of the gear and pull sections. The slope of this dotted line -) can be arbitrarily set by changing the size of the gear. The iron cores 12a and 12b are connected to the AC excitation power source 1 in FIG.
7 and control resistor 16. It is excited by an AC excitation coil 13. Here, the AC excitation voltage a17 is a commercial source (sine wave 5
0.60Hz) will be described.

The relationship among the AC applied voltage, magnetic flux density, exciting current, and induced voltage of the iron cores 12a and 12b is expressed by equation (11, (2)).

B Ea ” i B+ ” l Rz + Na
Ac □---- (11t B Es "Ns Ac □----・----
-1-・-I2)t However, E: AC applied voltage i: AC excitation current R1: Value of the control resistor 16 connected in series R1: Resistance value of AC excitation coil 3 N,: AC lII magnetic coil 13 Number of turns A: Magnetic path cross-sectional area of cores 12a and 12b B: Core 12a
, 12b magnetic flux density t: waiting time, : induced voltage of the detection coil 14 Ns : number of turns of the detection coil 14 Here, when set as in equation (3), if E is constant, the magnetic field due to the current of the conductor 15 Even if the excitation current i
does not change.0 The present invention is set to this condition.

B i R1+ l R1 >> Ng A(--(3)
t Note that the detection current HI Hr However, the relationship between the AC excitation current i and the magnetic field is expressed by Equation (4) 1 The relationship between I and the magnetic field is expressed by Equation (5).

=(NAXi)/L ・~ (4)-(NIX
I) /L (51HL: Magnetic field L due to AC excitation current l: Magnetic path length of iron cores 12a, 12b HI: Magnetic field N due to detected current I: Number of turns of conductor 15 around iron cores 12a, 12b (usually 1 turn) 3 is a diagram schematically showing the characteristics of the magnetic hysteresis curves of the iron cores 12a and 12b in order to simplify the explanation.When the detected current ■ of the iron cores 12a and 12b is 0, It is excited with alternating current in the range of Hr (B+) and HI (Bz) shown in Figure 3, and the amount of change in magnetic flux becomes B++.The waveform changes as shown in Figure 4, and the detection coil 14 has the following equation (2). The voltage induced by

Next, when a DC current ■ flows through the conductor 15, a DC magnetic field 1 H1 according to equation (5) is added, and the magnetic field of the iron cores 12a and 12b becomes the sum of Hr and Hl, resulting in H3 (B I) in FIG.

H# (moves to the B- range, and the amount of change in magnetic flux becomes B+4, which becomes smaller. The magnetic flux waveform becomes as shown in Fig. 5, and the induced voltage in the detection coil 14 becomes smaller. When the detected current ■ further increases, The variation range of the magnetic flux is reduced, and the induced voltage of the detection coil 14 is also reduced.The induced voltage of the detection coil 14 is returned to the magnetic flux waveform through the integrator 18, and the value of B II + 814 in FIG. 3 is converted by the positive/negative amplitude converter 19. The detected current I can be obtained by converting it into a DC voltage proportional to . Here, the case where the detected current I is positive is described, but the same applies to the case where it is negative. The output of the positive/negative amplitude converter 19 The voltage becomes smaller as the detected current I increases, as shown in FIG.

To match the output voltage and the zero point of the detected current ■, input the output of the positive/negative amplitude converter 19 and the voltage of the DC reference power supply 21 into the subtracter 20, and when the detected current I is at the point O, the output of the subtracter 20 is It is sufficient to set it so that it becomes 0.

The relationship between the detected current I and the output voltage in this case is shown in FIG.

Next, a second method in the present invention will be explained. Second
This method simplifies the configuration of the detection section in the first method and further reduces its size. The main configuration of the device is shown in FIG. 8, and parts common to those in FIG. be. The device shown in FIG. 8 differs from the device shown in FIG. 1 in that the detection coil 14 shown in FIG. 1 is omitted. In FIG. 8, the AC excitation power supply 17 uses a commercial power supply, and the voltage across the AC excitation coil 13 is the sum of the second and third terms in equation (1), but in equation (6). The condition, that is, the second term in equation (1) i R! ＜ ＜ N@Ac
"-1...----1-...-(6) If the value of t is set very small compared to the value of the third term, the second term iRl can be ignored, and the first It can be considered to be equivalent to the induced voltage of the detection coil 14 in the first method. Therefore, the change in the voltage across the AC excitation coil 13 due to the detected current ■ is the same as the voltage change in the detection coil 14 in the first method. Since the value is N A / N s times that of the first method, DC current can be detected.

As shown in FIG. 9, the output side circuit uses a detection coil 14 and a double wave rectifier 22. It is also possible to connect a smoother 23 and convert the average value of the induced voltage into direct current, and even when the detection coil 14 is not used as shown in FIG. 8, the integrator 18. The positive/negative amplitude converter 19 can be replaced by a double-wave rectifier 22 and a smoother 23. Further, the waveform of the AC excitation power source 17 is not a sine wave, but may be another waveform such as a square wave.

Next, a third method in the present invention will be explained. 1st
FIG. 0 is a schematic diagram showing the main part configuration of an apparatus to which the third method is applied, and the same reference numerals are used for parts common to FIGS. 1 and 8. FIG. 10 shows the AC excitation coil 13. The configuration is exactly the same as in FIG. 1 except that a half-wave rectifier 24 is connected in series with the m-control resistor 16.

FIG. 11 shows a schematic diagram showing the magnetic hysteresis curve when the cores 12a and 12b are excited in the device shown in FIG. 10. The excitation of the cores 12a and 12b is the same as in the device shown in FIG. 1 described above (3) When the detected current I is 0 under the conditions of the formula, HS (B I) in Fig. 11 and H,
It is excited in the range from the point where B is 0, and the amount of change in magnetic flux is B. When the detected current +■1 flows here, a magnetic field H11 is added and HA (Bl) and H? (B t) range,
The amount of change in magnetic flux is small and is B+t. When the current to be detected -■□ flows, the range is Hs (B+), H, (Bl), and the amount of change in magnetic flux becomes 81. , the current to be detected in the conductor 15 and the positive/negative amplitude converter 19. The relationship between the outputs of the subtracter 20 is as shown in FIGS. 12 and 13, and direct current can be detected.

In the third method, by setting the conditions of equation (6), it is possible to omit the detection coil 14 and detect the current from the voltage across the AC excitation coil 13, as shown in the schematic diagram of the device in FIG. It is possible.

In the explanation so far, the shape of the iron cores 12a and 12b has been described as one in which a cylindrical integral iron core is divided, but for example, as shown in the schematic cross-sectional view of FIG. A gap may be formed by removing a portion, but this makes it difficult to adjust the gap size. Moreover, the shape of the iron core may, of course, be one in which a rectangular cylindrical body is divided, as shown in the schematic cross-sectional view of FIG. 16.

The basic matters have been explained above regarding the device configuration and operation to which the DC current detection method of the present invention is applied. Next, a specific example using the method of the present invention will be described. The iron core is commercially available C.
A wound core was formed from an o-based amorphous alloy ribbon, subjected to a prescribed heat treatment, impregnated with resin, and then cut. FIG. 17 is a schematic sectional view showing the iron core and coil portion. This is the 17th
As shown in the figure, the excitation coil 13a and the detection coil 14a are overlapped and circulated using a coil frame 25 made of a thin plastic plate, and the obtained iron cores 12c and 12d are inserted into the coil frame 2.
Figure 5 Inserted in Figure 2] Figure Figure Figure Figure Nagikai Figure 12 Figure 13 Figure 15 Figure 16 Figure 18

Claims (1)

[Claims] 1) A gap is formed in a part of the magnetic circuit of an iron core made of a material with a rectangular magnetic hysteresis curve and a low coercive force, and a high resistance is connected in series to an excitation coil wound around this iron core. Then, a constant current with positive and negative symmetry is applied and an alternating magnetic field is applied.
A detection coil that is wound around the iron core separately from the excitation coil by passing a conductor through which a current to be detected flows through the center of the inner space of the iron core, changing the magnetic flux density range of the iron core by the magnetic field of the current flowing through the conductor. A method for detecting a direct current, comprising detecting a direct current flowing through the conductor from a change in the induced voltage of the conductor. 2) A gap is formed in a part of the magnetic circuit of an iron core whose magnetic hysteresis curve is square and is made of a material with low coercive force, and a high resistance is connected in series to the excitation coil wound around this iron core to generate a constant current with positive and negative symmetry. is applied and an alternating magnetic field is applied.
A conductor through which a current to be detected flows passes through the center of the inner space of the iron core, the magnetic flux density range of the iron core is changed by the magnetic field of the current flowing through this conductor, and a DC current flows through the conductor from voltage changes at both ends of the excitation coil. A direct current detection method characterized by detecting. 3) A gap is formed in a part of the magnetic circuit of an iron core whose magnetic hysteresis curve is rectangular and is made of a material with low coercive force, and a constant positive or negative current is passed through the excitation coil wound around this iron core to generate a half wave. an alternating current magnetic field is applied, a conductor through which the current to be detected flows is passed through the center of the inner space of the iron core,
The magnetic flux density range of the iron core is changed by the magnetic field of the current flowing through the conductor, and the DC current flowing through the conductor is detected from the change in the induced voltage of a detection coil wound around the iron core separately from the excitation coil. DC current detection method. 4) A gap is formed in a part of the magnetic circuit of an iron core whose magnetic hysteresis curve is rectangular and is made of a material with low coercive force, and a constant positive or negative current is passed through the excitation coil wound around this iron core to generate a half wave. an alternating current magnetic field is applied, a conductor through which the current to be detected flows is passed through the center of the inner space of the iron core,
A direct current detection method comprising changing the magnetic flux density range of the iron core by the magnetic field of the current flowing through the conductor, and detecting the direct current flowing through the conductor from voltage changes across the excitation coil.