JP2586156B2 - AC / DC dual-purpose current detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for a zero-phase current detector, various leak current detectors, and the like, and uses a magnetic phenomenon of an iron core to electrically and non-contact DC. And a method for detecting an alternating current.

[Conventional technology]

As a device for detecting a small current electrically in a non-contact manner, a zero-phase current transformer used for an earth leakage breaker, an earth leakage protection relay and the like is known. FIG. 19 is a schematic diagram showing a configuration of a main part of the zero-phase current transformer in order to explain the operation thereof. As shown in FIG. 19, the zero-phase current transformer comprises two conductors 2 passing through a center hole of an annular core 1 having high magnetic permeability, and a detection coil 3 wound around the iron core 1.
Of the conductor 2 is connected to both ends of the
Each is connected to an AC power supply 5 and a load 6 of the main circuit.
In a normal state, the values of the reciprocating currents I ₁ and I ₂ indicated by arrows and flowing in the two conductors 2 are the same but opposite in direction, so that the iron core 1 is not magnetized and the detection coil 3 No voltage is induced. When a leakage occurs on the load 6 side, the values of the currents I ₁ and I ₂ change, the core 1 is magnetized by the difference current, a current flows through the resistor 4 by the induced voltage, and the voltage drop of the resistor 4 is used as a control signal. Can be taken out. In FIG. 19, the case of a single phase is shown, but in the case of a three phase, three conductors 2 may be represented, and the principle is the same as the single phase. In principle, this zero-phase current transformer can detect only an AC zero-phase current, and cannot be used for DC.

On the other hand, to detect DC current without contacting the main circuit,
Although illustration of the apparatus is omitted, the following method is available.

One is the DC current transformer method, which uses two iron cores in a closed magnetic circuit, and excites both AC cores so that their magnetic flux directions are reversed. Changes, and a DC current can be detected based on the change. In addition, according to the Hall element method, it is possible to obtain a current to be detected by providing a gap in the iron core and inserting the Hall element into the gap.

[Problems to be solved by the invention]

However, in recent years, preventive maintenance has been regarded as important, and it has been demanded that DC devices be applied to earth leakage breakers and earth leakage protection relays. There is a problem that cannot be achieved.

That is, in the zero-phase current transformer, only the alternating current can be detected as described above. Also, when the alternating current is detected, the detection current is small. Therefore, the iron core 1 is made of an Fe-Ni alloy, for example, a trade name of Permalloy. Even if such a high magnetic permeability material is used, since the detection magnetic field is small as in the magnetization curve shown in FIG. 20, the obtained magnetic flux is low, and the size and weight of the detection section are large. On the other hand, the method using a DC current transformer for detecting DC requires two iron cores, which increases the size of the detection unit. In addition, it is not suitable for small current even though it is good for large current in principle. However, it is very difficult to detect a small current such as a zero-phase current. When detecting direct current using a Hall element, there is a gap in the iron core, so it is easily affected by an external magnetic field, and the size of the detection part becomes large because it requires magnetic shielding. When the main current is large even if the current to be detected is small like a container,
Under the influence of the iron core gap, the magnetic field due to the main current is not balanced to zero, and this case cannot be applied. As described above, conventionally, no suitable device for detecting a DC difference current has been obtained. The direct current that is desired to be detected by an earth leakage breaker, an earth leakage protection relay, or the like includes not only a complete DC but also a pulsating current like a rectified AC waveform.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method capable of detecting both AC and DC current without increasing the size of the device.

[Means for solving the problem]

In order to solve the above-mentioned problem, the method of the present invention provides a method in which high-frequency excitation is performed under the same conditions in both the positive side and the negative side until the magnetic field of the magnetic hysteresis curve of the iron core is larger than the coercive force. The object of the present invention is to utilize a phenomenon in which a high-frequency excitation current changes depending on a magnetic field generated.

That is, a high-frequency excitation coil is wound around an iron core having a good squareness of magnetic hysteresis and a small coercive force, and a detection resistance smaller than the reactance of the iron core and the high-frequency excitation coil unit is connected in series to the high-frequency power supply. When the magnetic field is excited to a point where the magnetic field is larger than the coercive force, and a small magnetic field generated by the detected current flowing through the conductor passing through the center hole of the iron core is applied in this state, the range of the hysteresis curve moves. The range of the magnetic flux density and the magnetic field also moves, and the high-frequency excitation current changes, so this change in the high-frequency excitation current is taken out as the voltage drop of the detection resistor or the voltage change across the high-frequency excitation coil, and the signal is processed by an electronic circuit. This is for obtaining the current of the main circuit. In addition, a detection circuit for a large current that flows instantaneously can be detected together with the above-described current detection signal.

[Action]

According to the method of the present invention, as described above, when the iron core is excited at a high frequency, a small magnetic field generated by the detected current can be used.
Since the excitation range on the hysteresis curve of the iron core moves, and the value near the coercive force of the high-frequency excitation current and the maximum value also change, the DC and AC currents are calculated from the difference between the positive and negative absolute values of these values. Can be detected. It is also possible to detect a large current flowing instantaneously from the sum of the absolute values.

〔Example〕

 Hereinafter, the method of the present invention will be described based on examples.

FIG. 1 is a schematic diagram showing an example of the configuration of a main part of an apparatus used for explaining the basic items of a method for detecting a small current for both AC and DC in the present invention. In FIG. 1, an iron core 1a is made of a material having a square hysteresis curve and a small coercive force, for example, in a ring shape. The conductor 2a is connected to the power supply and the load of the main circuit through the center hole of the annular core 1a, but these power supply and the load are not shown. In order to detect the zero-phase current, two or three conductors 2a are used, and the difference current between the conductors is used. However, in principle, this is the same as detecting a single-line current. In the following description, the conductor 2a is represented by a single line, and the detected current whose direction is indicated by an arrow is represented by I _O , and the following description will proceed. A high-frequency excitation coil 7 is connected to a high-frequency power supply 9 via a detection resistor 8 having a smaller value than the reactance of the iron core in a thick portion of the iron core 1a. The high frequency exciting current i flows in the direction of the dotted arrow. A terminal for extracting a signal from the detection resistor 8 is a terminal, and a terminal for extracting a signal from the high-frequency excitation coil 7 is. The terminal is common to both.

Next, FIG. 2 shows the entire shape of the magnetic hysteresis curve of the iron core 1a. FIG. 3 shows the curve of FIG. 2 as a linear approximation for convenience of the following description. It is a magnetic characteristic diagram. FIG. 4 is a waveform diagram of the magnetic field and the high-frequency excitation current, and FIGS. 5 (a) and 5 (b) are waveform diagrams showing the current to be detected and the voltage across the detection resistor 8.

Hereinafter, the operation in the method of the present invention will be described with reference to the apparatus configuration diagram of FIG. 1, FIG. 3 is a magnetic characteristic diagram, and each waveform diagram of FIGS. 4, 5 (a) and (b). explain. The resistor 1a is excited by the high frequency power supply 9, the resistor 8 and the high frequency exciting coil 7 shown in FIG. The relationship between the high-frequency applied voltage of the iron core 1a, the magnetic flux density, and the exciting current is expressed by equation (1).

Where E _H : High frequency applied voltage i: High frequency excitation current R: Detection resistance N _H : Number of turns of high frequency excitation coil A _C : Magnetic path cross-sectional area B: Magnetic flux density t: Time , E _H are constant, B does not change even if a magnetic field due to the current of another coil is applied.

The relationship between the magnetic field and the current is expressed by equation (3).

H _i = N _H (i / L) (3) where H _i : the magnetic field due to the high-frequency excitation current L: the magnetic path length In order to simplify the explanation, the magnetic circuit condition is expressed by equation (4). The case where the setting is made as follows will be described.

N _H = L (4) Therefore, when the condition of the expression (3) is set under the condition of the expression (4),
Equation (5) is obtained.

H _i = i (5) However, since the conductor 2a passes through the center hole of the iron core 1a,
The number of turns is one.

Magnetic field H ₁ generated by the detection current I _O is (6).

H ₁ = I _O / L (6) Next, referring to the magnetic characteristic diagram of FIG. 3 and the waveform diagram of FIG. 4, the method of the present invention will be described based on the relationship between these diagrams. explain. Here, for convenience of description, the detected current I _O is treated as I _{D in} the case of direct current.

3 and 4, when the detected current _ID flowing through the conductor 2a is 0, the point 0 of the magnetic field coincides with the point 0 of the high-frequency exciting current i. As shown by the solid line, the excitation is performed in the range of the high frequency excitation current i _{1 to} i ₂ , and the waveform of the high frequency excitation current i changes as shown by the solid line in FIG. 4, and the high frequency excitation current i is the coercive force of the iron core 1a. It becomes almost constant at i ₃ and i ₄ in the vicinity. When the magnetic flux substantially enters the saturation region, i rapidly increases to i ₁ and i ₂ .

Here, when a DC positive current _ID flows through the conductor 2a and a magnetic field _ID / L corresponding to the above equation (6) is applied, the hysteresis curve shown in FIG. Moves to the negative side as indicated by the dotted line, and the maximum value of i is i ₅ ,
i ₆ and i near the coercive force become i ₇ and i ₈ , and the waveform of the current i is as shown by the dotted line in FIG. That is, the magnetic field when the detected current _ID flows is such that the zero point is on the negative side as shown by the dotted line in FIG.
It moves by I _D / L, and when I _D flows through the conductor 2a, the maximum value of the high-frequency excitation current i increases on the positive side (i ₁ →
i _5), the negative side is smaller (i ₂ → i _6), the current i ₃ and i ₄ corresponding to the coercive force is increased on the negative side and i _7, i _8, respectively. conductor
When the current of 2a is negative, the phenomenon is the same as that of the above, except that the change in the magnetic field and the current is reversed in the positive and negative directions.

FIGS. 5 (a) and 5 (b) show a change in _ID when a DC current _ID flows through the conductor 2a, and the waveform of the voltage across the detection resistor 8, that is, the high-frequency excitation current i. When a DC current _ID flows through the conductor 2a as shown in FIG. 5A, a voltage drop having the same waveform as the high-frequency excitation current waveform shown in FIG. When the detected current _ID is 0, the high-frequency excitation current i is symmetric in positive and negative directions. When the positive detected current _ID flows, the positive maximum value of the high-frequency excitation current i increases and the negative maximum value decreases. The opposite is true when the detected current _ID is negative. On the other hand, the value of the coercive force near the high-frequency excitation current i is moved to the negative side if positive is I _D, when I _D is negative moves to the positive side. Therefore, the detected current _ID can be obtained from a value near the coercive force of the high-frequency exciting current i or a change in the maximum value. When the current to be detected is an alternating current, only the phenomenon is accelerated. Therefore, it is basically the same as the case of a direct current and can be detected.

As described above, the high-frequency excitation current i, that is, the voltage change at both ends of the detection resistor 8 [the change in iR in equation (1)] is described. However, since E _H is constant, N _H A in the second term on the right side of equation (1) is used. _The detected current _ID can also be obtained from _C dB / dt, that is, the voltage at both ends of the high-frequency excitation coil 7 in FIG.

First, a method for detecting the detected current _ID from a value near the coercive force of the high-frequency exciting current i will be described as a first method. Here, the current to be detected is calculated from the voltage between both ends of the detection resistor 8.
A method for obtaining _ID will be described. FIG. 6 is a schematic diagram showing an example of the device configuration, and the same reference numerals are used for the same parts as in FIG. In FIG. 6, an inverting amplifier 10 and a low-pass filter 11 are connected in this order from both ends of the detection resistor 8, and the following signal processing is performed. When the detected current waveform diagram of FIG. 5A is obtained by using the apparatus of FIG. 6, FIG. 7A is obtained as an inverting amplifier output waveform diagram. This waveform is the fifth
The maximum value of the voltage between both ends of the detection resistor shown in FIG. When the voltage shown in FIG. 7A is input to the low-pass filter 11, the output becomes as shown in FIG. 7B, and the output is a value proportional to FIG. Output voltage is the detected current I _D
It becomes a voltage proportional to.

Comparing these details in more detail, when the DC detected current _ID is 0, as shown in FIG.
Since the output of 10 has the same positive and negative values, the low-pass filter 11
Is 0 as shown in FIG. 7 (b). When the next DC detected current _ID is positive, the output of the inverting amplifier 10 is in a region (time zone) corresponding to the coercive force as shown in FIG.
Moves to the positive side, and the output of the low-pass filter 11 is a positive voltage as shown in FIG. When _ID is negative, the polarity is reversed from the above, and the output of the low-pass filter 11 becomes a negative voltage. As described above, an output voltage proportional to the detected current _ID is obtained from the low-pass filter 11.

When the current to be detected is an alternating current, FIGS. 5 (a), (b),
Only the change of each value of FIGS. 7 (a) and 7 (b) becomes faster,
This is basically the same as the case of direct current, and this current can be detected. According to the method of the present invention, it is possible to detect a small current having any waveform such as a distorted wave or a square wave, as is apparent from the above operating principle.

Current detection zone according to the invention, Figure 3, Figure 4 from the detected current I _D is between the positive when i ₄ and i _2, when the detected current I _D is negative i ₃ and i ₁ be between, but the number of turns of the high-frequency excitation coil 7 of FIG. 1, the detection resistor 8, can be arbitrarily set by changing the high frequency applied voltage E _H. Since the material of the iron core 1a is excited at a high frequency, it is necessary to have good high-frequency characteristics. Frequency of the high-frequency excitation power supply 9 is better high in principle, practically, must be determined by taking into consideration the frequency components of the detected current i _D, required detection accuracy, and the frequency characteristic of the core material .

The method of obtaining the current to be detected _ID from the voltage change between both ends of the high-frequency excitation coil 7 described above is basically the same as the method for calculating the current between both ends of the detection resistor 8, and thus the description thereof is omitted.

Next, the second method will be described. This is a method of obtaining a detected current _ID from a change in the maximum value of the high-frequency excitation current i. FIG. 8 is a schematic diagram showing an example of the configuration of the apparatus. Here, the same reference numerals are used for the parts common to FIG. In FIG. 8, a half-wave rectifier circuit 12 capable of rectifying even a low voltage with an operational amplifier and a rectifier is provided at both ends of the detection resistor 8.
a, a high-frequency peak hold unit 13a, a half-wave rectifier circuit 12b having the same performance in parallel with these, and a peak hold unit 13b are connected, and both output sides are led to an adder 14 to perform the following signal processing. . Here, a case where a current having the waveform of FIG. 5A is detected using the apparatus of FIG. 8 will be described. At this time, the voltage across the detection resistor 8 becomes as shown in FIG. By the peak hold devices 13a and 13b, the positive side,
FIG. 9 (a) shows a form in which the maximum value of each negative side is plotted. When the detected current _ID is 0 (t ₁ to
At t ₂ ), since the outputs of the high-frequency peak hold units 13a and 13b have the same positive and negative values as shown in FIG. 9A, the output of the adder 14 is also shown in FIG. 9B. It is 0 as described above. If the detected current I _D of the direct current positive (t ₂ ~t _4), the peak hold circuit 13a, the output of 13b is greater positive, both negative,
Since the output of the adder 14 becomes the sum of these, it takes a positive value.
If I _D is negative (t ₄ ~t _5), the peak hold circuit 13a, 13b
Is smaller on both the positive side and the negative side, and the output of the adder 14 has a negative value. In this way, the output of the adder 14 becomes a voltage proportional to the current I _D [FIG. 5 (a)] as shown in FIG. 9 (b).

When the current to be detected is an alternating current, the various changes in FIGS. 5A and 5B only become faster as in the above-described method using the vicinity of the coercive force. And this current can be detected. Also in the case of the second method, the current to be detected _ID can be obtained from both ends of the high-frequency excitation coil 7.

By the way, as described above, in the current detection method of the present invention, the core is excited at a high frequency, and the exciting current is changed by changing the point at which the exciting current is near the coercive force or the maximum value on the hysteresis curve of the iron core. Is particularly effective for detecting zero-sequence current.However, when this is used for an earth leakage breaker, a problem may occur if a load causes a ground fault. is there. That is, the method described above can detect well in a small current range, but when a large current flows and the detector cannot follow, the magnetic flux of the iron core enters a saturation region, and the high-frequency excitation current is positive and negative. That is, detection becomes impossible. Therefore, when applied to earth leakage breaker, there is no problem in the normal earth leakage current range, but a large current flows instantaneously due to ground fault etc.
It is necessary to take measures in consideration of the case where the leakage current cannot be detected.

A method for detecting a current when a large current flows due to a ground fault or the like will be described below. FIG. 10 is a schematic diagram of a device that operates appropriately for an instantaneous large current (ground fault current), and the same reference numerals are used for the same parts as in the previous drawings. In FIG. 10, the detection of the small current side (normal leakage current)
And the output side is an output combiner 15
Connected to The detection of the large current side (current due to ground fault or the like) is performed by detecting the double-wave rectifier 16a and the smoother 17a from both ends of the detection resistor 8.
To the waveform comparator 18 and a voltage divider 19 for taking out the voltage of the high-frequency excitation power supply 9 by another circuit, a double-wave rectifier 16b,
The waveform comparator 18 is connected to the waveform comparator 18 in this order, and the waveform comparator 18 is connected to the output combiner 15 by a circuit.

FIG. 11 (a) shows the change of the detected current with time,
FIG. 11 (b) shows the change over time of the voltage across the detection resistor 8, that is, the high-frequency excitation current i. FIG. 11 (a), (b)
Between the t ₆ ~t ₇ FIG. 5 described above in a range to be detected current is small (a), is the same as (b). Figure 11 (a), when the detected current is very large in t ₈ (b), the variation range of the magnetic flux density for the magnetic flux density of the iron core 1a approaches the saturation region becomes small, (1) hand side The value of the two terms decreases,
The high-frequency exciting current i is expressed by the following equation (7), and has a large value with a sine wave and positive and negative symmetry as shown in FIG. 11 (b). The high-frequency power supply waveform is a case where a sine wave is used.

i = E _H / R (7) Since the output of the low-pass filter 11 in FIG. 10 is the sum of the positive and negative of the high frequency exciting current i (the difference between the positive and negative absolute values), FIG. a), a substantially becomes 0, the detected current is not sought at all t ₈ after the (b). The detection of an increase in the positive and negative values of the high frequency exciting current i on the large current side is the second step.
The circuit in the middle (16a → 17a → 18 → 15) and the lower (19
→ 16b → 17b → 18 → 15) It is necessary that no output is generated on the small current side. The middle stage circuit prevents the voltage drop due to the high-frequency excitation current i from being output through the dual-wave rectifier 16a even in the positive / negative symmetry, and the smoother 17a
The influence of the pulse-like portion of the high-frequency excitation current i generated on the small current side is reduced. Lower circuit is intended to create a reference voltage, since the voltage is divided and the magnetic flux density of the iron core 1a at a large current side is changed slightly, it needs to be smaller than E _H and resistive voltage drop caused by the detection resistor R, After the voltage is divided by the voltage divider 19, it is rectified and smoothed by the double-wave rectifier 16b and the smoother 17b. In the waveform comparator 18, the output of the smoothing unit 17a is small in the range where the current to be detected is small, and the magnetic flux density change range of the iron core 1a is small when the current to be detected is large, and the smoothing unit 17a
Output increases to produce an output.
The reference voltage from 17b must be set such that the output of waveform comparator 18 occurs. The output combiner 15 is configured to output the larger value of the input from the small current detection side (low-pass filter 11) and the input from the large current detection side (waveform comparator 18).

FIG. 12 is a relationship diagram between the detected current and the output voltage,
The output of the small current side detection circuit (low-pass filter 11) in FIG. 10 is indicated by a solid curve A, and the output of the large current side detection circuit (waveform comparator 18) is indicated by a broken line B. Since the output of the output combiner 15 is the larger of the two outputs, even if a large current flows instantaneously due to a ground fault or the like, the output occurs, so there is no problem at all. Note that the leakage detector only needs to detect that a current is flowing on the large current side, and it is not necessary to detect the value, so that it is sufficient to obtain the characteristics shown in FIG.

As the reference voltage, another DC power supply can be used as shown in FIG. FIG. 13 is a schematic diagram in which a part of FIG. 10 is omitted, in which the device is configured using a DC power supply 20 instead of the voltage divider 19, the double-wave rectifier 16b, and the smoothing device 17b of FIG. .
Further, the detection of the large current side in the above-described second method can be basically performed in the same manner as the above-described method, and thus the description thereof is omitted.

As above, the basic matters of the device configuration and operation of the DC and AC current detection method according to the present invention have been described. Next, a specific example using the method of the present invention will be described again with reference to FIG. The iron core 1a used had a composition of 82Co-2Ni-
A 4.5Fe-8.5Si-3B amorphous alloy ribbon was formed into a cylindrical wound core, subjected to a predetermined heat treatment, and then placed in a plastic case. This amorphous alloy has excellent magnetic properties of high frequency as well as direct current, and also has a small magnetostriction, so that the influence of stress on the magnetic properties is small, handling is easy, and it is suitable for use as the iron core 1a. . The dimensions of iron core 1a are outer diameter 13mm, inner diameter 10mm,
The height (width of the ribbon) is 2 mm. The conductor 2a was a copper wire having a diameter of 1 mm. The high-frequency excitation coil 7 was manufactured by using a formal copper wire having a diameter of 0.1 mm and winding 90 times around the thick portion of the iron core 1a. Since the current flowing through the high-frequency excitation coil 7 is small, it is sufficient to use such a copper wire. The inverting amplifier 10 has an amplification factor of 10 times and a saturation point of ± 12V. The low-pass filter 11 has a cut-off frequency of 1 KHz in two stages. The high frequency excitation power supply 9
The square wave generation circuit by IC, frequency was 10KHz, voltage was about 6V.

FIG. 14 is a diagram showing the relationship between the output voltage obtained when a DC current is detected and the detected current value obtained by the method of the present invention as described above. The output characteristic lines A, B and C in FIG. 14 are obtained when the detection resistor 8 is set to 500, 200 and 100Ω, respectively. The minimum detectable current is 1m under condition (a).
It is about 2 mA under A and B conditions and about 5 mA under C conditions. These characteristics have good linearity, can detect the positive / negative of the current, and have a large output voltage. FIG. 15 is a characteristic diagram showing a relationship between an effective value of an output voltage and an effective value of a detected current when a 50 Hz AC sine wave current is detected with a detection resistance of 500Ω according to the method of the present invention. FIG. 15 shows, for comparison, FIG.
The output characteristics obtained by the conventional method described in Fig. 19 are also added.
The solid line represents the method of the present invention, and the dotted line represents the conventional method. In the conventional method, for example, permalloy (trade name) is used for the iron core 1, the dimensions of the iron core 1 are made the same as those in the embodiment of the present invention, and the number of turns of the detection coil 3 is set to 500, and the core is amplified 10 times. As can be seen from FIG. 15, according to the method of the present invention, the output voltage is larger than that of the conventional method, and is about twice as large. Further, it is needless to say that a current in which DC and AC are superimposed can be detected by using the method of the present invention.

As described above, in the present embodiment, the case where the high-frequency power supply 9 is a square wave has been described. However, the waveform may be other wave diameters such as a sine wave and a triangular wave. The maximum value of the high-frequency exciting current i was saturated by the inverting amplifier 10 to reduce its influence. However, since this portion is pulse-shaped and the average value is much smaller than the current average value near the coercive force, the excitation condition Can be neglected, and the inverting amplifier 10 can be omitted. If the inverting amplifier 10 is omitted, the positive / negative relationship between the current to be detected and the output is reversed, but the conductor 2a and the high-frequency excitation coil 7
By reversing the winding direction, it is possible to make the detected current coincide with the sign of the output, and there is no problem in practice.

Next, a specific example using the above-described second method in the present invention will be described again with reference to FIG. The iron core 1a used is the same as that used in the first method described above. The high-frequency excitation power supply 9 used a square wave of 10 KHz, and the voltage was about 6V. In order to avoid the influence of the electric resistance of the rectifiers themselves, the half-wave rectifiers 12a and 12b are combined with an operational amplifier to form an ideal rectifier circuit. In the adder 14, the positive side component is kept in that state, and only the negative side component is inverted by the IC circuit, and then both components are put into the differential amplifier.

FIG. 16 is a diagram showing the relationship between the voltage obtained when DC current is detected and the current to be detected by the method of the present invention as described above. This characteristic is linear, and it is possible to detect whether the current is positive or negative, and the output voltage is large. 17th
The figure is a characteristic diagram showing a relationship between an output voltage effective value and a detected current effective value when a sine wave current of AC 50 Hz is detected by the method of the present invention. FIG. 17 shows, for comparison, FIG.
The output characteristics obtained by the conventional method described in Fig. 19 are also added.
The solid line represents the method of the present invention, and the dotted line represents the conventional method. As can be seen from FIG. 17, according to the method of the present invention, the output voltage is much larger than that of the conventional method, that is, about 50 times. Further, it is needless to say that a current in which DC and AC are superimposed can be detected by using the method of the present invention.

As described above, the small current detection method of the present invention has been described as using one conductor. However, since a small current can be detected as described above, two or three conductors can be detected. Of course, the present invention is sufficiently applicable to a zero-phase detector for detecting a difference current, and furthermore, by using the method of the present invention, there is a great advantage that the detection device can be smaller than the conventional one.

Next, FIG. 18 is a characteristic diagram in which a large current flows due to a ground fault or the like by using the method of the present invention for an earth leakage breaker, and a small current side and a large current side are actually measured by the apparatus of FIG. is there.
The iron core and circuit conditions are the results of the first method (second
It is the same as the case of Fig. 14). In FIG. 18, the output of the small current detecting circuit and the characteristic line B of the characteristic line A are the outputs of the large current detecting circuit, and the output of the output combiner 15 is the larger of the two outputs. When applied to the operation sensitivity of the earth leakage breaker of 20mA, the output voltage must always be larger than the output voltage _{EZO at} 20mA in the current region of 20mA or more.In this example, the output voltage of the small current detection side is 3A or more. Become smaller. The large current detection circuit compensates for this. In this example, the current value at which the high current side output is generated is between 200 and 3000 mA.However, from the viewpoint of reliability, it is desirable to set the current value slightly larger than the current value at which the low current side output is maximum.
0 to 300 mA. The point at which the output of the large current detection circuit is generated can be arbitrarily set by adjusting the voltage divider 19 shown in FIG.

In the method of the present invention, by providing a large current detection circuit as described above, a large current flows instantaneously, the small current side detection unit cannot follow this, and the operation of the circuit breaker, the relay, etc. is not performed. Even if possible, these devices can be operated by detecting the current with the high current side detection unit. Also, according to this method, without combining with the small current detection,
It is also possible to detect a large current alone.

〔The invention's effect〕

Conventionally, a small current such as a zero-phase current can be detected only by an alternating current, and a direct current leakage breaker or the like cannot be obtained.On the other hand, according to the method of the present invention, as described in the embodiment. As described above, the high-frequency excitation of the iron core is performed up to a point larger than the coercive force, and the magnetic field generated by the detected current of the conductor passing through the center hole of the iron core utilizes the fact that the high-frequency exciting current near or at the maximum value changes. Since the current is detected by extracting the change in the high-frequency excitation current from the voltage drop of the detection resistor or the voltage change in the high-frequency excitation coil, the output voltage and the current to be detected show very good linearity. Of course, it is also possible to easily detect a small current in which both DC and AC and DC currents are superimposed, and to manufacture a DC leakage breaker in addition to the conventional AC equipment without increasing the size of the device. Possible It became. Also, the method of the present invention,
Even when a small alternating current is detected, the output is larger than in the conventional method, and a control circuit, a cutoff circuit, and the like using this output can be simplified. Furthermore, when a ground fault current such as an earth leakage circuit breaker flows, the output voltage decreases and the circuit breaker cannot be operated. In contrast, the method of the present invention adds a circuit to prevent this from occurring. By doing so, an output that can be cut off is always maintained even on the large current side.
That is, the present invention can be said to be a current detection method for a wide range of alternating current from a small current to a large current.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main part of a device for detecting a small current to which the method of the present invention is applied, FIG. 2 is a conceptual diagram showing a shape of a magnetic hysteresis curve of an iron core material, and FIG. FIG. 4 is a magnetic characteristic diagram showing a magnetic hysteresis curve approximated by a single line, FIG. 4 is a diagram showing the relationship between a magnetic field generated in an iron core and a high-frequency excitation current waveform, and FIG. FIG. 5 (b) is a voltage waveform diagram across the detection resistor, and FIG. 6 is a diagram showing the detected current from the voltage across the detection resistor for the device of FIG. FIG. 7 (a) is an output voltage waveform diagram of an inverting amplifier in the device of FIG. 6, and FIG. 7 (b) is an output voltage waveform of a low-pass filter similarly. 8 and FIG. 8 show the current to be detected from the voltage across the high-frequency excitation coil for the apparatus of FIG. FIG. 9 (a) is an output voltage waveform diagram of a peak hold device in the device of FIG. 8, and FIG. 9 (b) is an output voltage waveform diagram of an adder. , FIG. 10 is a schematic diagram showing a main configuration of an apparatus for detecting a large current to which the method of the present invention is applied,
FIG. 11 (a) is a relationship diagram showing a change in time and a current to be detected in the apparatus of FIG. 10, FIG. 11 (b) is an output voltage waveform diagram of both ends of the detection resistor, and FIG. A relationship diagram showing the relationship between the current and the output voltage on the small current side and the large current side,
FIG. 13 is a partial schematic diagram showing a configuration of a device using a DC power source as a modification of FIG. 10, and FIG. 14 is an output voltage obtained when DC current is detected using the device of FIG. FIG. 15 is a diagram showing the relationship between the output voltage effective value and the detected current effective value when an AC sine wave current is detected, and FIG. FIG. 17 is a relationship diagram between an output voltage obtained when a DC current is detected and a detected current, and FIG. 17 is a relationship line between an output voltage RMS value and a detected current RMS value when an AC sinusoidal current is also detected. FIG. 18 is a graph showing the relationship between the output voltage and the detected current obtained when the small current side and the large current side are actually measured using the apparatus of FIG.
FIG. 20 is a schematic diagram showing a main part configuration for explaining the operation of the zero-phase current transformer, and FIG. 20 is a conceptual diagram showing a shape of a magnetization curve of the iron core material in FIG. 1,1a: Iron core, 2, 2a: Conductor, 3: Detection coil, 4: Resistance, 5: AC power, 6: Load, 7: High frequency excitation coil, 8: Detection resistance, 9: High frequency power, 10: Inverting amplifier , 11: low-pass filter, 12a, 12b: half-wave rectifier circuit, 13a, 13b: peak hold device, 14: adder, 1
5: output combiner, 16a, 16b: double wave rectifier, 17a, 17b: smoother,
18: Waveform comparator, 19: Voltage divider, 20: DC power supply.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-148966 (JP, A) JP-A-63-35962 (JP, U) JP-B-63-131070 (JP, B2)

Claims (4)

(57) [Claims] 1. A coercive force of a hysteresis curve of a closed magnetic path iron core having a rectangular magnetic hysteresis curve formed of a material having a high permeability and connecting an excitation coil wound around a thick portion of the iron core and a high-frequency power supply. Up to a larger region, high-frequency excitation is performed under the same conditions in both the positive and negative directions of the magnetic field, and the magnetic field generated by the detected current flowing through the conductor passing through the center hole of the iron core is applied to move and maintain the magnetization range of the hysteresis curve. The high-frequency excitation current in the vicinity of the magnetic force is changed, and the change is taken out as a voltage drop change of a detection resistor connected in series with the excitation circuit or a voltage change of the excitation coil, and subjected to signal processing. An AC / DC dual-purpose current detection method, wherein the detected current is obtained from a difference between values. 2. In performing the current detection according to claim 1), for a current in which the magnetic flux density of the iron core changes only in the saturation region, the output is maintained from the sum of the positive and negative absolute values of the signal processed voltage. An AC / DC dual-purpose current detection method. 3. A coercive force of a hysteresis curve of a closed magnetic circuit iron core having a rectangular magnetic hysteresis curve made of a material having a high magnetic permeability, which is connected to an exciting coil wound around a thick portion of the iron core and a high-frequency power supply. Up to a larger area, high-frequency excitation is performed under the same conditions in both the positive and negative directions of the magnetic field, and the magnetization range of the hysteresis curve is moved by applying a magnetic field generated by a detected current flowing through a conductor passing through the center hole of the iron core. The maximum value of the high-frequency excitation current is changed, the change is taken out as a voltage drop change of a detection resistor connected in series to the excitation circuit or a voltage change of the excitation coil, and signal processing is performed, and the positive and negative absolute values of the signal voltage are obtained. Wherein the detected current is obtained from the difference between the two. In the current detection according to the third aspect, the output is maintained from the sum of the positive and negative absolute values of the signal processed voltage for the current in which the magnetic flux density of the iron core changes only in the saturation region. An AC / DC dual-purpose current detection method.