JPH0619379B2 - Current detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a current detection device for detecting a leakage of a load or a power line.

BACKGROUND ART In the prior art, a magnetic multivibrator circuit including a saturable reactor for detecting a current to be detected, which is provided in association with a line through which the current to be detected is to be detected, has a leakage current in a line through which the current to be detected flows. Even without
The larger the balanced current in that line, the higher the oscillation frequency. When the oscillation frequency becomes high in this way, each circuit connected to the subsequent stage of the magnetic multivibrator circuit malfunctions, and it is difficult to detect the leakage current normally.

FIG. 1 is a perspective view of a saturable reactor included in a prior art magnetic multivibrator circuit. Core K has
The coil L1 and the coil L2 are wound. Near the center of the core K, a line 11 and a line 12 through which a current to be detected flows are penetrated. This saturable reactor has a BH characteristic as shown in FIG. Assuming that the saturable reactor has the ability to be excited up to the exciting force Ha in a circuit manner, the oscillation frequency of the magnetic multivibrator circuit is generally as shown in the following first equation.

Where E is the applied voltage, 8 is the cross-sectional area of the core K, N is the core K
Is the number of turns of the coil wound around.

When a large balanced current flows through the lines l1 and l2, the third
As shown in FIG. 1A, the magnetic flux density in the regions K1 and K2 of the core K becomes high, and the core K is saturated. As shown in FIG. 3 (2), the magnetic force lines 3D are dense near the center of the core K, and the magnetic force lines 3C and 3E near the top and bottom of the core K are coarse. Therefore, the B-H characteristic of the entire saturable reactor changes as shown in FIG. 4, so that the oscillation frequency becomes as shown in the second equation below.

When the equilibrium currents of the lines l1 and l2 further increase, the oscillation frequency becomes as shown in the following third equation.

Here, in the first to third equations, each oscillation frequency, ′, ″ has the following fourth equation due to the relation of Bm> Bm ′> Bm ″.

<<'<''(4) As shown in the fourth formula, the oscillation frequency of the magnetic multivibrator circuit increases as the equilibrium current of the lines l1 and l2 increases. The oscillation frequency of the circuit fluctuates even if the currents flowing in the lines l1 and l2 are balanced, and the original operation purpose cannot be achieved because the currents flowing in the lines l1 and l2 are unbalanced. Only when is, the duty of the output pulse of the magnetic multivibrator circuit is changed, and the leakage current is detected by the circuit in the subsequent stage.

It is an object of the present invention to solve the above technical problems, to provide a current detection device capable of preventing malfunction due to a balanced current in a detected line and accurately detecting a leak current.

Structure of the Invention The present invention is provided in connection with two lines in which a current to be detected to be detected flows, and is saturable having a first coil and a second coil for detecting the current to be detected. A magnet that includes a reactor and a resistor that controls a current flowing through the first coil and the second coil, oscillates by changing a duty of a predetermined cycle according to the detected current, and outputs output signals that are inverted from each other. The multivibrator circuit and a pair of duty detection circuits that detect the duty of each output signal of the magnetic multivibrator circuit, and the output signal corresponding to the duty of the signal from each duty detection circuit are input, and the level difference between the output signals is calculated. Rectify the voltage level corresponding to the rectified current to the capacitor C
The high-frequency oscillation of the magnetic multivibrator circuit including the voltage / current conversion circuit derived from 7 and the saturable reactor is detected to detect the capacitor C.
7, a high-frequency detection circuit for charging 7, a detection circuit for detecting that the output voltage of the capacitor C7 exceeds a predetermined value, a magnetic multivibrator circuit, a duty detection circuit, a voltage / current conversion circuit, and a high-frequency detection circuit. And a control circuit that stops the oscillation of the magnetic multivibrator circuit until the output of the power circuit reaches a predetermined value. The saturation reactor is formed by winding the first and second coils around the annular magnetic core, and the two lines in which the detected current flows pass through the annular magnetic core in a twisted state. It is a current detection device.

Embodiment FIG. 5 is an electric circuit diagram of a current detecting device to which a saturable reactor according to an embodiment of the present invention is connected.

The operation of the electric circuit A will be described. Switches S1 and S2 are turned on, and electric power from AC power supply E0 is applied to lines 11 and 12. The alternating voltage applied to the lines l1 and l2 is rectified by the circuit composed of the diodes D1, D2, D3, 4, the coil L, the resistor R1 and the capacitor C1 and becomes a direct voltage. At the same time when the electric power from the AC power source E0 is input, the transistor Tr1 is turned on by the direct current flowing through the line 13 and the capacitor C2 is charged.
When the transistor Tr1 turns on, the transistor T
The r2 is turned on, and the line 14 of the emitter obtains a constant voltage that does not include a ripple component. When the collector potential of the transistor Tr2 exceeds a predetermined potential, the comparator 1 operates and a base current flows through the transistor Tr3. As a result, the transistor Tr3 turns on and the transistor Tr3
1 draws the base current to turn off the transistor Tr1. On the other hand, at the same time, the output of the comparator 1 turns on the transistor Tr12 to lower the threshold voltage applied to the non-inverting input terminal of the comparator 1. The load circuit connected to the power supply circuit A consumes energy, and the capacitor C2
Potential of the comparator 1 decreases, the potential of the inverting input terminal of the comparator 1 decreases, and the output of the comparator 1 inverts. As a result, the transistors Tr3 and Tr12 are turned off, and the transistor Tr1
Turns on and charges the capacitor C2.

Next, the operation of the control circuit B will be described. Until the potential of the emitter line 14 of the transistor Tr1 of the power supply circuit A reaches a predetermined value, the control circuit stops the oscillation of the magnetic multivibrator circuit C in order to prevent malfunction of the circuit at the subsequent stage. When the potential of the line 14 reaches a predetermined value, the comparator 2 operates and turns on the switches S3 and S4 of the magnetic multivibrator circuit C.

Next, the operation of the magnetic multivibrator circuit C will be described.
The magnetic multivibrator circuit C includes switches S3 and S4.
The oscillation operation is started as is turned on. A saturable reactor having a coil L1 and a coil L2 for detecting a current flowing through the lines 11 and 12 is provided in association with the lines 11 and 12 connected to the load L0. One ends of the coil L1 and the coil L2 of the saturable reactor are connected to the line 14 via the resistor R. The other end of the coil L1 is connected to the collector of the transistor Tr4, and the other end of the coil L2 is connected to the transistor Tr5.
Connected to the collector. With the circuit including the coils L1 and L2 and the transistors Tr4 and Tr5, the transistor Tr5 is turned off when the transistor Tr4 is turned on,
Conversely, when the transistor Tr5 is turned on, the transistor Tr4 is turned off and oscillation is performed. When there is no leakage current in the line l1 or the line l2, the reactances of the coil 1 and the coil L2 do not change, so that the on / off duty ratio of the transistors Tr4 and Tr5 is 1 :.
It remains 1. When a leakage current occurs in the line 11 or the line 12, the reactance of the coils L1 and L2 changes, so that the transistors Tr4 and Tr5 are turned on / off.
Off duty ratio varies from 1: 1. The magnetic multivibrator circuit C sends out pulse signals whose phases are mutually inverted from the collector of the transistor Tr4 and the collector of the transistor Tr5.

Next, the operation of the duty detection circuit D will be described. The switch S is synchronized with ON / OFF of the transistors Tr4 and Tr5 of the magnetic multivibrator circuit C.
5 to S8 are turned on / off. The switches S5 and S8 turn on when the transistor Tr5 is on. Switch S
6, S7 is turned on when the transistor Tr4 is turned on.

Here, assuming that the magnetic multivibrator circuit C is performing a normal oscillation operation, the operation will be described below with reference to the waveform chart of FIG. In the duty detection circuit D,
A pulse signal as shown in FIG. 6 (2) is applied to the connection point a'of the switch S5, the switch S6 and the resistor R11. A pulse signal as shown in FIG. 6 (3) is applied to the connection point b'of the switch S7, the switch S (8) and the resistor 13. Yotsute thereto, from the connection point a between the resistor R11 and the resistor R12 and the capacitor C ₃ signal P1 of the DC voltage as shown in FIG. 6 (1) it is sent. From the connection point b between the resistor R13, the resistor R12 and the capacitor C4, FIG.
A DC voltage signal P2 as shown in (1) is transmitted.

Here, if a leakage current occurs, the signal P in FIG.
There is a difference between the average values of 1 and P2. These signals P1 and P2
Becomes an input of the voltage / current conversion circuit F.

Next, the operation of the high frequency detection circuit E will be described. The inverting input terminal of the comparator 8 has a connection point a ′ of the duty detection circuit D.
From the connection point b ′ of the date detecting circuit D is applied to the non-inverting input terminal of the comparator 8. As a result, the comparator 8 operates and activates the transistor Tr6. Collector of transistor Tr6
A capacitor C5 is connected between the emitters, and the signal P4 shown in FIG. 6 (4) is sent to the collector of the transistor Tr6. This signal P4 is applied to the non-inverting input terminal of the comparator 3, and the inverting input terminal of the comparator 3 is applied with the threshold voltage of the level of the line A4 shown in FIG. 6 (4). This causes the comparator 3 to operate and activate the transistor Tr7. A capacitor C6 is connected between the collector and the emitter of the transistor Tr7, and the signal P5 shown in FIG. 6 (5) is sent to the collector of the transistor Tr7. This signal P5 is given to the non-inverting input terminal of the comparator 4, and the inverting input terminal of the comparator 4 has the line A5 shown in FIG. 6 (5).
A threshold voltage of the level is given. Thus, the level of the signal P5 is set by the comparator 3 to be lower than the threshold voltage of the level shown by the line A5. In this state, the switch S9 is not turned on by the output of the comparator 4.

Here, for example, a large leakage current is generated in the line l1,
The operation when the output pulse of the magnetic multivibrator circuit C reaches a high frequency will be described. At this time, a pulse signal as shown in FIG. 7 (2) is given to the connection point a'of the duty detection circuit D, and a pulse signal as shown in FIG. 7 (3) is given to the connection point b '. To be Therefore, the signal P11 as shown in FIG. 7 (1) is transmitted from the connection point a of the duty detection circuit D, and the signal P12 as shown in FIG. 7 (1) is transmitted from the connection point b. The comparator 8 is shown in FIG. 7 (2).
The transistor Tr6 is activated by operating with the pulse signal shown in FIG. 7 and the pulse signal shown in FIG. 7 (3). From the collector of the transistor Tr6, the signal P1 shown in FIG.
4 is sent out. The level of this signal P14 is determined by the comparator 3
Is lower than the threshold voltage of the level indicated by the line A4 applied to the inverting input terminal of. Therefore, the output of the comparator 3 is
The transistor Tr7 is turned off and the capacitor C6 is charged by the current of the constant current source E6. As a result, the collector voltage of the transistor Tr7 rises like the line A6 shown in FIG. 7 (5) and becomes higher than the threshold voltage of the level shown at the line A5 given to the inverting input terminal of the comparator 4, The device 4 turns on the switch S9.

Next, the operation of the voltage / current conversion circuit F will be described. When the switch S9 of the high frequency detection circuit E is turned on, the current of the constant current source E8 flows into the capacitor C7 and charges the capacitor C7. Comparator 6 and diode D13
, Transistor Tr9, comparator 5, and diode D14
And a transistor Tr ₈ form a buffer, and a potential difference between a signal applied to the non-inverting input terminal of the comparator 6 and a signal applied to the non-inverting input terminal of the comparator 5 is divided by the resistor R14.
Converted into a current value divided by the resistance value of
And the capacitor C7 is charged by the current from the collector of Tr8. The non-inverting input terminal of the comparator 6 is connected to the connection point a of the duty detection circuit D, and the non-inverting input terminal of the comparator 5 is connected to the connection point b of the duty detection circuit D. On the other hand, the constant current drawing circuit composed of the resistor R15, the transistor Tr10, and the transistor Tr11 does not raise the potential of the capacitor C7 up to a preset current value. Therefore, when the leakage current is equal to or more than the set current value, the capacitor C7 is charged, and the output circuit G detects that the output voltage of the capacitor C7 is equal to or more than a predetermined value.

The output circuit G sends a signal from the comparator 7 to turn off the switches S1 and S2 when the potential of the capacitor C7 exceeds a predetermined value. Yotsute thereto, the load L0 is disconnected from the AC power source E _0.

As described above, when the detected currents on the lines 11 and 12 are small, the duty ratio of the output pulse of the magnetic multivibrator circuit C is detected by the voltage / current conversion circuit F. When the detected current is large, the frequency of the output pulse of the magnetic multivibrator circuit C becomes high, and the high frequency detection circuit E detects the frequency. Therefore, the high frequency detection circuit E and the voltage / current conversion circuit F can reliably detect the detected current.

FIG. 8 shows the detected current Ig which is the leakage current of the load L0.
6 is a graph showing the relationship between the average output current I0 sent from the collectors of the transistors Tr9 and Tr8 of the voltage / current conversion circuit L. In contrast to the characteristic of the conventional voltage / current conversion circuit shown by the broken line, the characteristic of the voltage / current conversion circuit F of one embodiment of the present invention is shown by the solid line. The characteristic indicated by this solid line is the case where the output signal of the duty detection circuit D contains ripples, and due to such characteristic, FIG.
Even if the detected current is as shown in Fig. 9 (3), Fig. 9 (4)
It is possible to sufficiently approach the same detection operation state as that in which the alternating current as shown in FIG. Although the voltage between the connection points a and b of the duty detection circuit D is given to the low-pass filter as the input of the conventional high frequency detection circuit and differentiated to detect only the ripple, the voltage between the connection points a and b is detected by noise. Change, a sharp voltage change occurs in the ripple, the high-frequency detection circuit is likely to malfunction, and the noise resistance is poor. However, since the voltage / current conversion circuit F of the present embodiment operates regardless of the voltage change between the connection points a and b of the duty detection circuit D, the noise resistance can be improved.

FIG. 10 is a perspective view of a saturable reactor according to an embodiment of the present invention. In FIG. 10, the same reference numerals are assigned to the components corresponding to those shown in FIG. A coil L1 and a coil L2 are wound around the core K. Core K
A line 11 and a line 12 through which a current to be detected flows are twisted in the vicinity of the center of the line. As shown in FIG. 11, the current I flowing through the line l1 is applied to the core K by the magnetic flux a1,
The current I flowing through the line 12 causes the magnetic fluxes b1 and b2 in the core K. However, magnetic flux a1 and speed b
2 cancel each other, and the magnetic flux a2 and the magnetic flux b1 cancel each other. Therefore, the magnetic flux density of the core K becomes small and the core K does not saturate. As a result, the fourth
It is possible to prevent the change of the oscillation frequency in the relation as shown in the equation, and to reduce the change of the oscillation frequency of the magnetic multivibrator circuit C shown in FIG. be able to.

FIG. 12 is a perspective view of a saturable reactor according to another embodiment of the present invention. In FIG. 12, the elements corresponding to those shown in FIG. 10 are designated by the same reference numerals. A coil L1 and a coil L2 are wound around the core K. Core K
A line 11 and a line 12 through which a current to be detected flows are twisted in the vicinity of the center of the line. Coil L of core K
Magnetic shields H1 and H2 are provided on both side surfaces including 1 and L2, respectively. The magnetic flux will be described with reference to FIG. The magnetic fluxes a1, b1, a2 and b2 have been described with reference to FIG. Magnetic fluxes e1, g1 generated by the current flowing in the line l1 and the line l2
The magnetic fluxes e2 and g2 generated by the current flowing in the cores K are absorbed by the shield plates H1 and H2, so that the core K is not affected by the magnetic field. As a result, the effect as described with reference to FIG. 10 can be obtained.

FIG. 14 is a perspective view of a saturable reactor according to still another embodiment of the present invention. In FIG. 14, the same reference numerals are given to those corresponding to the components shown in FIG. A coil L1 and a coil L2 are wound around the core K.
In the vicinity of the center of the core K, the line 11 and the line 12 through which the current to be detected flows are twisted and penetrates. A magnetic shield plate H3 is provided on the inner peripheral surface of the core K including the coils L1 and L2. With this configuration, it is possible to reduce the influence of the magnetic flux on the core K due to the balanced current flowing in the lines l1 and l2.

FIG. 15 is a perspective view of a saturable reactor according to another embodiment of the present invention. In FIG. 15, elements corresponding to those shown in FIG. 14 are designated by the same reference numerals. A coil L1 and a coil L2 are wound around the core K. Core K
A line 11 and a line 12 through which a current to be detected flows are twisted in the vicinity of the center of the line. Coil L of core K
A magnetic shield plate H4 is provided on the outer peripheral surface including 1 and L2. With this configuration, the lines l1,
The influence of the magnetic flux on the core K due to the equilibrium current flowing in 12 can be reduced.

FIG. 16 is a perspective view of a saturable reactor according to another embodiment of the present invention. In FIG. 16, the elements corresponding to those shown in FIG. 10 are designated by the same reference numerals. A coil L1 and a coil L2 are wound around the core K. Core K
A line 11 and a line 12 through which a current to be detected flows are twisted in the vicinity of the center of the line. Coil L of core K
Magnetic shields H5 are provided on the outer peripheral surface including 1 and L2, both side surfaces and the inner side surface. With this configuration, the influence of the magnetic flux on the core due to the balanced currents flowing in the lines l1 and l2 is reduced, and the magnetic shield plate H5 also serves as the outer case of the core K.

As described above, according to the present invention, by screwing at least a section related to detection of the line, an increase in the oscillation frequency of the magnetic multivibrator circuit at the time of application of a balanced current flowing in the line is reduced, It is possible to reduce the possibility of malfunction due to the large balanced current and the increase in the sensitivity current of the detected current, and it is possible to accurately detect the leakage current.

Particularly, according to the present invention, in the current / voltage conversion circuit, the capacitor C7 is charged according to the output of the duty detection circuit. The output circuit detects that the output voltage of the capacitor C7 has exceeded a predetermined value. Therefore, even if the high-frequency detection circuit malfunctions, the detection output is not immediately derived from the output circuit due to this, and the excellent effect of improving noise resistance is achieved.

Further, according to the present invention, power is supplied to the magnetic multivibrator circuit, the duty detection circuit, the voltage / current conversion circuit, the high frequency detection circuit and the output circuit by the power supply circuit.
The oscillation operation of the magnetic multivibrator circuit is stopped by the control circuit until the output of the power supply circuit reaches a predetermined value. As a result, it is possible to prevent malfunction of the magnetic multivibrator circuit immediately after the power is turned on, for example, and it is possible to accurately detect the leakage current.

[Brief description of drawings]

FIG. 1 is a perspective view of a saturable reactor in the prior art,
FIG. 2 illustrates a BH characteristic curve of the saturable reactor shown in FIG. 1 when the equilibrium current is zero, and FIG. 3 illustrates magnetic flux when a large equilibrium current flows in the saturable reactor shown in FIG. FIG. 4 is a BH characteristic curve when a large equilibrium current flows in the saturable reactor shown in FIG. 1, and FIG. 5 is a current to which the saturable reactor of one embodiment of the present invention is connected. An electric circuit diagram of the detection device, FIG. 6 is a magnetic multivibrator circuit C
FIG. 7 is a waveform diagram for explaining the operation of the circuit during normal oscillation of FIG. 7, FIG. 7 is a waveform diagram for explaining the operation of the circuit during high frequency oscillation of the magnetic multivibrator circuit C, and FIG.
FIG. 9 is a graph for explaining the operation of the voltage / current conversion circuit F, FIG. 9 is a waveform diagram for explaining the operation of the voltage / current conversion circuit F, and FIG. 10 is a saturable circuit of one embodiment of the present invention. FIG. 11 is a perspective view of the reactor, FIG. 11 is a diagram for explaining the magnetic flux of the saturable reactor of FIG. 10, FIG. 12 is a perspective view of the saturable reactor of another embodiment of the present invention, and FIG.
The figure for demonstrating the magnetic flux of the saturable reactor of a figure, 1st
FIG. 4 is a perspective view of a saturable reactor according to still another embodiment of the present invention, and FIGS. 15 and 16 are perspective views of saturable reactors according to other embodiments of the present invention. l1, l2 ... line, L1, L2 ... coil, C ...
Magnetic multivibrator circuit, D ... duty voltage conversion circuit, E ... high frequency detection circuit, K ... core, H1, H
2, H3, H4, H5 ... Magnetic shield

Claims (1)

[Claims] 1. A saturable reactor which is provided in association with two lines through which a current to be detected to be detected flows and which has a first coil and a second coil for detecting the current to be detected. , A magnetic multivibrator including resistors for controlling currents flowing in the first coil and the second coil, oscillating by changing a duty of a predetermined cycle according to a current to be detected, and transmitting output signals which are inverted from each other. Circuit, a pair of duty detection circuits that detect the duty of each output signal of the magnetic multivibrator circuit, and the output signal corresponding to the duty of the signal from each duty detection circuit are input, and the level difference between the output signals is rectified. , The voltage level corresponding to the rectified current is changed to the capacitor C.
The high-frequency oscillation of the magnetic multivibrator circuit including the voltage / current exchange circuit derived from 7 and the saturable reactor is detected, and the capacitor C is detected.
7, a high-frequency detection circuit for charging 7, a detection circuit for detecting that the output voltage of the capacitor C7 exceeds a predetermined value, a magnetic multivibrator circuit, a duty detection circuit, a voltage / current conversion circuit, and a high-frequency detection circuit. And a control circuit that stops the oscillation of the magnetic multivibrator circuit until the output of the power circuit reaches a predetermined value. The saturation reactor is formed by winding the first and second coils around the annular magnetic core, and the two lines in which the detected current flows pass through the annular magnetic core in a twisted state. Current detection device.