JPH0535381B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a current detection device for detecting leakage current in a power line or the like.

(Background Art) When a magnetic multivibrator circuit in a conventional current detection device detects a large detected current of several amperes or more, the magnetization characteristics of a saturable reactor provided in connection with a line through which the detected current flows changes. High-frequency oscillation occurs due to changes in magnetization characteristics when a small current is applied. Therefore, when the current to be detected is large, the linearity between the current to be detected and the duty change of the output signal of the magnetic multivibrator circuit is impaired, and the responsive circuit cannot be operated. In addition, conventional circuits that detect high-frequency signals in magnetic multivibrator circuits operate through a low-pass filter consisting of a resistor and a capacitor, which tends to generate voltage across the resistor due to noise, leading to malfunctions and poor noise resistance. It was.

(Objective) The object of the present invention is to solve the above-mentioned technical problem,
It is an object of the present invention to provide a current detection device that operates a responsive circuit even when the current to be detected is a large current and improves noise resistance.

(Structure of the Invention) The present invention provides a saturable reactor that is provided in relation to a line through which a current to be detected flows and has a first coil and a second coil for detecting the current to be detected. , a magnetic multivibrator circuit that is equipped with a resistor that controls the current flowing through the first coil and the second coil, and that oscillates while changing the duty of a predetermined period according to the detected current, and sends out mutually inverted signals. , a duty detection circuit for detecting a duty difference between each output signal of the magnetic multivibrator circuit; and rectifying a voltage level difference between output signals corresponding to the duty difference from the duty detection circuit;
a voltage/current conversion circuit that charges the capacitor C7 with a current value corresponding to the voltage level difference; a high frequency detection circuit that detects high frequency oscillation of the saturable reactor and charges the capacitor C7; and the capacitor C7. an output circuit that detects that the output voltage of the output voltage reaches a predetermined value; a power supply circuit that supplies power to the magnetic multivibrator circuit, the duty detection circuit, the voltage/current conversion circuit, the high frequency detection circuit, and the output circuit; Until the output of the current circuit reaches a predetermined value,
A current detection device characterized in that it includes a control circuit that stops oscillation of a magnetic multivibrator.

(Embodiment) FIG. 1 is an electrical circuit diagram of an embodiment of the present invention. First, the operation of power supply circuit A will be explained. When switches S1 and S2 are turned on and AC voltage is supplied from AC power supply E0 to lines l1 and l2, it is rectified into DC voltage by a circuit consisting of diodes D1 to D4, coil L, resistor R1, and capacitor C1. . At the same time that power from the AC power supply E0 is turned on, the transistor Tr1 is turned on by the DC current flowing through the line l3, and the capacitor C2 is charged. When the voltage across the capacitor C2 reaches a preset voltage, the transistor Tr2 is turned on, and its emitter line l4 obtains a constant voltage that does not include ripple. When the collector voltage of the transistor Tr2 exceeds a predetermined potential (a potential higher than the predetermined potential mentioned above), the comparator 1 operates and supplies the base current to the transistor Tr3, turning on the transistor Tr3 and increasing the base current of the transistor Tr1. A current is drawn to turn off the transistor Tr1. Meanwhile, at the same time, the transistor Tr12 is turned on at the output of the comparator 1, lowering the threshold voltage applied to the non-inverting input terminal of the comparator 1. Next, when the load circuit connected to power supply circuit A consumes energy and the potential of capacitor C2 decreases,
The potential of the inverting input terminal decreases to comparator 1, and comparator 1
The output of is inverted, transistors Tr3 and Tr12 are turned off, the base current of transistor Tr1 is supplied, transistor Tr1 is turned on, and the capacitor C
2 continues to charge, and the threshold voltage applied to the non-inverting input terminal of comparator 1 returns to its original state (becomes higher). By operating in this manner, the voltage between the collector and emitter of transistors Tr1 and Tr2 can be suppressed to a low level, and the power consumption/heat generation of transistors Tr1 and Tr2 can be reduced.
A constant voltage that does not include (very little) ripple can be obtained on the line l4.

Next, the operation of control circuit B will be explained. Power supply circuit A
The output of the comparator 2 remains low and the switches S3 and S4 of the magnetic multivibrator circuit C remain off (open) until the potential of the line l4 of the emitter of the transistor Tr1 reaches a predetermined value. When the potential of the emitter line l4 of the transistor Tr1 of the power supply circuit A reaches a predetermined value, the comparator 2 operates and the output becomes high, turning on switches S3 and S4 of the magnetic multivibrator circuit C, and turning on the magnetic multivibrator circuit. Make C operate (oscillate). In this way, the control circuit B can stop the oscillation of the magnetic multivibrator circuit C until the potential of the line l4 reaches a predetermined value in order to prevent malfunction of the subsequent circuit.

The following operation of the magnetic multivibrator circuit C will be explained. The magnetic multivibrator circuit C starts oscillating when switches S3 and S4 are turned on. A saturable reactor is provided which is associated with the load L0 and the connection lines l1, l2 and has coils L1, L2 for detecting the difference in the currents flowing in the lines l1, l2. One ends of the coil L1 and the coil L2 of the saturable reactor are connected to the line l4 via a 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 collector of the transistor Tr5. In a circuit including coils L1 and L2, transistors Tr4 and Tr5, diodes D8 to D11, and resistors R9 and R10, when transistor Tr4 is turned on, transistor Tr5 is turned off, and transistor Tr5 is turned off.
When Tr5 is turned on, oscillation is performed by turning off transistor Tr4. If there is no leakage current in line l1 or line l2, the reactances of coils L1 and L2 do not change, and L1
≒L2, so transistors Tr4 and Tr5 are turned on/
The off duty ratio remains 1:1, and the resistor R
Oscillates at the oscillation frequency (reference frequency) set in . Next, when a leakage current occurs in lines l1 and l2, the reactance of coil L1 and coil L2 changes and L1≠L2, and transistors Tr4 and Tr
The on/off duty ratio of 5 will vary from 1:1. To explain in more detail, as shown in Figure 6, (1) When there is no leakage current, oscillation occurs at the reference frequency set by the resistor R, and since the coil reactance L1≒L2≒L00, the transistor Tr4,
The on/off duty ratio of Tr5 is 1:1
(2) If a small leakage current does not occur, magnetic flux is superimposed on the saturable reactor due to the leakage current, and the reactance of the coil becomes L1≠L2, and the on/off duty ratio of transistors Tr4 and Tr5 is 1:1. It changes in response to the leakage current. Note that the oscillation frequency of the saturable reactor at this time does not change much from the reference frequency when the leakage current is extremely small, but as the leakage current gradually increases, the oscillation frequency also gradually increases. However, the change in duty ratio increases proportionally as the leakage current increases. However, as the current to be detected increases beyond a certain level, the linearity deteriorates.

(3) When a large leakage current occurs, a large magnetic flux is superimposed on the saturable reactor due to the leakage current, and the reactance of the coil becomes much smaller than the initial value, L1≒L2<L00, and the transistor Tr4,
The on/off duty ratio of Tr5 is 1:1
As it is, the oscillation frequency of the magnetic multivibrator becomes extremely high.

The magnetic multivibrator circuit C has the above-mentioned characteristics with respect to leakage current, and outputs pulse signals whose phases are inverted from each other from the collectors of the transistors Tr4 and Tr5 (see Fig. 2).
3, Fig. 3 2, 3, Fig. 7 2, 3).

Next, the operation of duty detection circuit D will be explained. Switches S5 to S8 are turned on and off in synchronization with the on and off of transistors Tr4 and Tr5 of the magnetic multivibrator circuit C. Switch S
5, S8 is turned on when transistor Tr5 is on, and switches S6 and S7 are turned on when transistor Tr4 is turned on.
Turns on when is on. Here, the operating state of the magnetic multivibrator circuit C will be explained.

(1) When there is no leakage current, as shown in the waveform of Fig. 2, in response to the oscillation of the magnetic multivibrator circuit C, the contact a' between the switches S5 and S6 of the duty detection circuit D and the resistor R11 is Second
A pulse signal as shown in FIG. 2 is provided. Also, the contact points between switches S7 and S8 and resistor R13
A pulse signal is applied to b' as shown in FIG. As a result, the DC voltage signal P1 shown in FIG.
From the connection point b between the capacitor C4 and the capacitor C4,
A DC voltage signal P2 shown in is output.

(2) When a small leakage current occurs, the duty ratio of the oscillation of the magnetic multivibrator circuit C is changed from 1:1 to the switch S5 of the duty detection circuit D as shown in the waveform of FIG. , S6 and the resistor R11 are supplied with a pulse signal as shown in FIG. 72.
Further, a pulse signal as shown in FIG. 7 is applied to the contact point b' between the switches S7 and S8 and the resistor R13. As a result, the DC voltage signal P1 shown in FIG.
From the connection point b between the capacitor C4 and the capacitor C4,
A DC voltage signal P2 shown in is output. In this way, when leakage current occurs, the DC signal P
1, a difference corresponding to the leakage current will occur in the average value of P2.

(3) When a large leakage current occurs, as shown in the waveform of Fig. 3, contact a between switches S5 and S6 of duty detection circuit D and resistor R11 responds to high-frequency oscillation of magnetic multivibrator circuit C. ' is given a pulse signal as shown in FIG. Further, a pulse signal as shown in FIG. 3 is applied to the contact point b' between the switches S7 and S8 and the resistor R13. This results in resistance R
The DC voltage signal P1 shown in FIG.
A DC voltage signal P2 shown in FIG. 3 is output from the circuit. When such a large leakage current occurs, it is not possible to detect a difference between the average values of the DC signals P1 and P2 as described in (2) above, and only the oscillation frequency increases.

Next, the operation of the high frequency detection circuit E will be explained. The inverting input terminal of the comparator 8 is given a signal from the connection point a' of the duty detection circuit D, and the non-inverting input terminal of the comparator 8 is given a signal from the connection point b' of the duty detection circuit D. . This results in
Comparator 8 operates to turn on/off transistor Tr6. The on/off operation of the transistor Tr6 and the potential of the capacitor C5 between the constant current power supply E5 and the capacitor C5 differ depending on the operating state of the magnetic multivibrator circuit C, but are shown in Fig. 2 4, Fig. 3 4, Fig. 7 4. signal P4. This signal P4 is applied to the non-inverting input terminal of the comparator 3, and the Zener diode D is connected to the inverting input terminal of the comparator 3.
12 (line A4 shown in FIG. 2). As a result, the comparator 3 operates to turn on/off the transistor Tr7.
The on/off operation of the transistor Tr7 and the potential of the capacitor C6 at the power failure current source E6 and the capacitor C6 differ depending on the operating state of the magnetic multivibrator circuit C, but are as shown in FIG. 25, FIG. 35, and FIG. signal P5. This signal P5 is the comparator 4
A threshold voltage (line A5 shown in FIG. 2) set by the Zener diode D12 is applied to the inverting terminal of the comparator 4. As a result, the operation of the comparator 4 differs depending on the operating state of the magnetic multivibrator circuit C. (1) When there is no leakage current, the magnetic multivibrator circuit C oscillates at the reference frequency, and the second
When the signal P4 in FIG. 4 becomes higher than the threshold value A4, the output of the comparator 3 becomes low/high, and the transistor Tr7 turns off/on, and as shown in FIG.
Since the signal P5 is always lower than the threshold value A5, the output of the comparator 4 becomes low, and the switch S9 remains off.

(2) When a small leakage current occurs, the magnetic multivibrator circuit C oscillates at approximately the reference frequency, and the signal P4 in FIG.
As the voltage becomes higher, comparator 3 becomes low/high, transistor Tr7 turns off/on,
Since signal P5 in FIG. 7 is always lower than threshold A5, the output of comparator 4 is low and switch S9 remains off. However, although it is not a normal leakage current, if the leakage current becomes considerably large and the oscillation frequency increases, the signal P4 in FIG. Tr7 is turned off and the signal P5 is the threshold value A
5, the output of comparator 4 becomes high and switch S9 is turned on.

(3) When a large leakage current occurs, the magnetic multivibrator circuit C oscillates at a high frequency, and the output of the comparator 3 becomes low because the signal P4 in Fig. 3 is always lower than the threshold value A4. Therefore, the transistor Tr7 is turned off, the signal P5 in FIG. 3 is always higher than the threshold value A4, the output of the comparator 4 is high, and the switch S9 is turned on. Then, the switch S9 is turned on/off in accordance with the operating state (oscillation frequency) of the magnetic multivibrator circuit C.

Next, the operation of the voltage/current conversion circuit F will be explained. The voltage/current conversion circuit F includes a comparator 6, a diode D13, a transistor Tr9, and a comparator 5.
, diode D14, transistor Tr8,
The resistor R14 separates the signal applied to the non-inverting input terminal of the comparator 6 (signal a of the duty detection circuit D) and the signal applied to the non-inverting input terminal of the comparator 5 (signal b of the duty detection circuit SD). The potential difference is converted into a current divided by the resistance value of the resistor R14, the capacitor C7 is charged with this current, and the current value after the voltage/current exchange is determined by a constant current extraction circuit consisting of the resistor R15 and transistors Tr10 and Tr11. but,
The potential of capacitor C7 is not increased up to a predetermined current value. As a result, (1) When there is no leakage current, the DC voltages of signals a and b of duty detection circuit D are the same, the charging current of capacitor C7 becomes almost zero (some ripple current flows), and the capacitor C
The potential at point 7 remains almost zero.

(2) When a small leakage current occurs, a difference occurs between the DC voltages of the signals a and b of the duty detection circuit D, and a current is generated that charges the capacitor C7, but the current that is set in the constant current extraction circuit is When the leakage current is below the value, the potential of capacitor C7 remains zero. On the other hand, when the leakage current exceeds the current value set in the constant current extraction circuit, the capacitor C7 is charged with a charging current obtained by subtracting the set current, and the potential of the capacitor C7 gradually rises.

(3) When a large leakage current occurs, the magnetic multivibrator circuit C oscillates at a high frequency, and the high frequency detection circuit E operates as described above, turning on the switch S9 and turning on the capacitor with a constant current E8. C7 charges quickly.

Next, in the output circuit G, when the potential of the capacitor C7 rises above a threshold value set in advance by the constant current source E9 and the Zener diode D15, the comparator 7 operates (the output becomes high), and the above-mentioned A signal is sent to turn off switches S1 and S2. As a result, the load L0 is cut off from the AC power source E0.

As described above, (1) When the detected currents of lines l1 and l2 are small, the detected current value is detected as the duty ratio of the output pulse of the magnetic multivibrator circuit C, and the duty ratio is determined by the detection circuit D. is detected, the voltage/current exchange circuit F converts the potential difference into a current, and when the current value exceeds a preset value, the capacitor C7 is charged,
It operates when the potential of the capacitor C7 exceeds a certain threshold value, thereby accurately detecting a small current to be detected.

(2) When the detected current is large, the oscillation frequency of the magnetic multivibrator circuit C becomes high, and the duty ratio of the output pulse is approximately 1:
1, and the current to be detected cannot be detected as the duty ratio of the output pulse, but the high frequency detection circuit E described above detects a large current to be detected at the high oscillation frequency of the magnetic multivibrator, and the voltage /By rapidly charging the capacitor C7 of the current conversion circuit F into the constant current source E8 and operating when the potential of the capacitor C7 exceeds a certain threshold value, even large currents to be detected can be accurately detected. .

Figure 4 shows the detected current Ig, which is the leakage current of the load L0, and the transistor of the voltage/current exchange circuit F.
It is a graph showing the relationship with the average current I0 sent out from the collectors of Tr9 and Tr8. In the present invention,
Since ripples are superimposed on the output of the duty detection circuit D, the characteristics of the voltage/current conversion circuit F according to the embodiment of the present invention are shown as a solid line, in contrast to the characteristics of the conventional voltage/current conversion circuit shown with a broken line. However,
In practice, there is no particular problem. Furthermore, by adopting such characteristics, even if the current to be detected is "distorted" or "DC" as shown in Fig. 5 1 to 3, "AC" as shown in Fig. ” can be detected in the same way as the current to be detected.

In addition, as an input to the conventional high frequency detection circuit (the voltage between the connection points a and b of the duty detection circuit D is applied to a low-pass filter and only the DC component is detected as a potential difference), the connection points a and b of the duty detection circuit D are High frequency was detected by differentiating the voltage between them and detecting only the ripple component, but noise caused the voltage between connection points a and b to change, causing a sudden voltage change in the ripple component, causing the high frequency detection circuit to fail. It was easy to malfunction and had poor noise resistance, but by configuring a high frequency detection circuit as in the present invention and further configuring the capacitor of the voltage/voltage conversion circuit to be charged with the output of the high frequency detection circuit, Noise resistance can be improved.

(Effects) As described above, according to the present invention, when the detected current is small, the detected current value is detected as the duty ratio of the output pulse of the magnetic multivibrator circuit C, and the duty ratio is determined by the duty detection circuit D. Detected as a potential difference at
The current conversion circuit F converts the potential difference into a current to charge the capacitor C7, and when the detected current is large, the oscillation frequency of the magnetic multivibrator circuit C becomes high, and the duty ratio of the output pulse becomes approximately 1:1. However, the high frequency detection circuit E described above detects a large current to be detected at the high oscillation frequency of the magnetic multivibrator, and calculates the voltage/current. The capacitor C7 of the conversion circuit F is rapidly charged by the constant current source E8, and the output circuit is connected to this capacitor C7.
Detects when the output voltage of Since it takes time to charge C7 and reach the threshold value), the noise resistance can be improved.

Furthermore, according to the present invention, the magnetic multivibrator circuit is operated until the output of the power supply circuit that supplies power to the magnetic multivibrator circuit, the duty detection circuit, the voltage/current conversion circuit, the high frequency circuit, and the output circuit reaches a predetermined value. Since the control circuit is configured to stop the oscillation operation of the current detection device, malfunction of the current detection device can be prevented, for example, immediately after the power is turned on, and reliability is improved.

[Brief explanation of the drawing]

Fig. 1 is an electrical circuit diagram of an embodiment of the present invention;
The figure is an explanatory diagram of the circuit operation of the magnetic multivibrator circuit C during normal oscillation (no leakage current), Figure 3 is an explanatory diagram of the circuit operation of the magnetic multivibrator circuit C during high frequency oscillation (with large leakage current), and Figure 4 5 is an explanatory diagram of the operation of the voltage/current exchange circuit, 5th is an example of the detected current waveform, 6 is an explanatory diagram of the relationship between the detected current and the oscillation frequency of the magnetic multivibrator, and 7th is an explanatory diagram of the operation of the voltage/current exchange circuit.
The figure is an explanatory diagram of the circuit operation of the magnetic multivibrator circuit C during normal oscillation (at the time of small leakage current). A...Power supply circuit, B...Control circuit, C...Magnetic multivibrator circuit, D...Duty detection circuit, E...High frequency detection circuit, F...Voltage/
Current conversion circuit, G...output circuit.

Claims (1)

[Claims] 1. A saturable reactor that is provided in connection with a line through which a current to be detected flows and has a first coil and a second coil for detecting the current to be detected; a magnetic multivibrator circuit that is equipped with a resistor that controls the current flowing through the first coil and the second coil, oscillates with a predetermined duty cycle changed according to the detected current, and sends out mutually inverted signals; a duty detection circuit that detects the duty difference between each output signal of the magnetic multivibrator circuit; and a duty detection circuit that rectifies the voltage level difference between the output signals corresponding to the duty difference from the duty detection circuit.
a voltage/current conversion circuit that charges the capacitor C7 with a current value corresponding to the voltage level difference; a high frequency detection circuit that detects high frequency oscillation of the saturable reactor and charges the capacitor C7; and the capacitor C7. an output circuit that detects that the output voltage of the output voltage reaches a predetermined value; a power supply circuit that supplies power to the magnetic multivibrator circuit, the duty detection circuit, the voltage/current conversion circuit, the high frequency detection circuit, and the output circuit; Until the output of the current circuit reaches a predetermined value,
A current detection device comprising: a control circuit for stopping oscillation of a magnetic multivibrator.