JPH0588429B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to an earth leakage detection device for detecting earth leakage in loads, power lines, etc., which includes an oscillation circuit whose amplitude is small in a high frequency range and large in a low frequency range, and whose oscillation output The present invention relates to an earth leakage detection device including a frequency detection circuit that detects the frequency of .

BACKGROUND ART Such a frequency detection circuit is required when a magnetic multivibrator circuit is used, for example, for current detection. In a magnetic multivibrator circuit, the output frequency changes as the detected current of the coil wound around the saturable reactor included in the circuit changes, and accordingly, the amplitude is small in the high frequency range, It changes significantly in the low frequency range. By detecting the frequency of the output from such a magnetic multivibrator circuit, the magnitude of the detected current can be identified.

It is desired that such a frequency detection circuit has the simplest possible configuration and operates reliably.

Purpose An object of the present invention is to provide an earth leakage detection device including a frequency detection circuit that has a simple configuration, can operate reliably, and has improved reliability.

Structure of the Invention The present invention provides a core 43 through which lines 2 and 3 for supplying power from an AC power supply 10 to a load 1 are inserted.
, a pair of secondary coil 44 and tertiary coil 45
, one end of each coil 44, 45 is commonly connected, and a pair of switching elements 46, 47 are connected to the other end of each coil 44, 45, respectively. The magnetic multivibrator circuit 4 is a first integrating circuit in which one end of a resistor 16 and one end of a capacitor 18 are connected in series at a connection point 20, and the other end of the resistor 16 is connected to one switching element 46 of the magnetic multivibrator circuit 4. and the other end of the secondary coil 44. Such a first integrating circuit, and a second integrating circuit in which one end of the resistor 14 and one end of the capacitor 17 are connected in series at a connection point 19, the other end of the resistor 14 being connected to the other switching circuit of the magnetic multivibrator circuit 4. It is connected to the connection point between the element 47 and the other end of the tertiary coil 45. Such a second integrating circuit, a low-pass filter 25 that removes AC components included in the output between the connection points 20 and 19 of the first and second integrating circuits, and an input to the low-pass filter 25 and an input from the low-pass filter 25 Amplifier circuit 2 that amplifies the difference with the output
8, and a first level discrimination circuit 2 that discriminates the level of the output from the amplifier circuit 28 at a predetermined first discrimination level l1.
9, a switching element 36 that is switched by the output from the first level discrimination circuit 29, an integrating capacitor 37 connected in parallel to the output side of the switching element 36, and a current value I2 that predetermines the integrating capacitor 37. This is an earth leakage detection device characterized in that it includes a constant current source 38 that charges the output of the integrating capacitor 37 at a predetermined second discrimination level l2.

Embodiment FIG. 1 is an electrical circuit diagram of one embodiment of the present invention. Power is supplied to the load 1 from an AC power supply 10 via lines 2 and 3. Switches 11 and 12 are interposed between the lines 2 and 3. The lines 2 and 3 pass through the core 43 of the saturable reactor 41 of the magnetic multivibrator circuit 4. When a leakage occurs in the lines 2 and 3, the frequency of the magnetic multivibrator circuit 4 changes as described later.

The magnetic multivibrator circuit 4 includes a saturable reactor 41 and a multivibrator 42. The core 43 of the saturable reactor 41 includes a secondary coil 44 and a tertiary coil 4 having the same number of turns.
5 is wound. In the multivibrator 42, transistors 46 and 47 alternately perform conduction and cutoff operations. When the currents flowing in lines 2 and 3 are equal, and therefore no leakage occurs, the voltage induced in coils 44 and 45 is zero, and therefore the duty ratio of transistors 46 and 47 is 50%. . When the transistor 46 is conductive and the transistor 47 is cut off, the current from the resistor 40 does not flow to the transistor 47 via the tertiary coil 45 but flows to the transistor 46 via the secondary coil 44. At this time, since the base voltage of the transistor 46 is low, the constant current I1 from the constant current source 50 flows to the transistor 46 via the diode 56, and does not flow to the transistor 47 via the diode 55. Further, the constant current I1 from the constant current source 49 does not flow to the transistor 47 via the diode 54, but instead flows to the transistor 46 via the diode 53. When the base voltage of the transistor 46 increases, the base current of the transistor 46 is ib, and the current amplification factor is hfe, when the collector-emitter current becomes ib·hfe, the transistor 46 enters the active region.

When the base voltage of transistor 46 increases,
The constant current I1 from the constant current source 50 flows through the diode 5
6 no longer flows to the transistor 46,
The current flows through the diode 55 to the transistor 47, and the transistor 47 becomes conductive. Further, the constant current I1 from the constant current source 49 no longer flows to the transistor 46 via the diode 53, the transistor 46 is cut off, and flows to the transistor 47 via the diode 54. Therefore, the current from the resistor 40 does not flow through the secondary coil 44 to the transistor 46 but flows through the tertiary coil 45 to the transistor 47.

Therefore, the peak value of the collector-emitter voltage of the transistors 46 and 47 and the resistor 40
The peak value of the voltage is set constant, and outputs having the same waveform and having the same peak value are sequentially derived from the magnetic multivibrator circuit 4.

Assume that a sufficiently constant current I2, which is larger than the above-mentioned constant current I1, is caused to flow from the constant current sources 49 and 50. In this case, set the resistance value of resistor 40 to R40
When the collector-emitter currents of the transistors 46 and 47 reach 2.Vcc/R40, that is, when they enter the active region, the transistors 46 and 47 are sharply cut off at different duty cycles, and oscillation continues. Therefore, the diodes 53, 54, 5
Even if an error occurs in the forward voltages of the transistors 46 and 47, the peak values of the collector-emitter voltage of the transistors 46 and 47 and the voltage of the resistor 40 are fixed, and the magnetic multivibrator circuit 4 outputs the same peak values. Outputs of the same waveform are sequentially derived.

When a current leakage occurs, the core 43 of the saturable reactor 41 becomes saturated even if the current flowing through the coils 44, 45 is smaller than when no current leakage occurs. Therefore, the time required for the current to increase and reach saturation becomes shorter, the oscillation period of the magnetic multivibrator circuit 4 becomes shorter, and the oscillation frequency becomes higher. This output is resistor 14,1
5, 16 and capacitors 17, 18. Of this circuit, a series circuit consisting of resistor 16 and capacitor 18 constitutes a first integrating circuit, and a series circuit consisting of resistor 14 and capacitor 17 constitutes a second integrating circuit. The output of the magnetic multivibrator circuit 4 has a low frequency and a large amplitude of the alternating current component during normal operation and when the leakage current is small. On the other hand, when the leakage current is large, the magnetic multivibrator circuit 4
The frequency of is high and the amplitude of the AC component is small. Connection points 19, 20 of magnetic multivibrator circuit 4
The outputs at are applied to amplifier circuits 21 and 22, respectively, and then to a low-pass filter 25 consisting of a resistor 23 and a capacitor 24.

FIG. 2 shows operating waveforms when the leakage current is small, and FIG. 3 shows operating waveforms when the leakage current is large. The waveform at the connection point 19 is indicated by the reference mark P1 in FIG. 2 1 and FIG. 3 1.
The waveforms at the connection point 20 are indicated by reference marks P2 and P7, respectively. The waveforms derived from the amplifier circuit 21 to the connection point 26 are shown in FIG. 2 and FIG. 3, respectively.
The low-pass filter 25 removes the AC component of the output from the four magnetic multivibrator circuits, and determines the difference between this DC component and the signal before passing through the low-pass filter 25. 3 and 3. Only the AC components shown in FIG. 3 are derived. This AC component is amplified by the amplifier circuit 28. Resistor 2 in connection with amplifier circuit 28
9, 30, and 31 are connected. A constant current circuit 30 and a diode 31 are connected in association with a comparison circuit 29 which is a first level discrimination circuit. As described above, the AC component at the connection point 27 has a small amplitude in a high frequency range and a large amplitude in a low frequency range. Therefore, in the comparator circuit 29, the frequency to be detected can be selected by changing the reference voltage. During normal oscillation, therefore, when the leakage current is small, the amplitude of the AC component is small, and therefore the first
It exceeds the reference level l1 which is the discrimination level. Therefore, at the connection point 34 to which the voltage divided by the resistors 32 and 33 is applied, the pulse shown in FIG. 2 is obtained. When the frequency of the magnetic multivibrator 4 increases and the amplitude of the AC component decreases, the amplitude becomes less than the reference level l1 of the comparator circuit 29, and the connection point 34 remains at a low level as shown in FIG. .

The voltage at the connection point 34 is applied to a transistor 36 as a switching element. transistor 3
6 is connected in parallel to the integrating capacitor 37. A constant current I2 flows into this capacitor 37 by a constant current source 38. This causes the voltage of capacitor 37 to rise as a linear function of time. Therefore, when transistor 36 is conducting, capacitor 37 is discharged, and when transistor 36 is cut off, the voltage of capacitor 37 increases linearly over time. Due to the on/off operation of the transistor 36, the voltage of the capacitor 37 at the connection point 39 has the waveforms shown in FIG. 25 and FIG. 35. The voltage at connection point 39 is applied to comparator circuit 40, which is a second level discrimination circuit. A reference voltage l2, which is a second discrimination level, is applied to this comparison circuit 40 by a power supply 41.

During normal operation and when the leakage current is small, the second
As shown in FIG. 5, the voltage on the capacitor 37 is below the reference level l2, and therefore
The transistor 43 is cut off via the resistor 42. When the leakage current is large, the voltage across the capacitor 37 is at the reference level as shown in FIG.
l2 is exceeded, which causes comparator circuit 40 to turn transistor 43 on. Therefore, the capacitor 44
When the voltage increases and exceeds a value determined by the level discrimination circuit 46, the level discrimination circuit 46 applies a high level signal from the resistor 48 to the transistor 49. This causes transistor 49 to conduct. Therefore, the trip coil 51 of the switching means 50 is excited. The switches 11 and 12 are cut off by the excitation of the trip coil 51.

Another embodiment of the invention is shown in FIG. Connection point 19 of magnetic multivibrator circuit 4
The output at is converted by the voltage-current conversion circuit 60 into a current value corresponding to the voltage at the connection point 19. Current I3 from this voltage-current conversion circuit 60
charges the integrating capacitor 61. A constant current source 62 for discharging is connected in parallel to the capacitor 61, and the current of this constant current source 62 is indicated by reference symbol I4.
is shown.

FIG. 5 1 shows the low frequency output waveform at the connection point 19 under normal conditions and when the leakage current is small, and FIG. 6 1 shows the output waveform when the magnetic multivibrator circuit 4 oscillates at high frequency when the leakage current is large. shows. The waveforms at the connection point 63 of the capacitor 61 are shown in FIG. 52 and FIG. 62, respectively. The voltage of this capacitor 61 is applied to a comparator circuit 64. The comparison circuit 64 includes a power supply 65.
The reference level l3 is set by. When the output pulse at connection point 19 is at a high level, capacitor 61 is charged with current (I3-I4), and connection point 1
When 9 is at low level, it is discharged with current I4. Therefore, the voltage at the connection point 63 during charging and discharging of the capacitor 61 is a linear function of time. Since the currents I3 and I4 are constant, the voltage of the capacitor 61 at the connection point 63 depends on the pulse width of the output pulse of the magnetic multivibrator circuit 4 at the connection point 19. When the leakage current is large, the magnetic multivibrator 4 oscillates at a high frequency and the pulse width becomes small. Therefore, the voltage at the connection point 63 of the capacitor 61 becomes low.
Therefore, under normal conditions and when the leakage current is small, the comparator circuit 64 applies the pulse shown in FIG. 5 to the transistor 66. When a large leakage current occurs, high frequency oscillation occurs, and the output of the comparison circuit 64 remains at a low level as shown in FIG. 63.

The circuit after transistor 66 is similar to the circuit after transistor 36 described above, and includes an integrating capacitor 67, a constant current source 68, a comparison circuit 69, a voltage source 70 for setting a reference level, a resistor 71, a transistor 72, a capacitor 73, and a level. Discrimination circuit 7
4 is connected. The output from the level discrimination circuit 74 becomes high level when the magnetic multivibrator circuit 4 is oscillating at a high frequency, thereby causing the switches 11 and 12 of the switching means 50 to shut off as described above.

Effects As described above, according to the present invention, it is possible to obtain an earth leakage detection device that includes a frequency detection circuit that has a simple configuration and reliable operation, and that has improved reliability.

In other words, since the line for supplying power from the AC power source to the load is inserted through the core that makes up the magnetic multivibrator circuit, if leakage current flows, it will be a small value compared to the load voltage and load current. However, it can be reliably detected as a frequency difference.

First and second integrating circuits are connected to the output of the magnetic multivibrator circuit. As a result, the output that has a large amplitude in the low frequency range when the leakage current is small is further attenuated, and the output that has a small amplitude in the high frequency range when the leakage current is large is further attenuated, thereby increasing the difference in amplitude. I can do it. Furthermore, the difference between the output from which AC components have been removed by the low-pass filter and the output input to the low-pass filter is amplified, and the first level discrimination circuit discriminates the level at the first discrimination level. Operate switching. An integrating capacitor is connected to the output of the switching element, and when the switching element is in a cut-off state, it is charged with a predetermined current value from a constant current source, and its output is set at a second discrimination level by a second level discrimination circuit. Level-discriminated. Since the integrating capacitor is charged by a constant output current from a constant current source, the rate of change in charging voltage over time until it reaches the second discrimination level is constant, ensuring the level discrimination operation of the second level discrimination circuit. can be performed, improving reliability.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of one embodiment of the present invention, and FIG.
3 and 3 are waveform diagrams for explaining the operation of the frequency detection circuit, FIG. 4 is an electric circuit diagram of another embodiment of the present invention, and FIGS. 5 and 6 are waveform diagrams for explaining the operation of the pulse width detection circuit. It is a waveform diagram for explanation. DESCRIPTION OF SYMBOLS 1...Load, 10...AC power supply, 4...Magnetic multivibrator circuit, 25...Low pass filter, 29
... Comparison circuit, 36... Transistor, 37... Integrating capacitor, 38... Constant current source, 40... Comparing circuit.

Claims (1)

[Claims] 1. A saturable reactor in which a pair of secondary coils 44 and a tertiary coil 45 are wound around a core 43 through which lines 2 and 3 for supplying power from an AC power source 10 to a load 1 are inserted. 41, each coil 44,
One end of the coils 45 is commonly connected, and each coil 44, 4
5 has a pair of switching elements 46, 4 at the other end.
A first integrating circuit includes a magnetic multivibrator circuit 4 configured by connecting a magnetic multivibrator 7 and a capacitor 18, and one end of a resistor 16 and one end of a capacitor 18 connected in series at a connection point 20, and the other end of the resistor 16 is a magnetic multivibrator circuit. Such a first integrating circuit is connected to the connection point between one switching element 46 of the vibrator circuit 4 and the other end of the secondary coil 44, and one end of the resistor 14 and one end of the capacitor 17 are connected in series at the connection point 19. A second integrating circuit is connected, and the other end of the resistor 14 is connected to the connection point between the other switching element 47 of the magnetic multivibrator circuit 4 and the other end of the tertiary coil 45. an integrating circuit; a low-pass filter 25 that removes alternating current components included in the output between the connection points 20 and 19 of the first and second integrating circuits; and a difference between the input to the low-pass filter 25 and the output from the low-pass filter 25. Amplifying circuit 2 to amplify
8, and a first level discrimination circuit 2 that discriminates the level of the output from the amplifier circuit 28 at a predetermined first discrimination level l1.
9, a switching element 36 that is switched by the output from the first level discrimination circuit 29, an integrating capacitor 37 connected in parallel to the output side of the switching element 36, and a current value I2 that predetermines the integrating capacitor 37. An earth leakage detection device comprising: a constant current source 38 that charges the output of the integrating capacitor 37; and a second level discrimination circuit 40 that discriminates the level of the output of the integrating capacitor 37 based on a predetermined second discrimination level l2.