JP3748314B2 - Earth leakage detector - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a leakage detector used for a leakage breaker, and more particularly to a leakage detector that does not malfunction due to an external surge.
[0002]
[Prior art]
Conventionally, in a leakage detector that detects leakage current flowing in an AC circuit, the leakage current is detected by a zero-phase current transformer, and the leakage signal output from this zero-phase current transformer has a constant peak value and width (time). ) Exceeded the limit, some were judged to be leaking.
[0003]
[Problems to be solved by the invention]
The types of earth leakage breakers that are judged to be leaking, that is, the type of earth leakage breaker incorporating the earth leakage detector are high-speed type (operating within 0.1 second), time delay type (operating within 0.1 second and within 2 seconds). There is an inverse time type (operation is inversely proportional to the magnitude of electric leakage), and the performance and the like of each is defined by standards such as JIS C 8371 and the Electrical Appliance and Material Control Law technical standards.
In the time delay type earth leakage breaker, within the technical standards of the Electrical Appliance and Material Control Law, the operating time / inertia non-operating current at the time of the earth leakage (standard: leakage current of 10A or leakage current 20 times the rated sensitivity current) is fixed for a certain time. (50% of operation time) It is specified that the device is not operated when energized, and it is necessary to conform to these standards.
For example, in the case of a time-delayed earth leakage circuit breaker with a rated sensitivity current of 0.5 A and an operating time of 0.3 seconds, a 10 A inertial non-operating current is energized for 0.15 seconds, and a 0.5 A leakage current is generated. When the power is turned on, the operation is interrupted between 0.15 seconds and 0.45 seconds.
However, immediately after the 10 A inertial non-operating current is applied for 0.15 seconds, the back electromotive force is long (0.1 seconds) due to the internal inductance of the zero-phase current transformer used as a sensor for detecting leakage. Therefore, it is necessary to increase the lower limit value (0.15 seconds in the above example) of the operation time, and the standard range of the operation time is narrow (0.25 to 0.45 in the above example). Second).
Further, considering the error due to the temperature characteristics of the electronic components constituting the circuit of the earth leakage detector, the time required for the mechanical operation of the circuit breaker, etc., the standard range of the operation time becomes further narrow.
As described above, the conventional technology has a narrow operating time standard due to electric leakage, and when the leakage breaker is manufactured, there are cases where the operating time is out of specification due to variations in electronic components. There was a disadvantage that extra adjustment work (work to replace a time delay capacitor, etc.) was required.
Further, the high-speed earth leakage breaker has a problem that it is likely to malfunction due to a surge current (shock wave current) caused by lightning or the like.
[0004]
OBJECT OF THE INVENTION
Accordingly, the present invention has an object to provide a leakage detector that eliminates such unnecessary adjustment work in the leakage breaker and reduces the manufacturing cost, and that does not malfunction due to an external surge.
[0005]
[Means and Actions for Solving the Problems]
The leakage current in the AC circuit is detected and a leakage signal proportional to the leakage current is generated. When the leakage signal exceeds a specified level, the AC circuit is interrupted by operating via a switching element. In the leakage detector, an amplification circuit that amplifies the leakage signal, a first determination circuit that generates an output when an output of the amplification circuit exceeds a predetermined magnitude, and an output of the first determination circuit A differentiating circuit that differentiates the output of the differentiating circuit, a second determining circuit that determines whether or not the output of the differentiating circuit exceeds a predetermined magnitude and generates an output when the predetermined magnitude is exceeded, and an output of the differentiating circuit is predetermined. A reset circuit that instantaneously discharges the reset capacitor when the size exceeds a predetermined value and gradually integrates the reset capacitor with a constant current when the size is equal to or less than a predetermined size, and the output of the reset circuit is less than a predetermined size An integration circuit that integrates the integration capacitor with a constant current, a third determination circuit that generates an output when the output of the integration circuit exceeds a predetermined magnitude, an output of the second determination circuit, and the third A zero-phase current transformer that is generated by an excessive current such as an inertial non-operating current in the time delay type by incorporating a leakage detector that operates by triggering the switching element by the logical product with the output of the determination circuit The back electromotive force is judged in a short time, neglecting a certain period of time, lowering the lower limit of the operating time standard to widen the standard, and in the high-speed type, it does not malfunction due to surge currents caused by lightning, etc. It is what.
[0006]
[Explanation of Examples]
FIG. 1 is a circuit block diagram of a leakage detector showing an embodiment of the present invention.
[0007]
First, the block configuration of FIG. 1 will be described.
ZCT detects a leakage current of an AC circuit with a zero-phase current transformer, and outputs a voltage proportional to the magnitude of the leakage current.
The amplifying unit is an analog circuit that amplifies the output of the zero-phase current transformer and outputs it as a leakage signal.
The first determination circuit is a circuit that generates an output when an instantaneous value of the leakage signal amplified by the amplification unit exceeds a predetermined magnitude.
The differentiation circuit is a differentiation circuit that differentiates and outputs the output of the first determination circuit. The second determination circuit is a circuit that determines whether or not the output of the differentiating circuit is greater than or equal to a predetermined magnitude and generates an output when the output exceeds a predetermined magnitude.
The reset circuit is a circuit that discharges the reset capacitor instantaneously when the output of the differentiating circuit exceeds a predetermined magnitude, and gradually integrates the reset capacitor with a constant current when the output is below a predetermined magnitude.
The integration circuit is an integration circuit that integrates the integration capacitor with a constant current when the output of the reset circuit is equal to or less than a predetermined magnitude.
The third determination circuit is a circuit that generates an output when the output of the integration circuit is greater than or equal to a predetermined magnitude.
The logical product circuit is a circuit that outputs a logical product of the output of the second determination circuit and the output of the third determination circuit.
The SCR is a switching element that operates according to the output of the AND circuit.
[0008]
Next, waveforms A to G in the time chart of FIG. 4 will be described in association with the functions of the respective blocks of FIG.
A is a leakage current waveform of the AC circuit (zero-phase current transformer primary side).
B is the output waveform of the amplifier of FIG.
C is an output waveform of the first determination circuit of FIG.
D is the output waveform of the differentiating circuit of FIG.
E is an output waveform of the reset circuit of FIG.
F is the output waveform of the integrating circuit of FIG.
G is an output waveform of the second determination circuit in FIG.
H is the third determination circuit output waveform of FIG.
I is the AND circuit output waveform of FIG.
[0009]
Next, the operation of the differentiation circuit of the present invention will be described with reference to FIG.
When a leakage occurs in the primary circuit of the zero-phase current transformer and the output of the zero-phase current transformer exceeds the judgment value VH1 of the judgment circuit 1, the current I1 is supplied by the constant current circuit.
Due to this current, charges are accumulated in C1 and C2, and the voltage VC1 across C1 and the voltage VR1 across R1 rise according to the theoretical formulas (1) and (2) shown in (1) below.
By the set internal circuit, the voltage of VC1 is set to be the determination value VH2 + 0.6V (= VMAX) of the determination circuit 2.
VR1 is highest when VC1 rises to VMAX.
When VC1 becomes VMAX constant according to the theoretical formula (3), VR1 gradually decreases according to the theoretical formula (4) shown in the following (2).
(1) Theoretical formula until VC1 = VMAX (1) VC1 (t) = I1 × {(A / B) × t + (C / B) × (1-EXP (-B × t))} / C11
Where A = 1 / (C2 × R1)
B = (C1 + C2) / (C1 x C2 x R1)
C = 1- (A / B)
(2) VR1 (t) = I1 × (1-EXP (-t / D)) / D
Here, D = (C2 × R1) / (C1 + C2)
(2) Assuming that the time until VC1 (t) = VMAX after reaching VC1 (t) = VMAX is t1, (3) VC1 (t1) = VMAX (constant)
(4) VR1 (t) = VR (t1) × EXP {-(t-t1) / (C2 × R1)}
(3) Thereafter, when the time t2 until VR1 (t) falls again to VH2 is obtained, t2 = −ln {VH2 / VR1 (t1)} / A + t1 from the equation (4).
(4) When the output of the first determination circuit becomes VH1 or less, C1 is instantaneously discharged and VR1 becomes low level.
[0010]
FIG. 2 is a waveform diagram (time chart) for explaining the operation of the present invention when leakage occurs.
A is a leakage current waveform of the AC circuit (zero-phase current transformer primary side).
B is the leakage signal waveform of the amplified zero-phase current transformer output.
C is a waveform of the first determination output, and becomes a high level when the voltage of B is equal to or higher than the determination level VH1.
D is a waveform of the differentiation circuit output, and becomes a high level by the first determination output, and the voltage gradually decreases according to the following theoretical formula.
V (t) = VMAX × EXP (−t / T), where T = C30 × R30
E is the waveform of the reset circuit output, which is high during normal operation and low during leakage detection.
F is the waveform of the integration circuit output. When the output voltage of the reset circuit of E is lower than the judgment value VH3, the capacitor C4 starts to be integrated at a constant current. When E becomes high level, the integration capacitor is instantaneously discharged. Reset.
G is an output waveform of the second determination circuit, and becomes high level when the differentiation circuit output exceeds the determination value VH2 of the second determination circuit, and becomes low level when VH2 or less.
H is an output of the third determination circuit, and becomes high level when the integration circuit output exceeds the third determination circuit VH4, and becomes low level when VH4 or less.
I is an output of the AND circuit, and when the second determination circuit and the third determination circuit are simultaneously at the high level, a trigger is output to the switching element.
[0011]
Next, when the circuit of the present invention is applied to a time delay type earth leakage circuit breaker, it is possible to widen the manufacturing standard width of the operating time than before, and to greatly improve the production work efficiency. This will be described with reference to FIGS. 3 and 6 in comparison with the conventional example.
3 shows a time chart during an inertial non-operation test in the inventive circuit, FIG. 5 shows a conventional circuit example, and FIG. 6 shows a time chart in the conventional circuit.
A is a waveform in which an inertial non-operating current (10 A or sensitivity current × 20 times current) flowing on the primary side of the zero-phase current transformer is energized for an inertia non-operating time T (0.15 seconds in the above example).
At this time, the back electromotive force due to the internal inductance of the zero-phase current transformer is generated at the output of the zero-phase current transformer B after the inertial inactive current is applied, and it continues for about 0.1 second.
The waveform of the first judgment output of C becomes high level while the counter electromotive force of the zero-phase current transformer continues (TG).
The waveform of the differential circuit output of D falls below the second determination value VH1 in about 0.01 seconds (t1 + t2) after the generation of the counter electromotive force of the zero-phase current transformer, according to the above-described theoretical formula of the differential circuit.
Thereafter, since the waveform of the differentiating circuit does not exceed VH2, the non-operation time may be set to T + t1 + t2. Therefore, the difference from the conventional non-operation time is (T + TG) − (T + t1 + t2) = TG− (t1 + t2). For example, if t1 + t2 = 0.01 seconds, TG− (t1 + t2) = 0 .1-0.01 = 0.09 seconds The manufacturing standard lower limit of the operating time can be lowered.
The waveform of the reset circuit output of E starts integration when the output of D is at a low level, and resets to zero when it exceeds the determination level VH3.
The waveform of the F integration circuit output becomes a high level exceeding the judgment value level VH3 for a while after the generation of the counter electromotive force of the zero-phase current transformer.
The second determination circuit output of G remains at the low level after receiving the differential output of D, and immediately after energization of the inertial non-operational current and becomes high for t1 + t2.
The third decision circuit output of H remains at the low level until the output of the integrating circuit exceeds VH3.
Since the AND circuit of I does not simultaneously become high level in this case, it does not output the SCR trigger output.
Therefore, the test fails without malfunction in the inertial malfunction test.
However, as shown in FIG. 5, the conventional leakage detector does not have the function of the differentiation circuit / second determination circuit (there is no logical product circuit because there is no function of the second determination circuit), and the third determination circuit. 5 is operated at the time when the value of F in FIG. 5 exceeds the determination level VH3, so that the operation time needs to be increased to 0.15 s + 0.1 s + trs seconds as shown in FIG. There is. Here, trs is the time until the reset circuit returns after the first determination circuit output is lost.
[0012]
Next, when the present invention is applied to a high-speed earth leakage breaker, how the malfunction due to a large shock wave current caused by lightning or the like is solved by the present invention will be described with reference to FIGS. 4 shows the case of the present invention, and FIG. 7 shows the case of the conventional circuit.
A is a waveform when a shock wave current (2000 A, 8 × 20 μS) flowing through the primary side of the zero-phase current transformer is energized.
At this time, the back electromotive force due to the internal inductance of the zero-phase current transformer is generated at the output of the zero-phase current transformer B after the shock wave current is applied, and continues for about 0.1 second.
The waveform of the first judgment output of C becomes high level during TG2 while the back electromotive force of the zero-phase current transformer continues.
The waveform of the differential circuit output of D is set so that the judgment value level VH2 is rotated at t1 + t2 after the back electromotive force of the zero-phase current transformer is generated according to the above-described theoretical formula of the differential circuit.
Thereafter, the waveform of the differentiating circuit does not exceed the judgment value level. For example, when t1 + t2 = 0.01 seconds is set and the operation time is set between 0.02 and 0.1 seconds, no malfunction occurs due to the impact current.
The waveform of the reset circuit output of E starts integration when the output of D is at the zero level, and resets the integration circuit to zero when it exceeds the determination level VH3.
The waveform of the F integration circuit output is integrated with a constant current from when the reset circuit output becomes VH3 or less. When the reset circuit exceeds VH3, it is reset to zero.
G is the output of the second determination circuit, and is high when the differentiation circuit output is VH2 or higher.
H is the output of the third determination circuit, and is high when VH4 or higher.
I is a logical product output, and since the second determination output and the third determination output do not simultaneously become high level, a trigger output to the SCR does not occur and no malfunction occurs.
Therefore, it does not malfunction in the shock wave non-operation test and passes the test.
However, as shown in FIG. 5, the conventional leakage detector does not have the function of the differentiation circuit / second determination circuit (there is no logical product circuit because there is no function of the second determination circuit), and the third determination circuit. Since the operation is performed only by the determination, the operation is performed when the value of F in FIG. 7 exceeds the determination level VH4.
[0013]
【The invention's effect】
By implementing the present invention, in the time-delayed form, the lower limit specification value for the operation time can be greatly lowered, and the standard range can be widened, so there is no adjustment work for the operation time, the manufacturing cost is low, An earth leakage circuit breaker that satisfies the inertial non-operation performance and that does not malfunction due to a surge (shock wave) caused by lightning or the like in the high-speed type can be provided.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of a leakage detector of the present invention.
FIG. 2 is an operation explanatory waveform diagram (time chart) when a leakage occurs in the primary power line of the leakage detector of the present invention.
FIG. 3 is an operation explanatory waveform diagram (time chart) when an inertial non-operation test current is applied to the primary power line of the time-delayed leakage detector of the present invention.
FIG. 4 is an operation explanatory waveform diagram (time chart) when a shock wave current is applied to the primary power line of the leakage detector of the present invention.
FIG. 5 is a circuit block diagram of a conventional leakage detector.
FIG. 6 is an operation explanatory waveform diagram (time chart) when an inertial non-operation test current is applied to a primary power line of a conventional time delay type leakage detector.
FIG. 7 is an operation explanatory waveform diagram (time chart) when a shock wave current is applied to a primary power line of a conventional leakage detector.

Claims (1)

The leakage current in the AC circuit is detected by a zero-phase current transformer, and a leakage signal proportional to the magnitude of this leakage current is generated. When the magnitude of this leakage signal exceeds a specified value, the switching element is activated. In the leakage detector that interrupts the AC circuit, the amplification circuit that amplifies the leakage signal, the first determination circuit that generates an output when the output of the amplification circuit exceeds a predetermined magnitude, and the first A differentiating circuit for differentiating the output of one determining circuit; a second determining circuit for determining whether the output of the differentiating circuit exceeds a predetermined magnitude and generating an output when the predetermined magnitude is exceeded; A reset circuit that instantaneously discharges the reset capacitor when the output of the differentiating circuit exceeds a predetermined magnitude and gradually integrates the reset capacitor with a constant current when the output is below a predetermined magnitude, and the output of the reset circuit is An integration circuit that integrates an integration capacitor with a constant current when a predetermined magnitude or less, a third determination circuit that generates an output when the output of the integration circuit exceeds a predetermined magnitude, and the second determination circuit And an operation of the switching element triggered by a logical product of the output of the third determination circuit and the output of the third determination circuit.

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