Leakage detection device

Abstract

To provide a leakage detection device that can accurately detect a leakage current and suppress power consumption during steady state operation.SOLUTION: In a DC power supply leakage detection device, a first resistance element a, a first semiconductor element Q1, a first semiconductor switch S1, a second semiconductor switch S1, a second semiconductor element Q2, and a second resistance element b are connected in a line between a low-voltage power supply portion PS, a positive terminal 1, and a negative terminal 2, a third resistance element c is connected between a connection point N of the first semiconductor switch S1 and the second semiconductor switch S2 and a ground FG, the first semiconductor element Q1 and the second semiconductor element Q2 are set to DC bias conditions corresponding to a sensitivity current and are always in a conductive state, the first semiconductor switch S1 is in a conductive state when there is a leakage current between the negative power line L2 and ground FG and is in a cut-off state otherwise, and the second semiconductor switch S2 is in a conductive state when there is a leakage current between the positive power line L1 and the ground FG and is in a cut-off state otherwise.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a leakage detection device for a DC power supply. [Background technology]

[0002] Conventionally, a neutral point grounding method is known as a leakage current detection device for a DC power supply. The neutral point grounding method has a configuration in which two resistance elements are connected in series and the connection point is grounded in order to set a neutral point between the positive transmission line and the negative transmission line of a DC power supply (for example, Patent Documents 1 to 3). In the neutral point grounding method, when leakage current (ground fault, etc.) occurs in the transmission line, the ground fault is detected by detecting a change in the voltage across both ends or the divided voltage due to the leakage current flowing through the resistance element, or by detecting the leakage current flowing through the resistance element and the neutral point.

[0003] In the above-mentioned earth leakage detection device with neutral grounding, if the two series-connected resistance elements are made high resistance in order to suppress the power consumption during normal operation (when no leakage current occurs), the device becomes sensitive to noise and malfunctions frequently. Also, it was necessary to use high-power resistance elements for the two resistance elements through which the DC power supply voltage is applied and through which the leakage current flows.

[0004] Therefore, in the leakage current detection devices of Patent Documents 4 and 5, in addition to the two series-connected high-resistance resistor elements to which the DC power supply voltage is applied, a separate circuit for passing leakage current is provided, thereby preventing the leakage current from flowing through the two resistor elements, thereby achieving accurate leakage current detection while simultaneously suppressing steady-state power consumption by the two resistor elements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-296316 A [Patent Document 2] JP 2009-261039 A [Patent Document 3] JP 2013-130536 A [Patent Document 4] Patent Publication No. 2022-104280 [Patent Document 5] JP 2023-53772 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, even in the earth leakage detection devices of Patent Documents 4 and 5, the neutral point is set by two series-connected resistance elements to which a DC power supply voltage is applied. Therefore, power consumption due to the current flowing through these two resistance elements during steady state operation still occurs.

[0007] An object of the present invention is to provide a leakage current detection device that can accurately detect leakage current and reduce power consumption during steady state operation without using two resistive elements to which a DC power supply voltage is applied to set a neutral point. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides the following configuration: Note that the reference characters in parentheses are reference characters in the drawings described later, and are provided for reference.

[0009] 1) An aspect of the present invention is a leakage current detection device connected between a positive transmission line (L1) or a negative transmission line (L2) of a DC power supply and a ground (FG) in order to detect a leakage current between both transmission lines (L1, L2), a low-voltage power supply unit (PS) configured to output a constant voltage between a negative terminal (2) and a positive terminal (2) whose midpoint potential is the same as the midpoint potential of the DC power supply and is smaller than that of the DC power supply, and to be capable of discharging a current from the negative terminal (2) to the negative side transmission line (L2) and of sinking a current from the positive side transmission line (L1) to the positive terminal (1); a first circuit as a leakage current path, in which a first resistance element (a), a current path of a first semiconductor element (Q1), a current path of a first semiconductor switch (S1), a current path of a second semiconductor switch (S1), a current path of a second semiconductor element (Q2), and a second resistance element (b) are connected in series between the positive terminal (1) and the negative terminal (2), the first resistance element (a) and the second resistance element (b) have the same value (Rx), and a third resistance element (c) is connected between a connection point (N) of the first semiconductor switch (S1) and the second semiconductor switch (S2) and the ground (FG); the first semiconductor element (Q1) and the second semiconductor element (Q2) are set to a predetermined DC bias condition corresponding to a predetermined sensitivity current and are configured to be always in a conductive state; the first semiconductor switch (S1) is configured to be in a conductive state when there is a leakage current between the negative transmission line (L2) and the ground (FG) and to be in a cut-off state otherwise; The second semiconductor switch (S2) is configured to be in a conductive state when there is a leakage current between the positive power line (L1) and the ground (FG) and to be in a cut-off state otherwise. 2) In the above embodiment, a second circuit is provided in which two circuit elements (d, e) having the same value (Ry) are connected in series between the positive terminal (1) and the negative terminal (2), The control terminals of the second semiconductor switch (S1) and the second semiconductor switch (S2) are connected to a connection point (M) between the two circuit elements (d, e). 3) In the above aspect, a third circuit is provided in which a positive resistance element (f), a central resistance element (g), and a negative resistance element (h) are connected in series between the positive terminal (1) and the negative terminal (2), and the positive resistance element (f) and the negative resistance element (h) have the same value (Rz); A control end of the first semiconductor element (Q1) is connected to a connection point (X) between the positive resistance element (f) and the central resistance element (g), The control end of the second semiconductor element (Q2) is connected to a connection point (Y) between the negative resistance element (h) and the central resistance element (g), the first semiconductor element (Q1) is set to the DC bias condition by a characteristic curve of the first semiconductor element (Q1), a value (Rx) of the first resistance element (a), a value (Rz) of the positive side resistance element (f), and a value (Ru) of the central resistance element (g); The second semiconductor element (Q2) is characterized in that it is set to the DC bias condition by a characteristic curve of the second semiconductor element (Q2), a value (Rx) of the second resistance element (b), a value (Rz) of the negative resistance element (h), and a value (Ru) of the central resistance element (g). 4) In the above aspect, the detection unit (DT) is provided, and the detection unit (DT) is Detecting a sensitive current at the time of leakage current between the negative transmission line (L2) and the ground (FG) based on a change in potential at a connection point (A) between the first semiconductor element (Q1) and the first semiconductor switch (S1); and The present invention is characterized in that a sensitivity current during leakage current between the positive transmission line (L1) and the ground (FG) is detected by a change in potential at the connection point (B) between the second semiconductor element (Q2) and the second semiconductor switch (S2). 5) In the above aspect, the detection unit (DT) does not detect the occurrence of a leakage current when the current flowing through the first semiconductor element (Q1) or the current flowing through the second semiconductor element (Q2) is less than a sensitivity current, but detects the occurrence of a leakage current after the sensitivity current is reached. 6) In the above aspect, the central resistance element (g) is selected from a plurality of resistance elements having different values ​​(Ru) by switching a mechanical switch. Effect of the Invention

[0010] According to the present invention, a leakage current detection device is realized that can accurately detect leakage current and reduce power consumption during steady state operation without using two resistive elements to which a DC power supply voltage is applied in order to set a neutral point. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of a circuit configuration of an electric leakage detection device according to the present invention. [Diagram 2] FIG. 2(a) shows a schematic diagram of a DC bias circuit for a first semiconductor element on the positive side, and (b) is a diagram for explaining a method of setting the DC bias conditions. [Diagram 3] FIG. 3 shows a schematic diagram of the steady state of the earth leakage detection circuit of FIG. [Figure 4] FIG. 4 shows a schematic diagram of a state in which a leakage current occurs between the negative power line and the ground in the leakage current detection device of FIG. [Diagram 5] FIG. 5 shows a schematic diagram of a state in which a leakage current occurs between the positive power line and the ground in the leakage current detection device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an earth leakage detection device according to the present invention will be described in detail with reference to the drawings.

[0013] (1) Circuit configuration 1 is a diagram showing an example of a leakage current detection device and its peripheral circuit configuration according to the present invention. The leakage current detection device of the present invention is disposed between a positive power line L1 and a negative power line L2 of a DC power source (not shown). The DC power source is, for example, but not limited to, a solar power generation device or a storage battery. As an example, the potential of the positive power line L1 is +190V, the potential of the negative power line L2 is -190V, and the midpoint potential is 0V.

[0014] The leakage current detection device of the present invention is mainly used to detect leakage current between the transmission lines L1, L2 of a DC power supply and a ground FG (frame ground, chassis ground, etc.). A ground is a conductor that serves as a reference potential for a DC power supply and various circuits that operate from it. In this specification, the term "ground" is used in a broad sense, and includes both cases where it is connected (earthed) to the earth and cases where it is not connected. In the following, a frame ground will be described as an example of a ground FG.

[0015] <Low voltage power supply section PS> The earth leakage detection device has a low-voltage power supply unit PS, which is its driving power supply. "Low voltage" means a voltage lower than the DC power supply voltage. The low-voltage power supply unit PS uses the DC power supply voltage and outputs a constant voltage lower than it. The output terminals are the positive terminal 1 and the negative terminal 2 shown in Figure 1. The midpoint potential of the output voltage of the low-voltage power supply unit PS is configured to match the midpoint potential of the DC power supply.

[0016] As an example, a resistive element m, a Zener diode Z, and a resistive element n are connected in series between a positive transmission line L1 and a negative transmission line L2 of a DC power supply. The Zener voltage is, for example, 30V. The resistive elements m and n, which are set to high resistance, have the same resistance value Rv (for example, 1MΩ). This ensures a constant voltage range of 30V from -15V to 15V with a midpoint potential of 0V as the center. In the present invention, instead of setting the midpoint potential at the connection point of two resistive elements as in the prior art, a constant voltage range is set with the midpoint potential as the center using the Zener diode Z. The two diodes D1 and D2 connected across the Zener diode Z are not essential, but are provided to prevent the output voltage range of the low-voltage power supply unit PS from fluctuating significantly with respect to the ground FG.

[0017] In the low-voltage power supply section PS, the current flowing through the high-resistance (e.g., 1 MΩ) resistor elements m and n and the Zener diode Z is the same both in steady state and during leakage current, and is extremely small (e.g., less than 0.1 mA), so power consumption is not a problem.

[0018] The cathode of the Zener diode Z is connected to the gate of the transistor T1, which is an n-channel MOSFET, and the anode is connected to the gate of the transistor T2, which is a p-channel MOSFET.

[0019] The drain of the transistor T1 is connected to the positive power line L1 and the source is connected to the positive terminal 1. The drain of the transistor T2 is connected to the negative power line L2 and the source is connected to the negative terminal 2. Since a plurality of resistive elements are connected between the positive terminal 1 and the negative terminal 2 of the leakage current detector as described later, a predetermined bias voltage is applied to the transistors T1 and T2. As a result, the transistors T1 and T2 are always maintained in a conductive state. If the gate-source voltage of the transistors T1 and T2 is, for example, 4V, the potential of the positive terminal 1 is maintained at +11V, which is a drop of 4V from +15V, and the potential of the negative terminal 2 is maintained at -11V, which is a rise of 4V from -15V. This allows the leakage current detector to be driven by a power supply voltage of ±11V.

[0020] Moreover, the transistor T1 functions as a current path for drawing in current from the positive transmission line L1 to the positive terminal H, and the transistor T2 functions as a current path for discharging current from the negative terminal 2 to the negative transmission line L2. No current flows through the transistors T1 and T2 in the steady state, but they become a current path for the leakage current when a ground fault occurs.

[0021] <Main parts of the earth leakage detection device> The main part of the earth leakage detection device is provided between the positive electrode terminal 1 and the negative electrode terminal 2. The main part has a first circuit as an earth leakage current path, a second circuit and a third circuit for controlling the components of the first circuit, and a detection unit DT. In the following explanation of the potential within the circuit, an example will be given in which the potential of the positive electrode terminal 1 is +11V and the potential of the negative electrode terminal 2 is -11V.

[0022] First Circuit The first circuit, which serves as a leakage current path, includes a first resistance element a, a first semiconductor element Q1 (its current path), a first semiconductor switch S1 (its current path), a second semiconductor switch S2 (its current path), a second semiconductor element Q2 (its current path), and a second resistance element b, which are connected in a row between a positive terminal 1 and a negative terminal 2. The first semiconductor switch S1 and the second semiconductor switch S2, which are located in the center, are connected at a connection point N. Each of the semiconductor elements Q1, Q2 and the semiconductor switches S1, S2 has a current path through which a main current flows and a control end for controlling the current path, and in the illustrated configuration example, all of them are bipolar transistors.

[0023] The first circuit is configured symmetrically on the positive and negative sides with respect to the connection point N. That is, the first resistance element a and the second resistance element b have the same resistance value Rx. The first semiconductor element Q1 on the positive side and the second semiconductor element Q2 on the negative side are pnp and npn bipolar transistors, respectively, and the first semiconductor switch S1 on the positive side and the second semiconductor switch S2 on the negative side are npn and pnp bipolar transistors, respectively.

[0024] The emitter of the first resistance element a is connected to the first semiconductor element Q1, the collectors of the first semiconductor element Q1 and the first semiconductor switch S1 are connected to each other, the emitters of the first semiconductor switch S1 and the second semiconductor switch S2 are connected to each other, the collectors of the second semiconductor switch S2 and the second semiconductor element Q2 are connected to each other, and the emitter of the second semiconductor element Q2 is connected to the second resistance element b.

[0025] Furthermore, the connection point N between the first semiconductor switch S1 and the second semiconductor switch S2 is connected to the ground FG via a third resistor element c. The resistance value Rt of the third resistor element c is, for example, 100 Ω. In a steady state, the potential of the connection point N is a midpoint potential (0 V) between the potential of the positive terminal 1 (+11 V) and the potential of the negative terminal 2 (-11 V).

[0026] The positive-side first resistance element a, the current path of the first semiconductor element Q1, and the current path of the first semiconductor switch S1 in the first circuit form a leakage current path in the event of a leakage current between the negative power line L2 and the ground FG. The current path of the negative-side second semiconductor switch S2 in the first circuit, the current path of the second semiconductor element Q2, and the second resistance element b form a leakage current path in the event of a leakage current between the positive-side power line L1 and the ground FG. The third resistance element c carries the leakage current in the event of a leakage current on either side.

[0027] Second Circuit The second circuit is provided to control each control terminal of the first semiconductor switch S1 and the second semiconductor switch S2. The second circuit includes two circuit elements d and e having the same value Ry connected in series between the positive terminal 1 and the negative terminal 2. As an example, the circuit elements d and e are resistive elements having the same resistance value Ry (e.g., 100 kΩ). When the circuit elements d and e are resistive elements, the connection point M between the circuit elements d and e becomes the midpoint potential (0 V) in the steady state.

[0028] The control terminals (here, the bases) of the first semiconductor switch S1 and the second semiconductor switch S2 are connected to a connection point M between circuit elements d and e. The first semiconductor switch S1 and the second semiconductor switch S2 function as switching elements that are in a cut-off state during normal operation and in a conductive state during leakage current.

[0029] In steady state, both connection point N and connection point M are at the midpoint potential, so that the first semiconductor switch S1 and the second semiconductor switch S2 are in an off state because no bias voltage is applied between the base and emitter of each of them and no base current flows.

[0030] In the event of a leakage current, when the potential at the connection point N drops, a bias voltage is applied to the first semiconductor switch S1, causing it to become conductive, and when the potential at the connection point N rises, a bias voltage is applied to the second semiconductor switch S2, causing it to become conductive. The control end of the first semiconductor switch S1 is controlled so as to be in a conductive state when there is a leakage current between the negative power line L2 and the ground FG, and to be maintained in a cut-off state otherwise. The second semiconductor switch S2 has a control end controlled to be in a conductive state when there is a leakage current between the positive power line L1 and the ground FG, and to be maintained in a cut-off state otherwise. The details of the operation will be described later.

[0031] Although not shown, as another example of the second circuit, the circuit elements d and e may each be a Zener diode, or the circuit elements d and e may each be a Zener diode and a resistor connected in series. The positive circuit element d and the negative circuit element e are configured to have the same value (Zener voltage or resistance value). The Zener voltage is set so that the Zener voltage is not applied to both ends of the Zener diode during normal operation, and the Zener voltage is applied during leakage current. As a result, the control terminals (bases here) of the first semiconductor switch S1 and the second semiconductor switch S2 are in an open state during normal operation, so that the first semiconductor switch S1 and the second semiconductor switch S2 are both in an off state because no DC bias voltage is applied between the base emitter and no base current flows. The operation during leakage current is almost the same as when the circuit elements d and e are resistor elements.

[0032] Third Circuit The third circuit is provided to control each control terminal of the first semiconductor element Q1 and the second semiconductor element Q2. In the third circuit, a positive resistance element f, a central resistance element g, and a negative resistance element h are connected in series between a positive terminal 1 and a negative terminal 2. The positive resistance element f and the negative resistance element h have the same resistance value Rz, and the central resistance element g has a predetermined resistance value Ru.

[0033] The control end (here, the base) of the first semiconductor element Q1 is connected to a connection point X between the positive resistance element f and the central resistance element g. The control end (here, the base) of the second semiconductor element Q2 is connected to a connection point Y between the negative resistance element h and the central resistance element g.

[0034] The central resistive element g is selected from among a number of resistive elements with different resistance values ​​Ru by switching a mechanical switch SW. This is to set the sensitivity current. "Sensitivity current" generally means the magnitude of the current at which an earth leakage circuit breaker operates. The maximum value of the current flowing through the earth leakage current path of the first circuit described above corresponds to the sensitivity current. In the earth leakage detection device, even if an earth leakage occurs, the detection unit DT does not operate while the earth leakage current is less than the sensitivity current, and the detection unit DT operates when it reaches the sensitivity current.

[0035] The first semiconductor element Q1 and the second semiconductor element Q2 are set to a predetermined DC bias condition corresponding to a predetermined sensitivity current so that they are always in a conductive state. The setting of the DC bias condition involves the resistance elements f, g, and h on the third circuit and the first resistance element a and the second resistance element b on the first circuit.

[0036] A method for setting a predetermined DC bias condition corresponding to a predetermined sensitivity current will be described with reference to Fig. 2. Fig. 2(a) is a simplified diagram showing only the positive side of the first circuit and the third circuit in the earth leakage detection device of Fig. 1. The negative side is substantially the same as the positive side, so illustration and description are omitted.

[0037] When leakage current Ic flows, the first semiconductor switch S1 is in a conductive state, so in Fig. 2(a) it is simply shown as a closed switch. Since only the positive side is present, the resistance value of the central resistive element g is Ru / 2. The collector of the first semiconductor element Q1 is grounded, and the first resistive element a serves as the emitter resistor (load resistor).

[0038] In the procedure for setting the DC bias condition, first, a DC load line is determined, a base current Ib when a predetermined sensitivity current flows as a collector current Ic of the first semiconductor element Q1 is obtained from a characteristic curve, and an operating point P is obtained, which is an intersection point between the characteristic curve and the DC load line at the base current Ib. Then, resistance values ​​Rz and Ru / 2 of the resistance elements f and g are determined so that a DC bias voltage required for the base current Ib to flow at the operating point P is applied as a divided voltage of the resistance elements f and g. An example of this procedure will be described with reference to FIG. 2(b).

[0039] FIG. 2(b) shows a schematic characteristic curve of the collector-emitter voltage Vce versus collector current Ic of the first semiconductor element Q1 (for convenience, the current from the emitter to the collector is depicted as positive here). The power supply voltage Vcc is set to 11 V. First, the first resistance element a, which is the load resistance, is set to determine the DC load line. The resistance value Rx of the first resistance element a is determined so that the DC load line covers the desired range of collector current (sensitivity current) Ic. If the resistance value Rx is set to 68 Ω, the DC load line shown in the figure is obtained. In this case, a sensitivity current of approximately 150 mA or less can be covered.

[0040] When the sensitivity current is 100 mA, the value of the base current Ib(100) (e.g., 0.6 mA) can be determined from the characteristic curve. When the sensitivity current is 50 mA and 10 mA, the base currents are Ib(50) (e.g., 0.3 mA) and Ib(10) (e.g., 0.06 mA), respectively. The operating points P(100), P(50), and P(10) are determined from the intersections of each characteristic curve and the DC load line. The values ​​of the resistance elements f and g in the third circuit are determined so that a DC bias voltage corresponding to this operating point P is applied to the first semiconductor element Q1.

[0041] For example, when the collector current (sensitivity current) Ic is 100mA, the voltage drop at the first resistance element a (68Ω) is 6.8V and the emitter-base voltage drop is 0.6V, the DC bias condition is that the voltage across resistance element f is 7.4V and the voltage across resistance element g is 3.6V. Resistance elements f and g are set so that the 11V power supply voltage Vcc is divided at a ratio of 7.4:3.6. For example, if the resistance value Ry of resistance element f is 33kΩ and the resistance value Ru / 2 of resistance element g is 16kΩ (Ru is 32kΩ), the DC bias condition is almost met.

[0042] When the set value of the collector current (sensitivity current) Ic is changed, the DC bias conditions also change, and the voltage division ratio of resistance elements f and g also changes. In the circuit shown in Figure 1, resistance element f is kept constant, and the voltage division ratio, i.e., the sensitivity current, is changed by selecting resistance element g.

[0043] Detector DT Referring again to FIG. 1, the earth leakage detector is provided with a detection unit DT for detecting a sensitivity current at the time of earth leakage and outputting it to the outside. The detection unit DT has two comparators Cm1 and Cm2, which are powered by the low-voltage power supply unit PS. Each comparator Cm1 and Cm2 compares the potentials of two input terminals, + and -, and outputs a voltage of H level or L level depending on whether the potentials are high or low. In order to generate the reference potentials of the comparators Cm1 and Cm2, three resistance elements i, j, and k having the same resistance value Rs (for example, 100 kΩ) are connected in series between the positive terminal 1 and the negative terminal 2, and the power supply voltage of ±11 V is divided into three. Therefore, the C point potential of the reference terminal (+) of the positive side comparator Cm1 is about 3.7 V, and the D point potential of the reference terminal (-) of the negative side comparator Cm2 is about -3.7 V.

[0044] The detection terminal (-) of the comparator Cm1 is connected to a connection point A between the first semiconductor element Q1 and the first semiconductor switch S1. The output terminal 3 of the comparator Cm1 is at an L level when the potential at point A is higher than the reference potential of 3.7 V, and is at an H level when the potential is lower. The detection terminal (+) of the comparator Cm2 is connected to the connection point B between the second semiconductor switch S2 and the second semiconductor element Q2. The output terminal 4 of the comparator Cm2 is at L level when the potential at point B is lower than the reference potential of −3.7 V, and is at H level when it is higher.

[0045] The output terminals 3 and 4 of the comparators Cm1 and Cm2 are at L level in a steady state, and become H level when there is a leakage current (when the sensitivity current is reached), thereby activating a leakage current breaker or an alarm in the subsequent stage.

[0046] (2) Steady-state operation FIG. 3 shows a schematic diagram of the earth leakage detection device in a steady state. A DC bias voltage is applied to the positive side first semiconductor element Q1 and the negative side second semiconductor element Q2 on the first circuit by applying a voltage between the positive terminal 1 and the negative terminal 2 via resistance elements a, b on the first circuit and resistance elements f, g, h on the third circuit, respectively, so that a predetermined base current Ib1 flows and the first semiconductor element Q1 and the second semiconductor element Q2 are maintained in a conductive state.

[0047] On the other hand, the first semiconductor switch S1 on the positive side and the second semiconductor switch S2 on the negative side in the first circuit are in a cut-off state (shown by dotted lines) because the connection point M to which the base is connected and the connection point N to which the emitter is connected are both at the midpoint potential (the potential of ground FG).

[0048] Since the first semiconductor switch S1 is in a cutoff state, even if the first semiconductor element Q1 is in a conductive state, its collector is in an open state, so no collector current flows. With reference to FIG. 2(a), this is the state in which the switch of the first semiconductor switch S1 is open. The first semiconductor element Q1 is in a state that is out of the original operating point P set in FIG. 2(b), and the collector-emitter voltage Vce is 0V. Therefore, the potential at point A of the collector of the first semiconductor element Q1 is +11V, which is almost the same as the positive terminal 1. This is higher than the reference potential of 3.7V at point C of the comparator Cm1, so the output terminal 3 of the comparator Cm1 is at the L level.

[0049] Similarly, because the second semiconductor switch S2 is in a cutoff state, even if the second semiconductor element Q2 is in a conductive state, its collector is in an open state, so no collector current flows. The potential at point B of the collector of the second semiconductor element Q2 is -11V, which is almost the same as that of the negative terminal 2. This is lower than the reference potential of -3.7V at point D of the comparator Cm2, so the output terminal 4 of the comparator Cm2 is at the L level.

[0050] In a steady state, the leakage current path (first circuit) in the leakage current detection device is cut off, so no current flows. The base currents of the first and second semiconductor elements Q1 and Q2 and the current for the reference potential of the detection unit DT flow, but since both are configured with a relatively high resistance of several tens to several hundreds of kΩ and the voltage between the positive terminal 1 and the negative terminal 2 is about 22 V, only a very small current (for example, less than about 1 mA) flows. Therefore, power consumption in a steady state is suppressed.

[0051] (3) Operation during electric leakage <When there is a leakage current on the negative transmission line L2> Fig. 4 shows a situation where a leakage current occurs between the negative transmission line L2 and the ground FG. Note that the base current Ib1 shown in Fig. 3 flows all the time, but is omitted in Fig. 4.

[0052] When leakage current occurs between the negative power line L2 and ground FG, a leakage current Ic of a predetermined magnitude flows according to the resistance value Rg of the intervening leakage resistance (ground fault resistance in the case of a ground fault). When leakage current occurs between the negative power line L2 and the negative power line L2, the potential of the ground FG drops, causing the potential of the emitter (connection point N) of the first semiconductor switch S1 to drop, resulting in a bias voltage being applied to the first semiconductor switch S1 and a base current Ib2 flowing. The base current Ib2 flows from the positive terminal 1 through the circuit element d on the second circuit to the base and emitter of the first semiconductor switch S1, and further flows through the third resistance element c to the ground FG.

[0053] The base current Ib2 flows, and the first semiconductor switch S1 is turned on. As a result, the leakage current Ic flows from the positive power line L1 to the transistor T1 to the first resistance element a to the first semiconductor element Q1 to the first semiconductor switch S1 to the third resistance element c to the ground FG to the negative power line L2.

[0054] At the time when the leakage current Ic is still zero, the potential at point A is approximately the potential at the positive terminal 1, and the voltage drop at the first resistance element a and the collector-emitter voltage Vce of the first semiconductor element Q1 are approximately 0 V. At this point, the voltage Vf across the resistance element f in the third circuit is approximately equal to the base-emitter voltage (approximately 0.6 V) of the first semiconductor element Q1.

[0055] When the leakage current Ic increases, the voltage drop in the first resistive element a increases, and accordingly the voltage Vf across the resistive element f in the third circuit also increases. However, while the leakage current Ic does not reach the set sensitivity current, the collector-emitter voltage Vce of the first semiconductor element Q1 remains at 0V (see FIG. 2(b)). During this period, the potential of the collector (point A) of the first semiconductor element Q1 is higher than the reference potential (point C) of the comparator Cm1, so the output terminal 3 of the comparator Cm1 remains at the L level.

[0056] We will now explain the case where the leakage current Ic reaches the set maximum value, i.e., the sensitivity current. For example, the sensitivity current set in FIG. 2(b) is 100 mA. At this point, the voltage drop across the first resistor element a is 6.8 V (68 Ω × 100 mA). The voltage Vf across the resistor element f also reaches the value of the set DC bias condition, 7.4 V (6.8 V + 0.6 V). When the set sensitivity current reaches 100 mA, the collector-emitter voltage Vce of the first semiconductor element Q1 is still 0 V, and the potential at point A is 4.2 V (11 V - 6.8 V), which is higher than the reference potential of the comparator Cm1 of 3.7 V, so the comparator Cm1 does not yet operate.

[0057] After that, when the leakage current Ic tries to increase further, the collector-emitter voltage Vce of the first semiconductor element Q1, which had been 0V until then, increases. When the sensitivity current is 100mA, Vce increases from 0V toward the operating point P(100) from point 0 in Figure 2. When Vce exceeds 0.5V, the potential at point A falls below 3.7V, so the comparator Cm1 operates and the output terminal 3 goes to the H level. This activates the earth leakage breaker and alarm in the downstream stage. Eventually, the collector-emitter voltage Vce reaches 4.2 V at the operating point P(100) in Figure 2. The potential at point A at this time is approximately 0 V. The first semiconductor element Q1 remains at the operating point P(100) under the originally set DC bias conditions, and the leakage current Ic does not increase beyond the sensitivity current.

[0058] <When there is a leakage current on the positive transmission line L1> Fig. 5 shows a situation where a leakage current occurs between the positive transmission line L1 and the ground FG. Note that the base current Ib1 shown in Fig. 3 flows all the time, but is omitted in Fig. 5.

[0059] When leakage current occurs between the positive transmission line L1 and ground FG, a leakage current Ic of a predetermined magnitude flows according to the resistance value Rg of the intervening leakage resistance (ground fault resistance in the case of a ground fault). When leakage current occurs between the positive transmission line L1 and ground FG, the potential of the ground FG rises, which raises the potential of the emitter (connection point N) of the second semiconductor switch S2, causing a bias voltage to be applied to the second semiconductor switch S2 and causing a base current Ib2 to flow. The base current Ib2 flows from the ground FG through the third resistance element c to the emitter to the base of the second semiconductor switch S2, and further flows to the negative terminal 2 through circuit element e on the second circuit.

[0060] The base current Ib2 flows, and the second semiconductor switch S2 is turned on. As a result, the leakage current Ic flows from the positive power line L1 to the ground FG to the third resistance element c to the second semiconductor switch S2 to the second semiconductor element Q2 to the second resistance element b to the transistor T2 to the negative power line L2.

[0061] The operation during the period when the leakage current Ic is less than the sensitivity current and the operation after it reaches the sensitivity current are similar to those during leakage in the negative side power line L2 described above, and therefore a description thereof will be omitted.

[0062] (4)Other Although embodiments of the present invention have been described with reference to example configurations, embodiments of the present invention are not limited to these example configurations. For example, the first semiconductor element Q1, the second semiconductor element Q2, the first semiconductor switch S1, and the second semiconductor switch S2 are not limited to bipolar transistors, and may be configured with IGBTs or MOSFETs. For example, when a MOSFET is used, the characteristic curve of Fig. 2(b) becomes a characteristic curve of the drain-source voltage and the drain current, and the resistive elements a, b, f, g, h, etc. are set so as to satisfy the gate-source voltage of the operating point set according to the sensitivity current as a DC bias condition. As long as the principles of the present invention are followed, various modifications are within the scope of the present invention. [Explanation of symbols]

[0063] 1 Positive end 2 negative extreme 3, 4 Output terminals L1 positive transmission line L2 negative transmission line Q1 First semiconductor element Q2 Second semiconductor element S1 First semiconductor switch S2 Second semiconductor switch T1 Transistor T2 transistor a, b, c resistance elements d, e Circuit elements f, g, h resistance elements i, j, k resistance elements m, n resistance element Cm1, Cm2 comparator Z Zener diode D1, D2 Diodes Rx, Ry, Rz, Ru, Rs, Rt, Rg Resistance values

Claims

1. A leakage current detection device connected between a positive transmission line (L1) or a negative transmission line (L2) of a DC power supply and a ground (FG) in order to detect a leakage current between both transmission lines (L1, L2), a low-voltage power supply unit (PS) configured to output a constant voltage between a negative terminal (2) and a positive terminal (2) whose midpoint potential is the same as the midpoint potential of the DC power supply and is smaller than that of the DC power supply, and to be capable of discharging a current from the negative terminal (2) to the negative side transmission line (L2) and of sinking a current from the positive side transmission line (L1) to the positive terminal (1); a first circuit as a leakage current path, in which a first resistance element (a), a current path of a first semiconductor element (Q1), a current path of a first semiconductor switch (S1), a current path of a second semiconductor switch (S1), a current path of a second semiconductor element (Q2), and a second resistance element (b) are connected in series between the positive terminal (1) and the negative terminal (2), the first resistance element (a) and the second resistance element (b) have the same value (Rx), and a third resistance element (c) is connected between a connection point (N) of the first semiconductor switch (S1) and the second semiconductor switch (S2) and the ground (FG); the first semiconductor element (Q1) and the second semiconductor element (Q2) are set to a predetermined DC bias condition corresponding to a predetermined sensitivity current and are configured to be always in a conductive state; the first semiconductor switch (S1) is configured to be in a conductive state when there is a leakage current between the negative transmission line (L2) and the ground (FG) and to be in a cut-off state otherwise; The second semiconductor switch (S2) is configured to be in a conductive state when there is a leakage current between the positive power line (L1) and the ground (FG) and to be in a cut-off state otherwise.

2. A second circuit has two circuit elements (d, e) having the same value (Ry) connected in series between the positive terminal (1) and the negative terminal (2), The leakage current detection device according to claim 1, characterized in that each control end of the second semiconductor switch (S1) and the second semiconductor switch (S2) is connected to a connection point (M) between the two circuit elements (d, e).

3. a third circuit in which a positive resistance element (f), a central resistance element (g) and a negative resistance element (h) are connected in series between the positive terminal (1) and the negative terminal (2), and the positive resistance element (f) and the negative resistance element (h) have the same value (Rz); A control end of the first semiconductor element (Q1) is connected to a connection point (X) between the positive resistance element (f) and the central resistance element (g), The control end of the second semiconductor element (Q2) is connected to a connection point (Y) between the negative resistance element (h) and the central resistance element (g), the first semiconductor element (Q1) is set to the DC bias condition by a characteristic curve of the first semiconductor element (Q1), a value (Rx) of the first resistance element (a), a value (Rz) of the positive side resistance element (f), and a value (Ru) of the central resistance element (g); The leakage current detection device according to claim 1, characterized in that the second semiconductor element (Q2) is set to the DC bias condition by a characteristic curve of the second semiconductor element (Q2), a value (Rx) of the second resistance element (b), a value (Rz) of the negative resistance element (h), and a value (Ru) of the central resistance element (g).

4. The detection unit (DT) includes: Detecting a sensitive current at the time of leakage current between the negative transmission line (L2) and the ground (FG) based on a change in potential of a connection point (A) between the first semiconductor element (Q1) and the first semiconductor switch (S1); and The leakage current detection device according to claim 3, characterized in that a sensitivity current during a leakage current between the positive transmission line (L1) and the ground (FG) is detected based on a change in potential at a connection point (B) between the second semiconductor element (Q2) and the second semiconductor switch (S2).

5. The leakage current detection device according to claim 4, characterized in that the detection unit (DT) does not detect the occurrence of a leakage current when the current flowing through the first semiconductor element (Q1) or the current flowing through the second semiconductor element (Q2) is less than a sensitivity current, but detects the occurrence of a leakage current after the sensitivity current is reached.

6. 6. The leakage current detection device according to claim 3, wherein the central resistance element (g) is selected from a plurality of resistance elements having different values ​​(Ru) by switching a mechanical switch.

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