Leakage detector for DC power source

Abstract

To surely detect a time point in which a leakage current achieves a sensitivity current, and prevent a value of the sensitivity current from being changed even if a DC power supply voltage is fluctuated in a leakage detector for a DC power source.SOLUTION: A leakage detector for a DC power source comprises: resistive elements R1 and R2 connected at a neutral point N; a semiconductor element Q1 having a current path connected to a positive electrical path 3 and a control end connected to the neutral point N; a semiconductor element Q2 having a current path connected to a negative electrical pat 4 and a control end connected to the neutral point N; a resistive element Re for sensitivity setting connected between the other end E of the current paths of the semiconductor elements Q1 and Q2 and a ground G; constant voltage Zener diodes Z1 and Z2 connected in series in mutually reverse directions between the control ends of the semiconductor elements Q1 and Q2 and the ground G and respectively having a Zener voltage Vz equal to a product of a resistance value of the resistive element Re for sensitivity setting and a sensitivity current Is; and a detection section 20 for detecting the sensitivity current Is based on a change in a potential of the positive electrical path 3 or the negative electrical path 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, a neutral grounding method has been known as a leakage detector for DC power supplies. The neutral grounding method has a configuration in which two resistance elements are connected in series to set a neutral point between the positive and negative electric circuits of a DC power supply, and the connection point is grounded (for example, Patent Documents 1 to 3). In the neutral grounding method, when a leakage current (such as a ground fault) occurs in the electric circuit, the leakage current 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 earth-grounded neutral leakage detectors like the one described above, if high resistance is used to suppress power consumption by the resistor elements during normal operation (when no leakage current is occurring), the detector becomes sensitive to noise and malfunctions frequently. Also, it was necessary to use high-power resistors for the two resistor elements through which leakage current flows when DC power supply voltage is applied.

[0004] Therefore, in the earth leakage detectors of Patent Documents 4 and 5, a circuit for passing earth leakage current is provided in addition to the resistance element for setting the neutral point, thereby preventing the earth leakage current from flowing into the resistance element for setting the neutral point, thereby achieving accurate earth leakage detection while simultaneously reducing power consumption during steady state operation. [Prior art documents] [Patent documents]

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

[0006] Generally, leakage current detectors are designed to detect leakage current when the leakage current reaches a predetermined sensitivity current. However, in the case of methods that directly monitor the magnitude of the leakage current or methods that monitor the voltage across a predetermined resistive element through which the leakage current flows, the change when the leakage current reaches the sensitivity current from a region below the sensitivity current is continuous and not significant. Therefore, when the leakage current is close to the sensitivity current, it is susceptible to noise, which can easily cause malfunctions in downstream leakage current breakers, etc.

[0007] Furthermore, in the leakage detectors of Patent Documents 4 and 5, the circuit constant corresponding to a predetermined sensitivity current is set according to the DC power supply voltage, but the leakage detector cannot be applied as is to DC power supplies of different voltages, and there is a problem that the value of the sensitivity current changes if the DC power supply voltage fluctuates during leakage detection.

[0008] The object of the present invention is to realize a DC power supply leakage detector that can reliably detect the point at which the leakage current reaches the sensitivity current, and that does not change the value of the sensitivity current even if the DC power supply voltage fluctuates. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides the following configuration: Note that the reference numerals in parentheses are reference numerals in the drawings to be described later, and are provided for reference. [1] An aspect of the present invention is a leakage current detector for detecting a leakage current between a positive side electric circuit (3) or a negative side electric circuit (4) of a DC power supply and a ground (G), a first resistance element (R1) and a second resistance element (R2) having the same resistance value, one end of which is connected to the positive side electric circuit (3) and one end of which is connected to the negative side electric circuit (4), and the other end of which is connected to each other at a midpoint (N); a first semiconductor element (Q1) through which a leakage current (I4) flows when a leakage current occurs between the negative electric path (4) and the ground (G) and having one end of a current path connected to the positive electric path (3) and a control end connected to the midpoint (N); a second semiconductor element (Q2) through which a leakage current (I4) flows when a leakage current occurs between the positive side electric path (4) and the ground (G) and having one end of a current path connected to the negative side electric path (4) and a control end connected to the midpoint (N); a sensitivity setting resistive element (Re) connected between the other end (E) of each current path of the first semiconductor element (Q1) and the second semiconductor element (Q2) and the ground (G); a first constant voltage diode (Z1) and a second constant voltage diode (Z2) connected in series in opposite directions between the control terminals of the first semiconductor element (Q1) and the second semiconductor element (Q2) and the ground (G), and having a Zener voltage (Vz) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and a sensitivity current (Is); The present invention is characterized by comprising a detection unit (20) that detects that the leakage current (I4) has reached the sensitivity current (Is) based on a change in the potential of the positive side electric circuit (3) or the negative side electric circuit (4). [2] In the above aspect [1], the potential of the negative electric circuit (4) when there is a leakage current between the negative electric circuit (4) and the ground (G) is: When the leakage current (I4) is less than the sensitivity current (Is), the potential is higher than the potential of the negative side electric circuit (4) when there is no leakage current by a voltage (Ve) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and the leakage current (I4), and When the leakage current (I4) reaches the sensitive current (Is), the potential becomes substantially equal to the potential of the ground (G). [3] In the above aspect [1], the potential of the positive electric circuit (3) when there is a leakage current between the positive electric circuit (3) and the ground (G) is: When the leakage current (I4) is less than the sensitivity current (Is), the potential is lower than the potential of the positive side electric circuit (3) when there is no leakage current by a voltage (Ve) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and the leakage current (I4), and When the leakage current (I4) reaches the sensitive current (Is), the potential becomes substantially equal to the potential of the ground (G). [4] In the above aspect [2] or [3], the detection unit (20) has three resistance elements (R3, R4, R5) having the same resistance value connected in sequence between the positive side electric circuit (3) and the negative side electric circuit (4), The device is characterized in that it is configured so that a detection current (I5) flows depending on the level relationship between the potential of the two connection points (A, B) of the three resistance elements (R3, R4, R5) and the potential of the ground (G). [5] In the aspect of [1] above, the first semiconductor element (Q1) and the second semiconductor element (Q2) are characterized in that they form an emitter follower circuit or a source follower circuit with the other end (E) of each current path as the emitter or source. [6] In the above aspect [1], the sensitivity setting resistance element (Re) is selected from a plurality of resistance elements having different resistance values ​​by switching a mechanical switch. [Effects of the Invention]

[0010] According to the present invention, in a DC power supply leakage detector, it is possible to reliably detect the point in time when the leakage current reaches the sensitivity current, and to ensure that the sensitivity current does not change even if the DC power supply voltage fluctuates. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram schematically showing an example of the circuit configuration of an earth leakage detector according to the present invention. [Figure 2] FIG. 2 is a diagram for explaining the state of the circuit of FIG. 1 when there is no leakage current. [Figure 3]FIG. 3 is a diagram for explaining a state in which the leakage current is less than the sensitivity current when a leakage current occurs in the negative side electric path in the circuit of FIG. [Figure 4] FIG. 4 is a diagram for explaining a state when the leakage current in FIG. 3 reaches the sensitivity current. [Figure 5] FIG. 5 is a diagram for explaining a state in which the leakage current is less than the sensitivity current when there is a leakage current in the positive side electric circuit in the circuit of FIG. [Figure 6] FIG. 6 is a diagram for explaining a state when the leakage current in FIG. 5 reaches the sensitivity current. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the earth leakage detector according to the present invention will be described in detail with reference to the drawings. (1) Circuit configuration FIG. 1 shows an example of the circuit configuration of a ground fault detector according to the present invention, along with the electrical circuit of a DC power supply. The ground fault detector according to the present invention is disposed between a positive electrical circuit 3 connected to a positive output terminal 1 of a DC power supply (not shown) and a negative electrical circuit 4 connected to a negative output terminal 2 of the DC power supply. The DC power supply may be, for example, a solar power generation device or a storage battery, but is not limited to these. As an example, the DC power supply voltage is ±300V.

[0013] The earth leakage detector of the present invention is used to detect an earth leakage between the positive electric circuit 3 of a DC power supply and ground G, or between the negative electric circuit 4 and ground G. Ground G is a conductor that serves as the reference potential for the DC power supply and various circuits that operate from it, and is the frame ground, chassis ground, etc. The potential of ground G is always 0V regardless of whether there is an earth leakage or not. In this specification, the term "ground" is used in a broad sense, and includes both cases where it is connected (grounded) to the earth and cases where it is not connected to the earth. Therefore, "earth leakage current" is not limited to only earth fault current that flows to the earth. The earth leakage detector has a main circuit 10 and a detection unit 20.

[0014] <Configuration of main circuit 10> The main circuit 10 includes a circuit consisting of two resistance elements R1 and R2 for setting the neutral point through which a steady current flows (these are not exactly the same as the neutral point of a typical neutral-point grounding system, and are therefore referred to as "midpoints" rather than "neutral points"). The first resistance element R1 has one end connected to the positive-side electrical circuit 3 and the other end connected to the midpoint N. The second resistance element R2 has one end connected to the negative-side electrical circuit 4 and the other end connected to the midpoint N. The resistance elements R1 and R2 essentially have the same resistance value, and by setting a high resistance of, for example, about 1 MΩ, power consumption during non-leakage periods can be reduced. The "resistance elements" can be composed of a single resistance element (linear resistance element) or multiple resistance elements connected in series.

[0015] The main circuit 10 further includes a circuit through which a leakage current flows in the event of a ground fault, the circuit including a first semiconductor element Q1 and a second semiconductor element Q2. In the illustrated example, the first semiconductor element Q1 is an npn-type bipolar transistor. The collector, which is one end of the collector-emitter current path, is connected to the positive-side current path 3, and the base, which is the control end, is connected to the midpoint N. The second semiconductor element Q2 is a pnp-type bipolar transistor. The collector, which is one end of the collector-emitter current path, is connected to the negative-side current path 4, and the base, which is the control end, is also connected to the midpoint N. The emitters, which are the other ends of the current paths of the first semiconductor element Q1 and the second semiconductor element Q2, are connected to each other at a connection point E. A leakage current flows through the current path of the first semiconductor element Q1 in the event of a ground fault between the negative-side current path 4 and ground G. A leakage current flows through the current path of the second semiconductor element Q2 in the event of a ground fault between the positive-side current path 3 and ground G.

[0016] As another example, the semiconductor elements Q1 and Q2 may be FETs or IGBTs. In either case, the semiconductor elements Q1 and Q2 form an emitter follower circuit or a source follower circuit, and operate so that the base potential and the emitter potential, or the gate potential and the source potential, which are the control terminals, are approximately equal.

[0017] The main circuit 10 further includes a sensitivity-setting resistive element Re connected between a connection point E between the first semiconductor element Q1 and the second semiconductor element Q2 and ground G. In the illustrated example, the sensitivity-setting resistive element Re is selected from a plurality of resistive elements with different resistance values ​​by switching a mechanical switch SW. This selection is made according to the desired sensitivity current.

[0018] The main circuit 10 further includes a first zener diode Z1 and a second zener diode Z2 connected between the control terminals (midpoint N) of the first semiconductor element Q1 and the second semiconductor element Q2 and ground G. The zener diodes Z1 and Z2 are connected in series in opposite directions. The Zener voltage Vz of the zener diodes Z1 and Z2 is set to be equal to the product of the resistance value of the sensitivity setting resistor element Re and the desired sensitivity current Is, and is expressed by the following equation: Vz=Re×Is...Equation 1 Vz: Zener voltage Re::Resistance value of sensitivity setting resistor element Is: Sensitivity current For example, when the Zener voltage Vz is set to 20 V, if the sensitivity current is desired to be 100 mA, 10 mA, or 1 mA, the resistance values ​​of the sensitivity setting resistive element Re are selected to be 200 Ω, 2 kΩ, or 20 kΩ, respectively.

[0019] <Configuration of detection unit 20> The detector 20 detects when the leakage current reaches the sensitivity current during a ground fault. This detection is performed based on the change in potential of the positive or negative electric circuit during a ground fault. Here, the change in potential of the positive or negative electric circuit refers to the change relative to the potential of ground G (0 V).

[0020] There are various configurations for the detection unit 20 for detecting changes in the potential of the positive or negative electric circuit, and the configuration shown in the figure is one example. Three resistance elements R3, R4, and R5, each with the same resistance value, are connected in sequence between the positive electric circuit 3 and the negative electric circuit 4. The connection point between the resistance elements R3 and R4 is indicated by symbol A, and the connection point between the resistance elements R4 and R5 is indicated by symbol B. Since a steady current flows through these resistance elements when there is no leakage current or when there is a leakage current less than the sensitivity current, it is preferable to set the resistance elements R3, R4, and R5 to a high resistance in order to reduce power consumption.

[0021] The output terminals 5 and 6 of the detection unit 20 are output terminals of an SSR (Solid State Relay) which is a photo MOSFET. A rectifier diode D2 is connected in the same direction between the cathode of the SSR's input photodiode and connection point A. A rectifier diode D1 is connected in the same direction between the anode of the SSR's input photodiode and connection point B.

[0022] Furthermore, photodiode L1 is connected in the same direction between the cathode of the input-side photodiode of the SSR and ground G. Photodiode L2 is connected in the same direction between the anode of the input-side photodiode of the SSR and ground G.

[0023] (2) Operation when there is no leakage current FIG. 2 is a diagram illustrating the state of the circuit of FIG. 1 when there is no leakage current. The sensitivity-setting resistor element Re is shown as a single element selected according to the desired sensitivity current. As an example, the DC power supply voltage is set to ±300 V relative to ground G, which has a potential of 0 V. Therefore, when there is no leakage current, the potential of the positive-side circuit 3 is +300 V, and the potential of the negative-side circuit 4 is -300 V.

[0024] When there is no leakage current, a steady-state current I1 flows through the resistance elements R1 and R2 used to set the midpoint. A steady-state current I2 also flows through the resistance elements E3, R4, and R5 in the detection section. By setting the resistance values ​​of these resistance elements to between several hundred kΩ and several MΩ, power consumption when there is no leakage current is reduced. For example, if the resistance elements R1 and R2 are set to 1 MΩ, the steady-state current I1 is 0.6 mA, and if the resistance elements R3, R4, and R5 are set to 300 kΩ, the steady-state current I2 is 0.7 mA, both of which are very small.

[0025] At this time, the potential at midpoint N is 0V, the median value of the ±300V DC power supply. In other words, the bases of each of the semiconductor elements Q1 and Q2 are at 0V. The potential at point E, which is the emitter of both semiconductor elements, is also 0V, so no base current flows. Therefore, both semiconductor elements Q1 and Q2 are in the off state, so no current flows in the current path between the collector and emitter. No current also flows through the constant voltage diodes Z1 and Z2 or the sensitivity setting resistor element Re.

[0026] The potential of connection point A of the detection unit is +100V, and the potential of connection point B is -100V. On the other hand, ground G is 0V, so the diodes connected between connection point A and ground G, and between connection point B and ground G, are in the opposite direction relative to the potential level, so no current flows through these diodes. As a result, the detection unit does not operate.

[0027] (3) Operation in the event of a leakage current in the negative circuit (3-1) When the leakage current is less than the sensitive current FIG. 3 is a diagram for explaining a state in which the leakage current is less than the sensitivity current when there is a leakage current in the negative side electric circuit 4 in the circuit of FIG.

[0028] In Figure 3, the main circuit is shown as an equivalent circuit. The second semiconductor element Q2, which maintains the off state, is omitted, and a leakage resistance Rg (located outside the circuit) between the negative side current path 4 and ground G is added. When the leakage current is a ground fault, the leakage resistance Rg is called a ground fault resistance.

[0029] When a current leaks between the negative side circuit 4 and ground G, the potential at the midpoint N rises, causing a base current I3 to flow, the first semiconductor element Q1 to become conductive, and a leakage current I4 (<sensitivity current Is) flows. The leakage current I4 flows from the positive side circuit 3 through the current path of the first semiconductor element Q1, through the sensitivity setting resistance element Re to ground G, and then through the leakage resistor Rg to the negative side circuit 4. The magnitude of the base current I3 is the leakage current I4 / h FE (h FE is the DC current amplification factor of the semiconductor element), which is extremely small compared to the steady-state current I1.

[0030] The voltage Ve across the sensitivity setting resistance element Re becomes Re×I4 due to the leakage current I4 flowing, and is expressed by the following formula. Ve = Re × I4 Equation 2 Ve: Voltage across the resistance element Re for sensitivity setting Re: Resistance value of the resistance element for sensitivity setting I4: Leakage current (However, I4 <Is)

[0031] The potential at point E is increased by a voltage Ve relative to ground G. Therefore, when the Zener voltage Vz is 20 V, the potential φ at point E is E is 0<φ E <+20V.

[0032] Because it is an emitter follower, the potential at point E and the potential at point N are the same. In reality, there is a difference of about 0.6 to 0.7 V between the base and emitter voltages, but this will be ignored here. Therefore, the voltage between the midpoint N and ground G is smaller than the Zener voltage Vz of the voltage regulator diode Z1 shown in equation 1. Therefore, the voltage regulator diode Z1 in Figure 2 does not flow Zener current and is equivalent to an open state, so it is not shown in Figure 3.

[0033] Like the potential at point E, the potential at midpoint N also rises by a voltage Ve relative to ground G, varying within the range of 0 to +20 V. Accordingly, the potentials of the positive and negative electric circuits 3 and 4 also become higher by a voltage Ve relative to the potentials when there is no leakage current, with the potential of the positive electric circuit 3 varying within the range of +300 to +320 V and the potential of the negative electric circuit 4 varying within the range of -300 to -280 V.

[0034] As the potentials of the positive and negative electric circuits 3 and 4 change within the above ranges, the potential at connection point A of the detection unit changes between +100 and +120V, and the potential at connection point B changes between -100 and -80V. At this stage, the diodes connected between connection point A and ground G, and between connection point B and ground G, are in the opposite direction relative to the high and low potentials, so no current flows through these diodes. Therefore, the detection unit does not operate, just as it does when there is no leakage current.

[0035] (3-2) When the leakage current reaches the sensitive current Figure 4 is a diagram for explaining the state when the leakage current I4 in Figure 3 reaches the sensitivity current Is. As in Figure 3, the main circuit is shown as an equivalent circuit. Here, the second semiconductor element Q2, which remains off, is omitted, and a leakage resistance Rg (external to the circuit) between the negative current path 4 and ground G is added.

[0036] 3 reaches the sensitivity current Is, the voltage across the sensitivity setting resistor Re reaches the Zener voltage Vz as shown in Equation 1 above, as shown in Fig. 4, so that the Zener voltage Vz is applied to the first constant voltage diode Z1, causing the Zener current Iz to flow. The Zener current Iz flows from the positive-side electrical circuit 3 through the first resistance element R1 and the first constant voltage diode Z1 to ground G, and then flows to the negative-side electrical circuit 4 via the leakage resistor Rg.

[0037] At the moment the sensitivity current Is is reached, a Zener current Iz, which is larger than the steady-state current I1, flows only through the first resistance element R1, causing the voltage across the first resistance element R1 to suddenly increase, so that the potential of the positive current path 3 becomes approximately +600 V, and the potential of the negative current path 4 becomes approximately equal to the potential of ground G, 0 V. The term "approximately equal" is used because the voltage drop across the leakage resistance Rg is taken into consideration, but the resistance value of the leakage resistance Rg is extremely small compared to the first resistance element R1, so it is negligible compared to the voltage drop across the resistance element R1.

[0038] At this time, the voltage across the sensitivity setting resistor element Re is fixed at the Zener voltage Vz and does not increase any further. Therefore, the sensitivity current Is does not increase beyond the set value. For example, even if the DC power supply voltage fluctuates after reaching the sensitivity current Is, the sensitivity current Is does not change.

[0039] The detector detects a sudden change in the potential of the negative circuit 4 at the moment the leakage current reaches the sensitivity current Is. When the potential of the negative circuit 4 becomes approximately 0 V (slightly lower than 0 V), the potential of node B also becomes approximately 0 V (slightly higher than 0 V), and the diodes connected between node B and ground G are in the forward direction. As a result, detection current I5 flows from the positive circuit 3 through resistive elements R3 and R4, rectifier diode D1, the SSR input photodiode, and photodiode L1 to ground G, and then through leakage resistor Rg to the negative circuit 4. Light emitted by photodiode L1 indicates a leakage current in the negative circuit 4. The output of the SSR also triggers the activation of downstream devices such as an alarm or earth leakage circuit breaker. The potential at the connection point A is approximately 300 V, and the diode between the connection point A and the ground G is in the reverse direction, so no current flows.

[0040] Conventionally, the sensitivity current has been detected by directly monitoring the leakage current or by monitoring the voltage across a resistive element through which the leakage current flows, but in such cases, the change in the detected value when the leakage current reaches the sensitivity current from a region below the sensitivity current is continuous, which can easily cause malfunctions or unstable operation due to noise, etc. In contrast, the leakage detector of the present invention detects the sensitivity current by utilizing the discontinuous and large change in the potential of the DC power supply circuit when the leakage current reaches the sensitivity current, thereby enabling reliable detection that is resistant to noise.

[0041] (4) Operation in the event of a leakage current in the positive circuit FIG. 5 is a diagram for explaining a state in which the leakage current is less than the sensitivity current when there is a leakage in the positive side electric circuit 3, and FIG. 6 is a diagram for explaining a state in which the leakage current reaches the sensitivity current. The circuit operation of Figures 5 and 6 is essentially the same as that of Figures 3 and 4, except that the polarity is reversed, so it will only be briefly explained. When a leakage current occurs in the positive current path 3, a leakage current flows through the second semiconductor element Q2. The first semiconductor element Q1 is in the off state, so it is not shown, and a leakage resistance Rg (external to the circuit) is connected between the positive current path 3 and ground G.

[0042] In Figure 5, leakage current I4 (<sensitivity current Is) flows from the positive side electrical circuit 3 through leakage resistance Rg to ground G, and from ground G through the current path of sensitivity setting resistance element Re and second semiconductor element Q2 to the negative side electrical circuit 4.

[0043] When a current leaks between the positive current path 3 and ground G, the potential at the midpoint N drops, causing a base current I3 to flow, the second semiconductor element Q2 to become conductive, and a leakage current I4 (<sensitivity current Is) flows. The leakage current I4 flows from the positive current path 3 to ground G via the leakage resistance Rg, and then flows from the sensitivity-setting resistance element Re to the negative current path 4 through the current path of the second semiconductor element Q2.

[0044] The voltage Ve across the sensitivity setting resistance element Re is Re×I4, and the potential at point E is a potential that is dropped by the voltage Ve with respect to the ground G. Therefore, when the Zener voltage Vz is 20 V, the potential φ at point E is E is 0>φE >-20V. Here again, the potential at midpoint N and the potential at point E are the same. Therefore, the voltage between midpoint N and ground G is smaller than the Zener voltage Vz of the second voltage constant diode Z2 shown in equation 1, and no Zener current flows through the second voltage constant diode Z2 in Figure 2, which is equivalent to an open state, so it is not shown in Figure 5.

[0045] Like the potential at point E, the potential at midpoint N drops by a voltage Ve relative to ground G, varying within the range of 0 to +20 V. Accordingly, the potentials of the positive and negative electric circuits 3 and 4 also become lower by a voltage Ve relative to the potentials when there is no leakage current, with the potential of the positive electric circuit 3 varying within the range of +300 to +280 V and the potential of the negative electric circuit 4 varying within the range of -300 to -320 V.

[0046] As the potentials of the positive and negative electric circuits 3 and 4 change within the above ranges, the potential of the detection unit's connection point A changes between +100 and +80V, and the potential of connection point B changes between -100 and -120V. At this stage, the diodes connected between connection point A and ground G, and between connection point B and ground G, are in the opposite direction relative to the high and low potentials, so no current flows through these diodes. Therefore, the detection unit does not operate, just as it does when there is no leakage current.

[0047] When the leakage current I4 in Fig. 5 reaches the sensitivity current Is, the voltage across the sensitivity setting resistor Re reaches the Zener voltage Vz as shown in Equation 1 above, as shown in Fig. 6, so that the Zener voltage Vz is applied to the second voltage regulator diode Z2, causing the Zener current Iz to flow. The Zener current Iz flows from the positive-side current path 3 through the leakage resistor Rg to ground G, and then from the second voltage regulator diode Z2 through the second resistance element R2 to the negative-side current path 4.

[0048] At the moment the sensitivity current Is is reached, a Zener current Iz, which is larger than the steady-state current I1, flows only through the second resistance element R2, causing the voltage across the second resistance element R1 to suddenly increase, the potential of the negative current path 4 to become approximately -600 V, and the potential of the positive current path 3 to become 0 V, which is approximately equal to the potential of ground G. The potential of the midpoint N becomes a potential lower than the potential of ground G by the Zener voltage Vz, which is -20 V in this case.

[0049] At this time, the voltage across the sensitivity setting resistance element Re is fixed to the Zener voltage Vz, and the sensitivity current Is does not increase beyond the set value.

[0050] The detector detects a sudden change in the potential of the positive electric circuit 3 at the moment when the leakage current reaches the sensitivity current Is. When the potential of the positive electric circuit 3 reaches approximately 0 V (slightly higher than 0 V), the potential of Node A also reaches approximately 0 V (slightly lower than 0 V), and the diodes connected between Node A and ground G are in the forward direction. As a result, detection current I5 flows from the positive electric circuit 3 through leakage resistance Rg to ground G, and then through photodiode L2, the input photodiode of the SSR, rectifier diode D2, and resistive elements R4 and R5 to the negative electric circuit 4. The light emitted by photodiode L2 indicates a leakage current in the positive electric circuit 3, and the output of the SSR triggers the activation of an alarm device, earth leakage circuit breaker, or other device installed downstream. The potential at connection point B is approximately -300V, and the diode between connection point B and ground G is in the reverse direction, so no current flows.

[0051] (4) Other Although the embodiments of the present invention have been described with reference to exemplary configurations, the embodiments of the present invention are not limited to these exemplary configurations, and various modifications are also within the scope of the present invention as long as they comply with the principles of the present invention. The earth leakage detector of the present invention detects the sensitive current by utilizing the potential of the ground G, which changes significantly and discontinuously when the earth leakage current reaches the sensitive current. Therefore, it is possible to realize stable detection of the sensitive current that is less susceptible to the influence of noise. Furthermore, since the voltage across the sensitivity setting resistor element through which the sensitivity current flows is fixed to the Zener voltage, the value of the sensitivity current does not change even if the DC power supply voltage changes. Therefore, the leakage detection device of the present invention can be applied as is to other DC power supplies with different voltages. [Explanation of symbols]

[0052] 1 DC power supply positive output terminal 2 DC power supply negative output terminal 3 Positive side circuit 4 Negative circuit 5, 6 Detector output terminals 10 Main circuit 20 Detector Q1 First semiconductor element Q2 Second semiconductor element R1 First resistance element (for midpoint setting) R2 2nd resistance element (for midpoint setting) R3, R4, R5 Resistive elements (for detection) Re Resistance element (for sensitivity setting) SW changeover switch Z1 First constant voltage diode Z2 Second constant voltage diode D1, D2 rectifier diodes L1, L2 light-emitting diodes N midpoint E emitter G Ground SSR Solid State Relay

Claims

1. A leakage current detector for detecting leakage current between a positive circuit (3) or a negative circuit (4) of a DC power supply and a ground (G), a first resistance element (R1) and a second resistance element (R2) having the same resistance value, one end of which is connected to the positive side electric circuit (3) and one end of which is connected to the negative side electric circuit (4), and the other end of which is connected to each other at a midpoint (N); a first semiconductor element (Q1) through which a leakage current (I4) flows when a leakage current occurs between the negative electric path (4) and the ground (G), and which has one end of a current path connected to the positive electric path (3) and a control end connected to the midpoint (N); a second semiconductor element (Q2) through which a leakage current (I4) flows when a leakage current occurs between the positive electric path (4) and the ground (G), and which has one end of a current path connected to the negative electric path (4) and a control end connected to the midpoint (N); a sensitivity setting resistive element (Re) connected between the other end (E) of each current path of the first semiconductor element (Q1) and the second semiconductor element (Q2) and the ground (G); a first constant voltage diode (Z1) and a second constant voltage diode (Z2) connected in series in opposite directions between the control terminal of each of the first semiconductor element (Q1) and the second semiconductor element (Q2) and the ground (G), and having a Zener voltage (Vz) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and a sensitivity current (Is); and a detection unit (20) that detects that the leakage current (I4) has reached a sensitivity current (Is) based on a change in the potential of the positive side electric circuit (3) or the negative side electric circuit (4).

2. When a leakage current occurs between the negative electric circuit (4) and the ground (G), the potential of the negative electric circuit (4) is When the leakage current (I4) is less than the sensitivity current (Is), the potential is higher than the potential of the negative side electric circuit (4) when there is no leakage current by a voltage (Ve) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and the leakage current (I4), and 2. The earth leakage detector according to claim 1, wherein when the earth leakage current (I4) reaches the sensitivity current (Is), the potential becomes substantially equal to the potential of the ground (G).

3. The potential of the positive electric circuit (3) when a leakage current occurs between the positive electric circuit (3) and the ground (G) is When the leakage current (I4) is less than the sensitivity current (Is), the potential is lower than the potential of the positive side electric circuit (3) when there is no leakage current by a voltage (Ve) equal to the product of the resistance value of the sensitivity setting resistance element (Re) and the leakage current (I4), and 2. The earth leakage detector according to claim 1, wherein when the earth leakage current (I4) reaches the sensitivity current (Is), the potential becomes substantially equal to the potential of the ground (G).

4. The detection unit (20) has three resistance elements (R3, R4, R5) having the same resistance value and sequentially connected between the positive electric circuit (3) and the negative electric circuit (4), 4. The earth leakage detector according to claim 2 or 3, characterized in that the detection current (I5) flows depending on the level relationship between the potential of the two connection points (A, B) of the three resistance elements (R3, R4, R5) and the potential of the ground (G).

5. The leakage current detector according to claim 1, characterized in that the first semiconductor element (Q1) and the second semiconductor element (Q2) form an emitter follower circuit or a source follower circuit with the other end (E) of each current path as the emitter or source.

6. 2. The earth leakage detector according to claim 1, wherein the sensitivity setting resistance element (Re) is selected from a plurality of resistance elements having different resistance values ​​by switching a mechanical switch.

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