JP2009270999A - Earth fault detecting circuit and earth fault detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an earth fault detecting circuit detecting not only the occurrence of earth fault and its place but also whether DC voltage is applied on a load or not simultaneously. <P>SOLUTION: This earth fault detecting circuit 20 for detecting earth fault in a positive side feed line and a negative side feed line which connect a DC voltage source with a load, is provided with: a constant current element 23 and a photocoupler 22 connected mutually in series between the positive side feed line 32 and a grounding point 24; and a constant current element 27 and a photocoupler 26 connected mutually in series between the negative side feed line 34 and the grounding point 24. The constant current elements 23 and 27 are the elements maintaining the passing current at a constant value, and the photocouplers 22 and 26 are the elements detecting flow of the current having the constant value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ground fault detection circuit, and more particularly to a circuit for detecting a ground fault in a voltage supply line from a DC voltage source.

  Conventionally, as a technique for detecting a ground fault in a voltage supply line from a DC voltage source, a method for detecting a current that flows only during a ground fault has been proposed (see, for example, Patent Document 1).

  FIG. 6 is a ground fault detection circuit disclosed as the prior art of Patent Document 1. In FIG. This ground fault detection circuit includes a DC power source 1, a load 2, resistors 3 and 4, meter relays 6 and 7, and rectifiers 8 and 9 connected as shown in FIG.

In this ground fault detection circuit, if the positive side of the DC power source 1 causes a grounding fault, a current flows through the meter relay 6, so that a positive side grounding fault is indicated by the fluctuation of the pointer, while the negative side of the DC power source 1 is negative. When a grounding accident occurs on the side, a current flows through the meter relay 7, so that a negative grounding accident is indicated by a swing of the pointer. Thereby, not only the occurrence of the ground fault but also the location of the ground fault (positive side / negative side) can be known.
Japanese Utility Model Publication No. 39-20945

  However, although the above-mentioned conventional ground fault detection circuit can detect the occurrence of a ground fault, whether or not the circuit to be detected is in an operating state in the first place, that is, a DC voltage is supplied between the positive side terminal and the negative side terminal. There is a problem of not knowing whether or not it has been done. That is, in the conventional ground fault detection circuit shown in FIG. 6, the meter relays 6 and 7 do not operate in the case of a power supply abnormality in which the DC voltage is not supplied to the load 2, so the DC voltage is supplied to the load 2. However, it is indistinguishable from a normal case where no ground fault has occurred. In other words, in the conventional ground fault detection circuit, a power supply abnormality case where a DC voltage is not supplied to the load is distinguished from a normal case where the DC voltage is supplied to the load but no ground fault occurs. There is a problem that can not be.

  Further, in the above-described conventional ground fault detection circuit, whether or not the meter relays 6 and 7 operate normally cannot be known unless a ground fault current is passed, that is, when it is desired to detect a ground fault. There is also a problem that it is not known whether or not will operate normally.

  Therefore, the present invention has been made in view of the above problems, and it is possible to simultaneously detect not only the occurrence of a ground fault and the location of the ground fault, but also whether or not a DC voltage is supplied to the load. An object of the present invention is to provide a ground fault detection circuit and a method thereof.

  In order to achieve the above object, a ground fault detection circuit according to the present invention is a ground fault detection circuit for detecting a ground fault in a positive supply line and a negative supply line connecting a DC voltage source and a load, A first constant current element and a first current detection element connected in series between the positive supply line and the ground point, and a second constant current element connected in series between the negative supply line and the ground point. A current element and a second current detection element, wherein the first and second constant current elements are elements that maintain a constant current passing therethrough, and the first and second current detection elements are the constant value. It is an element which detects that the electric current of this is flowing.

  As a result, when a DC voltage is being supplied to the load, when a positive fault occurs in the positive supply line in that state, a negative fault occurs in the negative supply line. Because the combination of whether or not current is detected by the first and second constant current elements (ON / OFF) is different for the four cases at the time of power failure and when the power supply is abnormal when no DC voltage is supplied to the load. In addition to the occurrence of the ground fault and the location of the ground fault, it is possible to simultaneously detect whether or not a DC voltage is supplied to the load. Furthermore, since the current always flows through the ground fault detection circuit during the steady state, the ground fault detection circuit operates normally even during the steady state unlike the conventional ground fault detection circuit that flows the current to the meter relay only during the ground fault. It can be confirmed that it works.

  Here, the ground fault detection circuit is further connected in series with the first constant current element and the first current detection element between the positive supply line and a ground point, and the positive side A first diode that allows a current to flow in a forward direction from the supply line toward the ground point; and between the negative supply line and the ground point, and in series with the second constant current element and the second current detection element. It is preferable to include a second diode that is connected and flows a current in a forward direction from the ground point toward the negative supply line.

  Thereby, an abnormal voltage such as a high voltage is externally applied to the DC voltage source and the load, and the DC voltage source and the load can be protected from being broken.

  The first and second current detection elements are preferably photocouplers. As a result, the occurrence of the ground fault can be transmitted to a (floating) circuit independent of the DC voltage source and the potential of the load, and a safe alarm circuit can be constructed.

  The ground fault detection circuit may further include an adjustment circuit that adjusts a current value for turning on a light receiving transistor included in the photocoupler. Thereby, it is possible to arbitrarily set a threshold value at which the photocoupler is turned on, and a ground fault detection circuit capable of detecting a ground fault more reliably is realized.

  The present invention can be realized not only as a ground fault detection circuit, but also by determining a combination of whether or not a constant value of current flows through the first and second current detection elements in the ground fault detection circuit. It can also be realized as a ground fault detection method for detecting.

  According to the present invention, when a DC voltage is supplied to the load, in a normal state, a ground fault occurs in the positive supply line in that state, and in a negative side, a ground fault occurs in the negative supply line in that state. Four cases are distinguished when there is a ground fault and when there is a power failure when DC voltage is not supplied to the load. Whether or not a DC fault is supplied to the load as well as the occurrence and location of the ground fault. Is detected at the same time.

  This eliminates the need for a special circuit for monitoring whether the power supply is steady or when the power supply is abnormal.

  Hereinafter, embodiments of a ground fault detection circuit according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram of a ground fault detection circuit 20 according to an embodiment of the present invention. In this figure, a DC voltage source 30 and a load 40 are also shown together with the ground fault detection circuit 20.

  The DC voltage source 30 is a power source that generates a DC voltage V, for example, DC 48 V, DC 280 V boosted by a DC / DC converter, or the like between the positive terminal 31 and the negative terminal 33.

  The load 40 is a load connected to the positive side terminal 31 and the negative side terminal 33 of the DC voltage source 30 via the positive side supply line 32 and the negative side supply line 34 which are power supply lines, respectively. Motors and electrical equipment.

  The ground fault detection circuit 20 is a circuit that detects a ground fault in the positive supply line 32 and the negative supply line 34, and includes a diode 21 and a photo diode connected in series between the positive supply line 32 and the grounding point 24. A coupler 22 and a constant current element 23, and a diode 25, a photocoupler 26, and a constant current element 27 connected in series between a negative supply line 34 and a ground point 24 are provided.

  The diode 21 is a rectifier diode having an anode connected to the positive supply line 32 (connection point 32 a) and flowing a forward current from the positive supply line 32 toward the ground point 24. It protects the abnormal voltage from being applied.

  The photocoupler 22 includes a light emitting diode 22 a and a light receiving transistor 22 b, and the anode of the light emitting diode 22 a is connected to the cathode of the diode 21. The light receiving transistor 22b is a transistor that is turned on when a current defined by the constant current element 23 or more flows through the photocoupler 22 (that is, the light emitting diode 22a), and is connected from the positive supply line 32. The circuit is connected to a circuit (not shown) for notifying whether or not current is flowing toward the point 24.

  The constant current element 23 is connected between the photocoupler 22 and the ground point 24, and maintains a current passing therethrough at a constant value (for example, 0.5 mA) when a voltage higher than a certain voltage is applied. For example, a constant current diode or the like.

  The diode 25 is a rectifier diode having a cathode connected to the negative supply line 34 (connection point 34 a) and flowing a current in the forward direction from the ground point 24 toward the negative supply line 34. It protects the abnormal voltage from being applied.

  The photocoupler 26 includes a light emitting diode 26 a and a light receiving transistor 26 b, and the cathode of the light emitting diode 26 a is connected to the anode of the diode 25. The light receiving transistor 26b is a transistor that is turned on when a current defined by the constant current element 27 or a current higher than the constant current element 27 flows through the photocoupler 26 (that is, the light emitting diode 26a). The circuit is connected to a circuit (not shown) for notifying whether or not a current is flowing toward the line 34.

  The constant current element 27 is an element that is connected between the photocoupler 26 and the ground point 24 and maintains a current passing therethrough at a constant value (for example, 0.5 mA), such as a constant current diode. . The constant current elements 23 and 27 have a function of flowing a constant current regardless of the voltage of the current DC voltage source 30 and the size of the load 40.

  Next, the operation of the ground fault detection circuit 20 in the present embodiment configured as described above will be described.

(1) Steady state First, the operation when a ground fault has not occurred (steady state) will be described with reference to FIG.

  When the DC voltage V generated by the DC voltage source 30 is applied to the load 40 and no ground fault has occurred in any of the positive supply line 32 and the negative supply line 34, the ground fault detection circuit 20 A constant current (0.5 mA in this embodiment) flows in the direction indicated by the arrow in FIG. 1, and as a result, the photocouplers 22 and 26 are turned on.

  That is, in this case, the DC voltage V is applied to both ends (the connection point 32a and the connection point 34a) of the ground fault detection circuit 20, and in the meantime, the constant current element 23 and the constant current element 27 are constant. A current (0.5 mA in this embodiment) flows. The DC voltage source 30 itself (that is, a single unit) is independent of the ground point 24 in terms of potential (floating), and in this case, the current flowing through the ground fault detection circuit 20 is grounded. (Earth) does not flow.

(2) When the positive supply line 32 has a ground fault Next, the case where a ground fault has occurred in the positive supply line 32 will be described with reference to FIG.

  When the DC voltage V generated by the DC voltage source 30 is applied to the load 40 and a ground fault occurs in the positive supply line 32, the ground fault detection circuit 20 has a direction indicated by an arrow in FIG. In addition, a constant current (0.5 mA in the present embodiment) flows, and as a result, the photocoupler 26 is turned on.

  That is, in this case, since the potential of the connection point 32a of the ground fault detection circuit 20 becomes the ground potential due to the ground fault, the connection point 32a and the ground point 24 become the same potential (ground potential), and no current flows during this time. That is, the photocoupler 22 is turned off. On the other hand, since the positive side supply line 32 is grounded, the positive side terminal 31 and the grounding point 24 are short-circuited, so that the DC voltage V is applied between the grounding point 24 and the connection point 34a. Thus, a current flows from the ground point 24 toward the connection point 34a, and the photocoupler 26 is turned on.

  Therefore, in this case, the photocoupler 22 is turned off and the photocoupler 26 is turned on.

(3) When the negative supply line 34 has a ground fault Next, the case where a ground fault occurs in the negative supply line 34 will be described with reference to FIG.

  When the DC voltage V generated by the DC voltage source 30 is applied to the load 40 and a ground fault occurs in the negative supply line 34, the ground fault detection circuit 20 has a direction indicated by an arrow in FIG. In addition, a constant current (0.5 mA in the present embodiment) flows, and as a result, the photocoupler 22 is turned on.

  That is, in this case, since the negative side supply line 34 is grounded, the negative side terminal 33 and the grounding point 24 are short-circuited. Therefore, a DC voltage is connected between the positive side supply line 32 and the grounding point 24. V is applied, current flows from the positive supply line 32 toward the ground point 24, and the photocoupler 22 is turned on. On the other hand, since the potential of the connection point 34a of the ground fault detection circuit 20 becomes the ground potential due to the ground fault, the ground point 24 and the connection point 34a have the same potential (ground potential), and no current flows during this time. That is, the photocoupler 26 is turned off.

  Therefore, in this case, the photocoupler 22 is turned on and the photocoupler 26 is turned off.

(4) When voltage is not supplied (when power is abnormal)
Next, a case where the DC voltage V is not applied between the positive supply line 32 and the negative supply line 34 will be described with reference to FIG.

  As shown in FIG. 4, when the DC voltage source 30 is not connected to the positive supply line 32 and the negative supply line 34, or the DC voltage source 30 is connected to the positive supply line 32 and the negative supply line 34. If the output is 0 V for some reason, no voltage is applied between the connection point 32a and the connection point 34a, and therefore a current is detected in the ground fault detection circuit 20. Not flowing.

  Therefore, in this case, the photocoupler 22 and the photocoupler 26 are turned off.

  As described above, according to the ground fault detection circuit 20 of the present embodiment, the combination of the ON / OFF states of the photocoupler 22 and the photocoupler 26 is different in the above four cases. From the 26 ON / OFF combinations, it can be determined which of the above four cases has occurred. That is, it is possible to detect not only the occurrence of a ground fault and the location of the ground fault (positive side / negative side) but also whether or not a DC voltage is supplied to the load. Furthermore, since the current always flows through the ground fault detection circuit in the steady state, unlike the conventional ground fault detection circuit in which the current is supplied to the meter relay only during the ground fault, the ground fault detection circuit operates normally even in the steady state. It can be confirmed that it works.

  The ground fault detection circuit according to the present invention has been described based on the embodiment, but the present invention is not limited to this embodiment.

  For example, in the present embodiment, the photocoupler 22 and the photocoupler 26 are turned on when a constant current determined by the constant current element 23 and the constant current element 27 flows. However, as shown in FIG. An adjustment circuit for adjusting the current value to be turned on may be provided.

  FIG. 5 is a circuit diagram of an adjustment circuit that adjusts the current value at which the photocoupler is turned on. Here, a circuit for adjusting the current value of the photocoupler 22 is shown. The collector of the light receiving transistor 22b constituting the photocoupler 22 is connected to a + 5V power source, and the base of the transistor 36 and the variable resistor 35 are connected to the emitter thereof. The other terminal of the variable resistor 35 is grounded.

  According to such a circuit, by adjusting the resistance value of the variable resistor 35, a part of the current flowing through the light receiving transistor 22b can be supplied to the ground without flowing to the base of the transistor 36. The current value that should flow through the light emitting diode 22a to turn on, that is, the threshold value can be adjusted. Therefore, when the transistor 36 is regarded as an output transistor of the photocoupler, the threshold value for turning on the photocoupler can be adjusted by the variable resistor 35.

  By applying such an adjustment circuit to the ground fault detection circuit 20 shown in FIG. 1, for example, when the constant current element 23 is an element that flows a constant current of 0.5 mA, the resistance value of the variable resistor 35 is changed. By adjusting, the photocoupler 22 can be set to be turned on when a current of 0.4 mA (or 0.3 mA) or more flows through the photocoupler 22, and a constant current determined by the constant current element 23 is It is possible to reliably detect whether or not it is flowing. 5 shows an example in which an adjustment circuit is added to the photocoupler 22 in FIG. 1, it goes without saying that a similar adjustment circuit can be added to the photocoupler 26 in FIG.

  Further, in the present embodiment, the diode 21 and the diode 25 are connected to the ground fault detection circuit 20, but these protect the DC voltage source 30 and the load 40 from disturbances such as high voltage. It is not necessarily an essential component for the purpose of detecting.

  In the ground fault detection circuit 20 shown in FIG. 1, the diode, the photocoupler, and the constant current element are connected in series in this order from the high potential point to the low potential point. It is not limited to the connection order, and these may be switched and connected.

  The present invention is a ground fault detection circuit for detecting a ground fault in a positive supply line and a negative supply line connecting a DC voltage source and a load, in particular, not only the occurrence of a ground fault and the location of a ground fault, but also a DC fault. This is useful as a ground fault detection circuit that can simultaneously detect whether or not voltage is supplied to a load.

Circuit diagram of a ground fault detection circuit in an embodiment of the present invention Diagram showing current flow when a ground fault occurs on the positive supply line Diagram showing the flow of current when a ground fault occurs on the negative supply line Explanatory drawing when no DC voltage is applied between the positive supply line and the negative supply line Circuit diagram of the adjustment circuit that adjusts the current value at which the photocoupler turns on Circuit diagram of conventional ground fault detection circuit

Explanation of symbols

20 Ground fault detection circuit 21, 25 Diode 22, 26 Photocoupler 22a, 26a Light emitting diode 22b, 26b Light receiving transistor 23, 27 Constant current element 24 Ground point 30 DC voltage source 31 Positive side terminal 32 Positive side supply line 32a Connection point 33 Negative side terminal 34 Negative side supply line 34a Connection point 35 Variable resistance 36 Transistor 40 Load

Claims (5)

A ground fault detection circuit for detecting a ground fault in a positive supply line and a negative supply line connecting a DC voltage source and a load,
A first constant current element and a first current detection element connected in series between the positive supply line and a ground point;
A second constant current element and a second current detection element connected in series between the negative supply line and a ground point;
The first and second constant current elements are elements that maintain a constant current passing therethrough,
The ground fault detection circuit, wherein the first and second current detection elements are elements that detect that the constant current flows. The ground fault detection circuit further includes:
Between the positive supply line and the grounding point, connected in series with the first constant current element and the first current detection element, and forward from the positive supply line toward the grounding point A first diode for passing current;
Between the negative supply line and the ground point, connected in series with the second constant current element and the second current detection element, and forward from the ground point toward the negative supply line The ground fault detection circuit according to claim 1, further comprising: a second diode through which a current flows. The ground fault detection circuit according to claim 1, wherein the first and second current detection elements are photocouplers. The ground fault detection circuit further includes:
The ground fault detection circuit according to claim 3, further comprising an adjustment circuit that adjusts a current value for turning on a light receiving transistor included in the photocoupler. A ground fault detection method for detecting a ground fault in a positive supply line and a negative supply line connecting a DC voltage source and a load,
The ground fault detection method characterized by detecting a ground fault by determining whether the said constant value electric current is flowing into the 1st and 2nd current detection element in the ground fault detection circuit of Claim 1.

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