JP6472620B2 - DC ground fault detector - Google Patents

Description

  The present invention relates to a DC ground fault detector used to monitor a ground fault occurring in a DC circuit in order to protect a DC circuit having a power source such as a solar battery panel in a photovoltaic power generation system.

  Conventionally, as a DC circuit having a power source, for example, a photovoltaic power generation system has been spreading not only for industrial use but also for general household use. Since this solar power generation system is wide in area due to its circuit configuration, ground faults occur not at local but at every potential, and fires caused by ground faults occur. It is important to prevent this from happening. In addition, since solar power generation systems are usually operated in conjunction with the power grid, ground faults that occur in the solar power generation system also affect the power grid, so monitoring for the occurrence of ground faults is monitored. It is very important to do.

  One of means for detecting a ground fault occurring in such a photovoltaic power generation system is a DC potential detection method in which a neutral point of a circuit is grounded to detect potential imbalance. As shown in FIG. 5, a DC ground fault detector 1 that employs this DC potential detection system has an anode side connected to the anode (P) side of a DC circuit 3 in which a plurality of solar cell panels 2 are connected in series. A resistor 4, a cathode side resistor 5 connected to the cathode (N) side of the DC circuit 3, and an intermediate connection point of a series circuit composed of the anode side resistor 4 and the cathode side resistor 5 and the ground. It comprises a detection resistor 6.

  In the DC ground fault detector 1 having the above configuration, when a ground fault occurs on the anode side of the DC circuit 3, as shown in FIG. 6, the solar cell panel 2-ground fault resistor 7-ground-detection resistor 6 is provided. -Cathode side resistance 5-A ground fault electric current will flow into the closed loop circuit (refer broken line in the figure) which consists of the solar cell panel 2. FIG. By detecting the ground fault current flowing in the closed loop circuit with the detection resistor 6, the ground fault occurring on the anode side of the DC circuit 3 is monitored.

  When a ground fault occurs on the cathode side of the DC circuit 3, as shown in FIG. 7, from the solar cell panel 2-anode side resistance 4-detection resistance 6-ground-ground fault resistance 8-solar cell panel 2 A ground fault current flows through the closed loop circuit (see the broken line in the figure). By detecting the ground fault current flowing in the closed loop circuit with the detection resistor 6, a ground fault accident occurring on the cathode side of the DC circuit 3 is monitored.

JP 2013-130536 A

  By the way, the above-described DC ground fault detector 1 has a structure in which the connection point of the anode-side resistor 4 and the cathode-side resistor 5, that is, the neutral point is grounded via the detection resistor 6. Therefore, as shown in FIG. 8, when a ground fault occurs at an intermediate point between the plurality of solar battery panels 2, a ground potential of the detection resistor 6 in the DC ground fault detector 1 and an intermediate point between the solar battery panels 2 are detected. The ground potential of the ground fault resistor 9 becomes the same potential. As described above, when the ground potential of the DC ground fault detector 1 and the ground potential at the intermediate point of the solar battery panel 2 become the same potential, the ground fault current does not flow. It becomes impossible to detect accidents.

  In order to solve this problem, there has been proposed a DC ground fault detector capable of detecting a ground fault even when a ground fault occurs at the midpoint of the solar cell panel. (For example, refer to Patent Document 1). The DC ground fault detector disclosed in Patent Document 1 employs a DC potential detection method called a ground point sequential movement type.

  The DC ground fault detector of Patent Document 1 connects a series circuit composed of two resistors and one constant voltage element (zener diode) between the anode side and the cathode side of a DC circuit having a solar cell panel. In addition, a configuration is provided in which a switch for switching a connection point between one resistor and the constant voltage element and a connection point between the constant voltage element and the other resistor is provided. In this DC ground fault detector, a ground fault is detected from the intermediate potential at one of the connection points by periodically switching the intermediate potential at the two connection points with a switch.

  However, in the DC ground fault detector of Patent Document 1, there is a case where a ground fault occurs at the midpoint of the solar battery panel and a case where a ground fault occurs on the anode side or the cathode side of the other DC circuit. The ground fault detection sensitivity varies. For example, when a ground fault occurs at the midpoint of the solar panel, the electromotive force by the solar panel is halved compared to when a ground fault occurs on the anode side or the cathode side of the DC circuit, The ground fault detection sensitivity also becomes dull. This decrease in the ground fault detection sensitivity becomes more prominent due to the provision of the constant voltage element. Thus, when the ground fault detection sensitivity decreases, it becomes difficult to accurately detect a ground fault accident.

  Therefore, the present invention has been proposed in view of the above-described problems, and the object of the present invention is to prevent a ground fault from occurring at a certain sensitivity regardless of the location of the DC fault. An object of the present invention is to provide a DC ground fault detector that can be detected by the following.

As technical means for achieving the above-described object, the present invention provides an anode side resistor connected to the anode side of a DC circuit having a power source, a cathode side resistor connected to the cathode side of the DC circuit, and an anode side. A DC ground fault detector comprising a switch that is periodically switched and connected to a resistor or a cathode side resistor, and a detection resistor connected between the switch and the ground, the switch being switched and connected to an anode side resistor If the absolute value of the current that flows through the detection resistor and the absolute value of the current that flows through the detection resistor when the switch is connected to the cathode side resistance are combined , a ground fault occurs at any point in the DC circuit. Is also provided with a detection unit that always detects a constant sum as a ground fault current.

  In the detection unit of the DC ground fault detector according to the present invention, the absolute value of the current flowing through the detection resistor when the switch is switched to the anode-side resistor and the detection resistor when the switch is switched to the cathode-side resistor Since the absolute value of the current is summed and the sum value is detected as a ground fault current, the sum value as the ground fault current is always constant no matter where a ground fault occurs in any part of the DC circuit. Therefore, it becomes possible to detect a ground fault accident with a certain sensitivity.

  The detection unit according to the present invention is configured so that the absolute value of the current flowing through the detection resistor when the switch is switched to the anode side resistor and the absolute value of the current flowing through the detection resistor when the switch is switched to the cathode side resistance are large and small. It is desirable to be configured to compare the two. In this way, the magnitude of the absolute value of the current flowing through the detection resistor when the switch is connected to the anode-side resistor and the absolute value of the current flowing through the detection resistor when the switch is connected to the cathode-side resistor are compared. For example, it is possible to identify the location where the ground fault occurred.

  According to the present invention, the absolute value of the current flowing through the detection resistor when the switch is switched and connected to the anode-side resistance by the detection unit, and the absolute value of the current flowing through the detection resistor when the switch is switched and connected to the cathode-side resistance. Because the sum value is detected as a ground fault current, even if a ground fault occurs in any part of the DC circuit, the sum value as a ground fault current is always constant. It becomes possible to detect a ground fault accident with a certain sensitivity. As a result, since a ground fault accident occurring in the DC circuit can be detected accurately, a highly reliable DC ground fault detector can be provided.

In embodiment of this invention, it is a circuit diagram which shows the structure which installed the direct-current ground fault detector in the direct current circuit which has a solar cell panel. When a ground fault occurs on the anode side of the DC circuit of FIG. 1, (A) is a circuit diagram showing a state where the switch is connected to the anode side, and (B) is a state where the switch is connected to the cathode side. FIG. When a ground fault occurs on the cathode side of the DC circuit of FIG. 1, (A) is a circuit diagram showing a state where the switch is connected to the anode side, and (B) is a state where the switch is connected to the cathode side. FIG. When a ground fault occurs at the midpoint of the DC circuit of FIG. 1, (A) is a circuit diagram showing a state where the switch is connected to the anode side, and (B) is a state where the switch is connected to the cathode side. FIG. It is a circuit diagram which shows the structure which installed the conventional DC ground fault detector in the DC circuit which has a solar cell panel. FIG. 6 is a circuit diagram showing a case where a ground fault has occurred on the anode side of the DC circuit of FIG. 5. FIG. 6 is a circuit diagram illustrating a case where a ground fault occurs on the cathode side of the DC circuit of FIG. 5. FIG. 6 is a circuit diagram illustrating a case where a ground fault occurs at an intermediate point of the DC circuit of FIG. 5.

  An embodiment of a DC ground fault detector according to the present invention will be described below in detail with reference to the drawings. The following embodiment is an application example to a photovoltaic power generation system, and illustrates a case where the embodiment is applied to a DC circuit having a solar battery panel. The present invention can be applied to a DC circuit having another power source such as a battery of an electric vehicle in addition to the solar battery panel.

  FIG. 1 shows a schematic circuit configuration in which the DC ground fault detector 11 of the embodiment is installed in a DC circuit 13 having a plurality (four in the figure) of solar cell panels 12 connected in series. The DC ground fault detector 11 shown in the figure includes an anode-side resistor 14 (limiting resistor) connected to the anode (P) side of the DC circuit 13 and a cathode connected to the cathode (N) side of the DC circuit 13. Side resistor 15 (limit resistor), switch 21 periodically switched to anode side resistor 14 or cathode side resistor 15, detection resistor 16 connected between switch 21 and ground, and ground fault The main part is composed of a detection unit 22 that detects a ground fault based on a voltage generated at both ends of the detection resistor 16 due to a ground fault current flowing through the detection resistor 16 at the time of occurrence.

  The anode-side resistor 14 and the cathode-side resistor 15 of the DC ground fault detector 11 exhibit a function of suppressing an overcurrent from flowing through the DC circuit 13 when a ground fault occurs. Further, since the switch 21 is periodically switched and connected to the anode side resistor 14 or the cathode side resistor 15 in order to monitor the occurrence of the ground fault, the semiconductor switch is effective in consideration of durability. It is. The switch 21 may be a mechanical switch. Furthermore, the detection unit 22 includes a lamp or a buzzer that is activated by detection of a ground fault, although not shown. When a ground fault is detected, the detection unit 22 notifies the worker by lighting a lamp or sounding a buzzer.

  The ground fault detection operation of the DC ground fault detector 11 having the above configuration will be described in detail below. In the following, when a ground fault occurs on the anode side of the DC circuit 13 (see FIGS. 2A and 2B) and when a ground fault occurs on the cathode side of the DC circuit 13 [FIG. A) and (B)] and a case where a ground fault occurs at an intermediate point of the solar battery panel 12 of the DC circuit 13 [see FIGS. 4A and 4B]. In the description of FIGS. 2A and 2B and FIGS. 3A and 3B, a case where a ground fault occurs at a location outside the series circuit of the solar cell panel 12 is exemplified. In addition, the “cathode side” means that the position on the anode side and the cathode side having the middle point as a boundary in the series circuit of the solar cell panel 12 is also included.

  First, when a ground fault occurs on the anode side of the DC circuit 13, when the switch 21 of the DC ground fault detector 11 is switched and connected to the anode side resistor 14 as shown in FIG. No ground fault current flows in the circuit 13. On the other hand, when the switch 21 of the DC ground fault detector 11 is switched and connected to the cathode-side resistor 15 as shown in FIG. A ground fault current flows through a closed loop circuit (see the broken line in the figure) including the battery panel 12-the ground fault resistor 17-the ground-the detection resistor 16-the cathode side resistor 15-the solar cell panel 12. In this way, when the switch 21 is switched and connected to the cathode-side resistor 15, the ground fault current flows through the detection resistor 16, so that the voltage appearing at both ends of the detection resistor 16 is detected by the detection unit 22. The occurrence of a ground fault can be recognized.

  Next, when a ground fault occurs on the cathode side of the DC circuit 13, as shown in FIG. 3A, when the switch 21 of the DC ground fault detector 11 is switched and connected to the anode side resistor 14, A closed loop circuit composed of a solar cell panel 12-an anode side resistor 14-a detection resistor 16-a ground-ground fault resistor 18-a solar cell panel 12 by the electromotive force of all four solar cell panels 12 in the figure (refer to the broken line in the figure). A ground fault current flows in As described above, when the switch 21 is connected to the anode-side resistor 14, the ground fault current flows through the detection resistor 16, and the voltage appearing at both ends of the detection resistor 16 is detected by the detection unit 22. The occurrence of a ground fault can be recognized. As shown in FIG. 5B, when the switch 21 of the DC ground fault detector 11 is switched and connected to the cathode side resistor 15, no ground fault current flows in the DC circuit 13.

  Finally, when a ground fault occurs at the midpoint of the solar battery panel 12 of the DC circuit 13, the switch 21 of the DC ground fault detector 11 is switched to the anode-side resistor 14 as shown in FIG. When closed, a closed loop circuit comprising a solar cell panel 12-an anode side resistor 14-a detection resistor 16-a ground-ground fault resistor 19-a solar cell panel 12 by the electromotive force of the two upper solar cell panels 12 in the figure ( A ground fault current flows in the broken line). Further, as shown in FIG. 5B, when the switch 21 of the DC ground fault detector 11 is switched to the cathode-side resistor 15, the electromotive force of the two lower solar cell panels 12 in the figure A ground fault current flows in a closed loop circuit (see the broken line in the figure) including the solar cell panel 12-the ground fault resistor 19-the ground-the detection resistor 16-the cathode side resistor 15-the solar cell panel 12. As described above, when the switch 21 is switched and connected to the anode-side resistor 14 and when the switch 21 is switched and connected to the cathode-side resistor 15, the ground fault current flows through the detection resistor 16, so that the detection resistor 16 The occurrence of a ground fault can be recognized by detecting the voltage appearing at both ends by the detection unit 22.

The ground fault detection operation of the DC ground fault detector 11 described above is summarized for each location where a ground fault occurs, as shown in the table below. Here, the current flowing through the detection resistor 16 when the ground fault occurs due to the electromotive force of all four solar battery panels 12 is, for example, 10 mA. The switching position of the switch 21 is the P side when the switch 21 is switched and connected to the anode side resistor 14, and the N side when the switch 21 is switched and connected to the cathode side resistor 15.

  As is apparent from this table, when a ground fault occurs on the anode side of the DC circuit 13, the current flowing through the detection resistor 16 when the switch 21 is located on the P side is 0 mA. Since the current flowing through the detection resistor 16 is 10 mA when positioned on the N side, a ground fault occurring on the anode side of the DC circuit 13 can be detected.

  When a ground fault occurs on the cathode side of the DC circuit 13, the current flowing through the detection resistor 16 when the switch 21 is located on the N side is 0 mA, but the detection resistor 16 is present when the switch 21 is located on the P side. Since the current flowing through is 10 mA, a ground fault that has occurred on the cathode side of the DC circuit 13 can be detected.

  Furthermore, when a ground fault occurs at the midpoint of the solar battery panel 12 of the DC circuit 13, when the switch 21 is located on the P side, the current flowing through the detection resistor 16 is 5 mA, and when the switch 21 is located on the N side. Since the current flowing through the detection resistor 16 is also 5 mA, it is possible to detect a ground fault occurring at the midpoint of the solar cell panel 12 of the DC circuit 13.

  Here, if the current flowing through the detection resistor 16 is the ground fault current when the switch 21 is at either the P side or the N side, the ground fault detection sensitivity varies depending on the location where the ground fault occurs. become. That is, when a ground fault occurs on the anode side or the cathode side of the DC circuit 13, the ground fault current is 10 mA, but when a ground fault occurs at the midpoint of the solar battery panel 12 of the DC circuit 13. In this case, the ground fault current is 5 mA. Thus, when a ground fault occurs at the midpoint of the solar cell panel 12, compared with a case where a ground fault occurs on the anode side or the cathode side of the DC circuit 13, the electromotive force generated by the solar cell panel 12 is reduced. Since the ground fault current based is halved, the ground fault detection sensitivity becomes dull.

  Therefore, the detection unit 22 in the DC ground fault detector 11 of this embodiment includes the absolute value of the current flowing through the detection resistor 16 when the switch 21 is located on the P side and the detection resistor 16 when the switch 21 is located on the N side. The absolute value of the current flowing through the sum is added, and the sum is detected as a ground fault current. Here, the “absolute value” is based on the fact that the direction of the current flowing through the detection resistor 16 is reversed when the switch 21 is located on the P side and when the switch 21 is located on the N side. .

  When a ground fault occurs on the anode side of the DC circuit 13, the current 0 mA when the switch 21 is located on the P side and the current 10 mA that flows when the switch 21 is located on the N side are added together, and the total value 10 mA. Is the ground fault current. In addition, when a ground fault occurs on the cathode side of the DC circuit 13, the current 10mA that flows when the switch 21 is located on the P side and the current 0mA when the switch 21 is located on the N side are added together. A value of 10 mA is defined as a ground fault current. Furthermore, when a ground fault occurs at the midpoint of the solar battery panel 12 of the DC circuit 13, a current 5mA that flows when the switch 21 is positioned on the P side and a current 5mA that flows when the switch 21 is positioned on the N side are The total value is 10 mA as the ground fault current (see Table 1).

  Thus, the ground fault current is obtained by adding the absolute value of the current flowing through the detection resistor 16 when the switch 21 is located on the P side and the absolute value of the current flowing through the detection resistor 16 when the switch 21 is located on the N side. Thus, the ground fault current detected when a ground fault occurs at the midpoint of the solar battery panel 12 is detected when a ground fault occurs on the anode side and the cathode side of the DC circuit 13. Since it becomes the same as the ground fault current, the ground fault detection sensitivity can always be kept constant regardless of where the ground fault occurs. As a result, since a ground fault accident occurring in the DC circuit 13 can be accurately detected, the highly reliable DC ground fault detector 11 can be provided.

  The detection unit 22 compares the absolute value of the current flowing through the detection resistor 16 when the switch 21 is positioned on the P side with the absolute value of the current flowing through the detection resistor 16 when the switch 21 is positioned on the N side. Is configured to do. In this way, by comparing the magnitude of the absolute value of the current flowing through the detection resistor 16 when the switch 21 is positioned on the P side with the absolute value of the current flowing through the detection resistor 16 when the switch 21 is positioned on the N side. It becomes possible to specify the location where the ground fault occurred.

  That is, when the absolute value of the current that flows when the switch 21 is located on the P side is larger than the absolute value of the current that flows when the switch 21 is located on the N side, a ground fault occurs on the cathode side of the DC circuit 13. Can be determined. Conversely, if the absolute value of the current that flows when the switch 21 is located on the P side is smaller than the absolute value of the current that flows when the switch 2 is located on the N side, a ground fault will occur on the anode side of the DC circuit 13. It can be determined that it has occurred. Further, when the absolute value of the current that flows when the switch 21 is positioned on the P side is equal to the absolute value of the current that flows when the switch 21 is positioned on the N side, a ground fault occurs in the solar panel 12 of the DC circuit 13. It can be determined that it occurs at an intermediate point.

  When the difference between the absolute value of the current that flows when the switch 21 is positioned on the P side and the absolute value of the current that flows when the switch 21 is positioned on the N side is a maximum value (for example, 10 mA), It can be determined that a ground fault has occurred at a location on the anode side or cathode side of the DC circuit 13 located outside the series circuit to which the solar cell panel 12 is connected. As the difference between the absolute value of the current that flows when the switch 21 is positioned on the P side and the absolute value of the current that flows when the switch 21 is positioned on the N side becomes smaller than the maximum value, the occurrence of a ground fault occurs. The location approaches the midpoint of the plurality of solar cell panels 12 connected in series.

  In the DC ground fault detector 11 of this embodiment, the switching cycle of the switch 21 may be set to be constant at all times, but can be temporarily changed. That is, even when the switching cycle is set to 1 minute, for example, when the ground fault current is detected by the switch 21 being switched and connected to either the anode side resistor 14 or the cathode side resistor 15. Thus, it is effective to immediately switch the switch 21 to the other pole side without waiting for a switching period of one minute. In this way, it is possible to quickly determine the occurrence of a ground fault and to provide the DC ground fault detector 11 having excellent responsiveness.

  Furthermore, it is also effective to prevent the switch 21 from being switched and connected to either the anode-side resistor 14 or the cathode-side resistor 15 after the determination of the occurrence of the ground fault is confirmed. As described above, when the occurrence of the ground fault is determined, the ground fault current does not flow through the DC circuit 13 by opening the switch 21. Therefore, the work for recovering the ground fault can be performed safely. it can.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

11 DC ground fault detector 12 Power supply (solar cell panel)
13 DC circuit 14 Anode-side resistance 15 Cathode-side resistance 16 Detection resistance housing 21 Switch 22 Detection unit

Claims (2)

An anode-side resistor connected to the anode side of a DC circuit having a power source, a cathode-side resistor connected to the cathode side of the DC circuit, and a switch periodically connected to the anode-side resistor or the cathode-side resistor And a DC ground fault detector comprising a detection resistor connected between the switch and the ground,
Said switch summing the absolute value of the current flowing in the detection resistor when it is switched connected to the anode-side resistor, the absolute value of the current flowing in the detection resistor when the switch is switched connected to the cathode-side resistor, wherein What is claimed is: 1. A DC ground fault detector, comprising: a detection unit that detects a constant sum as a ground fault current even if a ground fault occurs in any part of a DC circuit .   The detection unit includes an absolute value of a current flowing through the detection resistor when the switch is connected to the anode-side resistor, and an absolute value of a current flowing through the detection resistor when the switch is connected to the cathode-side resistor. The DC ground fault detector according to claim 1, wherein the DC ground fault detector is configured to compare the magnitudes of.