Ground fault detection circuit and ground fault detection method

Abstract

To detect a ground fault in the case where a capacitor is connected to an AC system via a current transformer and a rectification circuit.SOLUTION: A ground fault detection circuit comprises: a detection circuit that is provided to an AC system in each phase; and a determination circuit that determines a ground fault of the AC system by the detection circuit. The detection circuit includes: a current transformer that changes a current flowing in one phase line of the AC system; a diode bridge into which the current changed by the current transformer is input; and an output registration that is electrically connected to a first output end of the diode bridge. A second output end of each diode bridge is electrically connected to the output resistance of the detection circuit via a capacitor, and the determination circuit calculates an actual value of the output voltage generated by the output resistance of each detection circuit, and determines the ground fault of the AC system by using a difference of the actual value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a ground fault detection circuit and a ground fault detection method. [Background technology]

[0002] When detecting a ground fault in a three-phase AC system, the instantaneous values ​​of the current or voltage flowing through the lines of each phase are detected and all phases are combined (added together). If the zero-sequence component resulting from this combination is zero, it is determined that there is no ground fault, and if it indicates a certain value, it is determined that a ground fault has occurred (see, for example, Patent Document 1).

[0003] Also, a circuit breaker is known that utilizes a capacitor connected to an AC system via a current transformer and a rectifier circuit as a control power supply for a control circuit or a trip coil (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 1-316673 [Patent Document 2] JP 2002-027656 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a capacitor is connected to an AC system via a current transformer and a rectifier circuit, when the detection signals of the instantaneous values ​​of the currents flowing through the lines of each phase are all combined, the combined waveform has a predetermined value regardless of the presence or absence of a ground fault, making it difficult to detect a ground fault using conventional technology.

[0006] The present disclosure provides a ground fault detection circuit and a ground fault detection method capable of detecting a ground fault when a capacitor is connected to an AC system via a current transformer and a rectifier circuit. [Means for solving the problem]

[0007] The first aspect is A detection circuit provided for each phase of the AC system; a determination circuit for determining a ground fault in the AC system by the detection circuit, The detection circuits each include a current transformer that transforms a current flowing in a line of one phase of the AC system, a diode bridge to which the current transformed by the current transformer is input, and an output resistor that is electrically connected to a first output terminal of the diode bridge, a second output terminal of each of the diode bridges is electrically connected to the output resistor of each of the detection circuits via a capacitor; The determination circuit is a ground fault detection circuit that calculates an effective value of an output voltage generated by the output resistance of each of the detection circuits and determines a ground fault in the AC system using a difference between the effective values.

[0008] A second aspect is the ground fault detection circuit of the first aspect, The determination circuit determines that a ground fault has occurred in the AC system when any of the differences between the effective values ​​falls outside a predetermined range including zero.

[0009] A third aspect is the ground fault detection circuit of the first or second aspect, The determination circuit determines that there is no earth fault in the AC system when all of the differences between the effective values ​​are within a predetermined range including zero.

[0010] The fourth aspect is A method for detecting a ground fault in an AC system by a detection circuit provided for each phase of the AC system, comprising: The detection circuits each include a current transformer that transforms a current flowing in a line of one phase of the AC system, a diode bridge to which the current transformed by the current transformer is input, and an output resistor that is electrically connected to a first output terminal of the diode bridge, a second output terminal of each of the diode bridges is electrically connected to the output resistor of each of the detection circuits via a capacitor; The method for detecting a ground fault includes calculating an effective value of an output voltage generated by the output resistance of each of the detection circuits, and determining whether or not a ground fault has occurred in the AC system using a difference between the effective values. Effect of the Invention

[0011] According to the present disclosure, a ground fault can be detected when a capacitor is connected to an AC system via a current transformer and a rectifier circuit. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram illustrating an example of a configuration of a ground fault detection circuit according to an embodiment. [Diagram 2] 11 is a diagram showing an example of a composite waveform of detection signals of each phase when no ground fault occurs in the AC system; FIG. [Diagram 3] 11 is a diagram showing an example of a composite waveform of detection signals of each phase when a ground fault occurs in an AC system; FIG. [Figure 4] FIG. 2 is a functional block diagram illustrating an example of a determination circuit. [Diagram 5] FIG. 13 is a diagram illustrating an example of the effective values ​​of each phase when the R phase has a ground fault. [Figure 6] FIG. 13 is a diagram illustrating an example of a difference in effective value between each phase when the R phase has a ground fault. [Figure 7] 11 is a diagram illustrating an example of the effective values ​​of each phase when an R phase and an S phase have a ground fault. FIG. [Figure 8] 11 is a diagram illustrating an example of a difference between the effective values ​​of each phase when an R phase and an S phase have a ground fault. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The following describes the embodiments.

[0014] Fig. 1 is a diagram showing an example of a configuration of a ground fault detection circuit according to an embodiment. The ground fault detection circuit 101 is mounted, for example, on a circuit breaker that cuts off lines 11, 12, and 13 of each phase (R phase, S phase, and T phase) of an AC system 10. The ground fault detection circuit 101 shown in Fig. 1 includes a plurality of detection circuits 21, 22, and 23 provided for corresponding lines among the lines 11, 12, and 13 of multiple phases of the three-phase, three-wire AC system 10. The AC currents flowing through the lines 11, 12, and 13 are shifted in phase from each other by 120°.

[0015] The R-phase detection circuit 21 detects the current flowing through the R-phase line 11, and outputs the detection result to the determination circuit 60. The detection circuit 21 includes a current transformer 14, a resistor 17, a diode bridge 113, and an output resistor 110.

[0016] The current transformer 14 transforms the current flowing through the R-phase line 11 of the AC system 10. The primary side of the current transformer 14 is connected to the line 11. Between one end and the other end of the secondary side of the current transformer 14, a current-limiting resistor 17 and a diode bridge 113 are connected in series.

[0017] The diode bridge 113 receives the current transformed by the current transformer 14. The diode bridge 113 is a full-wave rectifier circuit having a first input terminal 35, a second input terminal 36, a first output terminal 37, a second output terminal 38, and a plurality of diodes 31, 32, 33, and 34. The diode 31 has an anode connected to the first output terminal 37 and a cathode connected to the first input terminal 35. The diode 32 has an anode connected to the first output terminal 37 and a cathode connected to the second input terminal 36. The diode 33 has an anode connected to the first input terminal 35 and a cathode connected to the second output terminal 38. The diode 34 has an anode connected to the second input terminal 36 and a cathode connected to the second output terminal 38.

[0018] The first output terminal 37 is electrically connected to one end of the output resistor 110 and is grounded via the output resistor 110. The second output terminal 38 is electrically connected to one end of the capacitor 116 and is grounded via the capacitor 116. The second output terminal 38 is electrically connected to the other end of the output resistor 111 via the capacitor 116.

[0019] The S-phase detection circuit 22 and the T-phase detection circuit 23 have the same configuration as the R-phase detection circuit 21. That is, the S-phase detection circuit 22 has a current transformer 15, a resistor 18, a diode bridge 114, and an output resistor 111, and the T-phase detection circuit 23 has a current transformer 16, a resistor 19, a diode bridge 115, and an output resistor 112.

[0020] The second output terminals 38 of the detection circuits 21, 22, 23 are connected to each other and grounded via a capacitor 116. The capacitor 116 is used as a control power supply for the circuit breaker in which the ground fault detection circuit 101 is mounted.

[0021] In the detection circuits 21, 22, 23, the AC currents flowing through the lines 11, 12, 13 are transformed by current transformers 14, 15, 16, respectively, and the transformed currents are full-wave rectified by diode bridges 113, 114, 115 via resistors 17, 18, 19. The full-wave rectified currents flow from capacitor 116 to output resistors 110, 111, 112 via ground. Therefore, when all the DC detection signals detected by the output resistors 110, 111, 112 are combined, the combined waveform has a predetermined value regardless of the presence or absence of a ground fault.

[0022] For example, Fig. 2 shows an example of the composite waveform of the detection signals of each phase when there is no ground fault in any of the lines 11, 12, and 13. In contrast to this, Fig. 3 shows an example of the composite waveform of the detection signals of each phase when a ground fault (ground fault current 50 [A]) occurs in any of the lines 11, 12, and 13. As is clear from Figs. 2 and 3, in the circuit shown in Fig. 1, the composite waveform of the detection signals of each phase has a predetermined value regardless of whether a ground fault occurs. For this reason, it is difficult to detect a ground fault using the conventional detection method (a method in which if the composite waveform is zero, it is determined that there is no ground fault, and if it indicates a certain value, it is determined that a ground fault has occurred).

[0023] Therefore, the ground fault detection circuit 101 of the present embodiment includes a determination circuit 60 that determines a ground fault in the AC system 10 using a ground fault detection method different from the conventional method, based on the detection results from the multiple detection circuits 21, 22, and 23. The determination circuit 60 calculates the effective values ​​of each output voltage from the waveforms of the output voltages generated by the output resistors 110, 111, and 112 of the R, S, and T phases, and determines a ground fault in the AC system 10 using the difference between the calculated effective values.

[0024] The determination circuit 60 has, for example, a memory and a processor (for example, a CPU (Central Processing Unit)), and each function of the determination circuit 60 is realized by the processor operating according to a program stored in the memory. Each function of the determination circuit 60 may be realized by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0025] 4 is a functional block diagram showing an example of a determination circuit. The output voltage V1 is a signal output from the output resistor 110 by full-wave rectifying the current transformed by the R-phase current transformer 14 with the diode bridge 113, and represents an R-phase detection signal corresponding to the amount of voltage drop occurring in the output resistor 110. The output voltage V2 is a signal output from the output resistor 111 by full-wave rectifying the current transformed by the S-phase current transformer 15 with the diode bridge 114, and represents an S-phase detection signal corresponding to the amount of voltage drop occurring in the output resistor 111. The output voltage V3 is a signal output from the output resistor 112 by full-wave rectifying the current transformed by the T-phase current transformer 16 with the diode bridge 115, and represents a T-phase detection signal corresponding to the amount of voltage drop occurring in the output resistor 112.

[0026] The decision circuit 60 converts each of the analog output voltages V1, V2, and V3 into a digital output voltage value. The decision circuit 60 calculates the effective value of each of the output voltages V1, V2, and V3 using the digital output voltage value of each phase. The decision circuit 60 calculates the difference ΔRS between the effective value of the R phase and the effective value of the S phase, the difference ΔST between the effective value of the S phase and the effective value of the T phase, and the difference ΔRT between the effective value of the R phase and the effective value of the T phase.

[0027] The determination circuit 60 determines that there is no ground fault in the AC system 10 when all of the differences ΔRS, ΔST, and ΔRT are within a predetermined range including zero (hereinafter also referred to as the predetermined range X). On the other hand, the determination circuit 60 determines that there is a ground fault in the AC system 10 when any of the differences ΔRS, ΔST, and ΔRT is outside the predetermined range X. When the determination circuit 60 determines that there is a ground fault in the AC system 10, it shuts off, for example, the lines 11, 12, and 13 of each phase of the AC system 10. This makes it possible to prevent failures such as line disconnection due to a ground fault.

[0028] Fig. 5 is a diagram illustrating an example of the effective values ​​of the output voltages V1, V2, and V3 of the respective phases when a ground fault occurs in the R phase. Fig. 6 is a diagram illustrating an example of the differences ΔRS, ΔST, and ΔRT in the effective values ​​of the output voltages V1, V2, and V3 of the respective phases when a ground fault occurs in the R phase. A first example of a method for detecting a ground fault in the AC system 10 when a ground fault occurs in a line of only one of the three phases will be described below with reference to Figs. 5 and 6.

[0029] 5, a determination circuit 60 calculates the effective values ​​of output voltages V1, V2, and V3 from the waveforms of output voltages V1, V2, and V3 of output resistors 110, 111, and 112 of the R, S, and T phases. Since only one phase, the R phase, is grounded, the effective value of the R phase output voltage V1 is lower than the effective value of the S phase output voltage V2 and the effective value of the T phase output voltage V3.

[0030] 6, when the R-phase current is 250 [A], this indicates that there is no ground fault in any of the lines 11, 12, and 13 of the respective phases, and when the R-phase current is other than 250 [A], this indicates that only the R-phase line 11 is grounded. When the R-phase current is 250 [A], the differences ΔRS, ΔST, and ΔRT in the effective values ​​of the respective phases are all 0 [V]. Therefore, when all of the differences ΔRS, ΔST, and ΔRT are within a predetermined range X including zero, the determination circuit 60 can determine that there is no ground fault in the AC system 10.

[0031] On the other hand, when a ground fault occurs in the R-phase line 11 and the R-phase current is a value other than 250 [A], the difference ΔST between the effective values ​​of the S-phase with no ground fault and the T-phase with no ground fault is always almost zero. However, the difference ΔRS between the effective values ​​of the R-phase with a ground fault and the S-phase with no ground fault, and the difference ΔRT between the effective values ​​of the R-phase with a ground fault and the T-phase with no ground fault are non-zero. Therefore, the determination circuit 60 can determine that there is a ground fault in the AC system 10 when any of the differences ΔRS, ΔST, and ΔRT is outside the predetermined range X including zero.

[0032] It should be noted that a single-phase earth fault can be detected not only in the R phase, but also in the S phase or T phase by the same method.

[0033] The upper and lower thresholds of the predetermined range X may be determined based on the manufacturing tolerances of the current transformers 14, 15, and 16, for example.

[0034] Fig. 7 is a diagram illustrating an example of the effective values ​​of the output voltages V1, V2, and V3 of each phase when a ground fault occurs between the R phase and the S phase. Fig. 8 is a diagram illustrating an example of the differences ΔRS, ΔST, and ΔRT between the effective values ​​of the output voltages V1, V2, and V3 of each phase when a ground fault occurs between the R phase and the S phase. A second example of a method for detecting a ground fault in the AC system 10 when a ground fault occurs in the lines of two of the three phases will be described below with reference to Figs. 7 and 8.

[0035] In Fig. 7, a judgment circuit 60 calculates the effective values ​​of output voltages V1, V2, and V3 from the waveforms of output voltages V1, V2, and V3 of output resistors 110, 111, and 112 of the R, S, and T phases. Fig. 7 shows a state in which a ground-fault current of 100 [A] flows through the R-phase line 11 and a ground-fault current of 125 [A] flows through the S-phase line 12. Since two phases, R and S, are grounded, the effective values ​​of the R-phase output voltage V1 and the S-phase output voltage V2 are lower than the effective value of the T-phase output voltage V3. Since the ground-fault current is larger in the S-phase than in the R-phase, the effective value of the S-phase output voltage V2 is lower than the effective value of the R-phase output voltage V1.

[0036] 8 shows the relationship between the change in the ground-fault current flowing through the R-phase and the differences ΔRS, ΔST, and ΔRT of each phase when a ground-fault current of 125 [A] is flowing through the S-phase line 12. Even if the ground-fault current flowing through the R-phase line 11 has any value, any of the differences ΔRS, ΔST, and ΔRT is a value other than zero. Therefore, the determination circuit 60 can determine that there is a ground fault in the AC system 10 when any of the differences ΔRS, ΔST, and ΔRT is outside a predetermined range X that includes zero.

[0037] In addition, two-phase ground faults can be detected not only between the R phase and the S phase, but also between the R phase and the T phase or between the S phase and the T phase using the same method.

[0038] As described above, the ground fault detection circuit 101 of the present embodiment includes detection circuits provided for each phase of the AC system 10 (specifically, detection circuits 21, 22, and 23 in which a capacitor 116 is connected to the AC system 10 via current transformers 14, 15, and 16 and diode bridges 113, 114, and 115). The ground fault detection circuit 101 includes a determination circuit 60 that calculates effective values ​​of output voltages generated by output resistors 110, 111, and 112 of the detection circuits 21, 22, and 23, respectively, and determines a ground fault in the AC system 10 using a difference between the effective values. Therefore, according to the ground fault detection circuit or the ground fault detection method of the present embodiment, a ground fault can be detected when a capacitor is connected to the AC system via a current transformer and a rectifier circuit. For example, if any of the differences between the effective values ​​falls outside a predetermined range including zero, the judgment circuit 60 judges that there is a ground fault in the AC system 10, and if all of the differences between the effective values ​​are within a predetermined range including zero, the judgment circuit 60 judges that there is no ground fault in the AC system 10.

[0039] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0040] For example, the determination circuit 60 that calculates the effective values ​​of the output voltages generated by the output resistances 110, 111, 112 of the detection circuits 21, 22, 23 and determines whether or not there is a ground fault in the AC system 10 using the difference between the effective values ​​may be provided in an external device connected to the circuit breaker by wire or wirelessly. Alternatively, the calculation unit that calculates the effective values ​​of the output voltages generated by the output resistances 110, 111, 112 may be mounted on the circuit breaker, and the determination unit that determines whether or not there is a ground fault in the AC system 10 using the difference between the effective values ​​may be provided in an external device connected to the circuit breaker by wire or wirelessly. [Explanation of symbols]

[0041] 10 AC system 11,12,13 railroad tracks 14, 15, 16 Current transformers 17, 18, 19 Resistance 21, 22, 23 Detection circuit 31, 32, 33, 34 Diodes 35 First input terminal 36 Second input terminal 37 First output terminal 38 Second output terminal 60 Judgment circuit 101 Earth fault detection circuit 110,111,112 Output resistance 113,114,115 Diode bridge 116 Capacitor

Claims

1. A detection circuit provided for each phase of the AC system; a determination circuit for determining a ground fault in the AC system by the detection circuit, The detection circuits each include a current transformer that transforms a current flowing in a line of one phase of the AC system, a diode bridge to which the current transformed by the current transformer is input, and an output resistor that is electrically connected to a first output terminal of the diode bridge, a second output terminal of each of the diode bridges is electrically connected to the output resistor of each of the detection circuits via a capacitor; The determination circuit calculates an effective value of an output voltage generated by the output resistance of each of the detection circuits, and determines a ground fault in the AC system using a difference between the effective values.

2. 2. The ground fault detection circuit according to claim 1, wherein the determination circuit determines that a ground fault has occurred in the AC system when any of the differences between the effective values ​​falls outside a predetermined range including zero.

3. 3. The ground fault detection circuit according to claim 1, wherein the determination circuit determines that there is no ground fault in the AC system when all of the differences between the effective values ​​are within a predetermined range including zero.

4. A method for detecting a ground fault in an AC system by a detection circuit provided for each phase of the AC system, comprising: The detection circuits each include a current transformer that transforms a current flowing in a line of one phase of the AC system, a diode bridge to which the current transformed by the current transformer is input, and an output resistor that is electrically connected to a first output terminal of the diode bridge, a second output terminal of each of the diode bridges is electrically connected to the output resistor of each of the detection circuits via a capacitor; A ground fault detection method comprising: calculating an effective value of an output voltage generated by the output resistance of each of the detection circuits; and determining whether or not a ground fault occurs in the AC system using a difference between the effective values.

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