Ground Fault Detection System

Abstract

To provide an earth fault detection system capable of determining an occurrence place of an earth fault in a state where a power supply and a configuration including an inverter are disconnected when the earth fault occurs, in a voltage type converter.SOLUTION: An earth fault detection system comprises: a frequency conversion device; a first circuit breaker provided on an input side of the frequency conversion device; a second circuit breaker provided on an output side of the frequency conversion device; an earth fault detection device provided in the frequency conversion device; and a control unit connected to at least the first circuit breaker, the second circuit breaker, and the earth fault detection device. When an earth fault is detected by the earth fault detection device, the control unit switches the first circuit breaker to OFF while keeping the second circuit breaker ON. Further, when the earth fault detection device does not detect the earth fault in a state where the first circuit breaker is OFF and the second circuit breaker is ON, an occurrence place of the earth fault is determined to be outside the first circuit breaker.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a ground fault detection system that determines the location of a ground fault. [Background technology]

[0002] Patent Document 1 discloses a technique for determining whether a ground fault occurs on the inverter side or the motor side when a ground fault occurs. In this technique, when a ground fault occurs, a second circuit breaker provided between the inverter and the motor is switched off, and the location of the ground fault is determined based on the state of a ground fault detection device provided in the inverter.

[0003] Specifically, if the ground fault detection device detects a ground fault with the second circuit breaker switched OFF, it determines that the ground fault is located on the inverter side. In this case, the first circuit breaker installed between the inverter and the power supply is switched OFF, and the third circuit breaker installed between the power supply and the motor is switched ON. This allows the motor to continue operating even if a ground fault occurs in the inverter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3831702 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a ground fault occurs, the location of the ground fault is determined while the first circuit breaker is kept ON. If the location of the ground fault is in the power supply, there is a risk that unstable power will be supplied to the inverter. Furthermore, even if it is determined that the location of the ground fault is included in the inverter side, if the location of the ground fault is in the power supply, there is a risk that unstable power will be supplied to the motor, and the motor will continue to operate in that state. Furthermore, when determining the location of the ground fault with the power supply stopped, if the inverter side is configured with a current-type converter, the operation of the inverter will be interrupted when the power supply is stopped. Therefore, with this configuration, the location of the ground fault must be determined individually with the power supply side, inverter side, and motor side disconnected, making it difficult to easily determine the location of the ground fault.

[0006] One object of the present disclosure is to provide a ground fault detection system in a voltage-type converter that can determine the location of a ground fault when the ground fault occurs while disconnecting the power source from a configuration including an inverter. [Means for solving the problem]

[0007] The first aspect relates to a ground fault detection system. The ground fault detection system includes a frequency converter, a first circuit breaker provided on the input side of the frequency converter, a second circuit breaker provided on the output side of the frequency converter, a ground fault detection device provided in the frequency converter, and a control unit connected to at least the first circuit breaker, the second circuit breaker, and the ground fault detection device. When a ground fault is detected by the ground fault detection device, the control unit switches the first circuit breaker OFF while keeping the second circuit breaker ON. Furthermore, when a ground fault is not detected by the ground fault detection device with the first circuit breaker OFF and the second circuit breaker ON, the control unit is configured to determine that the ground fault has occurred outside the first circuit breaker.

[0008] The second aspect has the following characteristics in addition to those of the first aspect. When a ground fault is detected by the ground fault detection device while the first circuit breaker is OFF and the second circuit breaker is ON, the control unit switches the second circuit breaker OFF. Furthermore, when a ground fault is detected by the ground fault detection device while the first circuit breaker is OFF and the second circuit breaker is OFF, the control unit determines that the location of the ground fault is the frequency conversion device. Furthermore, when a ground fault is not detected by the ground fault detection device while the first circuit breaker is OFF and the second circuit breaker is OFF, the control unit is configured to determine that the location of the ground fault is outside the second circuit breaker.

[0009] The third aspect relates to a ground fault detection system. The ground fault detection system includes a frequency converter, a first circuit breaker provided on the input side of the frequency converter, a second circuit breaker provided on the output side of the frequency converter, a ground fault detection device provided in the frequency converter, and a control unit connected to at least the first circuit breaker, the second circuit breaker, and the ground fault detection device. The control unit switches both the first and second circuit breakers OFF when a ground fault is detected by the ground fault detection device. Furthermore, the control unit is configured to determine that the ground fault is occurring in the frequency converter when a ground fault is detected by the ground fault detection device with the first circuit breaker OFF and the second circuit breaker OFF.

[0010] The fourth aspect has the following characteristics in addition to the third aspect. When the ground fault detection device detects no ground fault while the first circuit breaker is OFF and the second circuit breaker is OFF, the control unit switches the second circuit breaker ON. Furthermore, when the ground fault detection device detects a ground fault while the first circuit breaker is OFF and the second circuit breaker is ON, the control unit determines that the ground fault has occurred outside the second circuit breaker. Furthermore, when the ground fault detection device detects no ground fault while the first circuit breaker is OFF and the second circuit breaker is ON, the control unit is configured to determine that the ground fault has occurred outside the first circuit breaker.

[0011] A fifth aspect has the following features in addition to any one of the first to fourth aspects. The frequency conversion device is composed of three single-phase frequency conversion units. Each of the three single-phase frequency conversion units includes a converter that converts an input AC voltage into a DC voltage and an inverter that converts the DC voltage into an output AC voltage. One ground fault detection device is connected between the output side of the three single-phase frequency conversion units and the ground. When it is determined that the ground fault has occurred in the frequency conversion device, the control unit calculates a ratio between the DC voltage and each of three neutral point voltages or currents flowing between the neutral point and the ground, which are obtained when the three single-phase frequency conversion units are operated individually. Furthermore, the control unit is configured to determine that the ground fault has occurred in the single-phase frequency conversion unit that is the output source of the neutral point voltage for which the ratio is equal to or greater than a threshold value.

[0012] A sixth aspect has the following features in addition to any one of the first to fourth aspects. The frequency conversion device is composed of three single-phase frequency conversion units. Each of the three single-phase frequency conversion units includes a converter that converts an input AC voltage into a DC voltage and an inverter that converts the DC voltage into an output AC voltage. One ground fault detection device is connected between the output side of the three single-phase frequency conversion units and the ground. When it is determined that the ground fault has occurred in the frequency conversion device, the control unit calculates a ratio between the DC voltage and each of three neutral point voltages or currents flowing between the neutral point and the ground, which are obtained when the three single-phase frequency conversion units are operated individually. Furthermore, the control unit is configured to determine that the single-phase frequency conversion unit that outputs the neutral point voltage for which the ratio is greatest includes the location of the ground fault.

[0013] A seventh aspect has the following feature in addition to any one of the first to fourth aspects: when a ground fault is detected by the ground fault detection device with the first circuit breaker and the second circuit breaker both in an OFF state, the control unit places the inverter of the frequency conversion device in a gate-blocked state. Furthermore, when a ground fault is detected by the ground fault detection device with the inverter in a gate-blocked state, the control unit is configured to determine that the ground fault detection device is malfunctioning. [Effects of the Invention]

[0014] According to the present disclosure, when a ground fault is detected by the ground fault detection device, the ground fault detection system switches the first circuit breaker OFF while keeping the second circuit breaker ON. Furthermore, when the first circuit breaker is OFF and the second circuit breaker is ON and no ground fault is detected by the ground fault detection device, the ground fault detection system determines that the ground fault has occurred outside the first circuit breaker. This prevents an unstable power supply from being supplied to the motor when the ground fault occurs in the power supply. Therefore, when a ground fault occurs, it becomes possible to easily determine the location of the ground fault while disconnecting the power supply from the configuration including the inverter. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram showing an example of the configuration of a ground fault detection system according to a first embodiment. [Figure 2] 4 is a diagram showing a first example of determination of the location of a ground fault in the control unit of the ground fault detection system according to the first embodiment. FIG. [Figure 3] 5 is a flowchart showing a first example of processing in a control unit of the ground fault detection system according to the first embodiment. [Figure 4] 10 is a diagram showing a second example of determination of the location of a ground fault in the control unit of the ground fault detection system according to the first embodiment. FIG. [Figure 5] 6 is a flowchart showing a second processing example in the control unit of the ground fault detection system according to the first embodiment. [Figure 6] 10 is a flowchart showing a third example of processing in the control unit of the ground fault detection system according to the first embodiment. [Figure 7] FIG. 10 is a block diagram showing an example of the configuration of a ground fault detection system according to a second embodiment. [Figure 8] 10 is a diagram showing an example of determining the location of a ground fault in a control unit of a ground fault detection system according to a second embodiment. FIG. [Figure 9] 10 is a flowchart showing an example of processing in a control unit of the ground fault detection system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0017] 1. First Embodiment 1-1. Example of a ground fault detection system configuration 1 is a block diagram showing an example configuration of a ground fault detection system 1 according to embodiment 1. The ground fault detection system 1 is applied to factory equipment, for example, for detecting an abnormality in an electric motor system including a frequency conversion device that controls the rotation speed of an electric motor such as a motor.

[0018] As shown in Fig. 1, the ground fault detection system 1 includes a frequency converter 20, a power supply 10 that generates an AC voltage (hereinafter referred to as an input AC voltage) to be supplied to the frequency converter 20, and an electric motor 30 that is driven by the AC voltage (hereinafter referred to as an output AC voltage) output from the frequency converter 20. The power supply 10 may be configured as a commercial power supply only, or may be configured as a commercial power supply and a transformer. The electric motor 30 is an example of a load that is driven by the output AC voltage output from the frequency converter 20.

[0019] The frequency converter 20 includes a first circuit breaker 21 connected to the power source 10 on the input side of the frequency converter 20, a converter 22 converting the input AC voltage supplied from the power source 10 into a DC voltage, a DC capacitor 29 smoothing the DC voltage, an inverter 23 converting the smoothed DC voltage into an AC voltage of a desired voltage and frequency and outputting the AC voltage, a second circuit breaker 24 on the output side of the frequency converter 20, and a ground fault detector 25 connected between a neutral point voltage indicating the voltage at the neutral point of the inverter 23 and ground. For example, if the inverter 23 is a three-level inverter, the DC capacitor 29 is connected between the positive DC line 51a and the neutral conductor 51c of the DC circuit, and another DC capacitor 29 is connected between the negative DC line 51b and the neutral conductor 51c of the DC circuit. The neutral point refers to the portion of the three-level inverter connected to the neutral conductor 51c of the DC circuit. Alternatively, it refers to the center of a star connection when three single-phase inverters, each with two output terminals, are star-connected. The inverter 23 shown in Fig. 1 is an example of a three-level inverter, and the frequency conversion device 20 is configured with a voltage-type converter. Also, as shown in Fig. 1, a configuration including the converter 22, the inverter 23, the DC capacitor 29, the positive DC line 51a, the negative DC line 51b, and the neutral line 51c may be referred to as a frequency conversion unit 52.

[0020] The ground fault detection system 1 further includes a control unit 40. The control unit 40 is connected to at least the first circuit breaker 21, the second circuit breaker 24, and the ground fault detection device 25. The control unit 40 controls the first circuit breaker 21, which switches between connecting and disconnecting the power source 10 and the frequency conversion device 20, and controls the second circuit breaker 24, which switches between connecting and disconnecting the frequency conversion device 20 and the electric motor 30.

[0021] The control unit 40 further monitors the state of the ground fault detection device 25. Monitoring the state of the ground fault detection device 25 means, for example, acquiring ground fault detection information indicating whether or not a ground fault has been detected by the ground fault detection device 25. Specifically, the ground fault detection information is expressed as 1 (ground fault detected), 0 (ground fault not detected), etc. When the ground fault detection information is 1 (ground fault detected), the control unit 40 performs control to switch at least the first circuit breaker 21 OFF.

[0022] The determination of whether a ground fault has been detected or not is made by the ground fault detection device 25. Specifically, the determination of whether a ground fault has been detected or not is made based on the neutral point voltage. For example, if the neutral point voltage is equal to or higher than a predetermined voltage, the determination is 1 (ground fault detected), and if the neutral point voltage is lower than the predetermined voltage, the determination is 0 (ground fault not detected). Even if a ground fault has not been detected, when the frequency conversion device 20 is in operation, a voltage containing at least one of harmonic components of the power supply frequency and harmonic components and carrier frequency components of the inverter output frequency is generated at the neutral point. Therefore, these harmonic components may be removed using a predetermined filter or the like before the determination of whether a ground fault has been detected or not by the ground fault detection device 25.

[0023] 1, the control unit 40 may be provided outside the frequency conversion device 20, or may be provided inside the frequency conversion device 20. The control unit 40 may also be a circuit made up of IC components or the like, or may be made up of an information processing device (a computer or the like).

[0024] 1-2. First example of determining the location of a ground fault 2 is a diagram showing a first example of how the control unit 40 of the ground fault detection system 1 determines the location of a ground fault. When the ground fault detection information is 1 (ground fault detected), the control unit 40 switches the first circuit breaker 21 to OFF while keeping the second circuit breaker 24 ON. In this state, the frequency conversion device 20 operates. Therefore, the control unit 40 determines the location of a ground fault when the first circuit breaker 21 is OFF and the second circuit breaker 24 is ON, that is, when the frequency conversion device 20 and the power source 10 are disconnected and the frequency conversion device 20 and the electric motor 30 are connected.

[0025] The location of the ground fault determined by the control unit 40 differs depending on whether the pattern (pattern A1 shown in FIG. 2) is when the ground fault detection information is 1 (ground fault detected) or when the pattern (pattern A2 shown in FIG. 2) is when the ground fault detection information is 0 (ground fault not detected). When the ground fault detection information is pattern A1, the control unit 40 determines that the location of the ground fault is outside the first circuit breaker 21 (i.e., on the power source 10 side of the first circuit breaker 21). On the other hand, when the ground fault detection information is pattern A2, the control unit 40 determines that the location of the ground fault is outside the frequency conversion device 20 or the second circuit breaker 24 (i.e., on the motor 30 side of the second circuit breaker 24).

[0026] When the determination result of the location of the ground fault is pattern A2 shown in FIG. 2, the location of the ground fault includes two locations: the frequency conversion device 20 and the outside of the second circuit breaker 24. In this case, since the location of the ground fault has not been identified, a mechanism for determining the location of the ground fault is further required. Therefore, when the determination result of the location of the ground fault is pattern A2, the control unit 40 further switches the second circuit breaker 24 to OFF while keeping the first circuit breaker 21 OFF. In this state, the frequency conversion device 20 operates. Therefore, the control unit 40 determines the location of the ground fault when the first circuit breaker 21 is OFF and the second circuit breaker 24 is OFF, that is, when the frequency conversion device 20 and the power source 10 are disconnected and the frequency conversion device 20 and the electric motor 30 are disconnected.

[0027] The location of the ground fault determined by the control unit 40 differs between a pattern (pattern A3 shown in FIG. 2) when the ground fault detection information is 1 (ground fault detected) and a pattern (pattern A4 shown in FIG. 2) when the ground fault detection information is 0 (ground fault not detected). When the ground fault detection information is pattern A3, the control unit 40 determines that the location of the ground fault is the frequency conversion device 20. When the location of the ground fault is the frequency conversion device 20, this means that the location of the ground fault exists between the connection point of the frequency conversion device 20 and the first circuit breaker 21 and the connection point of the frequency conversion device 20 and the second circuit breaker 24. On the other hand, when the ground fault detection information is pattern A4, the control unit 40 determines that the location of the ground fault is outside the second circuit breaker 24.

[0028] As described above, when a ground fault is detected by the ground fault detection device 25, the ground fault detection system 1 according to the first embodiment can appropriately determine the location of the ground fault based on the ground fault detection information obtained by controlling the first circuit breaker 21 and the second circuit breaker 24. More specifically, the ground fault detection system 1 according to the first embodiment can easily determine whether the location of the ground fault is outside the first circuit breaker 21 (i.e., closer to the power source 10 than the first circuit breaker 21), outside the second circuit breaker 24 (i.e., closer to the motor 30 than the second circuit breaker 24), or inside the frequency conversion device 20. Furthermore, when a ground fault is detected, the ground fault detection system 1 according to the first embodiment can immediately shut off the first circuit breaker 21, that is, shut off the current from the power source 10, and then determine the location of the ground fault using the energy stored in the DC capacitor 29. As a result, when the power source 10 includes the location of the ground fault, the influence of an escalating fault due to the ground fault current from the power source 10 is suppressed.

[0029] 1-3. First processing example Fig. 3 is a flowchart showing a first processing example in the control unit 40 of the ground fault detection system 1 according to Embodiment 1. The routine shown in Fig. 3 is repeatedly executed at predetermined intervals.

[0030] In step S100, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If it is determined that the ground fault detection information indicates "ground fault detected," the process proceeds to step S110. Otherwise, the process ends.

[0031] In step S110, the control unit 40 switches the first circuit breaker 21 to OFF while maintaining the second circuit breaker 24 in ON state. After that, the process proceeds to step S120.

[0032] In step S120, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If the ground fault detection information is not determined to indicate "ground fault detected," the process proceeds to step S170. In step S170, the control unit 40 determines that the location of the ground fault is outside the first circuit breaker 21. Then, the control unit 40 instructs the frequency conversion device 20 to gate block (stop operation).

[0033] If it is determined in step S120 that the ground fault detection information indicates "ground fault detected," the process proceeds to step S130. In step S130, the control unit 40 switches the second circuit breaker 24 to OFF while keeping the first circuit breaker 21 OFF. Thereafter, the process proceeds to step S140.

[0034] In step S140, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If the ground fault detection information is not determined to indicate "ground fault detected," the process proceeds to step S160. In step S160, the control unit 40 determines that the location of the ground fault is outside the second circuit breaker 24. Then, the control unit 40 instructs the frequency conversion device 20 to gate block (stop operation).

[0035] If it is determined in step S140 that the ground fault detection information indicates "ground fault detected," the process proceeds to step S150. In step S150, the control unit 40 determines that the location of the ground fault is the frequency conversion device 20. Then, the control unit 40 instructs the frequency conversion device 20 to gate block (stop operation).

[0036] 1-4. Second example of determining the location of a ground fault Here, a determination example different from the first determination example of the location of a ground fault shown in Fig. 2 will be described with reference to Fig. 4. Fig. 4 is a diagram showing a second determination example of the location of a ground fault in the control unit 40 of the ground fault detection system 1. When the ground fault detection information is 1 (ground fault detected), the control unit 40 switches both the first circuit breaker 21 and the second circuit breaker 24 to OFF. In this state, the frequency conversion device 20 is operated. Therefore, the control unit 40 determines the location of a ground fault when the first circuit breaker 21 is OFF and the second circuit breaker 24 is OFF, that is, when the frequency conversion device 20 and the power source 10 are disconnected and the frequency conversion device 20 and the electric motor 30 are disconnected.

[0037] The location of the ground fault determined by the control unit 40 differs depending on whether the pattern (pattern B1 shown in FIG. 4) is when the ground fault detection information is 1 (ground fault detected) or the pattern (pattern B2 shown in FIG. 4) is when the ground fault detection information is 0 (ground fault not detected). When the ground fault detection information is pattern B1, the control unit 40 determines that the location of the ground fault is the frequency conversion device 20. On the other hand, when the ground fault detection information is pattern B2, the control unit 40 determines that the location of the ground fault is outside the first circuit breaker 21 (i.e., on the power source 10 side of the first circuit breaker 21) or outside the second circuit breaker 24 (i.e., on the motor 30 side of the second circuit breaker 24).

[0038] When the determination result of the location of the ground fault is pattern B2 shown in FIG. 4, the location of the ground fault includes two locations: outside the first circuit breaker 21 and outside the second circuit breaker 24. In this case, the location of the ground fault has not been identified, so a mechanism for determining the location of the ground fault is required. Therefore, when the determination result of the location of the ground fault is pattern B2, the control unit 40 further switches the second circuit breaker 24 ON while keeping the first circuit breaker 21 OFF. In this state, the frequency conversion device 20 operates. Therefore, the control unit 40 determines the location of the ground fault when the first circuit breaker 21 is OFF and the second circuit breaker 24 is ON, that is, when the frequency conversion device 20 and the power source 10 are disconnected and the frequency conversion device 20 and the electric motor 30 are connected.

[0039] The location of the ground fault determined by the control unit 40 differs between a pattern (pattern B3 shown in FIG. 4) when the ground fault detection information is 1 (ground fault detected) and a pattern (pattern B4 shown in FIG. 4) when the ground fault detection information is 0 (ground fault not detected). When the ground fault detection information is pattern B3, the control unit 40 determines that the location of the ground fault is outside the second circuit breaker 24. On the other hand, when the ground fault detection information is pattern B4, the control unit 40 determines that the location of the ground fault is outside the first circuit breaker 21.

[0040] As described above, when a ground fault is detected by the ground fault detection device 25, the ground fault detection system 1 according to the first embodiment can appropriately determine the location of the ground fault based on the ground fault detection information obtained by controlling the first circuit breaker 21 and the second circuit breaker 24, even in the second determination example. More specifically, the ground fault detection system 1 according to the first embodiment can easily determine whether the location of the ground fault is outside the first circuit breaker 21 (i.e., on the power source 10 side of the first circuit breaker 21), outside the second circuit breaker 24 (i.e., on the motor 30 side of the second circuit breaker 24), or inside the frequency conversion device 20. Furthermore, as in the first determination example of the location of the ground fault described above, when a ground fault is detected, the first circuit breaker 21 is immediately shut off, that is, the current from the power source 10 is shut off, and the location of the ground fault is determined using the energy stored in the DC capacitor 29. As a result, when the power source 10 includes the location of the ground fault, the influence of an escalating fault due to the ground fault current from the power source 10 is suppressed.

[0041] 1-5. Second processing example According to a first processing example of the ground fault detection system 1 according to the first embodiment, when a ground fault is detected by the ground fault detection device 25, the location of the ground fault is determined starting from a state in which the first circuit breaker 21 is switched OFF while the second circuit breaker 24 is maintained ON. In a second processing example of the ground fault detection system 1 according to the first embodiment, the location of the ground fault is determined starting from a state in which both the second circuit breaker 24 and the first circuit breaker 21 are switched OFF. As a result, the determination of whether the location of the ground fault is in the frequency conversion device 20 is given top priority.

[0042] Fig. 5 is a flowchart showing a second processing example in the control unit 40 of the ground fault detection system 1 according to Embodiment 1. The routine shown in Fig. 5 is repeatedly executed at predetermined intervals.

[0043] In step S200, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If it is determined that the ground fault detection information indicates "ground fault detected," the process proceeds to step S210. Otherwise, the process ends.

[0044] In step S210, the control unit 40 switches off both the first circuit breaker 21 and the second circuit breaker 24. After that, the process proceeds to step S220.

[0045] In step S220, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If it is determined that the ground fault detection information indicates "ground fault detected," the process proceeds to step S250. In step S250, the control unit 40 determines that the location of the ground fault is the frequency conversion device 20.

[0046] If it is determined in step S220 that the ground fault detection information is not "ground fault detected," the process proceeds to step S230. In step S230, the control unit 40 switches the second circuit breaker 24 ON while keeping the first circuit breaker 21 OFF. Thereafter, the process proceeds to step S240.

[0047] In step S240, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If it is determined that the ground fault detection information indicates "ground fault detected," the process proceeds to step S260. In step S260, the control unit 40 determines that the location of the ground fault is outside the second circuit breaker 24 (i.e., on the motor 30 side of the second circuit breaker 24).

[0048] If it is not determined in step S240 that the ground fault detection information is "ground fault detected," the process proceeds to step S270. In step S270, the control unit 40 determines that the ground fault has occurred outside the first circuit breaker 21 (i.e., on the power source 10 side of the first circuit breaker 21).

[0049] 1-6.Third processing example According to the first and second processing examples of the ground fault detection system 1 according to the first embodiment, it is possible to identify the location of the ground fault. However, it cannot be ruled out that the detected ground fault may be due to a malfunction of the ground fault detection device 25.

[0050] Therefore, in the third processing example of the ground fault detection system 1 according to the first embodiment, it is determined whether the detected ground fault is due to a malfunction of the ground fault detection device 25.

[0051] Fig. 6 is a flowchart showing a third example of processing by the control unit 40 of the ground fault detection system 1 according to Embodiment 1. The routine shown in Fig. 6 is repeatedly executed at predetermined intervals.

[0052] In step S300, control unit 40 determines whether or not the ground fault detection information acquired from ground fault detection device 25 indicates "ground fault detected." If the ground fault detection information is not determined to indicate "ground fault detected," the process proceeds to step S360. In step S360, control unit 40 determines that ground fault detection device 25 is not malfunctioning.

[0053] If it is determined in step S300 that the ground fault detection information indicates "ground fault detected," the process proceeds to step S310. In step S310, the control unit 40 switches off both the first circuit breaker 21 and the second circuit breaker 24. Thereafter, the process proceeds to step S320.

[0054] In step S320, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If the ground fault detection information is not determined to indicate "ground fault detected," the process proceeds to step S360. In step S360, the control unit 40 determines that the ground fault detection device 25 is not malfunctioning.

[0055] If it is determined in step S320 that the ground fault detection information indicates "ground fault detected," the process proceeds to step S330. In step S330, control unit 40 switches inverter 23 of frequency conversion device 20 to the gate-blocked state. Thereafter, the process proceeds to step S340.

[0056] In step S340, the control unit 40 determines whether the ground fault detection information acquired from the ground fault detection device 25 indicates "ground fault detected." If the ground fault detection information is not determined to indicate "ground fault detected," the process proceeds to step S360. In step S360, the control unit 40 determines that the ground fault detection device 25 is not malfunctioning.

[0057] If it is determined in step S340 that the ground fault detection information indicates that a ground fault has been detected, the process proceeds to step S350. In step S350, the control unit 40 determines that the ground fault detection device 25 has malfunctioned.

[0058] 1-7. Variation 1 In the ground fault detection system 1 according to the first embodiment, when a ground fault is detected with both the first circuit breaker 21 and the second circuit breaker 24 in the OFF state, it is determined whether or not the ground fault detection device 25 has malfunctioned. According to the ground fault detection system 1 according to the first modification of the first embodiment, when the location where the above-mentioned ground fault has occurred is in the state of pattern A2 shown in FIG. 2 (i.e., the first circuit breaker 21 is in the OFF state and the second circuit breaker 24 is in the ON state), the inverter 23 of the frequency conversion device 20 is once set to a gate-blocked state, and then it is determined whether or not the ground fault detection device 25 has malfunctioned. This makes it possible to determine whether or not the ground fault detection device 25 has malfunctioned before both the first circuit breaker 21 and the second circuit breaker 24 are set to the OFF state.

[0059] 1-8. Variation 2 In the ground fault detection system 1 according to the first embodiment, in steps S100, S120, and S140 of FIG. 3, it is determined whether a ground fault has been detected based on the ground fault detection information. Similarly, in steps S200, S220, and S240 of FIG. 5, it is determined whether a ground fault has been detected based on the ground fault detection information. In each step, the ground fault detection information generated based on the neutral point voltage information is used as the criterion for determining whether a ground fault has been detected. However, the criterion does not have to be limited to the ground fault detection information generated based on the neutral point voltage information. For example, the criterion may be the ground fault detection information generated based on the ratio of the neutral point voltage to the DC voltage (neutral point voltage / DC voltage) as described in the second embodiment. Furthermore, the criterion may be different for each step. Furthermore, the criterion may be a combination of multiple pieces of ground fault detection information. In this way, according to the ground fault detection system 1 according to the second modification of the first embodiment, it is determined whether or not a ground fault has been detected based on ground fault detection information with different determination criteria for each step. This makes it possible to appropriately determine whether or not a ground fault has been detected at each step.

[0060] 2. Second Embodiment 2-1. Example of a ground fault detection system configuration FIG. 7 is a block diagram showing a configuration example of a ground fault detection system 1 according to a second embodiment. As shown in FIG. 7, a frequency conversion device 20 in the ground fault detection system 1 includes a first circuit breaker 21a, a first circuit breaker 21b, a first circuit breaker 21c, a second circuit breaker 24, a first single-phase frequency conversion unit 26, a second single-phase frequency conversion unit 27, a third single-phase frequency conversion unit 28, and a ground fault detection device 25 connected between the neutral points (neutral point voltages) of the three single-phase frequency conversion units and ground. Each single-phase frequency conversion unit includes a converter 22, a DC capacitor 29, an inverter 23, a positive-side DC line 51a, a negative-side DC line 51b, and a neutral line 51c. The inverter 23 in each single-phase frequency conversion unit may be a three-level inverter or the like. The configuration including first circuit breaker 21a, first circuit breaker 21b, and first circuit breaker 21c may be referred to as first circuit breaker 21. Furthermore, the configuration including first single-phase frequency conversion unit 26, second single-phase frequency conversion unit 27, and third single-phase frequency conversion unit 28 may be referred to as frequency conversion unit 52.

[0061] 7, a first circuit breaker 21 (i.e., first circuit breaker 21a, first circuit breaker 21b, and first circuit breaker 21c) is provided for each single-phase frequency converter. One second circuit breaker 24 may be provided on the output side of the three single-phase frequency converters, or one may be provided for each single-phase frequency converter.

[0062] As shown in FIG. 7, the power supply 10 is composed of three power supplies: power supply 10a, power supply 10b, and power supply 10c, each of which is provided for a single-phase frequency conversion unit. Power supply 10a is connected to a first circuit breaker 21a, power supply 10b is connected to a first circuit breaker 21b, and power supply 10c is connected to a first circuit breaker 21c. Power supply 10a, power supply 10b, and power supply 10c are each insulated by a transformer or the like (not shown), and each power supply may be a single-phase power supply, a three-phase power supply, or a multi-phase power supply with more than one phase. The electric motor 30 is connected to a second circuit breaker 24. An example of the electric motor 30 is a three-phase electric motor.

[0063] As shown in FIG. 7, the control unit 40 is connected to at least the first circuit breaker 21a, the first circuit breaker 21b, the first circuit breaker 21c, the second circuit breaker 24, the frequency conversion unit 52, and the ground fault detection device 25. Although not shown in FIG. 7, the control unit 40 may be connected to each of the first single-phase frequency conversion unit 26, the second single-phase frequency conversion unit 27, and the third single-phase frequency conversion unit 28. The control unit 40 has a mechanism for individually controlling the operation of the first single-phase frequency conversion unit 26, the second single-phase frequency conversion unit 27, and the third single-phase frequency conversion unit 28 (also referred to as gate deblocking). This enables the ground fault detection system 1 according to the second embodiment to more precisely determine the location of a ground fault.

[0064] 2-2. Example of determining the location of a ground fault FIG. 8 is a diagram illustrating an example of determining the location of a ground fault in the control unit 40 of the ground fault detection system 1 according to the second embodiment. The determination of the location of the ground fault shown in FIG. 8 is performed when both the first circuit breaker 21 and the second circuit breaker 24 are in the OFF state, i.e., when it is determined that the location of the ground fault is the frequency conversion device 20. Specifically, the control unit 40 calculates the ratio of the neutral point voltage to the DC voltage (neutral point voltage / DC voltage) based on the neutral point voltage acquired by the ground fault detection device 25 when the single-phase frequency conversion unit is operated individually and the DC voltage input to the single-phase frequency conversion unit. Thereafter, the control unit 40 determines whether the calculated ratio is equal to or greater than a threshold value. If it is determined that the calculated ratio is equal to or greater than the threshold value, it determines that the location of the ground fault is included in the single-phase frequency conversion unit, which is the output source of the neutral point voltage used to calculate the ratio. Note that the control unit 40 may determine the location of the ground fault using only information about the calculated ratio. For example, it may be determined that the single-phase frequency converter that is the output source of the neutral point voltage that exhibits the maximum calculated ratio includes the location where the ground fault has occurred.

[0065] Here, let us consider the DC voltage used to calculate the ratio. When the inverter 23 in each single-phase frequency conversion unit is a three-level inverter, it can be said that the DC voltage between the positive DC line 51a and the neutral conductor 51c of the DC circuit is equal to the voltage between the neutral conductor 51c and the negative DC line 51b. Therefore, the DC voltage may be based on the voltage of the positive DC circuit, the voltage of the negative DC circuit, or both the voltages of the positive DC circuit and the negative DC circuit.

[0066] In the example shown in Fig. 8, the ratios calculated when the inverter 23 in the first single-phase frequency conversion unit 26 and the inverter 23 in the second single-phase frequency conversion unit 27 are operated are both determined to be less than the threshold value, and the ratio calculated when the inverter 23 in the third single-phase frequency conversion unit 28 is operated is determined to be equal to or greater than the threshold value. In this case, it is determined that the location of the ground fault is within the third single-phase frequency conversion unit 28. The threshold value used to evaluate the calculated ratio may be, for example, a predetermined value, or, if the calculated ratio fluctuates when there is no location of a ground fault, may be the average value of the ratio in a predetermined section plus a predetermined value.

[0067] The control unit 40 may calculate the ratio in real time while the single-phase frequency converters are operating individually, or may calculate the ratio offline after the single-phase frequency converters are operating individually. The processing example described below is for the latter case.

[0068] 2-3. Processing example Fig. 9 is a flowchart showing an example of processing by the control unit 40 of the ground fault detection system 1 according to Embodiment 2. The routine shown in Fig. 9 is repeatedly executed at predetermined intervals.

[0069] In step S400, the control unit 40 acquires the neutral point voltage and the DC voltage when the inverters 23 in the three single-phase frequency conversion units are operated individually, and then the process proceeds to step S410.

[0070] In step S410, the control unit 40 calculates a ratio based on the neutral point voltage and DC voltage for each single-phase frequency conversion unit, after which the process proceeds to step S420.

[0071] In step S420, the control unit 40 determines whether the ratio of the first single-phase frequency conversion unit 26 is equal to or greater than a threshold value. If it is determined that the ratio of the first single-phase frequency conversion unit 26 is equal to or greater than the threshold value, the process proceeds to step S440. In step S440, the control unit 40 determines that the location of the ground fault is the first single-phase frequency conversion unit 26.

[0072] If it is determined in step S420 that the ratio of first single-phase frequency converter 26 is less than the threshold, the process proceeds to step S430. In step S430, control unit 40 determines whether the ratio of second single-phase frequency converter 27 is equal to or greater than the threshold. If it is determined that the ratio of second single-phase frequency converter 27 is equal to or greater than the threshold, the process proceeds to step S450. In step S450, control unit 40 determines that the location of the ground fault is second single-phase frequency converter 27.

[0073] If it is determined in step S430 that the ratio of second single-phase frequency converter 27 is less than the threshold value, the process proceeds to step S460. In step S460, control unit 40 determines that the location of the ground fault is third single-phase frequency converter .

[0074] Note that the ground fault detection system 1 according to the second embodiment may be configured in combination with the first embodiment. For example, when it is determined in step S150 of FIG. 3 shown in the first embodiment that the location of the ground fault is in frequency conversion device 20, control unit 40 may further execute steps S400 to S460 of FIG. 9 shown in the second embodiment. Furthermore, when it is determined in step S250 of FIG. 5 shown in the first embodiment that the location of the ground fault is in frequency conversion device 20, control unit 40 may further execute steps S400 to S460 of FIG. 9 shown in the second embodiment.

[0075] 3. Embodiment 3 In the ground fault detection systems 1 according to the first and second embodiments, the ground fault detection device 25 determines whether or not a ground fault has been detected based on the voltage value between the neutral point voltage and the ground. In the ground fault detection system 1 according to the third embodiment, the value of the current flowing between the neutral point (or neutral wire) and the ground point is measured, and whether or not a ground fault has been detected is determined based on the current value. This makes it possible for the ground fault detection device 25 to detect a ground fault even if the current value is abnormal.

[0076] 4. Embodiment 4 In the ground fault detection systems 1 according to the first and second embodiments, the first circuit breaker 21 and the second circuit breaker 24 are configured to be included inside the frequency conversion device 20. However, the first circuit breaker 21 and the second circuit breaker 24 may be configured external to the frequency conversion device 20. According to the ground fault detection system 1 according to the third embodiment, the frequency conversion device 20 has a minimal configuration that does not include the first circuit breaker 21 and the second circuit breaker 24. This makes it possible to shorten the time required to identify whether the location of the ground fault is the frequency conversion device 20.

[0077] 5. Embodiment 5 The ground fault detection system 1 according to the fifth embodiment may have a configuration that combines the first and third process examples in the first embodiment described above, or a configuration that combines the second and third process examples in the first embodiment described above. In the former case, for example, the control unit 40 may execute steps S330 to S360 in FIG. 6 that illustrate the third process example instead of step S150 in FIG. 3 that illustrates the first process example. In the latter case, for example, the control unit 40 may execute steps S330 to S360 in FIG. 6 that illustrate the third process example instead of step S250 in FIG. 5 that illustrates the second process example. In these configurations, if the control unit 40 determines that the ground fault is not due to a malfunction of the ground fault detection device 25 (step S360), it further determines that the location of the ground fault is the frequency conversion device 20. This makes it possible to appropriately determine whether the cause of the ground fault detection by the ground fault detection device 25 is a malfunction of the ground fault detection device 25 or the location of the ground fault. [Explanation of symbols]

[0078] 1. Ground fault detection system 10 Power supply 20 Frequency conversion device 21 First Circuit Breaker 22 Converter 23 Inverter 24 Second circuit breaker 25 Earth fault detection device 26 First single-phase frequency converter 27 Second single-phase frequency converter 28 Third single-phase frequency converter 29 DC capacitor 30 Electric motor 40 Control Unit 51a Positive DC line 51b Negative side DC line 51c neutral wire 52 Frequency conversion section

Claims

1. a frequency conversion device; a first circuit breaker provided on an input side of the frequency conversion device, for connecting or disconnecting a power source supplied to the frequency conversion device and the frequency conversion device; a second circuit breaker provided on the output side of the frequency conversion device, for connecting or disconnecting between the frequency conversion device and a load driven by the frequency conversion device; a ground fault detection device connected between a neutral point voltage indicating a voltage at a neutral point of the frequency conversion device and ground and detecting whether a ground fault has occurred based on the neutral point voltage; a control unit connected to at least the first circuit breaker, the second circuit breaker, and the ground fault detection device; Equipped with The control unit When a ground fault is detected by the ground fault detection device, the first circuit breaker is switched OFF while the second circuit breaker is kept ON so as to cut off the connection between the frequency conversion device and the power source while maintaining the connection between the frequency conversion device and the load; When the ground fault detection device does not detect a ground fault in a state in which the first circuit breaker is OFF and the second circuit breaker is ON, the location of the ground fault is determined to be outside the first circuit breaker. Ground fault detection system.

2. 2. The ground fault detection system according to claim 1, The control unit when a ground fault is detected by the ground fault detection device in a state in which the first circuit breaker is OFF and the second circuit breaker is ON, switching the second circuit breaker OFF to disconnect the frequency conversion device from the load; When a ground fault is detected by the ground fault detection device in a state in which the first circuit breaker and the second circuit breaker are both OFF, the location of the ground fault is determined to be the frequency conversion device; When the ground fault is not detected by the ground fault detection device in a state in which the first circuit breaker and the second circuit breaker are both OFF, the occurrence location of the ground fault is determined to be outside the second circuit breaker. Ground fault detection system.

3. a frequency conversion device; a first circuit breaker provided on an input side of the frequency conversion device, for connecting or disconnecting a power source supplied to the frequency conversion device and the frequency conversion device; a second circuit breaker provided on the output side of the frequency conversion device, for connecting or disconnecting between the frequency conversion device and a load driven by the frequency conversion device; a ground fault detection device connected between a neutral point voltage indicating a voltage at a neutral point of the frequency conversion device and ground and detecting whether a ground fault has occurred based on the neutral point voltage; a control unit connected to at least the first circuit breaker, the second circuit breaker, and the ground fault detection device; Equipped with The control unit When a ground fault is detected by the ground fault detection device, the connection between the frequency conversion device and the power source is interrupted, and both the first circuit breaker and the second circuit breaker are switched OFF to interrupt the connection between the frequency conversion device and the load; When the ground fault detection device does not detect a ground fault while the first circuit breaker and the second circuit breaker are both OFF, switching the second circuit breaker ON to connect the frequency conversion device and the load; When a ground fault is detected by the ground fault detection device in a state in which the first circuit breaker is OFF and the second circuit breaker is ON, the occurrence location of the ground fault is determined to be outside the second circuit breaker, When the ground fault is not detected by the ground fault detection device in a state where the first circuit breaker is OFF and the second circuit breaker is ON, the occurrence location of the ground fault is determined to be outside the first circuit breaker. Ground fault detection system.

4. 4. The ground fault detection system according to claim 1, The frequency conversion device is composed of three single-phase frequency conversion units, Each of the three single-phase frequency conversion units includes a converter that converts an input AC voltage into a DC voltage, and an inverter that converts the DC voltage into an output AC voltage, the ground fault detection device is connected between the output sides of the three single-phase frequency conversion units and the ground; The control unit If it is determined that the ground fault occurs in the frequency conversion device, Calculating a ratio between each of three neutral point voltages or currents flowing between the neutral point and the ground point, which are acquired when the three single-phase frequency conversion units are operated individually, and the DC voltage; and determining that the single-phase frequency converter that is the output source of the neutral point voltage for which the ratio is equal to or greater than the threshold value includes a location where a ground fault has occurred. Ground fault detection system.

5. 4. The ground fault detection system according to claim 1, The frequency conversion device is composed of three single-phase frequency conversion units, Each of the three single-phase frequency conversion units includes a converter that converts an input AC voltage into a DC voltage, and an inverter that converts the DC voltage into an output AC voltage, the ground fault detection device is connected between the output sides of the three single-phase frequency conversion units and the ground; The control unit If it is determined that the ground fault occurs in the frequency conversion device, Calculating a ratio between each of three neutral point voltages or currents flowing between the neutral point and the ground point, which are acquired when the three single-phase frequency conversion units are operated individually, and the DC voltage; It is configured to determine that the location of the earth fault is included in the single-phase frequency conversion unit that is the output source of the neutral point voltage for which the ratio is maximum. Ground fault detection system.

6. 4. The ground fault detection system according to claim 1, The frequency conversion device is composed of three single-phase frequency conversion units, Each of the three single-phase frequency conversion units includes a converter that converts an input AC voltage into a DC voltage, and an inverter that converts the DC voltage into an output AC voltage, The control unit When a ground fault is detected by the ground fault detection device in a state in which the first circuit breaker and the second circuit breaker are both OFF, the inverter is put into a gate blocked state; When the ground fault is detected by the ground fault detection device while the inverter is in the gate-blocked state, it is determined that the ground fault detection device has malfunctioned. Ground fault detection system.

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