Short circuit detector and short circuit detection method of power supply system

Abstract

To provide a short circuit detector and a short circuit detection method capable of accurately detecting a short circuit of a wiring to a power load in a power supply system regardless of magnitude of supply power for each power load.SOLUTION: A short circuit detector includes, in each of a plurality of load units 4, a plurality of measurement units 5 that measure a voltage value and a current value between a transformer 41 and a bus 2, and a short circuit detection unit 8 that detects a short circuit between the transformer 41 and a power load 42 in each of the plurality of load units 4. The short circuit detection unit 8 calculates, for each of the plurality of load units 4, an overload rate with respect to a rated load of the transformer 41 from the voltage value and the current value measured by the plurality of measurement units 5, and uses the fact that the overload rate exceeds a threshold value determined for each load unit 4 for the short circuit determination between the transformer 41 and the power load 42 of the load unit 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a short-circuit detection device and a short-circuit detection method for a power supply system.

Background Art

[0002] Patent Document 1 discloses a protection device for coping with a short-circuit accident in a power supply system. This protection device includes a harmonic supply means, a current measurement means, a voltage measurement means, a current component extraction means, a voltage component extraction means, a calculation means, and a determination means. The harmonic supply means supplies a harmonic having a frequency higher than a predetermined frequency to a bus to which an AC voltage of a predetermined frequency is supplied. The current measurement means measures the current value of a distribution line connected to the bus. The voltage measurement means measures the voltage value of the bus or the distribution line. The current component extraction means extracts a current component, which is a Fourier coefficient of the harmonic, from the time-varying waveform of the current value measured by the current measurement means. The voltage component extraction means extracts a voltage component, which is a Fourier coefficient of the harmonic, from the time-varying waveform of the voltage value measured by the voltage measurement means. The calculation means calculates an impedance or an admittance as a calculated value from the current component extracted by the current component extraction means and the voltage component extracted by the voltage component extraction means. The determination means determines whether or not a short-circuit accident has occurred in the distribution line based on the calculated value.

[0003] Patent Document 2 discloses a protection device and a protection method for a power distribution system with an inverter as the main power source. This protection device is a protection device that detects and protects against a short-circuit accident in a power distribution system in which an inverter as the main power source is connected to a bus. This protection device takes as inputs a bus voltage detection signal obtained by detecting the voltage of the bus and distribution line current detection signals obtained by detecting the currents flowing through a plurality of distribution lines connected to the bus. This protection device includes a first protection element, a second protection element, and a third protection element. The first protection element operates with a time limit only when the logical product of the output of a first overcurrent relay set to a current value at which the inverter can operate without stopping due to overcurrent and the output of an under-voltage relay that detects a decrease in the line-to-line voltage of the plurality of distribution lines is established. The second protection element has an instantaneous element of a second overcurrent relay and operates instantaneously when the input current exceeds the set overcurrent level. The third protection element has a time-limit element of the second overcurrent relay and operates with a time limit when the input current exceeds the set overcurrent level. This protection device determines that there is a short-circuit accident when the logical sum condition of the operations of the first to third protection elements is satisfied.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, a microgrid is known as one form of the power supply system. A microgrid is a small-scale power supply system that integrates power generation, storage, distribution, and consumption within a certain area. The microgrid combines renewable energy sources such as solar power generation or wind power generation, energy storage devices, and diesel generators to provide stable power supply to specific areas or facilities. In addition, the microgrid can be operated independently of the large-scale power grid and can continue to supply power even when the power grid stops due to disasters or the like. Furthermore, the microgrid can contribute to the efficient use of power, energy conservation, and reduction of CO 2 emissions by adjusting the power supply and demand balance within the area.

[0006] For example, in a power supply system such as the above microgrid, power is supplied from a bus connected to a power supply device to power loads such as electrical equipment connected to each distribution line via a plurality of distribution lines. Conventionally, in such a power supply system, when a short circuit occurs in any of the distribution lines, the distribution line is cut off by an overcurrent relay provided in the distribution line where the short circuit has occurred, thereby protecting other parts of the power supply system.

[0007] However, since the power consumption usually differs for each power load, the magnitude of the power supplied to each distribution line also differs for each distribution line. When detecting a short circuit based only on the magnitude of the current flowing through the distribution line, even if a short circuit occurs in a distribution line with a small normal supply power, the current flowing through that distribution line may only be equivalent to the current flowing through a distribution line with a large normal supply power. Therefore, there is a risk that it may be difficult to accurately detect a short circuit in a distribution line with a small normal supply power.

[0008] The present disclosure has been made in view of such problems, and an object thereof is to provide a short circuit detection device and a short circuit detection method capable of accurately detecting a short circuit in the wiring to a power load in a power supply system regardless of the magnitude of the supply power for each power load.

Means for Solving the Problems

[0009] [1] The short-circuit detection device according to the present disclosure is a short-circuit detection device provided in a power supply system. The power supply system includes a power supply unit having an AC output power supply device connected to a bus, and a plurality of load units each having a transformer connected to the bus and a power load connected to the bus via the transformer. The rated loads of the transformers of at least two of the plurality of load units are different from each other. The short-circuit detection device includes a plurality of measurement units and a short-circuit detection unit. The plurality of measurement units measure the voltage value and the current value between the transformer and the bus in each of the plurality of load units. The short-circuit detection unit detects a short circuit between the transformer and the power load in each of the plurality of load units. The short-circuit detection unit calculates, for each of the plurality of load units, an overload rate with respect to the rated load of the transformer from the voltage value and the current value measured by the plurality of measurement units. The short-circuit detection unit uses the fact that the overload rate has exceeded a threshold value determined for each load unit for the short-circuit determination between the transformer and the power load of the load unit.

[0010] In the short-circuit detection device of the above [1], the overload rate with respect to the rated load of the transformer is calculated for each of the plurality of load units, and the fact that the overload rate has exceeded a threshold value determined for each load unit is used for the short-circuit determination between the transformer and the power load in that load unit. In this way, by determining a short circuit based on the overload rate of the transformer, it is possible to accurately detect a short circuit regardless of the magnitude of the supply power for each load unit.

[0011] [2] The short-circuit detection device of [1] may further include an inspection signal supply unit and a first measurement unit. The inspection signal supply unit has an AC output current source connected to the bus, and outputs an inspection signal having a frequency different from the frequency of the AC power output from the AC output power supply device from the AC output current source. The first measurement unit is provided separately from the plurality of measurement units. And the power supply unit further has a transformer, the AC output power supply device is connected to the bus via the transformer, the first measurement unit measures the voltage value and current value of the inspection signal between the transformer and the bus in the power supply unit, and the short-circuit detection unit calculates the overload rate with respect to the rated load of the transformer of the power supply unit from the voltage value and current value measured by the first measurement unit, and when the overload rate exceeds a threshold value defined for the power supply unit, it may be determined that a short circuit has occurred between the transformer of the power supply unit and the AC output power supply device. According to this short-circuit detection device, even when a short circuit occurs between the transformer of the power supply unit and the AC output power supply device, the short circuit can be accurately detected.

[0012] [3] In the short-circuit detection device of [1], when the overload rate exceeds the threshold value over a certain duration, the short-circuit detection unit determines that a short circuit has occurred between the transformer and the power load, and the duration may be set to be longer as the current value is smaller and longer as the overload rate is smaller. In that case, even when the current and overload caused by the short circuit are small, the short circuit can be accurately detected over time.

[0013] [4] The short - circuit detection method according to the present disclosure is a short - circuit detection method used in a power supply system. The power supply system includes a power supply unit having an AC output power supply device connected to a bus, and a plurality of load units each having a transformer connected to the bus and a power load connected to the bus via the transformer. The rated loads of the transformers of at least two of the plurality of load units are different from each other. This short - circuit detection method includes a measurement step and a short - circuit detection step. In the measurement step, in each of the plurality of load units, the voltage value and the current value between the transformer and the bus are measured. In the short - circuit detection step, a short - circuit between the transformer and the power load in each of the plurality of load units is detected. In the short - circuit detection step, from the voltage value and the current value measured in the measurement step, the overload ratio with respect to the rated load of the transformer is calculated for each of the plurality of load units. In the short - circuit detection step, the fact that the overload ratio exceeds a threshold value determined for each load unit is used for the short - circuit determination between the transformer and the power load of the corresponding load unit. According to this short - circuit detection method of [4], similar to the short - circuit detection device of [1] above, regardless of the magnitude of the supply power for each load unit, a short - circuit can be accurately detected.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to provide a short - circuit detection device and a short - circuit detection method capable of accurately detecting a short - circuit in the wiring to a power load in a power supply system regardless of the magnitude of the supply power for each power load.

Brief Description of the Drawings

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[0016] Hereinafter, embodiments of the short - circuit detection device and the short - circuit detection method according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] FIG. 1 is a diagram schematically showing the configuration of a power supply system 1 including a short-circuit detection device according to an embodiment of the present disclosure. The power supply system 1 constitutes a microgrid. As shown in FIG. 1, the power supply system 1 includes a bus 2, a power supply unit 3, and a plurality of load units 4. The bus 2 is a wiring for sending the power output from the power supply unit 3 to the plurality of load units 4.

[0018] The power supply unit 3 is connected to the bus 2. The power supply unit 3 includes a transformer 31 and an AC output power supply device 32. The AC output power supply device 32 is connected to the bus 2 via the transformer 31. That is, the primary coil of the transformer 31 is connected to the AC output power supply device 32 via a feeder line 33, and the secondary coil of the transformer 31 is connected to the bus 2 via a feeder line 34. The AC output power supply device 32 includes, for example, a power source such as a renewable energy source such as a solar cell or a storage battery, and an inverter connected to the power source and converting the DC power output from the power source into AC power. The frequency (fundamental frequency) of the AC power P output from the AC output power supply device 32 is, for example, 50 Hz or 60 Hz.

[0019] The plurality of load units 4 are connected to the bus 2 in parallel with each other. Each load unit 4 includes a transformer 41 and a power load 42. The power load 42 is a power load such as electrical equipment provided for each consumer. The power load 42 includes a capacitor, a rectifier, a motor, and the like. The power load 42 is connected to the bus 2 via the transformer 41. That is, the primary coil of the transformer 41 is connected to the bus 2 via a distribution line 43, and the secondary coil of the transformer 41 is connected to the power load 42 via a distribution line 44. The rated loads of the transformers 41 of at least two of the plurality of load units 4 are different from each other. In one example, the rated load of the transformer 41 of a certain load unit 4 is 400 kVA, and the rated load of the transformer 41 of another load unit 4 is 100 kVA. Thus, the rated load of the transformer 41 of a certain load unit 4 may be four times or more the rated load of the transformer 41 of another load unit 4.

[0020] The short-circuit detection device of this embodiment includes a plurality of measurement units 5 provided in each of a plurality of load units 4, a measurement unit 6 (first measurement unit) provided separately from the plurality of measurement units 5, an inspection signal supply unit 7, and a short-circuit detection unit 8 and a measurement unit 9.

[0021] Each measurement unit 5 is provided on a power distribution line 43 between a transformer 41 and a bus 2 in the corresponding load unit 4, and measures the voltage value and current value on the power distribution line 43. That is, each measurement unit 5 includes a voltage measuring device that measures the voltage value of the power distribution line 43 and a current measuring device that measures the current value of the power distribution line 43. The measurement unit 6 is provided on a power supply line 34 between a transformer 31 and a bus 2 in the power supply unit 3, and measures the voltage value and current value on the power supply line 34. That is, the measurement unit 6 includes a voltage measuring device that measures the voltage value of the power supply line 34 and a current measuring device that measures the current value of the power supply line 34. In the case of three-phase AC power, the voltage values and current values detected by the measurement unit 5 and the measurement unit 6 are the voltage values and current values of at least one of the three phases.

[0022] The inspection signal supply unit 7 is connected to the bus 2 in parallel with the power supply unit 3 and the plurality of load units 4. The inspection signal supply unit 7 has a transformer 71 and an AC output current source 72. The AC output current source 72 is connected to the bus 2 via the transformer 71. That is, the primary coil of the transformer 71 is connected to the AC output current source 72 via a power supply line 73, and the secondary coil of the transformer 71 is connected to the bus 2 via a power supply line 74. The AC output current source 72 outputs an inspection signal S. The frequency (non-fundamental frequency) of the inspection signal S is different from the frequency (fundamental frequency) of the AC power P output from the AC output power supply device 32. The inspection signal S is, for example, a harmonic of the fundamental frequency. The frequency of the inspection signal S may be higher or lower than the frequency of the AC power P.

[0023] The measuring unit 9 is provided on the power supply line 74 between the transformer 71 and the bus bar 2 in the inspection signal supply unit 7, and measures the voltage value and the current value in the power supply line 74. That is, the measuring unit 9 includes a voltage measuring device that measures the voltage value of the power supply line 74 and a current measuring device that measures the current value of the power supply line 74.

[0024] The short-circuit detection unit 8 detects a short circuit in the wiring (power distribution line 44) between the transformer 41 and the power load 42 in each of the plurality of load units 4. More specifically, the short-circuit detection unit 8 includes a plurality of portions 8A provided in each of the plurality of load units 4, and calculates, for each of the plurality of load units 4 and for each portion 8A, the overload rate with respect to the rated load of the transformer 41 from the voltage value and the current value measured by the measuring unit 5. Then, each portion 8A of the short-circuit detection unit 8 uses the fact that the overload rate has exceeded the threshold value determined for each load unit 4 for the short-circuit determination between the transformer 41 and the power load 42 of that load unit 4.

[0025] At this time, each portion 8A of the short-circuit detection unit 8 determines that a short circuit has occurred between the transformer 41 and the power load 42 when the overload rate has exceeded the threshold value for a certain duration. The duration is set to be longer as the current value is smaller and longer as the overload rate is smaller. The duration will be described later.

[0026] In addition, the short-circuit detection unit 8 detects a short circuit in the wiring (power supply line 33) between the transformer 31 and the AC output power supply device 32 in the power supply unit 3. More specifically, the short-circuit detection unit 8 includes a portion 8B provided in the power supply unit 3, and calculates, in the portion 8B, the overload rate with respect to the rated load of the transformer 31 from the voltage value and the current value measured by the measuring unit 6. Then, the portion 8B of the short-circuit detection unit 8 uses the fact that the overload rate has exceeded the threshold value determined for the power supply unit 3 for the short-circuit determination between the transformer 31 and the AC output power supply device 32.

[0027] In addition, the short-circuit detection unit 8 detects a short circuit in the wiring (power supply line 73) between the transformer 71 and the AC output current source 72 in the test signal supply unit 7. More specifically, the short-circuit detection unit 8 is configured to include a portion 8C provided in the test signal supply unit 7, and calculates, in the portion 8C, the overload rate with respect to the rated load of the transformer 71 from the voltage value and the current value measured by the measurement unit 9. Then, the portion 8C of the short-circuit detection unit 8 uses the fact that the overload rate has exceeded the threshold value defined for the test signal supply unit 7 for the short-circuit determination between the transformer 71 and the AC output current source 72.

[0028] Figure 2 is a diagram schematically showing several forms in which a short circuit occurs. Fig. 2(a) shows the case where short circuits A1 and A2 occur in the power distribution line 44 of a certain load unit 4 and the power supply line 73 of the test signal supply unit 7. In that case, since the power supply unit 3 supplies the currents B1 and B2 that rapidly increase due to the short circuits A1 and A2, each of the measurement unit 5 and the measurement unit 9 can measure the current value and the voltage value in the power distribution line 43 and the power supply line 74, respectively. Therefore, the short-circuit detection unit 8 can detect these short circuits A1 and A2. Fig. 2(b) shows the case where a short circuit A3 occurs in the power supply line 33 of a certain power supply unit 3 when a plurality of power supply units 3 are provided. In that case, since another power supply unit 3 supplies the current B3 that rapidly increases due to the short circuit A3, the measurement unit 6 of the power supply unit 3 in which the short circuit A3 has occurred can measure the current value and the voltage value in the power supply line 34. Therefore, the short-circuit detection unit 8 can also detect the short circuit A3. Fig. 2(c) shows the case where a short circuit A4 occurs in the power supply line 33 of the power supply unit 3 when only one power supply unit 3 is provided. In that case, since the test signal supply unit 7 supplies the current B4 that rapidly increases due to the short circuit A4, the measurement unit 6 can measure the current value and the voltage value in the power supply line 34. Therefore, the short-circuit detection unit 8 can also detect the short circuit A4.

[0029] FIG. 3 is a block diagram showing the detailed configuration of portions 8A, 8B, and 8C of the short-circuit detection unit 8. As shown in FIG. 3, portions 8A, 8B, and 8C of the short-circuit detection unit 8 include fundamental wave extraction filters 81, 83 and non-fundamental wave extraction filters 82, 84. Further, portions 8A, 8B, and 8C of the short-circuit detection unit 8 include a voltage drop determination unit 85, a power flow direction determination unit 86, an overload determination unit 87, a current determination unit 88, an overload determination unit 89, and determination units 90A, 90B.

[0030] The voltage measurement value V1 input from each of the measurement units 5, 6, and 9 to each of the portions 8A, 8B, and 8C of the short-circuit detection unit 8 is input to the fundamental wave extraction filter 81 and the non-fundamental wave extraction filter 82. The fundamental wave extraction filter 81 extracts a fundamental wave component V2 having a fundamental frequency (in other words, a component caused by the AC power P) from the voltage measurement value V1. The non-fundamental wave extraction filter 82 extracts a non-fundamental wave component V3 having a non-fundamental frequency (in other words, a component caused by the inspection signal S) from the voltage measurement value V1. Also, the current measurement value J1 input from each of the measurement units 5, 6, and 9 to each of the portions 8A, 8B, and 8C of the short-circuit detection unit 8 is input to the fundamental wave extraction filter 83 and the non-fundamental wave extraction filter 84. The fundamental wave extraction filter 83 extracts a fundamental wave component J2 having a fundamental frequency (in other words, a component caused by the AC power P) from the current measurement value J1. The non-fundamental wave extraction filter 82 extracts a non-fundamental wave component J3 having a non-fundamental frequency (in other words, a component caused by the inspection signal S) from the current measurement value J1.

[0031] The voltage drop determination unit 85 compares the magnitude of the fundamental wave component V2 with a threshold value, and determines that there is a voltage drop when the fundamental wave component V2 is smaller than the threshold value. The power flow direction determination unit 86 determines that the current direction is different from normal based on the value obtained by dividing the fundamental wave component J2 from the fundamental wave component V2 (V2 / J2), that is, the impedance R. For example, when the impedance R is positive, the power flow direction determination unit 86 determines that the current direction is different from normal. The overload determination unit 87 calculates the overload rate from the fundamental wave component V2 and the fundamental wave component J2, and determines that there is an overload when the overload rate is greater than the threshold value. The overload determination unit 89 calculates the overload rate from the non-fundamental wave component V3 and the non-fundamental wave component J3, and determines that there is an overload when the overload rate is greater than the threshold value. The calculation methods of the overload rates are different between the overload determination unit 87 and the overload determination unit 89. In the overload determination unit 87, when the product of the current value flowing through the transformer and the voltage value is Y, and the rated capacity of the transformer is 100%Y, the overload rate is expressed as Y / 100%Y (pu). 0 pu indicates no load, and 1 pu indicates the rated load. When it exceeds 1 pu, it is an overload. The maximum load is, for example, 1 / %Z. As an example, when %Z = 4%, the maximum load is 25 pu. The threshold value of the overload rate is, for example, 1 pu. Also, in the overload determination unit 89, when Y≧0, the overload rate is expressed as Y / (100%Y×h) (pu). When Y<0, the overload rate is expressed as Y / (100%Y / h) (pu). Alternatively, regardless of the magnitude of Y, the overload rate may be expressed as X / (100%X / h) (pu). Note that h is the order of the non-fundamental wave. The threshold value of the overload rate is, for example, 1 pu.

[0032] The determination unit 90A determines that a short circuit has occurred when the state in which the voltage drop determination unit 85 determines a voltage drop, the power flow direction determination unit 86 determines that the current direction is different from normal, and the overload determination unit 87 determines an overload continues for a certain duration T'. Further, the determination unit 90B determines that a short circuit has occurred when the state in which the voltage drop determination unit 85 determines a voltage drop, the current determination unit 88 determines an overcurrent, and the overload determination unit 89 determines an overload continues for a certain duration T'. When it is determined that a short circuit has occurred in either of the determination units 90A and 90B, the portions 8A, 8B, and 8C of the short circuit detection unit 8 determine that a short circuit has occurred.

[0033] Figure 4 is a graph for explaining the duration. Figure 4(a) shows the relationship between the current value and the basic duration T. Jmax in the figure represents the maximum value of the current supply amount by the inverter of the AC output power supply device 32. As shown in Figure 4(a), the basic duration T is set longer as the current value of the fundamental wave component J2 is smaller. Further, Figure 4(b) shows the relationship between the magnification N with respect to the basic duration T calculated from the relationship in Figure 4(a) and the overload rate. The magnification N with respect to the basic duration T is set larger as the overload rate is smaller, and N = 1 / %Z when the overload rate is 1 (i.e., in the rated load state). Therefore, the final duration T' = T × N has the characteristic (inverse time limit characteristic) of being set longer as the current value is smaller and being set longer as the overload rate is smaller. Note that %Z is the impedance of the corresponding transformer 31, 41, or 71. The final duration T' is, for example, 10 milliseconds. In this way, the determination units 90A and 90B input the current value of the fundamental wave component J2 and the overload rate (arrows C1 and C2 in Figure 3) and determine the duration T' based on them. Note that the duration T' of the determination unit 90B may be set to be constant regardless of the current value of the fundamental wave component J2 and the overload rate.

[0034] FIG. 5 is a diagram showing the internal configuration of the determination unit 90A. The determination unit 90A includes a counter 91, an amplitude calculation unit 92, a duration setting unit 93, a magnification calculation unit 94, a multiplication unit 95, a comparison unit 96, and a determination unit 97. The counter 91 counts a signal E (see FIG. 3) indicating that the voltage drop determination unit 85 determines a voltage drop, the power flow direction determination unit 86 determines that the current direction is different from normal, and the overload determination unit 87 determines an overload. The amplitude calculation unit 92 calculates the amplitude of the fundamental wave component J2 of the current. The duration setting unit 93 sets the basic duration T based on the amplitude of the fundamental wave component J2 (i.e., the current amount of the AC power P) and the relationship shown in FIG. 4(a). The magnification calculation unit 94 inputs the reciprocal of the impedance of the transformer (1 / %Z) and the overload rate (Y / 100%Y), and calculates the magnification N based on these. The multiplication unit 95 calculates the final duration T' by obtaining the product of the basic duration T and the magnification N. The comparison unit 96 compares the output from the counter 91 with a threshold value over the duration T'. The determination unit 97 determines that a short circuit has occurred when the output from the counter 91 is greater than the threshold value over the duration T'.

[0035] FIG. 6 is a flowchart showing a short circuit detection method according to an embodiment. This short circuit detection method can be preferably implemented using the above-described short circuit detection device. As shown in FIG. 6, the short circuit detection method includes an inspection signal supply step ST1, a measurement step ST2, and a short circuit detection step ST3.

[0036] In the inspection signal supply step ST1, an inspection signal S having a frequency different from the frequency of the AC power P output from the AC output power supply device 32 is output from the AC output current source 72 to the bus 2. In the measurement step ST2, at each of the plurality of load units 4, the voltage value and current value between the transformer 41 and the bus 2 are measured by each measurement unit 5. In addition, in the measurement step ST2, in the power supply unit 3, the voltage value and current value of the inspection signal S between the transformer 31 and the bus 2 are measured by the measurement unit 6. Further, in the measurement step ST2, in the inspection signal supply unit 7, the voltage value and current value between the transformer 71 and the bus 2 are measured by the measurement unit 9.

[0037] In the short-circuit detection step ST3, a short circuit between the transformer 41 and the power load 42 in each of the plurality of load units 4 is detected. Specifically, from the AC power P measured by the measurement unit 5 and the voltage value and current value of the inspection signal S, the overload ratio with respect to the rated load of the transformer 41 is calculated for each of the plurality of load units 4 for each frequency of the AC power P and the inspection signal S. Then, the fact that the overload ratio exceeds the threshold value determined for each load unit 4 is used for the short-circuit determination between the transformer 41 and the power load 42 of the load unit 4. In addition, in the short-circuit detection step ST3, from the voltage value and current value of the inspection signal S measured by the measurement unit 6, the overload ratio with respect to the rated load of the transformer 31 of the power supply unit 3 is calculated. Then, the fact that the overload ratio exceeds the threshold value determined for the power supply unit 3 is used for the short-circuit determination between the transformer 31 and the AC output power supply device 32 of the power supply unit 3. Further, in the short-circuit detection step ST3, from the voltage value and current value of the AC power P measured by the measurement unit 9, the overload ratio with respect to the rated load of the transformer 71 of the inspection signal supply unit 7 is calculated. Then, the fact that the overload ratio exceeds the threshold value determined for the inspection signal supply unit 7 is used for the short-circuit determination between the transformer 71 and the AC output current source 72 of the inspection signal supply unit 7.

[0038] The effects obtained by the short - circuit detection device and the short - circuit detection method according to the present embodiment described above will be described together with the conventional problems. FIG. 7 is a diagram for explaining conventional problems, and shows a simplified configuration of a conventional power supply system 100. As shown in FIG. 7, the conventional power supply system 100 includes a bus 102, a power supply unit 103 connected to the bus 102, and a plurality of load units 104A and 104B connected to the bus 102. Each of the load units 104A and 104B has a single - stage or multi - stage transformer 141 and one or more power loads 142. The number of power loads 142 represents the magnitude of the power load in that load unit. The smaller the power load 142, the greater the number of stages of the transformer 141. Immediately before each transformer 141, a current detection unit 143 is connected. Assume that the rated output current of the power supply unit 103 is 500 kW, the power load of the load unit 104A is 300 kW, the rated capacity of the transformer 141 in the load unit 104A is 400 kVA, and the impedance of the transformer 141 is 5%. At this time, a current 0.6 times the rated current of the power supply unit 103 is supplied to the load unit 104A. Also, assume that the rated capacity of the first - stage transformer 141 in the load unit 104B is 100 kVA, the impedance is 5%, the rated capacity of the second - stage transformer 141 in the load unit 104B is 15 kVA, and the impedance is 5%.

[0039] Now, assume that a short - circuit A5 occurs in the load unit 104B with a small power load. At this time, since 15 kVA / 5% = 300 kVA, a current 0.6 times the rated current of the power supply unit 103 also flows into the load unit 104B. FIG. 8 is a graph showing the time variations of the load voltage common to the load units 104A and 104B (FIG. 8(a)), the current value of the load unit 104A (FIG. 8(b)), the current value of the load unit 104B (FIG. 8(c)), and the output current value of the power supply unit 103 (FIG. 8(d)). The timing D1 in the figure is the occurrence timing of the short - circuit A5. As shown in FIG. 8, in the load unit 104B, the current value increases significantly due to the occurrence of the short - circuit A5. However, even after the occurrence of the short - circuit A5, the current value of the load unit 104B is almost no different from the current value of the load unit 104A. Therefore, it is difficult to identify the load unit in which the short - circuit has occurred.

[0040] In response to this problem, in the present embodiment, the overload rate with respect to the rated load of the transformer 41 is calculated for each of the plurality of load units 4, and it is determined that the overload rate has exceeded the threshold value defined for each load unit 4, and this is used for the short-circuit determination between the transformer 41 and the power load 42 in that load unit 4. In this way, by determining a short circuit based on the overload rate of the transformer 41, it is possible to accurately detect a short circuit regardless of the magnitude of the supplied power for each load unit 4. Similarly, even when a short circuit occurs between the transformer 31 of the power supply unit 3 and the AC output power supply device 32, or when a short circuit occurs between the transformer 71 of the inspection signal supply unit 7 and the AC output current source 72, the short circuit can be accurately detected.

[0041] The operation simulation of the short-circuit detection device according to the present embodiment will be described. FIG. 9 is a graph showing the simulation results regarding the time changes of the line voltage common to the plurality of load units 4 (FIG. 9(a)), the current value of a certain load unit 4 with a large power load (FIG. 9(b)), the current value of another load unit 4 with a small power load (FIG. 9(c)), and the output current value of the power supply unit 3 (FIG. 9(d)). In this simulation, it is assumed that a short circuit has occurred in the load unit 4 with a small power load. The timing D2 in the figure is the occurrence timing of the short circuit in the load unit 4 with a small power load. The timing D3 is the release (cut-off) timing of the load unit 4 in which the short circuit has occurred.

[0042] FIGS. 10 to 13 are graphs showing (a) the time waveform of the voltage value, (b) the time waveform of the current value, (c) the time waveform of the overload rate, and (d) the logical product of these determination results in the same simulation. FIG. 10 shows the results obtained from the voltage value and the current value of the AC power P in the power supply unit 3. FIG. 11 shows the results obtained from the voltage value and the current value of the AC power P in the load unit 4 with a large power load. FIG. 12 shows the results obtained from the voltage value and the current value of the AC power P in the load unit 4 with a small power load. FIG. 13 shows the results obtained from the voltage value and the current value of the inspection signal S in the power supply unit 3.

[0043] As shown in FIGS. 10 to 13, when a short circuit occurs in the load section 4 with a small power load, the power supply section 3 and the load section 4 with a large power load are not determined to have a short circuit, and the load section 4 with a small power load is accurately determined to have a short circuit.

[0044] Further, FIG. 14 is a graph showing another simulation result regarding the time change of the system voltage (FIG. 14(a)) common to a plurality of load sections 4, the current value of a certain load section 4 with a large power load (FIG. 14(b)), the current value of another load section 4 with a small power load (FIG. 14(c)), and the output current value of the power supply section 3 (FIG. 14(d)). In this simulation, it is assumed that a short circuit has occurred in the power supply section 3. The timing D2 in the figure is the occurrence timing of the short circuit in the power supply section 3. The timing D3 is the release (cut-off) timing of the power supply section 3.

[0045] FIGS. 15 to 18 are graphs showing (a) the time waveform of the voltage value, (b) the time waveform of the current value, (c) the time waveform of the overload rate, and (d) the logical product of these determination results in the same simulation. FIG. 15 shows the results obtained from the voltage value and the current value of the AC power P in the power supply section 3. FIG. 16 shows the results obtained from the voltage value and the current value of the AC power P in the load section 4 with a large power load. FIG. 17 shows the results obtained from the voltage value and the current value of the AC power P in the load section 4 with a small power load. FIG. 18 shows the results obtained from the voltage value and the current value of the inspection signal S in the power supply section 3.

[0046] As shown in FIGS. 15 to 18, when a short circuit occurs in the power supply section 3, each load section 4 is not determined to have a short circuit, and based on the voltage value and the current value of the inspection signal S, the power supply section 3 is accurately determined to have a short circuit.

[0047] As in this embodiment, the duration T' for determining that the overload rate exceeds the threshold may be set to be longer as the current value of the AC power P is smaller, and also longer as the overload rate is smaller. In that case, even when the current or overload caused by a short circuit is small, the short circuit can be detected accurately over time.

[0048] The short-circuit detection device and the short-circuit detection method according to the present disclosure are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment, the short-circuit detection unit 8 is configured to include a plurality of parts 8A, 8B, and 8C, but a common short-circuit detection unit connected to the plurality of measurement units 5, measurement unit 6, and measurement unit 9 may perform the operations of the plurality of parts 8A, 8B, and 8C in a unified manner.

Description of Reference Numerals

[0049] 1... Power supply system, 2... Bus, 3... Power supply unit, 4... Load unit, 5... Measurement unit, 6... Measurement unit (first measurement unit), 7... Inspection signal supply unit, 8... Short-circuit detection unit, 8A, 8B, 8C... Parts, 9... Measurement unit, 31, 41, 71... Transformers, 32... AC output power supply device, 33, 34... Feeder lines, 42... Electric load, 43, 44... Distribution lines, 72... AC output current source, 73, 74... Feeder lines, 81, 83... Fundamental wave extraction filters, 82, 84... Non-fundamental wave extraction filters, 85... Voltage drop determination unit, 86... Power flow direction determination unit, 87, 89... Overload determination units, 88... Current determination unit, 90A, 90B... Determination units, 91... Counter, 92... Amplitude calculation unit, 93... Duration setting unit, 94... Multiplication factor calculation unit, 95... Multiplication unit, 96... Comparison unit, 97... Determination unit, 100... Power supply system, 102... Bus, 103... Power supply unit, 104A, 104B... Load units, 141... Transformer, 142... Electric load, 143... Current detection unit, A1~A5... Short circuits, B1~B4... Currents, D1~D3... Timings, E... Signals, J1... Current measurement value, J2... Fundamental wave component, J3... Non-fundamental wave component, P... AC power, S... Inspection signal, ST1... Inspection signal supply step, ST2... Measurement step, ST3... Short-circuit detection step, V1... Voltage measurement value, V2... Fundamental wave component, V3... Non-fundamental wave component.

Claims

1. A power supply system provided with a power supply unit having an AC output power supply device connected to a bus, and a plurality of load units each having a transformer connected to the bus and a power load connected to the bus via the transformer, wherein the rated loads of the transformers of at least two of the plurality of load units are different from each other. A short-circuit detection device, comprising: a plurality of measurement units that measure voltage values and current values between the transformer and the bus in each of the plurality of load units; a short-circuit detection unit that detects a short circuit between the transformer and the power load in each of the plurality of load units; The short-circuit detection unit calculates, for each of the plurality of load units, an overload rate with respect to the rated load of the transformer from the voltage value and the current value measured by the plurality of measurement units, and determines that the overload rate has exceeded a threshold value determined for each load unit, and uses this to determine a short circuit between the transformer and the power load of the load unit. A short-circuit detection device for a power supply system.

2. A test signal supply unit that has an AC output current source connected to the bus and outputs a test signal having a frequency different from the frequency of the AC power output from the AC output power supply device; a first measurement unit provided separately from the plurality of measurement units; The power supply unit further has a transformer, and the AC output power supply device is connected to the bus via the transformer. The first measurement unit measures the voltage value and the current value of the test signal between the transformer and the bus in the power supply unit. The short-circuit detection unit calculates an overload rate with respect to the rated load of the transformer of the power supply unit from the voltage value and the current value measured by the first measurement unit, and determines that the overload rate has exceeded a threshold value determined for the power supply unit, and uses this to determine a short circuit between the transformer and the AC output power supply device of the power supply unit. The short-circuit detection device for a power supply system according to Claim 1.

3. When the overload rate exceeds the threshold value over a certain duration, the short-circuit detection unit determines that a short circuit has occurred between the transformer and the power load. The duration is set to be longer as the current value is smaller and longer as the overload rate is smaller. The short-circuit detection device for a power supply system according to Claim 1.

4. ​ ​ A power supply system having a power supply unit with an AC output power supply device connected to a bus, and a plurality of load units each having a transformer connected to the bus and a power load connected to the bus via the transformer, wherein the rated loads of the transformers of at least two of the plurality of load units are different from each other. A short-circuit detection method used for the power supply system, comprising: In each of the plurality of load units, a measurement step of measuring a voltage value and a current value between the transformer and the bus; A short-circuit detection step of detecting a short circuit between the transformer and the power load in each of the plurality of load units; Including: In the short-circuit detection step, from the voltage value and the current value measured in the measurement step, an overload rate with respect to the rated load of the transformer is calculated for each of the plurality of load units, and it is determined that the overload rate has exceeded a threshold value determined for each load unit, and this is used for short-circuit determination between the transformer and the power load of the load unit. A short-circuit detection method for a power supply system.

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