JP7550412B1 - SHORT-CIRCUIT DETECTION DEVICE, SHORT-CIRCUIT DETECTION METHOD, AND PROGRAM - Google Patents

Abstract

[Problem] To provide a short circuit detection device, method, and program capable of accurately detecting a short circuit in a power system even when reverse power flow originating from a distributed power source occurs. [Solution] In the short circuit detection device, a processing unit 100 includes an acquisition unit 131 that periodically acquires an instantaneous value of a phase current of each phase in the power system and an instantaneous value of a phase voltage of each phase or a line voltage between each phase, a calculation unit 132 that calculates an effective value of the line voltage between each phase and a difference vector that is a difference between a latest phase current vector in each phase and a phase current vector at a time point before the short circuit occurred, based on the instantaneous value of the phase current of each phase and the instantaneous value of the phase voltage of each phase or the line voltage between each phase acquired by the acquisition unit, and a determination unit 133 that determines that a short circuit has occurred in the power system when the effective value of any of the line voltages calculated by the calculation unit decreases, the magnitude of the difference vector of any of the phases is equal to or greater than a set value, and the phase of the difference vector is within a preset short circuit detection range. [Selected Figure] Figure 2

Description

Applicable under Article 30, Paragraph 2 of the Patent Act Publisher: Denki Hyoronsha Co., Ltd. Publication name: Denki Hyoron No. 705 Publication date: November 25, 2022

The present invention relates to a short circuit detection device, a short circuit detection method, and a program.

A power distribution system protection device is known that is used in combination with a switch to protect the power distribution line and the associated equipment from short circuits. The power distribution system protection device is configured to cause the switch to cut off the power distribution line when the current value on the load side reaches or exceeds a set value, and may also operate when reverse power flow from a distributed power source increases. To solve this problem, for example, the power distribution system protection device of Patent Document 1 calculates a current increment value based on the current value and current flow direction at every fixed time, and opens and closes the switch based on the calculated current increment value.

JP 2018-152955 A

In the power distribution system protection device of Patent Document 1, judging from its mechanism, it is believed that the difference in effective values is used as the current increment value. In addition, the current flow direction is expressed in two patterns, forward and reverse. For this reason, it is not possible to grasp the phase of the short-circuit current based on the instantaneous value of the short-circuit current or the voltage waveform, and there is room for improvement in distinguishing between a short circuit and a reverse flow resulting from a distributed power source. Such problems exist not only in the detection of a short circuit in a distribution line by a power distribution system protection device, but also in the detection of a short circuit in other power systems, including transmission lines.

The present invention was made based on this background, and aims to provide a short circuit detection device, a short circuit detection method, and a program that can accurately detect a short circuit in a power system even when reverse power flow occurs due to a distributed power source.

In order to achieve the above object, a short circuit detection device according to the present invention comprises:
an acquisition unit that periodically acquires an instantaneous value of a phase current of each phase in the power system and an instantaneous value of a phase voltage of each phase or an instantaneous value of a line voltage between each phase;
a calculation unit that calculates an effective value of the line voltage between each phase and a difference vector that is a difference between a latest phase current vector in each phase and a phase current vector at a time point before a short circuit occurs, based on the instantaneous value of the phase current of each phase and the instantaneous value of the phase voltage of each phase or the line voltage between each phase acquired by the acquisition unit;
a determination unit that determines that a short circuit has occurred in the power system when an effective value of any of the line voltages calculated by the calculation unit decreases, and a magnitude of a difference vector of any of the phases is equal to or greater than a set value and a phase of the difference vector is within a preset short circuit detection range;
Equipped with.

The present invention provides a short circuit detection device, a short circuit detection method, and a program that can accurately detect a short circuit in a power system even when reverse power flow occurs due to a distributed power source.

1 is a schematic diagram showing a configuration of a power distribution system according to a first embodiment of the present invention; 1 is a block diagram showing a hardware configuration of a short circuit detection device according to a first embodiment of the present invention; 1A is a diagram showing an example of a data table of an instantaneous value storage unit, FIG. 1B is a diagram showing an example of a data table of an effective value/phase storage unit, and FIG. 1C is a diagram showing an example of a data table of a detection condition storage unit. 1 is a graph showing the relationship between a waveform and sampling of an instantaneous value. 4 is a vector diagram illustrating a method for determining whether or not detection condition 1 is satisfied by the short circuit detection device according to the first embodiment of the present invention. 11 is another vector diagram illustrating the technique for determining whether detection condition 1 is satisfied by the short circuit detection device according to the first embodiment of the present invention. 5 is a vector diagram illustrating a method for determining whether detection condition 2 is satisfied by the short circuit detection device according to the first embodiment of the present invention. 5A and 5B are graphs each illustrating a method for setting a reference value by the short circuit detection device according to the first embodiment of the present invention. 4 is a flowchart showing a flow of a short circuit detection process according to the first embodiment of the present invention. 10 is a graph illustrating the influence of a frequency shift when extracting a waveform for one cycle according to the second embodiment of the present invention. 13A to 13D are vector diagrams each showing a procedure for frequency correction when extracting one cycle of a waveform according to the second embodiment of the present invention.

The short circuit detection device, short circuit detection method, and program according to the embodiment of the present invention will be described in detail below with reference to the drawings. In each drawing, the same or equivalent parts are denoted by the same reference numerals.

In the embodiments, the term "power system" refers to a facility that supplies power to a consumer's power receiving facility, and includes, for example, a power distribution system and a power transmission system. Below, an example will be described in which short circuit detection is performed in a power distribution line using a three-phase, three-wire system consisting of R phase, S phase, and T phase. The rotation direction of each phase is R phase → S phase → T phase.

(Embodiment 1)
Hereinafter, a short circuit detection device, a short circuit detection method, and a program according to the first embodiment will be described. The short circuit detection device according to the first embodiment is a device that detects whether a short circuit has occurred in a target distribution line based on data of instantaneous values of phase current and phase voltage measured in the target distribution line. As shown in Fig. 1, the short circuit detection device 1 is, for example, a distribution system protection device attached to the distribution line.

The distribution system protection device is installed on the load side of the distribution transformer. The distribution system protection device includes a switch capable of interrupting the line, and a low-voltage slave station device communicatively connected to the switch and controlling the opening and closing of the switch. When the low-voltage slave station device detects a short circuit in the distribution line, it issues a command to the switch to interrupt the distribution line. The distribution system protection devices may be installed at different positions on the distribution line.

The short circuit detection device 1 includes three current sensors and three voltage sensors provided on each phase of the power distribution line, and a processing unit that determines the presence or absence of a short circuit in the power distribution line based on the measurements taken by the current and voltage sensors. The current and voltage sensors and the processing unit are connected to each other via a communication cable so that they can communicate with each other.

The current sensor periodically measures the instantaneous value of the phase current, and the voltage sensor periodically measures the instantaneous value of the phase voltage. The current sensor and the voltage sensor measure the instantaneous value of the phase current and the instantaneous value of the phase voltage, respectively, at timings synchronized with each other, and transmit the data of these instantaneous values to the processing unit.

The processing unit is, for example, a control device equipped with a computer. The processing unit constantly monitors whether the state of the power distribution line satisfies any of detection conditions 1 to 3, and if any of the conditions is satisfied, it determines that a short circuit has occurred in the power distribution line.

Detection condition 1 is when the effective values of all line voltages are equal to or greater than a threshold, the magnitude of any of the phase current vectors is equal to or greater than a set value, and the phase is within the short circuit detection range for a period of time equal to or greater than a preset detection time. When a short circuit occurs on the load side of the short circuit detection device 1, a current with a large lagging power factor continues to flow in the forward direction, so that a short circuit can be detected by detection condition 1. Note that the phase current measured by the current sensor when a short circuit occurs is a phase current that is a vectorial synthesis of the load current and the short circuit current.

The phase current vector is generated based on the instantaneous value of the phase current for one cycle, and its phase is set with the voltage vector as the reference. The reference voltage vector is, for example, the line voltage vector between the lagging phase. Specifically, when calculating the R phase phase, the R-S line voltage is used as the reference, when calculating the S phase phase, the S-T line voltage is used as the reference, and when calculating the T phase phase, the T-R line voltage is used as the reference.

Detection condition 2 is when the effective value of any line voltage drops, and the magnitude of the difference vector of any phase current vector before and after the drop in the effective value of the line voltage is equal to or greater than the set value, and the phase is within the short circuit detection range for a period of time that is longer than a preset detection time. The magnitude of the difference vector of the two phase current vectors before and after the drop in the line voltage corresponds to the magnitude of the short circuit current. When reverse power flow continues in a distribution system with a small terminal short circuit current, even if a short circuit occurs, the phase current may not change to forward power flow or the absolute value of the measured current value may remain smaller than the set value. Even in such cases, a short circuit can be detected by detection condition 2.

The difference vector is obtained by calculating the difference between the latest phase current vector and the phase current vector calculated at a point before the short circuit occurred (e.g., two cycles ago). The phase of the difference vector is set based on the voltage vector before the short circuit occurred, for example, based on the line voltage vector between the lagging phase before the short circuit occurred. Specifically, the calculation of the R phase phase uses the R-S line voltage before the short circuit occurred as the reference, the calculation of the S phase phase uses the S-T line voltage before the short circuit occurred as the reference, and the calculation of the T phase phase uses the T-R line voltage before the short circuit occurred as the reference.

Detection condition 3 is when the effective value of any line voltage drops and the absolute value of any phase current remains equal to or greater than the set value for a period of time that is longer than a preset detection time. Detection condition 3 can detect a short circuit even when detection conditions 1 and 2 cannot detect a short circuit, for example, when the phase cannot be calculated due to the effects of frequency fluctuations. However, because detection condition 3 requires a long time for detection, it is used as a backup protection to supplement detection conditions 1 and 2, which are the primary protection.

Next, the hardware configuration of the processing unit 100 according to the first embodiment will be described. As shown in FIG. 2, the processing unit 100 includes a communication unit 110, a storage unit 120, and a control unit 130. The individual units of the processing unit 100 are connected to each other via an internal bus.

The communication unit 110 is a communication interface that allows the processing unit 100 to communicate with external devices. The communication unit 110 communicates with switches and other external devices via a communication network such as the Internet or an input/output terminal such as a Universal Serial Bus (USB).

The storage unit 120 includes, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, and a hard disk. The storage unit 120 stores programs executed by the control unit 130 and various data. The storage unit 120 also temporarily stores various information and functions as a work memory for the control unit 130 to execute processing. Furthermore, the storage unit 120 includes an instantaneous value storage unit 121, an effective value/phase storage unit 122, and a detection condition storage unit 123.

As shown in FIG. 3(a), the instantaneous value storage unit 121 stores, in the order of sampling time, the instantaneous values of the phase current and phase voltage of each phase periodically measured by the current sensor and the voltage sensor, and the instantaneous values of the line voltage between each phase calculated based on the instantaneous values of the phase voltage. The instantaneous values are data acquired at a sampling period shorter than one cycle of the waveform. The sampling period is set to include a plurality of sampling time points t0, t1, t2, ... arranged at equal intervals within the period T1, T2, T3, ... of one cycle of the waveform, as shown in FIG. 4. For example, in the case of a frequency of 50 Hz, the period of one cycle of the waveform is 20 ms, and, for example, 128 sampling points may be set within this period of one cycle of the waveform. By arranging the instantaneous value data in the order of time, waveform data as shown in FIG. 4 can be obtained.

As shown in FIG. 3B, the effective value/phase memory unit 122 stores the effective values of the phase current, phase voltage, and line voltage calculated for each cycle in order of cycles. The effective value/phase memory unit 122 also stores the phase of the phase current vector of each phase based on the line voltage with the lagging phase calculated for each cycle, and the phase of the difference vector of the phase current vector, in order of cycles. The magnitude and phase of each vector are calculated based on one cycle's worth of waveform data extracted from the data of the instantaneous values of the phase current, phase voltage, and line voltage stored in the instantaneous value memory unit 121.

The start point for extracting one cycle of waveform may be the start point of sampling performed in synchronization with each instantaneous value. As an example, as shown in FIG. 4, if the zero crossing point where the instantaneous value becomes zero is set as the start point, a data group of 128 instantaneous values showing one cycle of waveform from the zero crossing point may be extracted. In this case, if it is assumed that the frequency is constant, the periods T1, T2, ... for extracting one cycle of waveform may be set at regular intervals from each extraction start point. For example, in the case of a frequency of 50 Hz, the period for extracting the waveform may be set to a period of 20 ms from each zero crossing point. For example, if the waveform in FIG. 4 is the R-phase voltage Vr and the zero crossing point is the start point, the S-phase voltage Vs will start at a point 120° before the phase, and the T-phase voltage Vt will start at a point 240° before the phase. In addition, the start points of the R-phase current Ir, the S-phase current Is, and the T-phase current It are the points at which the phase is shifted by the power factor.

As shown in FIG. 3(c), the detection condition storage unit 123 stores the setting values for detection conditions 1 to 3. The setting values are, for example, a setting value for the absolute value of the phase current, a short circuit detection range, a threshold for the effective value of the line voltage, a threshold for the rate of decrease of the effective value of the line voltage, a setting value for the magnitude of the difference vector, and a detection time. The short circuit detection range is defined by the upper and lower limits of the phase. Details of these conditions will be described later.

Returning to FIG. 2, the control unit 130 includes a processor and controls each part of the processing unit 100. The processor is, for example, a CPU (Central Processing Unit). The control unit 130 includes an internal timer that counts time. The control unit 130 also executes the program stored in the memory unit 120 to perform the short circuit detection process of FIG. 9.

The control unit 130 functionally comprises an acquisition unit 131, a calculation unit 132, a determination unit 133, and an output unit 134. In the control unit 130, each functional configuration may be realized by one processor executing a program stored in the storage unit 120, or each functional configuration may be realized by an individual processor executing a program stored in the storage unit 120.

The acquisition unit 131 periodically acquires the instantaneous values of the phase current and phase voltage of each phase from the current sensor and voltage sensor, and sequentially stores the acquired instantaneous values of the phase current and phase voltage of each phase in the instantaneous value storage unit 121. The acquisition unit 131 may also acquire the instantaneous values stored in the instantaneous value storage unit 121 and the effective values and phases stored in the effective value/phase storage unit 122.

The calculation unit 132 calculates the instantaneous values of the line voltages between each phase based on the instantaneous values of the phase voltages of each phase acquired by the acquisition unit 131, and stores them sequentially in the instantaneous value storage unit 121. As the line voltages, the R-S line voltage, the S-T line voltage, and the T-R line voltage are calculated.

In addition, the calculation unit 132 calculates the magnitude (effective value) and phase of the phase current vector, the magnitude and phase of the difference vector, which is the difference between the latest phase current vector and the phase current vector at the time before the short circuit occurred, the effective value of the phase voltage of each phase, and the effective value of the line voltage between each phase, for each cycle based on the phase current and phase voltage of each phase for one cycle stored in the instantaneous value storage unit 121, and stores them sequentially in the effective value/phase storage unit 122.

The magnitude and phase of the phase current vector can be calculated sequentially based on, for example, the instantaneous value vector of the phase current of each phase for one cycle and the instantaneous value vector of the line voltage between each phase. The magnitude and phase of the difference vector of the phase current vector can be calculated based on, for example, the instantaneous value vector of the phase current of each phase for the latest one cycle, the instantaneous value vector of the phase current of each phase for one cycle at a time point before the short circuit occurs, the instantaneous value vector of the phase voltage of each phase, the instantaneous value vector of the line voltage between each phase, the effective value of the phase voltage of each phase, and the effective value of the line voltage between each phase. The instantaneous value vector is expressed by the instantaneous value of the phase current, phase voltage, or line voltage, and the sampling timing at which the instantaneous value is sampled. The sampling timing of the instantaneous value vector is set to be the same for all of the phase current, phase voltage, and line voltage, and is expressed by a phase based on a preset reference waveform.

Taking as an example the calculation of the phase θr of the R-phase current with reference to the RS line voltage, the phase θr of the R-phase is expressed by the following equation (1).
θr=tan ^-1 (Qr/Pr)...(1)

In the above formula (1), Pr is the active power component based on the R-S line voltage, and Qr is the reactive power component based on the R-S line voltage, both of which are scalar quantities. If the period is T, they can be expressed by the following formulas (2) and (3), respectively.
Pr=1/T×Σ(ir×vrs)…(2)
Qr=1/T×Σ(ir×vrs _+90° )…(3)
For example, if one cycle is sampled at 128 points, then T=128.

Here, ir is the instantaneous value vector of the R-phase current, vrs is the instantaneous value vector of the R-S line voltage, and vrs _+90° is the instantaneous value vector of the R-S line voltage based on data in which the R-S line voltage is delayed by a phase of 90° (5 ms for a frequency of 50 Hz). Also, the symbol Σ in equations (2) and (3) means the sum for one cycle.

Next, taking as an example the calculation of the phase Δθr of the difference vector of the R-phase current vector based on the RS line voltage, the phase Δθr of the difference vector of the R-phase current vector is expressed by the following equation (4).
Δθr=tan ^-1 (ΔQr/ΔPr)...(4)

In the above formula (4), ΔPr is the active power component of the difference vector, and ΔQr is the reactive power component of the difference vector, both of which are scalar quantities. If the period is T, these are expressed by the following formulas (5) and (6), respectively.
ΔPr=1/T×Σ((ir'-ir)×vrs)...(5)
ΔQr=1/T×Σ((ir'-ir)×-vt×Vrs/Vt)...(6)
For example, if one cycle is sampled at 128 points, then T=128.

Here, ir' is the latest instantaneous value vector of the R-phase current, ir is the instantaneous value vector of the R-phase current at a time when no short circuit has occurred, vrs is the instantaneous value vector of the R-S line voltage when ir is measured, and vt is the instantaneous value vector of the T-phase voltage when ir is measured. The difference vector Ir'-Ir of the R-phase current vector can be expressed by the magnitude calculated from the difference vector ir'-ir of the instantaneous value vectors of the phase currents for one cycle, and the phase Δθr calculated by the above equation (4). Below, the difference vector Ir'-Ir may be simplified and expressed as ΔIr.

In addition, in the above formula (6), Vrs/Vt is the T-phase voltage ratio, which is a scalar quantity. Vrs is the effective value of the R-S line voltage, and Vt is the effective value of the T-phase voltage, both of which are values when the R-phase current vector Ir is measured. The T-phase voltage ratio is multiplied to calculate the reactive power component ΔQr of the difference vector in order to correct the phase determination error caused by the voltage imbalance when the R-phase current vector Ir is measured. In a three-phase, three-wire distribution system, before a short circuit occurs, the phase difference between the effective value Vrs of the R-S line voltage and the effective value Vt of the T-phase voltage is 90°. Therefore, in detection condition 2, in which the phase current and line voltage before the short circuit are fixed and the difference vector is calculated, the T-phase voltage vector before the short circuit occurs is used, and then correction is performed by multiplying it by Vrs/Vt to match the peak value.

The determination unit 133 determines whether a short circuit has occurred in the distribution line based on the magnitude and phase of the phase current vector calculated by the calculation unit 132 for each cycle, the magnitude and phase of the difference vector of the phase current vector, and the effective value of the line-to-line voltage between each phase.

Specifically, the determination unit 133 determines that a short circuit has occurred in the distribution line when the effective values of all line voltages are equal to or greater than the threshold, the magnitude of any of the phase current vectors is equal to or greater than the set value, and the phase is within the short circuit detection range for a preset detection time or more (detection condition 1). Using FIG. 5 as an example, the magnitude of the R-phase current vector Ir is greater than the radius of the circle drawn with a dashed line indicating the set value, and the phase θr of the R-phase calculated based on the R-S line voltage vector Vrs is within the short circuit detection range. If such a state continues for the detection time, it can be determined that a short circuit has occurred in the R-phase. Note that in FIG. 5, the R-phase current vector Ir is illustrated with the lagging side positive and the leading side negative with respect to the reference R-S line voltage vector Vrs.

The threshold value of the effective value of the line voltage is, for example, 200 V. The set value of the absolute value of the phase current is set to be smaller than the minimum current value of the phase current when a short circuit occurs on the line (for example, the current value of the terminal short circuit current) and larger than the load current. The detection time may be set taking into consideration short circuit detection in the distribution substation, and is, for example, a time equivalent to 8 cycles (0.16 seconds at a frequency of 50 Hz).

The short circuit detection range is set individually for each phase, and is a range that includes the phase when the phase current is forward flow. Since the line voltages are shifted from each other by 120°, the respective short circuit detection ranges are also set to be shifted from each other by 120°. When the phase of the phase current is set based on the line voltage vector between the lagging phase, the short circuit detection range may be set, for example, in the range of -30° to 0° to 120° with respect to the line voltage vector set to 0°. This range is set because the short circuit current has a lagging power factor with respect to the line voltage, and is set so as not to detect reverse flow due to distributed power sources.

To explain in more detail, a range of 0° to 90° is set with respect to the reference line voltage vector to detect a single-phase short circuit, and a similar range of 30° to 120° (0° to 90° with respect to the reference phase voltage) is set to detect a three-phase short circuit. In addition, a 30° margin is set on the leading side to take into account errors in phase calculation, making the range -30° to 0° to 120°. Neither reverse power flow nor short circuits occur when the phase is near 120°, and no margin is set on the lagging side to avoid false detection of a short circuit in a reverse power flow state if the phase is near 120°.

Detection condition 1 can also be applied when the phase current changes from reverse flow to forward flow before and after the occurrence of a short circuit. In the example of Figure 6, the R-phase current vector Ir before the short circuit occurs is within the short circuit non-detection range, but the phase of the R-phase current vector Ir' after the short circuit occurs is within the short circuit detection range and its magnitude is equal to or greater than the set value. If this state continues for the detection time, it can be determined that a short circuit has occurred in the R phase.

Although the above description was given using an example of an R-phase short circuit, similar calculations can be performed for the S-phase and T-phase. If detection condition 1 is satisfied in any of the phases, it can be determined that a short circuit has occurred in that phase.

In addition, the determination unit 133 determines that a short circuit has occurred in the distribution line when the effective value of any line voltage drops, the magnitude of the difference vector of any phase current vector before and after the drop in the effective value of the line voltage is equal to or greater than a set value, and the phase of the difference vector is within the short circuit detection range for a preset detection time or more (detection condition 2). Using FIG. 7 as an example, the magnitude of the difference vector ΔIr of the R-phase current vector before and after the short circuit is equal to or greater than a set value, and the phase Δθr of the difference vector ΔIr of the R-phase current vector is included in the short circuit detection range. If such a state continues for the detection time, it can be determined that a short circuit has occurred in the R phase. Note that in FIG. 7, the starting points of the difference vectors ΔIr and ΔIs of the R-phase current vector and the S-phase current vector in FIG. 6 are moved to the origin.

Detection condition 2 uses a drop in the effective value of the line voltage as a trigger in order to distinguish between reverse power flow fluctuations caused by a short circuit and distributed power sources. When reverse power flow decreases due to the disconnection of a distributed power source, the drop in line voltage is small, so the degree of the drop in line voltage makes it possible to distinguish between reverse power flow fluctuations caused by a short circuit and distributed power sources.

The line voltage effective value may be determined to have decreased if the effective value of any of the line voltages changes from a first threshold or more to less than the threshold, and the rate of decrease of the effective value of the line voltage becomes equal to or greater than the second threshold based on the line voltage set before the short circuit. For example, in the case of a rated voltage of 6600 V, the effective value of the line voltage is determined to have decreased if the effective value of any of the line voltages changes from a state in which the effective values of all the line voltages are 5000 V or more to less than 5000 V, and the rate of decrease of the effective value of the line voltage becomes 10% or more based on the line voltage set before the short circuit. The rate of decrease of the effective value of the line voltage is also taken into consideration because, when a reclosing accident occurs in the upper system (power transmission system) while reverse power flow is occurring, the line voltage may become less than 5000 V, and in this state, if the distributed power source in the power distribution system is de-paralleled late, it may be erroneously determined to be a short circuit.

When the effective value of the line voltage drops and the other conditions of short circuit condition 2 are also satisfied, a count is started to determine whether the detection time has elapsed. If the effective values of all line voltages return to the third threshold or higher during this time, it is determined that the drop in the line voltage has stopped, and the count is ended. The third threshold is greater than the first threshold so as to provide hysteresis in the count of the detection time. For example, if the first threshold is 5000V, the third threshold is set to 6000V. Hereinafter, such a condition will be called a return condition. The reason for setting such a return condition is that if the line voltage falls below the first threshold and a short circuit is detected again immediately after the detection condition 2 is deviated and the count is cleared, the effective value of the phase current and the effective value of the line voltage immediately after the count is cleared will become the reference value.

To calculate the rate of decrease in the effective value of the line voltage and the differential vector of the phase current vector before and after the occurrence of a short circuit, it is necessary to set the instantaneous value of the phase current before the occurrence of a short circuit, the instantaneous value and effective value of the phase voltage, and the instantaneous value and effective value of the line voltage as reference values in advance. The reference value is, for example, the instantaneous value or effective value two cycles ago, and is updated every cycle unless a preset condition is met and it is held. The reference value is held when the condition related to the effective value of the line voltage in detection condition 2 is met. Therefore, the reference value of the line voltage is always equal to or greater than the first threshold value.

Even if at least some of the parameters deviate from the conditions in detection condition 2 regarding the effective value of the line voltage, the magnitude and phase of the difference vector while counting the detection time, the detection time count continues. If the deviation continues for a period longer than the period preset for calculating the difference vector, the detection time count is terminated and the hold on the reference value is released. For example, if the instantaneous value or effective value from two cycles ago is used as the reference value, the detection time count is terminated when three cycles have elapsed.

Below, we will explain using a specific example with reference to Figure 8. In Figure 8, the passage of time is expressed as the "latest cycle" which advances one at a time from zero for each cycle. Furthermore, the numerical value in V for the line voltage is the effective value, and the percentage value is the rate of decrease in the line voltage based on the rated voltage of 6600 V.

In the example of Figure 8 (a), the condition related to the effective value of the line voltage in detection condition 2 is met in most recent cycles 2 to 4, so the reference value for most recent cycles 2 to 4 is the value in most recent cycle 0. The effective value of the line voltage does not meet the condition in most recent cycle 5, but since it has been less than three cycles since the condition was not met in most recent cycles 5 to 7, the reference value is held at the value in most recent cycle 0. In most recent cycle 8, it has been more than three cycles since the effective value of the line voltage did not meet the condition, so the reference value is updated to the value in most recent cycle 6, and thereafter, it is determined for each cycle whether to update the reference value.

In the example of Figure 8(b), since the condition regarding the effective value of the line voltage in detection condition 2 is met in latest cycle 2, the reference value in latest cycles 2 to 4 is held at the value in latest cycle 0. On the other hand, since the magnitude of the difference vector of the phase current vector in latest cycles 2 to 4 is less than the set value, the reference value is updated to the value in latest cycle 3 in latest cycle 5, three cycles later. At this point, the voltage is less than 5000V and does not meet the return condition, so the value in latest cycle 3 is not held as the reference value. Thereafter, a decision is made every cycle as to whether to update the reference value.

The short circuit detection range is set individually for each phase and is a range that includes the phase when the phase current is forward flow. Since the phase voltages are shifted by 120° from each other, the short circuit detection ranges are also set to be shifted by 120° from each other. When the phase current phase is set based on the line voltage vector with the lagging phase, the short circuit detection range can be set to the range of -30° to 0° to 120° with respect to the line voltage vector set to 0°, as in the case of detection condition 1.

The detection time is, for example, the time equivalent to 8 cycles (0.16 seconds at a frequency of 50 Hz) as in the case of detection condition 1. However, if the zero-phase voltage, which is the neutral point voltage to ground, is detected and the zero-phase voltage is 1000 V or more, short circuit detection is not performed at the above detection time, and it is determined that a short circuit has occurred if only a load side earth fault, earth fault overcurrent, or zero-phase voltage with DGI = 0.0 A setting is detected within the short circuit interruption output time. The short circuit interruption output time is the time from when the short circuit detection device 1 detects the occurrence of a short circuit to when it instructs the switch to interrupt the line. DGI is a setting value related to the earth fault interruption current, and is usually set to 0.2 A and is used for earth fault direction detection and earth fault interruption, but when set to 0.0 A, it switches to a mode in which only zero-phase voltage is interrupted.

In the above, we have taken the example of a short circuit in the R phase, but similar calculations can be performed for the S and T phases. If detection condition 2 is satisfied in any of the phases, it can be determined that a short circuit has occurred in that phase.

In addition, if the effective value of any line voltage drops and the absolute value of the phase current remains equal to or greater than the set value for a period of time that is longer than a preset detection time, the determination unit 133 determines that a short circuit has occurred in the distribution line (detection condition 3).

In detection condition 3, the effective value of the line voltage can be determined to have decreased if the effective value of any line voltage falls below the first threshold. On the other hand, the condition for voltage drop recovery is when the effective values of all line voltages are equal to or greater than the third threshold. The first and third thresholds in detection condition 3 can be set to, for example, 5000 V and 6000 V, as in detection condition 2. The condition for detecting a decrease in the effective value of the line voltage in detection condition 3 is simpler than detection condition 2 in order to detect short circuits without missing any.

The detection time in detection condition 3 is set longer than in detection conditions 1 and 2. Even if reclosing of the upper system and reverse power flow of the distributed power source occur simultaneously, the state in which the effective value of the line voltage drops and the absolute value of the phase current exceeds the set value may continue for a certain period of time, and the two can be distinguished by setting the detection time to be longer. The detection time is, for example, a time equivalent to 40 cycles (0.8 seconds at a frequency of 50 Hz).

However, if detection occurs during Y time limit after X time limit is turned on, or if the turn-on X time limit is set to 0 seconds, the detection time is 8 cycles (0.16 seconds). X time limit is the time counted from when system power is applied to the short circuit detection device 1, and the switch is turned on when this X time limit is exceeded. Y time limit is the time counted from when the switch is turned on, and the count ends before another switch turns on the X time limit. This time limit is used to determine whether the cause of the accident is in the area where the local switch turned on and transmitted power, and if it is determined that the cause of the accident is in the area, the switch is opened and locked, so that the time limit will not be turned on even if system voltage is applied again.

The switch is closed for X time limit when the distribution line on the power source side of the switch is pressurized and the distribution line on the load side is not pressurized (power outage). Detection condition 3 is a backup protection when a short circuit cannot be detected by detection conditions 1 and 2, so the detection time is usually set long, but when X time limit is closed, the distributed power source is in a disconnected state so there is no need to consider its impact, and it is possible to determine that a short circuit has occurred from the absolute value of the phase current, so the detection time can be shortened. Also, if the detection time remains at 40 cycles, coordination with the short circuit detection device 1 on the power source side cannot be achieved, so short circuit detection is accelerated during Y time limit.

In addition, if the zero-phase voltage is 1000V or higher, short circuit detection with a detection time of 40 cycles will be suspended, and a short circuit will be detected if a load side earth fault, earth fault overcurrent, or only zero-phase voltage is detected with DGI = 0.0A set within the short circuit cut-off output time.

When determining whether detection conditions 2 and 3 are satisfied, the determination unit 133 may also require that a load-side earth fault occurs when a zero-phase voltage occurs. In a short circuit without an earth fault, no zero-phase voltage occurs, whereas in a load-side short circuit with an earth fault, a load-side earth fault is detected and a zero-phase voltage occurs. Zero-phase voltage also occurs in a loss of phase. For this reason, by requiring that a load-side earth fault occurs when a zero-phase voltage occurs, a short circuit can be distinguished from a loss of phase under reverse power flow. Whether a ground fault occurs on the power supply side or on the load side can be determined by a known method based on the zero-phase current and zero-phase voltage.

The output unit 134 opens the switch when it is determined by the determination unit 133 that a short circuit has occurred. More specifically, when the determination unit 133 determines that any of the detection conditions 1 to 3 is satisfied, the output unit 134 waits for the short circuit interruption output time and then transmits a control signal to the switch to instruct it to interrupt the line.

In detection conditions 1 and 2, taking into consideration cooperation with other short circuit detection devices on the power supply side, the short circuit shutoff output time is set to a time shorter than the short circuit shutoff time, for example, "short circuit shutoff time - 0.02 seconds." In detection condition 3, in order to reliably detect and shut off a short circuit even if cooperation with other short circuit detection devices on the power supply side cannot be achieved, the short circuit shutoff output time is set to a fixed time, for example, 1.78 seconds. The short circuit shutoff time is one of the set values, and is the period from when a short circuit occurs to when the switch is shut off.

Even if the detection condition is not met during the count of the short circuit breaker output time, the count of the short circuit breaker output time is continued as it is, but when the condition is not met for three consecutive cycles, the count of the short circuit breaker output time is terminated and the closed state of the switch is maintained.
The processing unit 100 has the above configuration.

(Short circuit detection process)
The flow of the short circuit detection process executed by the processing unit 100 will be described below with reference to the flowchart in Fig. 9. The short circuit detection process is a process for detecting whether or not a short circuit has occurred in the distribution line based on instantaneous values of phase current and phase voltage measured in the distribution line. The short circuit detection process is started when a power supply voltage from a system power supply is applied.

First, the acquisition unit 131 acquires the instantaneous values of the phase current and phase voltage of each phase and stores them in the instantaneous value storage unit 121 (step S1).

Next, the calculation unit 132 calculates the instantaneous values of the line voltages between the phases based on the instantaneous values of the phase voltages of each phase acquired in the processing of step S1, and stores them in the instantaneous value storage unit 121 (step S2).

Next, the calculation unit 132 calculates the effective value of the phase voltage of each phase, the effective value of the line voltage between each phase, and the magnitude (effective value) and phase of the phase current vector in the most recent cycle based on the instantaneous values of the phase current, the phase voltage, and the line voltage for the most recent cycle stored in the instantaneous value storage unit 121, and stores them in the effective value/phase storage unit 122 (step S3). The magnitude and phase of the phase current vector are calculated from the instantaneous value vector of the phase current of each phase for one cycle and the instantaneous value vector of the line voltage between each phase.

Next, the calculation unit 132 calculates a difference vector of the latest phase current vector based on the latest phase current vector calculated in the process of step S3 and the phase current vector from two cycles ago stored in the effective value/phase storage unit 122, and stores the magnitude (effective value) and phase of the difference vector in the effective value/phase storage unit 122 (step S4). The magnitude and phase of the difference vector of the phase current vector are calculated from the instantaneous value vector of the phase current of each phase for the latest cycle, the instantaneous value vector of the phase current of each phase for one cycle at the time before the short circuit occurred, the instantaneous value vector of the phase voltage of each phase, the instantaneous value vector of the line voltage between each phase, the effective value of the phase voltage of each phase, and the effective value of the line voltage between each phase.

Next, the determination unit 133 executes a determination process to determine whether the state of the power distribution line satisfies any one of detection conditions 1 to 3 based on the phase current vectors of each phase and the line voltage vectors between each phase calculated in the process of step S3 and the difference vector of the phase current vectors calculated in the process of step S4 (step S5).

Specifically, first, the determination unit 133 determines whether the effective value of any line voltage and the magnitude and phase of any phase current vector satisfy detection condition 1. In parallel with the process of determining whether detection condition 1 is satisfied, the determination unit 133 also determines whether the effective value of any line voltage and its rate of decline, and the magnitude and phase of any phase difference vector satisfy detection condition 2. Then, in parallel with the process of determining whether detection conditions 1 and 2 are satisfied, the determination unit 133 determines whether the effective value of any line voltage and any phase current absolute value satisfy detection condition 3.

In the process of step S5, if it is determined that the state of the power distribution line satisfies any of detection conditions 1 to 3, a detection flag Ftx is set to indicate that the detection condition was satisfied in the latest cycle tx for each detection condition. If it is determined that the same detection condition is satisfied in the process of step S5 in a new cycle, a new detection flag Ftx+1 is set, and the same process is performed in the following cycle.

In addition, in the process of step S5, the instantaneous value vectors of the phase current, phase voltage, and line voltage, and the effective values of the phase voltage and line voltage two cycles prior to the time when it is determined that the trigger condition for the decrease in the effective value of the line voltage in detection condition 2 is satisfied are held as reference values. When the reference value is held, the update of the reference value every cycle is temporarily stopped until the hold of the reference value is released.

If the result of the process in step S5 is Yes, the determination unit 133 determines whether the detection time has elapsed while any one of the detection conditions 1 to 3 is satisfied in the process in step S5 (step S6). In the process in step S6, it can be determined whether the detection time has elapsed based on whether the detection flags Ftx, Ftx+1, Ftx+2, ... have been set consecutively for a preset number of cycles. On the other hand, if the result of the process in step S5 is No, the process returns to step S1.

If it is determined that the detection time has elapsed while any one of detection conditions 1 to 3 is satisfied (step S6; Yes), the output unit 134 determines whether the short circuit interruption output time has elapsed since the detection time elapsed (step S7). On the other hand, if it is determined that the detection time has not elapsed while any one of detection conditions 1 to 3 is satisfied (step S6; No), the process returns to step S1.

If it is determined that the short circuit interruption output time has elapsed since the detection time has elapsed (step S7; Yes), the output unit 134 opens the switch to be operated (step S8) and returns to step S1. If the switch is not locked, the switch is closed again after a preset re-closing time has elapsed. When the switch is closed again, the execution of the short circuit detection process shown in FIG. 9 can be started again. On the other hand, if it is determined that the short circuit interruption output time has not elapsed since the detection time has elapsed (step S7; No), the process returns to step S1.
The above is the flow of the short circuit detection process.

As described above, the short circuit detection device 1 according to the first embodiment includes an acquisition unit 131 that periodically acquires instantaneous values of the phase current and phase voltage of each phase in the distribution line, a calculation unit 132 that calculates the effective value of the line voltage between each phase and a difference vector that is the difference between the latest phase current vector in each phase and the phase current vector at the time point before the short circuit occurs, based on the instantaneous values of the phase current and phase voltage of each phase acquired by the acquisition unit 131, and a determination unit 133 that determines that a short circuit has occurred in the distribution line when the effective value of any of the line voltages calculated by the calculation unit 132 decreases, the magnitude of the difference vector of any of the phases is equal to or greater than a set value, and the phase of the difference vector is within a preset short circuit detection range. Therefore, a short circuit in the distribution line can be accurately detected even when a reverse power flow originating from a distributed power source occurs.

(Embodiment 2)
The following describes a short circuit detection device, a short circuit detection method, and a program according to embodiment 2. In embodiment 1, the description is based on the premise that the frequency does not fluctuate, but in embodiment 2, a method for performing detection under detection condition 2 even when the frequency fluctuates is described. The following description focuses on the differences from embodiment 1.

Taking the example of extracting one cycle of waveform from the zero crossing point, when the frequency is lower than the reference frequency of 50 Hz, the waveform widens in the time direction as shown in Figure 10, so the zero crossing point moves slightly to the right from its original position. On the other hand, when the frequency is higher than the reference frequency of 50 Hz, the waveform narrows in the time direction, so the zero crossing point moves slightly to the left from its original position. If this deviation accumulates, the phase of the difference vector of the phase current vector cannot be calculated accurately, and short circuit detection under detection condition 2 cannot be performed.

This phenomenon is explained using the vector diagram shown in Figure 11. If the frequency deviates from the reference frequency, the magnitude of the R-phase current vector after the short circuit does not change, but if the frequency is less than 50 Hz, it moves clockwise to Ir', Ir'', and Ir''', over time, and the phase difference with the R-phase current vector Ir before the short circuit also changes. As a result, the difference vector changes to ΔIr', ΔIr'', and ΔIr''', and the magnitude of the difference vector gradually decreases and the phase also changes, so that at the point of difference vector ΔIr''', it falls outside the short circuit detection range and short circuit detection according to detection condition 2 cannot be performed. Note that in the vector diagram in Figure 11, the short circuit detection range is illustrated as a ring-shaped area for ease of understanding, but in reality it is the area outside the circle with the radius of the setting value.

To eliminate the effects of such frequency fluctuations, when the frequency is less than 50 Hz, the start point of one cycle extraction is delayed so that it becomes a zero cross point as shown in FIG. 10, and data within the range of periods T2, T3, ... starting from the delayed start point is extracted as one cycle waveform. On the other hand, when the frequency is greater than 50 Hz, the start point of one cycle extraction is advanced so that the start point becomes a zero cross point, and data within the range of periods T2, T3, ... starting from the advanced start point is extracted as one cycle waveform. Note that in the above explanation, the start point of one cycle extraction is the zero cross point, but the start point of one cycle extraction may be any sampling point at which sampling of each instantaneous value is performed.

In the short circuit detection device according to the second embodiment, in order to realize the above function without performing frequency counting, the calculation unit 132 repeatedly calculates the phase difference between the phase voltage vector from one cycle ago and the latest phase voltage vector based on the phase voltage vector for each cycle in the phase least affected by the short circuit, and performs frequency correction to correct the phase of the phase current vector of the short-circuited phase based on the repeatedly calculated phase difference. The phase least affected by the short circuit during a three-phase short circuit is, for example, the phase with the highest voltage.

The calculation of frequency correction when an R-S short circuit occurs in a distribution line will be explained below using the specific example in Figure 11. When the frequency is higher than the reference frequency, if one cycle of waveform is repeatedly sampled at a fixed time interval from the extraction start point after an R-S short circuit occurs in the distribution line, the T-phase voltage vector Vt' will deviate from its correct orientation to Vt'', Vt''', as shown in Figures 11(b) to (d). Therefore, to perform frequency correction, first calculate the phase difference between the T-phase voltage vector Vt' at the sampling point n cycles ago (for example, n = 1) (the dashed vector in Figure 11(c)) and the latest T-phase voltage vector Vt'' (the solid vector in Figure 11(c)).

Next, the R-phase current vector Ir'' after the short circuit is corrected based on the phase difference of the calculated phase voltage vectors, and the difference vector ΔIr'' is calculated based on the corrected R-phase current vector Ir'' after the short circuit. At this time, the R-phase current vector Ir'' can be corrected by rotating the T-phase voltage vector Vt'' and the R-phase current vector Ir'' counterclockwise together so that the T-phase voltage vector Vt'' coincides with the T-phase voltage vector Vt'' while maintaining the angle between them. This causes the R-phase current vector Ir'' shown in Figure 11(c) to be corrected to its correct orientation.

Specific processing involves accumulating the phase difference between the phase voltage vector of the previous cycle calculated for each sampling and the latest phase voltage vector, and when the accumulated value of this phase difference is equal to or greater than an angle corresponding to one sampling, correcting the R-phase current vector Ir'' after the short circuit by that angle. However, if the phase difference calculated for each sampling is large, there is a possibility that factors other than frequency fluctuations exist, so it is advisable to determine whether to accumulate the phase difference using a threshold value. Specifically, if the phase difference calculated for each sampling is less than the threshold value, the phase difference is accumulated, and if the phase difference calculated for each sampling is equal to or greater than the threshold value, the phase difference is not accumulated. The threshold value in this case may be set to, for example, 3° (equivalent to approximately 0.4 Hz when the frequency is 50 Hz).

As described above, the short circuit detection device 1 according to the second embodiment includes a calculation unit 132 that calculates the phase difference between the phase voltage vector of one cycle before in a phase where no short circuit has occurred and the latest phase voltage vector, and corrects the phase of the phase current vector in the short-circuited phase based on the calculated phase difference. Therefore, even when the frequency fluctuates, the difference vector can be accurately calculated, and short circuit detection can be performed according to detection condition 2. In addition, since frequency correction does not require a frequency counter or calculations for zero-cross detection, detection delays due to calculations can be reduced, and the distribution line can be quickly shut off when a short circuit occurs.

The present invention is not limited to the above embodiment, and the following modifications are also possible.

(Modification)
In the above embodiment, the instantaneous value of the phase voltage of each phase is measured, and the line voltage between each phase is calculated based on the phase voltage of each phase, but the present invention is not limited to this. For example, the instantaneous value of the line voltage between each phase may be measured by a voltage sensor connected between each phase, and the phase voltage of each phase may be calculated based on the line voltage between each phase.

In the above embodiment, the phase of the phase current is set based on the line voltage, but the present invention is not limited to this. For example, the phase of the phase current may be set based on the phase voltage of the same phase.

In the above embodiment, the short circuit detection range set for the phase of the phase current and the short circuit detection range set for the phase of the difference vector of the phase current vector are the same, but the present invention is not limited to this. For example, the short circuit detection range set for the phase of the phase current and the short circuit detection range set for the phase of the difference vector of the phase current vector may be set separately.

In the above embodiment, it was determined whether the absolute values of all line voltages are equal to or greater than the threshold value in detection condition 1, but the present invention is not limited to this. For example, depending on the form of the power distribution system, it may be possible to omit the determination of whether all line voltages are equal to or greater than the threshold value.

In the above embodiment, it was determined that a short circuit had occurred when the set conditions for each of detection conditions 1 and 2 were satisfied for a period of time or longer that the detection time was exceeded, but the present invention is not limited to this. For example, it may be determined that a short circuit has occurred when the set conditions are satisfied.

In the above embodiment, the reactive power component ΔQr of the difference vector is multiplied by the T-phase voltage ratio, but the present invention is not limited to this. If there is no need to correct the phase determination error due to voltage imbalance, the multiplication by the T-phase voltage ratio in the calculation of the reactive power component ΔQr of the difference vector may be omitted, and the voltage ratio may be multiplied by √3. Also, if it is possible to use the instantaneous value of the R-S line voltage based on data obtained by delaying the sampling of the R-S line voltage by 90° (5 ms for a frequency of 50 Hz) instead of the instantaneous value of the T-phase voltage, there is no need to multiply by the T-phase voltage ratio.

In the above embodiment, the instantaneous values of the phase current and line voltage two cycles before the trigger condition related to the decrease in the effective value of the line voltage in detection condition 2 is satisfied, and the hold of the reference value is released when at least some parameters deviate from detection condition 2 for three consecutive cycles, but the present invention is not limited to this. For example, the instantaneous values of the phase current and line voltage three cycles before the trigger condition related to the decrease in the effective value of the line voltage in detection condition 2, and the effective values of the phase current, phase voltage, and line voltage may be used as the reference value, and the hold of the reference value may be released when at least some parameters deviate from the detection condition for four consecutive cycles.

In the above embodiment, when determining whether detection conditions 2 and 3 are satisfied, a load-side earth fault must also occur when a zero-phase voltage is generated, but the present invention is not limited to this. If the short-circuit detection device 1 does not have the function of determining an earth fault or if there is no need to consider a missing phase, the determination of whether a load-side earth fault occurs when a zero-phase voltage is generated may be omitted.

In the above embodiment, the hold on the reference value is released when the effective values of all the line voltages become equal to or greater than the third threshold, but the present invention is not limited to this. For example, when the effective value of any of the line voltages becomes equal to or greater than the third threshold, the hold on the reference value may be released only for the line voltage that has become equal to or greater than the third threshold.

In the above-mentioned second embodiment, the phase difference between the phase voltage vector at the previous sampling point and the latest phase voltage vector is calculated, but the present invention is not limited to this. For example, the phase difference between the phase voltage vector at the second previous sampling point and the latest phase voltage vector may be calculated.

In the above-mentioned second embodiment, the phase difference of the phase voltage calculated for each sampling is accumulated, and when the accumulated value of the phase difference is equal to or greater than an angle corresponding to one sampling, the phase current vector after the short circuit is corrected by that angle, but the present invention is not limited to this. For example, the frequency correction may be performed on the phase current vector for each sampling.

In the above-mentioned second embodiment, the frequency correction is performed on the phase current vector based on the phase difference of the phase voltage vector, but the present invention is not limited to this. For example, a frequency counter or a zero crossing point may be detected, and frequency correction may be performed based on the frequency counter or the zero crossing point. In addition, in the case of a single-phase short circuit, the phase difference of the phase current vector of the non-short-circuited phase may be calculated, and frequency correction may be performed based on the calculated phase difference of the phase current vector.

In the above-mentioned second embodiment, the phase difference of the phase voltage vectors is calculated, and frequency correction is performed on the phase current vector based on the calculated phase difference, but the present invention is not limited to this. For example, the phase difference of the line voltage vectors may be calculated, and frequency correction is performed on the phase current vector based on the calculated phase difference. Furthermore, the target of frequency correction is not limited to the phase current vector, and may be a phase voltage vector or a line voltage vector.

In the above embodiment, the short circuit detection device 1 is used to detect a short circuit in a three-phase, three-wire distribution line, but the present invention is not limited to this. The short circuit detection device 1 may be used to detect a short circuit in a distribution line other than a three-phase, three-wire distribution line, for example, a single-phase, two-wire or three-phase, four-wire distribution line, or may be used to detect a short circuit in a transmission line.

In the above embodiment, various data are stored in the memory unit 120 of the processing unit 100, but the present invention is not limited to this. For example, all or part of the various data may be stored in an external control device or processing unit via a communication network.

In the above embodiment, the processing units 100 each operate based on a program stored in the storage unit 120, but the present invention is not limited to this. For example, the functional configuration realized by the program may be realized by hardware.

In the above embodiment, the processing unit 100 is, for example, a control device provided in the short circuit detection device 1, but the present invention is not limited to this. For example, the processing unit 100 may be realized as a processing unit provided on the cloud.

In the above embodiment, the processing performed by the processing unit 100 is realized by a device having the above-mentioned physical configuration executing a program stored in the memory unit 120, but the present invention may also be realized as a program or as a storage medium on which the program is recorded.

In addition, a program for executing the above-mentioned processing operations may be stored and distributed on a non-transitory recording medium that can be read by a processing unit, such as a flexible disk, a CD-ROM (Compact Disk Read-Only Memory), a DVD (Digital Versatile Disk), or an MO (Magneto-Optical Disk), and the program may be installed in the processing unit to configure a device that executes the above-mentioned processing operations.

The above embodiments are illustrative, and the present invention is not limited to these, and various embodiments are possible within the scope of the invention described in the claims. The components described in each embodiment and variant can be freely combined. Furthermore, inventions equivalent to the inventions described in the claims are also included in the present invention. In addition, even if the components of the inventions described in the claims have the same names as the components described in the above embodiments, they are not limited to the components described in the above embodiments themselves, and can be modified and applied as appropriate.

REFERENCE SIGNS LIST 1: Short circuit detection device 100: Processing unit 120: Storage unit 130: Control unit 131: Acquisition unit 132: Calculation unit 133: Determination unit 134: Output unit

Claims (9)

an acquisition unit that periodically acquires an instantaneous value of a phase current of each phase in the power system and an instantaneous value of a phase voltage of each phase or an instantaneous value of a line voltage between each phase;
a calculation unit that calculates an effective value of the line voltage between each phase and a difference vector that is a difference between a latest phase current vector in each phase and a phase current vector at a time point before a short circuit occurs, based on the instantaneous value of the phase current of each phase and the instantaneous value of the phase voltage of each phase or the line voltage between each phase acquired by the acquisition unit;
a determination unit that determines that a short circuit has occurred in the power system when an effective value of any of the line voltages calculated by the calculation unit decreases, and a magnitude of a difference vector of any of the phases is equal to or greater than a set value and a phase of the difference vector is within a preset short circuit detection range;
A short circuit detection device comprising: The calculation unit calculates the phase of the difference vector based on a line voltage vector between a phase for which the phase of the difference vector is calculated and a lag phase.
The short circuit detection device according to claim 1 . the determination unit determines that the effective value of the line voltage has decreased when the effective value of any one of the line voltages is less than a first threshold value and a rate of decrease in the effective value of the line voltage based on a reference value of the line voltage at a time before the occurrence of a short circuit is less than a second threshold value.
3. The short circuit detection device according to claim 1 or 2. the calculation unit calculates a phase difference between a phase voltage vector at a time point a preset number of cycles before in a phase that is least affected by a short circuit and a latest phase voltage vector, and corrects a phase current vector in the short-circuited phase based on the calculated phase difference.
3. The short circuit detection device according to claim 1 or 2. the calculation unit calculates a phase current vector for each phase based on an instantaneous value of a phase current for each phase and a line voltage between each phase;
the determination unit determines that a short circuit has occurred in the power system when a magnitude of a phase current vector of any of the phases calculated by the calculation unit is equal to or greater than a set value and a phase of the phase current vector is within a preset short circuit detection range.
The short circuit detection device according to claim 1 . The determination unit determines that a short circuit has occurred in the power system when a state in which any line voltage drops and a phase current absolute value of any phase is equal to or greater than a set value continues for a predetermined detection time or longer.
The short circuit detection device according to claim 1 . The short circuit detection device further includes an output unit that opens a switch provided in the power system when the determination unit determines that a short circuit has occurred.
7. The short circuit detection device according to claim 1, 2, 5 or 6. A short circuit detection method performed by a short circuit detection device, comprising:
periodically acquiring an instantaneous value of a phase current of each phase in the power system and an instantaneous value of a phase voltage of each phase or an instantaneous value of a line voltage between each phase;
calculating an effective value of the line voltage between each phase and a difference vector which is a difference between a latest phase current vector in each phase and a phase current vector at a time point before the short circuit occurs, based on the obtained instantaneous value of the phase current in each phase and the instantaneous value of the phase voltage in each phase or the line voltage between each phase;
determining that a short circuit has occurred in the power system when the effective value of any of the calculated line voltages decreases, the magnitude of a difference vector of any of the phases is equal to or greater than a set value, and the phase of the difference vector is within a preset short circuit detection range;
The short circuit detection method includes: Computer,
A means for periodically acquiring an instantaneous value of a phase current of each phase in the power system and an instantaneous value of a phase voltage of each phase or a line voltage between each phase;
a means for calculating an effective value of the line voltage between each phase and a difference vector which is a difference between a latest phase current vector in each phase and a phase current vector at a time point before the occurrence of a short circuit, based on the acquired instantaneous value of the phase current in each phase and an instantaneous value of the phase voltage in each phase or the line voltage between each phase;
means for determining that a short circuit has occurred in the power system when the effective value of any of the calculated line voltages drops, the magnitude of a difference vector of any of the phases is equal to or greater than a set value, and the phase of the difference vector is within a preset short circuit detection range;
A program to function as a

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