Reverse power interruption relay and method for interrupting reverse power in a reverse power interruption relay

Abstract

To provide a reverse power interruption relay having reverse power detection sensitivity that is raised while avoiding influence of noise or the like.SOLUTION: A spot network power supply system comprises a network relay that (1) determines whether or not a direction and magnitude of a detected reverse direction current value are lower than a first threshold function expression ax+b (a, b are coefficients, x is magnitude in a current delay 90° direction) and (2) determines whether or not the absolute value of the magnitude of the current value is smaller than a second threshold c (b<c) to determine the existence of reverse power by using the two types of thresholds. In the case of detecting reverse current exceeding both of the first threshold and the second threshold, the network relay interrupts a power circuit from a network bus by using a breaker provided in a power circuit.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a reverse power cutoff relay suitable for use in a spot network power receiving system power circuit. [Background technology]

[0002] A spot network power receiving system is known in which power is received from a power company substation via multiple lines (e.g., three 22 kV distribution lines), with the secondary sides connected in parallel to a network bus via a power receiving transformer installed on each line. This power receiving system allows power to be received without any interruption even if one distribution line goes out, enabling uninterruptible operation and improving the reliability of the power supply. Compared to conventional systems such as two-line regular standby power receiving and loop power receiving, the spot network power receiving system has the following features: high reliability thanks to a three-line regular power receiving system, space savings thanks to a simple configuration, and reduced maintenance thanks to the unique features of the spot network. Such spot network power receiving systems are disclosed, for example, in Patent Documents 1 and 2 listed below.

[0003] When adopting the spot network power receiving system, it is common to use a circuit breaker relay on the secondary side of the network transformer, which has protective functions such as reverse power blocking, differential voltage input, no-voltage input, overload warning, and power supply voltage detection. Here, "reverse power blocking" means that if the power supplied to the network is cut off due to the interruption of one of the multiple supply lines, a reverse current may flow from the network side to the network transformer side, so the circuit in which the reverse current occurs is detected and the circuit in which the reverse current occurs is cut off, and is one of the protective functions of the circuit breaker relay. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-322394 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-130609 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the use of amorphous transformers as network transformers has come under consideration. Amorphous transformers use amorphous metal for the core, resulting in low iron loss when no load is applied, and lower losses compared to conventional transformers that use silicon steel sheets. This allows for significant reductions in standby loss (no-load loss), enabling energy savings and greenhouse gas (CO2) reductions. However, when using amorphous transformers, the excitation current is reduced, which can lead to the problem of making it difficult to detect reverse power.

[0006] The present invention has been made in view of the above background, and an object of the present invention is to provide a reverse power cutoff relay that increases the detection sensitivity of reverse power while avoiding the influence of noise and the like. Another object of the present invention is to provide a reverse power cutoff relay that can determine whether or not reverse power cutoff is necessary through simple software calculations using the detected direction and magnitude of reverse power. It is still another object of the present invention to provide a spot network power receiving system using a highly accurate reverse power cutoff relay. [Means for solving the problem]

[0007] Representative features of the invention disclosed in this application are as follows. According to one feature of the present invention, a voltage detection unit for measuring the voltage of each phase of a three-phase AC power circuit; Flow The excitation current is calculated from the voltage measurement value detected by the current detection unit, the voltage measurement value detected by the voltage detection unit, and the current measurement value detected by the current detection unit, and when the excitation current exceeds the threshold value in the reverse direction, a circuit breaker installed in the power circuit is activated. Power lines A reverse power cutoff relay having a calculation unit that controls the reverse power cutoff relay to cut off the reverse power, and the calculation unit excitation The direction and magnitude of the style electric current are determined whether they are below the first threshold function formula ax + b ( however, where a and b are coefficients, and x is the magnitude in the direction of 90° lag of the current A variable indicating ), and (2) excitation The style absolute value of the magnitude of the electric current is determined whether it is less than c ( However, b <c) a second threshold value (where b < c)). Two types of threshold values are used I'll in this way. The reverse power cut-off relay is configured to cut off the line by a circuit breaker provided in the power line when detecting a reverse current that satisfies both the first threshold value or more and the second threshold value or more. The value of the second threshold Value c is preferably less than 0.05% of the "67 setting current value", and preferably about 0.025%. When determining the current value, the calculation unit Reverse excitation determines whether the style electric current exceeds the first threshold function formula in the reverse direction. If it does not exceed, the connection of the power line is maintained as "no reverse power amount requiring interruption" without using the second threshold value. On the other hand, Reverse excitation when the style electric current exceeds the first threshold function formula, it is determined whether the magnitude of the current value in the reverse direction is less than the second threshold value c. The magnitudes of the first threshold function formula ax + b and the second threshold value c are excitation such that the values of a and b of the function formula and the value of the threshold value c are set so that there exists a region where the magnitude in the reverse direction of the style electric current is equal to or greater than the first threshold function formula ax + b and less than the second threshold value c.

[0008] According to another feature of the present invention, when the calculation unit detects reverse power and causes the circuit breaker to trip, an alarm is displayed on the display unit. The present invention has a plurality of power lines from different power sources. In each power line, a network transformer, a protector fuse, and a circuit breaker are connected in series, and the plurality of power lines are commonly connected to a network bus so that power is supplied from the network bus to a load. It can be applied to a spot network power supply system, and the reverse power cut-off relay of the present invention is provided between the network transformer and the circuit breaker in each power line. [Effects of the Invention]

[0009] According to the present invention, even when an amorphous transformer with a small excitation current is used in a spot network power receiving system, it is possible to accurately detect small reverse currents flowing in the reverse direction. Furthermore, by improving detection accuracy, it is possible to avoid an increase in the probability of malfunction due to the influence of external noise, thereby realizing a highly reliable reverse power blocking relay. Furthermore, it is possible to realize a reverse power blocking function that is easily applicable to network power receiving systems using amorphous type transformers. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit diagram showing a schematic configuration of a spot network power receiving system 1 according to an embodiment of the present invention. [Figure 2] 2 is a block diagram showing a detailed configuration of a network relay 50 in FIG. 1. FIG. [Figure 3] FIG. 10 is a diagram for explaining a conventional reverse power detection method using a network relay, showing a threshold value 190 in the 67 operating range. [Figure 4] FIG. 10 is a diagram for explaining a state in which a threshold 191 in the 67 operating range is lowered to 1 / 2 level in a conventional reverse power detection method using a network relay. [Figure 5] FIG. 9 is a diagram showing a threshold value 91 for setting the 67 operating range according to this embodiment. [Figure 6] FIG. 6 is a diagram for explaining a situation in which the counter electromotive force cannot be detected properly in FIG. 5. [Figure 7] FIG. 10 is a diagram showing a threshold value 92 for setting the 67 operating range according to a modified example of the present embodiment. [Figure 8] 4 is a flowchart illustrating an operation procedure of the reverse power cutoff relay of the present embodiment. [Figure 9] FIG. 9 is a diagram showing an example of an alarm display in step 77 of FIG. 8. [Figure 10]FIG. 1 is a diagram for explaining the principle of reverse power generation in a spot network power receiving system. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are assigned the same reference numerals, and repeated explanations will be omitted. FIG. 1 is a circuit diagram showing the schematic configuration of a spot network power receiving system 1 according to an embodiment of the present invention. In order to increase supply reliability, the spot network power receiving system 1 enables uninterruptible operation by receiving power from multiple lines (three lines in FIG. 1) from the same consumer or different consumers, thereby improving the reliability of the power supply. This power receiving system 1 is widely used in urban skyscrapers and the like, and is capable of handling large-capacity loads, while also achieving high reliability and space savings due to its simple configuration. Furthermore, it is characterized by reduced maintenance due to functions unique to spot networks.

[0012] In FIG. 1 , power is supplied from a power company via three lines: a first line 10 designated "Power Receiving No. 1," a second line 20 designated "Power Receiving No. 2," and a third line 30 designated "Power Receiving No. 3." The first line 10, the second line 20, and the third line 30 may be supplied from the same or different power supply networks provided by the same power supplier, or from the same or different power supply networks provided by different power suppliers, or a combination thereof. The first line 10 to the third line 30 are, for example, 22 kV AC supplied via a three-phase, three-wire system. In FIG. 1 , each of the lines 10 to 30 is simply illustrated as a single line, rather than individually illustrating the three wires. The power supplied via the three lines 10 to 30 is connected to a common network bus 2 and supplied to consumers, power receiving rooms, etc. via wiring 3. Note that various devices, such as circuit breakers, are installed along the wiring 3, but are not shown here.

[0013] The first circuit 10, the second circuit 20, and the third circuit 30 have the same circuit configuration. The components 11-19 of the first circuit 10 correspond to the components 21-29 of the second circuit 20 and the components 31-39 of the third circuit 30, respectively, and can be configured with the same components (or equivalent components). Therefore, this specification will only describe the first circuit 10 in detail, and descriptions of the second circuit 20 and the third circuit 30 will be omitted. The area of ​​the first circuit above the illustrated portion in FIG. 1 is the circuit range (not shown) for which the power supplier is responsible. The first circuit 10 is first provided with a first voltage detector 11. The first voltage detector 11 is a voltage detector. A transformer 13 is provided on the load side of the first voltage detector 11 via a disconnector 12. The transformer 13 used in the spot network power receiving system is what is known as a network transformer. It is important to select one with high impedance and overload capacity in order to suppress short-circuit currents and to distribute the load between the transformers equally across multiple circuits (first circuit 10 to third circuit 30). It is also important to use the same transformer taps to prevent cross currents from occurring between the transformers, and to ensure that voltages between the high-voltage circuits are not uneven. In this embodiment, it is preferable to use an amorphous transformer to further promote energy conservation.

[0014] A protector fuse 14 is provided on the secondary side of the transformer 13. The protector fuse 14 trips in the event of a short circuit on the network bus 2, preventing unnecessary tripping at the substation on the power supply side. The protector fuse 14 can also be configured to be controllable by a network relay 50 (described later) or other relays. The network relay (NWRY) 50 is a device that controls the disconnection between the first circuit 10 and the network bus 2 to protect the first circuit 10 in the event of various events. One of the protective devices of the network relay 50 is a reverse power interruption function that prevents reverse current from other high-voltage circuits in the event of a power outage on the high-voltage side. In this specification, the term "reverse power interruption relay" refers to a part of the network relay 50 that has the reverse power interruption function. In the following description, the network relay 50 will be described as being substantially synonymous with the "reverse power interruption relay." The network relay 50 is provided on the secondary side of the network transformer 13, in the circuit between the network transformer 13 and the circuit breaker 19.

[0015] A spot network type protection device requires the use of a reverse power interruption relay to prevent reverse current from other high-voltage circuits (second circuit 20, third circuit 30) during a power outage on the high-voltage side. Here, the network relay 50 is configured to function as a reverse power interruption relay. The network relay 50 is a type of circuit breaker that satisfies the functions of automatic reclosing and switching control with the simplest structure, and consists of a circuit breaker section (circuit breaker 19) and a relay section (network relay 50). The circuit breaker 19 and network relay 50 are connected by a control signal line 64. The network relay 50 has three main functions: no-voltage input characteristics, overvoltage (differential voltage) input characteristics, and reverse power interruption characteristics.

[0016] Here, the principle of reverse power generation in the above-mentioned spot network power receiving system will be explained using Figure 10. The upper distribution lines 1-1, 1-2, and 1-3 are each three-phase, three-wire power lines, and are supplied by three power supply paths. Here, network transformers 113, 123, and 133 and circuit breakers 119, 129, and 139 are installed between distribution lines 1-1, 1-2, and 1-3 and network bus 102. The function required of the reverse power interruption relay is to interrupt the reverse current that flows from the network side to the transformer side when a feeder supplying the network is interrupted at a substation.

[0017] If a fault such as a short circuit or a ground fault occurs on the distribution line 1-3 (arrow (1)) for some reason, the electric power company that owns the distribution line 1-3 will shut off the power path using the circuit breaker 4-3 (arrow (2)). As a result, the power supply from the distribution line 1-3 to the third circuit 130 is cut off. At this time, because current continues to flow from the first circuit 110 and the second circuit 120 to the network bus 102, as shown by the dashed line (arrow (3)), the power supplied from the first circuit 110 and the second circuit 120 flows back through the network bus 102, the third circuit 130, and then to the distribution line 1-3. In such a case, it is necessary to provide some kind of safety function to shut off the circuit breaker 139 (arrow (4)) on the third circuit 130. This function is realized by a reverse power interruption relay (see network relay 50 in FIG. 1). In this way, when the flow of reverse power as indicated by arrow (3) is detected, the reverse power cutoff relay controls the switch 139 to cut off the path instantly, for example, within 0.1 seconds.

[0018] Returning to Fig. 1 again, a circuit breaker 19 is provided on the secondary side of the transformer 13 of the first circuit 10, closer to the transformer 13 than the connection point to the network bus 2. The opening and closing of the circuit breaker 19 can be controlled by the network relay 50 in response to a control signal transmitted via a control signal line 64. Normally, the circuit breaker 19 is closed to pass power, but if any abnormality occurs on the first circuit 10, the circuit breaker 19 is opened to electrically separate the connection between the first circuit 10 and the network bus 2.

[0019] A signal for detecting the voltage from the first line 10 and a signal for detecting the current are input to the network relay 50. A transformer 16 is provided to measure the voltage of the first line 10. The primary side of the transformer 16 is connected to the first line 10, and the secondary side is connected to the network relay 50. A signal for detecting the voltage of the first line 10 is connected to the network bus 2 side of the connection point between the transformer 16 and the first line 10. style A measurement current transformer 17 is provided to measure the current. The current detector of this embodiment is composed of three current transformers 17a to 17c (described later in FIG. 2) provided on each line of the first circuit 10, and a current detection unit (described later as 55 in FIG. 2).

[0020] Next, the configuration of the network relay 50 and its peripheral parts will be further described using Figure 2. The network relay 50 is mainly formed by a calculation unit 60 having a processor 61, a voltage detection unit 51, and a current detection unit 55. The network relay 50 is provided in the line 10 portion that runs from the power supply side, such as a transformer 13, to the network bus 2. The line 10 is an AC three-phase three-wire system, and has three electric wires (R phase, S phase, and T phase). The network relay 50 detects the magnitude of the current flowing through the line 10, and when the detected values ​​exceed a threshold, it controls the circuit breaker 19 to disconnect the line 10 from the network bus 2. The function of this network relay 50 is publicly known, so a detailed description thereof will be omitted here.

[0021] The network relay 50 also detects reverse power and prevents reverse current from flowing from a line that is normally supplied with power via the network bus 2 to a line that is not receiving power if the primary power supply of transformers 13, 23, or 33 of one or two of the three lines 10, 20, and 30 is interrupted. This current is extremely small compared to the forward power (e.g., several hundred amperes). When the network relay 50 detects reverse current, it instantly disconnects the line 10 from the network bus 2 by using a circuit breaker 19 (the so-called "67 operation"). Note that while FIG. 1 shows only one network bus 2, two or more lines may be used for redundancy. In such cases, the electrical connection from the first line 10 to all network buses 2 is interrupted.

[0022] Voltage detection unit 51 monitors the direction and magnitude of the voltage on line 10. This voltage is, for example, 400 V (in the case of low voltage), and the voltage transformed via transformer 16 is input to voltage detection unit 51. Transformer 16 is a combination of three single-phase transformers, which steps down the inter-phase voltage and outputs it to voltage detection unit 51 via three lines 52 to 54. Voltage detection unit 51 monitors the voltage value on line 10 in real time and outputs the measured value to calculation unit 60. The voltage detection unit 51 may be configured in the same way as a known network relay.

[0023] The current detection unit 55 detects the magnitude of the current flowing through the line 10. The direction of the current can be determined by the calculation unit 60 based on the direction of the voltage. Here, current transformers 17a to 17c are provided for each of the R, S, and T phases, and their outputs are output to the current detection unit 55 via output lines 56 to 58. In this manner, the current detection unit 55 measures the current flowing through the line 10 and outputs the measured values ​​to the calculation unit 60. Here, the voltage detection unit 51 and the current detection unit 55 may measure the voltage and current values ​​at regular time intervals and calculate the measured voltage and current values ​​using their average and effective values. The current transformers 17a to 17c and the current detection unit 55 may be configured similarly to known network relays. Note that an amplifier or a filter circuit that passes a 50 Hz or 60 Hz fundamental signal band of the output signal may be provided between the current detection unit 55 and the calculation unit.

[0024] The calculation unit 60 includes a processor 61. The type of processor 61 to be provided is arbitrary, and a microcomputer may be incorporated into the network relay 50 to form a device configuration. The calculation unit 60 is provided with a memory 62. The calculation unit 60 executes a program that is stored in advance in the memory 62 and that performs reverse power monitoring and cut-off functions when reverse power is detected. The memory 62 may take any form, and may include a non-volatile memory. A memory built into the microcomputer may also be used. The circuit breaker 19 is a device for disconnecting the line 10 from the network bus 2, and disconnects or connects all three-phase lines in response to an electrical signal sent from the calculation unit 60 via a control signal line 64.

[0025] Next, the reverse power interruption procedure in this embodiment will be described using FIGS. 3 to 7. FIG. 3 is a diagram illustrating the operation of a known network relay (a so-called AC power directional relay "67"). The network relay receives current and voltage and controls the circuit breaker 19 to trip when it detects power exceeding a predetermined threshold. FIG. 3 shows the magnitude and direction of the current excited in the line 10. The upward direction of the vertical axis represents the direction of current flow of 0°, which is the direction of reverse current flow from the network bus 2 to the transformer 13. The downward direction of the vertical axis (180° direction) represents the normal power supply direction from the transformer 13 to the network bus 2. The current phase may lag or lead the voltage phase, so lag cases are displayed on the right side of the horizontal axis (90° lag) and lead cases are displayed on the left side of the horizontal axis (90° lead).

[0026] When the spot network power receiving system is operating normally and the three circuits 10-30 are operating normally, the current values ​​are plotted as shown by dotted lines 87-88. Because the power supplied from the power source via the transformer 13 is extremely large, the magnitude of the current directed in the approximately 180° direction indicated by dotted lines 87-88 is incomparably larger than the arrows 81, 82, and 181. In reality, it would be inappropriate to plot 86-87 on the scale diagram of FIG. 3, but they have been included here to compare the direction with 81, 82, etc. When power is being supplied normally from the three circuits 10-30, the direction of the current detected by the network relay 50 is, for example, 87.

[0027] When one or two of the three circuits 10-30 are interrupted, the current detected in the network of the interrupted circuit is, for example, current 181. Current 181 corresponds to the excitation current consumed by transformer 13 when a conventional transformer other than an amorphous type is used. Current 181 is illustrated as being oriented in a lagging or leading direction, and the magnitude of current 181 is indicated by the length (absolute value) from the center point of the vertical and horizontal axes. In this way, when the calculation unit 60 of the network relay 50 detects current 181, it determines whether the magnitude is sufficient to interrupt circuit 10 as reverse power. A threshold value 190 is set for this determination. Here, a value expressed by a linear function ax+b1 is used as threshold value 190. x is a variable indicating the position on the horizontal axis, a is a coefficient indicating the slope of the linear function, and b1 is the intercept.

[0028] Suppose that reverse current 181 is detected by network relay 50. In this case, the tip of the arrow of current 181 is above threshold 190 indicated by ax+b1, i.e., it is within the range where the reverse current is large (the so-called "67 operating range"), so network relay 50 controls circuit breaker 19 to trip. Dashed line arrow 82 indicates the minimum power value at which reverse power can be detected; if the reverse current is a slightly leading current, it reaches threshold 190 at the minimum current value. The minimum absolute value of the current detected as this reverse power (67 setting value) is, for example, approximately 0.05% of the rated current of transformer 13.

[0029] In spot network power receiving systems, amorphous transformers 13 are commonly used. When an amorphous transformer is used as in this embodiment, current 81 consumed as an excitation current in transformer 13 when a reverse current occurs is smaller than conventional current 181 as shown in the figure, and therefore threshold 190 of conventional network relays does not fall within the 67 operating range. Therefore, when an amorphous transformer is used, if threshold 190 is set as in the past, there is a risk that a problem will occur in which processor 61 of calculation unit 60 will not be able to detect a small current 81 flowing in the reverse direction, even if such a current exists.

[0030] A simple solution to the problem of not being able to detect current 81 described in Figure 3 is to set threshold 190 more strictly and reduce the threshold setting value. Figure 4 shows this improvement. Here, the linear function representing threshold 191 can be defined as ax + b2 (where x is the horizontal axis position in Figure 3, a is a coefficient indicating the slope, and b2 is a coefficient indicating the intercept). The slope a of the linear function of threshold 191 is the same as in Figure 3, and the intercepts have the relationship b1 > b2. In the example in Figure 4, b2 = b1 / 2. With the currently used A / D converter for the input signal of calculation unit 60, it is theoretically possible to reduce threshold 190 to half the accuracy shown in Figure 3. Therefore, by setting threshold 191, small currents 81 flowing in the reverse direction fall within the operating range of 67, allowing them to be correctly detected as "reverse power." However, the minimum absolute value of the current detected as reverse power (setting value 67) becomes too small, at 0.025% of the rated current, as indicated by arrow 82, which increases the risk of malfunction due to noise, etc., and is therefore undesirable.

[0031] Therefore, in this embodiment, by using the improved threshold value 91, it is possible to detect a small current 81, while the minimum value (67 setting value) of the absolute value of the current detected as reverse power is set to 0.05% of the rated current as shown by the arrow 82. The magnitude of this threshold value corresponds to a threshold value that is half the magnitude of the conventional threshold value for currents greater than or equal to the minimum value (67 setting value) such as the current 81. As is clear from FIG. 5, this threshold value 91 is defined as the "67 operating range" within the range that satisfies both requirements: above the linear function ax + b2 shown in FIG. 4 and having an absolute distance of c or more from the intersection line of the vertical and horizontal axes. In particular, the values of a, b, and c are set such that there exists a region that is greater than or equal to the first threshold function formula ax + b2 and less than the second threshold value c. In this case, the relationship b < c holds. By setting the 67 operating range with such a threshold value 91, while ensuring that the minimum value (67 setting value) of the absolute value of the current detected as reverse power shown by the current 83 is 0.05% or more of the rated current, the shape near the intersection with the boundary region vertical axis is changed to a semicircular shape by using the threshold value 91 in combination with the linear function shown by ax + b2, enabling highly accurate reverse power detection. Note that even for the threshold value 91 in FIG. 5, depending on the conditions, a phenomenon may occur where it cannot be detected when combined with the advancing current of the cable. FIG. 6 shows this phenomenon.

[0032] FIG. 6 is the same as FIG. 5 except for the arrows 84 and 85. For example, when the AMT excitation current 81 and the advancing current 85 indicated by the dotted line (this is the current flowing in the cable on the power company side and is advanced by 90°) are combined, the current detection unit 55 detects it as the current indicated by the arrow 84, which is inside the semicircle and thus cannot be detected. Note that if the advancing current 85 of the cable is sufficiently larger than the magnitude of the arrow shown in the figure, the current indicated by the arrow 84 will enter the 67 operating range again and can be detected. On the other hand, the magnitude of the advancing current of the cable is controlled by the length of the cable. In reality, the cable is sufficiently long and the advancing current is sufficiently large, so this is rarely a problem.

[0033] Figure 7 shows an example in which the minimum value (67 setting) of the detected current 86 shown in Figures 4 and 5 is set to 0.025% or more of the rated current, further improving accuracy. This threshold 92 is defined as the "67 operating range"—the range that satisfies both the requirements of being above the linear function ax + b2 shown in Figure 3 and being at least c / 2 away from the intersection of the vertical and horizontal axes. By combining the 67 operating range determined by the linear function ax + b3 with a second criterion based on the magnitude of the current value (a distance of at least c / 2 away from the intersection of the vertical and horizontal axes), when one of the circuits is interrupted, it is possible to accurately detect reverse current flowing from other normal circuits to the transformer of the interrupted circuit. This reduces unnecessary power consumption, saving energy, and enabling an environmentally friendly reverse power interruption relay (network relay) with high detection accuracy.

[0034] Next, the reverse power detection procedure executed by the processor 61 of the calculation unit 60 will be described using the flowchart of FIG. 8. This procedure can be implemented by software, with the processor 61 executing a computer program (not shown) previously stored in the memory 62. The network relay 50 starts operating when power is supplied to the line 10 and continues to operate as long as the power supply continues. The control procedure of the flowchart of FIG. 8 is executed not only inside the network relay 50 provided on the first line 10, but also in the network relays 50 provided on the second line 20 and the third line 30 in the same manner in parallel. The network relay 50 can be supplied with operating power from each of the corresponding lines 10 to 30, but is configured to continue operating even if the power supply from the power supply source to the lines 10, 20, and 30 is interrupted by a battery backup (not shown) or the like.

[0035] First, the calculation unit 60 measures the voltage value of the line 10 from the output of the voltage detection unit 51 (step 71), and then the current detection unit 55 detects the value of the current flowing through the line 10 (step 72). At this time, the calculation unit 61 detects not only the magnitude of the current but also the phase lead or lag of the current to determine the direction of the current, thereby determining the vector value of the current, such as currents 81 and 82 shown in FIG. 5 (step 73). Next, the calculation unit 60 determines whether the absolute value of the detected current (e.g., current 81 in FIG. 5) is within the "67 operating range" in FIG. 4 using the function ax+b2 (step 74). If the absolute value is not within the "67 operating range" in step 74, it is determined that no reverse current is occurring, and the process returns to step 71.

[0036] If step 74 determines that the detected current is within the "67 operating range" shown in FIG. 4, it is determined whether the direction of the detected current value is between +90°, 0°, and -90° (i.e., the reverse direction) and whether its magnitude is equal to or greater than threshold C (step 75). If the absolute value is less than C, the current is not within the "67 operating range" shown in FIG. 5, and the process returns to step 71. If the absolute value is equal to or greater than C, this means that the leading edge of the measured current vector is within the "67 operating range" shown in FIG. 5. In this case (if Yes), the calculation unit 60 determines that reverse power has been detected and operates the circuit breaker 19 to disconnect the electrical connection between the first circuit 10 and the network bus 2, thereby interrupting the electrical circuit (step 76). An alarm is output on the display unit 65, and the process ends (step 77). Next, an example of alarm output will be described with reference to FIG. 9.

[0037] FIG. 9A shows the display unit 65 in a normal state where the network relay 50 is not detecting the occurrence of reverse power. A dot-matrix display screen 69 is provided in the center of the display unit 65, and three lamps 66a to 66c indicating the operating status are provided above the display screen 69. During normal operation, the ON lamp 66c is lit. Push buttons 68a to 68d are provided below the display screen 69 for the operator to operate. During normal operation, the display screen 69 displays the measured current value Ir in amperes. The upper side of the display screen 69 displays an OFF lamp 66a indicating that the network relay 50 is not operating, and an OPERATION lamp 68 indicating that the network relay 50 is operating normally. Between the OFF lamp 66a and the OPERATION lamp 68, a FAIL lamp 66b is provided to indicate that a fault due to reverse power has occurred on the line 10. A MEASURE button 68a and a RESET button 68d are provided below the display screen 69. The MEASURE button 68a is used to switch the content (various measurement data) displayed on the display screen 69. After pressing the measurement button 68a, pressing either the left button 68b or the right button 68c allows the selection of measurement data and the switching of the display screen 69. The return button 68d is a button for returning the display screen 69 switched by the measurement button 68a to the original screen.

[0038] FIG. 9(B) shows the display screen after the network relay 50 has detected the occurrence of reverse power and has shut off the circuit breaker 19. Here, the OFF lamp 66a lights up, indicating that power is not being supplied normally from the line 10 to the network relay 50, and the Fault lamp 66b flashes rapidly, indicating that some kind of malfunction has occurred on the line 10. The display screen 69 displays the relay operation log (displayed as "RY Log 01:") due to the detection of reverse power and the cause of the relay operation as a number (here, "67," indicating reverse power). Below "RY Log 01:67," the ********:**:** part displays the date and time. For example, if the date is October 1, 2022, 17:30:20, it displays "221001 17:30:20." When the circuit 10 is shut off by the circuit breaker 19 in this way, the Fault lamp 66b flashes, indicating that a malfunction has occurred, and necessary information is displayed to the operator on the display screen 69. At this time, a warning sound may be emitted by a sound source such as a buzzer (not shown).

[0039] As described above, according to this embodiment, reverse power can be detected more accurately than in the past, so even when an amorphous transformer with a small excitation current is used in a spot network power receiving system, small reverse power in the reverse direction can be accurately detected without malfunction. Note that the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention. [Explanation of symbols]

[0040] 1-1, 1-2, 1-3 distribution lines 2 Network Busbar 4-3 Switches 5, 5-1, 5-2, 5-3 circuit breakers 10 First Line 11 First VD 12 Disconnector 13 (Network) Transformers 14 Protector fuse 16 Transformer 17, 17a to 17c Measuring current transformers 19 Threshold 19 Circuit Breaker 20 Second Line 23 Transformer 30 Third Line 33 Transformer 50 Network relay (reverse power cut-off relay) 51 Voltage detection unit 52~54 line 55 Current detection section 56~58 output lines 60 Arithmetic section 61 processors 62 memory 64 control signal line 65 Display section 66a Off lamp 66b Malfunction lamp 66c Operation lamp 68a Measurement button 68b Left button 69c Right button 60d Return button 69 Display screen 81, 82 current 91, 92 Threshold 102 Network Bus 110 First Line 120 Second Line 130 Third Line 181 Current 190, 191 Threshold

Claims

1. a voltage detection unit for measuring the voltage of each phase of a three-phase AC power circuit; a current detection unit for measuring the current of each phase of the power circuit; A reverse power interruption relay having a calculation unit that calculates an excitation current from a voltage measurement value detected by the voltage detection unit and a current measurement value detected by the current detection unit, and controls a circuit breaker provided in the power circuit to interrupt the power circuit when the excitation current exceeds a threshold value in the reverse direction, The calculation unit Determine whether the direction and magnitude of the detected reverse excitation current are below a first threshold function ax+b (where a and b are coefficients, and x is a variable indicating the magnitude of the current delay in the 90° direction), and use a second threshold to determine whether the absolute value of the magnitude of the excitation current is less than c (where b<c); A reverse power cutoff relay characterized in that the circuit breaker cuts off the power circuit when both the first threshold function or more and the second threshold function or more are satisfied.

2. 2. The reverse power cutoff relay according to claim 1, wherein the value of c is less than 0.05% of the rated current of the transformer.

3. The reverse power cutoff relay according to claim 2, wherein the calculation unit maintains the connection of the power circuit without using the second threshold value when the excitation current is in the reverse direction and its magnitude does not exceed the first threshold value function formula.

4. The reverse power cutoff relay according to claim 3, wherein the values ​​of a, b, and c are set so that there is a region where the magnitude of the excitation current in the reverse direction is equal to or greater than the first threshold function expression ax+b and is less than the second threshold value c.

5. A display unit is provided, 5. The reverse power cutoff relay according to claim 4, wherein when the calculation unit detects reverse power and causes the circuit breaker to trip, the display unit displays an alarm.

6. a voltage detection unit for measuring the voltage of each phase of a three-phase AC power circuit; a current detection unit for measuring the current of each phase of the power circuit; A reverse power interruption method for a reverse power interruption relay having a calculation unit that calculates an excitation current from a voltage measurement value detected by the voltage detection unit and a current measurement value detected by the current detection unit, and controls a circuit breaker provided in the power circuit to interrupt the power circuit when the excitation current exceeds a threshold value in the reverse direction, The calculation unit (1) Determine whether the excitation current is in the reverse direction and whether its direction and magnitude are less than a predetermined function ax+b (where a and b are coefficients, and x is a variable indicating the magnitude of the current delay in the 90° direction); (2) If the value is less than the function ax+b, it is determined to be normal. (3) When the function expression is equal to or greater than ax+b, it is determined whether the absolute value of the excitation current is less than c (where b<c); (4) If it is less than c, it is judged as normal; (5) A reverse power interruption method characterized in that when the value is equal to or greater than c, it is determined that reverse power is flowing and the power circuit is interrupted by the circuit breaker.

7. 7. The reverse power interruption method according to claim 6, wherein the voltage detection unit and the current detection unit measure the voltage and the current intermittently at regular time intervals, and calculate the voltage measurement value and the current measurement value by using the average value of the measured voltage and current.

8. The reverse power cutoff relay has a display unit, 8. The reverse power cut-off method according to claim 7, wherein the calculation unit displays, on the display unit, a message indicating that the power line has been cut off and the time when the power line has been cut off.

9. a plurality of power lines from different sources, each of which has a network transformer, a protector fuse, and a circuit breaker connected in series; In a spot network power supply system in which a plurality of power lines are commonly connected to a network bus to supply power from the network bus to a load, A spot network power supply system, characterized in that the reverse power interruption relay according to any one of claims 1 to 4 is provided between the network transformer and the circuit breaker in each of the power lines.

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