WO2024105897A1

WO2024105897A1 - Reverse electric power breaker/relay and method for cutting off reverse electric power in reverse electric power breaker/relay

Info

Publication number: WO2024105897A1
Application number: PCT/JP2023/007657
Authority: WO
Inventors: 俊介加藤
Original assignee: 株式会社日立産機システム
Priority date: 2022-11-16
Filing date: 2023-03-01
Publication date: 2024-05-23
Also published as: JP2024072728A

Abstract

Provided is a reverse electric power breaker/relay that improves detection sensitivity of reverse electric power while avoiding the influence of noise and the like. In a spot network electric supply system, a network relay: (1) determines whether the direction and magnitude of a detected electric current value in a reverse direction are less than a first threshold value function formula ax + b2 (where a and b2 are coefficients, and x is a variable that indicates the magnitude of an electric current 90° delay direction); and further (2) determines whether the absolute value of the magnitude of the electric current value is less than a second threshold value (however, b2 < c), whereby it is determined whether reverse electric power has occurred using the two types of threshold values. When a reverse electric current that exceeds both the first threshold value and the second threshold value has been detected, the network relay cuts off an electric power line from the network bus by controlling a breaker that is provided in the electric power line.

Description

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

The present invention relates to a reverse power cutoff relay suitable for use in a power circuit using a spot network power receiving method.

A spot network power receiving method is known in which power is received from a power company substation through multiple lines (e.g., three 22 kV distribution lines) and the secondary side is connected in parallel to a network bus via a receiving transformer installed on each line. This power receiving method allows power to be received without any problems even if one distribution line stops due to multiple line power receiving, making it possible to operate without interruption and improving the reliability of the power supply. Compared to conventional examples such as regular standby two-line power receiving and loop power receiving, the spot network power receiving method has the features of high reliability due to constant three-line power receiving, space saving due to a simple configuration, and maintenance saving due to the functions unique to the spot network. Such a spot network power receiving method is disclosed, for example, in Patent Document 1 and Patent Document 2.

When adopting the spot network power receiving method, it is common to use a circuit breaker relay on the secondary side of the network transformer that has protective functions such as reverse power cut-off, differential voltage input, no-voltage input, overload warning, and power supply voltage detection. Here, "reverse power cut-off" refers to the detection of the occurrence of reverse current and cutting off the line in which the reverse current occurs when the power supplied to the network is cut off due to the cut-off of one of the multiple supply lines.

Japanese Patent Application Laid-Open No. 9-322394 JP 2005-130609 A

In recent years, the use of amorphous transformers as network transformers has come to be considered. Amorphous transformers are transformers that use amorphous metal as the iron core, and have low iron loss at no load, and less loss than conventional transformers that use silicon steel sheets. For this reason, they have the characteristic of being able to significantly reduce standby loss (no-load loss), enabling power saving and reducing greenhouse gases (CO ₂ ). On the other hand, when using amorphous transformers, the excitation current becomes smaller, so the excitation current during reverse power becomes smaller, making it difficult to detect reverse power.

The present invention has been made in view of the above-mentioned 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 cut-off relay that can determine the need for cutting off reverse power 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 cut-off relay.

Representative features of the invention disclosed in this application are as follows.
According to one feature of the present invention, a reverse power cutoff relay includes 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 value of each phase of the power circuit, and a calculation unit for calculating an excitation current from the voltage measurement value detected by the voltage detection unit and the current measurement value detected by the current detection unit, and for controlling a circuit breaker provided in the power circuit to cut off the power circuit when the excitation current exceeds a threshold in the reverse direction, the calculation unit detects reverse power by using two types of thresholds: (1) determining whether the direction and magnitude of the detected reverse current value are below a first threshold function formula ax+b (a and b are coefficients, and x is a variable indicating the magnitude of the current delay in the 90° direction), and (2) a second threshold (where b<c) for determining whether the absolute value of the current value is less than c. When the reverse power cutoff relay detects a reverse current that satisfies both the first threshold value or more and the second threshold value or more, the circuit breaker provided in the power circuit is used to cut off the circuit. The value of the second threshold c may be less than 0.05% of the "67 settling current value", and is preferably about 0.025%. When judging the current value, the calculation unit judges whether the current value exceeds the first threshold function formula in the reverse direction, and if it does not exceed it, it maintains the connection of the power line as "no reverse power amount that requires interruption" without using the second threshold. On the other hand, if the current value exceeds the first threshold function formula, it judges whether the magnitude of the current value in the reverse direction is less than the second threshold c. The values of a and b of the function formula and the threshold c are set so that the relationship between the first threshold function formula ax+b and the magnitude of the second threshold c is satisfied such that there is a region in which the magnitude of the current value in the reverse direction is equal to or greater than the first threshold function formula ax+b and less than the second threshold c.

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 can be applied to a spot network power supply system having multiple power lines from different power sources, each of which is connected in series with a network transformer, a protector fuse, and a circuit breaker, and in which the multiple power lines are commonly connected to a network bus to supply power from the network bus to a load, and the reverse power interruption relay of the present invention is provided between the network transformer and the circuit breaker in each power line.

　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 now possible to accurately detect small reverse currents flowing in the reverse direction. Furthermore, in improving the detection accuracy, it has become possible to avoid an increase in the probability of malfunctions due to the influence of external noise, thereby realizing a highly reliable reverse power cut-off relay. Furthermore, it has become possible to realize a reverse power cut-off function that is easily applicable to network power receiving systems that use amorphous type transformers.

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. 2 is a block diagram showing a detailed configuration of a network relay 50 in FIG. 1. FIG. 13 is a diagram for explaining a reverse power detection method using a network relay in a conventional example, showing a threshold value 190 in the 67 operating range. FIG. 13 is a diagram for explaining a state in which a threshold 191 of the 67 operating range is lowered to 1/2 level in a reverse power detection method using a network relay of a conventional example. FIG. 9 is a diagram showing a threshold value 91 for setting the 67 operating range according to the present embodiment. FIG. 6 is a diagram for explaining a situation in which the back electromotive force cannot be detected well in FIG. 5 . FIG. 13 is a diagram showing a threshold value 92 for setting the 67 operating range according to a modified example of the present embodiment. 4 is a flowchart for explaining an operation procedure in the reverse power cutoff relay of the present embodiment. FIG. 10 is a diagram showing an example of an alarm display in step 77 of FIG. 8. 1 is a diagram for explaining the principle of reverse power generation in a spot network power receiving method. FIG.

Below, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are given the same reference numerals, and repeated explanations will be omitted. Figure 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 the reliability of supply, the spot network power receiving system 1 enables uninterrupted operation by receiving power from the same consumer or different consumers over multiple lines (three lines in Figure 1), thereby improving the reliability of the power supply. This power receiving system 1 is widely used in skyscrapers in urban areas, and can handle large-capacity loads, while also achieving high reliability and space savings due to its simple configuration. Furthermore, it has the characteristic of achieving reduced maintenance through functions unique to the spot network.

In FIG. 1, power is supplied from a power company through three lines, namely, a first line 10 indicated as "power receiving No. 1", a second line 20 indicated as "power receiving No. 2", and a third line 30 indicated as "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 may be supplied from the same or different power supply networks provided by different power suppliers, or may be a mixture of these. The first line 10 to the third line 30 are, for example, 22 kV AC supplied by three-phase three-wire. In FIG. 1, the three wires are not illustrated individually, but each of the lines 10 to 30 is simply illustrated as a single line. The power supplied by the three lines 10 to 30 is connected to a common network bus 2 and supplied to consumers, power receiving rooms, etc. by wiring 3. Various devices such as circuit breakers are provided in the path of the wiring 3, but are not illustrated here.

The circuit configurations of the first circuit 10, the second circuit 20, and the third circuit 30 are configured to be the same. The components 11 to 19 of the first circuit 10 correspond to the components 21 to 29 of the second circuit 20 and the components 31 to 39 of the third circuit 30, respectively, and can be configured with the same components (or equivalent components). Therefore, in this specification, only the first circuit 10 will be described in detail, and descriptions of the second circuit 20 and the third circuit 30 will be omitted. The part of the first circuit above the illustrated part in Figure 1 is the range of the circuit (not shown) for which the power supplier is responsible. The first circuit 10 is first provided with a first VD11. The first VD11 is a voltage detector. A transformer 13 is provided on the load side of the first VD11 via a disconnect switch 12. The transformer 13 used in the spot network power receiving method is what is called a network transformer, and it is important to select one with high impedance and overload capacity in order to suppress short circuit current and to distribute the load between the transformers equally across multiple lines (first line 10 to third line 30). It is also important to use the same transformer taps to prevent cross currents from occurring between the transformers, and to take care to prevent uneven voltages between the high-voltage lines. In this embodiment, it is preferable to use an amorphous transformer to further promote energy conservation.

A protector fuse 14 is provided on the secondary side of the transformer 13. The protector fuse 14 prevents unnecessary cutoff at the substation on the power supply side by cutting off the fuse in the event of a short circuit accident on the network bus 2. The protector fuse 14 can also be configured to be controllable by a network relay 50 or other relays, which will be described later. The network relay (NWRY) 50 is a device for controlling the disconnection of the first line 10 and the network bus 2 from the viewpoint of protecting the first line 10 when various events occur. One of the protective devices of the network relay 50 is a reverse power cutoff function for preventing reverse flow from other high-voltage lines in response to a power outage on the high-voltage side. In this specification, the "reverse power cutoff relay" refers to a part that has the reverse power cutoff function among the functions realized by using the network relay 50, and in the following specification, the network relay 50 will be described as being almost synonymous with the "reverse power cutoff relay". The network relay 50 is provided on the secondary side of the network transformer 13, on the line between the circuit breaker 19.

　For protection devices in the spot network system, a reverse power interruption relay is required 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 interruption device that satisfies the automatic reclosing characteristics and opening and closing control functions 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, namely, no-voltage input characteristics, overvoltage (differential voltage) input characteristics, and reverse power interruption characteristics.

The principle of reverse power generation in the above-mentioned spot network power receiving method will now 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 provided between the distribution lines 1-1, 1-2, and 1-3 and the 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.

If, for some reason, a fault such as a short circuit or a ground fault occurs in the distribution line 1-3 (arrow (1)), the power company that owns the distribution line 1-3 will cut 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, since the power supply from the first circuit 110 and the second circuit 120 to the network bus 102 continues, 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 to the third circuit 130 and into the distribution line 1-3. In such a case, it is necessary to provide some kind of safety function to cut off the circuit breaker 139 (arrow (4)) of the third circuit 130. This function is realized by a reverse power cutoff relay (see network relay 50 in FIG. 1). In this way, when reverse power flow is detected as shown by arrow (3), the reverse power cutoff relay instantly controls the switch 139 to cut off the path, for example within 0.1 seconds.

Returning to FIG. 1, 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 busbar 2. The opening and closing of the circuit breaker 19 can be controlled by the network relay 50 using a control signal transmitted via the 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 shut off to electrically separate the connection between the first circuit 10 and the network busbar 2.

A signal for detecting the voltage from the first circuit 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 circuit 10. The primary side of the transformer 16 is connected to the first circuit 10, and the secondary side is connected to the network relay 50. A measurement current transformer 17 is provided on the network busbar 2 side of the connection point between the transformer 16 and the first circuit 10 to measure the voltage of the first circuit 10. 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).

Next, the configuration of the network relay 50 and its peripheral parts will be further described with reference to FIG. 2. The network relay 50 is mainly formed of 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 a three-phase three-wire AC system with 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 current exceeds a threshold value, it controls the circuit breaker 19 to separate the line 10 from the network bus 2. The basic functions of this network relay 50 are publicly known, so a detailed description will be omitted here.

The network relay 50 also detects reverse power, and when the primary power supply of the

transformers

13, 23, 33 of one or two of the three

circuits

10, 20, 30 is interrupted, it prevents a reverse current from flowing from the circuit to which power is normally supplied via the network bus 2 to the circuit to which power supply has been stopped. This current is extremely small compared to the forward power (e.g., several hundred A). When the network relay 50 detects a current flowing in the reverse direction, it instantly cuts off the circuit breaker 19, electrically disconnecting the circuit 10 from the network bus 2 (the so-called "67 operation"). Note that while only one circuit of the network bus 2 is shown in FIG. 1, there may be two or more circuits to make the network bus 2 redundant. In that case, the electrical connection from the first circuit 10 to all of the network buses 2 is cut off.

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

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 way, the current detection unit 55 measures the current value flowing through the line 10 and outputs it to the calculation unit 60. Here, the voltage detection unit 51 and the current detection unit 55 measure the voltage value and the current value at regular time intervals, and calculate the voltage measurement value and the current measurement value by using the average value and effective value. The current transformers 17a to 17c and the current detection unit 55 may be configured in the same way as a known network relay. Note that an amplifier or a filter circuit that passes the fundamental signal band of 50 Hz or 60 Hz of the output signal may be provided between the current detection unit 55 and the calculation unit.

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 the device configuration. The calculation unit 60 is provided with a memory 62. The calculation unit 60 executes a program for performing reverse power monitoring and a cutoff function when reverse power is detected, which is stored in advance in the memory 62. 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 cutting off the line 10 from the network bus 2, and cuts off or connects all three-phase lines by an electrical signal sent from the calculation unit 60 via a control signal line 64.

Next, the reverse power interruption procedure in this embodiment will be described with reference to Figures 3 to 7. Figure 3 is a diagram for explaining the operation of a known network relay (so-called AC power directional relay "67"). The network relay takes in current and voltage, and controls the circuit breaker 19 to interrupt when it detects power exceeding a predetermined threshold. Figure 3 shows the magnitude and direction of the current excited in the line 10, with the upward direction on the vertical axis representing the direction of the current being 0°, and the direction of the reverse current flowing from the network busbar 2 to the transformer 13. The downward direction of the vertical axis (direction of 180°) represents the normal power supply direction from the transformer 13 to the network busbar 2. The phase of the current may lag or lead the phase of the voltage, so the lag case is displayed on the right side of the horizontal axis (lag 90°) and the lead case is displayed on the left side of the horizontal axis (lead 90°).

If the spot network power receiving method is operating normally and the three lines 10 to 30 are running normally, the current values will be plotted as shown by dotted lines 86 to 88. The power supplied from the power source via the transformer 13 is extremely large, so the magnitude of the current pointing in the direction of approximately 180 degrees as shown by dotted lines 86 to 88 is much larger than the

arrows

81, 82, and 181. In reality, it would be inappropriate to plot 86 to 88 on the scale of Figure 3, but they have been illustrated to compare the direction with 81, 82, etc. When power is being supplied normally from the three lines 10 to 30, the direction of the current detected by the network relay 50 is, for example, 87.

When one or two of the three circuits 10 to 30 are interrupted, the current detected in the network in the interrupted circuit is, for example, current 181. Current 181 corresponds to the excitation current consumed by transformer 13 when a conventional transformer that is not an amorphous type is used as transformer 13. Current 181 is illustrated in the direction along the lag or lead 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 or not the magnitude is such that the circuit 10 should be interrupted as reverse power. A threshold value 190 is set for this determination. Here, a value indicated 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 an intercept.

Assume that a reverse current 181 is detected by the network relay 50. In this case, the tip position of the arrow of the current 181 is above the threshold 190 indicated by ax+ _b1 , that is, it is included in the range where the reverse current is large (so-called "67 operating range"), so the network relay 50 controls the circuit breaker 19 to trip. The dashed arrow 82 indicates the minimum power value at which reverse power can be detected, and when the reverse current is a slightly leading current, it reaches the threshold 190 at the minimum current value. The minimum absolute value of the current detected as this reverse power (67 setpoint) is, for example, about 0.05% of the rated current of the transformer 13.

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

A simple method for solving the problem of not being able to detect the current 81 described in FIG. 3 is to make the threshold 190 stricter and to reduce the threshold setting value. This improvement plan is shown in FIG. 4. Here, the linear function indicating the threshold 191 can be defined as ax+ _b2 (where x is the horizontal axis position in FIG. 3, a is a coefficient indicating the slope, and _b2 is a coefficient indicating the intercept). The slope a of the linear function of the threshold 191 is the same as in FIG. 3, and the intercept is set to a relationship of _b1 > _b2 . In the example of FIG. 4, _b2 = _b1 /2 is set. With the A/D converter of the input signal of the calculation unit 60 currently used, it is theoretically possible to reduce the accuracy to half of the threshold 190 shown in FIG. 3. Therefore, by setting the threshold 191, the small current 81 flowing in the reverse direction is placed within the 67 operating range, and can be correctly detected as "reverse power". However, the minimum absolute value of the current detected as reverse power (set value 67) becomes too small, at 0.025% of the rated current, as indicated by arrow 82, which is undesirable as it increases the risk of malfunction due to noise, etc.

Therefore, in this embodiment, by using an improved threshold 91, while enabling detection of a small current 81, the minimum absolute value of the current detected as reverse power (67 setting value) is set to 0.05% of the rated current as shown by the arrow 82. The magnitude of this threshold corresponds to a threshold value that is half the magnitude of the conventional threshold value for a current equal to or greater than the minimum value (67 setting value) such as the current 81. As is clear from FIG. 5, the threshold 91 is set to the "67 operating range" as a range that satisfies both the requirements that it is above the linear function ax+b2 shown in FIG. ₄ and that the absolute distance from the intersection line of the vertical and horizontal axes is _c or more. In particular, the values of a, _b2 , and c are set so that there is a region that is equal to or greater than the first threshold function ax+b2 and less than the second threshold c. In this case, the relationship is _b2 <c. By setting the 67 operating range using such threshold value 91, the minimum absolute value (67 setting value) of the current detected as reverse power shown by current 83 is ensured to be 0.05% or more of the rated current, while the shape of the vicinity of the intersection with the vertical axis of the boundary range is changed to a semicircular shape using threshold value 91 in combination with a linear function shown by ax+ _b2 , enabling highly accurate reverse power detection. Note that even with threshold value 91 in Fig. 5, a phenomenon occurs in which detection is not possible when the current is combined with the leading current of the cable under certain conditions. This phenomenon is shown in Fig. 6.

Figure 6 is the same as Figure 5 except for

arrows

84 and 85. For example, when the AMT excitation current 81 and the leading current 85 indicated by the dotted line (this is the current flowing in the cable on the power company side and is 90° ahead) are combined, the current detection unit 55 detects it as the current indicated by arrow 84, which is inside the semicircle and cannot be detected. If the cable leading current 85 is sufficiently larger than the size of the arrow shown in the figure, the current indicated by arrow 84 will again be within the operating range 67 and can be detected. On the other hand, the size of the cable leading current is governed by the length of the cable, but in reality the cable is long enough and the leading current is large enough that it rarely poses a problem.

Fig. 7 shows an example in which the minimum value (67 set value) of the detected current 86 shown in Fig. 4 and Fig. 5 is set to 0.025% or more of the rated current to further improve accuracy. This threshold value 92 is set as the "67 operating range" as a range that satisfies both requirements of being above the linear function ax + _b2 shown in Fig. 3 and being at a distance of _b3 (=c/2) or more from the intersection line of the vertical axis and the horizontal axis. In this way, by using the second criterion based on the magnitude of the current value (distance of c/ ₂ or more from the intersection line of the vertical axis and the horizontal axis) in addition to the 67 operating range determined by the linear function ax + b2, when one of the lines is stopped receiving power, it is possible to accurately detect the current flowing back from the other normal line to the transformer side of the stopped circuit, thereby suppressing unnecessary power consumption and achieving energy saving, and realizing an environmentally friendly reverse power cutoff relay (network relay) with high detection accuracy.

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 realized by software, when the processor 61 executes 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 operating power of the network relay 50 can be supplied from each of the corresponding lines 10 to 30, but even if the power supply to the

lines

10, 20, and 30 from the power supply source is cut off, it is configured to be able to continue operating by a battery backup (not shown) or the like.

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 detects the current value flowing through the line 10 by the current detection unit 55 (step 72). At this time, the calculation unit 61 detects not only the magnitude of the current but also the phase lead and lag of the current to determine the direction of the current and determine the vector value of the current as shown by

currents

81 and 82 in Fig. 5 (step 73). Next, the calculation unit 60 determines whether the absolute value of the detected current (for example, current 81 in Fig. 5) is included in the "67 operating range" in Fig. 4 by the function ax+ _b2 (step 74). If it is not included in the "67 operating range" in step 74, it is determined that no reverse current is occurring and the process returns to step 71.

If the detected current value is within the "67 operating range" shown in FIG. 4 in step 74, it is determined whether the direction of the detected current value is +90° to 0° to -90° (i.e., the reverse direction) and whether its magnitude is equal to or greater than the threshold value C (step 75). If the absolute value is less than C, it is not included in the "67 operating range" shown in FIG. 5, so the process returns to step 71. If the absolute value is equal to or greater than C, it means that the tip position of the measured current vector is located within the "67 operating range" of 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 busbar 2, thereby interrupting the electrical circuit (step 76), and outputs an alarm on the display unit 65 to end the process (step 77). Next, an example of an alarm output will be described using FIG. 9.

9(A) is a diagram showing the display unit 65 in a normal state where the network relay 50 has not detected 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 are provided above it to indicate the operating state. 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. Under normal conditions, the display screen 69 displays the measured current value Ir in units of amperes. The example of FIG. 9(A) shows a state where no current is flowing, that is, the current value (Ir) is 0.00 A. On the upper side of the display screen 69, an OFF lamp 66a indicating that the network relay 50 is not operating and an ON lamp 66c indicating that it is operating normally are displayed. Between the OFF lamp 66a and the ON lamp 66c, a fault lamp 66b is provided to indicate that a fault due to reverse power has occurred on the line 10. Below the display screen 69, there are a measurement button 68a and a return button 68d. The measurement button 68a is a button for switching the content (various measurement data) displayed on the display screen 69. After pressing the measurement button 68a, the measurement data can be selected and the display screen of the display screen 69 can be switched by pressing either the left button 68b or the right button 68c. The return button 68d is a button for returning the display screen 69 switched by the measurement button 68a to the original screen.

9B shows the display screen after the network relay 50 has shut off the circuit breaker 19 due to the detection of reverse power. Here, the off lamp 66a is lit, indicating that power is not being normally supplied to the network relay 50 from the line 10, and the fault lamp 66b is flashing rapidly, indicating that some kind of malfunction has occurred in the line 10. The display screen 69 shows the relay operation log due to the detection of reverse power (displayed as "RY log 01:") and a number indicating which of the pre-classified numbers corresponds to the cause of the relay operation (here, "67" indicating reverse power). The date and time are displayed in the "****:****:****" section below "RY log 01:67". For example, if the date is 17:30:20 on October 1st, 2022, it will be displayed as "221001 17:30:20". When the circuit breaker 19 cuts off the line 10 in this way, the fault lamp 66b, which indicates that a fault has occurred, flashes and the necessary information is displayed to the operator via the display screen 69. When this display is made, a warning sound may be emitted by a sound source such as a buzzer (not shown).

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 can be accurately detected without malfunction. Note that the present invention is not limited to the above-mentioned embodiment, and various modifications are possible within the scope of the spirit of the invention.

1-1, 1-2, 1-3... distribution line, 2... network bus bar, 4-3... switch,
5, 5-1, 5-2, 5-3... circuit breaker, 10... first circuit, 11... first VD,
12... disconnector, 13... (network) transformer, 14... protector fuse,
16: transformer; 17, 17a to 17c: current transformers for measurement; 19: circuit breaker;
20... second circuit, 23... transformer, 30... third circuit, 33... transformer,
50...Network relay (reverse power cut-off relay), 51...Voltage detection unit,
52 to 54: lines, 55: current detection unit, 56 to 58: output lines, 60: calculation unit,
61: processor; 62: memory; 64: control signal line; 65: display unit;
66a...off lamp, 66b...fault lamp, 66c...operation lamp,
68a...measurement button, 68b...left button, 68c...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

A voltage detection unit for measuring the voltage of each phase of a three-phase AC power circuit;
A current detection unit for measuring a current value of each phase of the power circuit;
A reverse power cutoff 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 cut off the power circuit when the excitation current exceeds a threshold in a reverse direction,
The calculation unit is
A second threshold value is used to determine whether the direction and magnitude of the detected reverse current value 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 whether the absolute value of the magnitude of the current value is less than c (where b<c);
A reverse power cut-off relay, characterized in that when both the first threshold function or more and the second threshold function or more are satisfied, the circuit breaker cuts off the power circuit.
The reverse power cutoff relay of claim 1, characterized in that the value of c is less than 0.05% of the rated current of the transformer.
The reverse power cutoff relay according to claim 2, characterized in that the calculation unit maintains the connection of the power line without using the second threshold value if the current value is in the reverse direction and its magnitude does not exceed the first threshold value function formula.
The reverse power cutoff relay of claim 3, characterized in that the values of a, b, and c are set so that there is a region in which the magnitude of the current value in the reverse direction is equal to or greater than the first threshold function ax+b and less than the second threshold c.
A display unit is provided,
5. The reverse power cut-off relay according to claim 4, wherein the display unit displays an alarm when the calculation unit detects reverse power and causes the circuit breaker to cut off.
A voltage detection unit for measuring the voltage of each phase of a three-phase AC power circuit;
A current detection unit for measuring a current value of each phase of the power circuit;
A reverse power interruption method for a reverse power interruption relay having a calculation unit that calculates a current value 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 current value exceeds a threshold in a reverse direction,
The calculation unit is
(a) determining whether the current value is in the reverse direction and the direction and magnitude of the current value are below a predetermined functional formula ax+b (a and b are coefficients, and x is a variable indicating the magnitude of the current delay in the 90° direction);
(b) if it is below the function ax+b, it is determined to be normal;
(c) when the function expression is equal to or greater than ax+b, determining whether the absolute value of the current value is less than c (where c<b);
(c1) If it is less than c, it is determined to be normal;
(c2) A method for cutting off reverse power, comprising: determining that reverse power is flowing when the value is equal to or greater than c; and cutting off the power circuit by the circuit breaker.
The reverse power interruption method according to claim 6, characterized in that the voltage detection unit and the current detection unit measure the voltage value and the current value intermittently at regular time intervals, and calculate the voltage measurement value and the current measurement value by using the average value of the measured values.
The reverse power cutoff relay has a display unit,
8. The method according to claim 7, wherein the calculation unit displays, when the power line is cut off, a message indicating that the power line has been cut off and a time of the cut off on the display unit.
A power supply system comprising a plurality of power lines from different sources, each of which is connected in series with a network transformer, a protector fuse, and a circuit breaker;
In a spot network power supply system in which a plurality of power lines are commonly connected to a network bus so that power is supplied from the network bus to a load,
A spot network power supply system, comprising: a reverse power cutoff relay according to any one of claims 1 to 4, provided between the network transformer and the circuit breaker in each of the power lines.