Protection system

Abstract

To provide a protection system capable of avoiding zero missing without using a neutral point resistor.SOLUTION: A protection system (20) includes a control device (11) that receives an external interruption signal for interrupting a first circuit breaker (4) located between a power system (1) and a transformer (6), interrupts a second circuit breaker (9) connected in series to a neutral point compensation reactor (7) when a zero phase voltage of the transformer is not equal to or lower than a set value, and interrupts the first circuit breaker simultaneously with or after the interruption of the second circuit breaker.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a protection system for protecting a three-phase AC power system. [Background technology]

[0002] Non-Patent Document 1 discloses a protection system that protects a power system when a single-line or double-line ground fault occurs in a three-phase AC power system. In this protection system, a neutral point resistor is connected in series with a neutral point compensation reactor that is installed to compensate for the charging capacity of the power transmission cable. When a single-line or double-line ground fault occurs, a zero-phase sequence voltage is generated and a fault current flows through the neutral point compensation reactor. The DC component contained in the fault current is attenuated by the neutral point resistor. As a result, a zero-phase sequence error is avoided. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Kazuhiko Iiyama et al., "Earth fault zero-failure phenomenon and prevention method in long-distance cables of non-effectively grounded systems", 2006 National Convention of the Institute of Electrical Engineers of Japan Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the protection system disclosed in Non-Patent Document 1, the presence of a neutral point resistor increases the active current component of the fault current. In this case, the risk of electromagnetic induction interference to communication lines increases. For this reason, there are cases where the method of avoiding zero faults using a neutral point resistor cannot be applied.

[0005] One aspect of the present disclosure aims to realize a protection system that can avoid zero misses without using a neutral point resistor. [Means for solving the problem]

[0006] In order to solve the above problems, a protection system according to one embodiment of the present disclosure is a protection system for protecting a power transmission system including a power system that supplies three-phase AC power, a transformer that transforms the voltage of the three-phase AC power, and a neutral point compensation reactor connected to the neutral point of the transformer, the protection system including a first circuit breaker located between the power system and the transformer, a second circuit breaker connected in series with the neutral point compensation reactor, and a control device that controls the first circuit breaker and the second circuit breaker, and when the control device receives an external shutdown signal to shut off the first circuit breaker and detects that the zero-phase voltage of the transformer is not below a set value, it shuts off the second circuit breaker and shuts off the first circuit breaker simultaneously with or after shutting off the second circuit breaker.

[0007] Moreover, a protection system according to one embodiment of the present disclosure is a protection system for protecting a power transmission system including a power system that supplies three-phase AC power, a transformer that transforms the voltage of the three-phase AC power, a neutral point compensation reactor connected to the neutral point of the transformer, and a power transmission cable that is connected to a power supply device separate from the power system and that is interconnected with the power system, the protection system including a first circuit breaker located between the power system and the transformer, a third circuit breaker located between the power transmission cable and the first circuit breaker, and a control device that controls the first circuit breaker and the third circuit breaker, and when the control device receives an external shutoff signal to shut off the first circuit breaker and detects that the zero-phase voltage of the transformer is not below a set value, the control device shuts off the third circuit breaker and shuts off the first circuit breaker simultaneously with or after shutting off the third circuit breaker. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, a protection system capable of avoiding zero misses without using a neutral point resistor can be realized. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a power transmission system including a protection system according to a first embodiment. [Figure 2] 3 is a flowchart illustrating a process in the protection system according to the first embodiment. [Figure 3] 10 is a graph illustrating currents when a single-line ground fault occurs in a power transmission system of a comparative example and the power transmission system of embodiment 1. [Figure 4] FIG. 10 is a diagram illustrating a power transmission system including a protection system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] An embodiment of the present disclosure will be described in detail below.

[0011] 1 is a diagram illustrating a power transmission system 100 including a protection system 20 according to a first embodiment. The protection system 20 is a system that protects the power transmission system 100. As shown in FIG. 1, the power transmission system 100 includes a power grid 1, a first circuit breaker 4, a power transmission cable 5, a transformer 6, a neutral point compensation reactor 7, a second circuit breaker 9, a third circuit breaker 10, and a control device 11. Of these, the first circuit breaker 4, the second circuit breaker 9, and the control device 11 configure the protection system 20.

[0012] The power system 1 supplies three-phase AC power. Reference numeral 2 in FIG.

[0013] The power transmission cable 5 is connected to another power supply device (not shown) that is interconnected with the power system 1. That is, the power system 1 can be connected to the other power supply device via an interconnection point P2 shown in FIG.

[0014] The first circuit breaker 4 is disposed at the interconnection point P2 in order to interrupt the current at the interconnection point P2. In other words, the first circuit breaker 4 is located between the power system 1 and the transformer 6. FIG. 1 illustrates an example in which a single-line ground fault occurs at an accident point P1 on the power system 1 side of the interconnection point P2. When a single-line ground fault occurs in the power transmission system 100, a fault current flows from the power transmission cable 5 toward the first circuit breaker 4.

[0015] Transformer 6 transforms the voltage of three-phase AC power. In the example of FIG. 1, transformer 6 transforms the voltage of three-phase AC power supplied from power system 1. Transformer 6 is connected to power system 1 in parallel with power transmission cable 5 via first circuit breaker 4. Transformer 6 may be any type of transformer as long as it is a three-phase transformer. A filter, a phase modifying device, or the like is connected to the secondary side of transformer 6.

[0016] The neutral point compensation reactor 7 is connected to the neutral point of the transformer 6. The neutral point compensation reactor 7 is provided for the purpose of compensating for the charging capacity of the power transmission cable 5. The side of the neutral point compensation reactor 7 opposite to the side connected to the neutral point of the transformer 6 is grounded.

[0017] The second circuit breaker 9 is connected in series to the neutral point compensation reactor 7. Specifically, the second circuit breaker 9 is connected to the high-voltage side of the neutral point compensation reactor 7. In the power transmission system 100, when a single-line ground fault occurs at the fault point P1, a fault current flows from the fault point P1 to the neutral point compensation reactor 7 via the first circuit breaker 4 and the transformer 6. The second circuit breaker 9 interrupts the fault current.

[0018] The third circuit breaker 10 is located between the power transmission cable 5 and the first circuit breaker 4. Specifically, the third circuit breaker 10 is located on the power transmission cable 5 side of the transformer 6 and the power transmission cable 5, which are connected in parallel to the power system 1 via the first circuit breaker 4. Therefore, the operation of the third circuit breaker 10 does not affect the current path from the power system 1 to the transformer 6.

[0019] The control device 11 controls the first circuit breaker 4 and the second circuit breaker 9. The control device 11 includes a first circuit breaker relay 111, a second circuit breaker relay 112, and an EVT (Earthed Voltage Transformer) 113. The first circuit breaker relay 111 is a relay that causes the first circuit breaker 4 to interrupt current. The second circuit breaker relay 112 is a relay that causes the second circuit breaker 9 to interrupt current. The EVT 113 is a transformer that measures the zero-phase sequence voltage of the transformer 6.

[0020] Furthermore, the control device 11 includes a control processing unit (not shown) that controls the first circuit breaker relay 111 and the second circuit breaker relay 112. The control processing unit can be realized, for example, by a program that causes a computer to function as the control processing unit. The control processing unit can also be realized by a logic circuit. In the following description, for simplicity, the control of the first circuit breaker 4 via the first circuit breaker relay 111 or the control of the second circuit breaker 9 via the second circuit breaker relay 112 by the control processing unit is described as control of the first circuit breaker 4 or the second circuit breaker 9 by the control device 11.

[0021] The control device 11 controls the first circuit breaker 4 and the second circuit breaker 9 so that the power supply is appropriately cut off when the first circuit breaker relay 111 receives an external cutoff signal. The external cutoff signal is a cutoff signal sent from outside to isolate any equipment when a fault occurs in that equipment.

[0022] 1, the control device 11 receives an external tripping signal from the control system of the power grid 1. For example, when a first-line ground fault or a second-line ground fault occurs at the fault point P1, the control system of the power grid 1 outputs a tripping signal to the first circuit breaker relay 111. This allows the control device 11 to trip the current in response to the first-line ground fault or the second-line ground fault at the fault point P1.

[0023] 2 is a flowchart illustrating the processing in the protection system 20. In the processing illustrated in FIG. 2, the control device 11 first determines whether an external disconnection signal has been received (S1). If an external disconnection signal has been received (YES in S1), the control device 11 further determines whether the zero-phase-sequence voltage is equal to or less than a set value (S2). The set value is a value that is appropriately set by the designer of the power transmission system 100 as the value of the zero-phase-sequence voltage that is expected when a single-line ground fault or a double-line ground fault occurs in the power transmission system 100.

[0024] When the control device 11 receives an external tripping signal and the zero-phase-sequence voltage is not equal to or less than the set value (YES in S2), it is considered that a line-1 ground fault or line-2 ground fault has occurred. In this case, the control device 11 trips the second circuit breaker 9 (S3) and then trips the first circuit breaker 4 (S4). At this time, the control device 11 may trip the first circuit breaker 4 at the same time as tripping the second circuit breaker 9, rather than after tripping the second circuit breaker 9. After tripping the second circuit breaker 9 and the first circuit breaker 4, the control device 11 ends the processing.

[0025] When the control device 11 receives an external tripping signal and the zero-phase voltage is equal to or lower than the set value (NO in S2), it is considered that a short-circuit fault has occurred in the busbar. The busbar here refers to the overhead line and cable between the power grid 1 and the interconnection point P2. In this case, the control device 11 trips the first circuit breaker 4 without tripping the second circuit breaker 9 (S5). After tripping the first circuit breaker 4, the control device 11 ends the processing.

[0026] If the control device 11 does not receive a tripping signal from the outside (NO in S1), the control device 11 determines whether the zero-phase-sequence voltage is equal to or greater than the set value (S6). If the control device 11 does not receive a tripping signal from the outside and the zero-phase-sequence voltage is not equal to or less than the set value (YES in S6), it is considered that a ground fault has occurred inside or outside the equipment of the power transmission system 100. In this case, the control device 11 trips the first circuit breaker 4 if the fault is inside the equipment, and does not trip the first circuit breaker 4 if the fault is outside the equipment (S7). Thereafter, the control device 11 ends the processing.

[0027] The method by which the control device 11 determines whether the ground fault has occurred inside or outside the equipment in step S7 will not be described. Also, if the ground fault has occurred inside the equipment in step S7, the control device 11 may trip the second circuit breaker 9. If the ground fault has occurred outside the equipment, the control device 11 does not trip the second circuit breaker 9.

[0028] If the control device 11 does not receive an external disconnection signal and the zero-phase voltage is equal to or lower than the set value (NO in S6), it is possible that a short-circuit fault has occurred inside or outside the equipment of the power transmission system 100. In this case, the control device 11 determines whether or not a short-circuit fault has occurred (S8). Whether or not a short-circuit fault has occurred is detected by an overcurrent relay or the like.

[0029] If a short-circuit fault has occurred (YES in S8), it is considered that the short-circuit fault has occurred inside or outside the equipment of the power transmission system 100. In this case, the control device 11 will shut off the first circuit breaker 4 if the fault is inside the equipment, and will not shut off the first circuit breaker 4 if the fault is outside the equipment (S9). Thereafter, the control device 11 ends the processing. On the other hand, if a short-circuit fault has not occurred (NO in S8), it is considered that no particular accident has occurred in the power transmission system 100. In this case, the control device 11 will end the processing without shutting off either the first circuit breaker 4 or the second circuit breaker 9.

[0030] 3 is a graph illustrating currents when a single-line ground fault occurs in a power transmission system of a comparative example and the power transmission system 100 of embodiment 1. In the power transmission system of the comparative example, when a tripping signal is received from the outside, the control device 11 attempts to trip the first circuit breaker 4 without tripping the second circuit breaker 9.

[0031] In Fig. 3, reference numeral 301 indicates the current flowing in the first circuit breaker 4 in the power transmission system of the comparative example. Reference numeral 302 indicates the current flowing in the neutral point compensation reactor 7 in the power transmission system of the comparative example. Reference numeral 303 indicates the current flowing in the first circuit breaker 4 in the power transmission system 100. Reference numeral 304 indicates the current flowing in the neutral point compensation reactor 7 in the power transmission system 100. In all of the graphs of reference numerals 301 to 304, the horizontal axis indicates time (seconds) and the vertical axis indicates the magnitude of the current (A). In Fig. 3, the time when a single-line ground fault occurs is designated as t1.

[0032] In the power transmission system of the comparative example, after a line-to-ground fault occurs at time t1, as shown by reference numeral 302, the second circuit breaker 9 does not trip, and current continues to flow through the neutral point compensation reactor 7. Therefore, as shown by reference numeral 301, the first circuit breaker 4 does not trip either, and current continues to flow. In other words, the first circuit breaker 4 is in a zero-miss state.

[0033] In the power transmission system 100, after a single-line ground fault occurs at time t1, the second circuit breaker 9 is tripped at time t2 when the current flowing through the neutral point compensation reactor 7 first becomes zero, as indicated by reference numeral 304. Therefore, as indicated by reference numeral 303, the first circuit breaker 4 is tripped at the timing when the current flowing through the first circuit breaker 4 becomes zero after time t2.

[0034] As described above, according to the protection system 20, when the control device 11 receives an external tripping signal to trip the first circuit breaker 4 and detects that the zero-phase sequence voltage of the transformer 6 is not equal to or lower than the set value, it trips the second circuit breaker 9 and trips the first circuit breaker 4 simultaneously with or after tripping the second circuit breaker 9. This makes it possible to avoid a zero miss in the first circuit breaker 4 when a one-line ground fault or two-line ground fault occurs.

[0035] Furthermore, in the protection system 20, as in step S5, when the control device 11 receives an external tripping signal and does not detect that the zero-phase sequence voltage of the transformer 6 is not equal to or lower than the set value, it trips the first circuit breaker 4 without tripping the second circuit breaker 9. This allows the control device 11 to quickly trip the fault current even when a ground fault occurs on the bus.

[0036] [Embodiment 2] Other embodiments of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0037] Fig. 4 is a diagram illustrating a power transmission system 100A including a protection system 20A according to embodiment 2. In addition to the configuration of the power transmission system 100, the power transmission system 100A includes a transformer 6A, a neutral point compensation reactor 7A, and a second circuit breaker 9A. For simplicity, the neutral point compensation reactor 7 and the second circuit breaker 9 shown in Fig. 1 are omitted from Fig. 4. The power transmission system 100A also includes a control device 11A instead of the control device 11 included in the power transmission system 100. In the power transmission system 100A, the first circuit breaker 4, the second circuit breaker 9A, and the control device 11A configure the protection system 20A.

[0038] Transformer 6A is a transformer located between a power supply device separate from power system 1 and power transmission cable 5, which is connected to power system 1 via interconnection point P2. Transformer 6A transforms the voltage of the power supplied from a power supply device separate from power system 1. In FIG. 4, a power supply device (not shown) is connected in series to transformer 6A. However, a power supply device may be connected in parallel to transformer 6A.

[0039] The neutral point compensation reactor 7A is connected to the neutral point of the transformer 6A. The function of the neutral point compensation reactor 7A is the same as that of the neutral point compensation reactor 7. The second circuit breaker 9A is connected in series with the neutral point compensation reactor 7. The function of the second circuit breaker 9A is the same as that of the second circuit breaker 9.

[0040] The control device 11A differs from the control device 11 in that the control device 11A controls the second circuit breaker 9A instead of the second circuit breaker 9. The control device 11A includes a second circuit breaker relay 112A instead of the second circuit breaker relay 112, and an EVT 113A instead of the EVT 113. The second circuit breaker relay 112A is a relay that causes the second circuit breaker 9A to interrupt current. The EVT 113A is a transformer for measuring the zero-phase sequence voltage of the transformer 6A.

[0041] The control device 11A performs the same control on the second circuit breaker 9A as the control device 11 performed on the second circuit breaker 9. That is, the control device 11A trips the second circuit breaker 9A when it receives a tripping signal from outside and the zero-phase sequence voltage is not equal to or less than the set value. The control device 11A also trips the first circuit breaker 4 after tripping the second circuit breaker 9A or at the same time as tripping the second circuit breaker 9A. The protection system 20A, which includes the first circuit breaker 4, the second circuit breaker 9A, and the control device 11A, can also avoid a zero miss in the first circuit breaker 4 when a one-line ground fault or a two-line ground fault occurs.

[0042] [Embodiment 3] Further embodiments of the present disclosure are described below.

[0043] 1, the control device 11 may control the third circuit breaker 10 instead of the second circuit breaker 9. That is, in the power transmission system 100, the first circuit breaker 4, the third circuit breaker 10, and the control device 11 may configure the protection system 20.

[0044] In this case, when the control device 11 receives an external tripping signal and the zero-phase sequence voltage is not equal to or less than the set value, it trips the third circuit breaker 10 instead of the second circuit breaker 9. Furthermore, the control device 11 trips the first circuit breaker 4 after tripping the third circuit breaker 10 or at the same time as tripping the third circuit breaker 10. By operating the protection system 20 in this manner, a zero miss in the first circuit breaker 4 can be avoided when a one-line ground fault or a two-line ground fault occurs at the fault point P1.

[0045] 〔summary〕 The present disclosure can also be expressed as follows:

[0046] A protection system according to a first aspect of the present disclosure is a protection system for protecting a power transmission system including a power system that supplies three-phase AC power, a transformer that transforms the voltage of the three-phase AC power, and a neutral point compensation reactor connected to the neutral point of the transformer, the protection system including a first circuit breaker located between the power system and the transformer, a second circuit breaker connected in series with the neutral point compensation reactor, and a control device that controls the first circuit breaker and the second circuit breaker, and when the control device receives an external shutoff signal to shut off the first circuit breaker and detects that the zero-phase voltage of the transformer is not below a set value, it shuts off the second circuit breaker and shuts off the first circuit breaker simultaneously with or after shutting off the second circuit breaker.

[0047] A protection system according to a second aspect of the present disclosure is related to the first aspect, wherein the transformer transforms the voltage of three-phase AC power supplied from the power system.

[0048] A protection system according to aspect 3 of the present disclosure is the same as that of aspect 1, further comprising a transmission cable connected to a power supply device separate from the power system and interconnected with the power system, wherein the transformer is located between the power supply device and the transmission cable and transforms the voltage of the three-phase AC power supplied from the power supply device.

[0049] In a protection system according to aspect 4 of the present disclosure, in any one of aspects 1 to 3, the control device receives an external shutdown signal to shut off the first circuit breaker and shuts off the first circuit breaker without shutting off the second circuit breaker when it does not detect that the zero-phase voltage of the transformer is not below a set value.

[0050] A protection system according to a fifth aspect of the present disclosure is a protection system for protecting a power transmission system including a power system that supplies three-phase AC power, a transformer that transforms the voltage of the three-phase AC power, a neutral point compensation reactor connected to the neutral point of the transformer, and a transmission cable that is connected to a power supply device separate from the power system and that is interconnected with the power system, the protection system including a first circuit breaker located between the power system and the transformer, a third circuit breaker located between the transmission cable and the first circuit breaker, and a control device that controls the first circuit breaker and the third circuit breaker, and when the control device receives an external disconnection signal to shut off the first circuit breaker and detects that the zero-phase voltage of the transformer is not below a set value, it shuts off the third circuit breaker and shuts off the first circuit breaker simultaneously with or after shutting off the third circuit breaker.

[0051] A sixth aspect of the present disclosure relates to a protection system in any one of the first to fifth aspects, wherein the control device receives the external shutdown signal from a control system of the power grid.

[0052] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0053] 1 Power system 4. First circuit breaker 5. Power transmission cables 6, 6A transformer 7, 7A neutral point compensation reactor 9, 9A second circuit breaker 10. Third circuit breaker 11, 11A control device 20, 20A Protection System 100, 100A power transmission system

Claims

1. a power system that supplies three-phase AC power; a transformer that transforms the voltage of three-phase AC power; a neutral point compensation reactor connected to the neutral point of the transformer; A protection system for protecting a power transmission system comprising: The protection system comprises: a first circuit breaker located between the power grid and the transformer; a second circuit breaker connected in series to the neutral point compensation reactor; a control device that controls the first circuit breaker and the second circuit breaker, The control device a protection system that receives an external tripping signal to trip the first circuit breaker and, when detecting that the zero-phase sequence voltage of the transformer is not equal to or less than a set value, trips the second circuit breaker and trips the first circuit breaker simultaneously with or after tripping the second circuit breaker.

2. The protection system according to claim 1 , wherein the transformer is a transformer that transforms a voltage of three-phase AC power supplied from the power system.

3. a power transmission cable connected to a power supply device separate from the power grid that is interconnected with the power grid; The protection system according to claim 1 , wherein the transformer is located between the power supply device and the power transmission cable and transforms the voltage of the three-phase AC power supplied from the power supply device.

4. 2. The protection system according to claim 1, wherein the control device receives an external tripping signal to trip the first circuit breaker and trips the first circuit breaker without tripping the second circuit breaker when the control device does not detect that the zero-phase sequence voltage of the transformer is not equal to or less than a set value.

5. a power system that supplies three-phase AC power; a transformer that transforms the voltage of three-phase AC power; a neutral point compensation reactor connected to the neutral point of the transformer; a power transmission cable connected to a power supply device separate from the power system and interconnected with the power system; A protection system for protecting a power transmission system comprising: The protection system comprises: a first circuit breaker located between the power grid and the transformer; a third circuit breaker located between the power transmission cable and the first circuit breaker; a control device that controls the first circuit breaker and the third circuit breaker, The control device a protection system that receives an external tripping signal to trip the first circuit breaker and, when detecting that the zero-phase sequence voltage of the transformer is not equal to or less than a set value, trips the third circuit breaker, and trips the first circuit breaker simultaneously with or after tripping the third circuit breaker.

6. The protection system according to claim 1 or 5, wherein the control device receives the external interruption signal from a control system of the power grid.

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