Protection System

Abstract

Prevents malfunction of the circuit breaker in the event of a ground fault on another line. [Solution] A protection system (101) includes a first circuit breaker (6), a second circuit breaker (43) that shorts and opens both ends of a capacitor (42), and a control device (5) that controls the first circuit breaker (6) and the second circuit breaker (43). The control device (5) includes a first circuit breaker relay (52) that detects a fault in a bus bar (100a) of a power system (100) and shuts off the first circuit breaker (6), a zero-phase-sequence voltage detector (51) that detects a zero-phase-sequence voltage of a transformer (3), and a second circuit breaker relay (53) that controls the second circuit breaker (43) to short circuit when at least one of a fault non-detection event in which a fault in the bus bar (100a) is not detected and a voltage non-detection event in which a non-zero zero-phase-sequence voltage is not detected occurs.

Description

[Technical field]

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

[0002] In a three-phase AC power system, faults such as ground faults, short circuit faults, etc. have been occurring. Conventionally, measures have been taken to protect the power system from such faults.

[0003] For example, Patent Document 1 discloses a protection system in which the neutral point of a power system is grounded via a protection unit in order to prevent a current zero error when a one-phase ground fault occurs. The protection unit includes a neutral point compensation reactor and a neutral point capacitor connected in series to the neutral point compensation reactor.

[0004] When a ground fault occurs inside or outside the electrical equipment in which the protection unit is installed, a resonant current caused by the resonance phenomenon caused by the neutral compensation reactor and neutral capacitor flows from the protection unit to the fault point. The neutral compensation reactor is installed to compensate for the current flowing in the power transmission cable that is branched off from the electrical equipment to the power source. Therefore, the only current flowing at the fault point is the resonant current. If the zero cross point of this resonant current exists within the current zero miss evaluation time, it becomes possible for the circuit breaker to cut off the circuit, and a current zero miss is avoided. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7538457 Summary of the Invention [Problem to be solved by the invention]

[0006] As shown in Fig. 5, in a power system equipped with the above protection system, when a single-line ground fault occurs in another line 10 that is connected to a common busbar with an electrical equipment 9 in which a protection unit 8 is installed, the interconnection circuit breaker 11 of the line 10 is driven by a relay (not shown) to cut off the fault in order to clear the fault. In addition, in the event of a ground fault, as shown by the dashed line in Fig. 5, a low-frequency resonant current flows from the electrical equipment 9 to a fault point P through the closed circuit breaker 6. This resonant current has a longer period and a larger amplitude than the fundamental wave of the AC current, and therefore may cause the operation of the relay to become unstable.

[0007] One aspect of the present disclosure aims to prevent malfunction of a circuit breaker when a ground fault occurs in another line. [Means for solving the problem]

[0008] 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 system that supplies three-phase AC power, the protection system comprising: a transformer that transforms a voltage of three-phase AC power, a neutral point compensation reactor connected to a neutral point of the transformer, and a capacitor connected in series to the neutral point compensation reactor, the protection system comprising: a circuit breaker arranged between the power system and the transformer, a switch that shorts and opens both ends of the capacitor, and a control device that controls the circuit breaker and the switch, the control device having a fault detection unit that causes the circuit breaker to open by detecting a fault in a bus bar in the power system, a zero-phase voltage detection unit that detects a zero-phase voltage of the transformer, and an opening / closing control unit that controls the switch to short-circuit when at least one of a fault non-detection event in which a fault in the bus bar is not detected by the fault detection unit and a voltage non-detection event in which a non-zero zero-phase voltage is not detected by the zero-phase voltage detection unit occurs. Effect of the Invention

[0009] According to one aspect of the present disclosure, it is possible to prevent malfunction of a circuit breaker in the event of a ground fault in another line. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a power transmission system including a protection system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a circuit diagram showing a configuration of a transformer in the power system and a neutral point compensation reactor and a capacitor connected to the transformer. [Diagram 3] 4 is a flowchart showing a procedure of a process related to a protection operation of the power grid by the protection system. [Figure 4] 3 is a waveform diagram showing currents flowing through various parts of the protection system when a fault occurs. FIG. [Diagram 5] FIG. 1 is a diagram for explaining a defect caused by a conventional protection system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Embodiment] <Power system configuration> Hereinafter, one embodiment of the present disclosure will be described in detail.

[0012] Fig. 1 is a diagram showing a power system 100 including a protection system 101 according to embodiment 1. Fig. 2 is a circuit diagram showing the configuration of a transformer 3 in the power system 100, and a neutral point compensation reactor 41 and a capacitor 42 connected to the transformer 3.

[0013] The protection system 101 is a system that protects a three-phase power system 100, and transmits three-phase AC power through a three-phase electric circuit. As shown in Fig. 1, the power system 100 includes a power transmission cable 2, a transformer 3, an electric equipment 4, and a control device 5. The power system 100 also includes, as circuit breakers, a first circuit breaker 6, a second circuit breaker 43 (switch) in the electric equipment 4, and a third circuit breaker 7.

[0014] In the power system 100, a bus 100a is formed by an overhead line and a cable between the power source 1 and an interconnection point P2. The bus 100a has a back impedance Z.

[0015] The power transmission cable 2 is provided on one of the electric paths branching off from the electric path downstream of the interconnection point P2, and is connected to a power generation facility (not shown) and the like that is interconnected with the power system 100. That is, the power system 100 can be connected to the power generation facility and the like via the interconnection point P2 (first circuit breaker 6) shown in FIG.

[0016] The transformer 3 transforms the voltage of the three-phase AC power supplied from the power source 1. The transformer 3 is provided on the other electric path branched off from the electric path downstream of the interconnection point P2. The transformer 3 may be any type of three-phase transformer. The primary side of the transformer 3 is connected to the power source 1. The secondary side of the transformer 3 is connected to a filter, a phase modifying device, etc.

[0017] As shown in FIG. 2, the primary winding of the transformer 3 is Y-connected, and the secondary winding of the transformer 3 is Δ-connected. The neutral point NP is located at the junction of the Y-connection of the transformer 3. However, the location of the neutral point NP is not limited to this example. For example, if the transformer 3 is a grounding transformer, the neutral point NP may be located at the junction of the staggered windings of the grounding transformer. The neutral point NP is grounded via a neutral point compensation reactor 41 and a capacitor 42, which will be described later. For convenience, a second circuit breaker 43, which will be described later, is omitted in FIG. 2.

[0018] The first circuit breaker 6 is disposed at the interconnection point P2 and cuts off the current at the interconnection point P2. The first circuit breaker 6 is disposed between the power source 1 and the transformer 3. Fig. 1 illustrates an example in which a single-line ground fault occurs at a fault point P1 on the power source 1 side of the interconnection point P2. When a single-line ground fault occurs in the power system 100, a fault current flows from the power transmission cable 2 toward the first circuit breaker 6.

[0019] The third circuit breaker 7 is disposed between the power transmission cable 2 and the first circuit breaker 6. Specifically, the third circuit breaker 7 is located on the power transmission cable 2 side of the power transmission cable 2 and the transformer 3 which are connected to branch off from the electric path from the first circuit breaker 6. For this reason, the interrupting operation of the third circuit breaker 7 does not affect the current path from the power source 1 to the transformer 3.

[0020] The electrical equipment 4 is equipment that supplies lagging reactive power for compensating for the charging capacity of the power transmission cable 2. The electrical equipment 4 has a neutral point compensation reactor 41, a capacitor 42, and a second circuit breaker 43 (switch).

[0021] The neutral point compensation reactor 41 is provided for the purpose of compensating for the charging capacity of the power transmission cable 2. One end of the neutral point compensation reactor 41 is connected to the neutral point NP of the transformer 3, and the other end of the neutral point compensation reactor 41 is connected to one end of the capacitor 42. The other end of the capacitor 42 is connected to a ground terminal and is thereby grounded. In this manner, the capacitor 42 is connected in series with the neutral point compensation reactor.

[0022] The second circuit breaker 43 is a device that shorts and opens both ends of the capacitor 42. As described below, the second circuit breaker 43 opens when a fault occurs in the bus bar 100a and a ground fault occurs in the power system 100, and electrically connects the capacitor 42 to the neutral point compensation reactor 41. The second circuit breaker 43 also closes when there is no fault in the bus bar 100a and when there is no ground fault in the power system 100, and bypasses and connects the other end of the neutral point compensation reactor 41 to the ground terminal. In this way, the second circuit breaker 43 electrically disconnects the capacitor 42 from the neutral point compensation reactor 41.

[0023] The second circuit breaker 43 does not need to be capable of passing a large current like the first circuit breaker 6, but only needs to be capable of interrupting the current that flows when the rated voltage is applied to the neutral point compensation reactor 41. Therefore, a switch may be used instead of the second circuit breaker 43 to short-circuit and open both ends of the capacitor 42. The opening and closing of the second circuit breaker 43 is controlled by a control signal SG3 output from a second circuit breaker relay 53 described later.

[0024] The control device 5 controls the first circuit breaker 6 and the second circuit breaker 43. The control device 5 has a zero-phase-sequence voltage detector 51 (zero-phase-sequence voltage detection unit), a first circuit breaker relay 52 (fault detection unit), and a second circuit breaker relay 53 (opening / closing control unit).

[0025] The zero-phase voltage detector 51 detects the zero-phase voltage V0 of the transformer 3. The zero-phase voltage detector 51 is configured, for example, by an Earthed Voltage Transformer (EVT), but may be configured by other instruments. The zero-phase voltage V0 is 0 V when no earth fault occurs in the power system 100, and becomes a voltage other than 0 V when an earth fault occurs in the power system 100 because the three-phase voltages are unbalanced.

[0026] The first circuit breaker relay 52 is a relay that detects a fault (short circuit fault and ground fault) in the bus bar 100a and thereby shuts off the first circuit breaker 6. The first circuit breaker relay 52 detects a fault in the bus bar 100a by receiving an external shutoff signal SG1 supplied from the outside, for example, an electric power company, and shuts off the first circuit breaker 6. The first circuit breaker relay 52 also detects the occurrence of a fault in the bus bar 100a based on at least one of the voltage and current of the bus bar 100a.

[0027] The first circuit breaker relay 52 outputs a detection signal SG2 that becomes active (for example, H) when it receives an external cutoff signal SG1 or detects a fault in the bus bar 100a. The first circuit breaker relay 52 outputs a detection signal SG2 that becomes inactive (for example, L) when it does not receive an external cutoff signal S1 or does not detect a fault in the bus bar 100a.

[0028] The second circuit breaker relay 53 controls the opening and closing of the second circuit breaker 43 based on a fault detection event and a fault non-detection event by the zero-phase-sequence voltage detector 51 and a voltage detection event and a voltage non-detection event by the zero-phase-sequence voltage detector 51. A fault detection event is an event in which a fault in the bus bar 100a is detected. A fault non-detection event is an event in which a fault in the bus bar 100a is not detected. A voltage detection event is an event in which a non-zero (non-zero) zero-phase-sequence voltage V0 is detected. A voltage non-detection event is an event in which a non-zero zero-phase-sequence voltage is not detected.

[0029] The second circuit breaker relay 53 opens the second circuit breaker 43 when a fault detection event or a voltage detection event occurs in a steady state in which the second circuit breaker 43 shorts both ends of the capacitor 42. The second circuit breaker relay 53 also controls the second circuit breaker 43 to be short-circuited when at least one of a fault non-detection event and a voltage non-detection event occurs.

[0030] In other words, the second circuit breaker relay 53 outputs a control signal SG3, which is a logical product of the detection signal SG2 from the first circuit breaker relay 52 and the zero-phase voltage v0, to the electrical equipment 4. Specifically, when an active detection signal and a non-zero zero-phase voltage V0 are input, the second circuit breaker relay 53 outputs an active control signal SG3. Also, when at least one of an inactive detection signal and a zero zero-phase voltage V0 is input, the second circuit breaker relay 53 outputs an inactive control signal SG3.

[0031] The second circuit breaker relay 53 is preferably configured by, for example, an earth fault overvoltage relay. The earth fault overvoltage relay detects an earth fault in the circuit, and therefore can also function as the zero-phase voltage detector 51. Therefore, when an earth fault overvoltage relay is used as the second circuit breaker relay 53, the zero-phase voltage detector 51 can be omitted. Note that the second circuit breaker relay 53 may be configured by a relay other than an earth fault overvoltage relay.

[0032] <Protection System Operation> Fig. 3 is a flowchart showing a procedure of a process related to a protective operation of the power system 100 by the protection system 101. Fig. 4 is a waveform diagram showing a current flowing through each part in the protection system 101 when a fault occurs.

[0033] As shown in Fig. 3, first, the second circuit breaker relay 53 determines whether the first circuit breaker relay 52 has received an external shutoff signal SG1 or detected a fault in the busbar 100a (step S1). The second circuit breaker relay 53 makes the above determination based on the detection signal SG2 from the first circuit breaker relay 52. ​​Specifically, when the detection signal SG2 is active, the second circuit breaker relay 53 determines that the external shutoff signal SG1 has been received or a busbar fault has been detected. Also, when the detection signal SG2 is inactive, the second circuit breaker relay 53 determines that the external shutoff signal SG1 has not been received or a busbar fault has not been detected.

[0034] In step S1, when the second circuit breaker relay 53 determines that the first circuit breaker relay 52 has received an external shutoff signal SG1 or detected a fault in the bus bar 100a (YES), it determines whether the zero-phase voltage V0 output from the zero-phase voltage detector 51 is non-zero (step S2).

[0035] In step S2, when the second circuit breaker relay 53 determines that the zero-phase voltage V0 is non-zero (YES), it opens the second circuit breaker 43 (step S3) and ends the process. In step S2, the second circuit breaker relay 53 determines that a fault detection event and a voltage detection event have occurred, and outputs an active control signal SG3 for opening the second circuit breaker 43.

[0036] As a result, when the second circuit breaker 43 opens both ends of the capacitor 42, the capacitor 42 is connected to the neutral point compensation reactor 41. Then, due to resonance of the series circuit consisting of the neutral point compensation reactor 41 and the capacitor 42, an oscillating current i n (the above-mentioned resonant signal) is generated. Therefore, the first circuit breaker 6 generates an oscillating current i nThis makes it possible to interrupt the bus bar 100a. This makes it possible to avoid a current zero miss in which no zero cross point occurs for a long period of time when a single line-to-ground fault occurs.

[0037] In this case, as shown in FIG. 5, in the other circuit 10 described above, even if a one-line ground fault occurs, the power system 100 is interrupted at the interconnection point P2 by the first circuit breaker 6, so that the oscillating current i n does not flow through the first circuit breaker 6 to the line 10.

[0038] In addition, in step S1, if the first circuit breaker relay 52 determines that it has received the external shutoff signal SG1 or has not detected a fault in the busbar 100a (NO), the second circuit breaker relay 53 closes the second circuit breaker 43 (step S4) and ends the process. In step S1, the second circuit breaker relay 53 determines that a fault non-detection event has occurred and outputs an inactive control signal SG3 for closing the second circuit breaker 43.

[0039] As a result, when the second circuit breaker 43 shorts both ends of the capacitor 42, the neutral compensation reactor 41 is grounded via the second circuit breaker 43 without the capacitor 42 being connected. In this case, an oscillating current i n does not occur, so the oscillating current i n does not flow to the bus 100a. Therefore, as shown in FIG. 5, in order to remove the one-line ground fault that has occurred in the other line 10 described above, the oscillating current i flows through the circuit breaker 6 (equivalent to the first circuit breaker 6 in FIG. 1) toward the fault point P that causes the interconnection circuit breaker 11 to break. n Therefore, the operation of the relay that cuts off the interconnection breaker 11 is prevented from becoming unstable, and malfunction of the interconnection breaker 11 can be avoided.

[0040] In addition, in step S2, when the second circuit breaker relay 53 determines that the zero-phase voltage V0 is not non-zero (NO), the process proceeds to step S4 and ends. In step S2, the second circuit breaker relay 53 determines that a voltage non-detection event has occurred, and outputs an inactive control signal SG3 for closing the second circuit breaker 43.

[0041] Next, the current flowing in each part of the protection system 101 when a fault occurs will be described.

[0042] 4, when the second circuit breaker relay 53 recognizes both the fault detection event and the voltage detection event after a period of about 50 ms has elapsed since the time point 0.195 s when the fault occurred, it opens (breaks off) the second circuit breaker 43. During the above-mentioned period of time, the current flowing through the neutral point compensation reactor 41 flows through the second circuit breaker 43.

[0043] Furthermore, when the second circuit breaker 43 is cut off, the capacitor 42 is connected to the neutral point compensation reactor 41. As a result, a current in which a low-frequency (e.g., 10 Hz) oscillating waveform is superimposed on a fundamental wave of, for example, 50 Hz flows through the neutral point compensation reactor 41 and the capacitor 42. Then, a low-frequency oscillating current i n In addition, the above-mentioned elapsed period is shorter than the current zero miss evaluation time. This makes it possible to avoid a current zero miss as described above.

[0044] <Effects of the protection system> As described above, the protection system 101 according to this embodiment includes the control device 5 having the zero-phase voltage detector 51, the first circuit breaker relay 52, and the second circuit breaker relay 53. The zero-phase voltage detector 51 detects the zero-phase voltage V0 of the transformer 3. The first circuit breaker relay 52 shuts off the first circuit breaker 6 by detecting a fault in the bus 100a. The second circuit breaker relay 53 outputs a control signal SG3 based on the logical product of the detection signal SG2 from the first circuit breaker relay 52 and the zero-phase voltage v0, and opens and closes the second circuit breaker relay 53 based on the control signal SG3.

[0045] As a result, when no fault occurs in the bus 100a, when no earth fault occurs in the power system 100, or when no fault occurs in both, the second circuit breaker relay 53 closes the second circuit breaker 43, so that the second circuit breaker 43 shorts both ends of the capacitor 42. As a result, the capacitor 42 is not electrically connected to the neutral point compensation reactor 41. Therefore, the neutral point compensation reactor 41 and the capacitor 42 cause the oscillating current i n does not occur, so the oscillating current i n does not flow to the other lines 10 described above. Therefore, the relay that operates the interconnection breaker 11 does not allow the oscillating current i n Therefore, the operation does not become unstable, and malfunction of the interconnection breaker 11 can be prevented.

[0046] Furthermore, when a fault occurs in the busbar 100a and also when a ground fault occurs in the power system 100, the second circuit breaker relay 53 opens the second circuit breaker 43, which opens both ends of the capacitor 42. Therefore, the capacitor 42 is electrically connected to the neutral compensation reactor 41 to form a series circuit. Therefore, the low-frequency oscillating current i n can be passed through the first circuit breaker 6. Therefore, the first circuit breaker 6 can pass an oscillating current i n This allows the circuit breaker to perform a correct cutoff operation without causing a current zero error.

[0047] Furthermore, since the second circuit breaker 43 is a circuit breaker with excellent breaking performance, it can reliably cut off both ends of the capacitor 42 when a fault occurs in the bus bar 100a and a ground fault occurs in the power system 100.

[0048] 〔summary〕 A protection system according to a first aspect of the present disclosure is a protection system for protecting a power system that supplies three-phase AC power, comprising: a transformer that transforms the voltage of three-phase AC power, a neutral point compensation reactor connected to a neutral point of the transformer, and a capacitor connected in series with the neutral point compensation reactor, the protection system comprising: a circuit breaker arranged between the power system and the transformer, a switch that shorts and opens both ends of the capacitor, and a control device that controls the circuit breaker and the switch, wherein the control device has a fault detection unit that causes the circuit breaker to open by detecting a fault in a busbar in the power system, a zero-phase voltage detection unit that detects a zero-phase voltage of the transformer, and an opening / closing control unit that controls the switch to short-circuit when at least one of a fault non-detection event in which a fault in the busbar is not detected by the fault detection unit and a voltage non-detection event in which a non-zero zero-phase voltage is not detected by the zero-phase voltage detection unit occurs.

[0049] According to the above configuration, when at least one of a fault does not occur on the bus and a ground fault does not occur, the switch shorts both ends of the capacitor. As a result, the capacitor is bypassed and not connected to the neutral compensation reactor. Therefore, no oscillating current is generated by the neutral compensation reactor and the capacitor, and the oscillating current does not flow into other lines provided on the bus common to the transformer.

[0050] This makes it possible to prevent the relay that operates the circuit breaker that cuts off the line when a single-line ground fault occurs in another line from becoming unstable due to the oscillating current, thereby preventing the circuit breaker from malfunctioning.

[0051] In the protection system according to the second aspect of the present disclosure, in the first aspect, the opening / closing control unit may open the switch when a fault detection event occurs in which the fault detection unit detects a fault in the busbar and a voltage detection event occurs in which the zero-phase voltage detection unit detects a non-zero zero-phase voltage while the switch is short-circuiting both ends of the capacitor.

[0052] According to the above configuration, when a fault occurs in the busbar and a ground fault occurs, the switch opens both ends of the capacitor. This causes the oscillating current generated by the neutral compensation reactor and the capacitor to flow to the circuit breaker. This allows the circuit breaker to operate normally and prevents a current zero error from occurring.

[0053] A protection system according to a third aspect of the present disclosure is the protection system of the first or second aspect, wherein the switch is a circuit breaker.

[0054] According to the above configuration, a circuit breaker with excellent breaking performance is used as a switch, which can reliably open the switch when a fault occurs in the busbar and a ground fault occurs in the power grid.

[0055] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. In addition, embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0056] 3. Transformer 5. Control device 6. First Circuit Breaker (Circuit Breaker) 41 Neutral compensation reactor 42 Capacitor 43 Second circuit breaker (switch) 51 Zero-phase voltage detector (zero-phase voltage detector) 52 First circuit breaker relay (fault detection section) 53 Second circuit breaker relay (switching control section) 100 Power system 101 Protection System NP neutral point

Claims

1. A protection system for protecting a power system that supplies three-phase AC power, comprising: a transformer that transforms a voltage of three-phase AC power; a neutral point compensation reactor that is connected to a neutral point of the transformer; and a capacitor that is connected in series to the neutral point compensation reactor, a circuit breaker disposed between the power grid and the transformer; a switch for shorting and opening both ends of the capacitor; A control device for controlling the circuit breaker and the switch, The control device includes: a fault detection unit that detects a fault in a bus bar in the power system and causes the circuit breaker to trip; a zero-phase-sequence voltage detection unit for detecting a zero-phase-sequence voltage of the transformer; a switching control unit that controls the switch to short-circuit when at least one of a fault non-detection event in which the fault detection unit does not detect a fault in the busbar and a voltage non-detection event in which the zero-phase sequence voltage detection unit does not detect a non-zero zero-phase sequence voltage occurs.

2. 2. The protection system according to claim 1, wherein the switching control unit opens the switch when a fault detection event occurs in which the fault detection unit detects a fault in the busbar and a voltage detection event occurs in which the zero-phase-sequence voltage detection unit detects a non-zero zero-phase-sequence voltage with the switch short-circuiting both ends of the capacitor.

3. 3. The protection system of claim 1 or 2, wherein the switch is a circuit breaker.

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