Distance relay device

Abstract

To provide a distance relay device capable of more appropriately determining the presence or absence of a failure in a section from an installation point to a fixed point.SOLUTION: The relay device acquires a current time-series instantaneous value and a voltage time-series instantaneous value, calculates a current change vector of a protection target line from the current time-series instantaneous value, calculates a voltage change vector of a bus from the voltage time-series instantaneous value, calculates a reference voltage vector on the basis of a first voltage vector obtained by multiplying the current change vector by a transmission line impedance and the voltage change vector, calculates a pre-fault voltage vector of the bus from the voltage time-series instantaneous value, and calculates a first direction component of the reference voltage vector and a first direction component of the pre-fault voltage vector when a perpendicular direction of the current change vector is defined as a first direction. When the magnitude of the first direction component of the reference voltage vector is equal to or larger than the magnitude of the first direction component of the pre-fault voltage vector, it is determined that a fault has occurred in the protected zone.SELECTED DRAWING: Figure 18

Description

[Technical Field]

[0001] The present disclosure relates to distance relaying devices. [Background technology]

[0002] Distance relays have been known as protective relays that detect short-circuit and ground faults in power transmission lines and protect the lines. Distance relays are widely used as primary and backup protective relays in system protection because they can determine faults from the installation point to the setpoint by inputting voltage and current detected at the installation point.

[0003] The distance relay device disclosed in Patent Publication No. 2008-187825 (Patent Document 1) determines that a fault has occurred within the area when the starting voltage calculated using the change in current rotation vector, the change in voltage rotation vector, and the impedance to the assumed point is greater than the voltage at the assumed point before the fault, and outputs a trip command to the circuit breaker. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-187825 Summary of the Invention [Problem to be solved by the invention]

[0005] The distance relay according to Patent Document 1 is designed to achieve high-speed relay operation using the above-mentioned configuration. However, if there is arc resistance at the fault point, the phase angle of the voltage vector after the fault relative to the current change vector becomes smaller than the settling impedance angle due to the effect of the arc resistance. In this case, the distance relay according to Patent Document 1 has the problem that it cannot operate if a fault occurs at the settling point (i.e., the distance at which it can actually operate becomes shorter).

[0006] An object of one aspect of the present disclosure is to provide a distance relay that can more appropriately determine whether or not a fault exists in the section from the installation point to the settling point. [Means for solving the problem]

[0007] A distance relay device according to one embodiment includes an electrical quantity acquisition unit that acquires current time series instantaneous values ​​of current detected in a power system and voltage time series instantaneous values ​​of voltage detected in the power system; a current change vector calculation unit that calculates a current change vector of a protected line included in the power system from the current time series instantaneous values; a voltage change vector calculation unit that calculates a voltage change vector of a bus bar connected to the protected line from the voltage time series instantaneous values; a reference voltage vector calculation unit that calculates a reference voltage vector based on a first voltage vector obtained by multiplying the current change vector by the transmission line impedance from the detection location where the voltage and current of the power system are detected to the settling point and the voltage change vector; a pre-fault voltage vector calculation unit that calculates a pre-fault voltage vector of the bus bar from the voltage time series instantaneous values; a directional component calculation unit that calculates a first directional component of the reference voltage vector and the first directional component of the pre-fault voltage vector when the perpendicular direction of the current change vector is defined as the first direction; and a determination unit that determines that a fault has occurred within the protection area if the magnitude of the first directional component of the reference voltage vector is greater than or equal to the magnitude of the first directional component of the pre-fault voltage vector.

[0008] According to another embodiment, the power system includes an electrical quantity acquiring unit that acquires current time series instantaneous values ​​of current detected in the power system and voltage time series instantaneous values ​​of voltage detected in the power system, a current change vector calculating unit that calculates a current change vector of a line to be protected included in the power system from the current time series instantaneous values, a voltage change vector calculating unit that calculates a first voltage change vector of a bus bar connected to the line to be protected from the voltage time series instantaneous values, a first voltage vector obtained by multiplying the current change vector by a transmission line impedance from a detection location where voltage and current in the power system are detected to a settling point, and a reference voltage vector calculating unit that calculates a reference voltage vector based on the first voltage change vector, and a pre-fault voltage vector calculating unit that calculates a first pre-fault voltage vector of the bus bar from the voltage time series instantaneous values. The reference voltage vector calculating unit calculates the reference voltage vector from the first voltage vector and a second voltage change vector obtained by projecting the first voltage change vector onto the first voltage vector along the current change vector. The pre-fault voltage vector calculation unit further calculates a second pre-fault voltage vector by projecting the first pre-fault voltage vector along the current change vector relative to the first voltage vector. The distance relay device further includes a determination unit that determines that a fault has occurred in the protection area when the magnitude of the reference voltage vector is equal to or greater than the magnitude of the second pre-fault voltage vector. [Effects of the Invention]

[0009] According to the distance relay device of the present disclosure, it is possible to more appropriately determine whether or not there is a fault in the section from the installation point to the settling point. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the overall configuration of a distance relay device. [Figure 2] FIG. 10 is a diagram showing an equivalent circuit at the time of a two-phase short-circuit fault using the symmetric coordinate method. [Figure 3] 1 is a vector diagram showing the relationship between current and voltage before and after a short circuit fault in the absence of arc resistance. [Figure 4] This is a vector diagram obtained by rewriting FIG. 3 based on the current change vector. [Figure 5] FIG. 10 is a diagram for explaining an example of the relationship between the position from the power source and the line voltage. [Figure 6] FIG. 10 is a diagram for explaining another example of the relationship between the position from the power supply and the line voltage. [Figure 7] 1 is a vector diagram showing the relationship between current and voltage before and after a short circuit fault in the presence of arc resistance. [Figure 8] This is a vector diagram obtained by rewriting FIG. 7 based on the current change vector. [Figure 9] FIG. 2 is a diagram for illustrating a short-circuit fault determination method according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing an equivalent circuit at the time of a one-phase ground fault using the symmetric coordinate method. [Figure 11] A vector diagram showing the relationship between current and voltage before and after a ground fault in the absence of arc resistance. [Figure 12] This is a vector diagram obtained by rewriting FIG. 11 based on the current change vector. [Figure 13] A vector diagram showing the relationship between current and voltage before and after a ground fault in the presence of arc resistance. [Figure 14] This is a vector diagram obtained by rewriting FIG. 13 based on the current change vector. [Figure 15] FIG. 2 is a diagram for illustrating a ground fault determination method according to the first embodiment. [Figure 16] FIG. 10 is a diagram for explaining a short-circuit fault determination method according to a modification of the first embodiment. [Figure 17] FIG. 10 is a diagram for explaining a ground fault determination method according to a modification of the first embodiment. [Figure 18] FIG. 2 is a block diagram showing a functional configuration of the distance relay according to the first embodiment. [Figure 19] FIG. 10 is a diagram for explaining a short-circuit fault determination method according to the second embodiment. [Figure 20] FIG. 10 is a diagram for illustrating a ground fault determination method according to a second embodiment. [Figure 21]FIG. 10 is a block diagram showing a functional configuration of a distance relay according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the present embodiment will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of these components are also the same. Therefore, detailed description thereof will not be repeated.

[0012] Embodiment 1 <Overall structure> Fig. 1 is a diagram showing an example of the overall configuration of a distance relay. Referring to Fig. 1, distance relay 100 is a digital protective relay device and is installed, for example, inside a substation. The substation includes a circuit breaker 50 that disconnects transmission line 7 from the power system when a fault occurs in transmission line 7, a current transformer (CT) 60 for detecting current information of transmission line 7, and a voltage transformer (VT) 70 for detecting voltage information of a bus 8. Transmission line 7 is a three-phase transmission line.

[0013] The CT 60 detects the current (i.e., phase A current, phase B current, and phase C current) of each phase (e.g., phase A, phase B, and phase C) of the transmission line 7. More specifically, the CT 60 converts the magnitude of each phase current of the transmission line 7 into an input current level of the distance relay 100. The VT 70 detects the voltage of each phase of the bus 8 (i.e., phase A voltage, phase B voltage, and phase C voltage). More specifically, the VT 70 converts the magnitude of each phase voltage of the transmission line 7 into an input voltage level of the distance relay 100. Information on the current detected by the CT 60 and the voltage detected by the VT is input to the distance relay 100.

[0014] The distance relay 100 performs necessary calculations such as relay calculations using input electrical quantities (e.g., current and voltage) to determine whether a fault has occurred within the protection zone of the power transmission line, etc. When the distance relay 100 detects a fault within the protection zone, it outputs an opening command (e.g., a trip signal) to the circuit breaker 50 provided on the power transmission line 7. The distance relay 100 includes, as its hardware configuration, an auxiliary transformer 10, a signal conversion unit 20, and an arithmetic processing unit 30.

[0015] Auxiliary transformer 10 receives electrical quantities from CT 60 and VT 70, converts them into voltage signals suitable for signal processing in the internal circuitry, and outputs them. Signal converter 20 receives the electrical quantities (i.e., analog electrical quantities) output from auxiliary transformer 10 and converts them into digital data. Specifically, signal converter 20 includes filters 21 and 23, sample-and-hold circuits (corresponding to the SH circuits in the figure) 24 and 25, a multiplexer 26, and an A / D converter 27.

[0016] Filters 21 and 23 are analog filters that remove high-frequency noise components from the current and voltage waveform signals output from auxiliary transformer 10. The outputs of filters 21 and 23 are input to sample-and-hold circuits 24 and 25, respectively. Sample-and-hold circuits 24 and 25 sample the current and voltage waveform signals output from filters 21 and 23, respectively, at predetermined sampling periods.

[0017] Based on the sampling signal input from the arithmetic processing unit 30, the multiplexer 26 sequentially switches the waveform signals input from the sample-and-hold circuits 24 and 25 in time series and outputs the selected signal to the A / D converter 27. The A / D converter 27 converts the waveform signals input from the multiplexer 26 from analog data to digital data. The A / D converter 27 outputs the digitally converted waveform signals to the arithmetic processing unit 30.

[0018] The arithmetic processing unit 30 is mainly composed of a microcomputer. Specifically, the arithmetic processing unit 30 includes a CPU (Central Processing Unit) 32, a ROM (Read Only Memory) 33, a RAM (Random Access Memory) 34, a DO (Digital Output) circuit 36, a DI (Digital Input) circuit 37, a display 38, and an input interface 39. These are connected by a bus 31.

[0019] The CPU 32 controls the distance relay 100 by reading and executing a program stored in advance in the ROM 33. The RAM 34 as a volatile memory and the ROM 33 as a non-volatile memory are used as the main memory of the CPU 32. The ROM 33 stores programs, setting values ​​for signal processing, and the like. The CPU 32 retrieves digital data from the signal conversion unit 20 via the bus 31. The CPU 32 executes relay calculations for fault detection using the retrieved digital data in accordance with the program stored in the ROM 33. The CPU 32 determines the presence or absence of a fault based on the results of the relay calculations.

[0020] When the CPU 32 detects a fault (i.e., when it determines that a fault has occurred), it outputs an opening command to the circuit breaker 50 via the DO circuit 36 ​​to disconnect the faulted section from the power system. The DI circuit 37 receives, for example, a digital input signal that is a signal indicating the opening and closing information of the circuit breaker 50. The display 38 is, for example, a liquid crystal display. The input interface 39 is typically various buttons or the like, and accepts various operations from a user (e.g., an operator) of the distance relay device 100.

[0021] At least a part of the distance relay 100 may be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). At least a part of the distance relay 100 may also be configured using analog circuits.

[0022] <Short circuit fault detection method> Fig. 2 is a diagram showing an equivalent circuit when a two-phase short-circuit fault occurs using the symmetric coordinate method. Typically, the equivalent circuit shown in Fig. 2 is an equivalent circuit when a short-circuit fault occurs in two phases (specifically, phases B and C) out of three phases (e.g., phases A, B, and C) when there is no load current.

[0023] Referring to Figure 2, "E" is the power supply voltage, "V1" is the positive-sequence voltage at the installation point of the distance relay 100 (hereinafter also simply referred to as "installation point"), "I1" is the positive-sequence current at the installation point, "V2" is the negative-sequence voltage at the installation point, "I2" is the negative-sequence current at the installation point, "Z1S" is the positive-sequence back impedance from the power supply to the installation point, "Z1F" is the positive-sequence impedance from the installation point to the fault point, "Z2S" is the negative-sequence back impedance from the power supply to the installation point, "Z2F" is the negative-sequence impedance from the installation point to the fault point, and "R" is the arc resistance at the fault point. In the following explanation, the symbol "*" indicates a multiplication symbol. In a normal system, "Z1S = Z2S" and "Z1F = Z2F".

[0024] From the equivalent circuit in Figure 2, the following equation (1) holds: V1-V2=(Z1F+Z2F+2*R)*I1=2*(Z1F+R)*I1…(1) Also, if the vector operator is "a", the B-phase current is "Ib", the C-phase current is "Ic", and the zero-phase current is "I0", then "I0=0", so "Ib=I0+a 2 *I1+a*I2=(a 2 -a)*I1”, “Ic=I0+a*I1+a 2 *I2=(aa 2)*I1”. Therefore, from equation (1), the line voltage Vbc after a BC phase short-circuit fault is expressed by the following equation (2). “Ibc” is the line current of BC phase. If the zero-phase voltage is “V0”, then “V0=0”.

[0025] Vbc = Vb - Vc = (V0 + a 2 *V1+a*V2)-(V0+a*V1+a 2 *V2)=(a 2 -a)*(V1-V2)=2(Z1F+R)*(a 2 -a)I1=2*(Z1F+R)*Ib=(Z1F+R)*Ibc…(2) Here, we consider the derivation of the line voltage Vbc from another perspective. First, consider vector diagrams of the current and voltage before and after a short-circuit fault when there is no arc resistance at the fault point.

[0026] Figure 3 is a vector diagram showing the relationship between current and voltage before and after a short circuit fault in the absence of arc resistance. In Figure 3, the arc resistance R in Figure 2 is assumed to be 0.

[0027] In Figure 3, "Vax," "Vbx," and "Vcx" represent the vectors of the A-phase voltage, B-phase voltage, and C-phase voltage before the fault, respectively. "Va," "Vb," and "Vc" represent the vectors of the A-phase voltage, B-phase voltage, and C-phase voltage during the fault (i.e., after the fault), respectively. "ΔIb" represents the vector of the difference (i.e., the amount of change) in the B-phase current before and after the fault. "ΔIc" represents the vector of the amount of change in the C-phase current before and after the fault.

[0028] The vector of each phase current is calculated from the time-series instantaneous value data of each phase current detected by the CT 60. The vector of each phase voltage is calculated from the time-series instantaneous value data of each phase voltage detected by the VT 70. For example, the time-series instantaneous value data of current I from time (tn) to time (t) is I(tn),···I(t-1),I(t). Also, the time-series instantaneous value data of voltage V from time (tn) to time (t) is V(tn),···,V(t-1),V(t). Here, n indicates the number of samples equivalent to the number of positive integer cycles.

[0029] Here, the change in B-phase current at time t is defined as "ΔIb(t) = Ib(t) - Ib(tn)." The change in C-phase current at time t is defined as "ΔIc(t) = Ic(t) - Ic(tn)." The change in line voltage Vbc before and after a fault at time t is defined as "ΔVbc(t) = Vbc(t) - Vbc(tn)." For example, if the number of positive integer cycles is 2, n is the number of samples corresponding to the period of those 2 cycles. If the number of samples corresponding to 1 cycle is "12," then "n = 24." In this case, the change is only valid for 2 cycles, but for a normal fault, 2 cycles is sufficient for operation. Considering the change in this way, even when there is a load current, the effect of the load current can be eliminated, and the behavior is the same as when there is no load current.

[0030] Since "ΔIb = -ΔIc", "ΔIb = Ib", and "ΔIc = Ic" hold, the line voltage Vbc after a BC phase short-circuit fault is expressed by the following equation (3) using the object coordinate method. "Vbcx" indicates the line voltage before the fault. From the equivalent circuit in Figure 2, "V1 = E-Z1S*I1" and "V2 = -Z2S*I2". Also, "Ib = (a 2 -a)*I1”, “Ic=(aa 2 )*I1”, “Vbx=a 2 *E”, “Vcx=a*E”. Therefore, “ΔVbc”, which is the change in the line voltage Vbc before and after the fault, is expressed by the following equation (4).

[0031] Vbc = Vb - Vc = (V0 + a 2 *V1+a*V2)-(V0+a*V1+a 2 *V2)=(a 2 -a)V1+(aa 2 )V2={a 2 *E-(a 2 -a)*Z1S*I1}-{a*E-(aa 2 )*Z1S*I1}=(Vbx-Z1S*Ib)-(Vcx-Z1S*Ic)=Vbcx-Z1S*Ibc …(3) ΔVbc=Vbc-Vbcx=-Z1S*Ibc…(4) Here, since the load current is 0, the change in line current ΔIbc before and after the fault is equal to "Ibc," so from equation (4), "ΔVbc = -Z1S * ΔIbc" holds. Hereinafter, these will also be referred to as the "voltage change vector ΔVbc" and the "current change vector ΔIbc."

[0032] Figure 4 is a vector diagram obtained by rewriting Figure 3 based on the current change vector. Figure 4 assumes that a short-circuit fault occurs at the settling point. In Figure 4, the vector with the phase of the current change vector ΔIbc advanced by 90 degrees is represented as "j*ΔIbc."

[0033] Referring to Figure 4, "Zs" is the settling impedance from the installation point of the distance relay 100 (e.g., the location where the voltage of the bus bar 8 is detected) to the settling point. Typically, the protection range of the first stage operation of the distance relay 100 at the settling impedance is the positive sequence impedance up to a position 80% of the transmission line 7 (e.g., from the location where the voltage of the bus bar 8 is detected to 80% of the transmission line 7).

[0034] Here, it is assumed that a short-circuit fault occurs at the settling point, so the positive-sequence impedance Z1F in Figure 2 corresponds to the settling impedance Zs. If the short-circuit fault is not an arc fault, "R = 0". Also, considering the current change, the influence of the load current can be eliminated even if there is a load current. Therefore, equation (2) derived from the equivalent circuit shown in Figure 2 (i.e., the equivalent circuit using the symmetric coordinate method when the load current is 0) can be used and can be replaced with "ΔIbc = Ibc". Therefore, the line voltage Vbc after the fault is expressed by the following equation (5). The line voltage Vbcx before the fault is expressed by the following equation (6) from equation (5).

[0035] Vbc=Z1F*Ibc=Zs*ΔIbc …(5) Vbcx=-ΔVbc+Vbc=-ΔVbc+Zs*ΔIbc …(6) As shown in equation (6), when a short-circuit fault occurs at the settling point, the line voltage Vbcx before the fault coincides with "-ΔVbc+Zs*ΔIbc." Therefore, a short-circuit fault determination can be performed based on the result of comparing the magnitude of the vector of the line voltage Vbcx (hereinafter also referred to as "pre-fault voltage vector Vbcx") with the magnitude of the vector "-ΔVbc+Zs*ΔIbc."

[0036] Specifically, if "|Vbcx|=|-ΔVbc+Zs*ΔIbc|" holds, the fault point coincides with the settling point (i.e., it is a short-circuit fault within the protection zone), so the distance relay operates. If "|Vbcx|<|-ΔVbc+Zs*ΔIbc|" holds, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point (i.e., it is a short-circuit fault within the protection zone), so the distance relay operates. If "|Vbcx|>|-ΔVbc+Zs*ΔIbc|" holds, the distance GF is longer than the distance GS (i.e., it is a short-circuit fault outside the protection zone), so the distance relay does not operate. Here, |P| indicates the magnitude (e.g., effective value) of the vector P. The above matters will be further explained using Figures 5 and 6.

[0037] FIG. 5 is a diagram illustrating an example of the relationship between the position from the power source and the line voltage. Referring to FIG. 5, "Vst = -ΔVbc + Zs * ΔIbc" is defined. |Vst| is the same as |-ΔVbc + Zs * ΔIbc| described in FIG. 4. The vector Vst is obtained by adding the reverse polarity of the change ΔVbc in the BC phase line voltage at the installation point to the voltage change at the settling point (i.e., Zs * ΔIbc) when it is assumed that the fault current at the time of a short-circuit fault flows up to the settling point. Therefore, it can be understood that when the fault point coincides with the settling point, Vst coincides with the line voltage Vbcx before the fault.

[0038] Figure 6 is a diagram for explaining another example of the relationship between the position from the power source and the line voltage. In Figure 6, for example, "ΔVbc (settling point)" indicates "ΔVbc" when the fault point coincides with the settling point. "ΔVbc (F1)" indicates "ΔVbc" when the fault point is F1. "ΔVbc (F2)" indicates "ΔVbc" when the fault point is F2. The same applies to the other symbols.

[0039] Referring to Figure 6, as in Figure 5, it can be seen that |Vst (settling point)| coincides with the magnitude of the line voltage before the fault |Vbcx|. It can be seen that when the fault point is "F1" inside the protection zone, |Vst(F1)| is greater than |Vbcx|. It can also be seen that when the fault point is "F2" outside the protection zone, |Vst(F2)| is smaller than |Vbcx|.

[0040] Therefore, as explained in Figure 3, if "|Vbcx| ≦ |-ΔVbc+Zs*ΔIbc|" is true, the distance relay operates. On the other hand, if "|Vbcx| > |-ΔVbc+Zs*ΔIbc|" is true, the distance relay does not operate.

[0041] If there is no arc resistance at the fault point of a short circuit fault, the above fault determination method can be used to determine the short circuit fault. However, if there is arc resistance at the fault point, the following problem occurs when using the above fault determination method. Normally, the arc at the fault point is a resistive component.

[0042] FIG. 7 is a vector diagram showing the relationship between current and voltage before and after a short circuit fault in the presence of arc resistance.

[0043] From the equivalent circuit shown in Figure 2, "I1 = -I2 = E / (2 * Z1S + 2 * Z1F + 2 * R)." Therefore, when there is arc resistance (i.e., R ≠ 0) as in the equivalent circuit shown in Figure 2, the angle of the positive-sequence current I1 with respect to the power supply E corresponding to the A-phase power supply is smaller than the angle when there is no arc resistance (i.e., R = 0). Accordingly, the B-phase current Ib and C-phase current Ic also change during a fault. Therefore, as shown in Figure 7, when there is arc resistance (i.e., R ≠ 0), the phase angle of the voltage vector Vbc with respect to the current change vector ΔIbc (= Ibc) is smaller than the positive-sequence impedance angle.

[0044] Figure 8 is a vector diagram obtained by rewriting Figure 7 based on the current change vector. Figure 8 assumes that a short-circuit fault occurs at the settling point. Referring to Figure 8, due to the presence of arc resistance, the line voltage Vbc after the fault is "Zs*ΔIbc" plus "R*ΔIbc" (i.e., Vbc = (Zs + R)*ΔIbc). Therefore, the line voltage Vbcx before the fault is expressed by the following equation (7).

[0045] Vbcx=-ΔVbc+Vbc=-ΔVbc+(Zs+R)*ΔIbc …(7) In Figure 4, which assumes the absence of arc resistance, it has been explained that when the fault point coincides with the settling point, "|Vbcx|=|-ΔVbc+Zs*ΔIbc|" holds. However, in Figure 8, it can be seen that even when the fault point coincides with the settling point, "|Vbcx|=|-ΔVbc+Zs*ΔIbc|" does not hold, and "|Vbcx|>|-ΔVbc+Zs*ΔIbc|" holds.

[0046] Therefore, in the event of a short-circuit fault with arc resistance, the distance relay 100 cannot operate even if the fault point is a settling point. This shortens the distance over which the distance relay 100 can actually operate (i.e., the protection range becomes narrower). Therefore, the distance relay 100 according to this embodiment determines whether or not there is a short-circuit fault using the following fault determination method.

[0047] FIG. 9 is a diagram illustrating a short-circuit fault determination method according to the first embodiment. Referring to FIG. 9, the vector "-ΔVbc+Zs*ΔIbc" is defined as the reference voltage vector Vst. The reference voltage vector Vst corresponds to the vector Vst described in FIGS. 5 and 6. The direction perpendicular to the current change vector ΔIbc (for example, the direction of the vector "j*ΔIbc") is defined as the "D1 direction." In this case, the distance relay 100 performs short-circuit fault determination by comparing the D1 direction component of the reference voltage vector Vst with the D1 direction component of the pre-fault voltage vector Vbcx.

[0048] Specifically, the distance relaying device 100 generates a voltage vector Vst1 by projecting (i.e., orthogonally projecting) the reference voltage vector Vst along the current change vector ΔIbc with respect to a perpendicular line of the current change vector ΔIbc (for example, the vector "j*ΔIbc"). The distance relaying device 100 also generates a vector Vbcx1 by projecting the pre-fault voltage vector Vbcx along the current change vector ΔIbc with respect to a perpendicular line of the current change vector ΔIbc. Then, the distance relaying device 100 compares |Vbcx1| with |Vst1|.

[0049] Specifically, when "|Vbcx1|=|Vst1|" is true, the fault point coincides with the settling point, so the distance relay 100 operates. When "|Vbcx1|<|Vst1|" is true, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, so the distance relay 100 operates. When "|Vbcx1|>|Vst1|" is true, the distance GF is longer than the distance GS, so the distance relay 100 does not operate.

[0050] With the above configuration, the distance relay 100 can properly detect a short-circuit fault that occurs between the installation point and the settling point, even if there is arc resistance at the fault point. Note that if there is no arc resistance at the fault point, the pre-fault voltage vector Vbcx and the reference voltage vector Vst (=-ΔVbc+Zs*ΔIbc) have the relationship shown in Figure 4. Therefore, it goes without saying that even if there is no arc resistance at the fault point, it is possible to properly detect a short-circuit fault that occurs between the installation point and the settling point using the determination method described in Figure 9. In other words, the distance relay 100 can properly detect a short-circuit fault that occurs within the protection area, regardless of whether there is arc resistance at the fault point.

[0051] <Ground fault detection method> The method for determining a ground fault will be described in the same manner as the method for determining a short circuit fault described above.

[0052] Fig. 10 is a diagram showing an equivalent circuit at the time of a one-phase ground fault using the symmetric coordinate method. Representatively, the equivalent circuit shown in Fig. 10 is an equivalent circuit at the time of a ground fault in one phase (specifically, phase A) of three phases (e.g., phase A, phase B, and phase C) of a single-circuit transmission line when there is no load current. Referring to Fig. 10, "V0" denotes the zero-phase voltage at the installation point of the distance relay 100, "I0" denotes the zero-phase current at the installation point, "Z0S" denotes the zero-phase back impedance from the power source to the installation point, and "Z0F" denotes the zero-phase impedance from the installation point to the fault point. The other symbols are as explained in Fig. 2.

[0053] From the equivalent circuit in Figure 10, "I1 = I2 = I0", "V1 = E-Z1S*I1", "V2 = -Z2S*I2", and "V0 = -Z0S*I0". Also, "Z1S = Z2S" and "Z1F = Z2F". From these relationships, equations (8) and (9) can be derived.

[0054] Va=V0+V1+V2=E-(2*Z1S+Z0S)*I1 …(8) I1=E / (2*Z1S+2*Z1F+Z0S+Z0F+R) …(9) Furthermore, the following equation (10) holds from the equivalent circuit, and therefore equation (11) is obtained.

[0055] E=Z1S*I1+Z1F*I1+Z2S*I2+Z2F*I2+Z0S*I0+Z0F*I0+R*I0 …(10) E-(Z1S*I1+Z2S*I2+Z0S*I0)=Z1F*I1+Z2F*I2+Z0F*I0+R*I0 …(11) On the other hand, the following equation (12) holds for "Va".

[0056] Va=V0+V1+V2=E-(Z1S*I1+Z2S*I2+Z0S*I0)=E-(2*Z1S+Z0S)*I1 …(12) Furthermore, using equation (11), the following equation (13) holds for "Va".

[0057] Va=V0+V1+V2=E-(Z1S*I1+Z2S*I2+Z0S*I0)=Z1F*I1+Z2F*I2+Z0F*I0+R*I0=(2*Z1F+Z0F+R)*I1=Z1F*{3+((Z0F-Z1F) / Z1F)}*I1+R*I1…(13) Here, the zero-phase compensation coefficient is "K". If we define "K = (Z0F - Z1F) / Z1F" and "Iak = Ia + K * I0", the following equation (14) is established from equation (13). Also, "I1 = ΔIa / 3".

[0058] Va=Z1F*(3*I1+K*I1)+R*I1=Z1F*(Ia+K*I0)+R*I1=Z1F*Iak+R*I1 …(14) When there are two transmission lines, other line compensation using the zero-phase current of the adjacent line is further required, but since this is the same processing as above, a detailed description thereof will not be given.

[0059] Here, we consider the derivation of the A-phase voltage Va from a different perspective. First, consider vector diagrams of the current and voltage before and after a ground fault when there is no arc resistance at the fault point.

[0060] FIG. 11 is a vector diagram showing the relationship between current and voltage before and after a ground fault when there is no arc resistance. Here, the arc resistance R in FIG. 10 is assumed to be 0. Referring to FIG. 11, "ΔVa" indicates the vector of the amount of change in A-phase voltage before and after the fault. The other vectors are as described in FIG. 3.

[0061] Here, the change in A-phase voltage at time t is defined as "ΔVa(t) = Va(t) - Va(tn)", where n is the number of samples corresponding to a positive integer number of cycles. The change in A-phase current at time t is defined as "ΔIa(t) = Ia(t) - Ia(tn)". The change in zero-phase current at time t is defined as "ΔI0(t) = I0(t) - I0(tn)". Similarly, the change in positive-phase current at time t is defined as "ΔI1(t) = I1(t) - I1(tn)". Furthermore, the change in A-phase current after zero-phase compensation is defined as "ΔIak(t) = Iak(t) - Iak(tn)".

[0062] Using the positive-sequence rear impedance Z1S, the zero-sequence rear impedance Z0S, and the A-phase voltage Vax before the fault, the A-phase voltage Va after the fault is expressed by the following equation (15).

[0063] Va=Vax-(2*Z1S+Z0S)*I1 …(15) Therefore, the change ΔVa in the A-phase voltage before and after the fault is expressed by equation (16).

[0064] ΔVa=-(Z0S+2*Z1S)*I1 …(16) Hereinafter, they will also be referred to as "voltage change vector ΔVa" and "current change vector ΔIak".

[0065] Figure 12 is a vector diagram obtained by rewriting Figure 11 using the current change vector as the reference. In Figure 12, the vector with the phase of the current change vector ΔIak advanced by 90 degrees is represented as "j*ΔIak." Here, we assume that a ground fault occurs at the settling point, so the positive-sequence impedance Z1F in Figure 10 corresponds to the settling impedance Zs. Since the load current is zero, the current change vector ΔIak and the positive-sequence current vector I1 are in phase. Furthermore, the influence of the load current can be eliminated from the current change vector ΔIak and the positive-sequence current change vector ΔI1, even when there is a load current. Therefore, the current change vector ΔIak and the positive-sequence current change vector ΔI1 are in phase, just as when the load current is zero. In this case, the A-phase voltage Va after the fault is expressed by the following equation (17). Using equation (17), the A-phase voltage Vax before the fault is expressed by the following equation (18).

[0066] Va=Z1F*ΔIak=Zs*ΔIak …(17) Vax=-ΔVa+Va=-ΔVa+Zs*ΔIak…(18) As shown in equation (18), when a ground fault occurs at the settling point, the A-phase voltage Vax before the fault coincides with "-ΔVa+Zs*ΔIak." Therefore, a ground fault determination can be performed based on the result of comparing the magnitude of the A-phase voltage Vax vector (hereinafter also referred to as "pre-fault voltage vector Vax") with the magnitude of the vector "-ΔVa+Zs*ΔIak."

[0067] Specifically, if "|Vax|=|-ΔVa+Zs*ΔIak|" holds, the fault point coincides with the settling point, so the distance relay operates. If "|Vax|<|-ΔVa+Zs*ΔIak|" holds, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, so the distance relay operates. If "|Vax|>|-ΔVa+Zs*ΔIa|" holds, the distance GF is longer than the distance GS, so the distance relay does not operate.

[0068] In this way, if there is no arc resistance at the fault point of a ground fault, the above fault determination method can be used to determine the ground fault. However, if there is arc resistance at the fault point, the following problems arise when using the above fault determination method.

[0069] FIG. 13 is a vector diagram showing the relationship between current and voltage before and after a ground fault when there is arc resistance.

[0070] From equation (9) derived from the equivalent circuit shown in Figure 10, when there is arc resistance (i.e., R≠0), the phase angle of the positive-sequence current vector I1 relative to the power supply vector E corresponding to the A-phase power supply becomes smaller than the positive-sequence impedance angle due to the influence of the arc resistance R. In other words, as shown in Figure 13, the phase angle of the positive-sequence current vector I1 relative to the pre-fault voltage vector Vax becomes smaller than the positive-sequence impedance angle.

[0071] FIG. 14 is a vector diagram obtained by rewriting FIG. 13 based on the current change vector. In FIG. 14, it is assumed that a ground fault occurs at the settling point. Referring to FIG. 14, due to the presence of arc resistance, the A-phase voltage Va after the fault is the sum of "R*ΔI1" and "Zs*ΔIak" (i.e., Va=Zs*ΔIak+R*ΔI1). Therefore, the A-phase voltage Vax before the fault is expressed by the following equation (19).

[0072] Vax=-ΔVa+Va=-ΔVa+Zs*ΔIak+R*ΔI1 …(19) In Figure 12, which assumes the absence of arc resistance, it has been explained that when the fault point coincides with the settling point, "|Vax|=|-ΔVa+Zs*ΔIak|" holds. However, in Figure 14, it can be seen that even when the fault point coincides with the settling point, "|Vax|=|-ΔVa+Zs*ΔIak|" does not hold, and "|Vax|>|-ΔVa+Zs*ΔIak|" holds.

[0073] Therefore, in the event of a ground fault with arc resistance, the distance relay 100 cannot operate if the settling point is the fault point. This shortens the distance over which the distance relay 100 can actually operate (i.e., the protection range becomes narrow). Therefore, the distance relay 100 according to this embodiment determines whether or not a ground fault has occurred using the following fault determination method.

[0074] FIG. 15 is a diagram for explaining the ground fault determination method according to the first embodiment. Referring to FIG. 15, the vector "-ΔVa+Zs*ΔIak" is defined as the reference voltage vector Vet. Here, the perpendicular direction of the current change vector ΔIak (for example, the direction of the vector "j*ΔIak") is defined as the "D2 direction." In this case, the distance relay 100 performs ground fault determination by comparing the D2 direction component of the reference voltage vector Vet with the D2 direction component of the pre-fault voltage vector Vax.

[0075] Specifically, the distance relaying device 100 generates a vector Vet1 by projecting the reference voltage vector Vet along the current change vector ΔIak with respect to a perpendicular line of the current change vector ΔIak (for example, the vector "j*ΔIak"). The distance relaying device 100 also generates a vector Vax1 by projecting the pre-fault voltage vector Vax along the current change vector ΔIak with respect to a perpendicular line of the current change vector ΔIak. Then, the distance relaying device 100 compares |Vax1| with |Vet1|.

[0076] Specifically, when "|Vax1|=|Vet1|" is true, the fault point coincides with the settling point, so the distance relay 100 operates. When "|Vax1|<|Vet1|" is true, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, so the distance relay 100 operates. When "|Vax1|>|Vet1|" is true, the distance GF is longer than the distance GS, so the distance relay 100 does not operate.

[0077] With the above configuration, the distance relay 100 can properly detect a ground fault that occurs between the installation point and the settling point, even if there is arc resistance at the fault point. Note that if there is no arc resistance at the fault point, the pre-fault voltage vector Vax and the reference voltage vector Vet (=-ΔVa+Zs*ΔIak) have the relationship shown in Figure 12. Even if there is no arc resistance at the fault point, the determination method described in Figure 15 can properly detect a ground fault that occurs between the installation point and the settling point. In other words, the distance relay 100 can properly detect a ground fault that occurs within the protection area, regardless of whether there is arc resistance at the fault point.

[0078] Although the above description has been given of a configuration in which the D2 direction is perpendicular to the current change vector ΔIak, the present invention is not limited to this configuration. For example, the D2 direction may be perpendicular to the current change vectors ΔIa, ΔI0, and ΔI1, which are in phase with the current change vector ΔIak. When the load current is in a three-phase balanced state, the zero-phase current I0 before the fault is zero, and therefore is not affected by the load current. Therefore, "I0" may be used instead of "ΔI0".

[0079] <Modification of the fault determination method> (Short circuit fault detection method) Figure 9 describes a configuration in which the distance relay device 100 compares the D1 direction component of the reference voltage vector Vst with the D1 direction component of the pre-fault voltage vector Vbcx by projecting the reference voltage vector Vst and the pre-fault voltage vector Vbcx onto the perpendicular to the current change vector ΔIbc.

[0080] In a modified example of the short-circuit fault determination method, a configuration is described in which the D1 direction component of the reference voltage vector Vst and the D1 direction component of the pre-fault voltage vector Vbcx are compared using the phase angle of the reference voltage vector Vst and the phase angle of the pre-fault voltage vector Vbcx relative to the current change vector ΔIbc.

[0081] FIG. 16 is a diagram for explaining a short-circuit fault determination method according to a modification of the first embodiment. Referring to FIG. 16, the distance relay 100 generates a vector Vbcx2 by projecting the pre-fault voltage vector Vbcx along the current change vector ΔIbc relative to the vector "Zs*ΔIbc." Here, the impedance angle of the settling impedance Zs is φ, and the phase angle of the pre-fault voltage vector Vbcx relative to the current change vector ΔIbc is θ1. In this case, the following equation (20) holds for the pre-fault voltage vector Vbcx and the vector Vbcx2. Therefore, the relationship shown in the following equation (21) is obtained.

[0082] |Vbcx2|*sinφ=|Vbcx|*sinθ1 …(20) |Vbcx2|=|Vbcx|*(sinθ1 / sinφ) …(21) Similarly, the distance relay 100 generates a vector ΔVbc2 by projecting the voltage change vector ΔVbc along the current change vector ΔIbc relative to the vector "Zs*ΔIbc." Here, the phase angle of the reference voltage vector Vst (=-ΔVbc+Zs*ΔIbc) relative to the current change vector ΔIbc is set to θ2. In this case, the following equation (22) holds true for the vector "-ΔVbc2+Zs*ΔIbc" and the reference voltage vector Vst. Therefore, the relationship shown in the following equation (23) is obtained.

[0083] |-ΔVbc2+Zs*ΔIbc|*sinφ=|Vst|*sinθ2…(22) |-ΔVbc2+Zs*ΔIbc|=|Vst|*(sinθ2 / sinφ)…(23) When the settling point is the fault point, the relational expression "|Vbcx2|=|-ΔVbc2+Zs*ΔIbc|" holds. From this relational expression, equation (21) and equation (23), we obtain "|Vbcx|*(sinθ1 / sinφ)=|Vst|*(sinθ2 / sinφ)". Therefore, the relational expression (24) below holds.

[0084] |Vbcx|*sinθ1=|Vst|*(sinθ2) …(24) If the arc resistance R is not 0, a short-circuit fault is determined using the relationship in equation (24). If "|Vbcx|*sinθ1=|Vst|*(sinθ2)" holds, the fault point coincides with the settling point, and so the distance relay 100 operates. If "|Vbcx|*sinθ1<|Vst|*(sinθ2)" holds, the distance GF from the installation point to the fault point is closer than the distance GS from the installation point to the settling point, and so the distance relay 100 operates. If "|Vbcx|*sinθ1>|Vst|*(sinθ2)" holds, the distance GF is longer than the distance GF, and so the distance relay 100 does not operate. Note that when the arc resistance is zero, "θ1=θ2", and so in effect, |Vbcx| and |Vst| are compared.

[0085] In this way, the distance relay 100 according to the modified example also properly detects a short-circuit fault occurring within the protection area, regardless of the presence or absence of arc resistance at the fault point.

[0086] (Ground fault detection method) Figure 15 describes a configuration in which the distance relay device 100 compares the D2 direction component of the reference voltage vector Vet with the D2 direction component of the pre-fault voltage vector Vax by projecting the reference voltage vector Vet and the pre-fault voltage vector Vax onto the perpendicular to the current change vector ΔIak.

[0087] In a modified example of the ground fault determination method, a configuration is described in which the D2 direction component of the reference voltage vector Vet and the D2 direction component of the pre-fault voltage vector Vax are compared using the phase angle of the reference voltage vector Vet and the phase angle of the pre-fault voltage vector Vax relative to the current change vector ΔIax.

[0088] FIG. 17 is a diagram for explaining a ground fault determination method according to a modification of the first embodiment. Referring to FIG. 17, the distance relay 100 generates a vector Vax2 by projecting the pre-fault voltage vector Vax along the current change vector ΔIak relative to the vector "Zs*ΔIak." Here, the impedance angle of the settling impedance Zs is φ, and the phase angle of the pre-fault voltage vector Vax relative to the current change vector ΔIak is θ3. In this case, the following equation (25) holds for the pre-fault voltage vector Vax and the vector Vax2. Therefore, the relationship shown in the following equation (26) is obtained.

[0089] |Vax2|*sinφ=|Vax|*sinθ3 …(25) |Vax2|=|Vax|*(sinθ3 / sinφ) …(26) Similarly, the distance relay 100 generates a vector ΔVa2 by projecting the voltage change vector ΔVa along the current change vector ΔIak onto the vector "Zs*ΔIak." Here, the phase angle of the reference voltage vector Vet (=-ΔVa+Zs*ΔIak) relative to the current change vector ΔIak is set to θ4. In this case, the following equation (27) holds true for the vector "-ΔVa2+Zs*ΔIak" and the reference voltage vector Vet. Therefore, the relationship shown in the following equation (28) is obtained.

[0090] |-ΔVa2+Zs*ΔIak|*sinφ=|Vet|*sinθ4…(27) |-ΔVa2+Zs*ΔIak|=|Vet|*(sinθ4 / sinφ)…(28) When the settling point is the fault point, the relational expression "|Vax2|=|-ΔVa2+Zs*ΔIak|" holds. From this relational expression, equation (26) and equation (28), we obtain "|Vax|*(sinθ3 / sinφ)=|Vet|*(sinθ4 / sinφ)". Therefore, the relational expression (29) below holds.

[0091] |Vax|*sinθ3=|Vet|*(sinθ4) …(29) If the arc resistance R is not 0, a ground fault determination is performed using the relationship in equation (29). If "|Vax|*sinθ3=|Vet|*(sinθ4)" holds, the fault point coincides with the settling point, and so the distance relay 100 operates. If "|Vax|*sinθ3<|Vet|*(sinθ4)" holds, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, and so the distance relay 100 operates. If "|Vax|*sinθ3>|Vet|*(sinθ4)" holds, the distance GF is longer than the distance GS, and so the distance relay 100 does not operate. Note that when the arc resistance is zero, "θ3=θ4", and so in effect, |Vax| and |Vet| are compared.

[0092] In this way, the distance relay 100 according to the modified example also properly detects a ground fault occurring within the protection area, regardless of the presence or absence of arc resistance at the fault point.

[0093] <Functional configuration> Fig. 18 is a block diagram showing the functional configuration of the distance relay according to the first embodiment. Referring to Fig. 18, the distance relay 100 includes, as its main functional components, an electric quantity acquisition unit 101, a current change vector calculation unit 103, a voltage change vector calculation unit 105, a reference voltage vector calculation unit 107, a pre-fault voltage vector calculation unit 109, a directional component calculation unit 111, a determination unit 113, and an output control unit 115. These functions are realized, for example, by the CPU 32 of the distance relay 100 executing a program stored in a memory (for example, the ROM 33). Some or all of these functions may be configured to be realized by hardware.

[0094] The electric quantity acquiring unit 101 acquires current time series instantaneous values ​​of current detected in the power system and voltage time series instantaneous values ​​of voltage detected in the power system. Specifically, the electric quantity acquiring unit 101 acquires time series instantaneous values ​​sampled from each phase current of the transmission line 7 detected by the CT 60 (i.e., current time series instantaneous values) and time series instantaneous values ​​sampled from each phase voltage of the bus 8 detected by the VT 70 (i.e., voltage time series instantaneous values). The sampling and A / D conversion are performed by the signal converting unit 20 described above.

[0095] The current change vector calculation unit 103 calculates a current change vector of a line to be protected (e.g., transmission line 7) included in the power system from the current time series instantaneous values. In one aspect, the current change vector calculation unit 103 calculates a change vector (e.g., current change vector ΔIbc) of a line-to-line current (e.g., line-to-line current Ibc) between two phases (e.g., phase B and phase C) of the transmission line 7. In another aspect, the current change vector calculation unit 103 calculates a change vector (e.g., current change vector ΔIak) of a phase current (e.g., phase A current) of the transmission line 7.

[0096] The voltage change vector calculation unit 105 calculates a voltage change vector of a bus 8 connected to a line to be protected (e.g., a transmission line 7) from the instantaneous voltage time series values. In one aspect, the voltage change vector calculation unit 105 calculates a change vector (e.g., a voltage change vector ΔVbc) of a line voltage (e.g., a line voltage Vbc) between two phases (e.g., a B phase and a C phase) of the bus 8. In another aspect, the current change vector calculation unit 103 calculates a change vector (e.g., a voltage change vector ΔVa) of a phase voltage (e.g., an A phase voltage) of the bus 8.

[0097] The reference voltage vector calculation unit 107 calculates a reference voltage vector based on the voltage change vector and a first voltage vector obtained by multiplying the current change vector by the transmission line impedance (e.g., settling impedance Zs) from the detection location where the voltage and current of the power system are detected (e.g., the installation point of the distance relay device 100) to the settling point.

[0098] In one aspect, the reference voltage vector calculation unit 107 calculates a reference voltage vector Vst (=-ΔVbc+Zs*ΔIbc) from a first voltage vector "Zs*ΔIbc" obtained by multiplying the current change vector ΔIbc by the settling impedance Zs and the voltage change vector ΔVbc. In another aspect, the reference voltage vector calculation unit 107 calculates a reference voltage vector Vet (=-ΔVa+Zs*ΔIak) from a first voltage vector "Zs*ΔIak" obtained by multiplying the current change vector ΔIak by the settling impedance Zs and the voltage change vector ΔVa.

[0099] The pre-fault voltage vector calculation unit 109 calculates a pre-fault voltage vector of the bus 8 from the instantaneous voltage time series values. In one aspect, the pre-fault voltage vector calculation unit 109 calculates a vector of pre-fault line voltages Vbcx (i.e., pre-fault voltage vector Vbcx). In another aspect, the pre-fault voltage vector calculation unit 109 calculates a vector of pre-fault phase voltages Vax (i.e., pre-fault voltage vector Vax). Typically, the pre-fault line voltage Vbcx at time t is calculated from the B-phase voltage Vb(tn) and the C-phase voltage Vc(tn) acquired n sampling periods before time t, which corresponds to a positive integer number of cycles. For example, "Vbcx(t) = Vb(tn) - Vc(tn)". Similarly, the pre-fault A-phase voltage Vax at time t is, for example, "Vax(t) = Va(tn)".

[0100] When the direction of the perpendicular to the current change vector is defined as a first direction, the directional component calculation unit 111 calculates the first directional component of the reference voltage vector and the first directional component of the pre-fault voltage vector.

[0101] In one aspect, the first directional component is defined as the D1 direction, which is the direction of a perpendicular to the current change vector ΔIbc. The directional component calculation unit 111 calculates the magnitude of a voltage vector Vst1 (i.e., |Vst1|) obtained by projecting the reference voltage vector Vst along the current change vector ΔIbc with respect to a perpendicular to the current change vector ΔIbc, as the magnitude of the D1 direction component of the reference voltage vector Vst. Alternatively, the directional component calculation unit 111 calculates a product (e.g., |Vst| * sinθ2) obtained by multiplying the magnitude of the reference voltage vector Vst by the sine of the phase angle θ2 of the reference voltage vector Vst with respect to the current change vector ΔIbc, as the magnitude of the D1 direction component of the reference voltage vector Vst.

[0102] Next, the directional component calculation unit 111 calculates the magnitude of a voltage vector Vbcx1 obtained by projecting the pre-fault voltage vector Vbcx along the current change vector ΔIbc with respect to a perpendicular line of the current change vector ΔIbc (i.e., |Vbcx1|), as the magnitude of the D1 direction component of the pre-fault voltage vector. Alternatively, the directional component calculation unit 111 calculates the product (e.g., |Vbcx|*sinθ1) obtained by multiplying the magnitude of the pre-fault voltage vector Vbcx by the sine of the phase angle θ1 of the pre-fault voltage vector Vbcx with respect to the current change vector ΔIbc, as the magnitude of the D1 direction component of the pre-fault voltage vector Vbcx.

[0103] In another aspect, the first directional component is defined as the D2 direction, which is the direction of a perpendicular to the current change vector ΔIak. The directional component calculation unit 111 calculates the magnitude of a voltage vector Vet1 (i.e., |Vet1|) obtained by projecting the reference voltage vector Vet along the current change vector ΔIak with respect to a perpendicular to the current change vector ΔIak, as the magnitude of the D2 direction component of the reference voltage vector Vet. Alternatively, the directional component calculation unit 111 calculates a product (e.g., |Vet| * sin θ4) obtained by multiplying the magnitude of the reference voltage vector Vet by the sine of the phase angle θ4 of the reference voltage vector Vet with respect to the current change vector ΔIak (i.e., sin θ4) as the magnitude of the D2 direction component of the reference voltage vector Vet.

[0104] Next, the directional component calculation unit 111 calculates the magnitude of a voltage vector Vax1 obtained by projecting the pre-fault voltage vector Vax along the current change vector ΔIak with respect to a perpendicular to the current change vector ΔIak (i.e., |Vax1|), as the magnitude of the D2 direction component of the pre-fault voltage vector. Alternatively, the directional component calculation unit 111 calculates the product (e.g., |Vax|*sinθ3) obtained by multiplying the magnitude of the pre-fault voltage vector Vax by the sine of the phase angle θ3 of the pre-fault voltage vector Vax with respect to the current change vector ΔIak, as the magnitude of the D2 direction component of the pre-fault voltage vector Vax.

[0105] The determination unit 113 determines that a fault has occurred in the protection area when the magnitude of the first directional component of the reference voltage vector is equal to or greater than the magnitude of the first directional component of the pre-fault voltage vector. In one aspect, the determination unit 113 determines that a short-circuit fault has occurred in the protection area when the magnitude of the D1 directional component of the reference voltage vector Vst is equal to or greater than the magnitude of the D1 directional component of the pre-fault voltage vector Vbcx. In another aspect, the determination unit 113 determines that a ground fault has occurred in the protection area when the magnitude of the D2 directional component of the reference voltage vector Vet is equal to or greater than the magnitude of the D2 directional component of the pre-fault voltage vector Vax.

[0106] The output control unit 115 outputs an opening command (for example, a trip signal) to the circuit breaker 50 based on the determination result of the determination unit 113. Specifically, when the determination unit 113 determines that a fault has occurred in the protection zone (for example, at least one of a short-circuit fault and a ground fault has occurred), the output control unit 115 outputs the opening command.

[0107] <Advantages> According to the first embodiment, short-circuit faults and ground faults occurring within the protection area can be appropriately detected regardless of the presence or absence of arc resistance at the fault point.

[0108] Embodiment 2 In the above-described first embodiment, a configuration has been described in which a fault determination is performed based on a result of a comparison between a first directional component of a reference voltage vector and a first directional component of a pre-fault voltage vector. In the second embodiment, a configuration will be described in which a fault determination is performed based on a result of a comparison between the magnitude of a reference voltage vector generated by a different method and the magnitude of a pre-fault voltage vector.

[0109] <Short circuit fault detection method> 19 is a diagram for explaining a short-circuit fault determination method according to the second embodiment. Referring to FIG. 19, the distance relaying device 100 generates a voltage change vector ΔVbc3 by projecting the voltage change vector ΔVbc along the current change vector ΔIbc with respect to the voltage vector "Zs*ΔIbc". Next, the distance relaying device 100 calculates a reference voltage vector Vst3 (=-ΔVbc3+Zs*ΔIbc) by adding the voltage vector "Zs*ΔIbc" to the opposite polarity of the voltage change vector ΔVbc3.

[0110] The distance relaying device 100 also generates a voltage vector Vbcx3 by projecting the pre-fault voltage vector Vbcx along the current change vector ΔIbc relative to the voltage vector "Zs*ΔIbc." Note that the voltage vector Vbcx3 is the same as the voltage vector Vbcx2 in Figure 16. The distance relaying device 100 then compares |Vst3| with |Vbcx3|.

[0111] Specifically, when "|Vbcx3|=|Vst3|" is true, the fault point coincides with the settling point, and so the distance relay 100 operates. When "|Vbcx3|<|Vst3|" is true, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, and so the distance relay 100 operates. When "|Vbcx3|>|Vst3|" is true, the distance GF is longer than the distance GS, and so the distance relay 100 does not operate. As a result, the distance relay 100 can properly detect short-circuit faults that occur between the installation point and the settling point, even if there is arc resistance at the fault point.

[0112] The voltage change vector ΔVbc3 has the same phase as the voltage vector "Zs*ΔIbc." Here, since "ΔVbc = -Z1S*ΔIbc" holds, the phase difference between the voltage change vector ΔVbc and the voltage change vector ΔVbc3 is the phase difference between the positive-phase rear impedance Z1S and the settling impedance Zs (=Z1F). Therefore, when the phase difference is close to 0, the voltage change vector ΔVbc3 can be approximately replaced with the voltage change vector ΔVbc. In this case, the distance relay 100 only needs to perform the above projection process on the pre-fault voltage vector Vbcx to generate the pre-fault voltage vector Vbcx3.

[0113] <Ground fault detection method> Fig. 20 is a diagram for explaining a ground fault determination method according to the second embodiment. Referring to Fig. 20, the distance relaying device 100 generates a voltage change vector ΔVa3 by projecting the voltage change vector ΔVa along the current change vector ΔIak with respect to the voltage vector "Zs*ΔIak". Next, the distance relaying device 100 calculates a reference voltage vector Vet3 (=-ΔVa3+Zs*ΔIak) by adding the voltage vector "Zs*ΔIak" to the opposite polarity of the voltage change vector ΔVa3.

[0114] The distance relaying device 100 also generates a voltage vector Vax3 by projecting the pre-fault voltage vector Vax along the current change vector ΔIak relative to the voltage vector "Zs*ΔIak." Note that the voltage vector Vax3 is the same as the voltage vector Vax2 in Figure 17. The distance relaying device 100 then compares |Vet3| with |Vax3|.

[0115] Specifically, when "|Vax3| = |Vet3|" is true, the fault point coincides with the settling point, and therefore the distance relay 100 operates. When "|Vax3| < |Vet3|" is true, the distance GF from the installation point to the fault point is shorter than the distance GS from the installation point to the settling point, and therefore the distance relay 100 operates. When "|Vax3| > |Vet3|" is true, the distance GF is longer than the distance GS, and therefore the distance relay 100 does not operate. This allows the distance relay 100 to properly detect faults that occur within the protection area, even if there is arc resistance at the fault point.

[0116] The voltage change vector ΔVa3 is in phase with the voltage vector "Zs*ΔIak." When there is no load current, "ΔVa=-(2*Z1S+Z0S)*I1" holds, and the positive-sequence current vector I1 is in phase with the current change vectors ΔIa and ΔI0. When there is a load current, "ΔVa=-(2*Z1S+Z0S)*ΔI1" holds, and the positive-sequence current change vector ΔI1 is in phase with the current change vectors ΔIa and ΔI0. Therefore, the phase difference between the voltage change vector ΔVa and the voltage change vector ΔVa3 is the phase difference between the impedance "2*Z1S+Z0S" and the settling impedance Zs (=Z1F). Therefore, when this phase difference is close to 0, the voltage change vector ΔVa3 can be approximately replaced with the voltage change vector ΔVa. In this case, the distance relay 100 may execute the above-described projection process only on the pre-fault voltage vector Vax to generate the pre-fault voltage vector Vax3.

[0117] <Functional configuration> Fig. 21 is a block diagram showing the functional configuration of a distance relay according to the second embodiment. Referring to Fig. 21, distance relay 100A includes, as main functional components, an electric quantity acquisition unit 101, a current change vector calculation unit 103, a voltage change vector calculation unit 105, a reference voltage vector calculation unit 107A, a pre-fault voltage vector calculation unit 109A, a determination unit 113A, and an output control unit 115. Here, the functional configurations of reference voltage vector calculation unit 107A, pre-fault voltage vector calculation unit 109A, and determination unit 113A will be described. The other functional configurations are as described in Fig. 18.

[0118] The reference voltage vector calculation unit 107A calculates the reference voltage vector Vst3 based on the voltage vector "Zs*ΔIbc" and the voltage change vector ΔVbc. Specifically, the reference voltage vector calculation unit 107A calculates the reference voltage vector Vst3 (=-ΔVbc3+Zs*ΔIbc) from the voltage vector "Zs*ΔIbc" and the voltage change vector ΔVbc3 obtained by projecting the voltage change vector ΔVbc onto the voltage vector "Zs*ΔIbc" along the current change vector ΔIbc.

[0119] In another aspect, reference voltage vector calculation unit 107A calculates reference voltage vector Vet3 based on voltage vector "Zs*ΔIak" and voltage change vector ΔVa. Specifically, reference voltage vector calculation unit 107A calculates reference voltage vector Vet3 (=-ΔVa3+Zs*ΔIak) from voltage change vector ΔVa3 obtained by projecting voltage change vector ΔVa onto voltage vector "Zs*ΔIak" along current change vector ΔIak, and voltage vector "Zs*ΔIak."

[0120] The pre-fault voltage vector calculation unit 109A calculates a pre-fault voltage vector Vbcx3 by projecting the pre-fault voltage vector Vbcx along the current change vector ΔIbc with respect to the voltage vector "Zs*ΔIbc". In addition, the pre-fault voltage vector calculation unit 109A calculates a pre-fault voltage vector Vax3 by projecting the pre-fault voltage vector Vax along the current change vector ΔIak with respect to the voltage vector "Zs*ΔIak".

[0121] The determination unit 113A determines that a fault has occurred in the protection area when the magnitude of the reference voltage vector is greater than the magnitude of the projected pre-fault voltage vector. In one aspect, the determination unit 113A determines that a short-circuit fault has occurred in the protection area when the magnitude of the reference voltage vector Vst3 is equal to or greater than the magnitude of the pre-fault voltage vector Vbcx3. In another aspect, the determination unit 113A determines that a ground fault has occurred in the protection area when the magnitude of the reference voltage vector Vet3 is equal to or greater than the magnitude of the pre-fault voltage vector Vax3.

[0122] <Advantages> According to the second embodiment, the same advantages as those of the first embodiment can be obtained.

[0123] Other embodiments. (1) In the above-described second embodiment, a configuration has been described in which the voltage change vector and the pre-fault voltage vector are projected along the current change vector onto a voltage vector obtained by multiplying the current change vector by the settling impedance Zs (for example, voltage vector "Zs*ΔIbc" or "Zs*ΔIak"). However, the present invention is not limited to this configuration, and the configuration may be such that the voltage change vector and the pre-fault voltage vector are projected onto another vector (for example, a pre-fault voltage vector) that is close in direction to the voltage vector.

[0124] In this case, in the short-circuit fault determination method, the distance relay 100 generates a reference voltage vector Vst4 by projecting the reference voltage vector Vst (=-ΔVbc+Zs*ΔIbc) along the current change vector ΔIbc onto the pre-fault voltage vector Vbcx. The distance relay 100 then detects a short-circuit fault by comparing the magnitude of the generated reference voltage vector with the magnitude of the pre-fault voltage vector Vbcx in the same manner as above. For example, if "|Vbcx|≦|Vst4|", the distance relay 100 operates (i.e., it determines that a short-circuit fault has occurred in the protection zone), and if "|Vbcx|>|Vst4|", the distance relay 100 does not operate.

[0125] Furthermore, in the ground fault determination method, the distance relay 100 generates a reference voltage vector Vet4 by projecting the reference voltage vector Vet (=-ΔVa+Zs*ΔIak) onto the pre-fault voltage vector Vax along the current change vector ΔIak. The distance relay 100 then detects a ground fault by comparing the magnitude of the generated reference voltage vector with the magnitude of the pre-fault voltage vector Vax in the same manner as above. For example, if "|Vax|≦|Vet4|", the distance relay 100 operates (i.e., it determines that a ground fault has occurred in the protection zone), and if "|Vax|>|Vet4|", the distance relay 100 does not operate.

[0126] (2) The configurations exemplified as the above-described embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, within the scope of the gist of the present disclosure. Furthermore, the above-described embodiments may be implemented by appropriately adopting the processes and configurations described in other embodiments.

[0127] <Additional Notes> Various aspects of the present disclosure are summarized below as appendices.

[0128] (Appendix 1) an electric quantity acquiring unit that acquires current time series instantaneous values ​​of current detected in an electric power system and voltage time series instantaneous values ​​of voltage detected in the electric power system; a current change vector calculating unit that calculates a current change vector of a line to be protected included in the electric power system from the current time series instantaneous values; a voltage change vector calculating unit that calculates a voltage change vector of a bus connected to the line to be protected from the voltage time series instantaneous values; a first voltage vector obtained by multiplying the current change vector by a transmission line impedance from a detection location where the voltage and current of the electric power system are detected to a settling point; a pre-fault voltage vector calculation unit that calculates a pre-fault voltage vector of the bus from the voltage time series instantaneous values; a directional component calculation unit that calculates a first directional component of the reference voltage vector and the pre-fault voltage vector when the perpendicular direction of the current change vector is defined as a first direction; and a determination unit that determines that a fault has occurred within a protection area when the magnitude of the first directional component of the reference voltage vector is equal to or greater than the magnitude of the first directional component of the pre-fault voltage vector.

[0129] (Appendix 2) The distance relay device described in Appendix 1, wherein the directional component calculation unit calculates the magnitude of the voltage vector obtained by projecting the reference voltage vector along the current change vector to a perpendicular to the current change vector as the magnitude of the first directional component of the reference voltage vector, and calculates the magnitude of the voltage vector obtained by projecting the pre-fault voltage vector along the current change vector to a perpendicular to the current change vector as the magnitude of the first directional component of the pre-fault voltage vector.

[0130] (Appendix 3) The distance relay device described in Appendix 1, wherein the directional component calculation unit calculates the magnitude of the first directional component of the reference voltage vector by multiplying the magnitude of the reference voltage vector by the sine of the first phase angle of the reference voltage vector relative to the current change vector, and calculates the magnitude of the first directional component of the pre-fault voltage vector by multiplying the magnitude of the pre-fault voltage vector by the sine of the second phase angle of the pre-fault voltage vector relative to the current change vector.

[0131] (Appendix 4) A distance relay device as described in any one of Supplementary Note 1 to Supplementary Note 3, wherein the current change vector calculation unit calculates a change vector of the line-to-line current of the protected line as the current change vector, the voltage change vector calculation unit calculates a change vector of the line-to-line voltage of the bus as the voltage change vector, the pre-fault voltage vector calculation unit calculates a vector of the line-to-line voltage before the fault as the pre-fault voltage vector, and when the magnitude of the first directional component of the reference voltage vector is equal to or greater than the magnitude of the first directional component of the pre-fault voltage vector, the determination unit determines that a short-circuit fault has occurred within the protection area.

[0132] (Appendix 5) A distance relay device as described in any one of Supplementary Note 1 to Supplementary Note 3, wherein the current change vector calculation unit calculates a change vector of the phase current of the protected line as the current change vector, the voltage change vector calculation unit calculates a change vector of the phase voltage of the bus as the voltage change vector, the pre-fault voltage vector calculation unit calculates a vector of the phase voltage before the fault as the pre-fault voltage vector, and if the magnitude of the first directional component of the reference voltage vector is equal to or greater than the magnitude of the first directional component of the pre-fault voltage vector, the determination unit determines that a ground fault has occurred within the protection area.

[0133] (Appendix 6) an electric quantity acquiring unit that acquires current time series instantaneous values ​​of current detected in the power system and voltage time series instantaneous values ​​of voltage detected in the power system; a current change vector calculating unit that calculates a current change vector of a line to be protected included in the power system from the current time series instantaneous values; a voltage change vector calculating unit that calculates a first voltage change vector of a bus bar connected to the line to be protected from the voltage time series instantaneous values; a first voltage vector obtained by multiplying the current change vector by a transmission line impedance from a detection location where the voltage and current of the power system are detected to a settling point; and a reference voltage vector calculating unit that calculates a reference voltage vector based on the first voltage change vector; and a pre-fault voltage vector calculation unit that calculates a first pre-fault voltage vector of the bus from a column instantaneous value, wherein the reference voltage vector calculation unit calculates the reference voltage vector from the first voltage vector and a second voltage change vector that is obtained by projecting the first voltage change vector onto the first voltage vector along the current change vector, and the pre-fault voltage vector calculation unit further calculates a second pre-fault voltage vector that is obtained by projecting the first pre-fault voltage vector onto the first voltage vector along the current change vector, and the distance relay device further comprises a determination unit that determines that a fault has occurred within a protection area if the magnitude of the reference voltage vector is equal to or greater than the magnitude of the second pre-fault voltage vector.

[0134] (Appendix 7) A distance relay device as described in Appendix 6, wherein the current change vector calculation unit calculates a change vector of the line-to-line current of the protected line as the current change vector, the voltage change vector calculation unit calculates a change vector of the line-to-line voltage of the bus as the first voltage change vector, the pre-fault voltage vector calculation unit calculates a vector of the line-to-line voltage before the fault as the first pre-fault voltage vector, and if the magnitude of the reference voltage vector is greater than or equal to the magnitude of the second pre-fault voltage vector, the determination unit determines that a short-circuit fault has occurred within the protection area.

[0135] (Appendix 8) A distance relay device as described in Appendix 6, wherein the current change vector calculation unit calculates the change vector of the phase current of the protected line as the current change vector, the voltage change vector calculation unit calculates the change vector of the phase voltage of the bus as the first voltage change vector, the pre-fault voltage vector calculation unit calculates the vector of the phase voltage before the fault as the first pre-fault voltage vector, and if the magnitude of the reference voltage vector is greater than or equal to the magnitude of the first pre-fault voltage vector, the determination unit determines that a ground fault has occurred within the protection area.

[0136] (Appendix 9) A distance relay device according to any one of Supplementary Note 1 to Supplementary Note 8, further comprising an output control unit that outputs an opening command to a circuit breaker provided on the line to be protected when a fault occurs within the protection area.

[0137] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0138] 7 transmission line, 8 bus bar, 10 auxiliary transformer, 20 signal conversion unit, 21, 23 filter, 24, 25 sample and hold circuit, 26 multiplexer, 27 A / D converter, 30 calculation processing unit, 31 bus, 33 ROM, 34 RAM, 36 DO circuit, 37 DI circuit, 38 display, 39 input interface, 50 circuit breaker, 100, 100A distance relay device, 101 electrical quantity acquisition unit, 103 current change vector calculation unit, 105 voltage change vector calculation unit, 107, 107A reference voltage vector calculation unit, 109, 109A pre-fault voltage vector calculation unit, 111 directional component calculation unit, 113, 113A judgment unit, 115 output control unit.

Claims

1. an electric quantity acquiring unit that acquires a time-series instantaneous value of a current detected in a power system and a time-series instantaneous value of a voltage detected in the power system; a current change vector calculation unit that calculates a current change vector of a line to be protected included in the power system from the current time series instantaneous value; a voltage change vector calculation unit that calculates a voltage change vector of a bus connected to the line to be protected from the voltage time series instantaneous value; a reference voltage vector calculation unit that calculates a reference voltage vector based on a first voltage vector obtained by multiplying the current change vector by a transmission line impedance from a detection location where the voltage and current of the power grid are detected to a settling point, and the voltage change vector; a pre-fault voltage vector calculation unit that calculates a pre-fault voltage vector of the bus from the voltage time-series instantaneous values; a directional component calculation unit that calculates a first directional component of the reference voltage vector and a first directional component of the pre-fault voltage vector when a direction perpendicular to the current change vector is defined as a first direction; A distance relay device comprising a determination unit that determines that a fault has occurred within a protection area when the magnitude of the first directional component of the reference voltage vector is greater than or equal to the magnitude of the first directional component of the pre-fault voltage vector.

2. The directional component calculation unit calculating a magnitude of a voltage vector obtained by projecting the reference voltage vector along the current change vector onto a perpendicular line of the current change vector as a magnitude of a first directional component of the reference voltage vector; 2. The distance relay device according to claim 1, wherein the magnitude of the voltage vector projected along the current change vector relative to a perpendicular line of the current change vector is calculated as the magnitude of the first directional component of the pre-fault voltage vector.

3. The directional component calculation unit calculating a multiplication value obtained by multiplying the magnitude of the reference voltage vector by the sine of a first phase angle of the reference voltage vector with respect to the current change vector as the magnitude of a first direction component of the reference voltage vector; 2. The distance relay device of claim 1, wherein the magnitude of the pre-fault voltage vector is multiplied by the sine of the second phase angle of the pre-fault voltage vector relative to the current change vector, and the resulting multiplied value is calculated as the magnitude of the first directional component of the pre-fault voltage vector.

4. the current change vector calculation unit calculates, as the current change vector, a change vector of a line-to-line current of the line to be protected, the voltage change vector calculation unit calculates, as the voltage change vector, a change vector of a line voltage of the bus; the pre-fault voltage vector calculation unit calculates a vector of the line voltages before the fault as the pre-fault voltage vector, A distance relay device as described in any one of claims 1 to 3, wherein when the magnitude of the first directional component of the reference voltage vector is equal to or greater than the magnitude of the first directional component of the pre-fault voltage vector, the judgment unit judges that a short-circuit fault has occurred within the protection area.

5. the current change vector calculation unit calculates, as the current change vector, a change vector of a phase current of the line to be protected; the voltage change vector calculation unit calculates a change vector of a phase voltage of the bus as the voltage change vector; the pre-fault voltage vector calculation unit calculates a vector of the phase voltages before the fault as the pre-fault voltage vector; A distance relay device as described in any one of claims 1 to 3, wherein when the magnitude of the first directional component of the reference voltage vector is greater than or equal to the magnitude of the first directional component of the pre-fault voltage vector, the judgment unit judges that a ground fault has occurred within the protection area.

6. an electric quantity acquiring unit that acquires a time-series instantaneous value of a current detected in a power system and a time-series instantaneous value of a voltage detected in the power system; a current change vector calculation unit that calculates a current change vector of a line to be protected included in the power system from the current time series instantaneous value; a voltage change vector calculation unit that calculates a first voltage change vector of a bus connected to the line to be protected from the voltage time series instantaneous value; a reference voltage vector calculation unit that calculates a reference voltage vector based on a first voltage vector obtained by multiplying the current change vector by a transmission line impedance from a detection location where the voltage and current of the power grid are detected to a settling point, and the first voltage change vector; a pre-fault voltage vector calculation unit that calculates a first pre-fault voltage vector of the bus from the voltage time-series instantaneous values, the reference voltage vector calculation unit calculates the reference voltage vector from the first voltage vector and a second voltage change vector obtained by projecting the first voltage change vector along the current change vector onto the first voltage vector; the pre-fault voltage vector calculation unit further calculates a second pre-fault voltage vector by projecting the first pre-fault voltage vector onto the first voltage vector along the current change vector; The distance relay device further comprises a determination unit that determines that a fault has occurred in the protection area when the magnitude of the reference voltage vector is equal to or greater than the magnitude of the second pre-fault voltage vector.

7. the current change vector calculation unit calculates, as the current change vector, a change vector of a line-to-line current of the line to be protected, the voltage change vector calculation unit calculates, as the first voltage change vector, a change vector of a line voltage of the bus; the pre-fault voltage vector calculation unit calculates a vector of the line voltages before a fault as the first pre-fault voltage vector; The distance relay according to claim 6 , wherein the determining unit determines that a short-circuit fault has occurred in the protection area when the magnitude of the reference voltage vector is equal to or greater than the magnitude of the second pre-fault voltage vector.

8. the current change vector calculation unit calculates, as the current change vector, a change vector of a phase current of the line to be protected; the voltage change vector calculation unit calculates a change vector of a phase voltage of the bus as the first voltage change vector; the pre-fault voltage vector calculation unit calculates a vector of the phase voltages before the fault as the first pre-fault voltage vector; 7. The distance relay according to claim 6, wherein the determining unit determines that a ground fault has occurred in the protection zone when the magnitude of the reference voltage vector is equal to or greater than the magnitude of the first pre-fault voltage vector.

9. A distance relay device as described in any one of claims 1 to 3 and claims 6 to 8, further comprising an output control unit that outputs an open command to a circuit breaker installed on the protected line when a fault occurs within the protection area.

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