Phase judgment and line selection method for single-phase grounding fault based on vector scalar product

Abstract

The present invention discloses a single-phase grounding fault phase judgment and line selection positioning method based on vector scalar product. For a single-phase grounding fault in a small current grounding system, the scalar product between vectors is calculated during a single-phase grounding fault, and the angle between the vectors during the fault is represented by a scalar product value. The single-phase grounding fault phase is judged according to the size of the scalar product value, and a small current line is selected and the fault point is located according to the positive or negative sign of the scalar product value. The method of the present invention can effectively eliminate the influence of calculation errors on judgment, thereby accurately judging the fault phase, selecting the line and locating the fault.

Description

Technical Field

[0001] The present invention relates to a method for judging, selecting and locating a fault in a small current grounding system, and more specifically to a method for judging, selecting and locating a fault phase of a single-phase grounding fault. Background Art

[0002] The low-current grounding system has always been the most widely used grounding method in my country's distribution network. It has low investment and high power supply reliability. However, when arc grounding occurs in the system, the high overvoltage level threatens the insulation of electrical equipment in the system.

[0003] The small current grounding system has a small single-phase grounding fault current, and the arc ignition and extinction process of arc grounding is very complicated. The existing technologies all rely on precise calculations, which means errors. Large errors make it impossible to accurately judge and locate the fault. The inability to accurately select the line for single-phase grounding is a common problem of all current line selection devices. Summary of the invention

[0004] The present invention is to avoid the shortcomings of the above-mentioned prior art and provide a single-phase grounding fault phase judgment and line selection positioning method based on vector scalar product. According to the relationship between the scalar product and the vector angle, the fault phase judgment, line selection and fault point positioning when single-phase grounding is realized; the scalar product operation is used to eliminate calculation errors and realize logical judgment positioning; the logical judgment method is used without errors, so as to accurately judge the fault phase and line selection positioning.

[0005] The present invention adopts the following technical solutions to solve the technical problems:

[0006] The characteristics of the single-phase grounding fault phase judgment and line selection positioning method based on vector scalar product of the present invention are: for single-phase grounding fault in a small current grounding system, the scalar product between vectors during the single-phase grounding fault is calculated, the scalar product value is used to represent the angle between the vectors during the fault, the single-phase grounding fault phase is judged according to the size of the scalar product value, and the small current line is selected and the fault point is located according to the positive and negative signs of the scalar product value.

[0007] The single-phase grounding fault phase judgment and line selection location method based on vector scalar product of the present invention is also characterized in that:

[0008] The method of judging the single-phase grounding fault phase according to the size of the scalar product value is as follows:

[0009] definition:

[0010] The voltages of phases A, B, and C to ground are U a , U b and U c , the neutral point to ground voltage is U0;

[0011] The line voltages of the three phases A, B, and C are U ab, U bc and U ca , and U ab =U a -U b ; U bc =U b -U c , U ca =U c -U a ;

[0012] The phase voltages of phases A, B, and C are U A , U B and U C , and U A =U a -U0,U B =U b -U0,U C =U c -U0;

[0013] U a The scalar product with U0 is m a0 , U b The scalar product with U0 is m b0 , U c The scalar product with U0 is m c0 ;

[0014] U ab The scalar product with U0 is m ab0 , U bc The scalar product with U0 is m bc0 , U ca The scalar product with U0 is m ca0 ;

[0015] U A The scalar product with U0 is m A0 , U B The scalar product with U0 is m B0 , U C The scalar product with U0 is m C0 ;

[0016] Determine the single-phase grounding fault phase according to the following method A1, method A2 or method A3:

[0017] Method A1:

[0018] In each standard product m a0 、m b0 and m c0 In, if m c0 The value of is the largest, and m b0 ≤m c0 , then the fault phase is phase A;

[0019] In each standard product m a0 、m b0 and m c0 In, if m a0 The value of is the largest, and m c0 ≤m a0 , then the fault phase is phase B;

[0020] In each standard product m a0 、m b0 and m c0 In, if m b0 The value of is the largest, and m a0 ≤m b0 , the fault phase is phase C.

[0021] Method A2:

[0022] In each standard product m ab0 、m bc0 and m ca0 In, if m ca0 If the value of is the largest, the fault phase is phase A;

[0023] In each standard product m ab0 、m bc0 and m ca0 In, if m ab0 If the value of is the largest, the fault phase is phase B;

[0024] In each standard product m ab0 、m bc0 and m ca0 In, if m bc0 If the value of is the largest, the fault phase is phase C.

[0025] Method A3:

[0026] In each standard product m A0 、m B0 and m C0 In, if m C0 The value of is the largest, and m B0 ≤m c0 , then the fault phase is phase A;

[0027] In each standard product m A0 、m B0 and m C0 In, if m A0 The value of is the largest, and m C0 ≤m A0 , then the fault phase is phase B;

[0028] In each standard product m A0 、m B0 and m C0 If the value of mB0 is the largest, and m A0 ≤mB0 , the fault phase is phase C.

[0029] The single-phase grounding fault phase judgment and line selection location method based on vector scalar product of the present invention is also characterized in that:

[0030] The small current line selection based on the positive and negative of the scalar product value is performed as follows:

[0031] definition:

[0032] U g It is the voltage relative to the ground of a single-phase ground fault or the voltage of a fault phase line;

[0033] I 01 ,I 02 ,……,I 0w One-to-one correspondence is the zero-sequence current of the 1st, 2nd, ..., wth outgoing line, w is the number of outgoing lines;

[0034] Perform low current line selection in the following manner B1, B2 or B3:

[0035] Method B1:

[0036] Definition: U g with I 01 ,I 02 ,……,I 0w The scalar products are m 01 、m 02 ,……,m 0w ;

[0037] When a single-phase grounding fault occurs, 01 、m 02 ,……,m 0w Among them, only m 0k is positive, the kth outgoing line is a faulty line.

[0038] Method B2:

[0039] When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative;

[0040] If the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence currents of all other outgoing lines are negative, the kth outgoing line is a fault line; if the scalar product of the zero-sequence current of the k+1th outgoing line and the zero-sequence currents of all other outgoing lines are negative, the k+1th outgoing line is a fault line;

[0041] Method B3:

[0042] When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative;

[0043] If the zero-sequence current of the kth outgoing line is gIf the scalar product of the kth outgoing line is positive, the kth outgoing line is a fault line; if the zero-sequence current of the kth outgoing line is equal to U g If the scalar product of is negative, the k+1th outgoing line is a faulty line.

[0044] Where, k∈[1,w]; Definition: when k=w, k+1 is the first outgoing line;

[0045] The single-phase grounding fault phase judgment and line selection location method based on vector scalar product of the present invention is also characterized in that:

[0046] The fault point location based on the positive or negative sign of the scalar product value is performed as follows:

[0047] Definition: The kth outgoing line is a single-phase grounding fault line. e zero-sequence current monitoring terminals are set at intervals on the kth outgoing line. The fault point Z occurs between the qth and hth adjacent zero-sequence current monitoring terminals. The fault point Z is located according to the following method C1 or method C2:

[0048] Method C1:

[0049] The upstream zero-sequence current monitoring signals of each upstream side of the fault point Z and U g The scalar product of is always positive;

[0050] The zero-sequence current monitoring signals of each downstream side at the downstream side of the fault point Z and U g The scalar product of is negative.

[0051] Method C2:

[0052] The scalar products of the zero-sequence current monitoring signals on the upstream side of the fault point Z and the outgoing zero-sequence currents of the non-fault lines are both negative; the scalar products of the zero-sequence current monitoring signals on the downstream side of the fault point Z and the outgoing zero-sequence currents of the non-fault lines are both positive; the upstream side refers to the power supply side of the fault point, and the downstream refers to the load side of the fault point.

[0053] The single-phase grounding fault phase judgment and line selection location method based on vector scalar product of the present invention is also characterized in that:

[0054] The scalar product of two vectors is calculated as follows:

[0055] The synchronous sampling values ​​of the two vectors in one cycle are defined as F(t) and G(t), respectively, and:

[0056] F(t)=[f1,f2,……,f n ] and G(t)=[g1,g2,……,g n ]

[0057] in:

[0058] n is the number of sampling times in one cycle;

[0059] f i is the i-th sampling value of the vector F(t), i=1, 2, ..., n; g i is the i-th sampling value of the vector G(t);

[0060] The scalar product m and the angle θ of the vectors F(t) and G(t) can be calculated in any of the following ways:

[0061] Method 1: Calculate the scalar product m and the angle θ of the two vectors using equations (1) and (2) respectively:

[0062]

[0063]

[0064] in:

[0065]

[0066]

[0067] Method 2:

[0068] The vectors F(t) and G(t) are respectively subjected to (-1, 1) square wave processing in the following form, namely:

[0069] If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as -1;

[0070] If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as -1;

[0071] Or: For vector F(t) and vector G(t), square wave processing of (-1, 1) is performed in the following form, namely:

[0072] If fig i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as -1;

[0073] The scalar product m and the angle θ of the two vectors are calculated by equations (3) and (4) respectively:

[0074]

[0075]

[0076] Method 3:

[0077] The vectors F(t) and G(t) are respectively subjected to (0, 1) square wave processing in the following form, namely:

[0078] If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as 0;

[0079] If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as 0;

[0080] The scalar product m and the angle θ of the two vectors are calculated by equations (5) and (6) respectively:

[0081]

[0082]

[0083] in, It is for i and g i Perform logical XOR operation;

[0084] Method 4:

[0085] For f i g i Perform (0, 1) square wave processing, that is:

[0086] If f i g i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as 0;

[0087] The scalar product m and the angle θ of the two vectors are calculated by equations (7) and (8) respectively:

[0088]

[0089]

[0090] The any one method refers to any one method from method 1 to method 4.

[0091] The single-phase grounding fault phase judgment and line selection location method based on vector scalar product of the present invention is also characterized in that:

[0092] Method 2, method 3 and method 4 are applied to multiple monitoring terminals to reduce the amount of communication data of the monitoring terminals and shorten the communication time, thereby achieving fault judgment and positioning within 200ms and remotely controlling the nearest switch upstream of the fault point to open the circuit breaker.

[0093] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0094] 1. The single-phase grounding fault phase judgment and line selection positioning method based on vector scalar product of the present invention realizes fault phase judgment and line selection positioning through logical judgment. There is no calculation error in the process of logical judgment, so the fault phase and line selection positioning can be accurately judged.

[0095] 2. In the scalar product calculation after square wave conversion of the present invention, the scalar product value of two vectors is linearly related to their included angle. Therefore, the scalar product value can directly represent the included angle of the two vectors, which greatly reduces the amount of calculation and shortens the calculation time, and quickly determines the phase relationship between the vectors.

[0096] 3. The calculation method of the binary scalar product and the angle of the present invention converts the vector scalar product into a square wave, greatly reducing the communication data volume of multiple monitoring terminals and reducing the communication time, which is conducive to rapid fault diagnosis and positioning.

[0097] 4. The present invention utilizes the characteristics that the fault relative ground voltage is in phase with the zero-sequence current of the fault line when single-phase is grounded, and in opposite phase with the non-fault line. The scalar product of the same phase is positive, and the scalar product of the opposite phase is negative. There is no need for complex calculations such as Fourier transform to solve the vector amplitude and phase, which reduces the calculation process and reduces the CPU operation time, and realizes positive and negative logic judgment line selection and fault location.

[0098] 5. The present invention utilizes the characteristics of the zero-sequence current of the fault line and the non-fault line being in opposite phase when single-phase grounding occurs. The zero-sequence current scalar product of the fault line and the non-fault line is negative, and the zero-sequence current scalar product between the non-fault lines is positive. The line selection and fault point location are determined by logic. Not only is the calculation simple and the judgment accurate, but there is no need to determine the fault phase, which reduces the judgment link and is more conducive to rapid line selection and fault point location.

[0099] 6. The present invention uses a frequency product value to judge the fault phase, line selection and fault point location. Because the time is short and it is not affected by the arc extinguishing coil, it is efficient, fast and error-free, and can quickly remove the fault to prevent the fault from expanding;

[0100] 7. The present invention cooperates with distribution network automation, the present invention can quickly and accurately locate the fault point, start the nearest switch of the fault point to trip, minimize the power outage range, reduce the scope of fault impact, and improve power supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 This is the B-phase single-phase grounding vector relationship diagram;

[0102] Figure 2 This is a schematic diagram for locating a single-phase grounding fault;

[0103] The symbols in the figure are: O is the neutral point, M is the busbar, QS is the outgoing line switch of the substation; Z is the single-phase grounding fault point of phase B, Z1, Z2, Z3, and Z4 are the points on the outgoing line; I cz is the zero-sequence current of the fault line, I cf is the zero-sequence current of the non-fault line;

[0104] I 011 ,……,I 0x1 ,……,I 0y1 is the outgoing zero-sequence current of the line;

[0105] I 011 ,I 012 ,I 013 ,I 014 ,I 015 ,I 016 ,I 017 ,I 018 ,I 019 I is the zero-sequence current output by the zero-sequence current monitoring terminal distributed on the No. 01 outgoing line; 0y1 ,I 0y2 ,I 0y3 ,I 0y4 It is the zero-sequence current output by the zero-sequence current monitoring terminal distributed on the 0y outgoing line. DETAILED DESCRIPTION

[0106] This embodiment is for a single-phase grounding fault in a small current grounding system. The scalar product between vectors during a single-phase grounding fault is calculated, and the scalar product value is used to represent the angle between the vectors during the fault. The single-phase grounding fault phase is determined based on the size of the scalar product value, and the small current line is selected and the fault point is located based on the positive or negative sign of the scalar product value.

[0107] Embodiment 1: Determine the single-phase grounding fault phase of a small current grounding system according to the size of the scalar product:

[0108] Figure 1 As shown, the voltages of phases A, B, and C to ground are U a , U b and U c , the neutral point to ground voltage is U0;

[0109] The line voltages of the three phases A, B, and C are U ab , U bc and U ca , and Uab =U a -U b ; U bc =U b -U c , U ca =U c -U a , β is the phase voltage between U0 and the fault phase U B The acute angle of

[0110] The phase voltages of phases A, B, and C are U A , U B and U C , and U A =U a -U0,U B =U b -U0,U C =U c -U0;

[0111] U a The scalar product with U0 is m a0 , U b The scalar product with U0 is m b0 , U c The scalar product with U0 is m c0 ;

[0112] U ab The scalar product with U0 is m ab0 , U bc The scalar product with U0 is m bc0 , U ca The scalar product with U0 is m ca0 ;

[0113] U A The scalar product with U0 is m A0 , U B The scalar product with U0 is m B0 , U C The scalar product with U0 is m C0 .

[0114] When a single-phase grounding fault occurs, the single-phase grounding fault phase is determined according to the following method A1, method A2 or method A3:

[0115] Method A1:

[0116] If in m a0 、m b0 and m c0 Medium c0 The value of is the largest, and m b0 ≤m c0 , then the fault phase is phase A;

[0117] If in m a0 、m b0 and m c0 Medium a0 The value of is the largest, and m c0 ≤m a0 , then the fault phase is phase B;

[0118] If in m a0 、m b0 and m c0 Medium b0 The value of is the largest, and m a0 ≤m b0 , then the fault phase is phase C;

[0119] When phase B is metallically grounded, phase A is the leading phase, U a , U c The amplitude is the same, and in the angle between U0 and the three-phase voltage to ground, U0 and U a The angle between U0 and U c Angle = 60°, m a0 =m c0 ; When the non-metallic phase is single-phase grounded, the angle between U0 and the three-phase voltage to ground is a The angle between U0 and U a The angle between U0 and U c The smaller the angle, the larger the scalar product. The scalar product of an acute angle is positive, and the amplitude |U a |>|U c |, so m a0 >m c0 ; Theoretically, U0 and U b The angle is 90°, theoretically U0 and U b The scalar product m b0 = 0, in practice, due to the existence of non-power frequency and interference signals m b0 is not equal to 0; therefore, when phase B is single-phase grounded, the amplitude |U a |>|U c |, so m a0 Maximum, and m c0 ≤m a0 .

[0120] Similarly:

[0121] When phase A is single-phase grounded, the angle between U0 and the three-phase voltage to ground is c The angle between the two is the smallest and acute, and the amplitude |U c |≥|U b |, so m c0 Maximum, and m b0 ≤m c0 ;

[0122] When phase C is single-phase grounded, the angle between U0 and the three-phase voltage to ground is b The angle between the two is the smallest and acute, and the amplitude |U b |≥|U a |, so m b0 Maximum, and m a0 ≤m b0 .

[0123] Method A2:

[0124] If m ab0 、m bc0 and m ca0 Medium ca0 The maximum value is the fault phase A.

[0125] If m ab0 、m bc0 and m ca0 Medium ab0 The maximum value is the fault phase B.

[0126] If m ab0 、m bc0 and m ca0 Medium bc0 The maximum value is the fault phase C.

[0127] Use either method or both methods to determine the fault phase.

[0128] When phase B is single-phase grounded, phase A is the leading phase. In the angle between U0 and the three-phase line voltage, U0 and U ab The angle between m and m is the smallest and acute. ab0 Maximum; When the C phase is single-phase grounded, in the angle between U0 and the three-phase line voltage, U0 and U bc The angle between m and m is the smallest and acute. bc0 maximum.

[0129] Take phase B single-phase grounding as an example for further explanation. Figure 1 The figure shows the relationship between the single-phase grounding vector of phase B, where β is the voltage between U0 and the fault phase U B The acute angle is β∈(0, 90°).

[0130] Phase B metallic grounding β=0°, U0 leads U B is 180°, U0 lags behind U c is 60°, U0 leads U A is 60°, U0 leads U ab is 30°, U0 lags behind U ca is 90°, U0 leads U bc is 150°; when the B phase is metallically grounded, m c0=m a0 , scalar product m b0 The minimum is equal to 0; the three line voltage amplitudes are equal, and the scalar product is only related to the phase angle, m ab0 is positive, m bc0 is negative, m ca0 =0.

[0131] Phase B is non-metallic single-phase grounding. When 0°<β<90°, U0 and U a , U ab The angle between U0 and U b The vertical angle is 90°, U0 and U a , U ab The angle between U0 and U c , U ca The angle of U a The amplitude of >U c The magnitude of a Maximum and U0U c <U0U a , scalar product U0U ab >U0U ca .

[0132] When the high resistance of phase B high resistance grounding tends to infinity, β tends to 90°, but β<90°, U0 leads U B is 90°, U0 leads U B is 60°, U0 lags behind U A is 30°, U0 lags behind U ab is 60°, U0 lags behind U C The angle between them is 150°, and U0 lags behind U ca The angle between the two is 180°, so: a0 Maximum and m c0 ≤m a0 , scalar product m ab0 maximum.

[0133] also, Figure 1 When the B phase is single-phase grounded, the angle between U0 and the three-phase phase voltage is A The angle between them is the smallest and acute, so we can infer method A3:

[0134] If in m A0 、m B0 and m C0 Medium C0 The value of is the largest, and m B0 ≤m C0 , then the fault phase is phase A;

[0135] If in m A0 、mB0 and m C0 Medium A0 The value of is the largest, and m C0 ≤m A0 , then the fault phase is phase B;

[0136] If in m A0 、m B0 and m C0 Medium B0 The value of is the largest, and m A0 ≤m B0 , the fault phase is phase C.

[0137] For single-phase high-resistance grounding with an open triangle voltage less than 15V, the three-phase unbalanced voltage U′0 at the neutral point is added to the neutral point voltage U″0 generated by the fault to produce the neutral point voltage U0 to ground. Due to the existence of the three-phase unbalanced voltage U′0 at the neutral point, U0 may not correctly reflect the U″0 generated by the single-phase grounding fault. In this case, measures should be taken to eliminate the influence of the three-phase unbalanced voltage at the neutral point on the judgment criteria.

[0138] Embodiment 2 implements low current grounding line selection according to the size of the scalar product.

[0139] Definition: U g is the relative ground voltage of a single-phase ground fault or the fault phase line voltage, I 01 ,I 02 ,……,I 0w is the zero-sequence current of the 1st, 2nd, ..., wth outgoing line, w is the number of outgoing lines. Select the low current line according to the following method B1, method B2 or method B3:

[0140] Figure 1 As shown, the outgoing zero-sequence current I cz The voltage is in phase with the fault phase. In a single-phase ground fault, I cz with U b In phase with the fault phase line voltage U bc The angle is always acute, so I cz with U b and U bc The scalar product is positive. If the kth line has a single-phase ground fault, then I cz For I 0k , I 0k With fault phase line voltage U bc The angle is always acute, so I 0k with U b and U bc The scalar product m 0k is positive; the zero-sequence current I cf with I cz Opposite phase, with U bThe phase is opposite and is in the same phase as the fault line voltage U bc The angle is always an obtuse angle; by analogy, phases A and C are single-phase grounded, so we can get

[0141] Method B1:

[0142] Definition: U g with I 01 ,I 02 ,……,I 0w The scalar products are m 01 、m 02 ,……,m 0w ;

[0143] When a single-phase grounding fault occurs, 01 、m 02 ,……,m 0w Among them, only m 0k is positive and the other scalar products are negative, then the kth outgoing line is the fault line; that is to say: when a single-phase grounding fault occurs, the phase between the outgoing zero-sequence current of the faulty line and the fault-to-ground voltage or the fault-phase line voltage is an acute angle and the scalar product is positive, and the phase between the outgoing zero-sequence current of the non-faulty line and the fault-to-ground voltage or the fault-phase line voltage is an obtuse angle and the scalar product is negative.

[0144] When single-phase grounding occurs, the outgoing zero-sequence current of the faulty line is in opposite phase to the outgoing zero-sequence current of the non-faulty line. Then the outgoing zero-sequence current of the faulty line and the outgoing zero-sequence current of the non-faulty line are in opposite phase, and the scalar product is negative. The outgoing zero-sequence current of the non-faulty line and the outgoing zero-sequence current of the non-faulty line are in the same phase, and the scalar product is positive. Therefore, the positive and negative scalar product between the outgoing zero-sequence currents can be used to determine the faulty line, and method B2 is obtained:

[0145] When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative; then one of the kth and k+1th outgoing lines is a fault line. If the scalar products of the zero-sequence current of the kth outgoing line and the zero-sequence currents of all other outgoing lines are negative, then the kth outgoing line is a fault line. At this time, the zero-sequence currents of the non-fault lines are in phase, so the scalar products of the zero-sequence current of the k+1th outgoing line and the zero-sequence currents of all other outgoing lines are positive.

[0146] If the scalar product of the zero-sequence current of the k+1th outgoing line and the zero-sequence currents of all other outgoing lines are negative, then the k+1th outgoing line is a faulty line. At this time, the zero-sequence currents of the non-faulty lines are in phase with each other, and the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence currents of all other outgoing lines are positive.

[0147] Figure 2 As shown in the figure, if a single-phase grounding occurs at Z2, the zero-sequence current I 0x1 The zero-sequence current of the outgoing line of the non-fault line is I011 ,I 0y1 The scalar product is negative, and the outgoing zero-sequence current I 011 and I 0y1 The scalar product of is positive.

[0148] The criterion for small current line selection in method B2 can also be expressed as: when a single-phase grounding fault occurs, the scalar product of the outgoing zero-sequence current of the faulty line and the outgoing zero-sequence current of the non-fault line is negative, and the scalar product of the outgoing zero-sequence current of the non-fault line and the outgoing zero-sequence current of the non-fault line is positive.

[0149] Method B1 and method B2 can also be combined to form method B3: When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative, one of the kth and k+1th outgoing lines is a fault line. g The scalar product is positive, indicating that the zero-sequence current of the kth outgoing line is g The phase angle is acute, and the zero-sequence current of the k+1th outgoing line is g The phase angle is an obtuse angle and the scalar product is negative, then the kth outgoing line is a fault line;

[0150] If the zero-sequence current of the kth outgoing line is g The scalar product is negative, and the zero-sequence current of the k+1th outgoing line is equal to U g The phase angle is an acute angle, the scalar product is positive, and the zero-sequence current of the kth outgoing line is g If the phase angle is an obtuse angle and the scalar product is negative, then the k+1th outgoing line is a faulty line.

[0151] k∈[1,w]; Definition: when k=w, k+1 is the first outgoing line. A positive scalar product indicates that the product value is greater than 0, and a negative scalar product indicates that the product value is less than or equal to 0. The outgoing zero-sequence current of the line refers to the zero-sequence current on the bus side of the outgoing line.

[0152] Embodiment 3: Locate the fault point based on the positive or negative sign of the scalar product value:

[0153] Definition: According to the method of the present invention, it is determined that the kth outgoing line is a single-phase grounding fault line, and e zero-sequence current monitoring terminals are set at intervals on the kth outgoing line. The zero-sequence current monitoring signals obtained by monitoring the e zero-sequence current monitoring terminals are: I 0k1 ,I 0k2 ,……,I 0ke , which are numbered consecutively from the power supply side to the load side, I 0k1 It refers to the zero-sequence current signal obtained by monitoring the first zero-sequence current monitoring terminal on the kth outgoing line, I 0keIt means that the zero-sequence current signal is obtained by monitoring the e-th zero-sequence current monitoring terminal on the k-th outgoing line. The fault point Z occurs between the q-th and h-th adjacent zero-sequence current monitoring terminals. There is I on the upstream side of the fault point z. 0k1 ,I 0k2 ,..., and I 0kq Each upstream side monitors the zero-sequence current signal, and there is I on the downstream side of the fault point z. 0kh ,..., and I 0ke Each downstream side monitors the zero-sequence current signal;

[0154] Locate the fault point z using the following method C1 or method C2:

[0155] Figure 2 As shown, M is the busbar, QS is the outgoing line switch of the substation, and I 011 ,……,I 0x1 ,……,I 0y1 is the zero-sequence current of the substation outgoing line, I 011 ,I 012 ,I 013 ,I 014 ,I 015 ,I 016 ,I 017 ,I 018 ,I 019 is the zero-sequence current output by the zero-sequence current monitoring terminal distributed on the No. 01 outgoing line, I 0y1 ,I 0y2 ,I 0y3 ,I 0y4 is the zero-sequence current output by the zero-sequence current monitoring terminal distributed on the 0y outgoing line, and Z1, Z2, Z3, and Z4 are points on the outgoing line.

[0156] See also Figure 2 , single-phase grounding of phase B occurs at Z1 of No. 0y outgoing line, then q = 2, h = q + 1 = 3, and the zero-sequence current I output by the second zero-sequence current monitoring terminal on No. 0y outgoing line 0y1 ,I 0y2 Upstream of the fault point z1, the zero-sequence current I 0y3 ,I 0y4 ,I 0y5 Downstream of the fault point Z1, according to the law of single-phase grounding, we know that: I 0y1 ,I 0y2 The zero-sequence current is in phase with the voltage of fault phase B relative to ground, I 0y1 ,I 0y2 The angle between the zero-sequence current and the fault phase B line voltage is an acute angle, so I 0y1 ,I 0y2 The product of the voltage relative to the fault phase B or the line voltage is positive; the zero-sequence current I 0y3 ,I 0y4and I 011 ,I 012 ,I 013 ,I 0104 ,I 015 ,I 016 ,I 017 ,I 018 ,I 019 and I 0x1 , they are related to I 0y1 ,I 0y2 The zero-sequence currents are in opposite phases, and their scalar product with the ground voltage or line voltage of the fault phase B is a negative value; similarly, for single-phase grounding faults of phases A and C, the fault location method C1 is obtained.

[0157] Method C1:

[0158] The upstream zero-sequence current monitoring signals of each upstream side of the fault point Z and U g The scalar product of the zero-sequence current monitoring signals at the downstream side of the fault point Z and U g The scalar product of U g and the zero-sequence current I 01 ,I 02 ,……,I 0w The scalar product of the three-phase voltage is negative. In other words, mode C1 means that when a single-phase grounding occurs, the scalar product of the zero-sequence current of the upstream monitoring terminal of the fault point and the fault-phase voltage to ground or the fault-phase voltage is positive, the scalar product of the zero-sequence current of the downstream monitoring terminal of the fault point and the fault-phase voltage to ground or the fault-phase voltage is negative, and the scalar product of the non-fault line and the fault-phase voltage to ground or the fault-phase voltage is negative. The three-phase voltage and open delta voltage can be obtained from the PT on the bus and line, or can be obtained locally at the zero-sequence current monitoring terminal, such as a combination of a zero-sequence current transformer, a PT and a pole-mounted intelligent switch.

[0159] Similarly, the fault location is implemented by using the positive and negative scalar products of zero-sequence currents at various points on the outgoing line. The zero-sequence currents monitored at various points upstream of the fault point are basically equal and in opposite phase to the zero-sequence current of the non-fault line. The zero-sequence currents monitored at various points downstream of the fault point are in phase with the zero-sequence current of the non-fault line. This leads to the fault location method C2:

[0160] Method C2:

[0161] The scalar products of the zero-sequence current monitoring signals on the upstream side of the fault point z and the zero-sequence current of the outgoing lines of the non-fault lines are all negative; the scalar products of the zero-sequence current monitoring signals on the downstream side of the fault point Z and the zero-sequence current of the outgoing lines of the non-fault lines are all positive. 01 ,I 02 ,……,I 0w The zero-sequence current I of any outgoing line0p , zero sequence current I 0p The zero-sequence current I upstream of the fault point Z 0k1 ,I 0k2 ,……,I 0kq The scalar product is negative, and the zero-sequence current I 0p and Z downstream zero sequence current I 0kh ,……,I 0ke The scalar product of the fault point Z is positive; the zero-sequence current I 0k1 ,I 0k2 ,……,I 0kq The scalar product of any two zero-sequence currents in is positive, and the zero-sequence current I downstream of the fault point Z is 0kh ,……,I 0ke The scalar product of any two zero-sequence currents is positive, and the zero-sequence current I upstream of the fault point Z 0k1 ,I 0k2 ,……,I 0kq Any zero-sequence current in and the zero-sequence current I downstream of the fault point z 0kh ,……,I 0ke The scalar product of any zero-sequence current in is negative. That is to say, mode C2 means: the zero-sequence current I upstream of the fault point Z 0k1 ,I 0k2 ,……,I 0kq The scalar product of any two adjacent zero-sequence currents in is positive, and the zero-sequence current I downstream of the fault point Z is 0kh ,……,I 0ke The scalar product of any two adjacent zero-sequence currents is positive, and the two adjacent zero-sequence currents above and below the fault point I 0kq with I 0kh is negative, the zero-sequence current I upstream of the fault point Z 0k1 ,I 0k2 ,……,I 0kq Any zero-sequence current in and the zero-sequence current I downstream of the fault point z 0kh ,……,I 0ke The scalar product of any zero-sequence current in is negative. In other words, method C2 means: the zero-sequence current I upstream of the fault point Z 0k1 ,I 0k2 ,……,I 0kq Respectively with the zero sequence current I 01 ,I 02 ,……,I 0w The scalar products of the zero-sequence currents I 0kh ,……,I 0ke and each non-fault line zero-sequence current I 01 ,I 02 ,……,I 0w The scalar product of is always positive.

[0162] Example 4: When single-phase grounding occurs at Z3 or Z4:

[0163] If a single-phase grounding occurs at Z3, the zero-sequence current I 011 The zero-sequence current of the outgoing line of the non-fault line is I 0x1 ,I 0y1 The scalar product is negative, and the zero-sequence current downstream of the fault point is I 012 ,I 013 The zero-sequence current of the outgoing line of the non-fault line is I 0x1 ,I 0y1 The scalar product of the zero-sequence currents of the non-fault lines is positive. 0x1 with I 0y1 The scalar product is positive.

[0164] If a single-phase grounding occurs at Z4, the zero-sequence current I 011 ,I 013 The zero sequence current of the non-fault line is I 0x1 ,I 0y1 The scalar product is negative, and the zero-sequence current I 017 The zero-sequence current of the non-fault line, such as I 0x1 ,I 0y1 The scalar product is positive; I 012 ,I 014 ,I 015 ,I 016 ,I 017 ,I 018 ,I 019 It is the zero-sequence current of the non-fault branch line, and its phase is the same as the zero-sequence current of the non-fault line.

[0165] In addition, when single-phase grounding occurs at Z1 of No. 0y outgoing line, I 0y4 Since it is the end, its zero sequence current I 0y4 However, if a single-phase grounding occurs downstream, the zero-sequence current I 0y4 The value is equal to the sum of the zero-sequence currents of other outgoing lines, but the phase is opposite.

[0166] In engineering, due to the accuracy of current transformers, when the zero-sequence current is very small, the output zero-sequence current of the zero-sequence current transformer is not the zero-sequence current generated by the fault, but an interference signal. For example, if a single-phase grounding fault occurs upstream of the zero-sequence current transformer at the end of the line, the zero-sequence current generated by the fault at the zero-sequence current transformer at the end of the line is extremely small. At this time, the signal output by the zero-sequence current transformer at the end of the line may have an interference signal greater than the fault current signal. The minimum current fixed value shielding can be set. When the zero-sequence current of the monitoring terminal is less than this fixed value, it is considered that the fault point is not downstream of the monitoring terminal.

[0167] Upstream and downstream mean: on the fault line, the power supply side of the fault point is upstream, and the load side of the fault point is downstream.

[0168] In a specific implementation, the scalar product of two vectors is calculated as follows:

[0169] The synchronous sampling values ​​of the two vectors in one cycle are defined as F(t) and G(t) respectively, and:

[0170] F(t)=[f1,f2,……,f n ] and G(t)=[g1,g2,……,g n ]

[0171] in:

[0172] n is the number of sampling times in one cycle;

[0173] f i is the i-th sampling value of the vector F(t), i=1, 2, ..., n; g i is the i-th sampling value of the vector G(t);

[0174] The scalar product m and the angle θ of the vectors F(t) and G(t) can be calculated in any of the following ways:

[0175] Method 1: Calculate the scalar product m and the angle θ of the two vectors using equations (1) and (2) respectively:

[0176]

[0177]

[0178] in:

[0179]

[0180]

[0181] Method 2:

[0182] In order to reduce the amount of calculation, the vectors F(t) and G(t) are squared as follows:

[0183] If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as -1;

[0184] If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as -1;

[0185] Or: For vector F(t) and vector G(t), square wave processing of (-1, 1) is performed in the following form, namely:

[0186] If f i g i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as -1;

[0187] The scalar product m and the angle θ of the two vectors are calculated by equations (3) and (4) respectively:

[0188]

[0189]

[0190] Obviously, the amount of calculation of the scalar product and the angle in equations (3) and (4) is greatly reduced. After square wave conversion, the scalar product m and the angle θ are linearly related and no longer related to the vector amplitude (modulus). The size of the vector angle can be directly determined based on the size of the scalar product m. Therefore, the angle between several vectors can be directly determined by the size of their scalar product.

[0191] After square wave conversion, the scalar product of two vectors is linearly related to their included angle, and the size of the scalar product can directly represent the size of the included angle.

[0192] In order to facilitate computer calculation, the calculation of the scalar product and the angle is binarized. The vector needs to be binarized, that is, the vector is processed into a (0, 1) square wave. Therefore, the binary algorithm of the scalar product m and the angle θ of method three and method four is inferred.

[0193] Method 3:

[0194] The vectors F(t) and G(t) are respectively subjected to (0, 1) square wave processing in the following form, namely:

[0195] If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as 0;

[0196] If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as 0;

[0197] The scalar product m and the angle θ of the two vectors are calculated by equations (5) and (6) respectively:

[0198]

[0199]

[0200] in, It is for i and g i Perform logical XOR operation;

[0201] Method 4:

[0202] For f i g i Perform (0, 1) square wave processing, that is:

[0203] If f i g i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as 0;

[0204] The scalar product m and the angle θ of the two vectors are calculated by equations (7) and (8) respectively:

[0205]

[0206]

[0207] Any method refers to any method from method 1 to method 4.

[0208] The binary calculation method is not only beneficial to computer operations, but also to vector sampling data transmission and communication.

[0209] Method 2, method 3 and method 4 are applied to multiple monitoring terminals to reduce the amount of communication data of the monitoring terminals and shorten the communication time, thereby achieving fault judgment and positioning within 200ms and remotely controlling the nearest switch upstream of the fault point to open the circuit breaker.

[0210] Fault location requires networking of multi-terminal monitoring sensors distributed at different positions of the line. Networking requires communication. In existing power engineering technologies, AD sampling data mostly uses 16-bit chips, and one sampling point data occupies 16 bits. After square wave conversion, one sampling point occupies fewer bits: method two occupies 2 bits, and methods three and four occupy 1 bit. Therefore, the time for data communication and data transmission can be greatly reduced, and fault location can be quickly achieved within 200ms.

[0211] Since the present invention does not require precise calculation, 8-bit sampling does not affect the correctness of the scalar product judgment at all, thereby reducing the cost of the hardware circuit.

[0212] If n is the number of half-cycle sampling times, equations (1) to (8) for calculating the scalar product m and θ are still valid, further shortening the time for fault phase, line selection and fault point location.

[0213] Since the present invention uses one frequency product value to judge the fault phase, line selection and fault point location, the arc suppression coil current is still small and does not affect the judgment conclusion of the present invention, so the present invention is not affected by the arc suppression coil; the present invention cooperates with the distribution network automation to quickly and accurately locate the fault point, start the tripping of the switch closest to the fault point, thereby minimizing the power outage range and improving the power supply reliability.

[0214] The present invention eliminates the influence of calculation errors on judgment, and realizes accurate judgment of the fault phase, line selection and fault location.

Claims

1. A method for determining the phase and selecting the line for a single-phase ground fault based on vector scalar product, characterized by: For a single-phase grounding fault in a low-current grounding system, the scalar product between the vectors at the time of the single-phase grounding fault is calculated, and the scalar product value is used to represent the angle between the vectors at the time of the fault. The single-phase grounding fault phase is determined according to the size of the scalar product value, and the low-current line selection and fault point location are performed according to the positive and negative signs of the scalar product value. The determination of the single-phase grounding fault phase according to the size of the scalar product value is performed in the following manner: definition: The voltages of phases A, B, and C to ground are U a , U b and U c , the neutral point to ground voltage is U0; A, B, C three-phase electric wire division U ab , U bc Japanese ca , and U ab = U a -U b , U bc = U b -U c , U ca = U c -U a ; The phase voltages of phases A, B, and C are U A , U B and U C , and U A =U a -U0,U B =U b -U0,U C =U c -U0; U a The scalar product with U0 is m a0 , U b The scalar product with U0 is m b0 , U c The scalar product with U0 is m c0 ; U ab The scalar product with U0 is m ab0 , U bc The scalar product with U0 is m bc0 , U ca The scalar product with U0 is m ca0 ; U A The scalar product with U0 is m A0 , U B The scalar product with U0 is m B0 , U C The scalar product with U0 is m C0 ; Determine the single-phase grounding fault phase according to the following method A1, method A2 or method A3: Method A1: In each standard product m a0 、m b0 and m c0 In, if m c0 The value of is the largest, and m b0 ≤m c0 , then the fault phase is phase A; In each standard product m a0 、m b0 and m c0 In, if m a0 The value of is the largest, and m c0 ≤m a0 , then the fault phase is phase B; In each standard product m a0 、m b0 and m c0 In, if m b0 The value of is the largest, and m a0 ≤m b0 , then the fault phase is phase C; Method A2: In each standard product m ab0 、m bc0 and m ca0 In, if m ca0 If the value of is the largest, the fault phase is phase A; In each standard product m ab0 、m bc0 and m ca0 In, if m ab0 If the value of is the largest, the fault phase is phase B; In each standard product m ab0 、m bc0 and m ca0 In, if m bc0 If the value of is the largest, the fault phase is phase C; Method A3: In each standard product m A0 、m B0 and m C0 In, if m C0 The value of is the largest, and m B0 ≤m C0 , then the fault phase is phase A; In each standard product m A0 、m B0 and m C0 In, if m A0 The value of is the largest, and m C0 ≤m A0 , then the fault phase is phase B; In each standard product m A0 、m B0 and m C0 In, if m B0 The value of is the largest, and m A0 ≤m B0 , the fault phase is phase C.

2. The method for determining phase and selecting line for single-phase grounding fault based on vector scalar product according to claim 1 is characterized in that: The small current line selection based on the positive and negative of the scalar product value is performed as follows: definition: U g It is the voltage relative to the ground of a single-phase ground fault or the voltage of a fault phase line; I 01 ,I 02 ,……,I 0w One-to-one correspondence is the zero-sequence current of the 1st, 2nd, ..., wth outgoing line, w is the number of outgoing lines; Perform low current line selection in the following manner B1, B2 or B3: Method B1: Definition: U g with I 01 ,I 02 ,……,I 0w The scalar products are m 01 、m 02 ,……,m 0w ; When a single-phase grounding fault occurs, 01 、m 02 ,……,m 0w Among them, only m 0k is positive, then the kth outgoing line is a faulty line; Method B2: When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative; If the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence currents of all other outgoing lines is negative, the kth outgoing line is a fault line; If the scalar product of the zero-sequence current of the k+1th outgoing line and the zero-sequence currents of all other outgoing lines is negative, then the k+1th outgoing line is a fault line; Method B3: When the scalar product of the zero-sequence current of the kth outgoing line and the zero-sequence current of the k+1th outgoing line is negative; If the zero-sequence current of the kth outgoing line is g If the scalar product of the kth outgoing line is positive, the kth outgoing line is a fault line; if the zero-sequence current of the kth outgoing line is equal to U g If the scalar product of is negative, the k+1th outgoing line is a faulty line; Where k∈[1,w]; Definition: When k=w, k+1 is the first outgoing line.

3. The method for determining phase and selecting line for single-phase grounding fault based on vector scalar product according to claim 2 is characterized in that: The fault point location based on the positive or negative sign of the scalar product value is performed as follows: Definition: The kth outgoing line is a single-phase grounding fault line. e zero-sequence current monitoring terminals are set at intervals on the kth outgoing line. The fault point Z occurs between the qth and hth adjacent zero-sequence current monitoring terminals. The fault point Z is located according to the following method C1 or method C2: Method C1: The upstream zero-sequence current monitoring signals of each upstream side of the fault point Z and U g The scalar products of are all positive; The zero-sequence current monitoring signals of each downstream side at the downstream side of the fault point Z and U g The scalar products of are all negative; Method C2: The scalar products of the zero-sequence current monitoring signals on the upstream side of the fault point Z and the outgoing zero-sequence currents of the non-fault lines are all negative; The scalar products of the zero-sequence current monitoring signals of each downstream side of the fault point Z and the outgoing zero-sequence currents of each non-fault line are all positive; The upstream side refers to the power supply side of the fault point, and the downstream side refers to the load side of the fault point.

4. The method for determining phase and selecting line for single-phase ground fault based on vector scalar product according to claim 1, 2 or 3 is characterized in that: The scalar product of two vectors is calculated as follows: The synchronous sampling values ​​of the two vectors in one cycle are defined as F(t) and G(t), respectively, and: F(t) = [f1, f2, ……, f n and G(t) = [g1, g2, ……, g n ​ in: n is the number of sampling times in one cycle; f i is the i-th sampling value of the vector F(t), i=1, 2, ..., n; g i is the i-th sampling value of the vector G(t); The scalar product m and the angle θ of the vectors F(t) and G(t) can be calculated in any of the following ways: Method 1: Calculate the scalar product m and the angle θ of the two vectors using equations (1) and (2) respectively: in: Method 2: The vectors F(t) and G(t) are respectively subjected to (-1, 1) square wave processing in the following form, namely: If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as -1; If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as -1; Or: For vector F(t) and vector G(t), square wave processing of (-1, 1) is performed in the following form, namely: If f i g i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as -1; The scalar product m and the angle θ of the two vectors are calculated by equations (3) and (4) respectively: Method 3: The vectors F(t) and G(t) are respectively subjected to (0, 1) square wave processing in the following form, namely: If f i ≥0, then f i Defined as 1; if f i <0, then f i Defined as 0; If g i ≥0, then g is defined as 1; if g i <0, then g i Defined as 0; The scalar product m and the angle θ of the two vectors are calculated by equations (5) and (6) respectively: in, It is for i and g i Perform logical XOR operation; Method 4: For f i g i Perform (0, 1) square wave processing, that is: If f i g i ≥0, then f i g i Defined as 1; if f i g i <0, then f i g i Defined as 0; The scalar product m and the angle θ of the two vectors are calculated by equations (7) and (8) respectively: The any one method refers to any one method from method 1 to method 4.

5. The method for determining phase and selecting line for single-phase grounding fault based on vector scalar product according to claim 4 is characterized in that: Method 2, method 3 and method 4 are applied to multiple monitoring terminals to reduce the amount of communication data of the monitoring terminals and shorten the communication time, thereby achieving fault judgment and positioning within 200ms and remotely controlling the nearest switch upstream of the fault point to open the circuit breaker.

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