Distance protection method and system suitable for electronic transformer

Abstract

The invention relates to a distance protection method and system suitable for an electronic transformer. Measurement current of an electronic current transformer and measurement voltage of a conventional voltage transformer at a protection installation position before a fault occurs are restored to primary side current and primary side voltage; inputting the constructed compensation current time sequence and the fault point voltage time sequence before the fault into a virtual transmission link for processing to obtain a fault point reconstruction voltage after transmission; according to the transmitted measured voltage of the protection installation position, the transmitted reconstructed voltage of the fault point and the measured current of the protection installation position, an equation related to the fault distance is obtained in combination with a line model; and selecting a proper data window, solving a fault distance in the time window, substituting the fault distance into a preset criterion, and judging internal and external faults. Through the above process, distance protection can be carried out on single-phase and non-single-phase earth faults, and the problem that deviation exists in the solved fault distance due to the fact that the voltage of the fault point cannot be accurately reconstructed is avoided.

Description

Technical Field

[0001] The invention relates to a distance protection method and system suitable for an electronic mutual inductor, belonging to the field of relay protection of power systems. Background Art

[0002] Compared with electromagnetic current transformers with saturation effect, Rogowski coil current transformers have been widely used in power systems to participate in the calculation of distance protection due to a series of advantages such as large dynamic measurement range, wide frequency band response range, and no magnetic saturation phenomenon. Since the output signal of the Rogowski coil is proportional to the differential of the measured current, the Rogowski coil current transformer is usually equipped with an integrator to restore the measured current signal. However, the presence of the integrator will amplify the transient transmission error and analog-to-digital conversion error of the Rogowski coil itself, which may cause serious distortion of current transmission and even incorrect operation of relay protection. For this reason, relevant studies have proposed the idea of ​​canceling the integrator and constructing a virtual Rogowski coil, and directly using the differential signal output of the Rogowski coil to calculate the distance protection.

[0003] Distance protection needs to construct differential equations based on line parameters, voltage and current at the protection installation, fault point voltage and other information to solve the fault distance. The fault point voltage cannot be measured directly, so it is necessary to reconstruct it using existing information to characterize the fault point voltage as accurately as possible. Accurate reconstruction of the fault point voltage is a key technology for distance protection. At present, there is no accurate fault point voltage reconstruction method for the new scenario of eliminating the Rogowski coil integrator.

[0004] The Chinese patent document with the announcement number CN111985079B discloses a fast distance protection method based on Rogowski coil current transmission. The method includes the following steps: transient equivalent modeling analysis of the Rogowski coil current transmission circuit to construct a virtual equivalent Rogowski coil digital model; based on the virtual equivalent Rogowski coil digital model, virtual equivalent differential processing is performed on the voltage sampling value signal to obtain a differential voltage signal; the differential current signal and differential voltage signal transmitted by the Rogowski coil are applied to the software distance measurement operation; a data window is pre-set, and the timing starts from the fault start time. If the fault time is greater than the data window, the least square method is used to calculate the distance measurement result; otherwise, the virtual fault point voltage multiple iteration approximation method is used to calculate the distance measurement result. The sampling loop of the Rogowski coil current transformer does not contain the sampling signal integration link, which avoids the influence of the traditional Rogowski coil integrator link, simplifies the sampling loop, and has high distance measurement accuracy and fast action speed.

[0005] However, the fault point voltage reconstructed by this method cannot reflect the actual situation in this scenario, resulting in inaccurate fault distance solution equations and deviations in the solved fault distance; and this method is only applicable to the single-phase ground short circuit fault type. Therefore, it is urgent to study the fault point voltage reconstruction method in the scenario of canceling the Rogowski coil integrator and the distance protection method based on this. Summary of the invention

[0006] The purpose of the present invention is to provide a distance protection method and system suitable for an electronic mutual inductor, so as to solve the problem that the prior art cannot accurately reconstruct the fault point voltage in the scenario of canceling the Rogowski coil integrator, resulting in errors in the distance protection distance measurement results and a single applicable fault scenario.

[0007] To achieve the above object, the solution of the present invention includes:

[0008] A distance protection method applicable to an electronic mutual inductor of the present invention comprises the following steps:

[0009] 1) Obtain the three-phase measurement voltage and three-phase measurement current at the protection installation through conventional voltage transformers and electronic current transformers;

[0010] 2) The three-phase measured current is restored to the primary current according to the amplitude-frequency response and phase-frequency response characteristics of the electronic current transformer transfer function, and the three-phase measured voltage is restored to the primary voltage according to the conventional voltage transformer ratio;

[0011] 3) construct the compensation current time series according to the primary side current, and construct the fault point voltage time series before the fault according to the primary side current, primary side voltage and related line parameters;

[0012] 4) Input the compensation current time series and the fault point voltage time series before the fault into the virtual transmission link constructed according to the transmission characteristics of the electronic current transformer for processing, and obtain the measured voltage at the protection installation after the transmission and the reconstructed voltage at the fault point;

[0013] 5) Based on the measured voltage after transmission, the reconstructed voltage at the fault point and the three-phase measured current, the fault equation related to the fault distance is obtained in combination with the line model;

[0014] 6) Select a data window and obtain the corresponding fault equation, solve the corresponding fault distance, and bring the fault distance into the preset criterion to distinguish between in-zone and out-of-zone faults.

[0015] Furthermore, the method for restoring the primary current in step 2) is: using the formula The three-phase current measurement Restore to primary current During the restoration process, According to the transfer function of the Rogowski coil of the electronic current transformer, the amplitude response K and the phase angle response Δt corresponding to the power frequency are found; the method for restoring the primary side voltage in step 2) is: using the formula The three-phase voltage measurement Restore to primary voltage Where K' is the transformation ratio of the conventional voltage transformer.

[0016] Furthermore, the method for constructing the compensation current time series in step 3) is:

[0017]

[0018] Among them, t f is the fault time, i comp0 (t) is the compensation current before the fault moment; when the fault type is single-phase ground short circuit, i comp0 (t) Take the sum of the three phases of the primary side current obtained after the measured current at the protection installation before the fault is restored; when the fault type is not a single-phase ground short circuit, i comp0 (t) The primary current is obtained by restoring the fault phase measured current at the protection installation before the fault.

[0019] Furthermore, when the fault type is a single-phase ground short circuit, the method for constructing the compensation voltage time series in step 3) is:

[0020]

[0021] in It represents the primary voltage drop per unit length of the line, and the calculation formula is:

[0022]

[0023] Among them, i0'(t) is the zero-sequence current calculated by using the primary side current restored in step 2), and the calculation formula is: R1, L1, R0, L0 are respectively the positive sequence resistance, positive sequence inductance, zero sequence resistance, and zero sequence inductance per unit length of the line; d ini is the distance between the virtual fault point and the protection installation location; when the fault type is non-single-phase ground short circuit, the method for constructing the compensation voltage time series in step 3) is:

[0024]

[0025] in, To restore the primary side fault phase-to-phase voltage, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

[0026]

[0027] Furthermore, the process of the virtual transmission link in step 4) is expressed as:

[0028] u f '1'(t)=g(u f '1(t))

[0029] i co ” mp (t) = g(i comp (t))

[0030] Among them, u f '1'(t) is the voltage time series of the fault point before the fault after virtual transmission, i co ” mp (t) is the compensation current after virtual transformation, and g() is the virtual transformation function constructed according to the transformation link of the electronic current transformer.

[0031] Furthermore, the equation for reconstructing the fault point voltage in step 4) is: f (t) = u f '1'(t)+u f2 (t), where u f (t) is the voltage time series of the fault point in the whole process, u f '1'(t) is the voltage time series of the fault point before the fault after virtual transmission, u f2 (t) is the voltage time series of the fault point after the fault, which is the product of the difference between the fault current and the compensation current after virtual transmission and the transition resistance, that is, u f2 (t) = R f [i f (t)-i co ” mp (t)],R f is the transition resistance, i f (t) represents the fault current; when the fault type is single-phase ground short circuit, the i f (t) Take the sum of the three phases of the current measured at the protection installation; when the fault type is not a single-phase ground short circuit, the i f (t) Take the fault phase and measure the current at the protection installation.

[0032] Furthermore, when the fault type is a single-phase ground short circuit, the equation related to the fault distance in step 5) is: in, is the fault phase voltage at the protection installation after virtual transmission, It represents the fault phase voltage drop per unit length of the secondary side of the line obtained by measuring the current; when the fault type is not a single-phase ground short circuit, the equation related to the fault distance is: in, is the fault phase-to-phase voltage at the protection installation after virtual transmission, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

[0033]

[0034] Furthermore, in step 6), the time window length is T W1 , then [tT W1 ,t], the corresponding equation related to the fault distance in step 5) can be obtained for each sampling interval within the time window. The overdetermined equation can be solved by linear fitting to obtain the fault distance d(t) within the time window, where t represents the current time after the fault. The solution algorithm adopts the least squares algorithm.

[0035] Furthermore, in step 6), the method for distinguishing faults inside and outside the zone is: time window [tT W2 ,t], if d(t) continues to satisfy 0<d(t)<d set , where dset is the protection range setting value, it is considered that an internal fault has occurred; if it is not satisfied, it is considered that an external fault has occurred.

[0036] A distance protection system applicable to an electronic transformer of the present invention comprises a processor, and the processor is used to execute instructions for implementing the distance protection method applicable to the electronic transformer as described above.

[0037] The beneficial effects of the present invention are:

[0038] The present invention is a pioneering invention. In the present invention, according to the amplitude-frequency response and phase-frequency response characteristics of the transfer function of the electronic current transformer, the measured current of the electronic current transformer at the protection installation before the fault occurs is restored to the primary current; according to the transformation ratio of the conventional voltage transformer, the measured voltage of the conventional voltage transformer at the protection installation is restored to the primary voltage. Then, according to the primary current restored by the electronic current transformer measurement current, a compensation current time series is constructed; according to the primary current restored by the electronic current transformer measurement current, the primary voltage restored by the conventional voltage transformer measurement voltage, and the line parameters, a fault point voltage time series before the fault is constructed. According to the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed, and the compensation current time series and the fault point voltage time series before the fault are input into the virtual transmission link for processing to obtain the reconstructed voltage of the fault point after the transmission. According to the measured voltage at the protection installation after the transmission, the reconstructed voltage at the fault point after the transmission, and the measured current at the protection installation, the equation related to the fault distance is obtained in combination with the line model. Then, a suitable data window is selected to solve the fault distance within the time window, and the fault distance of the input distance protection criterion is brought into the preset criterion to distinguish between the faults inside and outside the area. Through the above process, distance protection can be performed for single-phase grounding faults and non-single-phase grounding faults, and the problem of deviation in the solved fault distance due to the inability to accurately reconstruct the fault point voltage is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of the distance protection method applicable to electronic transformers;

[0040] Figure 2 It is a two-terminal system topology diagram;

[0041] Figure 3 This is a schematic diagram of the distance measurement results when the A phase single-phase grounding metallic fault occurs;

[0042] Figure 4 This is a schematic diagram of the distance measurement results when there is a 10Ω transition resistance fault between phases AB. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0044] The concept of the present invention is to restore the measured current of the electronic current transformer at the protection installation before the fault occurs to the primary current according to the amplitude-frequency response and phase-frequency response characteristics of the transfer function of the electronic current transformer; and restore the measured voltage of the conventional voltage transformer at the protection installation to the primary voltage according to the transformation ratio of the conventional voltage transformer. Then, according to the primary current restored by the measured current of the electronic current transformer, a compensation current time series is constructed; according to the primary current restored by the measured current of the electronic current transformer, the primary voltage restored by the measured voltage of the conventional voltage transformer, and the line parameters, a fault point voltage time series before the fault is constructed. According to the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed, and the compensation current time series and the fault point voltage time series before the fault are input into the virtual transmission link for processing to obtain the reconstructed voltage of the fault point after the transmission. According to the measured voltage at the protection installation after the transmission, the reconstructed voltage at the fault point after the transmission, and the measured current at the protection installation, the equation related to the fault distance is obtained in combination with the line model. Then, a suitable data window is selected to solve the fault distance within the time window, and the fault distance of the input distance protection criterion is brought into the preset criterion to distinguish between in-zone and out-of-zone faults.

[0045] Method Example:

[0046] like Figure 1 A distance protection method applicable to an electronic transformer is shown, comprising the following steps:

[0047] S1: Get the three-phase measured voltage and current at the protection installation.

[0048] S2: According to the amplitude-frequency response and phase-frequency response characteristics of the electronic current transformer transfer function, the three-phase current measured by the electronic current transformer at the protection installation before the fault occurs is converted into Restore to primary current According to the transformation ratio of the conventional voltage transformer, the three-phase voltage measured by the conventional voltage transformer at the protection installation is converted to Restore to primary voltage The formulas for restoring the measured three-phase current (measured current) and three-phase voltage (measured voltage) to the primary side current and primary side voltage are:

[0049]

[0050] Among them, during the current reduction process, It is necessary to find the amplitude response K and phase angle response Δt corresponding to the power frequency according to the transfer function of the Rogowski coil of the electronic current transformer; in the voltage restoration process, K' is the transformation ratio of the conventional voltage transformer;

[0051] S3: Based on the primary current restored from the current measured by the electronic current transformer, construct the compensation current time series i comp (t); Based on the primary current restored by the current measured by the electronic transformer, the primary voltage restored by the voltage measured by the conventional voltage transformer, and the line parameters, the voltage time series u of the fault point before the fault is constructed f '1(t).

[0052] The construction method of the compensation current time series is:

[0053]

[0054] where t f is the fault moment; i comp0 (t) is the compensation current before the fault. When the fault type is a single-phase ground short circuit, the sum of the three phases of the primary side current obtained after the measured current at the protection installation before the fault in step 2 is restored, that is, i comp0 (t) = i m ' a (t)+i m ' b (t)+i m ' c (t); When the fault type is not single-phase ground short circuit, the primary side current is obtained by restoring the fault phase measured current at the protection installation before the fault in step 2, that is,

[0055] The construction method of the voltage time series of the fault point before the fault is: when the fault type is a single-phase ground short circuit, the voltage time series of the fault point before the fault is constructed using the following formula:

[0056]

[0057] in It represents the primary voltage drop per unit length of the line, and the calculation formula is:

[0058]

[0059] in is the zero-sequence current calculated by using the primary-side current restored in step S2, r1, l1, r0, l0 are respectively the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line; d ini is the distance between the virtual fault point and the protection installation, where When the fault type is not single-phase ground short circuit, the voltage time series of the fault point before the fault is constructed using the following formula:

[0060]

[0061] in, To restore the primary side fault phase-to-phase voltage, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

[0062]

[0063] in

[0064] S4: According to the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed to compensate the current time series i comp (t), the voltage time series uf'1(t) at the fault point before the fault is input into the virtual transmission link for processing, and the reconstructed voltage at the fault point after the transmission is obtained. The process of the virtual transmission link can be expressed as:

[0065] u f '1'(t)=g(u f '1(t))

[0066] i co ” mp (t) = g(i comp (t))

[0067] Among them, u f '1'(t) is the voltage time series of the fault point before the fault after virtual transmission, i co ” mp (t) is the compensation current after virtual transformation, and g() is the virtual transformation function constructed according to the transformation link of the electronic current transformer.

[0068] The equation for reconstructing the voltage at the fault point is: f (t) = u f '1'(t)+u f2 (t).

[0069] Among them, u f (t) is the voltage time series of the fault point in the whole process, u f '1'(t) is the voltage time series of the fault point before the fault after the virtual transmission mentioned above, u f2 (t) is the voltage time series of the fault point after the fault, which is the product of the difference between the fault current and the compensation current after virtual transmission and the transition resistance, that is, u f2 (t) = R f [i f (t)-i co ” mp (t)],R f is the transition resistance; i f (t) represents the fault current. When the fault type is a single-phase ground short circuit, the sum of the three-phase current measured at the protection installation is taken, that is, if (t) = i ma (t)+i ma (t)+i mc (t); When the fault type is not single-phase ground short circuit, take the fault phase measurement current at the protection installation, that is, in

[0070] S5: Based on the measured voltage at the protection installation after the transformation, the reconstructed voltage at the fault point after the transformation, and the measured current at the protection installation, a fault equation related to the fault distance is obtained in combination with the line model.

[0071] When the fault type is single-phase ground short circuit, the fault equation related to the fault distance is:

[0072] in, is the fault phase voltage at the protection installation after virtual transmission; It represents the secondary voltage drop per unit length of the line obtained by measuring the current. The calculation formula is:

[0073]

[0074] in is the zero-sequence current calculated by using the measured current of the electronic current transformer, r1, l1, r0, l0 are respectively the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line;

[0075] When the fault type is non-single-phase ground short circuit, the fault equation related to the fault distance is:

[0076] in, is the fault phase-to-phase voltage at the protection installation after virtual transmission, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

[0077]

[0078] in,

[0079] S6: Select a suitable time window and solve the fault distance within the time window.

[0080] Among them, let the time window length be T W1 , then [tT W1,t], the corresponding equation related to the fault distance in step 5 can be obtained for each sampling interval. The overdetermined equation can be solved by linear fitting to obtain the fault distance d(t) within the time window. t represents the current time after the fault, and the least squares algorithm can be used as the solution algorithm.

[0081] S7: The fault distance of the input distance protection criterion is brought into the preset criterion to distinguish between the fault inside and outside the zone.

[0082] Among them, let the time window length be T W2 , time window [tT W2 ,t]d(t) continues to satisfy 0<d(t)<d set , then it is considered that an internal fault has occurred; if it is not satisfied, then it is considered that an external fault has occurred. set It is the protection range setting value.

[0083] Specifically, the technical solution of the present invention is further described below in conjunction with a specific case. Based on a certain electromagnetic transient simulation software, a two-terminal system topology is constructed. Figure 2 The figure shows a double-terminal system topology diagram. The photovoltaic power station is connected to the external AC system through a step-up transformer and a transmission line. Different fault types and fault points are set on the transmission line to form a simulation model.

[0084] In conjunction with this specific case, the distance protection method of the present invention is used to calculate the distance protection, and the steps are as follows:

[0085] (1) The current and voltage signals are collected in real time by the Rogowski coil current transformer and conventional voltage transformer installed on one side of the line in the simulation software to obtain a continuously updated sequence of sampled current and voltage values.

[0086] In this case, the sampling rate is 4kHz, the line length is 60km, the positive-sequence impedance is (0.0372+j0.304)Ω / km, and the zero-sequence impedance is (0.316+j1.081)Ω / km; the system positive-sequence impedance is (0.582+j3.481)Ω / km, and the zero-sequence impedance is (1.110+j5.068)Ω / km.

[0087] (2) According to the amplitude-frequency response and phase-frequency response characteristics of the electronic transformer transfer function, the measured current of the electronic transformer at the protection installation before the fault occurs is calculated. Restore to primary current According to the transformation ratio of the conventional voltage transformer, the measured voltage of the conventional voltage transformer at the protection installation Restore to primary voltage The formulas for measuring current and voltage back to the primary side are:

[0088]

[0089]

[0090] Among them, during the current reduction process, It is necessary to find the amplitude response K and phase angle response Δt corresponding to the power frequency based on the transfer function of the Rogowski coil of the electronic current transformer; in the voltage restoration process, K' is the transformation ratio of the conventional voltage transformer.

[0091] (3) Based on the primary current restored by the current measured by the electronic transformer, the compensation current time series i is constructed. comp (t) and the fault point voltage time series uf'1(t) before the fault.

[0092] The construction method of the compensation current time series is:

[0093]

[0094] where t f is the fault moment; i comp0 (t) is the compensation current before the fault. When the fault type is a single-phase ground short circuit, the sum of the three phases of the primary side current obtained after the measured current at the protection installation before the fault in step (2) is restored, that is, i comp0 (t) = i m ' a (t)+i m ' b (t)+i m ' c (t); When the fault type is not single-phase ground short circuit, the primary side current is obtained by restoring the fault phase measured current at the protection installation before the fault in step (2), that is,

[0095] The construction method of the voltage time series of the fault point before the fault is: when the fault type is a single-phase ground short circuit, the voltage time series of the fault point before the fault is constructed using the following formula:

[0096]

[0097] in It represents the primary voltage drop per unit length of the line, and the calculation formula is:

[0098]

[0099] in is the zero-sequence current calculated using the primary current restored in step (2), r1, l1, r0, l0 are the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line respectively; d iniis the distance between the virtual fault point and the protection installation location; When the fault type is not single-phase ground short circuit, the voltage time series of the fault point before the fault is constructed using the following formula:

[0100]

[0101] in, To restore the primary side fault phase-to-phase voltage, is the fault phase-to-phase voltage drop on the secondary side per unit length of the line, and the calculation formula is:

[0102] In this case, r1, l1, r0, and l0 are the parameters set in step (1).

[0103] (4) According to the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed to convert the compensation current time series i comp (t), the voltage time series uf'1(t) at the fault point before the fault is input into the virtual transmission link for processing, and the reconstructed voltage at the fault point after the transmission is obtained. The process of the virtual transmission link can be expressed as:

[0104] u f '1'(t)=g(u f '1(t))

[0105] i co ” mp (t) = g(i comp (t))

[0106] Among them, u f '1'(t) is the voltage time series of the fault point before the fault after virtual transmission, i co ” mp (t) is the compensation current after virtual transformation, and g() is the virtual transformation function constructed according to the transformation link of the electronic current transformer.

[0107] The equation for reconstructing the voltage at the fault point is: f (t) = u f '1'(t)+u f2 (t).

[0108] Among them, u f (t) is the voltage time series of the fault point in the whole process, u f '1'(t) is the voltage time series of the fault point before the fault after the virtual transmission mentioned above, u f2 (t) is the voltage time series of the fault point after the fault, which is the product of the difference between the fault current and the compensation current after virtual transmission and the transition resistance, that is, u f2 (t) = R f [i f(t)-i co ” mp (t)],R f is the transition resistance; i f (t) represents the fault current. When the fault type is a single-phase ground short circuit, the sum of the three-phase current measured at the protection installation is taken, that is, i f (t) = i ma (t)+i ma (t)+i mc (t); When the fault type is not single-phase ground short circuit, take the fault phase measurement current at the protection installation, that is,

[0109] In this case, the fault types are single-phase grounding fault of phase A and phase-to-phase fault of phase AB.

[0110] (5) Based on the measured voltage at the protection installation after the transformation, the reconstructed voltage at the fault point after the transformation, and the measured current at the protection installation, the fault equation related to the fault distance is obtained in combination with the line model.

[0111] When the fault type is single-phase ground short circuit, the fault equation related to the fault distance is:

[0112] in, is the fault phase voltage at the protection installation after virtual transmission; It represents the fault phase voltage drop on the secondary side of the line per unit length obtained by measuring the current. The calculation formula is:

[0113]

[0114] in is the zero-sequence current calculated by measuring the current of the electronic transformer, r1, l1, r0, l0 are the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line, respectively.

[0115] When the fault type is non-single-phase ground short circuit, the fault equation related to the fault distance is:

[0116] in, is the fault phase-to-phase voltage at the protection installation after virtual transmission, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

[0117]

[0118] in,

[0119] (6) Select a suitable time window and solve the fault distance within the time window through a linear fitting algorithm.

[0120] Among them, let the time window length be T W1 , then [tT W1 ,t], the corresponding equation related to the fault distance in step (5) can be obtained for each sampling interval within the time window. The overdetermined equation can be solved by linear fitting to obtain the fault distance d(t) within the time window. The linear fitting algorithm can adopt the least squares algorithm.

[0121] In this case, T W1 Take 5ms, set a phase A grounding metallic fault 30km away from the protection installation on the photovoltaic power station side of the transmission line, and the fault distance solution within 20ms after the fault is as follows: Figure 3 The fault distance solution of the new method is shown in the figure, and the comparison with the solution of the old method (i.e. the distance protection method in the Chinese patent document CN111985079B in the background technology) is also as shown in the figure. Figure 3 As shown in the figure, a metallic fault between phases AB is set 30 km away from the protection installation on the photovoltaic power station side of the transmission line. The transition resistance is 10Ω. The fault distance solution within 20ms after the fault is as follows: Figure 4 The fault distance solution results of the new method are shown in the figure, and the comparison with the solution results of the old method (i.e. the distance protection method in the Chinese patent document CN111985079B in the background technology) is also as shown in the figure. Figure 4 shown.

[0122] (7) The fault distance of the input distance protection criterion is brought into the preset criterion to distinguish between in-zone and out-of-zone faults.

[0123] Among them, let the time window length be T W2 , time window [tT W2 ,t]d(t) continues to satisfy 0<d(t)<d set , then it is considered that an internal fault has occurred; if it is not satisfied, then it is considered that an external fault has occurred. set It is the protection range setting value.

[0124] In this case, T W2 Take 5ms, d set Take 60km.

[0125] System Example:

[0126] This embodiment provides a distance protection system applicable to an electronic transformer, including a processor for executing instructions for implementing a distance protection method applicable to an electronic transformer. The distance protection method applicable to an electronic transformer has been introduced clearly enough in the method embodiment and will not be repeated here.

Claims

1. A distance protection method applicable to an electronic transformer, characterized in that: The following steps are involved: 1) Obtain the three-phase measurement voltage and three-phase measurement current at the protection installation through conventional voltage transformers and electronic current transformers; 2) restoring the three-phase measured current to the primary side current according to the amplitude-frequency response and phase-frequency response characteristics of the electronic current transformer transfer function, and restoring the three-phase measured voltage to the primary side voltage according to the conventional voltage transformer transformation ratio; 3) constructing a compensation current time series according to the primary side current, and constructing a fault point voltage time series before the fault according to the primary side current, the primary side voltage and related line parameters; 4) Inputting the compensation current time series and the fault point voltage time series before the fault into a virtual transmission link constructed according to the transmission characteristics of the electronic current transformer for processing, and obtaining the measured voltage at the protection installation after the transmission and the reconstructed voltage at the fault point; 5) According to the measured voltage after the transmission, the reconstructed voltage at the fault point and the three-phase measured current, a fault equation related to the fault distance is obtained in combination with the line model; 6) Select a data window and obtain the corresponding fault equation, solve the corresponding fault distance, and bring the fault distance into a preset criterion to distinguish between in-zone and out-of-zone faults.

2. The distance protection method applicable to electronic mutual inductor according to claim 1 is characterized in that: The method for restoring the primary side current in step 2) is: using the formula The three-phase current measurement Restore to primary current During the restoration process, According to the transfer function of the Rogowski coil of the electronic current transformer, the amplitude response K and the phase angle response Δt corresponding to the power frequency are found; the method for restoring the primary side voltage in step 2) is: using the formula The three-phase voltage measurement Restore to primary voltage Where K' is the transformation ratio of the conventional voltage transformer.

3. The distance protection method applicable to electronic mutual inductor according to claim 2 is characterized in that: The method for constructing the compensation current time series in step 3) is: Among them, t f is the fault time, i comp0 (t) is the compensation current before the fault moment; when the fault type is single-phase ground short circuit, the i comp0 (t) Take the sum of the three phases of the primary side current obtained after the current measured at the protection installation before the fault is restored; when the fault type is not a single-phase ground short circuit, the i comp0 (t) The primary current is obtained by restoring the fault phase measured current at the protection installation before the fault.

4. The distance protection method applicable to electronic mutual inductor according to claim 3 is characterized in that: When the fault type is a single-phase ground short circuit, the method for constructing the compensation voltage time series in step 3) is: in It represents the primary voltage drop per unit length of the line, and the calculation formula is: Wherein, i0'(t) is the zero-sequence current calculated by using the primary side current restored in step 2), and the calculation formula is: R1, L1, R0, L0 are respectively the positive sequence resistance, positive sequence inductance, zero sequence resistance, and zero sequence inductance per unit length of the line; d ini is the distance between the virtual fault point and the protection installation location; when the fault type is non-single-phase ground short circuit, the method for constructing the compensation voltage time series in step 3) is: in, To restore the primary side fault phase-to-phase voltage, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

5. The distance protection method applicable to electronic mutual inductor according to claim 4 is characterized in that: The process of the virtual transmission link in step 4) is expressed as follows: u f '1'(t)=g(u f '1(t)) i co ” mp (t)=g(i comp (t)) Among them, u f '1'(t) is the voltage time series of the fault point before the fault after virtual transmission, i co ” mp (t) is the compensation current after virtual transformation, and g() is the virtual transformation function constructed according to the transformation link of the electronic current transformer.

6. The distance protection method applicable to electronic mutual inductor according to claim 5, characterized in that: The equation for reconstructing the fault point voltage in step 4) is: f (t) = u f '1'(t)+u f2 (t), where u f (t) is the voltage time series of the fault point in the whole process, u f '1'(t) is the voltage time series of the fault point before the fault after the virtual transmission, u f2 (t) is the voltage time series of the fault point after the fault, which is the product of the difference between the fault current and the compensation current after virtual transmission and the transition resistance, that is, u f2 (t) = R f [i f (t)-i co ” mp (t)],R f is the transition resistance, i f (t) represents the fault current; when the fault type is single-phase ground short circuit, the i f (t) Take the sum of the three phases of the current measured at the protection installation; when the fault type is not a single-phase ground short circuit, the i f (t) Take the fault phase and measure the current at the protection installation.

7. The distance protection method applicable to electronic mutual inductor according to claim 6, characterized in that: When the fault type is a single-phase ground short circuit, the equation related to the fault distance in step 5) is: in, is the fault phase voltage at the protection installation after virtual transmission, It represents the fault phase voltage drop per unit length of the secondary side of the line obtained by measuring the current; when the fault type is not a single-phase ground short circuit, the equation related to the fault distance is: in, is the fault phase-to-phase voltage at the protection installation after virtual transmission, is the fault phase-to-phase voltage drop on the secondary side of the line per unit length, and the calculation formula is:

8. The distance protection method applicable to electronic mutual inductor according to claim 7, characterized in that: The time window length in step 6) is T W1 , then [tT W1 ,t], the corresponding equation related to the fault distance in step 5) can be obtained for each sampling interval within the time window. The overdetermined equation can be solved by linear fitting to obtain the fault distance d(t) within the time window, where t represents the current time after the fault, and the solution algorithm adopts the least squares algorithm.

9. The distance protection method applicable to electronic mutual inductor according to claim 8, characterized in that: The method for distinguishing internal and external faults in step 6) is: time window [tT W2 ,t], if d(t) continues to satisfy 0<d(t)<d set , where d set If it is the protection range setting value, it is considered that an internal fault has occurred; if it is not satisfied, it is considered that an external fault has occurred.

10. A distance protection system suitable for electronic transformers, characterized in that: The method comprises a processor, wherein the processor is used to execute instructions for implementing the distance protection method applicable to an electronic mutual inductor as claimed in any one of claims 1 to 9.

Images