A distance protection method and system suitable for electronic transformers

Abstract

This invention relates to a distance protection method and system applicable to electronic current transformers. The method involves restoring the measured current of the electronic current transformer and the measured voltage of the conventional voltage transformer at the protection installation location before the fault occurs to the primary side current and primary side voltage. The constructed compensation current time series and the fault point voltage time series before the fault are input into a virtual transmission link for processing, resulting in the fault point reconstructed voltage after transmission. Based on the measured voltage at the protection installation location after transmission, the fault point reconstructed voltage after transmission, and the measured current at the protection installation location, combined with a line model, an equation related to the fault distance is obtained. An appropriate data window is selected, and the fault distance within that time window is solved. The fault distance is then substituted into a preset criterion to distinguish between faults within and outside the fault zone. Through this process, distance protection can be provided for single-phase and non-single-phase ground faults, avoiding the problem of inaccurate fault point voltage reconstruction leading to deviations in the calculated fault distance.

Description

Technical Field

[0001] This invention relates to a distance protection method and system applicable to electronic instrument transformers, belonging to the field of power system relay protection. Background Technology

[0002] Compared to electromagnetic current transformers, which suffer from saturation effects, Rogowski coil current transformers have a wide range of advantages, including a large dynamic measurement range, broad frequency response range, and no magnetic saturation phenomenon. They are widely used in power systems for distance protection calculations. Since the output signal of the Rogowski coil is proportional to the derivative of the measured current, Rogowski coil current transformers are typically equipped with an integrator to recover the measured current signal. However, the presence of the integrator amplifies the transient transmission error and analog-to-digital conversion error of the Rogowski coil itself, potentially causing severe distortion in current transmission or even incorrect relay protection operation. Therefore, some research has proposed eliminating the integrator and constructing a virtual Rogowski coil, directly using the derivative signal output of the Rogowski coil for distance protection calculations.

[0003] Distance protection requires constructing differential equations based on line parameters, voltage and current at the protection installation location, and fault voltage to determine the fault distance. Since the fault voltage cannot be directly measured, existing information must be used to reconstruct it to accurately characterize the fault voltage. Accurate fault voltage reconstruction is a key technology for distance protection. Currently, there is no accurate fault voltage reconstruction method for the new scenario of eliminating the Rogowski coil integrator.

[0004] Chinese patent document CN111985079B discloses a fast distance protection method based on Rogowski coil current transfer. The method includes the following steps: performing transient equivalent modeling analysis on the Rogowski coil current transfer circuit to construct a virtual equivalent digital model of the Rogowski coil; based on the virtual equivalent digital model of the Rogowski coil, performing virtual equivalent differentiation processing on the voltage sampling signal to obtain a differential voltage signal; applying the differential current signal and differential voltage signal from the Rogowski coil transfer to software ranging calculation; pre-setting a data window, starting timing from the fault initiation time; if the fault time is greater than the data window, calculating the ranging result using the least squares method; otherwise, calculating the ranging result using a virtual fault point voltage iterative approximation method. By eliminating the sampling signal integration stage in the Rogowski coil current-type transformer sampling circuit, the influence of the traditional Rogowski coil integrator stage is avoided, simplifying the sampling circuit, resulting in high ranging accuracy and fast response speed.

[0005] However, the fault point voltage reconstructed using this method cannot reflect the actual situation in this scenario, leading to inaccurate fault distance calculation equations and deviations in the calculated fault distance. Furthermore, this method is only applicable to single-phase ground faults. Therefore, it is urgent to study fault point voltage reconstruction methods for scenarios where the Rogowski coil integrator is eliminated, and distance protection methods based on this. Summary of the Invention

[0006] The purpose of this invention is to provide a distance protection method and system suitable for electronic instrument transformers, in order to solve the problems that existing technologies cannot accurately reconstruct the voltage at the fault point in scenarios where the Rogowski coil integrator is removed, resulting in errors in the distance protection ranging results and limited applicability to specific fault scenarios.

[0007] To achieve the above objectives, the present invention includes:

[0008] A distance protection method for electronic instrument transformers according to the present invention includes the following steps:

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

[0010] 2) Based on the amplitude-frequency response and phase-frequency response characteristics of the transfer function of the electronic current transformer, the three-phase measured current is restored to the primary side current, and based on the turns ratio of the conventional voltage transformer, the three-phase measured voltage is restored to the primary side voltage.

[0011] 3) Construct a compensation current time series based on the primary side current, and construct a fault point voltage time series before the fault based on the primary side current, primary side voltage, and relevant 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 point and the fault point reconstruction voltage after transmission.

[0013] 5) Based on the measured voltage after transmission, the reconstructed voltage at the fault point, and the measured current of the three phases, the fault equation related to the fault distance is obtained by combining the line model;

[0014] 6) Select the data window and obtain the corresponding fault equation, solve for the corresponding fault distance, and substitute the fault distance into the preset criteria to distinguish between faults inside and outside the area.

[0015] Furthermore, the method for restoring the primary side current in step 2) is as follows: using the formula Three-phase current measurement Restored to primary side current During the restoration process, Based on the transfer function of the Rogowski coil of the electronic current transformer, find the amplitude response K and phase angle response Δt corresponding to the power frequency; the method for restoring the primary voltage in step 2) is: using the formula Three-phase voltage measurement Restored to primary side voltage Where K' is the transformation ratio of a conventional voltage transformer.

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

[0017]

[0018] Among them, t f At the time of failure, i comp0 (t) represents the compensation current prior to the fault time; when the fault type is a single-phase ground fault, i comp0 (t) Take the sum of the three phases of the primary side current obtained after restoring the measured current at the protection installation point before the fault; when the fault type is a non-single-phase ground fault, i comp0 (t) The primary current is obtained by restoring the measured current of the faulty phase at the protection installation location before the fault.

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

[0020]

[0021] in The primary voltage drop per unit length of the line is calculated using the following formula:

[0022]

[0023] Where i0'(t) is the zero-sequence current calculated using the primary side current obtained in step 2), and the calculation formula is: r1, l1, r0, and l0 represent the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line, respectively; d ini The distance between the virtual fault point and the protection installation location; when the fault type is a non-single-phase ground fault, the method for constructing the compensation voltage time series in step 3) is as follows:

[0024]

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

[0026]

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

[0028] u” f1 (t)=g(u' f1 (t))

[0029] i” comp (t)=g(i comp (t))

[0030] Among them, u” f1 (t) represents the time series of the pre-fault point voltage after virtual transmission, i” comp (t) is the compensation current after virtual transmission, and g() is the virtual transmission function constructed based on the transmission link of the electronic current transformer.

[0031] Furthermore, the equation for fault point voltage reconstruction in step 4) is: u f (t)=u” f1 (t)+u f2 (t), where u f (t) represents the time series of voltage at the fault point throughout the entire process, u” f1 (t) is the time series of the pre-fault point voltage after virtual transmission, u f2 (t) is the time series of the fault point voltage 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, i.e., u f2 (t)=R f [i f (t)-i co " mp [(t)],R f For the transition resistance, i f (t) represents the fault current; when the fault type is a single-phase ground fault, i f (t) Take the sum of the three-phase currents measured at the protection installation point; when the fault type is a non-single-phase ground fault, the i f (t) Measure the current of the faulty phase at the protection installation location.

[0032] Furthermore, when the fault type is a single-phase-to-ground short circuit, the equation related to the fault distance in step 5) is: in, The fault phase voltage at the protection installation point after virtual transformer transformation. This represents the voltage drop across the fault phase on the secondary side per unit length of the line, obtained by measuring the current. When the fault type is a non-single-phase ground fault, the equation related to the fault distance is: in, The fault phase-to-phase voltage at the protection installation point after virtual transmission transformation. The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault on the line is:

[0033]

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

[0035] Furthermore, the method for distinguishing between faults inside and outside the zone in step 6) is: time window [tT] W2 Within the range [ ,t], if d(t) continuously satisfies 0 < d(t) < d set , where d set If the protection range setting value is met, it is considered that an in-zone fault has occurred; if it is not met, it is considered that an out-of-zone fault has occurred.

[0036] The present invention provides a distance protection system for electronic instrument transformers, comprising a processor for executing instructions to implement the distance protection method for electronic instrument transformers as described above.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention is a pioneering creation. In this invention, based on the amplitude-frequency and phase-frequency response characteristics of the transfer function of an electronic current transformer, the measured current of the electronic current transformer at the protection installation point before the fault occurs is restored to the primary side current; based on the turns ratio of a conventional voltage transformer, the measured voltage of the conventional voltage transformer at the protection installation point is restored to the primary side voltage. Then, based on the primary side current restored from the measured current of the electronic current transformer, a compensation current time series is constructed; based on the primary side current restored from the measured current of the electronic current transformer, the primary side voltage restored from the measured voltage of the conventional voltage transformer, and line parameters, a fault point voltage time series before the fault is constructed. Based on the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed. 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 fault point voltage after transmission. Based on the measured voltage at the protection installation point after transmission, the reconstructed fault point voltage after transmission, and the measured current at the protection installation point, combined with the line model, an equation related to the fault distance is obtained. Then, select an appropriate data window, calculate the fault distance within that time window, and substitute the fault distance from the input distance protection criterion into the preset criterion to distinguish between faults within and outside the protection zone. Through the above process, distance protection can be provided for both single-phase grounding faults and non-single-phase grounding faults, while avoiding the problem of deviations in the calculated fault distance caused by the inability to accurately reconstruct the fault point voltage. Attached Figure Description

[0039] Figure 1 This is a flowchart of a distance protection method applicable to electronic instrument transformers;

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

[0041] Figure 3 This is a schematic diagram of the ranging results during a single-phase grounding metallic fault in phase A.

[0042] Figure 4 This is a schematic diagram of the ranging results when there is a fault with a 10Ω transition resistance between phases A and B. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0044] The concept of this invention lies in restoring the measured current of the electronic current transformer at the protection installation point to the primary side current based on the amplitude-frequency and phase-frequency response characteristics of the transfer function of the electronic current transformer; and restoring the measured voltage of the conventional voltage transformer at the protection installation point to the primary side voltage based on the turns ratio of the conventional voltage transformer. Then, a compensation current time series is constructed based on the primary side current restored from the electronic current transformer's measured current; and a fault point voltage time series is constructed based on the primary side current restored from the electronic current transformer's measured current, the primary side voltage restored from the conventional voltage transformer's measured voltage, and line parameters. Based on 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 are input into the virtual transmission link for processing to obtain the reconstructed fault point voltage after transmission. Based on the measured voltage at the protection installation point after transmission, the reconstructed fault point voltage after transmission, and the measured current at the protection installation point, combined with the line model, an equation related to the fault distance is obtained. Then select an appropriate data window, calculate the fault distance within that time window, and input the fault distance of the distance protection criterion into the preset criterion to distinguish between faults within and outside the zone.

[0045] Method Implementation Examples:

[0046] like Figure 1 The distance protection method for electronic instrument transformers shown includes the following steps:

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

[0048] S2: Based on the amplitude-frequency response and phase-frequency response characteristics of the electronic current transformer's transfer function, the three-phase current measured by the electronic current transformer at the protection installation point before the fault occurred... Restored to primary side current Based on the transformation ratio of a conventional voltage transformer, the three-phase voltage measured by the conventional voltage transformer at the protection installation location is... Restored to primary side voltage The formulas for reverting the measured three-phase current (measuring current) and three-phase voltage (measuring voltage) to the primary side current and primary side voltage are as follows:

[0049]

[0050] During the current reduction process, Based on the transfer function of the Rogowski coil of the electronic current transformer, the amplitude response K and phase angle response Δt corresponding to the power frequency need to be found; during the voltage restoration process, K' is the turns ratio of a conventional voltage transformer;

[0051] S3: Construct the compensation current time series i based on the primary current reconstructed from the current measured by the electronic current transformer. comp (t); Based on the primary current reconstructed from the current measured by the electronic instrument transformer, the primary voltage reconstructed from the voltage measured by the conventional voltage transformer, and the line parameters, construct the time series u' of the voltage at the fault point before the fault. f1 (t).

[0052] The method for constructing the compensation current time series is as follows:

[0053]

[0054] Where t f At the time of failure; i comp0 (t) represents the compensation current before the fault. When the fault type is a single-phase ground fault, the sum of the three phases of the primary current obtained after restoring the current measured at the protection installation point before the fault in step 2 is taken, i.e., i comp0 (t)=i' ma (t)+i' mb (t)+i' mc (t); When the fault type is a non-single-phase ground fault, take the primary current obtained after restoring the measured current of the fault phase at the protection installation location before the fault in step 2, i.e.

[0055] The method for constructing the time series of voltage at the fault point before the fault is as follows: When the fault type is a single-phase ground fault, the time series of voltage at the fault point before the fault is constructed using the following formula:

[0056]

[0057] in The primary voltage drop per unit length of the line is calculated using the following formula:

[0058]

[0059] in The zero-sequence current is calculated using the primary current obtained in step S2, where r1, l1, r0, and l0 are the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line, respectively; d ini The distance between the virtual fault point and the protection installation location, where When the fault type is a non-single-phase ground fault, the voltage time series at the fault point before the fault is constructed using the following formula:

[0060]

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

[0062]

[0063] in

[0064] S4: Based on the transmission characteristics of the electronic current transformer, construct a virtual transmission link and convert the compensation current time sequence i comp (t), Time sequence of fault point voltage before fault u' f1 (t) The input is processed by the virtual transmission stage to obtain the reconstructed fault point voltage after transmission. The process of the virtual transmission stage can be represented as follows:

[0065] u” f1 (t)=g(u' f1 (t))

[0066] i” comp (t)=g(i comp (t))

[0067] Among them, u” f1 (t) represents the time series of the pre-fault point voltage after virtual transmission, i” comp (t) is the compensation current after virtual transmission, and g() is the virtual transmission function constructed based on the transmission link of the electronic current transformer.

[0068] The equation for voltage reconstruction at the fault point is: u f (t)=u” f1 (t)+u f2 (t).

[0069] Among them, u f (t) represents the time series of voltage at the fault point throughout the entire process, u” f1 (t) represents the time series of the pre-fault point voltage after virtual transmission, u f2 (t) is the time series of the fault point voltage 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, i.e., u f2 (t)=R f [i f (t)-i” comp [(t)],R f For transition resistance; i f (t) represents the fault current. When the fault type is a single-phase ground fault, the sum of the three-phase currents measured at the protection installation point is taken, i.e., i f (t)=i ma (t)+i ma (t)+i mc(t); When the fault type is a non-single-phase ground fault, the measured current of the fault phase at the protection installation location is taken, i.e. in

[0070] S5: Based on the measured voltage at the protection installation point after transmission, the reconstructed voltage at the fault point after transmission, and the measured current at the protection installation point, the fault equation related to the fault distance is obtained by combining the line model.

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

[0072] in, The fault phase voltage at the protection installation point after virtual transmission and transformation; The formula for calculating the secondary voltage drop per unit length of a line, obtained by measuring the current, is as follows:

[0073]

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

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

[0076] in, The fault phase-to-phase voltage at the protection installation point after virtual transmission transformation. The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault on the line is:

[0077]

[0078] in,

[0079] S6: Select an appropriate time window and calculate the fault distance within that time window.

[0080] Let the time window length be T. W1 Then [tT W1 For each sampling interval within [t], the corresponding equation related to the fault distance in step 5 can be obtained. The fault distance d(t) within this time window can be obtained by solving the overdetermined equation using linear fitting. t represents the current time after the fault, and the solution algorithm can be the least squares algorithm.

[0081] S7: Input the fault distance of the distance protection criterion into the preset criterion to distinguish between faults inside and outside the zone.

[0082] Let the time window length be T. W2 Time window [tT] W2 Within the interval ,t], d(t) continuously satisfies 0 < d(t) < d set If the condition is met, an intra-zone fault is considered to have occurred; otherwise, an extra-zone fault is considered to have occurred. Where d... set The protection range setting value.

[0083] Specifically, the technical solution of the present invention will be further described below with reference to specific examples. Based on a certain electromagnetic transient simulation software, a two-terminal system topology is constructed. Figure 2 The diagram shows the topology of a dual-end system. 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] Using this specific case as an example, the distance protection method of the present invention is used to calculate the distance protection, and the steps are as follows:

[0085] (1) Current and voltage signals are collected in real time by using Rogowski coil current transformers and conventional voltage transformers installed on one side of the line in the simulation software to obtain continuously updated sampled current and voltage sequences.

[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, 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) Based on the amplitude-frequency response and phase-frequency response characteristics of the transfer function of the electronic instrument transformer, the measured current of the electronic instrument transformer at the protection installation point before the fault occurred is... Restored to primary side current Based on the transformation ratio of a conventional voltage transformer, the measured voltage of the conventional voltage transformer at the protection installation location will be... Restored to primary side voltage The formulas for restoring the measured current and voltage to the primary side are as follows:

[0088]

[0089]

[0090] During the current reduction process, Based on the transfer function of the Rogowski coil of the electronic current transformer, the amplitude response K and phase angle response Δt corresponding to the power frequency need to be found; during the voltage restoration process, K' is the transformation ratio of a conventional voltage transformer.

[0091] (3) Construct the compensation current time series i based on the primary current reconstructed from the current measured by the electronic instrument transformer. comp (t) and the time series of the fault point voltage before the fault u' f1 (t).

[0092] The method for constructing the compensation current time series is as follows:

[0093]

[0094] Where t f At the time of failure; i comp0 (t) represents the compensation current before the fault time. When the fault type is a single-phase ground fault, the sum of the three phases of the primary side current obtained after restoring the current measured at the protection installation point before the fault in step (2) is taken, i.e., i comp0 (t)=i' ma (t)+i' mb (t)+i' mc (t); When the fault type is a non-single-phase ground fault, take the primary current obtained after restoring the measured current of the fault phase at the protection installation location before the fault in step (2), that is...

[0095] The method for constructing the time series of voltage at the fault point before the fault is as follows: When the fault type is a single-phase ground fault, the time series of voltage at the fault point before the fault is constructed using the following formula.

[0096]

[0097] in The primary voltage drop per unit length of the line is calculated using the following formula:

[0098]

[0099] in The zero-sequence current is calculated using the primary side current obtained in step (2), where r1, l1, r0, and l0 are the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line, respectively; d ini The distance between the virtual fault point and the protection installation location; When the fault type is a non-single-phase ground fault, the voltage time series at the fault point before the fault is constructed using the following formula:

[0100]

[0101] in, To restore the obtained primary-side fault phase-to-phase voltage, The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault is as follows:

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

[0103] (4) Based on the transmission characteristics of the electronic current transformer, a virtual transmission link is constructed, and the compensation current time sequence i comp (t), Time sequence of fault point voltage before fault u' f1 (t) The input is processed by the virtual transmission stage to obtain the reconstructed fault point voltage after transmission. The process of the virtual transmission stage can be represented as follows:

[0104] u” f1 (t)=g(u' f1 (t))

[0105] i” comp (t)=g(i comp (t))

[0106] Among them, u” f1 (t) represents the time series of the pre-fault point voltage after virtual transmission, i” comp (t) is the compensation current after virtual transmission, and g() is the virtual transmission function constructed based on the transmission link of the electronic current transformer.

[0107] The equation for voltage reconstruction at the fault point is: u f (t)=u” f1 (t)+u f2 (t).

[0108] Among them, u f (t) represents the time series of voltage at the fault point throughout the entire process, u” f1 (t) represents the time series of the pre-fault point voltage after virtual transmission, u f2 (t) is the time series of the fault point voltage 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, i.e., u f2 (t)=R f [i f (t)-i” comp [(t)],R f For transition resistance; i f (t) represents the fault current. When the fault type is a single-phase ground fault, the sum of the three-phase currents measured at the protection installation point is taken, i.e., i f (t)=i ma (t)+i ma(t)+i mc (t); When the fault type is a non-single-phase ground fault, the measured current of the fault phase at the protection installation location is taken, i.e.

[0109] In this case, the fault types are A-phase single-phase ground fault and AB-phase two-phase fault.

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

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

[0112] in, The fault phase voltage at the protection installation point after virtual transmission and transformation; The formula for calculating the secondary side fault phase voltage drop per unit length of the line, obtained by measuring the current, is as follows:

[0113]

[0114] in The zero-sequence current is calculated using the measured current of an electronic instrument transformer. r1, l1, r0, and l0 represent 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 a non-single-phase ground fault, the fault equation related to the fault distance is:

[0116] in, The fault phase-to-phase voltage at the protection installation point after virtual transmission transformation. The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault on the line is:

[0117]

[0118] in,

[0119] (6) Select an appropriate time window and use a linear fitting algorithm to solve the fault distance within that time window.

[0120] Let the time window length be T. W1 Then [tT W1For each sampling interval within [t], the corresponding equation related to the fault distance in step (5) can be obtained. The fault distance d(t) within the time window can be obtained by solving the overdetermined equation using linear fitting. The least squares algorithm can be used for linear fitting.

[0121] In this case, T W1 Taking 5ms, a metallic fault of phase A grounding is set at a distance of 30km from the protection installation point on the transmission line to the photovoltaic power station. The fault distance within 20ms after the fault is calculated as follows: Figure 3 The results of the fault distance calculation using the new method are shown in the figure. A comparison with the results obtained using the old method (i.e., the distance protection method in Chinese patent document CN111985079B in the background art) is also as follows. Figure 3 As shown; a two-phase metallic fault (A and B) is installed on the transmission line 30km from the photovoltaic power station protection installation point, with a transition resistance of 10Ω. The fault distance within 20ms after the fault is calculated as follows. Figure 4 The results of the fault distance calculation using the new method are shown in the figure. A comparison with the results obtained using the old method (i.e., the distance protection method in Chinese patent document CN111985079B in the background art) is also as follows. Figure 4 As shown.

[0122] (7) Input the fault distance of the distance protection criterion into the preset criterion to distinguish between faults inside and outside the zone.

[0123] Let the time window length be T. W2 Time window [tT] W2 Within the interval ,t], d(t) continuously satisfies 0 < d(t) < d set If the condition is met, an intra-zone fault is considered to have occurred; otherwise, an extra-zone fault is considered to have occurred. Where d... set The protection range setting value.

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

[0125] System Implementation Example:

[0126] This embodiment provides a distance protection system suitable for electronic instrument transformers, including a processor for executing instructions to implement a distance protection method suitable for electronic instrument transformers. The distance protection method suitable for electronic instrument transformers has been described clearly enough in the method embodiments and will not be repeated here.

Claims

1. A distance protection method applicable to electronic instrument transformers, characterized in that, Includes the following steps: 1) Obtain the three-phase measured voltage and three-phase measured current at the protection installation location using conventional voltage transformers and electronic current transformers; 2) Based on the amplitude-frequency response and phase-frequency response characteristics of the transfer function of the electronic current transformer, the three-phase measured current is restored to the primary side current, and based on the turns ratio of the conventional voltage transformer, the three-phase measured voltage is restored to the primary side voltage. 3) Construct a compensation current time series based on the primary side current, and construct a fault point voltage time series before the fault based on the primary side current, primary side voltage and relevant line parameters; 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 to obtain the measured voltage at the protection installation point and the fault point reconstruction voltage after transmission. 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 by combining the line model; 6) Select the data window and obtain the corresponding fault equation, solve for the corresponding fault distance, and substitute the fault distance into the preset criterion to distinguish between faults inside and outside the area.

2. The distance protection method for electronic instrument transformers according to claim 1, characterized in that, The method for restoring the primary current in step 2) is as follows: using the formula... Three-phase current measurement Restored to primary side current During the restoration process, Based on the transfer function of the Rogowski coil of the electronic current transformer, find the amplitude response K and phase angle response Δt corresponding to the power frequency; the method for restoring the primary voltage in step 2) is: using the formula Three-phase voltage measurement Restored to primary side voltage Where K' is the transformation ratio of a conventional voltage transformer.

3. The distance protection method for electronic instrument transformers according to claim 2, characterized in that, The method for constructing the compensation current time series in step 3) is as follows: Among them, t f At the time of failure, i comp0 (t) represents the compensation current prior to the fault time; when the fault type is a single-phase ground fault, i comp0 (t) Take the sum of the three phases of the primary side current obtained after restoring the measured current at the protection installation point before the fault; when the fault type is a non-single-phase ground fault, the i comp0 (t) The primary current is obtained by restoring the measured current of the faulty phase at the protection installation location before the fault.

4. The distance protection method for electronic instrument transformers according to claim 3, characterized in that, When the fault type is a single-phase ground fault, the method for constructing the compensation voltage time series in step 3) is as follows: in The primary voltage drop per unit length of the line is calculated using the following formula: Where i0'(t) is the zero-sequence current calculated using the primary side current obtained in step 2), and the calculation formula is: r1, l1, r0, and l0 represent the positive-sequence resistance, positive-sequence inductance, zero-sequence resistance, and zero-sequence inductance per unit length of the line, respectively; d ini The distance between the virtual fault point and the protection installation location; when the fault type is a non-single-phase ground fault, the method for constructing the compensation voltage time series in step 3) is as follows: in, To restore the obtained primary-side fault phase-to-phase voltage, The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault on the line is:

5. The distance protection method for electronic instrument transformers according to claim 4, characterized in that, The process of the virtual transmission link in step 4) is represented as follows: u″ f1 (t)=g(u’ f1 (t)) i co ” mp (t)=g(i comp (t)) Where, u″ f1 (t) is the time series of the pre-fault point voltage after virtual transmission, u′ f1 (t) represents the time series of the voltage at the fault point before the fault, i″ comp (t) is the compensation current after virtual transmission, and g() is the virtual transmission function constructed based on the transmission link of the electronic current transformer.

6. The distance protection method for electronic instrument transformers according to claim 5, characterized in that, The equation for fault point voltage reconstruction in step 4) is: u f (t)=u″ f1 (t)+u f2 (t), where u f (t) represents the time series of voltage at the fault point throughout the entire process, u″ f1 (t) represents the time series of the pre-fault point voltage after the virtual transformer, u f2 (t) is the time series of the fault point voltage 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, i.e., u f2 (t)=R f [i f (t)-i″ comp [(t)],R f For the transition resistance, i f (t) represents the fault current; when the fault type is a single-phase ground fault, i f (t) Take the sum of the three-phase currents measured at the protection installation point; when the fault type is a non-single-phase ground fault, the i f (t) Measure the current of the faulty phase at the protection installation location.

7. The distance protection method for electronic instrument transformers according to claim 6, characterized in that, When the fault type is a single-phase ground fault, the equation related to the fault distance in step 5) is: in, The fault phase voltage at the protection installation point after virtual transformer transformation. This represents the voltage drop across the fault phase on the secondary side per unit length of the line, obtained by measuring the current. When the fault type is a non-single-phase ground fault, the equation related to the fault distance is: in, The fault phase-to-phase voltage at the protection installation point after virtual transmission transformation. The formula for calculating the phase-to-phase voltage drop per unit length of the secondary side fault on the line is:

8. The distance protection method for electronic instrument transformers according to claim 7, characterized in that, The time window length in step 6) is T. W1 Then [tT W1 For each sampling interval within [t], the corresponding equation related to the fault distance in step 5) can be obtained. The fault distance d(t) within the time window can be obtained by solving the overdetermined equation using linear fitting, where t represents the current time after the fault. The solution algorithm uses the least squares algorithm.

9. The distance protection method for electronic instrument transformers according to claim 8, characterized in that, The method for determining faults inside and outside the zone in step 6) is: time window [tT] W2 Within the range [t], if d(t) continuously satisfies 0 < d(t) < d set , where d set If the protection range setting value is met, it is considered that an in-zone fault has occurred; if it is not met, it is considered that an out-of-zone fault has occurred.

10. A distance protection system suitable for electronic instrument transformers, characterized in that, Includes a processor for executing instructions to implement the distance protection method for electronic instrument transformers as described in any one of claims 1 to 9.

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