THREE-PHASE ADAPTIVE RECLOSING METHOD AND SYSTEM FOR WIND FARM TRANSMISSION LINES BASED ON PARALLEL REACTOR CURRENT

Abstract

A three-phase adaptive reclosing method and system for wind farm transmission lines based on parallel reactor current is provided. When a phase to phase or three-phase fault occurs in the transmission line, the circuit breakers at both ends trip. The current transformer is used to sample the three-phase current signal of the parallel reactor, calculate the differential mode current of the parallel reactor, and perform zero crossing detection to construct a fault nature identification criterion. The fault nature is determined within the maximum discrimination time limit combined with the sliding time window. For permanent faults, the reclosing device is locked; for transient faults, calculate the time when the fault disappears and determine the reclosing time, and open the reclosing device. The method and system identifies the nature of faults by detecting whether the differential current of parallel reactors crosses the zero axis, with low sampling rate requirements, and small errors.

Claims

1. A three-phase adaptive reclosing method for wind farm transmission lines based on parallel reactor current, comprising the following steps: Step 1: after a phase to phase or three-phase fault occurs in a transmission line, isolating the transmission line from the phase to phase or three-phase fault; Step 2: using current transformers to sample three-phase current signals of parallel reactors; Step 3: calculating a differential mode current of the parallel reactors within a sliding time window; Step 4: performing zero crossing detection on the differential mode current of the parallel reactors; Step 5: identifying a nature of the phase to phase or three-phase fault within a maximum discrimination time limit, and when the phase to phase or three-phase fault is determined to be a permanent fault, outputting a locking reclosing signal; when the phase to phase or three-phase fault is determined to be a transient fault, proceeding to Step6; and Step 6: calculating a time when the phase to phase or three-phase fault disappears and determining a three-phase reclosing time, and outputting a reclosing signal; wherein Step 4 comprises: Step 4.1: calculating a product of maximum and minimum values of the differential mode current within the sliding time window: $R_k=i_{\max ,k}{i}_{\min ,k}$ wherein k represents a sliding window number; i.sub.max,k and i.sub.min,k respectively represent the maximum and minimum values of the differential mode current within a k-th time window; and Step 4.2: calculating a sign function value of R.sub.k within the sliding time window: $\mathrm{sgn}\left(R_k\right)=\{\begin{array}{cc}1,& R_k>0\\ -1,& R_{k}0\end{array};$ wherein Step 5 comprises: Step 5.1: setting the maximum discrimination time limit T.sub.max; and Step 5.2: constructing fault nature identification criteria, when j-th, j+1 and j+2-nd sliding time windows occur within the maximum discrimination time limit, and satisfy: $\mathrm{sgn}\left(R_j\right)=-1\&\mathrm{sgn}\left(R_{j+1}\right)=-1\&\mathrm{sgn}\left(R_{j+2}\right)=-1$ the phase to phase or three-phase fault is determined as the transient fault, otherwise the phase to phase or three-phase fault is determined as the permanent fault; wherein Step 6 comprises: Step 6.1: according to the sliding window number j obtained in Step 5.2, calculating the time t.sub.end when the phase to phase or three-phase fault disappears: $t_{\mathrm{end}}={\mathrm{jT}}_s+t_{\mathrm{trip}}$ wherein T.sub.s is a length of the sliding time window, and t.sub.trip is the time when a circuit breaker trips; and Step 6.2: calculating the three-phase reclosing time t.sub.close based on an arc insulation recovery time T.sub.re, and outputting the reclosing signal: $t_{\mathrm{close}}=t_{\mathrm{end}}+T_{\mathrm{re}}.$

2. The three-phase adaptive reclosing method for the wind farm transmission lines based on the parallel reactor current according to claim 1, wherein in Step1, after the phase to phase or three-phase fault occurs in the transmission line, the circuit breakers installed at both ends of a fault line trip to isolate the phase to phase or three-phase fault.

3. The three-phase adaptive reclosing method for the wind farm transmission lines based on the parallel reactor current according to claim 1, wherein Step3 comprises: Step3.1: defining a sliding time window with a time length of T.sub.s and a sliding factor of s; Step3.2: calculating the differential mode current of a parallel reactor by a following formula: $\left[\begin{array}{c}{i}_{}\left(t\right)\\ i_{}\left(t\right)\\ i_{}\left(t\right)\end{array}\right]=\left[\begin{array}{ccc}1& -1& 0\\ 1& 0& -1\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{i}_a\left(t\right)\\ i_b\left(t\right)\\ i_c\left(t\right)\end{array}\right]=\left[\begin{array}{c}{i}_a\left(t\right)i_b\left(t\right)\\ i_a\left(t\right)i_c\left(t\right)\\ i_b\left(t\right)-i_c\left(t\right)\end{array}\right]$ wherein i.sub. is an mode current of the parallel reactor, i.sub. is a mode current of the parallel reactor, i.sub. is a y mode current of the parallel reactor, i.sub.a is an A-phase current of the parallel reactor, i.sub.b is a B-phase current of the parallel reactor, and i.sub.c is a C-phase current of the parallel reactor.

4. A system for implementing the three-phase adaptive reclosing method for the wind farm transmission lines based on the parallel reactor current according to claim 1, comprising: a protection processing module, used to receive protection signals in case of the phase to phase or three-phase fault in the transmission line, and to cause the circuit breakers at both ends to perform fault isolation actions; a data acquisition module, used to obtain digital signals of three-phase current of the parallel reactors on the transmission line; a signal processing module, used to calculate the differential mode current of the parallel reactors and perform zero crossing detection on the differential mode current; a fault nature discrimination module, used to combine the sliding time window to discriminate a fault nature within the maximum discrimination time limit and output a discrimination result; and a reclosing execution module, used to receive a reclosing execution signal or reclosing locking signal output by the fault nature discrimination module, and executing corresponding actions.

5. The system according to claim 4, wherein the protection processing module comprises: a protection receiving unit, used to receive circuit breaker trip signals; and a protection action unit, used to perform circuit breaker tripping processing.

6. The system according to claim 4, wherein the data acquisition module comprises: a current measurement unit, used to obtain a three-phase current analog signal of the parallel reactors on the transmission line; and an analog-to-digital conversion unit, used to convert the three-phase current analog signal of the parallel reactors into a digital signal.

7. The system according to claim 4, wherein the signal processing module comprises: a differential to analog conversion unit, used for differential to analog conversion of a three-phase current digital signal of the parallel reactors; and a zero crossing detection unit, used to calculate the product of the maximum and minimum values of the differential mode current within the sliding time window, and calculating a sign function value of the product.

8. The system according to claim 4, wherein the fault nature discrimination module comprises: a nature discrimination unit, used to construct the fault nature identification criteria and combine the sliding time window to discriminate the fault nature within the maximum discrimination time limit; and a closing signal unit, used to output a reclosing execution signal or a reclosing locking signal.

9. The system according to claim 4, wherein the reclosing execution module comprises: a reclosing start unit, used to start the circuit breakers at both ends of the transmission line to close again; and a reclosing locking unit, used to lock the circuit breakers at both ends of the transmission line to close again.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 is a topology diagram of the simulation system of the present invention;

[0055] FIG. 2 is a flowchart of the adaptive reclosing process of the present invention;

[0056] FIG. 3 is a functional block diagram of the adaptive reclosing system of the present invention;

[0057] FIGS. 4A-4C are schematic diagrams of the fault recognition results in Example 1 of the present invention;

[0058] FIG. 4A shows the waveform of the three-phase current of the parallel reactor in Example 1 of the present invention;

[0059] FIG. 4B shows the waveform of the alpha mode current of the parallel reactor in Example 1 of the present invention;

[0060] FIG. 4C is a schematic diagram of the sliding time window discrimination results in Example 1 of the present invention;

[0061] FIGS. 5A-5C are schematic diagrams of the fault recognition results in Example 2 of the present invention;

[0062] FIG. 5A shows the waveform of the three-phase current of the parallel reactor in Example 2 of the present invention;

[0063] FIG. 5B shows the waveform of the alpha mode current of the parallel reactor in Example 2 of the present invention;

[0064] FIG. 5C is a schematic diagram of the sliding time window discrimination results in Example 2 of the present invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0065] The present invention will be further explained in conjunction with the accompanying drawings and specific embodiments.

[0066] Example 1: The topology of the wind farm's AC transmission system is shown in FIG. 1. Among them, the length of the transmission line is 200 km, and overhead transmission lines are used for power transmission. The inductance of the parallel reactor is taken as L.sub.A=L.sub.B=L.sub.C=6.4203H, the inductance of the neutral point small reactance is taken as L.sub.d=1.7504H, and the main transformer between the wind farm collection line and the output line is 220/35 kV. Line parameters: R.sub.1=0.0103/km, R.sub.0=0.3156/km;L.sub.1=0.9694 mH/km,L.sub.0=3.156 mH/km;C.sub.1=0.0122 F/km,C.sub.0=0.00834 F/km. At the relative zero moment, an ABG fault occurs at a distance of 80 km from the station side of the transmission line, with a transient fault nature (transition resistance of 50 , fault duration of 386 ms) and a sampling rate of 10 kHz.

[0067] A three-phase adaptive reclosing method for wind farm transmission lines based on parallel reactor current. FIG. 2 shows the workflow of the present invention, and the specific implementation steps are as follows: [0068] Step 1: After an ABG fault occurs on the outgoing line at t.sub.0=0 ms, the circuit breakers installed at both ends of the faulty line trip three phases at t.sub.trip=93 ms to isolate the fault. [0069] Step 2: Using a current transformer to sample the three-phase current signal of the parallel reactor. In this embodiment, the three-phase current signal of the parallel reactor is shown in FIG. 4A. [0070] Step 3: Calculating the differential mode current of the parallel reactor within the sliding time window. Specifically: [0071] Step 3.1: Defining a sliding time window with a time length T.sub.s of 20 ms and a sliding factor s of 20 ms. [0072] Step 3.2: Calculating the differential mode current of the parallel reactor.

[00007]$\left[\begin{array}{c}{i}_{}\left(t\right)\\ i_{}\left(t\right)\\ i_{}\left(t\right)\end{array}\right]=\left[\begin{array}{ccc}1& -1& 0\\ 1& 0& -1\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{i}_a\left(t\right)\\ i_b\left(t\right)\\ i_c\left(t\right)\end{array}\right]=\left[\begin{array}{c}{i}_a\left(t\right)i_b\left(t\right)\\ i_a\left(t\right)i_c\left(t\right)\\ i_b\left(t\right)i_c\left(t\right)\end{array}\right]$

[0073] Among them, i.sub. is the mode current of the parallel reactor, i.sub. is the mode current of the parallel reactor, i.sub. is the mode current of the parallel reactor, i.sub.a is the A-phase current of the parallel reactor, i.sub.b is the B-phase current of the parallel reactor, and i.sub.c is the C-phase current of the parallel reactor.

[0074] In this embodiment, the differential mode current of the parallel reactor is shown in FIG. 4B. [0075] Step 4: Performing zero crossing detection on the differential current of the obtained parallel reactor. The specific implementation method is: [0076] Step 4.1: Calculating the product of the maximum and minimum values of the differential current within the sliding window.

[00008]$R_k=i_{\max ,k}{i}_{\min ,k}$

[0077] Among them, k represents the sliding window number; i.sub.max,k and i.sub.min,k, respectively represent the maximum and minimum values of the differential current within the k-th time window; [0078] Step4.2: Calculating the sign function value of R.sub.k within the sliding window:

[00009]$\mathrm{sgn}\left(R_k\right)=\{\begin{array}{cc}1,& R_k>0\\ -1,& R_{k}0\end{array}$ [0079] Step 5: Determining the nature of the fault within the maximum discrimination time limit. If it is determined to be a permanent fault, output a locking reclosing signal; If it is determined to be a transient fault, proceed to Step 6. [0080] Step 5.1: Setting the maximum discrimination time limit T.sub.max to 900 ms. [0081] Step 5.2: Constructing fault property identification criteria. If the j-th, j+1, and j+2-nd sliding time windows occur within the maximum discrimination time limit, they meet the following criteria:

[00010]$\mathrm{sgn}\left(R_j\right)=-1\&\mathrm{sgn}\left(R_{j+1}\right)=-1\&\mathrm{sgn}\left(R_{j+2}\right)=-1$

[0082] If it is determined as a transient fault, otherwise it is determined as a permanent fault. In this embodiment, the sliding time window discrimination result is shown in FIG. 4C. For the first time, the 15-th time window sign function value is 1, and the 16-th and 17-th time window sign function values are also 1, resulting in j=15. [0083] Step 6: Calculating the time when the fault disappears and determine the three-phase reclosing time, and outputting the reclosing signal. Specifically: [0084] Step 6.1: Based on the sliding window number j=15 obtained in Step 5.2, calculating the time when the fault disappears, denoted as t.sub.end. The calculation formula is:

[00011]$t_{\mathrm{end}}={\mathrm{jT}}_s+t_{\mathrm{trip}}=1520+93=393\mathrm{ms}$

[0085] Among them, T.sub.s=20 ms is the length of the sliding time window, and t.sub.trip=93 ms is the time when the circuit breaker trips.

[0086] In this embodiment, the calculated fault duration is 393 ms, and the actual fault disappearance time is 386 ms, with a calculation error of only 7 ms. [0087] Step 6.2: Based on the arc insulation recovery time T.sub.re=100 ms, calculating the three-phase reclosing time t.sub.close. and outputting the reclosing signal. The calculation formula for the moment of reclosing is:

[00012]$t_{\mathrm{close}}=t_{\mathrm{end}}+T_{\mathrm{re}}=393+100=493\mathrm{ms}$

[0088] After 493 ms of the fault, a closing signal is output, and the three-phase circuit breakers at both ends of the wind power transmission line are closed, restoring power supply to the system.

[0089] FIG. 3 is a functional block diagram of a three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current provided by the present invention, including: [0090] Protection processing module, used to receive protection signals in case of phase to phase or three-phase faults in the transmission line, and to make the circuit breakers at both ends perform corresponding actions; [0091] Data acquisition module, used to obtain digital signals of three-phase current of parallel reactors on the transmission line; [0092] Signal processing module, used to calculate the differential mode current of parallel reactors and perform zero crossing detection on it; [0093] Fault nature discrimination module, used to combine sliding time window to discriminate the fault nature within the maximum discrimination time limit and output the discrimination result; [0094] The reclosing execution module is used to receive the reclosing execution signal or reclosing locking signal output by the fault nature discrimination module, and execute corresponding actions.

[0095] The three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current is characterized in that the protection processing module specifically includes: [0096] Protecting the receiving unit for receiving circuit breaker trip signals; [0097] Protection action unit, used to perform circuit breaker tripping processing.

[0098] The three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current is characterized in that the data acquisition module specifically includes: [0099] Current measurement unit, used to obtain simulated three-phase current signals of parallel reactors on the transmission line; [0100] The analog-to-digital conversion unit is used to convert the obtained three-phase current analog signal of the parallel reactor into a digital signal.

[0101] The three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current is characterized in that the signal processing module specifically includes: [0102] Differential to analog conversion unit, used for differential to analog conversion of the obtained three-phase current digital signal of the parallel reactor; [0103] Zero crossing detection unit, used to calculate the product of the maximum and minimum differential current values within the sliding window, and calculate its sign function value.

[0104] The three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current is characterized in that the fault nature discrimination module specifically includes: [0105] Property discrimination unit, used to construct fault property recognition criteria and combine sliding time windows to discriminate fault properties within the maximum discrimination time limit; [0106] Closing signal unit, used to output closing execution signal or closing locking signal.

[0107] The three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current is characterized in that the reclosing execution module specifically includes: [0108] Closing start unit, used to start the circuit breakers at both ends of the outgoing line to close again; [0109] Closing locking unit, used to lock the circuit breakers at both ends of the outgoing line to close again.

[0110] Example 2: The topology of the wind farm's AC transmission system is shown in FIG. 1. Among them, the length of the transmission line is 200 km, and overhead transmission lines are used for power transmission. The inductance of the parallel reactor is taken as L.sub.A=L.sub.B=L.sub.C=6.4203H, the inductance of the neutral point small reactance is taken as L.sub.d=1.7504H, and the main transformer between the wind farm collection line and the output line is 220/35 kV. Line parameters: R.sub.1=0.0103/km, R.sub.0=0.3156/km;L.sub.1=0.9694 mH/km,L.sub.0=3.156 mH/km;C.sub.1=0.0122 F/km,C.sub.0=0.0 0834 F/km. At the relative zero moment, an ABG fault occurs at a distance of 80 km from the station side of the transmission line, with a permanent fault nature (transition resistance of 50 ) and a sampling rate of 10 kHz.

[0111] A three-phase adaptive reclosing method for wind farm transmission lines based on parallel reactor current. FIG. 2 shows the workflow of the present invention, and the specific implementation steps are as follows: [0112] Step 1: After an ABG fault occurs on the outgoing line at t.sub.0=0 ms, the circuit breakers installed at both ends of the faulty line trip three phases at t.sub.trip=93 ms to isolate the fault. [0113] Step 2: Using a current transformer to sample the three-phase current signal of the parallel reactor. In this embodiment, the three-phase current signal of the parallel reactor is shown in FIG. 5A. [0114] Step 3: Calculating the differential mode current of the parallel reactor within the sliding time window. Specifically: [0115] Step 3.1: Defining a sliding time window with a time length T.sub.s of 20 ms and a sliding factor s of 20 ms. [0116] Step 3.2: Calculating the differential mode current of the parallel reactor.

[00013]$\left[\begin{array}{c}{i}_{}\left(t\right)\\ i_{}\left(t\right)\\ i_{}\left(t\right)\end{array}\right]=\left[\begin{array}{ccc}1& -1& 0\\ 1& 0& -1\\ 0& 1& -1\end{array}\right]\left[\begin{array}{c}{i}_a\left(t\right)\\ i_b\left(t\right)\\ i_c\left(t\right)\end{array}\right]=\left[\begin{array}{c}{i}_a\left(t\right)i_b\left(t\right)\\ i_a\left(t\right)i_c\left(t\right)\\ i_b\left(t\right)-i_c\left(t\right)\end{array}\right]$

[0117] Among them, i.sub. is the a mode current of the parallel reactor, i.sub. is the mode current of the parallel reactor, i.sub. is the mode current of the parallel reactor, i.sub.a is the A-phase current of the parallel reactor, i.sub.b is the B-phase current of the parallel reactor, and i.sub.c is the C-phase current of the parallel reactor.

[0118] In this embodiment, the differential mode current of the parallel reactor is shown in FIG. 5B. [0119] Step 4: Performing zero crossing detection on the differential current of the obtained parallel reactor. The specific implementation method is: [0120] Step 4.1: Calculating the product of the maximum and minimum values of the differential current within the sliding window.

[00014]$R_k=i_{\max ,k}{i}_{\min ,k}$

[0121] Among them, k represents the sliding window number; i.sub.max,k and i.sub.min,k, respectively represent the maximum and minimum values of the differential current within the k-th time window; [0122] Step4.2: Calculating the sign function value of R.sub.k within the sliding window:

[00015]$\mathrm{sgn}\left(R_k\right)=\{\begin{array}{cc}1,& R_k>0\\ -1,& R_{k}0\end{array}$ [0123] Step 5: Determining the nature of the fault within the maximum discrimination time limit. If it is determined to be a permanent fault, output a locking reclosing signal; if it is determined to be a transient fault, proceed to Step 6. [0124] Step 5.1: Setting the maximum discrimination time limit T.sub.max to 900 ms. [0125] Step 5.2: Constructing fault property identification criteria. If the j-th, j+1, and j+2-nd sliding time windows occur within the maximum discrimination time limit, they meet the following criteria:

[00016]$\mathrm{sgn}\left(R_j\right)=-1\&\mathrm{sgn}\left(R_{j+1}\right)=-1\&\mathrm{sgn}\left(R_{j+2}\right)=-1$

[0126] If it is determined as a transient fault, otherwise it is determined as a permanent fault. In this embodiment, the sliding time window discrimination result is shown in FIG. 5C. From the moment of tripping of the circuit breaker, the differential mode current of the fault phase parallel reactor steadily decays and does not cross the zero axis until the maximum judgment time limit. There are no consecutive three times window sign function values of 1, which do not meet the fault nature identification criteria. The fault nature is identified as a permanent fault, and a locking signal is output without reclosing operation.

[0127] The technical features of a three-phase adaptive reclosing system for wind farm transmission lines based on parallel reactor current in this embodiment are the same as those in embodiment 1, and will not be repeated here.

[0128] At present, the reclosing device installed on the transmission line project of wind farms often adopts the traditional reclosing strategy, which means that when the transmission line fails and the circuit breaker trips, regardless of whether the transmission line experiences a transient or permanent fault, it will perform indiscriminate reclosing after a fixed delay. If it coincides with a permanent fault or closes at the moment when the secondary arc is not extinguished, the reclosing fails, causing a secondary impact on the system and affecting its stable operation. The present invention can correctly identify the nature of the fault before the circuit breaker recloses. If it is identified as a permanent fault, it will be locked and reclosed; If it is identified as a transient fault, calculate the time when the fault disappears, determine the specific reclosing time, and restore power supply in a timely manner, which is of great significance for the reliable operation of the wind power transmission system and the safety and stability of the power equipment.

[0129] The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of those skilled in the art without departing from the purpose of the present invention.