Distance protection method and system for phase-to-phase fault of new energy transmission line

Abstract

The invention discloses a distance protection method and system for an inter-phase fault of a new energy transmission line, and the method comprises the steps: measuring the three-phase voltage and current at a protection installation part in real time, and carrying out the measurement of the three-phase voltage and current when the protection is started and is an inter-phase fault; calculating a fault phase time domain compensation interphase voltage at a distance protection setting point based on the voltage and current measured in real time, and calculating a fault phase time domain negative sequence interphase voltage at a protection installation position based on the voltage measured in real time; calculating a correlation coefficient of the fault phase time domain compensation interphase voltage and the fault phase time domain negative sequence interphase voltage; and calculating a fault phase measurement impedance angle based on the voltage and current measured in real time, judging whether a new energy transmission line phase-to-phase fault action condition is met or not by combining the correlation coefficient, and performing protection action when the new energy transmission line phase-to-phase fault action condition is met. The method is not influenced by a new energy side non-constant voltage source, negative sequence current suppression and frequency instability, and the action precision of phase-to-phase distance protection can be improved.

Description

Technical Field

[0001] This invention belongs to the field of power transmission line fault identification technology, and relates to a distance protection method and system for phase-to-phase faults in new energy transmission lines. Background Technology

[0002] In new power systems dominated by new energy sources, the characteristics of power systems with a high proportion of power electronic equipment are becoming increasingly prominent. Currently, the main architecture is grid-connected, and the characteristics of power electronic equipment are determined by control strategies. These equipment have numerous parameters, complex models, and significant differences in characteristics, exhibiting features different from the constant voltage sources of traditional synchronous machine systems: uncertain underlying power supply impedance, non-equivalent voltage sources, nonlinear circuits, and controlled current sources, rendering superposition principle analysis methods inapplicable. Furthermore, constrained by low-voltage ride-through requirements, negative sequence current suppression strategies significantly alter the transient characteristics of the grid during asymmetrical faults. The fault current of doubly-fed induction generators deviates from the power frequency, particularly adversely affecting traditional phase-comparison distance relays, leading to incorrect distance protection operation in the field. In addition, the phase angle difference between the short-circuit current provided by new energy sources and the short-circuit current on the system side is large. During faults via transition resistors, compared to traditional systems, the additional impedance measured by distance protection on the new energy side is larger and more biased towards the third and fourth quadrants, making steady-state overrun problems more likely in distance protection. There is an urgent need to research new distance protection methods for new energy transmission lines for phase-to-phase fault distance protection. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a distance protection method and system for phase-to-phase faults in new energy transmission lines.

[0004] The present invention adopts the following technical solution.

[0005] The first aspect of this invention proposes a distance protection method for phase-to-phase faults in new energy transmission lines, comprising:

[0006] Step 1: Measure the voltage and current at the installation point of the protection for the new energy transmission line in real time, and proceed to Step 2 when it is determined that the protection has been activated and that it is a phase-to-phase fault;

[0007] Step 2: Calculate the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point based on the real-time measured voltage and current, and calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on the real-time measured voltage.

[0008] Step 3: Calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase;

[0009] Step 4: Calculate the measured impedance angle of the fault phase based on the real-time measured voltage and current, and determine whether the phase-to-phase fault operation conditions of the new energy transmission line are met by combining the correlation coefficient. If the conditions are met, the protection will operate.

[0010] Preferably, in step 2, the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point is calculated based on the real-time measured voltage and current, as follows:

[0011]

[0012] In the formula, u′ ΦΦ The calculated time-domain compensation phase-to-phase voltage ΦΦ at the distance protection setting point; u ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ is calculated based on the voltage measured at the protection installation location; ΦΦ Len is the phase-to-phase current of the fault phase ΦΦ calculated based on the current measured at the protection installation location; SET R1 is the length setting for distance protection; L1 is the positive sequence resistance per kilometer of line; L1 is the positive sequence inductance per kilometer of line; t is time.

[0013] Preferably, in step 2, when the fault phase ΦΦ is phase BC, phase CA, or phase AB, the time-domain negative sequence phase-to-phase voltage u of the fault phase at the protection installation location... 2ΦΦ u 2bc u 2ca u 2ab The calculation formula is as follows:

[0014]

[0015] In the formula, To protect the angle difference corresponding to the sampling interval, N is the number of sampling points to protect per cycle; u a (k), u b (k), u c (k) represents the instantaneous three-phase voltage value measured at the protection installation location at the current sampling time k; u a (k-1), u b (k-1), u c (k-1) is the instantaneous value of the three-phase voltage measured at the protection installation point k-1 at the previous sampling time.

[0016] Preferably, in step 3, the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative-sequence phase-to-phase voltage of the faulty phase is calculated, using the following formula:

[0017]

[0018] In the formula, ρ is the correlation coefficient; N is the number of sampling points per cycle for protection; k is the sampling point number; u 2ΦΦ To protect the time-domain negative sequence phase-to-phase voltage of the faulty phase at the installation location; u′ Φ′ The phase-to-phase voltage of the faulty phase ΦΦ at the distance protection setting point is compensated in the time domain.

[0019] Preferably, in step 4, the measured impedance angle of the fault phase is calculated based on the real-time measured voltage and current, as follows:

[0020] Substitute multiple sets of measured voltage and current values ​​into the equation. Construct a system of equations, and solve the system of equations using the least squares algorithm to obtain R. m L m ;

[0021] The obtained R m L m Substituting into the following formula, calculate the measured impedance angle Arg(Z) of the fault phase. m ):

[0022]

[0023] In the formula, u ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ is calculated based on the voltage measured at the protection installation location; ΦΦ R is the phase-to-phase current of the fault phase ΦΦ calculated based on the current measured at the protection installation location; m For measuring resistance; t is time; L m For measuring inductance; f is the system frequency; Arg(Z) m ( ) represents the measured impedance angle of the faulty phase.

[0024] Preferably, in step 4, when the fault measurement impedance angle is less than or equal to the positive sequence impedance angle of the line, the operating conditions are as follows:

[0025] Arg(Z m )≤θ and Arg(Z) m )≥θ1, and simultaneously satisfy ρ>sinδ;

[0026] In the formula, ρ is the correlation coefficient; Arg(Z) m ) represents the measured impedance angle of the faulted phase; δ represents the safety margin; θ represents the positive sequence impedance angle of the line; and θ1 represents the impedance offset angle in the fourth quadrant.

[0027] Preferably, δ is 6° to 12° and θ1 is -30° to -15°.

[0028] Preferably, in step 4, when the fault measurement impedance angle is greater than the positive sequence impedance angle of the line, the operating condition is:

[0029] Arg(Z m )>θ and Arg(Z) m ) < θ2, and simultaneously satisfy ρ < -sinδ;

[0030] In the formula, Arg(Z) m) represents the measured impedance angle of the faulted phase; ρ is the correlation coefficient; θ is the positive sequence impedance angle of the line; θ2 is the impedance offset angle in the second quadrant; δ is the safety margin.

[0031] Preferably, δ is 6° to 12° and θ2 is 105° to 120°.

[0032] A second aspect of this invention provides a distance protection system for phase-to-phase faults in new energy transmission lines, comprising:

[0033] The measurement module is used to measure the three-phase voltage and current at the protection installation point in real time, and enters the phase-to-phase voltage calculation module when the protection is detected to be activated and a phase-to-phase fault is detected.

[0034] The phase-to-phase voltage calculation module is used to calculate the time-domain compensated phase-to-phase voltage of the fault phase at the distance protection setting point based on real-time measured voltage and current; and to calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on real-time measured voltage.

[0035] The correlation coefficient calculation module is used to calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase.

[0036] The impedance angle calculation module is used to calculate the impedance angle of the fault phase based on real-time measured voltage and current.

[0037] The fault diagnosis module is used to determine the fault range and implement protection based on the measured impedance angle and correlation coefficient of the faulty phase.

[0038] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0039] This invention measures the voltage and current at the protection installation point of the renewable energy transmission line in real time. It then uses a time-domain algorithm to calculate the time-domain compensated phase-to-phase voltage of the faulty phase at the protection setting point and the time-domain negative-sequence phase-to-phase voltage of the faulty phase at the protection installation point. Based on the correlation coefficient between these two values ​​and the measured impedance angle of the faulty phase, it determines whether the phase-to-phase fault operation conditions of the renewable energy transmission line are met. This solves the problem of easy steady-state overshooting of distance protection during phase-to-phase faults involving renewable energy transmission lines via transition resistors, and addresses the issue of inaccurate vector algorithm calculations due to frequency offset during renewable energy faults. This method is unaffected by non-constant voltage sources, negative-sequence current suppression, and frequency instability on the renewable energy side, thus improving the operational accuracy of phase-to-phase distance protection. This invention requires only two sampling points to calculate the time-domain negative-sequence phase-to-phase voltage, significantly accelerating the protection operation speed compared to traditional algorithms requiring a 5ms data window. Attached Figure Description

[0040] Figure 1 A schematic diagram showing that the measured impedance angle for faults within the area is less than or equal to the positive sequence impedance angle of the line.

[0041] Figure 2 A schematic diagram showing that the measured impedance angle for faults within the area is greater than the positive sequence impedance angle of the line.

[0042] Figure 3 This is a flowchart of a distance protection method for phase-to-phase faults in new energy transmission lines. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0044] Embodiment 1 of the present invention provides a distance protection method for phase-to-phase faults in new energy transmission lines, which can be applied to... Figure 1 and Figure 2 The protection range during line faults. Figure 1 and Figure 2 This is the distance protection action zone, where Z m To measure impedance, Z SET F1 represents the set impedance for distance protection, and F2 represents the fault within the zone. Figure 1 A schematic diagram showing that the fault measurement impedance angle is less than or equal to the positive sequence impedance angle of the line, Z m Within the operating region, measure the impedance angle Arg(Z). m The measured impedance angle Arg(Z) is less than or equal to the positive sequence impedance angle θ of the line. m ) Greater than or equal to θ-180°; Figure 2 A schematic diagram showing that the fault measurement impedance angle is greater than the positive sequence impedance angle of the line, Z m Within the operating region, measure the impedance angle Arg(Z). m The measured impedance angle Arg(Z) is greater than the positive sequence impedance angle θ of the line. m The phase angle between the short-circuit current supplied by the new energy power source and the short-circuit current on the system side is large. When a fault occurs through the transition resistor, the additional impedance of the distance protection measurement on the new energy side is larger and more biased towards the third and fourth quadrants compared to the traditional system, which makes the distance protection prone to steady-state overrun.

[0045] Figure 1 and Figure 2 At point F2, outside the protection zone, a short-circuit fault occurred via the transition resistor. The measured impedance at this fault point should have been outside the protection zone. However, due to the influence of the transition resistor and the frequency deviation of the new energy system fault, the measured impedance Z calculated using the vector method was affected. mThis might fall within the distance protection operating zone, leading to malfunctions. Therefore, other algorithms are needed to address this issue. This invention can solve the problem of distance protection malfunctions caused by frequency domain calculation methods.

[0046] like Figure 3 As shown, this invention provides a distance protection method for phase-to-phase faults in new energy transmission lines. By acquiring the instantaneous voltage and current values ​​at the protection installation point and the line length at the setting point, the time-domain set point compensation phase-to-phase voltage and the time-domain negative-sequence phase-to-phase voltage at the protection installation point can be calculated. The correlation coefficient between the time-domain set point compensation phase-to-phase voltage and the protection installation point negative-sequence voltage is calculated to form a phase-to-phase fault protection criterion, used to determine whether the fault point is within the protection zone. This addresses the problem of easy steady-state overrunning of distance protection when a new energy phase-to-phase fault passes through a transition resistor. The time-domain algorithm is used to calculate the compensation voltage and negative-sequence voltage, which serves as the protection action criterion. This solves the problem of inaccurate vector algorithm calculations due to frequency offset during new energy faults. The specific steps are as follows:

[0047] Step 1: Measure the voltage and current at the protection installation point in real time, and proceed to Step 2 when it is determined that the protection has been activated and that it is a phase-to-phase fault;

[0048] More preferably, (1) the protection device collects the three-phase voltage and three-phase current at the installation location in real time;

[0049] The specific three-phase voltages collected include u a u b u c The collected three-phase currents include i a i b i c .

[0050] The phase-to-phase voltage u is calculated based on the phase voltage. ab u bc u ca The interphase current i is calculated based on the phase current. ab i bc i ca .

[0051] (2) Determine if the protection is activated, and proceed to step 2 if it is a phase-to-phase fault;

[0052] Specifically, the protection start-up judgment can be based on, but is not limited to, sudden change start-up. After the protection starts, it enters the phase selection logic. The phase selection can be based on, but is not limited to, low voltage phase selection. After the protection determines that there is a phase-to-phase fault, it enters step 3.

[0053] Step 2: Calculate the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point based on the real-time measured voltage and current, and calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on the real-time measured voltage.

[0054] More preferably, the time-domain compensation phase-to-phase voltage of the fault phase at the protection setting point is calculated based on the voltage and current collected in real time by the protection device.

[0055] The time-domain negative sequence phase-to-phase voltage of the faulty phase at the protection installation location is calculated based on the voltage collected in real time by the protection device.

[0056] Among them, (1) the time-domain compensation phase-to-phase voltage at the protection setting point can be expressed by the following formula, as follows:

[0057]

[0058] In the formula, ΦΦ represents the fault phase, which can be AB, BC, or CA, and u′ ΦΦ To calculate the time-domain compensation phase-to-phase voltage at the fault phase ΦΦ of the distance protection setting point, u ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ is calculated based on the voltage measured at the protection installation location. ΦΦ Len calculates the phase-to-phase current of the fault phase ΦΦ based on the current measured at the protection installation location. SET The distance protection setting is the length setting value, R1 is the positive sequence resistance per kilometer of the line, L1 is the positive sequence inductance per kilometer of the line, and t is the time.

[0059] The phase-to-phase voltage and phase-to-phase current can be expressed by the following formulas, taking phases AB as an example, as follows:

[0060] u AB =u A -u B

[0061] i AB =i A -i B

[0062] In the formula, u A u B To protect the A-phase and B-phase voltages measured at the installation location, i A i B To protect the A-phase current and B-phase current measured at the installation location.

[0063] (2) Calculate the negative sequence voltage u in the time domain 2ΦΦ It can be expressed by the following formula, which calculates u. 2bc u 2ca u 2ab In practice, only one of the faulty phases needs to be calculated, as follows:

[0064]

[0065]

[0066] In the formula, To protect the angle difference corresponding to the sampling interval, N is the number of sampling points to protect per cycle, u a (k), u b (k), u c (k) represents the instantaneous three-phase voltage value measured at the protection installation point at the current sampling time k, u a (k-1), u b (k-1), u c (k-1) is the instantaneous value of the three-phase voltage measured at the protection installation point k-1 at the previous sampling time.

[0067] The time-domain negative sequence phase-to-phase voltage algorithm of this invention only requires 2 sampling points, which significantly speeds up the protection action compared to the traditional data window algorithm that requires 5ms.

[0068] Step 3: Calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase;

[0069] More preferably, the correlation coefficient between the fault phase time-domain compensated phase-to-phase voltage at the protection setting point and the fault phase time-domain negative sequence phase-to-phase voltage at the protection installation point is calculated;

[0070] The correlation coefficient ρ between the time-domain compensated phase-to-phase voltage at the protection setting point and the time-domain negative-sequence phase-to-phase voltage at the protection installation point can be calculated using the following formula:

[0071]

[0072] In the formula, ρ is the correlation coefficient, N is the number of sampling points per cycle of the protection wave, and k is the sampling point number.

[0073] Step 4: Calculate the measured impedance angle of the fault phase based on the real-time measured voltage and current, and determine whether the phase-to-phase fault operation conditions of the new energy transmission line are met by combining the correlation coefficient. If the conditions are met, the protection will operate.

[0074] More preferably, the fault phase measurement impedance angle is calculated based on the voltage and current collected in real time by the protection device; the measurement impedance angle Arg(Z) m It can be calculated using the following formula:

[0075]

[0076] In the formula, R m To measure resistance, L m For measuring inductance, f is the system frequency.

[0077] Specifically, multiple sets of measured voltage and current values ​​are substituted into the equations to form a system of equations, and the least squares algorithm is used to calculate R. m L mThe measured impedance angle Arg(Z) can be calculated. m ).

[0078] Determine whether the operating conditions are met based on the measured impedance angle and correlation coefficient results. If the operating conditions are met, the protection will operate.

[0079] Specifically, if the measured impedance angle and correlation coefficient meet the criteria, it is determined that an intra-zone fault has occurred, and the protection device will operate; if the measured impedance angle and correlation coefficient do not meet the criteria, it is determined that an extra-zone fault has occurred, and the protection device will not operate.

[0080] (1) When the fault measurement impedance angle is less than or equal to the positive sequence impedance angle of the line, the protection will operate under the following conditions:

[0081] If Arg(Z) m )≤θ and Arg(Z) m If ρ ≥ θ1 and ρ > sinδ is satisfied, it is judged as an internal fault and the protection will operate; otherwise, it is judged as an external fault and the protection will not operate.

[0082] In the formula, ρ is the correlation coefficient, δ is the safety margin, which can be taken as 6° to 12°, θ is the positive sequence impedance angle of the line, and θ1 is the impedance offset angle in the fourth quadrant, preferably -30° to -15°.

[0083] (2) When the fault measurement impedance angle is greater than the positive sequence impedance angle of the line, the protection will operate under the following conditions:

[0084] If Arg(Z) m )>θ and Arg(Z) m If ρ < θ2, and ρ < -sinδ is also satisfied, it is judged as an internal fault and the protection will operate; otherwise, it is judged as an external fault and the protection will not operate.

[0085] In the formula, θ2 is the impedance offset angle in the second quadrant, preferably 105° to 120°.

[0086] Embodiment 2 of the present invention provides a distance protection system for phase-to-phase faults in new energy transmission lines, comprising:

[0087] The measurement module is used to measure the three-phase voltage and current at the protection installation point in real time, and enters the phase-to-phase voltage calculation module when the protection is detected to be activated and a phase-to-phase fault is detected.

[0088] Protection activation judgment: Protection is activated, and the fault judgment logic is entered;

[0089] Protection Phase Selection: After the selected phase is identified as an inter-phase fault, subsequent calculations and fault identification will proceed.

[0090] The phase-to-phase voltage calculation module is used to calculate the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point based on the real-time measured voltage and current; and to calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on the real-time measured voltage.

[0091] Calculation of phase-to-phase voltage in the time domain at the setting point: Calculate the phase-to-phase voltage in the time domain at the setting point based on the instantaneous values ​​of voltage and current measured by the protection device;

[0092] Negative-sequence phase-to-phase voltage at the protection installation location: Calculate the phase-to-phase voltage at the protection installation location based on the instantaneous voltage value measured by the protection device;

[0093] The correlation coefficient calculation module is used to calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase.

[0094] Calculate the correlation coefficient: Calculate the correlation coefficient between the time-domain phase-to-phase voltage at the setting point and the time-domain negative-sequence phase-to-phase voltage at the protection installation location;

[0095] The impedance angle calculation module is used to calculate the impedance angle of the fault phase based on the real-time measured voltage and current.

[0096] The fault diagnosis module is used to determine the fault range and perform protection based on the measured impedance angle and correlation coefficient of the faulty phase.

[0097] Impedance angle calculation: Calculate the impedance angle based on the measured voltage and current;

[0098] Fault diagnosis: Used to determine the fault range (fault type) and implement protection based on the measured impedance angle and correlation coefficient.

[0099] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0100] By measuring the voltage and current at the protection installation point of the renewable energy transmission line in real time, and using a time-domain algorithm to calculate the time-domain compensated phase-to-phase voltage of the faulty phase at the distance protection setting point and the time-domain negative-sequence phase-to-phase voltage of the faulty phase at the protection installation point, the method determines whether the phase-to-phase fault operation conditions of the renewable energy transmission line are met based on the correlation coefficient and the measured impedance angle of the faulty phase. This method can solve the problem of easy steady-state overrunning of distance protection when renewable energy experiences phase-to-phase faults through transition resistors, and solve the problem of inaccurate vector algorithm calculations caused by frequency offset during renewable energy faults. This method is not affected by non-constant voltage sources, negative-sequence current suppression, or frequency instability on the renewable energy side, and can improve the operating accuracy of phase-to-phase distance protection. This invention only requires data from two sampling points to calculate the time-domain negative-sequence phase-to-phase voltage, which significantly speeds up the protection operation compared to the traditional data window algorithm that requires 5ms.

[0101] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0102] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0103] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0104] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A distance protection method for phase-to-phase faults in new energy transmission lines, characterized in that, include: Step 1: Measure the voltage and current at the installation point of the protection for the new energy transmission line in real time, and proceed to Step 2 when it is determined that the protection has been activated and that it is a phase-to-phase fault; Step 2: Calculate the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point based on the real-time measured voltage and current; calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on the real-time measured voltage. Step 3: Calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase; Step 4: Calculate the measured impedance angle of the fault phase based on the real-time measured voltage and current, and determine whether the phase-to-phase fault operation conditions of the new energy transmission line are met by combining the correlation coefficient. If the conditions are met, the protection will operate.

2. The distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 2, the time-domain compensation phase-to-phase voltage of the fault phase at the distance protection setting point is calculated based on the real-time measured voltage and current, as follows: In the formula, u′ ΦΦ The calculated time-domain compensation phase-to-phase voltage ΦΦ at the distance protection setting point; u ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ is calculated based on the voltage measured at the protection installation location; ΦΦ Len is the phase-to-phase current of the fault phase ΦΦ calculated based on the current measured at the protection installation location; SET R1 is the length setting for distance protection; L1 is the positive sequence resistance per kilometer of line; L1 is the positive sequence inductance per kilometer of line; t is time.

3. The distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 2, when the faulty phase ΦΦ is phase BC, phase CA, or phase AB, the time-domain negative sequence phase-to-phase voltage u of the faulty phase at the protection installation location is... 2ΦΦ u 2bc u 2ca u 2ab The calculation formula is as follows: In the formula, To protect the angle difference corresponding to the sampling interval, N is the number of sampling points to protect per cycle; u a (k), u b (k), u c (k) represents the instantaneous three-phase voltage value measured at the protection installation location at the current sampling time k; u a (k-1), u b (k-1), u c (k-1) is the instantaneous value of the three-phase voltage measured at the protection installation point k-1 at the previous sampling time.

4. The distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 3, the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative-sequence phase-to-phase voltage of the faulty phase is calculated, using the following formula: In the formula, ρ is the correlation coefficient; N is the number of sampling points per cycle for protection; k is the sampling point number; u 2ΦΦ To protect the time-domain negative sequence phase-to-phase voltage of the faulty phase at the installation location; u′ ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ at the distance protection setting point is compensated in the time domain.

5. A distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 4, the measured impedance angle of the fault phase is calculated based on the real-time measured voltage and current, as follows: Substitute multiple sets of measured voltage and current values ​​into the equation. Construct a system of equations, and solve the system of equations using the least squares algorithm to obtain R. m L m ; The obtained R m L m Substituting into the following formula, calculate the measured impedance angle Arg(Z) of the fault phase. m ): In the formula, u ΦΦ The phase-to-phase voltage of the faulty phase ΦΦ is calculated based on the voltage measured at the protection installation location; ΦΦ R is the phase-to-phase current of the fault phase ΦΦ calculated based on the current measured at the protection installation location; m For measuring resistance; t is time; L m For measuring inductance; f is the system frequency; Arg(Z) m ( ) represents the measured impedance angle of the faulty phase.

6. A distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 4, when the fault measurement impedance angle is less than or equal to the positive sequence impedance angle of the line, the operating conditions are as follows: Arg(Z m )≤θ and Arg(Z) m )≥θ1, and simultaneously satisfy ρ>sinδ; In the formula, ρ is the correlation coefficient; Arg(Z) m ) represents the measured impedance angle of the faulted phase; δ represents the safety margin; θ represents the positive sequence impedance angle of the line; and θ1 represents the impedance offset angle in the fourth quadrant.

7. A distance protection method for phase-to-phase faults in new energy transmission lines according to claim 6, characterized in that: δ is taken as 6°~12°, and θ1 is taken as -30°~-15°.

8. A distance protection method for phase-to-phase faults in new energy transmission lines according to claim 1, characterized in that: In step 4, when the fault measurement impedance angle is greater than the positive sequence impedance angle of the line, the operating condition is: Arg(Z m ) > θ and Arg(Z m ) < θ2, and at the same time satisfy ρ < -sinδ; In the formula, Arg(Z) m ) represents the measured impedance angle of the faulted phase; ρ is the correlation coefficient; θ is the positive sequence impedance angle of the line; θ2 is the impedance offset angle in the second quadrant; δ is the safety margin.

9. A distance protection method for phase-to-phase faults in new energy transmission lines according to claim 8, characterized in that: δ ranges from 6° to 12°, and θ2 ranges from 105° to 120°.

10. A distance protection system for phase-to-phase faults in new energy transmission lines, comprising the method described in any one of claims 1-9, characterized in that, The system includes: The measurement module is used to measure the three-phase voltage and current at the protection installation location in real time, and enters the phase-to-phase voltage calculation module when the protection is detected to be activated and a phase-to-phase fault is detected. The phase-to-phase voltage calculation module is used to calculate the time-domain compensated phase-to-phase voltage of the fault phase at the distance protection setting point based on real-time measured voltage and current; and to calculate the time-domain negative sequence phase-to-phase voltage of the fault phase at the protection installation location based on real-time measured voltage. The correlation coefficient calculation module is used to calculate the correlation coefficient between the time-domain compensated phase-to-phase voltage of the faulty phase and the time-domain negative sequence phase-to-phase voltage of the faulty phase. The impedance angle calculation module is used to calculate the impedance angle of the fault phase based on real-time measured voltage and current. The fault diagnosis module is used to determine the fault range and perform protection based on the measured impedance angle and correlation coefficient of the faulty phase.

Images