New energy station sending-out line phase-to-phase distance protection method and device based on control switching

Abstract

The invention discloses a new energy station sending-out line phase-to-phase distance protection method and device based on control switching, and belongs to the field of power system relay protection. The built fault distance measurement equation not only considers the line impedance, but also considers the transition resistance, and also considers that the current at the transition resistance is not only from the protection installation side, but also from the power grid side; according to the invention, the control state of the new energy station is switched at intervals; respectively substituting the measured voltage and phase current difference at the protection installation position at each sampling moment and the sampling moment which is an integral multiple of a power frequency period at an interval from the sampling moment and is different from the control state at the sampling moment into a fault distance measurement equation, and then carrying out difference processing to eliminate a current item at the power grid side; accurate calculation of the fault distance under the transition resistance fault can be achieved, the problem that in the prior art, the transition resistance tolerance capacity of phase-to-phase distance protection is insufficient is solved, and reliable removal of the new energy transmission line fault is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and more specifically, relates to a method and device for phase-to-phase distance protection of new energy power plant transmission lines based on control switching. Background Technology

[0002] Large-scale development and utilization of new energy sources are crucial for building a new power system. A high proportion of new energy sources and a high proportion of power electronic equipment are important technical characteristics of my country's new power system. Currently, power frequency phasor distance protection is widely used in the power grid. With the large-scale integration of new energy power sources, the complex controlled characteristics of these sources during system faults severely impact the distance protection performance of new energy transmission lines. In particular, the extremely poor transition resistance tolerance of phase-to-phase distance protection may cause incorrect operation, threatening the safe and stable operation of the new energy transmission system. Therefore, researching a distance protection method for new energy power plant transmission lines is of great significance.

[0003] Existing distance protection methods for power transmission lines from new energy power plants typically calculate the impedance from the protection installation point to the fault point based on the voltage and current at the protection installation point, and estimate the fault distance based on this impedance and line parameters. However, when a fault occurs through the transition resistance, the above impedance includes not only the line impedance but also the transition resistance. Therefore, the above estimation results are biased, and the phase-to-phase distance protection is not strong enough to withstand the transition resistance. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method and device for phase-to-phase distance protection of new energy power station transmission lines based on control switching, so as to solve the technical problem of insufficient phase-to-phase distance protection withstanding transition resistance in the existing technology.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for phase-to-phase distance protection of power transmission lines of new energy power plants based on control switching, comprising: performing the following operations after a fault occurs: The measured voltage and phase current difference at the protection installation point of the new energy power station are continuously sampled, and the control state of the new energy power station is switched intermittently. From sampling time First, estimate the fault distance at each sampling time. The sampling time is after the first switch of the control state of the new energy power station, and ; The power frequency cycle; If the estimated fault distance is less than the preset distance for T consecutive sampling times, it is determined that there is a fault within the zone; otherwise, it is determined that there is a fault outside the zone; T is a positive integer. Among them, estimating any sampling time Methods for determining fault distance include: For sampling time For each sampling moment in the preset time window of the start time Obtain the corresponding sampling time ; In order to be in Previously with The interval time is The sampling time is an integer multiple of the sampling time, and and The control status of the new energy power stations is different; and After substituting the measured voltage and phase current difference at the lower protection installation point into the fault distance measurement equation, the difference is calculated to obtain... The improved distance measurement equation at time t; where, The fault distance measurement equation is constructed based on the transmission line model and represents the relationship between the measured voltage and phase current difference at the protection installation point, the fault distance, line parameters, and the voltage at the fault point; sampling time. Voltage at the fault point ; and Sampling time Phase current difference and grid-side current at the lower protection installation location; For transition resistance; Solve the system of equations consisting of the improved ranging equations at each moment within the preset time window to obtain the sampling time. The distance to the fault.

[0006] More preferably, the fault distance measurement equation is:

[0007] in, for The measured voltage at the current protection installation point; R is the positive sequence resistance per unit length. for The phase current difference at the current protection installation point; L is the positive sequence inductance per unit length; D is the fault distance; For the next The voltage at the fault point at that moment; ; for The phase current difference at the current protection installation point at any given time; for The grid-side current at a given time.

[0008] More preferably, the least squares method is used to solve the system of equations consisting of the improved ranging equations at each moment in the preset time window.

[0009] More preferably, the preset distance is 0.8 times the total length of the protected line.

[0010] Secondly, the present invention provides a phase-to-phase distance protection device for power transmission lines of new energy power plants based on control switching, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the phase-to-phase distance protection method provided in the first aspect of the present invention when executing the computer program.

[0011] Thirdly, the present invention provides a wind farm transmission system, comprising: a new energy power station, a new energy power station transmission line, and a phase-to-phase distance protection device provided in the second aspect of the present invention.

[0012] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device containing the storage medium to perform the phase-to-phase distance protection method provided in the first aspect of the present invention.

[0013] Fifthly, the invention also provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the phase-to-phase distance protection method provided in the first aspect of the invention.

[0014] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: This invention provides a phase-to-phase distance protection method for transmission lines of new energy power plants based on control switching. The constructed fault distance measurement equation considers not only the line impedance but also the transition resistance, and also takes into account that the current at the transition resistance comes from both the protection installation side and the grid side. Based on this, the invention continuously samples the measured voltage and phase current difference at the protection installation point of the new energy power plant and intermittently switches the control state of the new energy power plant. When solving for the fault distance at each sampling moment, the measured voltage and phase current difference at the protection installation point at the sampling moment and at sampling moments with an interval equal to an integer multiple of the power frequency cycle and a different control state than the sampling moment are substituted into the fault distance measurement equation and subtracted to eliminate the grid-side current term, resulting in an improved distance measurement equation unaffected by the opposite grid. The only unknowns in the constructed improved distance measurement equation set are the fault distance and the transition resistance, enabling accurate calculation of the fault distance under transition resistance faults. This solves the technical problem of insufficient phase-to-phase distance protection tolerance to transition resistance in existing technologies, and is beneficial for reliable fault clearing of new energy transmission lines. Attached Figure Description

[0015] Figure 1This is a schematic diagram of a typical new energy power station power transmission system provided in Embodiment 1 of the present invention; Figure 2 The fault distance curve obtained by using the conventional distance protection method when a phase-to-phase short circuit with transition resistance fault occurs on the power transmission line of a new energy power station as provided in Embodiment 1 of the present invention; Figure 3 When a phase-to-phase short circuit with transition resistance fault occurs on the transmission line of a new energy power station as provided in Embodiment 1 of the present invention, the fault distance curve obtained by the distance protection method provided by the present invention is shown. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Example 1 This embodiment uses a typical new energy wind farm power transmission system as an example for illustration. Figure 1 As shown, a typical wind farm transmission system includes equivalent power from external systems. Transmission line N-side relay protection device, transmission line M-side relay protection device, inverter-type new energy power station.

[0018] This embodiment provides a phase-to-phase distance protection method for power transmission lines of new energy power plants based on control switching, including: performing the following operations after a fault occurs: The measured voltage and phase current difference at the protection installation point of the new energy power station are continuously sampled, and the control state of the new energy power station is switched intermittently. From sampling time First, estimate the fault distance at each sampling time. The sampling time is after the first switch of the control state of the new energy power station, and ; The power frequency cycle; If the estimated fault distance is less than the preset distance for T consecutive sampling times, it is determined that there is a fault within the zone; otherwise, it is determined that there is a fault outside the zone; T is a positive integer. Among them, estimating any sampling time Methods for determining fault distance include: For sampling time For each sampling moment in the preset time window of the start time Obtain the corresponding sampling time ; In order to be in Previously with The interval time is The sampling time is an integer multiple of the sampling time, and and The control states of the new energy power stations are different; the sampling time will be different. and sampling time After substituting the measured voltage and phase current difference at the lower protection installation point into the fault distance measurement equation, the difference is calculated to obtain... The improved distance measurement equation at time t; where, The fault distance measurement equation is derived from a transmission line model and represents the relationship between the measured voltage at the protection installation point, the phase current difference at the protection installation point, the fault distance, line parameters, and the voltage at the fault point. Sampling time... Voltage at the fault point ; and Sampling time Phase current difference and grid-side current at the lower protection installation location; For transition resistance; Solve the system of equations consisting of the improved ranging equations at each moment within the preset time window to obtain the sampling time. The distance to the fault.

[0019] It should be noted that, considering that the grid-side current value is the same when the interval is an integer multiple of the power frequency cycle, that is... ; , The sampling time is a positive integer. and sampling time Substituting the measured voltage and phase current difference at the lower protection installation point into the fault distance measurement equation and then performing a difference operation eliminates this term from the equation, leaving only the fault distance and transition resistance as unknowns in the equation set, unaffected by the opposite power grid, thus facilitating the solution. The aforementioned control state switching ensures constant... and sampling time The measured voltage and phase current difference at the lower protection installation point are different to prevent them from being eliminated when the fault distance measurement equation is subtracted, thus providing a premise for the construction of the equation set.

[0020] It should be noted that the control states of new energy power plants include: outputting negative sequence reactive current, suppressing negative sequence reactive current, etc. There are no restrictions here, as long as the control states of new energy power plants are different before and after the switch. Among them, the active current command value can change with the switch, and the reactive power coefficient can also change with the switch when outputting negative sequence reactive current.

[0021] The fault distance measurement equation is expressed as: In this embodiment, the transmission line model is an AC line RL model, and the fault distance measurement equation is:

[0022] in, for The measured voltage at the current protection installation point; R is the positive sequence resistance per unit length. for The phase current difference at the current protection installation point; L is the positive sequence inductance per unit length; D is the fault distance; For the next The voltage at the fault point at that moment; ; for The phase current difference at the current protection installation point at any given time; for The grid-side current at a given time.

[0023] It should be noted that the aforementioned preset time window can be selected based on experience in actual engineering. A preset time window including only two sampling moments can be selected to obtain a system of two linear equations in two variables for solving, yielding the fault distance and transition resistance. To improve calculation accuracy, a preset time window including more than two sampling moments can be selected to obtain two or more improved ranging equations, constructing an overdetermined system of equations, which can then be solved using parameter fitting algorithms (such as least squares method, maximum likelihood estimation method, Bayesian estimation method, robust fitting method, etc.).

[0024] In this embodiment, The sampling interval is 0.25ms. In order to be in Previously with The interval time is The sampling time is set; the preset time window length is 20ms, and the least squares method is used to solve the system of equations formed by the improved ranging equations at each moment in the preset time window.

[0025] It should be noted that T and the preset distance can be selected based on experience in actual engineering projects, and the preset distance must be at least less than the total length of the protected line. Preferably, in this embodiment, The preset distance (i.e., the set distance) is 0.8 times the total length of the protected line.

[0026] In this embodiment, a phase-to-phase short-circuit fault is set to occur at F1 inside the transmitting line, with a fault distance of 50km and a transition resistance of 10Ω. The fault distance calculated using conventional distance protection methods is as follows: Figure 2 As shown, the distance is far from the actual fault distance, which is 50km. However, the fault distance calculated using the distance protection method provided in this embodiment is as follows:Figure 3 As shown, the actual fault distance is around 50km, and the obtained fault distance is less than the preset distance of 80km, indicating that the distance protection operates reliably.

[0027] It should be noted that the distance protection method proposed in this invention is applicable to various types of new energy transmission line scenarios, and can effectively solve the problem of insufficient tolerance to transition resistance of two-phase short-circuit faults in existing new energy power station-side distance protection, which is conducive to the reliable clearing of faults in new energy transmission lines.

[0028] Example 2 This embodiment provides a phase-to-phase distance protection device for the transmission line of a new energy power station based on control switching, including: a memory and a processor. The memory stores a computer program, and the processor executes the phase-to-phase distance protection method provided in Embodiment 1 of this invention when executing the computer program.

[0029] The related technical solutions are the same as the phase-to-phase distance protection method provided in Embodiment 1 of the present invention, and will not be described in detail here.

[0030] Thirdly, the present invention provides a wind farm transmission system, including: a new energy power station, a new energy power station transmission line, and a phase-to-phase distance protection device provided in Embodiment 2 of the present invention.

[0031] The related technical solutions are the same as those provided in Embodiment 2 of the present invention for the phase-to-phase distance protection device, and will not be described in detail here.

[0032] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device containing the storage medium to execute the phase-to-phase distance protection method provided in Embodiment 1 of the present invention.

[0033] The related technical solutions are the same as the phase-to-phase distance protection method provided in Embodiment 1 of the present invention, and will not be described in detail here.

[0034] Fifthly, the invention also provides a computer program product, including a computer program / instruction that, when executed by a processor, implements the phase-to-phase distance protection method provided in Embodiment 1 of the present invention.

[0035] The related technical solutions are the same as the phase-to-phase distance protection method provided in Embodiment 1 of the present invention, and will not be described in detail here.

[0036] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control switching-based inter-phase distance protection method for a new energy station sending-out line, characterized in that, The application relates to a phase-to-phase distance protection method and device. When a fault occurs, the following operations are performed: The measured voltage and phase current difference at the installation position of the new energy station protection are continuously sampled, and the control state of the new energy station is switched at intervals; from the sampling time starting, estimate the fault distance at each sampling time; for the sampling time after the first switching of the control state of the new energy station, and ; for the power frequency cycle; When the estimated fault distances at continuous T sampling instants are all less than a preset distance, it is determined that an in-zone fault exists; otherwise, it is determined that an out-of-zone fault exists; T is a positive integer; Among them, estimating any sampling time Methods for determining fault distance include: For each sampling time point in the preset time window with the sampling time point as the starting time point , the corresponding sampling time point is obtained; is the sampling time point before and is the interval time which is an integer multiple of , and is different from the control state of the new energy station under ; the measured voltage and phase current difference of the protection installation under and are respectively substituted into the fault distance measurement equation and then difference processing is performed to obtain the improved distance measurement equation at the time point ; wherein ; the fault distance measurement equation is obtained based on the transmission line model and is a relationship between the measured voltage and phase current difference of the protection installation, the fault distance, the line parameter and the voltage at the fault point; the voltage at the fault point at the sampling time point is ; and are the phase current difference and the grid side current at the sampling time point respectively; is the transition resistance; solving the equation group composed of the improved ranging equation at each time in the preset time window to obtain the fault distance at the sampling time .

2. The interphase distance protection method according to claim 1, characterized in that, The fault distance measurement equation is: wherein, is the measured voltage at the installation site at the moment of protection; is the measured voltage at the installation site at the moment of protection; is the difference between the phase currents at the installation site at the moment of protection; is the difference between the phase currents at the installation site at the moment of protection; is the voltage at the fault point at the moment of protection; is the voltage at the fault point at the moment of protection; ; is the difference between the phase currents at the installation site at the moment of protection; is the difference between the phase currents at the installation site at the moment of protection; is the difference between the phase currents at the installation site at the moment of protection; is the grid-side current at the moment of protection.

3. The interphase distance protection method of claim 1, wherein, The least square method is used to solve an equation group formed by the improved distance measurement equation at each instant in the preset time window.

4. The method of phase-to-phase distance protection according to any one of claims 1-3, characterized in that, The preset distance is 0.8 times the full length of the protected line.

5. A control switching based distance protection device for interphase distance protection of a sending line of a new energy station, characterized in that, The application relates to a phase-to-phase distance protection method and device. The application relates to a phase-to-phase distance protection method and device.

6. A wind farm transmission system characterized by, The application relates to a phase-to-phase distance protection method and device. The application relates to a phase-to-phase distance protection method and device.

7. A computer-readable storage medium, characterized in that, The application relates to a phase-to-phase distance protection method and device.

8. A computer program product, characterised in that, ​

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