Method for detecting short-circuit grounding power frequency overvoltage of ultra-high voltage transmission line

Abstract

The invention discloses a method for detecting short-circuit grounding power frequency overvoltage of an ultra-high voltage transmission line, and belongs to the technical field of ultra-high voltage transmission. In order to solve the problems of slow operation speed and low simulation precision of the existing overvoltage detection method of the ultra-high voltage power transmission system, the method comprises the following steps: introducing single-phase earth faults at four endpoints of a line head end, a position 1 / 3 away from the head end, a position 2 / 3 away from the head end and a line tail end, and simulating an overvoltage condition by adopting a distributed parameter model, two-phase grounding faults are introduced at four endpoints of the line head end, the position 1 / 3 away from the head end, the position 2 / 3 away from the head end and the line tail end, and a distributed parameter model is adopted to simulate the overvoltage condition; a fault phase is taken as a reference, the starting moment of the fault phase in one period is set as 0s, a peak point, a zero crossing point and a point between the peak point and the zero crossing point are taken, a single-phase earth fault is introduced at the corresponding moment, and a distributed parameter model is adopted to simulate the overvoltage condition. The method is used for overvoltage detection of the ultra-high voltage power transmission system.

Description

Technical Field

[0001] The invention relates to a method for detecting a short-circuit grounding power frequency overvoltage of an ultra-high voltage transmission line, and belongs to the technical field of ultra-high voltage transmission. Background Art

[0002] Ultra-high voltage transmission has the advantages of long transmission distance, large transmission capacity, small transmission channel area and low transmission loss. However, the uneven distribution of energy in my country makes ultra-high voltage transmission an inevitable development trend.

[0003] In UHV and long-distance power transmission systems, power frequency overvoltage plays a decisive role in determining the insulation level of the system. At the same time, power frequency overvoltage also determines the selection of electrical protection devices. If the system does not fully consider the impact of power frequency overvoltage on the system, it will pose a major threat to safety.

[0004] The power frequency overvoltages generated in the power system are mainly caused by the following aspects: (1) the capacitance effect caused by charging of long unloaded lines; (2) asymmetric grounding faults in the system; and (3) sudden load shedding of the generator.

[0005] Therefore, how to detect overvoltage is crucial. There are generally two methods for overvoltage detection: electromechanical simulation and electromagnetic model simulation. These two methods have the following problems:

[0006] 1. The electromechanical simulation step size is large and a vector model is used. Therefore, its calculation speed is fast but the simulation accuracy is low.

[0007] 2. The electromagnetic model has a small integral step and uses a three-phase instantaneous value model. It has high simulation accuracy and can output a time domain diagram of the waveform, but its simulation speed is relatively slow.

[0008] Therefore, proposing an overvoltage detection method with fast computing speed and high simulation accuracy is an urgent problem to be solved in the UHV power transmission system. Summary of the invention

[0009] The purpose of the present invention is to solve the problems of slow operation speed and low simulation accuracy in the existing overvoltage detection method of ultra-high voltage transmission system, and provide a detection method for short-circuit grounding power frequency overvoltage of ultra-high voltage transmission line.

[0010] The method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission line described in the present invention adopts electromechanical-electromagnetic transient hybrid simulation to perform overvoltage detection, specifically comprising:

[0011] S1. Number the two busbars as 1 and 6, divide the double-circuit overhead line between busbars 1 and 6 into three equal parts, and number the corresponding busbars at the sections as 2, 3, 4 and 5 respectively;

[0012] S2, introduce single-phase grounding faults at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and use the distributed parameter model to simulate the overvoltage situation;

[0013] Two-phase grounding faults are introduced at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and the distributed parameter model is used to simulate the overvoltage situation.

[0014] S3, taking the fault phase as the reference, setting the starting time of the fault phase within one cycle as 0s, taking the peak point, the zero-crossing point, and the point between the peak point and the zero-crossing point, introducing a single-phase grounding fault at the corresponding time, and using a distributed parameter model to simulate the overvoltage situation;

[0015] S4. According to the simulation results of S2 and S3, the relationship between the ground fault position and the overvoltage, and the relationship between the ground fault occurrence time and the overvoltage are obtained, that is, the overvoltage detection result is obtained.

[0016] Preferably, the relationship between the ground fault position and the overvoltage in S4 includes:

[0017] On the same line, when a ground fault occurs at one location, the power frequency overvoltage at different locations is different;

[0018] When the location of the ground fault changes, the location where the maximum overvoltage occurs on the line also changes;

[0019] When the fault location is the same, the overvoltage caused by two-phase grounding and three-phase disconnection is lower than the overvoltage caused by single-phase grounding and three-phase disconnection;

[0020] The power frequency overvoltage occurs in the non-fault phase;

[0021] On a line, the overvoltage tends to be higher in the middle and lower at both ends.

[0022] Preferably, the relationship between the ground fault occurrence time and the overvoltage in S4 includes:

[0023] When the fault occurs at the zero crossing point, the overvoltage is the lowest;

[0024] When the fault occurs at the peak position, the overvoltage is greater than the overvoltage at the zero-crossing fault;

[0025] When the fault occurs in the middle position, the overvoltage is the highest;

[0026] The healthy phase where the maximum overvoltage occurs is related to the time when the fault occurs.

[0027] Preferably, the specific method of introducing a single-phase grounding fault at four endpoints, namely, the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end, and the line end, and simulating the overvoltage situation using a distributed parameter model in S2 includes:

[0028] When a single-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.08pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.06pu, the power frequency overvoltage at the end of the line is 1.08pu, and the maximum overvoltage is 1.08pu;

[0029] When a single-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.21pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.44pu, and the power frequency overvoltage at the end of the line is 1.03pu, and the maximum overvoltage is 1.44pu;

[0030] When a single-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.42pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.16pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.42pu;

[0031] When a single-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.40pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.29pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.20pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.40pu.

[0032] Preferably, the specific method of introducing a two-phase grounding fault at four endpoints, namely, the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end, and the line end, and simulating the overvoltage situation using a distributed parameter model in S2 includes:

[0033] When a two-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 0.99pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.01pu;

[0034] When a two-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.09pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.09pu;

[0035] When a two-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.96pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.13pu, the power frequency overvoltage at the end of the line is 0.99pu, and the maximum overvoltage is 1.13pu;

[0036] When a two-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.02pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.06pu, the power frequency overvoltage at the end of the line is 1.00pu, and the maximum overvoltage is 1.06pu.

[0037] Preferably, the method described in S3 is to take the fault phase as a reference, set the starting time of the fault phase within a cycle as 0s, take the peak point, the zero crossing point, and the point between the peak point and the zero crossing point, introduce a single-phase grounding fault at the corresponding time, and use the distributed parameter model to simulate the overvoltage situation. The specific method includes:

[0038] Take a sine wave as one cycle, the peak is position 1, the trough is position 5, the zero crossing point is position 3, the position between 1 and 3 is position 2, the position between 3 and 5 is position 4, and the point between the trough and the starting point of the next cycle is position 6;

[0039] When a single-phase grounding fault is introduced at position 1, the corresponding time is 0.005s, the voltage of the healthy phase B is 984kV, and the voltage of the healthy phase C is 1071kV;

[0040] When a single-phase grounding fault is introduced at position 2, the corresponding time is 0.008s, the voltage of the healthy phase B is 1090kV, and the voltage of the healthy phase C is 954kV;

[0041] When a single-phase grounding fault is introduced at position 3, the corresponding time is 0.010s, the voltage of the healthy phase B is 915kV, and the voltage of the healthy phase C is 868kV;

[0042] When a single-phase grounding fault is introduced at position 4, the corresponding time is 0.012s, the voltage of the healthy phase B is 1088kV, and the voltage of the healthy phase C is 942kV;

[0043] When a single-phase grounding fault is introduced at position 5, the corresponding time is 0.015s, the voltage of the healthy phase B is 987kV, and the voltage of the healthy phase C is 1066kV;

[0044] When a single-phase grounding fault is introduced at position 6, the corresponding time is 0.017s, the voltage of the healthy phase B is 1092kV, and the voltage of the healthy phase C is 954kV.

[0045] Preferably, the double-circuit overhead line has a voltage level of 1000 kV between busbars 1-6 and a length of 420 km.

[0046] Advantages of the present invention: The present invention proposes a method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission lines, which performs electromechanical-electromagnetic transient hybrid simulation on a system with a maximum voltage level of 1000kV. It can obtain the influence of single-phase grounding and two-phase grounding faults of a 1000kV partial line in the system, and the influence of the fault occurring at different positions on the line on the overvoltage at each point in the system. At the same time, it can obtain the influence of the fault occurrence time on the overvoltage, with high simulation accuracy and fast calculation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a block diagram of electromagnetic simulation principle of a method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission line according to the present invention;

[0048] Figure 2 It is an electrical structure diagram of a method for detecting power frequency overvoltage of a short-circuit grounding of an ultra-high voltage transmission line according to the present invention;

[0049] Figure 3 It is a schematic diagram of the moment when the fault is connected to phase A within one cycle;

[0050] Figure 4 It is the three-phase time domain waveform at 2 / 3 of the distance from the head end under single-phase grounding fault;

[0051] Figure 5 It is the three-phase time domain waveform at 2 / 3 of the distance from the head end under two-phase grounding fault;

[0052] Figure 6 It is the load sequence network used for calculation of single-phase grounding system. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0055] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0056] Embodiment 1:

[0057] Combine the following Figure 1 and Figure 2 This embodiment is described. The method for detecting power frequency overvoltage of a UHV transmission line due to short circuit and grounding described in this embodiment uses electromechanical-electromagnetic transient hybrid simulation to perform overvoltage detection, specifically including:

[0058] S1. Number the two busbars as 1 and 6, divide the double-circuit overhead line between busbars 1 and 6 into three equal parts, and number the corresponding busbars at the sections as 2, 3, 4 and 5 respectively;

[0059] S2, introduce single-phase grounding faults at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and use the distributed parameter model to simulate the overvoltage situation;

[0060] Two-phase grounding faults are introduced at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and the distributed parameter model is used to simulate the overvoltage situation.

[0061] S3, taking the fault phase as the reference, setting the starting time of the fault phase within one cycle as 0s, taking the peak point, the zero-crossing point, and the point between the peak point and the zero-crossing point, introducing a single-phase grounding fault at the corresponding time, and using a distributed parameter model to simulate the overvoltage situation;

[0062] S4. According to the simulation results of S2 and S3, the relationship between the ground fault position and the overvoltage, and the relationship between the ground fault occurrence time and the overvoltage are obtained, that is, the overvoltage detection result is obtained.

[0063] Furthermore, the relationship between the ground fault position and the overvoltage in S4 includes:

[0064] On the same line, when a ground fault occurs at one location, the power frequency overvoltage at different locations is different;

[0065] When the location of the ground fault changes, the location where the maximum overvoltage occurs on the line also changes;

[0066] When the fault location is the same, the overvoltage caused by two-phase grounding and three-phase disconnection is lower than the overvoltage caused by single-phase grounding and three-phase disconnection;

[0067] The power frequency overvoltage occurs in the non-fault phase;

[0068] On a line, the overvoltage tends to be higher in the middle and lower at both ends.

[0069] Furthermore, the relationship between the ground fault occurrence time and the overvoltage in S4 includes:

[0070] When the fault occurs at the zero crossing point, the overvoltage is the lowest;

[0071] When the fault occurs at the peak position, the overvoltage is greater than the overvoltage at the zero-crossing fault;

[0072] When the fault occurs in the middle position, the overvoltage is the highest;

[0073] The healthy phase where the maximum overvoltage occurs is related to the time when the fault occurs.

[0074] Furthermore, the specific method of introducing a single-phase grounding fault at the four endpoints of the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the end of the line using the distributed parameter model to simulate the overvoltage situation includes:

[0075] When a single-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.08pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.06pu, the power frequency overvoltage at the end of the line is 1.08pu, and the maximum overvoltage is 1.08pu;

[0076] When a single-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.21pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.44pu, and the power frequency overvoltage at the end of the line is 1.03pu, and the maximum overvoltage is 1.44pu;

[0077] When a single-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.42pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.16pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.42pu;

[0078] When a single-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.40pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.29pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.20pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.40pu.

[0079] Furthermore, the specific method of introducing two-phase grounding faults at the four endpoints of the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the end of the line using the distributed parameter model to simulate the overvoltage situation includes:

[0080] When a two-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 0.99pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.01pu;

[0081] When a two-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.09pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.09pu;

[0082] When a two-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.96pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.13pu, the power frequency overvoltage at the end of the line is 0.99pu, and the maximum overvoltage is 1.13pu;

[0083] When a two-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.02pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.06pu, the power frequency overvoltage at the end of the line is 1.00pu, and the maximum overvoltage is 1.06pu.

[0084] In this embodiment, if Figure 2 As shown in the figure, it is an electrical structure diagram of the detection method of short-circuit grounding power frequency overvoltage of UHV transmission line. In order to study the influence of the position of the fault point in the line on the overvoltage, the double-circuit line between busbars 1-6 is divided into three equal parts of equal length, and the busbars are numbered 2, 3, 4, and 5 respectively. Each section of the line is simulated using a distributed parameter model. Single-phase grounding faults and two-phase grounding faults are introduced to the four points of the line head end, 1 / 3 from the head end, 2 / 3 from the head end, and the end. The overvoltage conditions are shown in Table 1. Table 1 shows the changes of overvoltage at different positions on the line with the fault position.

[0085] Table 1

[0086]

[0087]

[0088] The voltage reference value is

[0089] The instantaneous value of the reference voltage is

[0090] The first segment refers to node 1 and the last segment refers to node 6.

[0091] It can be seen from Table 1 that when the neutral point of the transformer is grounded:

[0092] (1) On the same line, when a ground fault occurs at one point, the power frequency overvoltage at different locations is different; the location where the maximum overvoltage occurs on the line also varies with the location of the fault point.

[0093] (2) When the fault location is the same, the overvoltage caused by two-phase grounding and three-phase disconnection is lower than the overvoltage caused by single-phase grounding and three-phase disconnection.

[0094] (3) Power frequency overvoltage often occurs in the non-fault phase.

[0095] (4) In most cases, due to the presence of high impedance at both ends of the line, the overvoltage tends to be high in the middle and low at both ends.

[0096] Figure 4 and Figure 5 They are the two situations in which the overvoltage is the largest when a single-phase grounding fault occurs and a two-phase grounding fault occurs, namely, the voltage waveforms of the three phases A, B, and C at the maximum overvoltage positions when a single-phase grounding fault occurs at 1 / 3 of the distance from the head end and a two-phase grounding fault occurs at 2 / 3 of the distance from the head end, as well as the voltage waveforms at four positions on the line.

[0097] Furthermore, in S3, taking the fault phase as a reference, assuming the starting time of the fault phase within a cycle as 0s, taking the peak point, the zero-crossing point, and the point between the peak point and the zero-crossing point, introducing a single-phase grounding fault at the corresponding time, and using the distributed parameter model to simulate the overvoltage situation include:

[0098] Take a sine wave as one cycle, the peak is position 1, the trough is position 5, the zero crossing point is position 3, the position between 1 and 3 is position 2, the position between 3 and 5 is position 4, and the point between the trough and the starting point of the next cycle is position 6;

[0099] When a single-phase grounding fault is introduced at position 1, the corresponding time is 0.005s, the voltage of the healthy phase B is 984kV, and the voltage of the healthy phase C is 1071kV;

[0100] When a single-phase grounding fault is introduced at position 2, the corresponding time is 0.008s, the voltage of the healthy phase B is 1090kV, and the voltage of the healthy phase C is 954kV;

[0101] When a single-phase grounding fault is introduced at position 3, the corresponding time is 0.010s, the voltage of the healthy phase B is 915kV, and the voltage of the healthy phase C is 868kV;

[0102] When a single-phase grounding fault is introduced at position 4, the corresponding time is 0.012s, the voltage of the healthy phase B is 1088kV, and the voltage of the healthy phase C is 942kV;

[0103] When a single-phase grounding fault is introduced at position 5, the corresponding time is 0.015s, the voltage of the healthy phase B is 987kV, and the voltage of the healthy phase C is 1066kV;

[0104] When a single-phase grounding fault is introduced at position 6, the corresponding time is 0.017s, the voltage of the healthy phase B is 1092kV, and the voltage of the healthy phase C is 954kV.

[0105] In this embodiment, the vector formula is used in the derivation process of overvoltage. The power frequency overvoltage is often an instantaneous process. At the same time, for the three-phase sinusoidal voltage with a phase difference of 120°, the peak value of the transfer overvoltage has a great relationship with the operating voltage of the system during the grounding or short circuit fault. Therefore, when the grounding or short circuit occurs at different times, the value of the overvoltage also changes to a certain extent.

[0106] When a single-phase is grounded, at the moment of grounding, the fault phase voltage curve is located at a different sine wave position, and the overvoltage of the healthy phase will also change accordingly. Taking the fault phase as the reference, assuming that the starting time of the fault phase in one cycle is 0s, take the peak value, zero crossing point, and several points in the middle to introduce the single-phase grounding fault at the corresponding time. Figure 3 The simulation is performed at positions 1 to 6 in Table 2. Table 2 shows the voltage value of the healthy phase when the fault occurs at the corresponding time of the sine wave. Table 2 shows the overvoltage corresponding to the fault at different times.

[0107] Table 2

[0108] 1 2 3 4 5 6 Time / s 0.005s 0.008s 0.010s 0.012s 0.015s 0.017s Phase B voltage / kV 984 1090 915 1088 987 1092 Phase C voltage / kV 1071 954 868 942 1066 954

[0109] It can be seen from Table 2 that when a single-phase grounding fault occurs in item A, among the healthy phases B and C, when the short-circuit fault occurs at the peak position, the overvoltage value of phase C is relatively large, which is converted into an effective value of 1.19pu. When the short-circuit position is at positions 2, 4, and 6 between the peak and the zero crossing point, the overvoltage of phase B is relatively large, which is converted into an effective value of 1.21pu. When the short-circuit position is at the zero crossing point, the overvoltage of phase B is relatively large, which is converted into an effective value of 1.02pu.

[0110] It can be seen that when the fault occurs at the zero crossing point, the overvoltage problem is the least obvious; the peak position is second, and the overvoltage in the middle position is the largest. The healthy phase where the maximum overvoltage occurs is also related to the time when the fault occurs.

[0111] Furthermore, Figure 1 As shown, it is an electromagnetic simulation principle block diagram of a detection method for short-circuit grounding power frequency overvoltage of an ultra-high voltage transmission line. The double-circuit overhead line is: the voltage level between busbars 1-6 is 1000kV, and the length is 420km.

[0112] In the present invention, in the UHV system, the overvoltage problem seriously affects the insulation performance of the system and the setting of the protection device. The overvoltage caused by the grounding fault is analyzed, and the electromechanical-electromagnetic transient hybrid simulation is performed on the system with the highest voltage level of 1000kV with the help of PSASP software and ETSDAC software. The influence of the fault occurring at different positions on the line on the overvoltage of each point in the system when the single-phase grounding and two-phase grounding faults occur in the 1000kV part of the line in the system is studied, and the influence of the fault occurrence time on the overvoltage is also studied.

[0113] In the present invention, when an asymmetric fault occurs in the system, the zero-sequence current caused by the short circuit will cause the power frequency voltage on the healthy phase to increase. The following is an analysis taking single-phase grounding as an example.

[0114] Figure 6 This is the load sequence network used for calculation of single-phase grounding system. In the figure, Z1, Z2, and Z0 are the positive sequence, negative sequence, and zero sequence impedances seen from the fault point. and They are respectively the positive sequence component, negative sequence component and zero sequence component of the voltage and current in the power grid. It is the phase A voltage (positive sequence) at the fault point during normal operation.

[0115] A phase has a ground fault, and the boundary conditions of the fault point are:

[0116]

[0117]

[0118] The current and voltage satisfy the following relationship:

[0119]

[0120]

[0121]

[0122]

[0123] The voltage of the healthy phase at the fault point is:

[0124]

[0125]

[0126] For systems with larger power capacity, the proportion of the generator in the input impedance is not large, so it can be considered that if the resistance component in each sequence impedance is ignored, the formula can be simplified to:

[0127]

[0128] in:

[0129]

[0130]

[0131] α——grounding coefficient. The value of α is related to the ratio of the zero-sequence reactance to the positive-sequence reactance of the system as seen from the fault point.

[0132] when As it approaches infinity, the voltage region limit of the healthy phase That is, it approaches the system line voltage.

[0133] In high voltage, extra high voltage and ultra high voltage systems, the neutral point is generally directly grounded. When the neutral point is directly grounded or grounded via low impedance, the zero-sequence reactance of the system is inductive, and the positive-sequence reactance of the system is inductive, so X0 / X1 is a positive value. Therefore, the voltage of the healthy phase increases with the increase of the value of K. When the topology of the system is determined, the maximum short-circuit overvoltage at a certain point in the system is theoretically a certain value. However, as the location of the fault point changes, the impedance from the fault point to the inside also changes. When a fault occurs at a certain point, overvoltages will also be generated at different locations on the line and adjacent buses.

[0134] Therefore, in the power frequency overvoltage caused by asymmetric grounding, the overvoltage occurs in the healthy phase. On the same line, when a ground fault occurs at one place, the power frequency overvoltage at different locations is different; the location where the maximum overvoltage occurs on the line also changes with the location of the fault point. And when the fault location is the same, the overvoltage caused by two-phase grounding and three-phase disconnection is lower than the overvoltage caused by single-phase grounding and three-phase disconnection.

[0135] For the overvoltage caused by a single ground fault, when a ground fault occurs at a certain point in a system with a certain structure, the maximum overvoltage is certain; but the actual overvoltage is also related to the time when the fault occurs. When the fault occurs at the zero crossing point, the overvoltage problem is least obvious; the peak position is second, and the overvoltage at the middle position is the largest. And the healthy phase where the maximum overvoltage occurs is also related to the time when the fault occurs.

[0136] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission lines, characterized in that: Overvoltage detection is performed using electromechanical-electromagnetic transient hybrid simulation, including: S1. Number the two busbars as 1 and 6, divide the double-circuit overhead line between busbars 1 and 6 into three equal parts, and number the corresponding busbars at the sections as 2, 3, 4 and 5 respectively; S2, introduce single-phase grounding faults at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and use the distributed parameter model to simulate the overvoltage situation; Two-phase grounding faults are introduced at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end and the line end of each busbar, and the distributed parameter model is used to simulate the overvoltage situation. S3, taking the fault phase as the reference, setting the starting time of the fault phase within one cycle as 0s, taking the peak point, the zero-crossing point, and the point between the peak point and the zero-crossing point, introducing a single-phase grounding fault at the corresponding time, and using a distributed parameter model to simulate the overvoltage situation; S4. According to the simulation results of S2 and S3, the relationship between the ground fault position and the overvoltage, and the relationship between the ground fault occurrence time and the overvoltage are obtained, that is, the overvoltage detection result is obtained.

2. A method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission line according to claim 1, characterized in that: The relationship between the ground fault position and the overvoltage described in S4 includes: On the same line, when a ground fault occurs at one location, the power frequency overvoltage at different locations is different; When the location of the ground fault changes, the location where the maximum overvoltage occurs on the line also changes; When the fault location is the same, the overvoltage caused by two-phase grounding and three-phase disconnection is lower than the overvoltage caused by single-phase grounding and three-phase disconnection; The power frequency overvoltage occurs in the non-fault phase; On a line, the overvoltage tends to be higher in the middle and lower at both ends.

3. The method for detecting short-circuit grounding power frequency overvoltage of a UHV transmission line according to claim 1, characterized in that: The relationship between the ground fault occurrence time and the overvoltage described in S4 includes: When the fault occurs at the zero crossing point, the overvoltage is the lowest; When the fault occurs at the peak position, the overvoltage is greater than the overvoltage at the zero-crossing fault; When the fault occurs in the middle position, the overvoltage is the highest; The healthy phase where the maximum overvoltage occurs is related to the time when the fault occurs.

4. The method for detecting short-circuit grounding power frequency overvoltage of a UHV transmission line according to claim 1, characterized in that: S2 introduces a single-phase grounding fault at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end, and the line end, and uses a distributed parameter model to simulate the overvoltage situation. The specific method includes: When a single-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.08pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.06pu, the power frequency overvoltage at the end of the line is 1.08pu, and the maximum overvoltage is 1.08pu; When a single-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.21pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.44pu, and the power frequency overvoltage at the end of the line is 1.03pu, and the maximum overvoltage is 1.44pu; When a single-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.42pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.16pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.42pu; When a single-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.40pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.29pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.20pu, the power frequency overvoltage at the end of the line is 1.06pu, and the maximum overvoltage is 1.40pu.

5. The method for detecting short-circuit grounding power frequency overvoltage of a UHV transmission line according to claim 1, characterized in that: S2 introduces two-phase grounding faults at the line head end, 1 / 3 of the distance from the head end, 2 / 3 of the distance from the head end, and the line end, and uses a distributed parameter model to simulate the overvoltage situation. The specific method includes: When a two-phase grounding fault is introduced at the beginning of the line, the power frequency overvoltage at the beginning of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 1.01pu, the power frequency overvoltage at 2 / 3 of the distance from the beginning is 0.99pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.01pu; When a two-phase grounding fault is introduced at 1 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.97pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.09pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at the end of the line is 0.97pu, and the maximum overvoltage is 1.09pu; When a two-phase grounding fault is introduced at 2 / 3 of the distance from the head end, the power frequency overvoltage at the head end of the line is 0.96pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.04pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.13pu, the power frequency overvoltage at the end of the line is 0.99pu, and the maximum overvoltage is 1.13pu; When a two-phase grounding fault is introduced at the end of the line, the power frequency overvoltage at the head end of the line is 1.02pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.03pu, the power frequency overvoltage at 2 / 3 of the distance from the head end is 1.06pu, the power frequency overvoltage at the end of the line is 1.00pu, and the maximum overvoltage is 1.06pu.

6. A method for detecting power frequency overvoltage of short-circuit grounding of ultra-high voltage transmission line according to claim 1, characterized in that: S3 takes the fault phase as the reference, assumes the starting time of the fault phase in one cycle as 0s, takes the peak point, the zero-crossing point, and the point between the peak point and the zero-crossing point, introduces a single-phase grounding fault at the corresponding time, and uses the distributed parameter model to simulate the overvoltage situation. The specific method includes: Take a sine wave as one cycle, the peak is position 1, the trough is position 5, the zero crossing point is position 3, the position between 1 and 3 is position 2, the position between 3 and 5 is position 4, and the point between the trough and the starting point of the next cycle is position 6; When a single-phase grounding fault is introduced at position 1, the corresponding time is 0.005s, the voltage of the healthy phase B is 984kV, and the voltage of the healthy phase C is 1071kV; When a single-phase grounding fault is introduced at position 2, the corresponding time is 0.008s, the voltage of the healthy phase B is 1090kV, and the voltage of the healthy phase C is 954kV; When a single-phase grounding fault is introduced at position 3, the corresponding time is 0.010s, the voltage of the healthy phase B is 915kV, and the voltage of the healthy phase C is 868kV; When a single-phase grounding fault is introduced at position 4, the corresponding time is 0.012s, the voltage of the healthy phase B is 1088kV, and the voltage of the healthy phase C is 942kV; When a single-phase grounding fault is introduced at position 5, the corresponding time is 0.015s, the voltage of the healthy phase B is 987kV, and the voltage of the healthy phase C is 1066kV; When a single-phase grounding fault is introduced at position 6, the corresponding time is 0.017s, the voltage of the healthy phase B is 1092kV, and the voltage of the healthy phase C is 954kV.

7. A method for detecting power frequency overvoltage caused by short circuit and grounding of an ultra-high voltage transmission line according to any one of claims 1 to 6, characterized in that: The double-circuit overhead line has a voltage level of 1000 kV between busbars 1-6 and a length of 420 km.

Images