Design method considering typical external overvoltage ZnO valve plate impact tolerance test current waveform

Abstract

The invention discloses a design method for a ZnO valve plate impact tolerance test current waveform considering typical external overvoltage, and the method comprises the steps: S1, drawing up a lightning overvoltage working condition according to a research demand, and analyzing system parameters and equipment parameters needed for building an electromagnetic transient simulation model; s2, building a high-frequency model required by lightning overvoltage simulation, wherein the high-frequency model comprises a high-frequency equivalent model of each key device and a lightning current source; s3, simulating the impulse current in the lightning arrester under the lightning overvoltage fault simulated by the actual lightning parameters; and S4, analyzing the wavefront time and the wave tail time of the impact current in the lightning arrester under each lightning overvoltage fault, and drawing up the wavefront time and the wave tail time of the impact current in combination with test conditions for the impact tolerance test of the ZnO valve plate. According to the method, the impact tolerance performance, the aging characteristic and the damage form of the valve plate / lightning arrester can be researched more close to the actual situation, and the failure problem of the lightning arrester can be analyzed.

Description

Technical Field

[0001] The invention relates to the field of overvoltage and insulation coordination of power systems, and in particular to a design method for a current waveform of a ZnO valve plate impulse withstand test taking into account a typical external overvoltage. Background Art

[0002] The impulse withstand test is an important way to study and analyze the state and performance of the arrester of the corresponding type of ZnO valve. Lightning overvoltage is one of the main reasons for the failure of arresters such as line arresters and distribution arresters. For this type of arrester, the waveform design of the impulse test mainly includes the wavefront time and wave tail time of the lightning current. Since most lightning currents in nature are negative polarity, the currents used to study lightning impulses in the test are designed to be negative polarity. At present, when various teams conduct impulse withstand tests on ZnO valves, they mostly use negative polarity 8 / 20μs impulse currents to conduct lightning impulse withstand tests based on IEC 60099-4:2014. Only a few teams conduct impulse aging tests on valves under negative polarity impulse currents of 4 / 10μs. Based on the commonly used impulse currents in current engineering design and experimental research, the main current waveforms used are 8 / 20μs and 4 / 10μs, and the impulse currents used in the test are mostly negative polarity.

[0003] At present, the existing technology mainly studies the impact tolerance performance, aging characteristics and damage forms of ZnO valve plates / lightning arresters through impact aging tests, and often uses a negative polarity current with a waveform of 8 / 20μs, and a few use a negative polarity current with a waveform of 4 / 10μs. However, in the operation of actual projects, there has been a failure in which the entire lightning arrester failed due to the side flash of the ZnO valve plate after the AC side line arrester of the converter station suffered three lightning strikes with a current amplitude that did not exceed the lightning resistance level. According to the existing aging mechanism research, it can no longer accurately explain the phenomenon that the lightning arrester still fails even though the lightning current amplitude does not exceed the lightning resistance level. By reproducing the impact current in the lightning arrester when the fault occurs in the PSCAD electromagnetic transient simulation software and analyzing the waveform characteristics of the current, it is found that the wavefront time of the current flowing through the lightning arrester is mostly less than 1μs, and the wave tail time is also small, which is quite different from the 8 / 20μs used to simulate lightning impulses in the impact aging test. Therefore, only the impulse test waveform specified in the existing standards to study and analyze the impulse tolerance performance, aging characteristics and damage forms of ZnO valve plates / arrester can no longer meet the fault analysis needs in actual projects, such as the aging characteristics of the arrester under the action of steep waves with a wavefront time of less than 1μs. Therefore, it is urgent to analyze the wavefront time and wave tail time of the impulse current flowing through the arrester under external overvoltage conditions, and use this as a basis to more finely design the current waveform of the ZnO valve plate impulse tolerance test. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, an object of the present invention is to provide a design method for a current waveform of a ZnO valve plate impulse withstand test taking into account a typical external overvoltage.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A design method for a current waveform of a ZnO valve plate impulse withstand test considering a typical external overvoltage, comprising:

[0007] S1. Formulate lightning overvoltage conditions according to research requirements, and analyze the system parameters and equipment parameters required to build an electromagnetic transient simulation model;

[0008] S2. Build the high-frequency model required for lightning overvoltage simulation, including the high-frequency equivalent model of each key equipment and the lightning current source;

[0009] S3, simulating the impact current in the arrester under the lightning overvoltage fault simulated by the actual lightning parameters;

[0010] S4. Analyze the wavefront time and wavetail time of the impulse current in the arrester under each lightning overvoltage fault, and formulate the wavefront time and wavetail time of the impulse current in combination with the test conditions for the ZnO valve plate impulse tolerance test.

[0011] Furthermore, the lightning overvoltage operating condition is a severe lightning overvoltage operating condition.

[0012] Furthermore, the key equipment includes transmission lines, poles and towers, insulator strings and flashover criteria, smoothing reactors, converter valves, circuit breakers and disconnectors.

[0013] Furthermore, the high-frequency model required for lightning overvoltage simulation is specifically constructed as follows:

[0014] The transmission line adopts a frequency-dependent model and does not consider the corona effect of the line;

[0015] The tower adopts a multi-conductor layered wave impedance model;

[0016] The insulator string and flashover criterion are simulated by ideal controllable switch parallel capacitor;

[0017] Other equipment in the converter station adopts the Bergeron model.

[0018] Furthermore, the high-frequency model of the converter valve is constructed according to the actual structure and parameters of the converter valve, and the calculation of the stray capacitance of the internal equipment of the valve hall is ignored.

[0019] Further, the impulse current in the arrester under the simulated lightning overvoltage fault in S3 is specifically:

[0020] The impulse current in the arrester under the lightning overvoltage fault is simulated and calculated, and the waveform parameters of the impulse current are recorded. The waveform parameters include the return stroke sequence number, the current amplitude, the current wave front time and the current wave tail time.

[0021] Furthermore, the frequency characteristics of multiple lightning strikes are determined according to the area where the lightning arrester is located, and the impulse current parameters in the lightning arrester during single lightning / multiple lightning strike faults are recorded.

[0022] Furthermore, the lightning current source waveform includes a Heidler waveform and a double exponential waveform.

[0023] Further, the S4 analyzes the wavefront time and wavetail time of the impulse current in the arrester under the lightning overvoltage fault simulated by each actual lightning parameter, and formulates the wavefront time and wavetail time of the impulse current in combination with the test conditions, specifically:

[0024] Based on the simulation results in S3, the range of impulse current wave front time and wave tail time in different arresters under the same type of fault is analyzed;

[0025] Based on the range of impulse current wavefront time and wavetail time, combined with the existing test conditions and the output range of the generator, the impulse current for the ZnO valve plate impulse aging test is proposed.

[0026] Furthermore, when the test conditions permit, when studying the impulse withstand performance of the arrester, a lightning impulse withstand test is carried out using a negative polarity 8 / 20μs impulse current in accordance with IEC 60099-4:2014, and at the same time, an impulse aging test is carried out on the valve plates of the same type of arrester using the withstand test current waveform determined by this method.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The design method of the present invention comprehensively considers the wavefront time and wavetail time of the impulse current in the ZnO valve plate under the action of typical external overvoltage, supplements the analysis of the wavefront time and wavetail time of the impulse current in the ZnO valve plate under multiple lightning impulses, and designs an impulse current waveform that is more in line with the actual fault situation for the impulse aging test of the ZnO valve plate, which is used to analyze the aging characteristics of the ZnO valve plate under lightning overvoltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart for realizing the design method of the ZnO valve plate impulse withstand test waveform considering the typical external overvoltage;

[0030] Figure 2 Schematic diagram of a multi-conductor layered wave impedance model of a DC transmission line tower, wherein (a) is a schematic diagram of a multi-conductor layered wave impedance model of a tension tower, and (b) is a schematic diagram of a multi-conductor layered wave impedance model of a straight tower;

[0031] Figure 3 It is a schematic diagram of the multi-conductor layered wave impedance model of the transmission line tower on the AC side of the converter station;

[0032] Figure 4 It is the equivalent model of the smoothing reactor in PSCAD simulation;

[0033] Figure 5 It is the equivalent model of the converter valve in PSCAD simulation, where (a) is the schematic diagram of the valve on state and (b) is the schematic diagram of the valve off state;

[0034] Figure 6 It is a high-frequency model of a converter station for lightning intrusion wave simulation;

[0035] Figure 7 It is a model of lightning current source, where (a) is a schematic diagram of double exponential current source and (b) is a schematic diagram of 1 / 200μs Heidler current source. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

[0037] Example

[0038] like Figure 1 As shown, a design method for a current waveform of a ZnO valve plate impulse withstand test considering a typical external overvoltage includes the following steps:

[0039] S1. Formulate lightning overvoltage conditions according to research requirements, and analyze the system parameters and equipment parameters required to build an electromagnetic transient simulation model; the equipment parameters specifically refer to the equipment that will be affected by the lightning intrusion wave, namely the key equipment, and the system parameters refer to the rated parameters of the AC system and the DC system, which are reflected in the setting of the parameters of the equivalent power supply when modeling the lightning overvoltage.

[0040] In this embodiment, the rated DC voltage of the DC system is ±800kV, the rated power is 5000MW, and the minimum power is 500MW; the normal continuous operating voltage range of the AC busbars of the sending-end converter station and the receiving-end converter station is 500kV-550kV, the extreme continuous operating voltage range is 475kV-550kV, and the normal operating frequency range is 50±0.2Hz.

[0041] S2. Build the high-frequency model required for lightning overvoltage simulation, including the high-frequency equivalent model of each key equipment and the lightning current source;

[0042] S3, simulating the impact current in the arrester under the lightning overvoltage fault simulated by the actual lightning parameters;

[0043] S4. Analyze the wavefront time and wavetail time of the impulse current in the arrester under each lightning overvoltage fault, and formulate the wavefront time and wavetail time of the impulse current based on the test conditions.

[0044] Further, step S1 formulates lightning overvoltage conditions according to research requirements and analyzes the parameters required to build an electromagnetic transient simulation model. Specifically, according to the requirements of engineering design, fault analysis, etc., combined with the actual parameters and topology of the project and lightning arrester, the system rated parameters, high-frequency equivalent model parameters of each key device and related parameters of lightning current required to build an electromagnetic transient simulation model are analyzed.

[0045] The parameters of the lightning current include the wave front time / wave tail time, amplitude, time interval between each ground lightning in multiple return lightning, and frequency of multiple return lightning.

[0046] Generally speaking, when an overhead line is struck back, most of the lightning current will flow into the ground through the tower or through the lightning conductor. Even if the insulator breaks down, only a small part of the current will flow through the conductor to the equipment in the station. When the line is struck by a shielding failure, most of the lightning current will invade the station through the conductor before the insulator flashes over. After the flashover, part of the lightning current will enter the ground through the tower or lightning conductor. It can be seen that the shielding failure intrusion wave generally has a greater impact on the equipment in the station. Therefore, the typical lightning overvoltage condition proposed in this embodiment is a severe lightning overvoltage, that is, the lightning shielding failure is the closest to the tower of the converter station. When building an electromagnetic transient model for simulation, it is necessary to perform high-frequency simulation of transmission lines, towers, smoothing reactors, converter valves, circuit breakers, disconnectors and other equipment.

[0047] Furthermore, step S2 builds a high-frequency calculation model for simulating external overvoltage (lightning overvoltage) according to the high-frequency requirements of lightning overvoltage simulation, providing support for the subsequent analysis of the waveform characteristics of the impulse current in the arrester.

[0048] The specific simulation method is as follows:

[0049] (1) Transmission lines

[0050] When studying the influence of lightning intrusion waves, the frequency response characteristics of the line need to be fully considered. Therefore, the line models in the simulation of this embodiment all use the frequency-dependent (phase) model (Frequency-Dependent (Phase) model). At the same time, because the corona effect of the line will increase the stray capacitance between the wire and the ground and between the wires, thereby reducing the amplitude and steepness of the lightning intrusion wave, from a conservative point of view, this embodiment does not consider the corona effect of the line.

[0051] (2) Tower

[0052] In lightning protection calculations, the selection of tower models will directly affect the accuracy of the calculation results. In the research process of this embodiment, a multi-conductor layered wave impedance model is used to analyze the stress characteristics of the arrester under lightning overvoltage conditions. The ground wire suspension methods of the DC transmission line straight tower and the tension tower are different, so the equivalent models used for calculation are also different. The multi-layer wave impedance models of the DC side and AC side line towers are as follows: Figure 2 and Figure 3 As shown, Figure 2 Figure (a) is a schematic diagram of the multi-conductor layered wave impedance model of the tension tower, and Figure (b) is a schematic diagram of the multi-conductor layered wave impedance model of the straight tower. Tables 1 and 2 show the wave impedance calculation values ​​of the multi-conductor layered wave impedance model of the DC line and the AC side tower of the converter station.

[0053] Table 1 Main materials and cross arm wave impedance of DC system tension tower and straight tower (Ω)

[0054]

[0055] Table 2 Main materials and cross arm wave impedance of AC system tension tower and linear tower (Ω)

[0056]

[0057] (3) Insulator string and flashover criteria

[0058] When calculating the lightning withstand level of transmission lines, the simulation of the insulator string and the accurate selection of the flashover criterion directly affect the size and waveform of the overvoltage invading the converter station. The model of the insulator string can be simulated by an ideal controllable switch parallel capacitor. When the insulator string does not flash over, the switch is open, and there is capacitance between the tower and the conductor due to coupling; when the insulator string flashes over, the switch is closed. Considering that the coupling capacitance between the conductor and the tower and the equivalent capacitance at both ends of the insulator are small, in the simulation, the insulator is simulated by an ideal controllable switch. There are four commonly used insulator lightning flashover criteria, namely U 50％ Method, volt-second characteristic definition method, volt-second characteristic intersection method and leader development method. This embodiment selects the currently more commonly used CIGRE leader development method as the lightning flashover criterion for insulators.

[0059] (4) Smoothing Reactor

[0060] The smoothing reactor is located between the DC transmission line and the converter valve, which can effectively reduce the impact of lightning overvoltage intrusion into the station. However, its reflection will also cause the pole line overvoltage to increase. At the same time, there is an uneven voltage distribution between the two series-connected smoothing reactors during actual operation. Therefore, it is necessary to reasonably and accurately model the smoothing reactor in the simulation calculation. According to the model provided by the manufacturer, the smoothing reactor needs to consider the end-to-ground capacitance and the end-to-end capacitance during calculation. In order to simulate the most serious working conditions, the resistance in series with the stray capacitance between the end-to-ground and end-to-end is not considered in the study of this embodiment. The model of the smoothing reactor used in the PSCAD simulation is as follows: Figure 4 The model parameters are shown in Table 3.

[0061] Table 3 Smoothing reactor model parameters

[0062] Component Number parameter Component Number parameter Component Number parameter <![CDATA[C e1 ]]> 150pF <![CDATA[C n1 ]]> 400 pF <![CDATA[L1]]> 76.5mH <![CDATA[C e2 ]]> 150pF <![CDATA[C n2 ]]> 400pF <![CDATA[L2]]> 76.5mH <![CDATA[C e3 ]]> 310pF <![CDATA[R1]]> 2000Ω — — <![CDATA[C e4 ]]> 310pF <![CDATA[R2]]> 2000Ω — —

[0063] (5) Flow control valve

[0064] When the converter station area is hit by a lightning intrusion wave, the lightning overvoltage will hardly intrude into the valve hall due to the configuration of a smoothing reactor on the DC side and the existence of a converter transformer on the AC side. This embodiment focuses on studying the impact of lightning intrusion waves on the electrical stress characteristics of the arrester. Therefore, detailed stray parameter calculation and modeling of the internal equipment of the valve hall are not performed. Based on the actual structure and parameters of the converter valve, a simulation model of the converter valve is built, such as Figure 5 As shown, (a) is a schematic diagram of valve conduction, and (b) is a schematic diagram of valve shutdown.

[0065] (6) Other equipment in converter station

[0066] The equivalent frequency of lightning intrusion waves is high and the duration is short. The transformers, circuit breakers, disconnectors and other equipment in the substation can be equivalent to the inlet capacitance. The equivalent capacitances of each device are separated by distributed parameter lines. This embodiment uses the Bergeron Model for simulation. The average geometric dimensions between the main equipment are calculated, and the polar line wave impedance is 325Ω and the neutral bus wave impedance is 342Ω. The equivalent inlet capacitances of each device in the study of this embodiment are shown in Table 4.

[0067] Table 4 Equivalent inlet capacitance of equipment in converter station (pF)

[0068] Device Name Inlet capacitance Pillar insulation 150 Wall Bushing 300 Voltage Divider 300 Disconnector 300 / 150(closed / open) breaker 300

[0069] According to the type of overvoltage, a typical fault condition is proposed. A lightning strike with a large impact on the line arrester and the station arrester is a shielding strike, and fault parameters such as shielding strike position and lightning current parameters need to be proposed. For example, in this embodiment, according to the attenuation characteristics of the lightning intrusion wave, multiple lightning shielding strikes are proposed on the #1 tower (hereinafter referred to as #1 tower) closest to the converter station on the DC side of the converter station. The lightning current amplitude adopts the maximum shielding strike current of 20kA calculated according to the actual parameters of the tower and the electrical geometry model. The lightning current waveform parameters adopt the actual lightning current parameters obtained by artificial lightning induction in Guangdong. Since the lightning current parameters of the first lightning strike are not obtained by artificial lightning induction, the parameters of the first lightning strike in Table 5 are the first lightning strike parameters in IEC 62305-1 (the first negative polarity lightning strike is 1 / 200μs), and the subsequent return stroke parameters are all parameters of actual multiple return strokes to ground lightning.

[0070] Table 5 Current waveform parameters of 2nd to 5th return-to-ground lightning

[0071]

[0072] In this embodiment, the specific steps of step S2 for building a high-frequency model required for lightning overvoltage simulation, including high-frequency equivalent models of key equipment and lightning current sources, are as follows: According to the simulation method and rated parameters of each equipment analyzed in S1, a high-frequency model capable of simulating lightning overvoltage is built. Figure 6 This is the 7-tower model on the DC side of the converter station. Figure 7 Figures (a) and (b) are schematic diagrams of the lightning current source model of the Heidler waveform and the double exponential waveform, respectively. (a) consists of a double exponential waveform generator, a current source, and a channel resistance of 800Ω during shielding failure. The double exponential waveform generator can simulate double exponential waves with different wave front times and wave tail times; (b) is based on the Heidler function, combined with the current source and the shielding failure channel resistance. According to the propagation characteristics of lightning intrusion waves and the existing research basis, 7 towers are usually built near substations / converter stations for related research on lightning current intrusion waves.

[0073] In this embodiment, the specific steps of simulating the surge current in the arrester under the lightning overvoltage fault in step S3 are as follows:

[0074] The impulse current in the arrester under a typical overvoltage fault is simulated and calculated, and the waveform parameters of the current are recorded. In this embodiment, when a severe lightning shielding fault occurs on the DC side of the converter station #1 tower 5, the parameters related to the impulse current in the arrester are shown in Table 6.

[0075] Table 6 Impact current in the arrester when 5 heavy lightning strikes the DC side pole line

[0076]

[0077] In the present embodiment, the wavefront time and wave tail time of the impulse current in the arrester under the overvoltage fault are analyzed in step S4, and the specific steps of formulating the wavefront time and wave tail time of the impulse current in combination with the test conditions are as follows: according to the current waveform parameters of each type of arrester obtained by simulation calculation in step S3, the wavefront time and wave tail time of the impulse current in the arrester under the studied overvoltage type are analyzed, and the impulse current waveform for the test is formulated according to the test conditions. In the present embodiment, Table 6 is the situation of the impulse current in the arrester during the 5-weight lightning shielding fault, combined with the simulation results of the impulse current in the arrester during the 2-weight lightning, 3-weight lightning and 4-weight lightning faults, it can be analyzed that when the actual subsequent return stroke waveform is used as the multiple lightning current waveform, the waveform of the impulse current in the D-type arrester is close to 1 / 2μs, the waveform of the impulse current in the Fdc1-type arrester is close to 5 / 11μs, and the waveform of the impulse current in the Fdc2-type arrester is close to 180 / 330μs. Therefore, when the test conditions permit, when studying the lightning withstand performance of the DC area arrester in the converter station, in addition to the impulse aging test using a current of 8 / 20μs, an impulse aging test of 1 / 2μs can be added to the valve plate of the D-type arrester, an impulse aging test of 5 / 11μs can be added to the Fdc1-type arrester, and an impulse aging test of 180 / 330μs can be added to the Fdc2-type arrester.

[0078] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A design method for the current waveform of a ZnO valve plate impulse withstand test considering a typical external overvoltage, characterized in that: include: S1. Formulate lightning overvoltage conditions according to research requirements, and analyze the system parameters and equipment parameters required to build an electromagnetic transient simulation model; S2. Build the high-frequency model required for lightning overvoltage simulation, including the high-frequency equivalent model of each key equipment and the lightning current source; S3, simulating the impact current in the arrester under the lightning overvoltage fault simulated by the actual lightning parameters; S4. Analyze the wavefront time and wavetail time of the impulse current in the arrester under each lightning overvoltage fault, and formulate the wavefront time and wavetail time of the impulse current in combination with the test conditions for the ZnO valve plate impulse tolerance test.

2. The design method according to claim 1, characterized in that: The lightning overvoltage operating condition is a severe lightning overvoltage operating condition.

3. The design method according to claim 2, characterized in that: The key equipment includes transmission lines, poles and towers, insulator strings and flashover criteria, smoothing reactors, converter valves, circuit breakers and disconnectors.

4. The design method according to claim 3, characterized in that: The high-frequency model required for lightning overvoltage simulation is specifically: The transmission line adopts a frequency-dependent model and does not consider the corona effect of the line; The tower adopts a multi-conductor layered wave impedance model; The insulator string and flashover criterion are simulated by ideal controllable switch parallel capacitor; Other equipment in the converter station adopts the Bergeron model.

5. The design method according to claim 4, characterized in that: The high-frequency model of the converter valve is constructed according to the actual structure and parameters of the converter valve, and the calculation of the stray capacitance of the internal equipment of the valve hall is ignored.

6. The design method according to claim 1, characterized in that: The impulse current in the arrester under the simulated lightning overvoltage fault in S3 is specifically: The impulse current in the arrester under the lightning overvoltage fault is simulated and calculated, and the waveform parameters of the impulse current are recorded. The waveform parameters include the return stroke sequence number, the current amplitude, the current wave front time and the current wave tail time.

7. The design method according to claim 6, characterized in that: Determine the frequency characteristics of multiple lightning strikes based on the area where the lightning arrester is located, and record the impulse current parameters in the lightning arrester during single lightning / multiple lightning strike failures.

8. The design method according to claim 1, characterized in that: The lightning current source waveform includes a Heidler waveform and a double exponential waveform.

9. The design method according to any one of claims 1 to 8, characterized in that: The S4, analyzing the wavefront time and wavetail time of the impulse current in the arrester under the lightning overvoltage fault simulated by each actual lightning parameter, and formulating the wavefront time and wavetail time of the impulse current in combination with the test conditions, specifically: Based on the simulation results in S3, the range of impulse current wave front time and wave tail time in different arresters under the same type of fault is analyzed; Based on the range of impulse current wavefront time and wavetail time, combined with the existing test conditions and the output range of the generator, the impulse current for the ZnO valve plate impulse aging test is proposed.

10. The design method according to claim 9, characterized in that: When the test conditions permit, when studying the impulse withstand performance of the arrester, a lightning impulse withstand test is carried out using a negative polarity 8 / 20μs impulse current in accordance with IEC 60099-4:2014. At the same time, an impulse aging test is carried out on the valve plates of the same type of arrester using the withstand test current waveform determined by this method.

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