Method for judging opening and closing states of isolating switch based on transient potential and current of shell

Abstract

The invention discloses an isolating switch opening and closing state judgment method based on shell transient potential and current, judgment is carried out through data of a GIS shell, and the method comprises the steps that S1, a transient circuit in a GIS is established; s2, establishing a GIS external transient circuit; s3, performing TEV simulation calculation generated by GIS isolation switch operation; and S4, judging the opening and closing positions of the isolating switch based on the transient potential and current of the shell. According to the disconnecting switch opening and closing state judgment method based on the transient potential and current of the shell, the opening and closing state of the disconnecting switch is judged by comparing different TEV characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of disconnector opening and closing state judgment, and particularly relates to a disconnector opening and closing state judgment method based on shell transient potential and current. Background Art

[0002] When a disconnector switches, the slow movement of the contacts and the lack of arc extinguishing devices can cause multiple re-breakdowns between them. Due to the capacitive and inductive characteristics of electrical components, each re-breakdown generates transient voltage waves with multiple frequency components on the line. As these voltage waves propagate, they refract and reflect when encountering nodes with discontinuous impedance. After multiple refractions and reflections, they ultimately form a fast transient overvoltage (VFTO).

[0003] VFTO is characterized by high amplitude, multiple frequency components, steep slope, and short duration. Its amplitude can reach 2.5 pu, its frequency typically ranges from a few kHz to hundreds of MHz, and its wavefront is approximately 3 to 20 ns. These characteristics of VFTO can potentially damage the insulation of GIS components and winding-carrying equipment, such as transformers. Disconnector operation has caused insulation breakdown in both China and abroad, all due to high-amplitude VFTO generated during disconnector operation. For example, in 2001, a main transformer at a local power plant was damaged, which was likely caused by VFTO. In 2009, a 500 kV GIS in China exploded when the disconnector was operated. In the early stages of operation at a Brazilian substation, VFTO generated during routine disconnector operation caused a 500 kV oil-paper bushing explosion and transformer failure. Therefore, VFTO is a significant factor affecting the insulation of substation equipment.

[0004] The connection between GIS and casing belongs to the multi-conductor transmission line model, such as Figure 1 As shown in the figure: the first transmission line, Z1, is formed between the outer surface of the busbar and the inner surface of the casing; the second transmission line, Z2, is formed between the outer surface of the casing and the ground; and the third transmission line, Z3, is formed between the overhead line and the ground. Due to the high-frequency characteristics of electromagnetic waves, most of them are confined to the interior of the GIS casing. When the VFTO propagates to the connection between the GIS and the bushing, a portion of the voltage wave is coupled to the outside of the GIS, resulting in voltage waves at Z2 and Z3. The voltage wave at Z2 causes a transient casing voltage increase, or TEV. High-frequency transient currents in the casing flow through the grounding wire into the ground grid, creating a potential difference between the grounding points. Since the secondary cable is grounded at both ends, this potential difference is coupled to the core through the transfer impedance between the cable sheath and the core. This transient voltage wave is then propagated into the secondary system, potentially damaging secondary equipment. Substation accidents caused by TEV are also common and account for a significant proportion of accidents.

[0005] Currently, the IEC insulation coordination standard has not yet determined the typical waveform and standard withstand voltage for the VFTO test, nor has it set numerical specifications for the TEV standard. VFTO is generally compared with the lightning impulse withstand voltage level, while TEV is described as the transient electromagnetic field generated by it, as long as it does not cause interference to secondary equipment. It is recommended that the TEV amplitude generated by the disconnector operation should not exceed 50kV.

[0006] TEV is generated by the operation of the disconnector in the GIS. During the opening and closing process, TEV will show different differences. The opening and closing status of the disconnector can be judged by comparing the differences in TEV characteristics. Summary of the Invention

[0007] The main purpose of the present invention is to provide a method for judging the opening and closing state of an isolating switch based on the transient potential and current of the shell, and to judge the opening and closing state of the isolating switch by comparing the differences in TEV characteristics.

[0008] To achieve the above objectives, the present invention provides a method for determining the opening and closing status of an isolating switch based on the transient potential and current of the housing. The method is performed using data from the GIS housing and includes the following steps:

[0009] Step S1: Establishing the internal transient circuit of GIS;

[0010] Step S2: Establishing the GIS external transient circuit;

[0011] Step S3: performing TEV simulation calculations generated by GIS disconnector operation;

[0012] Step S4: Determine the opening and closing position of the disconnector based on the transient potential and current of the housing.

[0013] As a further preferred technical solution of the above technical solution, step S1 is specifically implemented as follows:

[0014] Step S1.1: Establish a transient model of the concentrated inductor (the circuit model of the inductor is as follows Figure 2 shown):

[0015] For the lumped parameter inductor L, the inductor voltage drop u L (t) and the current i flowing through km (t) The following relationship exists:

[0016]

[0017] Using numerical calculation methods, time is discretized into a series of time periods with small time intervals Δt, and according to u at time t-Δt, L (t-Δt) and ikm (t-Δt) to find u at time t L (t) and i km (t), so we rewrite the above formula into an integral form from t-Δt to t, and further solve it to get:

[0018]

[0019] After integrating the right side of the above equation using the trapezoidal method, we can obtain:

[0020]

[0021] And u L (t) = u k (t)-u m (t), The above formula can be written as:

[0022]

[0023] Thus, we obtain ( Figure 3 The corresponding equivalent circuit shown in

[0024] (Depend on Figure 3 It can be seen that the equivalent circuit only contains the resistor R L and current source I L (t-Δt), further using the above formula Find the current i at the previous moment km (t-Δt), and thus the recursive formula of the current source is:

[0025]

[0026] Step S1.2: Establish a concentrated capacitor transient model (according to the derivation method of the concentrated inductor transient model in the previous article, the capacitor is also equivalent to a Norton circuit in the form of a resistor and a current source in parallel. The equivalent calculation circuit is as follows Figure 4 shown):

[0027] The recursive formula for the current source is

[0028]

[0029] In the formula is an equal value resistor;

[0030] Step S1.3: Establish a lumped resistor transient model (the derivation method of the lumped resistor transient model is the same as above, the only difference in the equivalent model is that the lumped resistor has no current source, or the current source is regarded as 0);

[0031] Step S1.4: Establish the Bergeron equivalent model of the busbar ( Figure 5 (a) shows a uniform lossless transmission line):

[0032] For a uniform lossless transmission line, its length is l, its wave impedance is Z, and the voltage and current at the beginning (x = 0) and the end (x = l) are u k (t),u m (t), i km (t), i mk (t), the positive direction of the current at the terminal is assumed to flow from the terminal to the circuit;

[0033] According to wave theory, the forward mixed wave emitted by the head end at time t-τ will reach the end of the line at time t. Therefore, the voltage and current at the end of the line at time t are expressed by the voltage and current at the head end at time t-τ, that is:

[0034] u k (t-τ)+Zi km (t-τ)=u m (t)+Z[-i mk (t)];

[0035] That is:

[0036]

[0037] If the order:

[0038]

[0039] get:

[0040]

[0041] According to the above formula (such as Figure 5 (b) The equivalent calculation circuit of the line end m at time t, where Z is equal to the resistance of the line wave impedance, is calculated as L and C are the unit inductance and unit capacitance to ground of the line respectively. m (t-τ) is the equivalent historical current source, which is the voltage u at the beginning of the line at time t-τ k (t-τ) and current i km (t-τ) decision;

[0042] Similarly, according to the concept of reverse mixed waves, the voltage and current at endpoint k at time t are expressed as the voltage and current at endpoint m at time t-τ, which can be written in the form of a Norton circuit as follows:

[0043]

[0044] According to the above formula (such as Figure 5(b) The equivalent circuit of the wire endpoint k at time t, the equivalent calculation formula and Combined with each other, a complete transient equivalent calculation circuit for single-phase uniform lossless line is formed;

[0045] (Using the derivation method of the recursive formula of the equivalent current source of concentrated inductance and concentrated capacitance above, the recursive formula of the equivalent current source of the single-phase uniform lossless line is obtained in the same way:

[0046]

[0047] As a further preferred technical solution of the above technical solution, step S2 is specifically implemented as follows: Step S2.1: (by Figure 7 It can be seen that there is electromagnetic coupling between the shells of GIS. Due to the horizontal arrangement of the shells, the shell wave impedance matrix is ​​symmetrical. The symmetrical component method is used to convert the wave impedance matrix from phasor to modulus through phase-mode transformation to eliminate the coupling between them:

[0048] The GIS three-phase shell wave impedance matrix is:

[0049]

[0050] After phase transformation:

[0051]

[0052] Among them, ZA, ZB, and ZC are the wave impedances of the three-phase shells of A, B, and C after transformation, respectively. The formula is:

[0053]

[0054]

[0055] Where, Z2 is the shell self-wave impedance; Z 21 is the mutual wave impedance between the shells of phases A and B or phases B and C; Z 22 is the mutual wave impedance between the A and C phase shells, and the calculation formulas are as follows:

[0056] The calculation formula of self-wave impedance is:

[0057]

[0058] Where h is the height of the shell above the ground, and r is the outer radius of the shell;

[0059] The calculation formula of mutual wave impedance is:

[0060]

[0061] Where Dkm is the distance between the mirror image of the m-phase shell and the k-phase shell; d km is the distance between the k-phase shell and the m-phase shell;

[0062] Similarly, the modulus matrix of the overhead line wave impedance matrix is ​​obtained, and the external coupling circuit is converted into independent single-phase circuits;

[0063] Step S2.2: Modeling of the ground wire. (There are three common methods for modeling the ground wire: one is equivalent paired lumped inductance; the second is a uniform transmission line model; and the third is a series connection of multiple uniform transmission lines. Comparisons show that the three models have little effect on the calculation results, so the first model is used.) The calculation formula is:

[0064]

[0065] Where l is the length of the shorting bar; w is the width of the shorting bar; and t is its thickness.

[0066] As a further preferred technical solution of the above technical solution, step S3 is specifically implemented as the following steps:

[0067] Step S3.1: Calculate the object and parameters (select a busbar bay of a 252kV GIS). When the disconnector is operated, calculate the TEV generated on its casing, and thus calculate the leakage current of the GIS casing. According to the leakage current, determine the opening and closing position of the disconnector (the GIS compartment section is as follows Figure 8 shown);

[0068] Step S3.2: Calculate the model based on the actual outage scenario, i.e., the IV busbar disconnector is closed and the circuit breaker is in the open position. (Because the busbar is energized, the disconnector contacts will re-strike multiple times during opening and closing, causing transients.) In the circuit, the opening and closing of the disconnector is actually the equivalent capacitance of the short-circuit between the disconnector and the circuit breaker.

[0069] (For the convenience of calculation, only one arcing is considered) The contact arcing mathematical model adopts the Maier time-varying resistance model, that is, R(t) = R s +R0e -t / T , R s is the static arc resistance; R0 is the resistance of the disconnector before arcing; T is the time constant (where C = 12pF, R0 = 10 12 Ω, R s =0.5Ω, T=1ns);

[0070] (In order to obtain the most demanding transient phenomenon, that is, before the isolation switch is operated, the initial value of the power supply side voltage is 1p.u. and the initial value of the load side voltage is -1p.u.; the current source at each point in the circuit is 0; the reference direction of the current source is: inflow is +1, outflow is -1, and the final simulation calculation model is as follows Figure 9 shown).

[0071] Step S3.3: Calculate the results;

[0072] Step S3.4: Result analysis:

[0073] TEV: When the switch is closed, the maximum voltage amplitude of the three-phase shell is positive; when the switch is opened, the maximum voltage amplitude of the three-phase shell is negative;

[0074] Leakage current: The shell leakage current during closing operation is greater than the shell leakage current during opening operation (about 2 times more);

[0075] Spectrum characteristics: Regardless of opening or closing operation, the spectrum characteristics of the shell transient voltage TEV are the same.

[0076] As a further preferred technical solution of the above technical solution, step S4 is specifically implemented as follows:

[0077] The TEV and leakage current on the GIS casing show (obvious) differences when the disconnector is open or closed, which is reflected in the amplitude and waveform. Therefore, the opening and closing positions of the disconnector are judged by utilizing the characteristics of TEV and leakage current, that is, when the maximum amplitude of TEV is positive, the disconnector is closed; when the maximum amplitude of TEV is negative, the disconnector is open; when the leakage current is large, the disconnector is closed; when the leakage current is small, the disconnector is open. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 It is a schematic diagram of a multi-conductor transmission line formed at the connection between the GIS and the casing of the present invention.

[0079] Figure 2 This is a circuit model diagram of the inductor of the present invention.

[0080] Figure 3 This is the inductor transient model diagram of the present invention.

[0081] Figure 4 This is a capacitor transient model diagram of the present invention.

[0082] Figure 5 This is a single-phase lossless line transient model diagram of the present invention.

[0083] Figure 6 It is the arc model diagram of the disconnector of the present invention.

[0084] Figure 7This is a circuit model diagram of the connection between GIS and casing of the present invention.

[0085] Figure 8 It is a schematic diagram of the busbar interval of the present invention.

[0086] Figure 9 It is a simulation calculation model diagram of the present invention.

[0087] Figure 10 It is a VFTO diagram on the closing operation disconnector of the present invention.

[0088] Figure 11 This is the TEV and spectrum diagram on the A-phase housing during the closing operation of the present invention.

[0089] Figure 12 It is a TEV diagram on the B-phase housing of the closing operation of the present invention.

[0090] Figure 13 It is a TEV diagram on the C-phase housing during the closing operation of the present invention.

[0091] Figure 14 It is a VFTO diagram on the opening operation disconnector of the present invention.

[0092] Figure 15 This is the TEV and spectrum diagram on the A-phase housing during the opening operation of the present invention.

[0093] Figure 16 This is the TEV diagram on the B-phase housing of the opening operation of the present invention.

[0094] Figure 17 This is the TEV diagram on the C-phase housing of the opening operation of the present invention.

[0095] Figure 18 This is a waveform diagram of the A-phase housing leakage current when the switch is opened according to the present invention.

[0096] Figure 19 This is a waveform diagram of the A-phase housing leakage current when the circuit breaker is closed. DETAILED DESCRIPTION

[0097] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are for illustrative purposes only, and those skilled in the art will readily appreciate other obvious variations. The basic principles of the present invention defined in the following description may be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the present invention.

[0098] In the preferred embodiment of the present invention, those skilled in the art should note that the disconnector of the GIS involved in the present invention may be regarded as prior art.

[0099] Preferred embodiment.

[0100] Analysis of TEV production mechanism

[0101] Switching the disconnector in a GIS triggers a rapid transient process. When the transient voltage wave propagates to the connection between the GIS and the bushing, a portion of the voltage wave is refracted between the GIS and the ground, causing a transient increase in the casing voltage. Part of this transient electromagnetic process occurs within the internal circuit formed by the wave impedance between the high-voltage busbar and the inner wall of the casing and the equivalent models of the electrical components; the other part occurs within the external circuit formed by the wave impedance between the outer wall of the casing and the ground, and the wave impedance between the overhead line and the ground.

[0102] Depend on Figure 1 As can be seen, when the VFTO propagates to the connection O between the GIS and the bushing, a portion of the voltage wave is coupled to the outside of the GIS, resulting in voltage waves at Z2 and Z3. The voltage wave at Z2 is the transient overvoltage (TEV) of the GIS casing. Because the casing has wave impedance, leakage current is generated in the casing.

[0103] The present invention discloses a method for judging the opening and closing state of an isolating switch based on the transient potential and current of the shell. The method is judged by using the data of the GIS (Gas Insulated Switchgear) shell, and includes the following steps:

[0104] Electrical components in substations are categorized into two main types: lumped parameter components and distributed parameter components. Lumped parameter equivalents are used for equipment, while distributed parameter equivalents are used for busbars. Regardless of the equivalent model, they are ultimately composed of a resistor and a current source in parallel, forming a Norton circuit, also known as a discrete circuit for transient calculations. The unified form of the discrete transient equivalent circuits for these components greatly facilitates the development of transient calculation programs for the entire network.

[0105] Electromagnetic transients in a GIS occur partially within the GIS and partially outside it. VFTO calculations must account for both transients, necessitating the establishment of internal and external transient circuits. Based on the propagation characteristics of transient wave processes within and outside the GIS substation, the GIS internal busbar is modeled using a distributed parameter transmission line model, while other key equipment is modeled using lumped parameter equivalent circuits.

[0106] Step S1: Establishing the internal transient circuit of GIS;

[0107] Step S2: Establishing the GIS external transient circuit;

[0108] Step S3: performing TEV simulation calculations generated by GIS disconnector operation;

[0109] Step S4: Determine the opening and closing position of the disconnector based on the transient potential and current of the housing.

[0110] Specifically, step S1 is implemented as follows:

[0111] Step S1.1: Establish a transient model of the concentrated inductor (the circuit model of the inductor is as follows Figure 2 shown):

[0112] For the lumped parameter inductor L, the inductor voltage drop u L (t) and the current i flowing through km (t) The following relationship exists:

[0113]

[0114] Using numerical calculation methods, time is discretized into a series of time periods with small time intervals Δt, and according to u at time t-Δt, L (t-Δt) and i km (t-Δt) to find u at time t L (t) and i km (t), so we rewrite the above formula into an integral form from t-Δt to t, and further solve it to get:

[0115]

[0116] After integrating the right side of the above equation using the trapezoidal method, we can obtain:

[0117]

[0118] And u L (t) = u k (t)-u m (t), The above formula can be written as:

[0119]

[0120] Thus, we obtain ( Figure 3 The corresponding equivalent circuit shown in

[0121] (Depend on Figure 3 It can be seen that the equivalent circuit only contains the resistor R L and current source I L (t-Δt), further using the above formula Find the current i at the previous moment km (t-Δt), and thus the recursive formula of the current source is:

[0122]

[0123] Step S1.2: Establish a concentrated capacitor transient model (according to the derivation method of the concentrated inductor transient model in the previous article, the capacitor is also equivalent to a Norton circuit in the form of a resistor and a current source in parallel. The equivalent calculation circuit is as follows Figure 4 shown):

[0124] The recursive formula for the current source is

[0125]

[0126] In the formula is an equal value resistor;

[0127] Step S1.3: Establish a lumped resistor transient model (the derivation method of the lumped resistor transient model is the same as above, the only difference in the equivalent model is that the lumped resistor has no current source, or the current source is regarded as 0);

[0128] Step S1.4: Establish the Bergeron equivalent model of the busbar ( Figure 5 (a) shows a uniform lossless transmission line):

[0129] For a uniform lossless transmission line, its length is l, its wave impedance is Z, and the voltage and current at the beginning (x = 0) and the end (x = l) are u k (t),u m (t), i km (t), i mk (t), the positive direction of the current at the terminal is assumed to flow from the terminal to the circuit;

[0130] According to wave theory, the forward mixed wave emitted by the head end at time t-τ will reach the end of the line at time t. Therefore, the voltage and current at the end of the line at time t are expressed by the voltage and current at the head end at time t-τ, that is:

[0131] u k (t-τ)+Zi km (t-τ)=u m (t)+Z[-i mk (t)];

[0132] That is:

[0133]

[0134] If the order:

[0135]

[0136] get:

[0137]

[0138] According to the above formula (such as Figure 5 (b) The equivalent calculation circuit of the line end m at time t, where Z is equal to the resistance of the line wave impedance, is calculated as L and C are the unit inductance and unit capacitance to ground of the line respectively. m (t-τ) is the equivalent historical current source, which is the voltage u at the beginning of the line at time t-τ k (t-τ) and current i km (t-τ) decision;

[0139] Similarly, according to the concept of reverse mixed waves, the voltage and current at endpoint k at time t are expressed as the voltage and current at endpoint m at time t-τ, which can be written in the form of a Norton circuit as follows:

[0140]

[0141] According to the above formula (such as Figure 5 (b) The equivalent circuit of the wire endpoint k at time t, the equivalent calculation formula and Combined with each other, a complete transient equivalent calculation circuit for single-phase uniform lossless line is formed;

[0142] (Using the derivation method of the recursive formula of the equivalent current source of concentrated inductance and concentrated capacitance above, the recursive formula of the equivalent current source of the single-phase uniform lossless line is obtained in the same way:

[0143]

[0144] Table 1 lists the equivalent models and parameters of key equipment inside the UHV GIS.

[0145] Table 1 Transient models and equivalent parameters of GIS key equipment

[0146]

[0147]

[0148] When the disconnector is in operation, multiple re-breakdowns occur between the contacts, causing arcs. The arc in the disconnector is a complex discharge process, and to date, there is no complete arc model. Currently, there are three methods for simulating the disconnector arc model: the first is to equate the arc to a static resistor, generally with a value of a few tenths of a ohm to a few ohms. Obviously, this model is too simple, but it is easy to simulate and calculate; the second is the time-varying resistance model, which is a simplification of the Maier arc model. The calculation formula is as follows:

[0149] R(t)=R s +R0e -t / T ;

[0150] Where: R s =0.5Ω, is the static arc resistance; R0 = 10 12 Ω is the resistance of the disconnector before arcing; T = 1ns is the time constant. This arc model is currently widely used. Building on previous research, this paper proposes a third arc model, the segmented arc model, by further expanding upon it. The segmented arc model fully describes the resistance changes before and after the arc zero, significantly improving upon the previous two models. To simplify calculations, this paper retains the time-varying resistance model as the arc model.

[0151] When establishing the disconnector arc model, the large size of the disconnector's moving and static contacts and the presence of residual charge were taken into account. Therefore, when the arc is ignited, in addition to equating the arc to a time-varying resistance R(t), the disconnector's closing resistance R = 500Ω was also considered. Furthermore, the capacitance C between the moving and static contacts and the GIS housing was also taken into account. The final equivalent model of the disconnector is as follows: Figure 6 Based on the analysis results of the three-dimensional electric field of the isolating switch and the calculation results of the relevant parameters of the isolating switch, the concentrated capacitance C is set to 12pF.

[0152] Specifically, step S2 is implemented as follows: (When the disconnector in the substation is switched, a rapid transient process is caused. When the transient voltage wave propagates to the connection between the GIS and the bushing, a portion of the voltage wave is refracted between the GIS and the ground, causing a transient increase in the housing voltage. Part of the transient electromagnetic process occurs in the internal circuit composed of the wave impedance between the high-voltage busbar and the inner wall of the housing and the equivalent models of each electrical component; the other part occurs in the external circuit composed of the wave impedance between the outer wall of the housing and the ground and the wave impedance between the overhead line and the ground.

[0153] When the three-phase shells are arranged in parallel, since the GIS three-phase shells and overhead lines are also multi-conductor transmission lines, there is electromagnetic coupling between them. Taking the operating phase A as an example, Figure 7 It is the circuit model of the connection between GIS and casing. 21 and Z 22 is the mutual wave impedance between the three-phase shells; Z 31 and Z 33 is the mutual wave impedance between three-phase overhead lines):

[0154] Step S2.1: (by Figure 7 It can be seen that there is electromagnetic coupling between the shells of GIS. Due to the horizontal arrangement of the shells, the shell wave impedance matrix is ​​symmetrical. The symmetrical component method is used to convert the wave impedance matrix from phasor to modulus through phase-mode transformation to eliminate the coupling between them:

[0155] The GIS three-phase shell wave impedance matrix is:

[0156]

[0157] After phase transformation:

[0158]

[0159] Among them, ZA, ZB, and ZC are the wave impedances of the three-phase shells of A, B, and C after transformation, respectively. The formula is:

[0160]

[0161] Where, Z2 is the shell self-wave impedance; Z 21 is the mutual wave impedance between the shells of phases A and B or phases B and C; Z 22 is the mutual wave impedance between the A and C phase shells, and the calculation formulas are as follows:

[0162] The calculation formula of self-wave impedance is:

[0163]

[0164] Where h is the height of the shell above the ground, and r is the outer radius of the shell;

[0165] The calculation formula of mutual wave impedance is:

[0166]

[0167] Where D km is the distance between the mirror image of the m-phase shell and the k-phase shell; d km is the distance between the k-phase shell and the m-phase shell;

[0168] Similarly, the modulus matrix of the overhead line wave impedance matrix is ​​obtained, and the external coupling circuit is converted into independent single-phase circuits;

[0169] Step S2.2: Modeling of the ground wire. (There are three common methods for modeling the ground wire: one is equivalent paired lumped inductance; the second is a uniform transmission line model; and the third is a series connection of multiple uniform transmission lines. Comparisons show that the three models have little effect on the calculation results, so the first model is used.) The calculation formula is:

[0170]

[0171] Where l is the length of the shorting bar; w is the width of the shorting bar; and t is its thickness.

[0172] Furthermore, step S3 is specifically implemented as the following steps:

[0173] Step S3.1: Calculate the object and parameters (select a busbar bay of a 252kV GIS). When the disconnector is operated, calculate the TEV generated on its casing. From this, calculate the leakage current of the GIS casing. Based on this leakage current, determine the open and closed positions of the disconnector (a cross-section of the GIS bay is shown in the figure below).

[0174] Since the VFTO phenomenon is more pronounced at voltage levels of 500kV and above, there are few existing research results and reference materials for VFTO issues at 220kV and below. The parameters in Table 2 below are obtained by reducing them accordingly based on the 500kV GIS.

[0175] Table 2 Technical parameters of GIS components

[0176]

[0177] The per-unit value of the power supply voltage is: 1p.u. = 252 ÷ 1.732 × 1.414 = 205.7 kV. The calculation software uses the electromagnetic transient calculation program EMTP.

[0178] Step S3.2: Calculate the model based on the actual outage scenario, i.e., the IV busbar disconnector is closed and the circuit breaker is in the open position. (Because the busbar is energized, the disconnector contacts will re-strike multiple times during opening and closing, causing transients.) In the circuit, the opening and closing of the disconnector is actually the equivalent capacitance of the short-circuit between the disconnector and the circuit breaker.

[0179] (For the convenience of calculation, only one arcing is considered) The contact arcing mathematical model adopts the Maier time-varying resistance model, that is, R(t) = R s +R0e -t / T , R s is the static arc resistance; R0 is the resistance of the disconnector before arcing; T is the time constant (where C = 12pF, R0 = 10 12 Ω, R s =0.5Ω, T=1ns);

[0180] In order to obtain the most demanding transient phenomenon, before the isolation switch is operated, the initial value of the power supply side voltage is 1p.u. and the initial value of the load side voltage is -1p.u.; the current source at each point in the circuit is 0; the reference direction of the current source is: inflow is +1, outflow is -1, and the final simulation calculation model is as follows Figure 9 shown.

[0181] Step S3.3: Calculate the results, set the calculation time to 10μs and the step size to 1ns. The results are shown in Table 3 below. The maximum overvoltage value of the conductor and the TEV waveform of the shell when closing and opening the circuit breaker are as follows: Figures 10-17 As shown;

[0182] Table 3 VFTO and TEV calculation results

[0183]

[0184] Step S3.4: Result analysis:

[0185] The above calculation results show that the TEV and leakage current on the GIS casing show obvious differences when the disconnector is opened or closed, mainly in terms of amplitude and waveform. The specific characteristics and rules are as follows:

[0186] TEV: When the switch is closed, the maximum voltage amplitude of the three-phase shell is positive; when the switch is opened, the maximum voltage amplitude of the three-phase shell is negative;

[0187] Leakage current: The shell leakage current during closing operation is greater than the shell leakage current during opening operation (about 2 times more);

[0188] Spectrum characteristics: Regardless of opening or closing operation, the spectrum characteristics of the shell transient voltage TEV are the same.

[0189] Furthermore, step S4 is specifically implemented as follows:

[0190] The TEV and leakage current on the GIS casing show (obvious) differences when the disconnector is open or closed, which is reflected in the amplitude and waveform. Therefore, the opening and closing positions of the disconnector are judged by utilizing the characteristics of TEV and leakage current, that is, when the maximum amplitude of TEV is positive, the disconnector is closed; when the maximum amplitude of TEV is negative, the disconnector is open; when the leakage current is large, the disconnector is closed; when the leakage current is small, the disconnector is open.

[0191] For ease of use, they are listed in Table 4 below.

[0192] Table 4 Relationship between TEV and leakage current and the position of the isolating switch

[0193]

[0194] It is worth mentioning that the technical features such as the GIS disconnector involved in the patent application of this invention should be regarded as prior art. The specific structure, working principle and possible control method and spatial layout method of these technical features can be selected by conventional means in the field and should not be regarded as the inventive point of this patent. This patent will not be further elaborated.

[0195] For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for judging the opening and closing state of an isolating switch based on transient potential and current of the shell, which is judged by data of the GIS shell, and is characterized in that: The following steps are involved: Step S1: Establishing the transient circuit inside GIS; Step S2: Establishing a transient circuit outside the GIS; Step S3: performing TEV simulation calculations generated by GIS disconnector operation; Step S4: Determine the disconnecting and closing positions of the isolating switch based on the transient potential and current of the housing.

2. A method for judging the opening and closing state of an isolating switch based on transient potential and current of a shell according to claim 1, characterized in that: Step S1 is specifically implemented as follows: Step S1.1: Establish the transient model of concentrated inductance: For the lumped parameter inductor L, the voltage drop u of the inductor is L (t) and the current i flowing km (t) The following relationship exists: Using numerical calculation methods, time is discretized into a series of time periods with a small time interval Δt. According to the u at the time t-Δt, L (t-Δt) and i km (t-Δt) to find u at time t L (t) and i km (t), so we rewrite the above formula into an integral form from t-Δt to t, and further solve it to get: After integrating the right side of the above equation using the trapezoidal method, we get: again The above formula can be written as: Thus, the corresponding equivalent circuit is obtained; The equivalent circuit only contains the resistor R L and current source I L (t-Δt), further using the above formula, we can get the current i at the previous moment km (t-Δt), so the recursive formula of the current source is: Step S1.2: Establish the transient model of concentrated capacitor: The recursive formula for the current source is: In the formula is an equal value resistor; Step S1.3: Establishing a concentrated resistance transient model; Step S1.4: Establish the Bergeron equivalent model of the busbar: For a uniform lossless transmission line, its length is l, its wave impedance is Z, and the voltage and current at the beginning (x = 0) and the end (x = l) are u k (t),u m (t),i km (t),i mk (t), the positive direction of the current at the endpoint is assumed to flow from the endpoint to the circuit; According to wave theory, the forward mixed wave emitted by the head end at time t-τ will reach the end of the line at time t. Therefore, the voltage and current at the end of the line at time t are expressed by the voltage and current at the head end at time t-τ, that is: u k (t-τ)+Zi km (t-τ)=u m (t)+Z[-i mk (t)]; That is: If the command: get: According to the above formula, we can get the equivalent calculation circuit of the line end m at time t, where Z is equal to the resistance of the line wave impedance, and the calculation formula is: L and C are the unit inductance and unit capacitance to ground of the line, respectively. m (t-τ) is the equivalent historical current source, which is the voltage u at the beginning of the line at time t-τ k (t-τ) and current i km (t-τ) decision; Similarly, according to the concept of reverse mixed waves, the voltage and current at endpoint k at time t are expressed by the voltage and current at endpoint m at time t-τ, which can be written in the form of a Norton circuit as follows: According to the above formula, we can get the equivalent circuit of the wire endpoint k at time t, and replace the equivalent calculation formula with and Combined with each other, a complete transient equivalent calculation circuit for a single-phase uniform lossless line is formed; The recursive formula for the equivalent current source of a single-phase uniform lossless line is:

3. A method for judging the opening and closing state of an isolating switch based on transient potential and current of a shell according to claim 2, characterized in that: Step S2 is specifically implemented as the following steps: Step S2.1: There is electromagnetic coupling between the shells of GIS. Due to the horizontal arrangement of the shells, the shell wave impedance matrix is ​​symmetrical. The symmetrical component method is used to transform the wave impedance matrix from phase to modulus through phase-mode transformation to remove the coupling between them: The GIS three-phase shell wave impedance matrix is: After phase transformation: Among them, ZA, ZB, and ZC are the wave impedances of the three-phase shells of A, B, and C after transformation, respectively, and the formula is: Where, Z2 is the shell self-wave impedance; Z 21 is the mutual wave impedance between the shells of phases A and B or phases B and C; Z 22 is the mutual wave impedance between the A and C phase shells, and the calculation formulas are as follows: The calculation formula of self-wave impedance is: In the formula, h is the height of the shell above the ground, and r is the outer radius of the shell; The calculation formula of mutual wave impedance is: Where D km is the distance between the mirror image shell of the m-phase shell and the k-phase shell; d km is the distance between the k-phase shell and the m-phase shell; Similarly, the modulus matrix of the overhead line wave impedance matrix is ​​obtained, and the external coupling circuit is transformed into single-phase circuits independent of each other; Step S2.2: Modeling of the grounding wire, the calculation formula is: Where l is the length of the shorting bar; w is the width of the shorting bar; and t is its thickness.

4. A method for judging the opening and closing state of an isolating switch based on transient potential and current of a shell according to claim 3, characterized in that: Step S3 is specifically implemented as the following steps: Step S3.1: Calculate the object and parameters. When the disconnector is operated, calculate the TEV generated on its shell, thereby calculating the leakage current of the GIS shell, and determine the opening and closing position of the disconnector according to the leakage current; Step S3.2: Calculate the model, and build a model based on the actual power outage mode on site, that is, the IV busbar disconnector is closed, and the circuit breaker is in the disconnected position. In the circuit, the opening and closing operation of the disconnector is actually to close the equivalent capacitance of the short line between the disconnector and the circuit breaker; The contact arcing mathematical model adopts the Maier time-varying resistance model, that is, R(t) = R s +R0e -t / T , R s is the static arc resistance; R0 is the resistance of the disconnector before arcing; T is the time constant; Step S3.3: Calculate the result; Step S3.4: Result analysis: TEV: When the switch is closed, the maximum voltage amplitude of the three-phase shell is positive; when the switch is opened, the maximum voltage amplitude of the three-phase shell is negative; Leakage current: The shell leakage current during closing operation is greater than the shell leakage current during opening operation; Spectrum characteristics: Regardless of opening or closing operation, the spectrum characteristics of the shell transient voltage TEV are the same.

5. A method for judging the opening and closing state of an isolating switch based on transient potential and current of a shell according to claim 4, characterized in that: Step S4 is specifically implemented as follows: The TEV and leakage current on the GIS housing are different when the disconnector is open or closed, which is reflected in the amplitude and waveform. Therefore, the opening and closing positions of the disconnector are judged by using the characteristics of TEV and leakage current. That is, when the maximum amplitude of TEV is positive, the disconnector is closed. When the maximum amplitude of TEV is negative, the isolating switch is open; when the leakage current is large, the isolating switch is closed; when the leakage current is small, the isolating switch is open.

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