A method for calculating lightning-induced voltage on overhead line-high voltage cable sheath

Abstract

The present invention discloses a method for calculating the lightning-induced voltage of an overhead line-high-voltage cable sheath. At present, for the instantaneous moment of on-site lightning striking an overhead line, it is impossible to obtain the voltages at the lightning strike point, the connection point between the overhead line and the cable, and the points inside the joint wells along the cable sheath. The present invention performs electromagnetic transient simulation modeling on the actual spatial position, structural parameters, and material parameters of the on-site overhead line and high-voltage cable, performs electromagnetic transient simulation modeling on the lightning current, and performs electromagnetic transient modeling on the normal operation of the power system and the actual lightning fault condition. After considering the randomness of the fault occurrence moment, the maximum value of the lightning-induced voltage at each point along the cable sheath after the lightning strike is calculated by electromagnetic transient simulation software, thereby providing a reference basis for the cable sheath insulation coordination design of the overhead line-cable hybrid line where lightning current invades, and laying a foundation for the subsequent design and evaluation of various voltage limiters and protectors.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission and transformation of power grids, and relates to calculation of lightning induced voltage on cable sheaths, in particular to a method for calculating lightning induced voltage on overhead line-high voltage cable sheaths. Background Art

[0002] With the gradual increase in urban electricity consumption in recent years, a transmission model has gradually emerged in urban centers, primarily using high-voltage cables, supplemented by overhead lines. As urban transmission channels evolve toward higher voltage levels and larger transmission capacities, overhead lines are susceptible to extreme weather conditions during operation, including lightning strikes that can cause lightning current intrusion. Cable lines connected to overhead lines are also at risk of lightning current intrusion.

[0003] Because lightning strikes occur at microsecond speeds, existing online monitoring devices cannot consistently detect voltage information such as the lightning strike point. Furthermore, the extensive installation of on-site online monitoring devices can also reduce the economic efficiency of power grid operations. Currently, the characteristics of lightning-induced voltages on the sheath of hybrid overhead and cable lines are unclear. It is impossible to obtain voltage values ​​at the moment of lightning strikes on overhead lines, at the lightning strike point, at the connection point between the overhead line and the cable, or at the various joint wells along the cable sheath. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide a method for calculating the lightning-induced voltage on the sheath of an overhead line-high-voltage cable. The method uses electromagnetic transient simulation software to construct an electromagnetic transient model of the overhead line, cable, lightning current, normal operation of the power system and fault points. After considering the randomness of the lightning current occurrence time, different lightning strike occurrence times are set in the electromagnetic transient simulation software, and electromagnetic transient calculations are performed to obtain the maximum lightning-induced voltage at each point along the cable sheath. This provides a reference basis for the insulation coordination design of the cable sheath of a hybrid line with lightning current intrusion into the overhead line-cable, and lays the foundation for the subsequent design and evaluation of various voltage limiters and protectors.

[0005] To this end, the present invention adopts the following technical solution: a method for calculating the lightning induced voltage of an overhead line-high voltage cable sheath, comprising the steps of:

[0006] a) Obtain the actual spatial location and model of the on-site overhead line, obtain the structural parameters and material parameters of the overhead line, and establish the overhead line model in the electromagnetic transient simulation software;

[0007] b) Obtain the actual spatial position and model of the on-site cable, obtain the cable structural parameters and material parameters, and establish the cable model in the electromagnetic transient simulation software;

[0008] c) Establish a normal operation model of the power system in the electromagnetic transient simulation software based on the normal operation parameters of the power system;

[0009] d) The overhead line model, cable model and power system normal operation model are connected to the ABC three-phase conductors in the electromagnetic transient simulation software;

[0010] e) Establish a lightning current model in electromagnetic transient simulation software based on lightning current parameters;

[0011] f) Establish a lightning fault point model in the electromagnetic transient simulation software based on actual lightning fault parameters;

[0012] g) The lightning current model and lightning fault point model are connected to the overhead line model through a single-phase conductor in the electromagnetic transient simulation software, and the lightning current is injected into the normally operating power system through the single-phase conductor;

[0013] h) Set different lightning strike occurrence times in the electromagnetic transient simulation software, use the electromagnetic transient simulation software to perform electromagnetic transient calculations, and obtain the maximum lightning induced voltage at each point along the overhead line-high voltage cable sheath.

[0014] Furthermore, in step a), the actual spatial position of the overhead line includes the height of the ABC three-phase line from the ground and the distance from the center crossarm of the tower, as well as the height of the ground wire from the ground and the distance from the center crossarm of the tower; the structural parameters and material parameters of the overhead line of the corresponding model are obtained through the overhead line model, and the structural parameters include: the outer diameter, total number of strands, number of strands in the outermost circle, single strand diameter and sag of the conductor of the ABC three-phase line, and the outer diameter and sag of the conductor of the ground wire; the material parameters include: the DC resistance and relative magnetic permeability of the conductor of the ABC three-phase line, as well as the DC resistance and relative magnetic permeability of the conductor of the ground wire.

[0015] Furthermore, in step b), the actual spatial position of the cable includes the height of the ABC three-phase cable from the ground and the distance from the origin of the horizontal coordinate; the structural parameters and material parameters of the corresponding model cable are obtained according to the cable model, the structural parameters including: the outer diameter of the conductor core, the outer diameter of the XLPE insulation layer, the outer diameter of the metal sheath, and the outer diameter of the outer insulation layer of the ABC three-phase cable; the material parameters include: the resistivity of the conductor at 90°C, the relative dielectric constant of the XLPE insulation layer, the resistivity of the metal sheath at 70°C, and the relative dielectric constant of the outer insulation layer.

[0016] Furthermore, in step c), the normal operating parameters of the power system include the effective value of the power frequency voltage of the power system, the equivalent internal inductance value of the power system, the load active power and the load reactive power;

[0017] Step d) specifically includes:

[0018] d1) The power system normal operation model consists of two modules: a module for the power system power frequency power supply connected to the equivalent internal inductance, and a module for the power system load;

[0019] d2) The power system power frequency power supply, power system operating equivalent internal inductance, overhead line model, cable model and power system load are connected in series in sequence using ABC three-phase conductors.

[0020] Furthermore, in step e), the lightning current model parameters include the lightning current peak value, wave front time and half-peak time, and the lightning current is described by a double exponential function model, as shown in the following formula:

[0021] ,

[0022] in, Indicates lightning current; Indicates the initial lightning current peak value, kA; is the peak current correction factor; t Indicates time, seconds; is the wave head time coefficient; is the half-peak time coefficient; e is a natural constant;

[0023] ,

[0024] in, is the peak value of lightning current, 、 and Jointly decided; the wave head time is determined by The half-peak time is determined by Decide.

[0025] Furthermore, in step f), the lightning fault parameters include the actual location of the fault point and the fault phase.

[0026] Furthermore, step g) is specifically as follows:

[0027] g1) connecting the lightning current model and the lightning fault point model using a single-phase conductor;

[0028] g2) Use a single-phase conductor to connect the lightning fault point model and the overhead line model, and select any phase of the ABC three-phase conductors to connect the overhead line model.

[0029] Furthermore, in step h), the maximum value of the lightning induced voltage at each point along the overhead line-high voltage cable sheath is obtained by the following steps:

[0030] In the cable model described in h1), voltage monitoring points are set at the cable sheath joints of each segment;

[0031] h2) In the electromagnetic transient simulation software, set different fault occurrence times. Within a normal operation cycle of the power system, set the fault occurrence time randomly N times and record the lightning induced voltage value of each phase at each point along the cable sheath;

[0032] h3) After the electromagnetic transient simulation software is repeatedly run, compare the lightning induced voltage values ​​of each phase ABC at each point along the cable sheath to obtain the maximum lightning induced voltage;

[0033] ,

[0034] in, is the maximum value of the lightning induced voltage; i Represents each point along the cable sheath, 0 is the beginning of the cable sheath; j Represents the ABC three-phase; It is the single-phase voltage value at each point along the cable sheath.

[0035] Compared with the existing technology, the present invention performs electromagnetic transient simulation modeling on the actual spatial position, structural parameters, and material parameters of on-site overhead lines and cables, performs electromagnetic transient simulation modeling on lightning current, and performs electromagnetic transient modeling on the normal operation of the power system and actual fault conditions. After considering the randomness of the fault occurrence time, the electromagnetic transient simulation software calculates the maximum lightning-induced voltage at each point along the cable sheath after the lightning strike occurs, thereby providing a reference basis for the insulation coordination design of cable sheaths in hybrid lines with lightning current intrusion into overhead lines and cables, and laying the foundation for the subsequent design and evaluation of various voltage limiters and protectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for calculating lightning induced voltage on an overhead line-high voltage cable sheath according to the present invention;

[0037] Figure 2 This is a flow chart for obtaining calculation results of sheath lightning induced voltage at random cable segment joints at the moment of a fault according to the present invention;

[0038] Figure 3 This is a diagram showing the calculation results of the lightning induced voltage at various points along the cable sheath at different lightning strike times in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following is an explanation and description of the technical solutions of the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. However, the following embodiments are only preferred embodiments of the present invention and are not exhaustive. Based on the embodiments in the implementation manner, other embodiments obtained by those skilled in the art without making any creative work are all within the scope of protection of the present invention.

[0040] This embodiment is a method for calculating the lightning induced voltage of an overhead line-high voltage cable sheath. Figure 1 The steps are as follows:

[0041] a) Obtain the actual spatial location and model of the on-site overhead line, obtain the structural parameters and material parameters of the overhead line, and establish the overhead line model in the electromagnetic transient simulation software;

[0042] b) Obtain the actual spatial position and model of the on-site cable, obtain the cable structural parameters and material parameters, and establish the cable model in the electromagnetic transient simulation software;

[0043] c) Establish a normal operation model of the power system in the electromagnetic transient simulation software based on the normal operation parameters of the power system;

[0044] d) The overhead line model, cable model and power system normal operation model are connected to the ABC three-phase conductors in the electromagnetic transient simulation software;

[0045] e) Establish a lightning current model in electromagnetic transient simulation software based on lightning current parameters;

[0046] f) Establish a lightning fault point model in the electromagnetic transient simulation software based on actual lightning fault parameters;

[0047] g) The lightning current model and lightning fault point model are connected to the overhead line model through a single-phase conductor in the electromagnetic transient simulation software, and the lightning current is injected into the normally operating power system through the single-phase conductor;

[0048] h) Set different lightning strike occurrence times in the electromagnetic transient simulation software, use the electromagnetic transient simulation software to perform electromagnetic transient calculations, and obtain the maximum lightning induced voltage at each point along the overhead line-high voltage cable sheath.

[0049] Specifically, in step a), the actual spatial position of the overhead line includes the height of the ABC three-phase line from the ground and the distance from the center crossarm of the tower, as well as the height of the ground wire from the ground and the distance from the center crossarm of the tower; the structural parameters and material parameters of the overhead line of the corresponding model are obtained through the overhead line model, and the structural parameters include: the outer diameter, total number of strands, number of strands in the outermost circle, single strand diameter and sag of the conductor of the ABC three-phase line, and the outer diameter and sag of the conductor of the ground wire; the material parameters include: the DC resistance and relative magnetic permeability of the conductor of the ABC three-phase line, as well as the DC resistance and relative magnetic permeability of the conductor of the ground wire.

[0050] Specifically, in step b), the actual spatial position of the cable includes the height of the ABC three-phase cable from the ground and the distance from the abscissa origin (the abscissa origin is defined in the electromagnetic transient simulation software); the structural parameters and material parameters of the corresponding cable model are obtained based on the cable model, the structural parameters including: the outer diameter of the conductor core, the outer diameter of the XLPE insulation layer, the outer diameter of the metal sheath, and the outer diameter of the outer insulation layer of the ABC three-phase cable; the material parameters including: the resistivity of the conductor at 90°C, the relative dielectric constant of the XLPE insulation layer, the resistivity of the metal sheath at 70°C, and the relative dielectric constant of the outer insulation layer.

[0051] Specifically, in step c), the normal operating parameters of the power system include the effective value of the power frequency voltage of the power system, the equivalent internal inductance value of the power system, the load active power and the load reactive power;

[0052] Specifically, step d) comprises:

[0053] d1) The normal operation model of the power system consists of two modules: a module for the equivalent internal inductance of the power system power frequency power supply connection and a module for the power system load;

[0054] d2) The power system's industrial frequency power supply, the power system's operating equivalent internal inductance, the overhead line model, the cable model, and the power system's load are connected in series in sequence using ABC three-phase conductors.

[0055] Specifically, in step e), the lightning current model parameters include the lightning current peak value, wave front time and half-peak time. The lightning current is described by a double exponential function model, as shown in the following formula:

[0056] ,

[0057] in, Indicates lightning current; Indicates the initial lightning current peak value, kA; is the peak current correction factor; t Indicates time, seconds; is the wave head time coefficient; is the half-peak time coefficient; e is a natural constant;

[0058] ,

[0059] in, is the peak value of lightning current, 、 and Jointly decided; the wave head time is determined by The half-peak time is determined by Decide.

[0060] Specifically, in step f), the lightning fault parameters include the actual location of the fault point and the fault phase difference.

[0061] Specifically, step g) is specifically:

[0062] g1) connecting the lightning current model and the lightning fault point model using a single-phase conductor;

[0063] g2) Use a single-phase conductor to connect the lightning fault point model and the overhead line model, and select any phase of the ABC three-phase conductors to connect the overhead line model.

[0064] Specifically, in step h), the maximum value of the lightning induced voltage at each point along the overhead line-high voltage cable sheath is obtained by the following steps: Figure 2 As shown:

[0065] In the cable model described in h1), voltage monitoring points are set at the cable sheath joints of each segment;

[0066] h2) In the electromagnetic transient simulation software, set different fault occurrence times. Within one cycle (20ms) of normal power system operation, set the fault occurrence time randomly N times and record the lightning induced voltage value of each phase at each point along the cable sheath;

[0067] h3) After the electromagnetic transient simulation software is repeatedly run, compare the lightning induced voltage values ​​of each phase ABC at each point along the cable sheath to obtain the maximum lightning induced voltage;

[0068] ,

[0069] in, is the maximum value of the lightning induced voltage; i Represents each point along the cable sheath, 0 is the beginning of the cable sheath; j Represents the ABC three-phase; It is the single-phase voltage value at each point along the cable sheath.

[0070] Taking a 220kV lightning-struck line fault as an example, the method for calculating the lightning-induced voltage of the overhead line-high-voltage cable sheath of the present invention is applied to obtain the lightning-induced voltage value of the cable sheath connected to the line. The specific steps are as follows:

[0071] 1) According to the actual spatial position and model of the overhead line on site, the structural parameters and material parameters of the overhead line are obtained.

[0072] 1.1) Obtain the actual spatial position of the overhead lines, including: the heights of the three-phase lines ABC from the ground are 66.45m, 54.4m, and 43.2m, respectively, and the distances from the center crossarm of the tower are 18.4m, 23.5m, and 20.0m, respectively; and the ground wire is 69.15m from the ground and 22.8m from the center crossarm of the tower.

[0073] 1.2) The actual overhead line conductor model on site is obtained as LGJ-630 / 45, and the structural parameters and material parameters of the corresponding overhead line model are obtained. The structural parameters include: the conductor outer diameter of the ABC three-phase line is 0.014636m, the total number of strands is 45, the number of strands in the outermost circle is 7, the diameter of a single strand is 0.00211m, and the sag is 12m; the conductor outer diameter of the ground wire is 0.00166m, and the sag is 12m. The material parameters include: the conductor DC resistance of the ABC three-phase line is 0.0459Ω / km, and the relative permeability is 1.0; and the conductor DC resistance of the ground wire is 0.045Ω / km, and the relative permeability is 1.0.

[0074] 1.3) Establish an overhead line model in the simulation software PSCAD.

[0075] 2) Obtain cable structural parameters and material parameters based on the actual spatial position and model of the cable on site.

[0076] 2.1) Obtain the actual spatial position of the cables, including the heights of the three-phase cables ABC at 0.5m, 0.64m, and 0.5m from the ground, and the distances of the three-phase cables from the horizontal coordinate origin (the horizontal coordinate origin is the center of the phase A cable) at 0, 0.1m, and 0.2m.

[0077] 2.2) The actual cable model obtained on site is YJLW-127 / 220kV-1×2500mm 2 , the structural parameters and material parameters of the corresponding cable model are obtained. The structural parameters include: the outer diameter of the conductor core of the ABC three-phase cable is 0.0310m, the outer diameter of the XLPE insulation layer is 0.0580m, the outer diameter of the metal sheath is 0.0730m, and the outer diameter of the outer insulation layer is 0.0790m; the material parameters include: the resistivity of the conductor at 90°C is 2.1*10 -8 Ω*m, the relative dielectric constant of the XLPE insulation layer is 2.3, and the resistivity of the metal sheath is 2.5*10 at 70℃. -7 Ω*m, the relative dielectric constant of the outer insulation layer is 2.3.

[0078] 2.3) Create a cable model in the simulation software PSCAD.

[0079] 3) Select typical lightning current parameters: peak-to-peak value -30kA, wave head / half-peak time 2.6 / 50μs, and wave impedance 300Ω. Create a lightning current model for the lightning strike point in the simulation software PSCAD.

[0080] 4) Under normal power system operation, the power system power frequency line voltage RMS value is 1.05 pu (231 kV), the power system operating equivalent internal inductance is 20 mH, the three-phase load active power is 200 MW, and the load reactive power is 0. The power system reaches steady state after 0.1 s of operation. A normal power system model was established in the simulation software PSCAD.

[0081] 5) Actual fault situation: The actual fault point is located on the overhead line, 500 meters from the cable head end. The fault phase is phase B. A lightning fault point model is created in the simulation software PSCAD.

[0082] 6) Considering the randomness of the lightning current occurrence time, different lightning strike times are set in the simulation software PSCAD. The calculation results of the lightning induced voltage at each point along the cable sheath at different lightning strike times are as follows: Figure 3 shown.

[0083] It can be seen that the induced overvoltage on the sheath is minimized when the lightning current is at the power frequency trough, reaching a level of 131.36 kV under the single-ended grounding method. The induced overvoltage reaches its maximum when the lightning current is at the peak, reaching a level of 322.22 kV under both grounding methods. Compared to the peak overvoltage, the overvoltage level generated by the same lightning current at the power frequency trough is significantly reduced by 60% under both grounding methods. Electromagnetic transient calculations reveal that the maximum lightning-induced voltage on the cable sheath is 322.22 kV.

[0084] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It is apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above embodiments. Any improvements or modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for calculating the lightning-induced voltage on the sheath of an overhead line-high voltage cable, characterized in that: Including steps: a) Obtain the actual spatial location and model of the on-site overhead line, obtain the structural parameters and material parameters of the overhead line, and establish the overhead line model in the electromagnetic transient simulation software; b) Obtain the actual spatial position and model of the on-site cable, obtain the cable structural parameters and material parameters, and establish the cable model in the electromagnetic transient simulation software; c) Establish a normal operation model of the power system in the electromagnetic transient simulation software based on the normal operation parameters of the power system; d) The overhead line model, cable model and power system normal operation model are connected to the ABC three-phase conductors in the electromagnetic transient simulation software; e) Establish a lightning current model in electromagnetic transient simulation software based on lightning current parameters; f) Establish a lightning fault point model in the electromagnetic transient simulation software based on actual lightning fault parameters; g) The lightning current model and lightning fault point model are connected to the overhead line model through a single-phase conductor in the electromagnetic transient simulation software, and the lightning current is injected into the normally operating power system through the single-phase conductor; h) Set different lightning strike occurrence times in the electromagnetic transient simulation software, use the electromagnetic transient simulation software to perform electromagnetic transient calculations, and obtain the maximum lightning induced voltage at each point along the overhead line-high voltage cable sheath; In step h), the maximum value of the lightning induced voltage at each point along the overhead line-high voltage cable sheath is obtained by the following steps: In the cable model described in h1), voltage monitoring points are set at the cable sheath joints of each segment; h2) In the electromagnetic transient simulation software, set different fault occurrence times. Within a normal operation cycle of the power system, set the fault occurrence time randomly N times and record the lightning induced voltage value of each phase at each point along the cable sheath; h3) After the electromagnetic transient simulation software is repeatedly run, compare the lightning induced voltage values ​​of each phase ABC at each point along the cable sheath to obtain the maximum lightning induced voltage; ， in, is the maximum value of the lightning induced voltage; i represents each point along the cable sheath, 0 is the beginning of the cable sheath; j Represents the ABC three-phase; It is the single-phase voltage value at each point along the cable sheath.

2. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1 is characterized in that: In step a), the actual spatial position of the overhead line includes the height of the ABC three-phase lines from the ground and the distance from the center cross arm of the tower, as well as the height of the ground wire from the ground and the distance from the center cross arm of the tower.

3. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1, characterized in that: In step a), the structural parameters and material parameters of the corresponding model of the overhead line are obtained according to the overhead line model. The structural parameters include: the conductor outer diameter, total number of strands, number of strands in the outermost circle, single strand diameter and sag of the ABC three-phase line, and the conductor outer diameter and sag of the ground wire; the material parameters include: the conductor DC resistance and relative magnetic permeability of the ABC three-phase line, and the conductor DC resistance and relative magnetic permeability of the ground wire.

4. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1, characterized in that: In step b), the actual spatial position of the cable includes the height of the ABC three-phase cable from the ground and the distance from the origin of the horizontal coordinate.

5. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1, characterized in that: In step b), the structural parameters and material parameters of the corresponding model cable are obtained according to the cable model, wherein the structural parameters include: the outer diameter of the conductor core, the outer diameter of the XLPE insulation layer, the outer diameter of the metal sheath, and the outer diameter of the outer insulation layer of the ABC three-phase cable; the material parameters include: the resistivity of the conductor at 90°C, the relative dielectric constant of the XLPE insulation layer, the resistivity of the metal sheath at 70°C, and the relative dielectric constant of the outer insulation layer.

6. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1, characterized in that: In step c), the normal operating parameters of the power system include the effective value of the power frequency voltage of the power system, the equivalent internal inductance of the power system, the load active power and the load reactive power; Step d) specifically includes: d1) The normal operation model of the power system consists of two modules: a module for the equivalent internal inductance of the power system power frequency power supply connection and a module for the power system load; d2) The power system's industrial frequency power supply, the power system's operating equivalent internal inductance, the overhead line model, the cable model, and the power system's load are connected in series in sequence using ABC three-phase conductors.

7. The method for calculating the lightning induced voltage of the overhead line-high voltage cable sheath according to claim 1, characterized in that: In step e), the lightning current model parameters include the lightning current peak value, wave front time and half-peak time. The lightning current is described by a double exponential function model, as shown in the following formula: ， in, Indicates lightning current; Indicates the initial lightning current peak value, kA; is the peak current correction factor; t Indicates time, seconds; is the wave head time coefficient; is the half-wave peak time coefficient; e is a natural constant; ， in, is the peak value of lightning current, 、 and Jointly decided; the wave head time is determined by The half-peak time is determined by Decide.

8. The method for calculating the lightning induced voltage on the sheath of an overhead line-high voltage cable according to claim 1, characterized in that: In step f), the lightning fault parameters include the actual location of the fault point and the fault phase difference.

9. The method for calculating the lightning induced voltage on the sheath of an overhead line-high voltage cable according to claim 1, characterized in that: Step g) is specifically: g1) connecting the lightning current model and the lightning fault point model using a single-phase conductor; g2) Use a single-phase conductor to connect the lightning fault point model and the overhead line model, and select any phase of the ABC three-phase conductors to connect the overhead line model.

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