CN113742895A - Lightning protection simulation method for 10kV distribution network composite cross arm - Google Patents
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Abstract
The invention relates to the technical field of lightning protection simulation of distribution networks, in particular to a lightning protection simulation method for a composite cross arm of a 10kV distribution network. Establishing a lightning current model, an induced lightning overvoltage model, a line and tower model, a composite cross arm flashover model, a distribution transformer model, a 10kV power supply model and a distribution line arrester model in ATP-EMTP software; connecting the models, adjusting the magnitude of lightning current amplitude in the lightning current model, calculating to obtain the magnitude of three-phase corresponding induced lightning voltage, observing whether flashover occurs in the corresponding composite cross arm flashover model, if flashover does not occur, increasing the magnitude of the lightning current in the lightning current model until the composite cross arm flashover model just generates flashover, recording the magnitude of the corresponding lightning current amplitude, and taking the magnitude of the lightning current as the lightning resistance level threshold value of the corresponding composite cross arm.
Description
Technical Field
The invention relates to the technical field of lightning protection simulation of distribution networks, in particular to a lightning protection simulation method for a composite cross arm of a 10kV distribution network.
Background
The distribution network is configured as a network for directly distributing electric energy to power consumers, and the operation efficiency of the distribution network directly affects the overall economic benefit of the operation of the power grid, so that the safety and the reliability of the distribution network are more and more emphasized. The power distribution network is threatened by direct lightning and induced lightning due to the fact that the insulation level of the line is generally low, and 10kV line tripping caused by the induced lightning accounts for more than 70% of line lightning stroke tripping. Lightning induced overvoltage is a main factor causing tripping of a power distribution network and overhead insulated line breakage, and in order to meet the requirements of power supply reliability in different areas, the composite insulating cross arm is adopted to improve the insulating level of the overhead insulated line, so that the effective measures for solving lightning trip of the power distribution network and lightning breakage of an insulated wire are taken.
At present, the cross arm of the distribution network is mostly made of iron materials, the cross arm is good in mechanical performance and excellent in fatigue resistance, the strength of the cross arm is not affected after the cross arm is drilled, and the cross arm has the advantages of being low in price and the like. However, 50% of lightning impulse discharge voltage of the insulator adopted on the 10kV traditional iron cross arm is lower, so that the lightning protection level of the iron cross arm is low, and the lightning trip-out rate is high. And in an insulated line, the lightning stroke is easy to break. In addition, a large amount of steel cross arm beams of the power distribution network transmission lines consume a large amount of steel, more ore energy is consumed, and the production process is accompanied with the problem of environmental pollution. In view of successful operation experience of the composite insulator, power grid enterprises gradually turn the attention to the composite cross arm, the advantages of high strength, low weight, corrosion resistance, excellent insulating property and the like of the composite material are fully utilized, the composite cross arm for the distribution network has the characteristics of good insulating property, high strength and light weight, and the composite cross arm is applied to the distribution network tower and is beneficial to improving the lightning protection performance of the distribution network. Therefore, the composite cross arm has good application prospect.
At present, few researches on the lightning protection performance of the composite insulating cross arm are carried out, and most of the researches mainly relate to the lightning protection performance of a common distribution network line and the performance of a composite insulating cross arm body. In order to research the lightning protection performance of the composite insulating cross arm of the distribution network and calculate the lightning resistance level of the composite insulating cross arm in a distribution network line, the invention provides a 10kV distribution network composite cross arm lightning protection simulation method based on ATP-EMTP simulation software, and can provide technical support for expanding the application range of the composite cross arm of the distribution network.
Disclosure of Invention
In order to solve the problems, the invention provides a lightning protection simulation method for a composite cross arm of a 10kV distribution network, which has the following specific technical scheme:
a lightning protection simulation method for a composite cross arm of a 10kV distribution network comprises the following steps:
s1: establishing a lightning current model, an induced lightning overvoltage model, a line and tower model, a composite cross arm flashover model, a distribution transformer model, a 10kV power supply model and a distribution line arrester model in ATP-EMTP software;
s2: sequentially connecting a 10kV power supply model, a line and tower model, a distribution transformer model and a distribution line arrester model; connecting the composite cross arm flashover model, the lightning current model and the induced lightning overvoltage model with the line and tower model;
s3: adjusting the magnitude of lightning current amplitude in the lightning current model, calculating to obtain the magnitude of three-phase corresponding induced lightning voltage, observing whether flashover occurs in the corresponding composite cross arm flashover model, if flashover does not occur, increasing the magnitude of the lightning current in the lightning current model until the flashover happens to the composite cross arm flashover model, recording the magnitude of the corresponding induced lightning current, and taking the magnitude of the induced lightning current as a lightning-resistant level threshold value of the corresponding composite cross arm.
Preferably, the step S3 further includes the steps of:
s31: setting the amplitude I of the initial lightning current0Calculating to obtain the corresponding induced lightning voltage UX0，X＝A,B,C；
S32: when the lightning resistant level threshold of the composite cross arm of the corresponding phase is simulated, if the lightning current is in the lightning current I0Composite cross arm flashover of lower corresponding phaseIf the model does not generate flashover, increasing delta I every time when the lightning current is adjusted until the flashover of the composite cross arm flashover model occurs when the lightning current is increased to be I ', recording the current amplitude I' and the corresponding phase induced lightning voltage U obtained by corresponding calculationX'；
Otherwise, if the current is lightning current I0And (4) carrying out flashover on the next corresponding phase composite cross arm flashover model, reducing delta I every time when adjusting the lightning current until the composite cross arm flashover model does not have flashover when reducing the lightning current to lightning current I ', recording the lightning current amplitude I' at the moment and correspondingly calculating the induction lightning voltage U of the corresponding phaseX'；
S33: reducing delta I ' every time on the basis of the lightning current I ' until no flashover occurs in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I" and I';
on the contrary, delta I ' is increased every time on the basis of the lightning current I ' until the flashover of the composite cross arm flashover model occurs when the lightning current I ' is adjusted, and the induced lightning voltage U of the corresponding phase is calculatedX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I' and I";
s34: increasing delta I ' every time on the basis of the lightning current I ' obtained in the step S33 until the flashover of the composite cross arm flashover model occurs when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX"', and Δ I" < Δ I'; then the lightning endurance level threshold value of the composite cross arm is between I 'and I';
otherwise, reducing the delta I ' every time on the basis of the lightning current I ' obtained in the step S33 until the flashover does not occur in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX"', and Δ I" < Δ I ', then the lightning withstand level threshold of the composite cross arm is between I ' "and I";
s35: and (5) circulating the step (S33) and the step (S34), adjusting the amplitude of the lightning current until the corresponding lightning current amplitude I just enabling the composite cross arm flashover model to generate flashover is obtained, and calculating the induced lightning voltage U of the corresponding phaseX。
Preferably, the method for establishing the 10kV power model in step S1 is as follows:
the method comprises the steps of selecting an AC source in ATP-EMTP software by adopting a three-phase AC voltage source with rated voltage of 10kV, defaulting to a single-phase grounded 50Hz voltage source after double-click opening, setting the voltage source to be 3 phases, inputting a voltage amplitude of 10000 √ 2 √ 14142V, and searching a SPLITTER phase splitting module in the ATP-EMTP software to obtain three-phase voltages USA, USB and USC at a power output node.
Preferably, the method for establishing the lightning current model in step S1 is as follows:
a Heidler model in ATP-EMTP software is adopted, a lightning voltage waveform of 1.2/50 mus is defaulted after double click opening, and parameters are required to be set: the lightning Current mode is selected, with T _ f 2.6E-6s, tau (37% im) 5E-5s, and amplitude set to-30000A. The lightning channel wave impedance takes 300 omega and is simulated by a 300 omega resistive element.
Preferably, the method for establishing the inductor overvoltage model in step S1 is as follows:
the induced lightning voltage of the line conductor without the overhead ground wire can be calculated according to the following formula:
X＝A,B,C；
UXthe induced lightning voltage value of the X phase is V; hdXThe height of the X-phase lead from the ground is m; sXThe horizontal distance, m, between a lightning stroke point and the X-phase lead; i is the lightning current amplitude, A; k' is a coefficient;
finding an FORTRAN element in a TACS module in the ATP-EMTP, setting the element type to be 88, namely an Inside mode, inputting a number or an expression in a text box of the FORTRAN expression, and naming an output node OUT; the X phase needs to have 3 FORTRAN elements set, Hd _ X, S _ X and UIL _ X, respectively.
Preferably, the method for establishing the line and tower model in step S1 is as follows:
selecting an LCC line Model in ATP-EMTP software, opening the Model page, selecting an overhead line, checking 3 phases and checking a skin effect; selecting JMarti from the model type, and selecting user default fitting for automatic adaptation; setting the earth resistivity to be 100 omega x m and the line length to be 50m in the standard data, namely, setting the tower span;
the pole adopts the multi-wave impedance model, and shaft tower wave impedance is:
h is the average height of the pole, m; r is the equivalent radius of the pole, m;
wherein, a is the maximum width of the electric pole of the section to be calculated, and b is the minimum width of the electric pole of the section to be calculated.
Preferably, the method for establishing the composite cross arm flashover model in step S1 is as follows:
in ATP-EMTP software, a model jointly built by TACS and MODELS modules is used for simulating a composite cross arm, the MODELS module is programmed, when the lead development length L is larger than or equal to the insulation distance d of the composite cross arm, flashover occurs, and a model switch is closed;
preferably, the programming process of the MODELS is as follows:
firstly, setting model parameters k, E0 and the length d of a cross arm, wherein k represents a lead speed development coefficient, and E0 represents the lowest field strength of lead development;
the model automatically measures the voltage of nodes at two ends of the composite cross arm, and the input is UP and UN;
initializing FLASH (0) by parameters, switching off switches at two ends of the cross arm, calculating voltage U (UP-UN) at two ends of the composite cross arm, then calculating field intensity E, judging whether E is greater than the lowest field intensity E0 of pilot development, and if the E is greater than E0, meeting the pilot initial development condition;
and then calculating the pilot development length L by using a rectangular integration method, judging whether the L is more than or equal to the cross arm length d, if the L is more than or equal to d, indicating that the pilot development is finished, the cross arm has flashover, outputting FLASH to be 1, and closing the switch.
Preferably, the method for establishing the distribution transformer model in step S1 is as follows:
when the distribution transformer calculates the lightning impulse, modeling is carried out according to the inlet capacitance, and the formula for calculating the inlet capacitance is as follows:
in the formula, STNThree-phase capacity, MVA, for the transformer; K. n are fitting coefficients respectively.
Preferably, the method for establishing the distribution line arrester model in step S1 includes: the MOV module input parameters in the ATP-EMTP software can simulate the volt-ampere characteristic of the arrester, the input reference voltage is 2 times of rated voltage 34000V in the MOV module, then data points of the volt-ampere characteristic curve of the arrester are input, and the MOV module automatically generates a corresponding arrester model.
The invention has the beneficial effects that: the invention provides a lightning protection simulation method for a composite cross arm of a 10kV distribution network, and provides a 10kV line lightning protection model with complete structure and accurate calculation, which comprises the following steps of; the lightning current model, the inductive lightning overvoltage model, the line and pole tower model, the composite cross arm flashover model, the distribution transformer model, the 10kV power model and the distribution line lightning arrester model which are connected with each other can simulate the condition that the composite cross arm suffers lightning overvoltage in the distribution line, thereby providing convenience for calculating the lightning resistance level of the composite cross arm and researching the lightning protection performance of the composite cross arm. The lightning-resistant level is the maximum current amplitude which can not cause flashover or the minimum lightning current amplitude (kA) which can cause insulation flashover when a lightning stroke line is adopted, the lightning-resistant level of the composite cross arm is simulated by adopting a continuous approaching method, the precision can be improved, and the simulation is carried out by adopting a software programming method, so that the three-phase voltage waveform of the composite cross arm corresponding to the lightning current can be directly observed only by adjusting the amplitude of the lightning current, and whether flashover occurs or not is observed, the method is convenient and rapid, the calculated amount is small, and the obtained precision is high. The invention adopts the leading development method as the more advanced insulation flashover criterion, and can more accurately simulate the flashover process of the composite cross arm.
Drawings
In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.
FIG. 1 is a diagram of a model constructed according to the present invention;
FIG. 2 is a programming flow diagram of a composite cross arm flashover model;
FIG. 3 is a flow chart of the present invention for testing lightning withstand levels of a composite crossarm;
FIG. 4 is a three-phase voltage waveform diagram of the composite cross arm when the lightning current amplitude is 40.0 kA;
FIG. 5 is a three-phase voltage waveform diagram of the composite cross arm when the lightning current amplitude is 39.9 kA.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
As shown in fig. 1, a lightning protection simulation method for a composite cross arm of a 10kV distribution network includes the following steps:
s1: establishing a lightning current model, an induced lightning overvoltage model, a line and tower model, a composite cross arm flashover model, a distribution transformer model, a 10kV power supply model and a distribution line arrester model in ATP-EMTP software;
as shown in fig. 1, the 10kV power model is established as follows:
the method comprises the steps of selecting an AC source in ATP-EMTP software by adopting a three-phase alternating current voltage source with the rated voltage of 10kV, defaulting to a single-phase grounded 50Hz voltage source after double-click opening, setting the voltage source to be 3 phases, inputting a voltage amplitude of 10000 √ 2 √ 14142V, and searching a SPLITTER phase splitting module in the ATP-EMTP software to obtain three-phase voltages USA, USB and USC at a power output node for calculating the induced lightning overvoltage at the back.
The method for establishing the lightning current model comprises the following steps:
a Heidler model in ATP-EMTP software is adopted, a lightning voltage waveform of 1.2/50 mus is defaulted after double click opening, and parameters are required to be set: the lightning Current mode is selected, T _ f is 2.6E-6s, tau (37% im) is 5E-5s, and the amplitude is-30000A, so that a 2.6/50 mu s negative polarity lightning Current waveform with the amplitude of 30kA can be simulated approximately. The lightning channel wave impedance takes 300 omega and is simulated by a 300 omega resistive element. The name of the output node of the Heidler model is set as I _ LEI, and the name is used for calculating the induced lightning voltage in the next step.
The method for establishing the inductive lightning overvoltage model comprises the following steps: the induced lightning voltage of the line conductor without the overhead ground wire can be calculated according to the following formula:
UXthe induced lightning voltage value of the X phase is V; hdXThe height of the X-phase lead from the ground is m; sXThe horizontal distance, m, between a lightning stroke point and the X-phase lead; i is the lightning current amplitude, A; k' is a coefficient, 25 is taken.
Finding an FORTRAN element in a TACS module in the ATP-EMTP, setting the element type to be 88, namely an Inside mode, inputting a number or an expression in a text box of the FORTRAN expression, and naming an output node OUT; the X-phase needs to have 3 FORTRAN elements, Hd _ X, S _ X and UIL _ X, respectively, where X ═ a, B, and C, respectively, represent A, B, C three phases.
Taking phase B as an example, the height Hd _ B (i.e. H) of phase B from the lightning strike point is inputdB) And a horizontal distance S _ B (i.e., S)B) Then the expression of the B-phase induced lightning overvoltage is input into the UIL _ B:
25*I_LEI*log(Hd_B/S_B+sqrt((Hd_B/S_B)**2+1))
both Hd _ B and S _ B are connected into the UIL _ B by a dashed line (relationship), indicating that they are logically sequential rather than electrically connected. And finally, superposing and summing the UIL _ B obtained just by calculation and the power supply voltage USB obtained previously through a summing element to obtain the final B-phase induced lightning voltage UILS _ B. UIL _ B and USB as the inputs to the summing element, and UILS _ B as the output of the summing element.
And finally, selecting a voltage source through a TACSSUR element in the TACS module, inputting UILS _ B into the Name of a TACS node, and connecting the UILS _ B to one end of a B-phase composite cross arm of a No. 0 tower in the line model to realize the condition that the composite cross arm is subjected to induced lightning overvoltage. A. The same applies to phase C.
The method for establishing the model of the line and the tower comprises the following steps:
a JMarti frequency characteristic overhead line model is adopted, and the model is a line model commonly adopted in the current lightning protection calculation. The soil resistivity is 100 omega × m, the total line length is 10km, and the tower span is 50 m. In order to improve the accuracy of the study and reduce the influence of the reflected wave, a relatively long line having the same characteristics as the line under study is connected to the end of the line as a line for eliminating the influence of the reflected wave.
Selecting an LCC line Model in ATP-EMTP software, opening the Model page, selecting an overhead line, checking 3 phases and checking a skin effect; selecting JMarti from the model type, and selecting user default fitting for automatic adaptation; and setting the ground resistivity to be 100 omega m and the line length to be 50m in the standard data, namely, the tower span.
After the Model page is set, clicking the Data page, and inputting the inner diameter (cm), the outer diameter (cm), the direct current resistance (omega/km), the interphase horizontal distance (m) and the ground clearance (m) of each phase of conducting wire of the overhead line.
And clicking a Run ATP button after the setting is finished, and finishing the setting of the line model after the operation is correct.
The electric pole adopts the multi-wave impedance model, ground resistance 20 omega. The wave speed was taken to be 300 m/. mu.s. The wave impedance of the small bus and the connecting line (connected to a power distribution transformer) is selected to be 150 omega according to conservation, and the length is 20 m. A standard 15m reinforced concrete pole and a single-loop wiring structure are adopted, the tip diameter of the pole is 0.19m, the root diameter of the pole is 0.39m, and the underground buried depth is 2.3 m.
The tower wave impedance is:
h is the average height of the pole, m; r is the equivalent radius of the pole, m;
wherein, a is the maximum width of the electric pole of the section to be calculated, and b is the minimum width of the electric pole of the section to be calculated.
After the wave impedance (206 Ω in this case) of the cement tower is calculated, a Linezt _1 wave impedance element is selected from the ATP, and the wave impedance value and the length are input, wherein the length is the height of the cement tower. The ground resistance is typically 10 to 30 Ω, depending on the nature of the soil, here 20 Ω.
The composite cross arm flashover model and flashover criterion have great influence on the accuracy of the calculation result of the lightning withstand level of the power transmission line, and the establishment of the accurate insulation flashover model is very important.
The pilot development method is based on the physical process of long air gap discharge, and whether flashover occurs or not is judged through the pilot development length. When the pilot development length L is larger than or equal to the composite cross arm insulation distance d, flashover occurs, and the model switch is closed. The lead development rate formula recommended in the report of CIGRE in 1991 was used:
in the formula: e0Minimum field strength, negative polarity E, representing lead development0Taking 670 kV/m; k represents a lead velocity development coefficient, and k having a negative polarity of 1 × 10-6m2v-2s-1。
The method for establishing the composite cross arm flashover model comprises the following steps:
in ATP-EMTP software, a model jointly built by TACS and MODELS modules is used for simulating a composite cross arm, MODELS is programmed, when the pilot development length L is larger than or equal to the insulation distance d of the composite cross arm, flashover occurs, and a model switch is closed. As shown in fig. 2, the process of programming the MODELS includes:
firstly, setting model parameters k, E0 and the length d of a cross arm, wherein k represents a lead speed development coefficient, and E0 represents the lowest field strength of lead development;
the model automatically measures the voltage of nodes at two ends of the composite cross arm, and the input is UP and UN;
initializing FLASH (0) by parameters, switching off switches at two ends of the cross arm, calculating voltage U (UP-UN) at two ends of the composite cross arm, then calculating field intensity E, judging whether E is greater than the lowest field intensity E0 of pilot development, and if the E is greater than E0, meeting the pilot initial development condition;
and then calculating the pilot development length L by using a rectangular integration method, judging whether the L is more than or equal to the cross arm length d, if the L is more than or equal to d, indicating that the pilot development is finished, the cross arm has flashover, outputting FLASH to be 1, and closing the switch.
The method for establishing the distribution transformer model comprises the following steps:
the capacity of the distribution transformer is 500kVA, referring to 'power system overvoltage calculation', the distribution transformer is modeled according to the inlet capacitance when calculating the lightning impulse, and the formula for calculating the inlet capacitance is as follows:
in the formula, STNThree-phase capacity, MVA, for the transformer; K. n are fitting coefficients respectively. Depending on the rated voltage of the system, K350 and n 3 are considered temporarily for the distribution system.
| Voltage class/ | K | n | |
| 10/35 | 350 | 3 | |
| 110/220 | 540 | 3 | |
| Over 500A | 940 | 4 |
The method for establishing the distribution line arrester model comprises the following steps: at present, most of lightning arresters adopted in a 10kV power distribution network are products with a nominal discharge current of 5kA series, typical lightning arresters with a nominal discharge current of 5kA are YH5WS5-17/50W, and rated voltages of the lightning arresters are all 17 kV. The MOV module input parameters in the ATP-EMTP software can simulate the volt-ampere characteristic of the arrester, the input reference voltage is 2 times of rated voltage 34000V in the MOV module, then data points (voltage and current) of the volt-ampere characteristic curve of the arrester are input, and the MOV module automatically generates a corresponding arrester model.
S2: sequentially connecting a 10kV power supply model, a line and tower model, a distribution transformer model and a distribution line arrester model; and connecting the composite cross arm flashover model, the lightning current model and the induced lightning overvoltage model with the line and tower model.
S3: as shown in fig. 3, adjusting the magnitude of the lightning current amplitude in the lightning current model, calculating to obtain the magnitude of the corresponding induced lightning voltage of three phases, observing whether flashover occurs in the corresponding composite cross arm flashover model, if flashover does not occur, increasing the magnitude of the lightning current in the lightning current model until the flashover just occurs in the composite cross arm flashover model, and recording the magnitude of the corresponding induced lightning current amplitude, wherein the magnitude of the induced lightning current is the lightning withstand level threshold of the corresponding composite cross arm. Step S3 further includes the steps of:
s31: setting the amplitude I of the initial lightning current0Calculating to obtain the corresponding induced lightning voltage UX0，X＝A,B,C；
S32: when the lightning withstand level threshold of the composite cross arm of the corresponding phase is simulated, if the lightning discharge current I is in the lightning discharge state0And if the flashover does not occur in the composite cross arm flashover model of the next corresponding phase, increasing delta I every time when the lightning current is adjusted until the flashover occurs in the composite cross arm flashover model when the lightning current I 'is increased, recording the lightning current I' at the moment and the induced lightning voltage U of the corresponding phase obtained by corresponding calculationX'；
Otherwise, if the current is lightning current I0And (4) carrying out flashover on the next corresponding phase composite cross arm flashover model, reducing delta I every time when adjusting the lightning current until the composite cross arm flashover model does not have flashover when reducing the lightning current to lightning current I ', recording the lightning current I' at the moment and the induction lightning voltage U of the corresponding phase obtained by corresponding calculationX'；
S33: reducing delta I ' every time on the basis of the lightning current I ' until no flashover occurs in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the corresponding phase inductanceLightning voltage UX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I" and I';
on the contrary, delta I ' is increased every time on the basis of the lightning current I ' until the flashover of the composite cross arm flashover model occurs when the lightning current I ' is adjusted, and the induced lightning voltage U of the corresponding phase is calculatedX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I' and I";
s34: increasing delta I ' every time on the basis of the lightning current I ' obtained in the step S33 until the flashover of the composite cross arm flashover model occurs when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX"', and Δ I" < Δ I'; then the lightning endurance level threshold value of the composite cross arm is between I 'and I';
otherwise, reducing the delta I ' every time on the basis of the lightning current I ' obtained in the step S33 until the flashover does not occur in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX"', and Δ I" < Δ I ', then the lightning withstand level threshold of the composite cross arm is between I ' "and I";
s35: and (5) circulating the step (S33) and the step (S34), adjusting the amplitude of the lightning current until the lightning current I which just enables the composite cross arm flashover model to be corresponding to the flashover is obtained, and calculating the induced lightning voltage U of the corresponding phaseX。
The technical problem to be solved by the model is to provide a complete-structure and accurate-calculation 10kV line lightning protection simulation method aiming at the defects of the lightning protection performance research of the composite cross arm of the distribution network, and the lightning protection simulation method can simulate the lightning overvoltage condition of the composite cross arm in the distribution line, so that convenience is provided for calculating the lightning resistance level of the composite cross arm and researching the lightning protection performance of the composite cross arm. The criterion of the pilot development method is a more advanced insulation flashover criterion, and the flashover process of the composite cross arm can be more accurately simulated.
Fig. 1 shows a 10kV line composite cross arm inductive lightning model, which is provided with 3 poles and towers in total, the left side of the line is a 10kV power supply, and the right side is a distribution transformer model. The line length is about 10 km. Setting lightning current amplitude to be 39kA, setting lightning distance to be 30m from the horizontal distance of a B phase of a line, running simulation to obtain a three-phase induction lightning overvoltage waveform of the composite cross arm, finding that flashover does not occur, taking 1kA as an interval, and increasing the lightning current amplitude to 40kA, wherein the voltage waveform is shown in figure 4, as can be seen from figure 4, the voltage of the B phase is 0 at 24us, the flashover just occurs, and no flashover occurs in A, C two phases. When the composite cross arm can not withstand 40kA of induction mines, the three-phase induction mine overvoltage waveform of the composite cross arm is obtained when the lightning current amplitude is reduced downwards by 0.2kA to 39.8kA, no flashover is found to occur, the lightning withstand level threshold value of the composite cross arm is between 39.8kA and 40kA, and the lightning current amplitude is increased by 0.1kA to 39.9kA, the three-phase induction mine overvoltage waveform of the composite cross arm is obtained as shown in figure 5, no flashover is found to occur, the composite cross arm can not withstand 40kA of induction mines, and the flashover is not occurred at 39.9kA, the lightning withstand level is determined to be 39.9 kA. If the precision needs to be improved, the next test can be continued, and details are not described in this embodiment.
The present invention is not limited to the above-described embodiments, which are merely preferred embodiments of the present invention, and the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A lightning protection simulation method for a composite cross arm of a 10kV distribution network is characterized by comprising the following steps: the method comprises the following steps:
s1: establishing a lightning current model, an induced lightning overvoltage model, a line and tower model, a composite cross arm flashover model, a distribution transformer model, a 10kV power supply model and a distribution line arrester model in ATP-EMTP software;
s2: sequentially connecting a 10kV power supply model, a line and tower model, a distribution transformer model and a distribution line arrester model; connecting the composite cross arm flashover model, the lightning current model and the induced lightning overvoltage model with the line and tower model;
s3: adjusting the magnitude of lightning current amplitude in the lightning current model, calculating to obtain the magnitude of three-phase corresponding induced lightning voltage, observing whether flashover occurs in the corresponding composite cross arm flashover model, if flashover does not occur, increasing the magnitude of the lightning current in the lightning current model until the flashover happens to the composite cross arm flashover model, recording the magnitude of the corresponding induced lightning current, and taking the magnitude of the induced lightning current as a lightning-resistant level threshold value of the corresponding composite cross arm.
2. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the step S3 further includes the steps of:
s31: setting the amplitude I of the initial lightning current0Calculating to obtain the corresponding induced lightning voltage UX0，X＝A,B,C；
S32: when the lightning resistant level threshold of the composite cross arm of the corresponding phase is simulated, if the lightning current is in the lightning current I0And if the flashover does not occur in the composite cross arm flashover model of the next corresponding phase, increasing delta I every time when the lightning current is adjusted until the flashover occurs in the composite cross arm flashover model when the lightning current I 'is increased, recording the lightning current amplitude I' at the moment and correspondingly calculating the induction lightning voltage U of the corresponding phaseX'；
Otherwise, if the current is lightning current I0And (4) carrying out flashover on the next corresponding phase composite cross arm flashover model, reducing delta I every time when adjusting the lightning current until the composite cross arm flashover model does not have flashover when reducing the lightning current to lightning current I ', recording the lightning current amplitude I' at the moment and correspondingly calculating the induction lightning voltage U of the corresponding phaseX'；
S33: reducing delta I ' every time on the basis of the lightning current I ' until no flashover occurs in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I" and I';
on the contrary, delta I ' is increased every time on the basis of the lightning current I ' until the flashover of the composite cross arm flashover model occurs when the lightning current I ' is adjusted, and the induced lightning voltage U of the corresponding phase is calculatedX", and Δ I '< Δ I, then it can be known that the lightning withstand level threshold of the composite cross arm is between I' and I";
s34: increases Δ I "every time on the basis of the lightning current I" obtained in step S33 untilWhen the lightning current I' ″ is adjusted, the flashover of the composite cross arm flashover model occurs, and the induced lightning voltage U of the corresponding phase is calculatedX"', and Δ I" < Δ I'; then the lightning endurance level threshold value of the composite cross arm is between I 'and I';
otherwise, reducing the delta I ' every time on the basis of the lightning current I ' obtained in the step S33 until the flashover does not occur in the composite cross arm flashover model when the lightning current I ' is adjusted, and calculating the induced lightning voltage U of the corresponding phaseX"', and Δ I" < Δ I ', then the lightning withstand level threshold of the composite cross arm is between I ' "and I";
s35: and (5) circulating the step (S33) and the step (S34), adjusting the amplitude of the lightning current until the corresponding lightning current amplitude I just enabling the composite cross arm flashover model to generate flashover is obtained, and calculating the induced lightning voltage U of the corresponding phaseX。
3. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the 10kV power supply model in the step S1 is as follows:
the method comprises the steps of selecting an AC source in ATP-EMTP software by adopting a three-phase AC voltage source with rated voltage of 10kV, defaulting to a single-phase grounded 50Hz voltage source after double-click opening, setting the voltage source to be 3 phases, inputting a voltage amplitude of 10000 √ 2 √ 14142V, and searching a SPLITTER phase splitting module in the ATP-EMTP software to obtain three-phase voltages USA, USB and USC at a power output node.
4. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the lightning current model in the step S1 is as follows:
a Heidler model in ATP-EMTP software is adopted, a lightning voltage waveform of 1.2/50 mus is defaulted after double click opening, and parameters are required to be set: the lightning Current mode is selected, with T _ f 2.6E-6s, tau (37% im) 5E-5s, and amplitude set to-30000A. The lightning channel wave impedance takes 300 omega and is simulated by a 300 omega resistive element.
5. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the induction lightning voltage model in the step S1 is as follows:
the induced lightning voltage of the line conductor without the overhead ground wire can be calculated according to the following formula:
UXthe induced lightning voltage value of the X phase is V; hdXThe height of the X-phase lead from the ground is m; sXThe horizontal distance, m, between a lightning stroke point and the X-phase lead; i is the lightning current amplitude, A; k' is a coefficient;
finding an FORTRAN element in a TACS module in the ATP-EMTP, setting the element type to be 88, namely an Inside mode, inputting a number or an expression in a text box of the FORTRAN expression, and naming an output node OUT; the X phase needs to have 3 FORTRAN elements set, Hd _ X, S _ X and UIL _ X, respectively.
6. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the line and tower model in the step S1 is as follows:
selecting an LCC line Model in ATP-EMTP software, opening the Model page, selecting an overhead line, checking 3 phases and checking a skin effect; selecting JMarti from the model type, and selecting user default fitting for automatic adaptation; setting the earth resistivity to be 100 omega x m and the line length to be 50m in the standard data, namely, setting the tower span;
the pole adopts the multi-wave impedance model, and shaft tower wave impedance is:
h is the average height of the pole, m; r is the equivalent radius of the pole, m;
wherein, a is the maximum width of the electric pole of the section to be calculated, and b is the minimum width of the electric pole of the section to be calculated.
7. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the composite cross arm flashover model in the step S1 is as follows:
in ATP-EMTP software, a model jointly built by TACS and MODELS modules is used for simulating a composite cross arm, the MODELS module is programmed, when the pilot development length L is larger than or equal to the insulation distance d of the composite cross arm, flashover occurs, and a model switch is closed.
8. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 7, characterized in that: the programming process of the MODELS comprises the following steps:
firstly, setting model parameters k, E0 and the length d of a cross arm, wherein k represents a lead speed development coefficient, and E0 represents the lowest field strength of lead development;
the model automatically measures the voltage of nodes at two ends of the composite cross arm, and the input is UP and UN;
initializing FLASH (0) by parameters, switching off switches at two ends of the cross arm, calculating voltage U (UP-UN) at two ends of the composite cross arm, then calculating field intensity E, judging whether E is greater than the lowest field intensity E0 of pilot development, and if the E is greater than E0, meeting the pilot initial development condition;
and then calculating the pilot development length L by using a rectangular integration method, judging whether the L is more than or equal to the cross arm length d, if the L is more than or equal to d, indicating that the pilot development is finished, the cross arm has flashover, outputting FLASH to be 1, and closing the switch.
9. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the distribution transformer model in step S1 is as follows:
when the distribution transformer calculates the lightning impulse, modeling is carried out according to the inlet capacitance, and the formula for calculating the inlet capacitance is as follows:
in the formula, STNThree-phase capacity, MVA, for the transformer; K. n are fitting coefficients respectively.
10. The lightning protection simulation method for the composite cross arm of the 10kV distribution network according to claim 1, characterized in that: the method for establishing the distribution line arrester model in the step S1 includes: the MOV module input parameters in the ATP-EMTP software can simulate the volt-ampere characteristic of the arrester, the input reference voltage is 2 times of rated voltage 34000V in the MOV module, then data points of the volt-ampere characteristic curve of the arrester are input, and the MOV module automatically generates a corresponding arrester model.
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