CN110765666A - Simulation method of lightning strike indirect breakdown fault of transmission line caused by bifurcated lightning - Google Patents

Abstract

The invention discloses a method for simulating a breakdown fault of a transmission line caused by a bifurcated lightning strike. Substations, transmission lines are erected by towers every few hundred meters; establish a lightning channel model: use the R‑C branch equivalent lightning pilot channel to discharge the ground; establish a simulation model: simulate the real transmission line route bifurcation caused by lightning strikes the process of wearing. The invention can quantitatively calculate the amplitude of the discharge pulse generated by the bifurcated lightning on the transmission line, can assist in judging the nature of the fault in actual operation, effectively prevent the fault caused by the bifurcated lightning and the indirect breakdown of the transmission line due to the lightning strike, and avoid the split The hidden danger to the line in the case of indirect breakdown of the fork lightning.

Description

Simulation method of lightning strike indirect breakdown fault of transmission line caused by bifurcated lightning

technical field

The invention relates to a simulation method for a breakdown fault of a transmission line caused by a bifurcated lightning strike and belongs to the technical field of lightning protection of a transmission line.

Background technique

Lightning current will produce strong electromagnetic field, thermal effect and stress, which will have adverse effects on transmission lines and electrical equipment. Due to the complexity of the lightning process and the various reasons for lightning strike accidents, in order to master the characteristics of lightning and accurately analyze the development process of lightning, a large number of lightning location systems, lightning current and lightning overvoltage monitoring systems are currently used to record fault waveforms and assist lightning strike faults. Find and identify.

A large number of theoretical studies have been done on lightning overvoltage at home and abroad, and a large number of lightning overvoltage simulation models have been established. Based on the simulation analysis, the impact of lightning impulse on ultra-high-speed transient protection and lightning resistance performance, and the characteristics of short-circuit faults have been identified and studied. . Since the 1980s, my country's power grid has begun to study lightning monitoring technology, and develop and build lightning positioning systems. At present, a power grid lightning monitoring network has been established nationwide, in order to achieve rapid lightning fault location, lightning accident identification, lightning parameter statistics, lightning protection Level assessment and lightning warning provide a reliable platform. In recent years, the induced overvoltage and counterattack overvoltage generated by the lightning strike on the top of the tower have been calculated and analyzed from the electromagnetic field theory, and the basis of lightning protection calculation and lightning protection design has been supplemented. In order to conduct in-depth research on the nature of line lightning strike accidents, combined with the monitoring data provided by the online monitoring system, the automatic identification and diagnosis system is studied to automatically identify and diagnose the type of lightning strike overvoltage, and take measures to suppress the overvoltage fast response according to the diagnosis results. .

In actual operation, it is impossible for all the lightning points of transmission lines to be concentrated on conductors, lightning protection lines and towers, so the study of lightning strikes is complicated and uncertain. At present, most of the existing researches are aimed at the lightning strike of direct breakdown, and there are few researches specifically aimed at indirect breakdown. The impact of the two breakdown methods on the power system is also different. In the case of indirect breakdown, there will be hidden dangers to the line, but the probability of causing line tripping is smaller than that of direct breakdown. Indirect breakdown is also different from direct breakdown in terms of lightning strike fault characteristics.

Forked lightning is when lightning strikes the ground, due to the randomness of the discharge in the long air gap, the lightning leader may simultaneously appear in several directions with similar electric field strength during the downward development process, and hit multiple ground objects at the same time. Happening. Due to the particularity of bifurcated lightning, there is currently a lack of research on lightning strike faults of bifurcated lightning. Therefore, it is necessary to propose a simulation method for the indirect breakdown fault of transmission line caused by bifurcation lightning.

SUMMARY OF THE INVENTION

Aiming at the shortcomings of the current research, the present invention proposes a simulation method for the indirect breakdown fault of the transmission line caused by the bifurcated lightning, which can effectively discriminate the fault of the transmission line's indirect breakdown caused by the bifurcation lightning.

The technical scheme adopted by the present invention to solve its technical problems is:

A method for simulating an indirect breakdown fault of a transmission line caused by a bifurcated lightning strike provided by an embodiment of the present invention includes the following steps:

Establish a transmission line model: the transmission line is powered by the sending-end substation, and the electric energy is transmitted to the receiving-end substation through the transmission line, and the transmission line is erected by poles and towers every few hundred meters;

Establish lightning channel model: use the discharge process of the R-C branch equivalent lightning pilot channel to the ground;

Establish a simulation model: simulate the process of indirect breakdown caused by bifurcated lightning in real transmission lines.

As a possible implementation manner of this embodiment, the transmission line model includes the geometric dimensions of the transmission line and conductor data.

As a possible implementation of this embodiment, the lightning channel model is that when the lightning leader moves down the channel, charges are stored in the channel, which is equivalent to the energy storage on the capacitor of the energy storage element in the circuit. When the streamer of the conductive corona reaches the ground, the final step of the discharge begins, and when the backlash develops upward, the charge in the channel discharges to the ground, which is equivalent to the energy stored instantaneously in the switching circuit and is released in the form of heat energy through the resistance in the circuit.

As a possible implementation of this embodiment, in the lightning channel model, the lightning strike conductor voltage u is estimated by the following formula:

In the formula, i is the magnitude of the lightning current, and Z is the wave impedance of the lightning channel.

As a possible implementation manner of this embodiment, a simulation model is established based on ATP-EMTP.

As a possible implementation manner of this embodiment, the J.Marti model is used to establish a transmission line model.

As a possible implementation manner of this embodiment, the simulation model does not involve towers.

As a possible implementation manner of this embodiment, the transmission line does not take into account the intermediate transformation power station.

The beneficial effects that the technical solutions of the embodiments of the present invention can have are as follows:

The technical solution of the embodiment of the present invention can quantitatively calculate the amplitude of the discharge pulse generated by the bifurcated lightning on the transmission line, which can assist in judging the nature of the fault in actual operation, and perform some measures on the fault of the transmission line caused by the bifurcation lightning. To prevent and avoid the hidden danger to the line in the case of the indirect breakdown of the bifurcated lightning.

Description of drawings:

FIG. 1 is a flowchart of a simulation method for a breakdown fault of a transmission line caused by a bifurcated lightning strike according to an exemplary embodiment;

Figure 2 is a schematic diagram of a bifurcated lightning discharge process;

Figure 3 is an equivalent circuit diagram of a lightning channel;

Figure 4 is a schematic diagram of a simulation model of indirect breakdown of transmission lines caused by bifurcated lightning;

Figure 5 is a schematic diagram of the geometric dimensions of a double-circuit line on the same tower;

Fig. 6 is a kind of faulty phase B-phase current schematic diagram;

Figure 7 is a schematic diagram of three-phase current at the moment of failure;

Fig. 8 is a schematic diagram of three-phase voltage at the moment of failure.

Detailed ways

Below in conjunction with accompanying drawing and embodiment, the present invention will be further described:

In order to clearly illustrate the technical features of the solution, the present invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the invention. In order to simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Furthermore, the present invention may repeat reference numerals and/or letters in different instances. This repetition is for the purpose of simplicity and clarity and does not in itself indicate a relationship between the various embodiments and/or arrangements discussed. It should be noted that the components illustrated in the figures are not necessarily drawn to scale. Descriptions of well-known components and processing techniques and processes are omitted from the present invention to avoid unnecessarily limiting the present invention.

FIG. 1 is a flowchart illustrating a method for simulating a breakdown fault of a transmission line caused by a bifurcated lightning strike, according to an exemplary embodiment. As shown in FIG. 1 , a simulation method for a breakdown fault of a transmission line caused by a bifurcated lightning strike provided by an embodiment of the present invention includes the following steps:

Establish a transmission line model: the transmission line is powered by the sending-end substation, and the electric energy is transmitted to the receiving-end substation through the transmission line, and the transmission line is erected by poles and towers every few hundred meters;

Establish lightning channel model: use the discharge process of the R-C branch equivalent lightning pilot channel to the ground;

Establish a simulation model: simulate the process of indirect breakdown caused by bifurcated lightning in real transmission lines.

The invention can quantitatively calculate the amplitude of the discharge pulse generated by the bifurcated lightning on the transmission line, and can assist in judging the fault nature in actual operation.

1. Characteristics of indirect breakdown of transmission lines caused by bifurcation lightning

Forked lightning is when lightning strikes the ground, due to the particularity of the electric charge accumulated near the ground, the lightning current is bifurcated, thus forming two discharge points on the ground. as shown in picture 2.

As shown in Figure 2, the lightning pilot generates multiple branches in the process of descending and approaching the ground. One pilot branch I hits a certain phase of the line, and the other pilot branch II hits the ground. A power frequency discharge channel from the wire to the ground is formed. However, due to the long arc discharge channel and high arc resistance, a stable power frequency arc cannot be formed, resulting in the discharge channel being extinguished. The short-term discharge pulse formed on the line wire during this process causes the differential current on both sides to be large and the current differential protection action trips. After being struck by lightning, the corresponding lightning channel is temporarily not formed inside, and the insulator is not broken down, so it is an indirect breakdown.

When the bifurcated lightning causes the indirect breakdown of the line, the lightning current is generally less than the lightning resistance level of the line shielding, and the power frequency freewheeling channel is unstable and easy to extinguish, so there will be no obvious discharge traces on the line.

2. Establishment of the simulation model

The invention establishes a simulation model based on ATP-EMTP, and simulates the process of indirect breakdown caused by bifurcated lightning in real transmission lines. Since the fault current does not pass through the tower, the tower is not involved in the model. A time-controlled switch is used for fault triggering.

The real transmission line structure is: the transmission line is powered by the sending-end substation, and the electric energy is transmitted to the receiving-end substation through the transmission line. The transmission line is erected by towers every few hundred meters. In practice, in order to reduce power loss, power stations will be converted during construction. This model does not consider the medium-transition power station. This model includes the sending-end power supply model, the transmission line model and the lightning strike channel model.

(1) Transmission line model

Simulation requires detailed transmission line geometry and conductor data. In the electromagnetic transient calculation, the change of the line parameters with the frequency affects the electromagnetic transient process. The J.Marti line equivalent model is relatively stable in transient calculation, and its calculation accuracy deviation is relatively small when the main frequencies such as ground faults are intensively calculated. Therefore, the J.Marti line equivalent model is selected as the line model.

(2) Lightning channel model

When the leader moves down the channel, the charge is stored in the channel, which is equivalent to the energy storage on the capacitor of the energy storage element in the circuit. When the streamer of the leader corona reaches the ground, the final step of the discharge begins. When the knockback develops upwards, the charge in the channel is discharged to the ground, which is equivalent to the energy stored in the moment of switching, which is released in the form of heat energy through the resistance in the circuit. Therefore, the discharge process of the R-C branch equivalent pilot channel to the ground can be used, as shown in Figure 3.

The voltage of the capacitor C is the voltage of the wire when the lightning strikes the wire, and the voltage of the lightning strike wire can be estimated by the following formula:

In the formula, i is the magnitude of the lightning current, and Z is the wave impedance of the lightning channel.

According to GB/T50064-2014 "Overvoltage Protection and Insulation Coordination Design Specification for AC Electrical Installations", when the lightning current is less than 20kA, the lightning channel wave impedance is greater than 1000 ohms, and when the lightning current is 20-40kA, the lightning channel wave Impedance is about 600-1000 ohms.

(3) Simulation model

The simulation model is shown in Figure 4, LCC is the line element, U1 and U2 are the line sending power supply, LINEZ-T is the ABC three-phase wire impedance, LINEZ is the ground wire impedance, U(0) is the charging capacitor, and R is the lightning channel Impedance, G is a time-controlled switch, I is a current detector, and V is a voltage detector.

implementation plan

Taking the 1000kV transmission line as an example, the B-phase conductor is struck by lightning, and the current size of the bifurcated lightning is 30kA. The lightning resistance level of the 1000kV line is about 40kA, which will not cause the line to trip.

(1) Line parameters

The double-circuit transmission line on the same tower, the conductor arrangement is shown in Figure 5, the conductor is 8×JL1/LHA1-465/210, the ground wire is OPGW-185, the calculated radius of the sub-conductor is 210mm, the eight splits, the split spacing is 400mm, the conductor pair The ground height is 84m, and the phases are arranged horizontally.

(2) Lightning channel parameters

The lightning current is 30kA, the lightning channel wave impedance is 800 ohms, and the initial voltage of capacitor C is 6000kV.

(3) The power supply is 1000kV AC power supply.

(4) The voltage and current waveforms of the conductors at the moment of lightning strike B-phase short-circuit are shown in Figures 6 to 8.

The B-phase current of the faulty phase increases rapidly at the moment of lightning short-circuit, the amplitude is 4.5kA, and it recovers after about 1ms. The AC phase current fluctuates slightly due to electromagnetic induction, and recovers after about 1ms. The three-phase voltage fluctuates due to the short-circuit of the B-phase, and recovers after about 1ms. The short-term discharge pulse of 4.5kA on the line wire will cause the protection action to trip, the fault disappears after 1ms, and the line reclosing is successful.

The above are only the preferred embodiments of the present invention. For those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the present invention. the scope of protection of the invention.

Claims (8)

1. the simulation method that a bifurcation lightning causes transmission line lightning strike indirect breakdown fault, it is characterized in that, may further comprise the steps: Establish a transmission line model: the transmission line is powered by the sending-end substation, and the electric energy is transmitted to the receiving-end substation through the transmission line, and the transmission line is erected by poles and towers every few hundred meters; Establish lightning channel model: use the discharge process of the R-C branch equivalent lightning pilot channel to the ground; Establish a simulation model: simulate the process of indirect breakdown caused by bifurcated lightning in real transmission lines. 2 . The method for simulating an indirect breakdown fault of a transmission line caused by a bifurcated lightning strike according to claim 1 , wherein the transmission line model includes transmission line geometric dimensions and conductor data. 3 . 3. bifurcated lightning according to claim 1 causes the simulation method of transmission line lightning strike indirect breakdown fault, it is characterized in that, described lightning channel model is that electric charge is stored in channel when lightning pilot moves downward along channel, etc. The effect is that there is energy storage on the capacitor of the energy storage element in the circuit. When the streamer of the lightning lead corona reaches the ground, the final step of the discharge begins. When the backlash develops upward, the charge in the channel discharges to the ground, which is equivalent to the moment of switching. The stored energy is released as heat energy through the resistance in the circuit. 4. the simulation method that bifurcated lightning according to claim 1 causes transmission line lightning strike indirect breakdown fault, it is characterized in that, in lightning channel model, lightning strike conductor voltage u is estimated by following formula:

In the formula, i is the magnitude of the lightning current, and Z is the wave impedance of the lightning channel. 5. The simulation method for the breakdown fault of transmission lines caused by bifurcated lightning according to any one of claims 1-4, wherein a simulation model is established based on ATP-EMTP. 6. The method for simulating a breakdown fault of a transmission line caused by a bifurcated lightning strike according to any one of claims 1 to 4, wherein the transmission line model is established by using the J.Marti model. 7 . The method for simulating the breakdown fault between lightning strikes of transmission lines caused by bifurcated lightning according to claim 1 , wherein the simulation model does not involve towers. 8 . 8 . The method for simulating a breakdown fault of a transmission line caused by a bifurcated lightning strike according to any one of claims 1 to 4 , wherein the transmission line does not consider a mid-transition power station. 9 .

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