CN114362198A - High-impedance design method for extra-high voltage limited power frequency overvoltage and secondary arc current - Google Patents

Abstract

The invention belongs to the technical field of power transmission and transformation engineering, and in particular relates to a high-resistance design method for ultra-high voltage limiting power frequency overvoltage and submerged supply current. The invention includes: step 1. establishing a system based on electromagnetic transient simulation model; step 2. determining the power frequency overvoltage at the end of the no-load long line of the ultra-high voltage transmission line; step 3. obtaining the power frequency voltage rise caused by the line load shedding Step 4. Determine the power frequency overvoltage caused by the single-phase short circuit of the UHV line; Step 5. Determine the high reactance value of the UHV line; Step 6. Determine the neutral point reactance of the high-voltage shunt reactor. The invention uses the method of adding neutral point reactance to the high-voltage shunt reactor to reduce the submerged supply current and recovery voltage, solve the problems of temporary power frequency overvoltage and submerged supply current exceeding the standard of the long-distance ultra-high voltage AC power grid, and improve the special Single-phase reclosing success rate of high-voltage lines. The calculation method is simple and practical, and provides technical support for power frequency overvoltage in UHV power grid and its influence on power grid equipment.

Description

A high-resistance design method for ultra-high voltage to limit power frequency overvoltage and submerged supply current

technical field

The invention belongs to the technical field of power transmission and transformation engineering, and in particular relates to a high-resistance design method for ultra-high voltage to limit power frequency overvoltage and submerged supply current, in particular to an ultra-high voltage shunt reactor and its neutral point small reactance to limit AC characteristics Methods for power frequency overvoltage and submerged supply current of high voltage transmission lines.

Background technique

The frequency of the power frequency overvoltage is the power frequency or close to the power frequency. The causes of power frequency overvoltage include the capacitive effect of long no-load lines, the normal phase voltage increase caused by asymmetric ground faults, and the sudden change of load, etc., which are related to the system structure, capacity, parameters and operation mode.

The UHV power grid has the power transmission capacity of longer distance, larger capacity and lower loss. However, the charging reactive power of the UHV transmission line per 1km line length can exceed 5.3MVA, which is about 4-6 times that of the 500kV line under the same line length. In the UHV power system, the magnitude of the power frequency overvoltage directly affects the amplitude of the operating overvoltage, and may endanger the safe operation of the equipment system. At the same time, the power frequency overvoltage is also an important basis for determining the rated voltage of the arrester, which in turn affects the overvoltage level of the system.

Due to the requirement of long-distance power transmission such as the interconnection of UHV grids and the mutual supply of north and south power grids in North China, Central China and East China, a considerable number of UHV lines are relatively long. The charging power of a single-segment line is very large, and a high-voltage shunt reactor (referred to as high reactance) must be used for compensation. After the UHV line is connected to the shunt reactor, the inductive reactive power of the reactor partially compensates the capacitive reactive power of the line, which is equivalent to reducing the line length and reducing the power frequency voltage rise value.

According to the national standard GB/Z24842-2009 "Overvoltage and Insulation Coordination of 1000kV UHV AC Power Transmission and Transformation Engineering", the power frequency overvoltage of 1000kV system generally needs to be limited to less than 1.3pu. In the case of single-phase grounding and three-phase load rejection, the line The side can be short-term (the duration does not exceed 0.5s) and is allowed to be below 1.4pu.

The compensation degree of high reactance should not be too high, so as not to make reactive power compensation and voltage control difficult during heavy load operation. According to the experience of UHV projects in operation in my country, in the early stage of UHV power grid construction, the high resistance compensation degree is controlled at 80%-90%. In areas with strong power grids or when UHV transmission lines are short, the compensation degree can be appropriately reduced.

The submerged supply current is not an overvoltage, but it is an electromagnetic transient phenomenon that needs attention during the single-phase reclosing process. The submerged supply current of UHV lines is large, the recovery voltage is high, and the submerged supply arc is difficult to extinguish, which may affect the no-current intermittent time and success rate of single-phase reclosing.

SUMMARY OF THE INVENTION

Aiming at the deficiencies in the above-mentioned prior art, the present invention provides a high-resistance design method for ultra-high voltage limiting power frequency overvoltage and submerged supply current. The purpose of the invention is to achieve the purpose of the invention to solve the problems of temporary power frequency overvoltage and submerged supply current exceeding the standard of the long-distance UHV AC power grid.

The technical scheme that the present invention adopts for realizing the above-mentioned purpose is:

A high-resistance design method for ultra-high voltage to limit power frequency overvoltage and submerged supply current, comprising the following steps:

Step 1. Establish a system based on electromagnetic transient simulation model;

Step 2. Determine the power frequency overvoltage at the end of the no-load long line of the UHV transmission line;

Step 3. Find the increase in power frequency voltage caused by line load shedding;

Step 4. Determine the power frequency overvoltage caused by the single-phase short circuit of the UHV line;

Step 5. Determine the high reactance value of the UHV line;

Step 6. Determine the neutral point reactance of the high-voltage shunt reactor.

Further, the establishment of the electromagnetic transient simulation model of the system described in step 1 is based on the collected system parameters, based on the electromagnetic transient modeling method, to establish the distributed model of the UHV power transmission and transformation line, the main transformer and the UHV Detailed models of networked engineering and equivalent models of regional grid power and loads.

Further, the collected system parameters include the main parameters of the local synchronous motor and the main parameters of the transmission line; the main parameters of the local synchronous motor include: synchronous motor, main transformer, series compensation, low-voltage reactor compensation, low-voltage capacitor compensation , Section load system parameters; the main parameters of the transmission line include: transmission line-to-ground capacitance, phase-to-phase capacitance, inductance per unit length, and susceptance (capacitance) line parameters.

Further, the determination of the power frequency overvoltage at the end of the no-load long line of the UHV transmission line in step 2 is obtained by comparing the capacity rise effect of the line simply with the capacity rise effect of the no-load line after considering the power supply reactance. The power supply reactance is equivalent to increasing the line length, which further increases the power frequency overvoltage and makes the resonance point earlier;

计算出首端电压

末端电压

及线路中某一点的电压

为式(1)：Let the length of the no-load lossless line be l, when the terminal current

Calculate the head-end voltage

terminal voltage

and the voltage at a point in the line

is formula (1):

为波阻抗；

为相位常数；x为离受端的距离，L₀为单位长度电抗；C₀为单位长度电容，l为线路长度；where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, L ₀ is the reactance per unit length; C ₀ is the capacitance per unit length, and l is the line length;

The voltage transfer coefficient from the end of the line to the head end is defined as formula (2):

末端电压

线路末端对首端的电压传递系数为K₁₂；In the formula: head-end voltage

terminal voltage

The voltage transfer coefficient from the end of the line to the head end is K ₁₂ ;

起逐渐上升，沿线按余弦曲线分布，线路末端电压

达到最大值，如当βl＝90°时，从线路首端看去，相当于发生串联谐振，K₁₂→∞，

此时线路长度即为工频空载长线路上的电压分布的0.25倍波长；同时，空载线路的电容电流在电源电抗上也会形成电压升高，使线路首端的电压高于电源电动势，进一步增加了工频过电压；From formula (2), it can be known that the voltage on the line is from the head end

It gradually rises from

When the maximum value is reached, for example, when βl=90°, when viewed from the head end of the line, it is equivalent to series resonance, K ₁₂ →∞,

At this time, the line length is 0.25 times the wavelength of the voltage distribution on the long power frequency no-load line; at the same time, the capacitive current of the no-load line will also form a voltage increase on the power supply reactance, so that the voltage at the head end of the line is higher than the power supply electromotive force, and further Increased power frequency overvoltage;

After considering the reactance of the power supply, the relationship between the voltage at the end of the line and the electromotive force of the power supply can be obtained, as follows:

为发电机电动势，j为虚数符号，Z_C为波阻抗，X_S为电源电抗，

为线路首端电流；In the above formula,

is the generator electromotive force, j is the imaginary number symbol, Z _C is the wave impedance, X _S is the power source reactance,

is the current at the head end of the line;

将式(3)变型，可得线路末端电压与电源电动式的传递函数K₀₂，如下式：make:

By modifying the formula (3), the transfer function K ₀₂ between the voltage at the end of the line and the electric power source can be obtained, as follows:

表示，当

时K₀₂→∞，

此时

相当于电源电抗增加了线路长度，谐振点提前，可知电源电抗也增加工频电压倍数；The influence of the mains reactance X _s through the angle

said that when

When K ₀₂ →∞,

at this time

It is equivalent to that the power supply reactance increases the line length, and the resonance point is advanced. It can be seen that the power supply reactance also increases the power frequency voltage multiple;

The transfer function of the voltage at the end of the line to the electric power supply is expressed as follows:

为波阻抗；

为相位常数。In formula (5):

is the wave impedance;

is the phase constant.

线路首端电流

功率因数为

则传输的有功功率

无功功率

若电源电抗X_s，则发电电动式E为：Further, in step 3, to obtain the rise in power frequency voltage caused by line load shedding, it is assumed that when the system is in normal operation, the voltage at the head end of the line is:

Line head current

The power factor is

then the transmitted active power

reactive power

If the power source reactance X _s , the generator electric formula E is:

Before load shedding, if a considerable amount of active and inductive reactive power is transmitted on the line, the power generation electric type E must be higher than the voltage value U ₁ at the head end of the line, E>U ₁ ;

After load shedding, according to the principle of constant flux linkage, it is considered that the transient electromotive force of the power supply remains unchanged, and the transient electromotive force of the power supply E′ _d ≈ E, E is the electromotive force of the generator; because the circuit breaker at the end of the line is opened, the power supply with no-load long line is formed. Operation mode: After the end of the load shedding, the voltage at the head end of the line is higher than the power supply electromotive force, and the overvoltage at the end of the long line is more serious.

Further, in step 4, it is determined that the single-phase short circuit of the UHV line causes the power frequency overvoltage, including:

则有：Assuming that a single-phase ground fault occurs in the A-phase of the system, its boundary conditions

Then there are:

为故障点处电压的正序、负序、零序分量；

为故障处电流的正序、负序、零序分量；in the formula

are the positive sequence, negative sequence and zero sequence components of the voltage at the fault point;

are the positive sequence, negative sequence and zero sequence components of the current at the fault;

According to the set boundary conditions, a composite sequence network is formed when the single phase is grounded, and the sequence current and the sound phase voltage can be obtained from the sequence network, as follows:

为电网B相电压，

为电网C相电压，

为电源A相电动势；以K⁽¹⁾表示单相接地故障后健全相电压升高，式(5)可简化为：In the above formula, a=e ^j120° ; Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point,

is the phase B voltage of the grid,

is the phase C voltage of the grid,

is the A-phase electromotive force of the power supply; with K ⁽¹⁾ representing the rise of the sound phase voltage after a single-phase ground fault, equation (5) can be simplified as:

为电网健全相电压；In the above formula,

Phase voltage for grid sound;

in:

In the above formula, Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point. For UHV transmission systems with large transmission capacity, Z ₁ ≈ Z ₂ , ignoring The resistance components of each sequence impedance are simplified as:

In the above formula: X ₀ is zero-sequence reactance, and X ₁ is positive-sequence reactance;

It can be seen from the above formula that the power frequency overvoltage has a great relationship with X ₀ /X ₁ (the ratio of zero sequence and positive sequence reactance) seen from the fault point; the increase of X ₀ /X ₁ will make the single-phase ground fault load shed. Overvoltage tends to increase;

Take X ₀ /X ₁ =2.6 for a typical UHV transmission line; then find K ⁽¹⁾ and U:

U=1.21E

In the above formula: E is the power supply potential, and U is the voltage.

Further, the determination of the high reactance value of the UHV line described in step 5 is based on the power frequency overvoltage of the three situations, and at the same time, combined with the reactive power compensation of the typical project, comprehensively determine the high reactance value of the UHV line;

The lossless long-line equation of the voltage and current along the UHV transmission line is:

为波阻抗；

为相位常数；x为离受端的距离，x₀为单位长度电抗；b₀为单位长度电纳，线路中某一点的电压为

电流为

受端电压为

电流为

虚数符号为j，sinβx为正弦函数，cosβx为余弦函数；where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, x ₀ is the reactance per unit length; b ₀ is the susceptance per unit length, and the voltage at a certain point in the line is

current is

The receiving terminal voltage is

current is

The imaginary number symbol is j, sinβx is a sine function, and cosβx is a cosine function;

为基准，若受端传输功率为：at the receiving terminal voltage

As the benchmark, if the transmission power of the receiving end is:

S _r =P _r +jQ _r (13)

In the above formula: S _r is the transmission power of the receiving end, P _r is the active power, Q _r is the reactive power, and j is the imaginary number symbol;

Then the expression form of formula (12) can be transformed into:

The charging reactive power generated by a line of length l is expressed in the integral form of the charging power of the susceptance b ₀ per unit length:

为x点电压共轭，b₀为单位电纳,Z_C为波阻抗,x为线路某点长度，

为线路中某一点的电压；In the above formula: Q _C is the long-line charging power,

is the voltage conjugate at point x, b ₀ is the unit susceptance, Z _C is the wave impedance, x is the length of a certain point of the line,

is the voltage at a point in the line;

Combined with the voltage equation in equation (13), the long-line charging power _QC is:

In the above formula, P _r is the active power, and Q _r is the reactive power;

It can be seen from equation (16) that the line charging reactive power is related to the line transmission power, the line length and the unit reactance and susceptance; in the power transmission process, the high reactance design is based on the long-line charging power Q _c , and Q _c varies slightly with the active power. There is an increase, but the capacitance of the line plays a major role; at the same time, the high-resistance design satisfies the suppression of the highest voltage under light load conditions, so the light-load line parameters are used as the control conditions for the high-resistance value;

Equation (16) is simplified to:

In the above formula: Q _c is the charging reactive power of the long line, U _e is the rated phase voltage of the system;

The high resistance design is determined by the following formula:

In the above formula, Q _L is the high resistance compensation capacity, Q _c is the charging reactive power of the long line, and B is the compensation coefficient.

即为潜供电流，其电弧称之为潜供电弧；Further, the neutral point reactance of the high-voltage shunt reactor is determined in step 6. When a single-phase grounding fault occurs in the line, after the circuit breakers at both ends of the faulty phase are tripped, the other two phases are still running and maintain the working voltage; Due to the action of capacitor C ₁₂ and mutual inductance M between phases, a certain current still flows through the fault point

It is the submerged supply current, and its arc is called the submerged supply arc;

The submerged supply current includes: capacitive component and inductive component;

The capacitive component refers to the current provided by the voltage _of the normal phase to the fault point through the phase-to-phase capacitor C12; at the same time, the load current on the normal phase induces an electromotive force on the faulty phase through the phase-to-phase mutual inductance, and the electromotive force is formed by the phase-to-ground capacitance and high reactance. The loop provides current to the fault point, and the capacitive component plays a major role in most uncompensated situations;

The inductance component means that the load current on the normal phase induces an electromotive force on the faulty phase through the mutual inductance between the phases, and the electromotive force provides current to the fault point through the loop formed by the relative-to-ground capacitance and high reactance;

Both the submersible supply current and the recovery voltage should be limited to a small value. When the submerged supply current is large and the recovery voltage is high, in order to limit the submerged supply current and its recovery voltage, the method of adding a neutral point reactance of a high-voltage shunt reactor is used. In order to reduce the submerged supply current and recovery voltage, including: accelerating the submerged arc extinguishing and suppressing the resonant overvoltage in two dimensions, the neutral point reactance of the high-voltage shunt reactor is calculated through the determined line-to-line capacitive reactance and high reactance values. numerical value.

Further, a small reactance is selected according to the requirement of accelerating submerged arc extinguishing;

The submerged supply current is less than (15～20)A;

From the perspective of compensating the interphase capacitance, the small reactance value can be approximated according to equation (19):

In the formula: the reactance value of the neutral point small reactance of X ₀ , the positive sequence reactance value of the X _L shunt reactor, and the phase-to-phase capacitive reactance value of the X ₁₂ line;

Select a small reactance according to the requirements for suppressing resonant overvoltage:

In order to suppress the resonant overvoltage transmitted by the power frequency, the small reactance of the neutral point is calculated according to the formula (20):

In the formula: the zero-sequence reactance value of _XL0 shunt reactor, for single-phase reactor, _XL0 = _XL ; for three-phase three-column reactor, _XL0 = _XL /2;

Single-phase reactor is used for high reactance compensation of UHV line, then formulas (19) and (20) are the same;

By analyzing the long-line capacity lift effect, line load rejection, and line single-phase grounding fault, and considering the reactive power compensation of the line, the parallel high reactance value is calculated; according to the determined high reactance value and line parameters, the final intermediate Sexual point small reactance value.

A computer storage medium, on which a computer program is stored, and the steps of implementing the above-described high-resistance design method for ultra-high voltage limiting power frequency overvoltage and potential supply current when the computer program is executed by a processor .

The present invention has the following beneficial effects and advantages:

The invention uses the method of adding neutral point reactance (also known as small reactance) to the high-voltage shunt reactor to reduce the latent supply current and recovery voltage, thereby solving the temporary power frequency overvoltage of the long-distance ultra-high voltage AC power grid in the prior art And the problem of submerged supply current exceeding the standard has improved the success rate of single-phase reclosing of UHV lines.

The calculation method of the invention is simple and practical, can be more easily used in engineering practice, and provides basic technical support for the power frequency overvoltage in the ultra-high voltage power grid and its influence on the power grid equipment.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is the capacitance effect diagram of the UHV no-load line of the present invention;

Fig. 2 is the composite sequence network when single-phase grounding of the present invention;

3 is a schematic diagram of a potential supply current of the present invention;

Fig. 4 is the equivalent circuit diagram of the UHV long line of the present invention.

In the picture:

Detailed ways

In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments may be combined with each other in the case of no conflict.

Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific details disclosed below. Example limitations.

The technical solutions of some embodiments of the present invention are described below with reference to FIGS. 1 to 4 .

Example 1

The present invention provides another embodiment, which is a high-resistance design method for ultra-high voltage to limit power frequency overvoltage and submerged supply current, as shown in FIG. .

The present invention is a high-resistance design method for ultra-high voltage limiting power frequency overvoltage and potential supply current, which specifically includes the following steps:

Step 1. Establish a system based on electromagnetic transient simulation model.

According to the collected system parameters, based on the electromagnetic transient modeling method, the distributed model of UHV transmission and transformation lines, the detailed model of main transformer and UHV interconnection engineering, and the equivalent model of regional power supply and load are established.

The collected system parameters include the main parameters of the local synchronous motor and the main parameters of the transmission line.

Among them, the main parameters of the local synchronous motor include: synchronous motor, main transformer, series compensation, low-voltage reactor compensation, low-voltage capacitor compensation, section load and other system parameters.

The main parameters of the transmission line include: transmission line-to-ground capacitance, phase-to-phase capacitance, inductance per unit length, susceptance (capacitance) and other main line parameters.

Step 2. Determine the power frequency overvoltage at the end of the no-load long line of the UHV transmission line;

By simply considering the capacity rise effect of the line and comparing the capacity rise effect of the no-load line after considering the power supply reactance, it is concluded that the power supply reactance is equivalent to increasing the length of the line, which further increases the power frequency overvoltage and advances the resonance point.

For long transmission lines, when the terminals are unloaded, the line's inlet impedance is capacitive. When taking into account the influence of the internal impedance (inductive) of the power supply, the capacitive effect not only makes the voltage at the end of the line higher than the head end, but also makes the voltage at the head and end of the line higher than the power supply electromotive force, which is caused by the power frequency overvoltage of the long no-load line. one of the reasons.

可计算出首端电压

末端电压

及线路中某一点的电压

为式(1)：To determine the power frequency overvoltage at the end of the UHV no-load long line, the no-load lossless line of length l is shown in Figure 1, which is the capacitance effect diagram of the UHV no-load line of the present invention. When the terminal current

The head-end voltage can be calculated

terminal voltage

and the voltage at a point in the line

is formula (1):

为波阻抗；

为相位常数；x为离受端的距离，L₀为单位长度电抗；C₀为单位长度电容，l为线路长度。where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, L ₀ is the reactance per unit length; C ₀ is the capacitance per unit length, and l is the line length.

Here, the voltage transfer coefficient from the end of the line to the head end is defined as formula (2):

末端电压

线路末端对首端的电压传递系数为K₁₂。In the formula: line head voltage

terminal voltage

The voltage transfer coefficient from the end of the line to the head end is K ₁₂ .

起逐渐上升，沿线按余弦曲线分布，线路末端电压

达到最大值，如当βl＝90°时，从线路首端看去，相当于发生串联谐振，K₁₂→∞，

此时线路长度即为工频空载长线路上的电压分布的0.25倍波长。同时，空载线路的电容电流在电源电抗上也会形成电压升高，使得线路首端的电压高于电源电动势，这进一步增加了工频过电压。It can be seen from equation (2) that the voltage on the line is from the head end

It gradually rises from

When the maximum value is reached, for example, when βl=90°, when viewed from the head end of the line, it is equivalent to series resonance, K ₁₂ →∞,

At this time, the line length is 0.25 times the wavelength of the voltage distribution on the long line with no-load power frequency. At the same time, the capacitive current of the no-load line will also form a voltage increase on the power supply reactance, so that the voltage at the head end of the line is higher than the power supply electromotive force, which further increases the power frequency overvoltage.

After considering the reactance of the power supply, the relationship between the voltage at the end of the line and the electromotive force of the power supply can be obtained as follows:

为发电机电势，j为虚数符号，Z_C为波阻抗，X_S为电源电抗，线路首端电流为

In the above formula,

is the generator potential, j is the imaginary number symbol, Z _C is the wave impedance, X _S is the power source reactance, and the current at the head end of the line is

将式(3)变型，可得线路末端电压与电源电动式的传递函数K₀₂，如下式：make:

By modifying the formula (3), the transfer function K ₀₂ between the voltage at the end of the line and the electric power source can be obtained, as follows:

表示出来，当

时K₀₂→∞，

此时

相当于电源电抗增加了线路长度，谐振点提前了，可以看出电源电抗也能增加工频电压倍数。The influence of the mains reactance X _s through the angle

expressed when

When K ₀₂ →∞,

at this time

It is equivalent to the increase of the line length of the power supply reactance and the advance of the resonance point. It can be seen that the power supply reactance can also increase the power frequency voltage multiple.

Here, the transfer function of the voltage at the end of the line to the electromotive force of the power supply can be expressed as:

为波阻抗；

为相位常数。In formula (5):

is the wave impedance;

is the phase constant.

For the convenience of analysis, the following calculation is carried out through a case. A power plant takes two 1000MW units and connects to the system bus through two 27/1000kV step-up transformers with a capacity of 1120MVA. The 2-circuit UHV line is used here to access the system.

The main calculation parameters of several equipments take 100MVA as the base value, the X' _d value of each unit is 0.024, the X _T1 of each 27/1000kV step-up transformer is 0.014, the single-circuit UHV line wave impedance Z _c is 0.025, β is 0.001. The calculation results are shown in Table 1.

Table 1 Calculation results of overvoltage generated by no-load long lines

Distance (km) 100 150 200 250 300 350 400 450 500 Overvoltage multiple 1.06 1.10 1.15 1.20 1.27 1.34 1.42 1.52 1.64

Step 3. Find the rise in power frequency voltage caused by line load shedding.

When the transmission line is running under heavy load, the circuit breaker at the end of the line suddenly trips and throws off the load for some reason, causing the power frequency voltage to rise, which is usually called the load rejection effect.

线路首端电流

功率因数为

则传输的有功功率

无功功率

若电源电抗X_s，则发电电动式E为：When the system is in normal operation, the voltage at the head end of the line is

Line head current

The power factor is

then the transmitted active power

reactive power

If the power source reactance X _s , the generator electric formula E is:

为线路首端电压。In the above formula,

is the line head voltage.

Before load shedding, if a considerable amount of active and inductive reactive power is transmitted on the line, the power generation electromotive force E must be higher than the voltage value U ₁ at the head end of the line, E>U ₁ . According to the parameter calculation in the case, the overvoltage multiple of the line can be obtained, and the calculation results are shown in Table 2.

Table 2 Overvoltage multiples generated after line load shedding

Distance (km) 100 150 200 300 350 400 450 500 Overvoltage multiple 1.01 1.01 1.02 1.05 1.06 1.09 1.11 1.14

After load shedding, according to the principle of constant flux linkage, it can be simply considered that the transient electromotive force of the power supply remains unchanged, and the transient electromotive force of the power supply E′ _d ≈ E, E is a generator-electric type. Since the circuit breaker at the end of the line is opened, the operation mode of the power supply with no-load long line is formed. After the load shedding at the end, taking into account the influence of the capacitive effect of the long line on the rise of the power frequency voltage, as shown in equation (6), the voltage at the beginning of the line will be higher than the power supply electromotive force, and the overvoltage at the end of the long line is more serious. According to the parameters, the overvoltage multiple of the line can be calculated, and the calculation results are shown in Table 2.

Step 4. Determine the power frequency overvoltage caused by the single-phase short circuit of the UHV line.

Asymmetric short-circuit is the most common failure mode of transmission lines. The zero-sequence component of short-circuit current will increase the power frequency voltage of the sound phase, which is often called asymmetric effect. Asymmetric short-circuit faults in the system, single-phase grounding faults are the most common. When one end of the line trips and sheds the load, the fault still exists, which may further increase the power frequency overvoltage. The ratio of zero-sequence and positive-sequence reactance of typical UHV engineering is analyzed and extracted by calculation. Obtain the single-phase short-circuit power frequency overvoltage of a typical UHV transmission line.

则有：Assuming that a single-phase-to-ground fault occurs in phase A in the system, its boundary conditions

Then there are:

为故障点处电压的正序、负序、零序分量；

为故障处电流的正序、负序、零序分量。in the formula

are the positive sequence, negative sequence and zero sequence components of the voltage at the fault point;

It is the positive sequence, negative sequence and zero sequence components of the current at the fault.

According to the assumed boundary conditions, a composite sequence network is formed when a single phase is grounded, as shown in Figure 2, from which the sequence current and sound phase voltage can be obtained.

为电网B相电压，

为电网C相电压，

为电源A相电动势。where a=e ^j120° ; Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point,

is the phase B voltage of the grid,

is the phase C voltage of the grid,

For the power supply phase A electromotive force.

Taking K ⁽¹⁾ to represent the rise of the sound phase voltage after a single-phase ground fault, equation (5) can be simplified as:

为电网健全相电压。In the above formula,

Sound phase voltage for the grid.

in:

In the above formula, Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point. For UHV transmission systems with large transmission capacity, Z ₁ ≈ Z ₂ , ignoring The resistance components of each sequence impedance can be simplified as:

In the above formula: X ₀ is zero-sequence reactance, and X ₁ is positive-sequence reactance.

It can be seen from the above formula that this type of power frequency overvoltage has a great relationship with X ₀ /X ₁ (the ratio of zero sequence and positive sequence reactance) seen from the fault point. The increase of X ₀ /X ₁ will make the single-phase ground fault load rejection overvoltage tend to increase.

Take X ₀ /X ₁ =2.6 for a typical UHV transmission line. Then K ⁽¹⁾ and U can be found:

U=1.21E

In the above formula: E is the power supply potential, and U is the voltage.

Through the calculation, it can be concluded that the line overvoltage multiple is 1.21 when the typical UHV single-phase fault occurs.

Step 5. Determine the high reactance value of the UHV line.

Specifically, according to the power frequency overvoltage of the three cases, combined with the reactive power compensation of the typical project, the high reactance value of the UHV line is comprehensively determined.

As shown in FIG. 4, FIG. 4 is an equivalent circuit diagram of the UHV long line of the present invention. The lossless long line equation of the voltage and current along the UHV transmission line is:

为波阻抗；

为相位常数；x为离受端的距离，x₀为单位长度电抗；b₀为单位长度电纳，线路中某一点的电压为

电流为

受端电压为

电流为为

序数符号为j，sinβx为正弦函数，cosβx为余弦函数。where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, x ₀ is the reactance per unit length; b ₀ is the susceptance per unit length, and the voltage at a certain point in the line is

current is

The receiving terminal voltage is

current is

The ordinal symbol is j, sinβx is a sine function, and cosβx is a cosine function.

为基准，若受端传输功率为：at the receiving terminal voltage

As the benchmark, if the transmission power of the receiving end is:

S _r =P _r +jQ _r (13)

In the above formula: S _r is the transmission power of the receiving end, P _r is the active power, Q _r is the reactive power, and j is the imaginary number symbol.

Then the expression form of formula (12) can be transformed into:

As shown in Figure 4, the charging reactive power generated by the line of length l is expressed in the form of the charging power integral of the susceptance b ₀ per unit length:

为x点电压共轭，b₀为单位电纳,Z_C为波阻抗，d为微分运算符号,x为线路某点长度，

为线路中某一点的电压。In the above formula: Q _C is the long-line charging power,

is the voltage conjugate at point x, b ₀ is the unit susceptance, Z _C is the wave impedance, d is the differential operation symbol, x is the length of a certain point of the line,

is the voltage at a point in the line.

Combined with the voltage equation in equation (13), the long-line charging power _QC is:

In the above formula, P _r is the active power, and Q _r is the reactive power.

It can be seen from equation (16) that the line charging reactive power is related to the line transmission power, line length and unit reactance and susceptance. In the process of power transmission, the high-resistance design is mainly based on the charging power Q _c of the long line. Q _c will increase slightly with the active power, but the capacitance of the line plays a major role. At the same time, the high-resistance design satisfies the suppression of the highest voltage under light load conditions, so the light-load line parameters are used as the control conditions for the high-resistance value. Equation (16) can be simplified as:

In the above formula: Q _c is the charging reactive power of the long line, U _e is the rated phase voltage of the system;

Take U _e as 1000kV, and take the line capacitance C ₀ per unit length as 0.01378uF/km. The charging reactive power of the calculation line is shown in Table 3 below.

Table 3 The settlement results of reactive power generated by UHV lines

Line distance (km) 100 150 200 250 300 350 400 450 500 Charging power (Mvar) 433 649 865 1082 1298 1514 1731 1947 2163

The high resistance design is determined by the following formula:

In the above formula, Q _L is the high resistance compensation capacity, Q _c is the charging reactive power of the long line, and B is the compensation coefficient.

In the initial stage of UHV power grid construction, the compensation degree of high reactance is controlled at 80%-90%. Here, the value of B is 90%, and the calculated high reactance value is shown in Table 4 below.

Table 4 Compensation results of high resistance

Line distance (km) 100 150 200 250 300 350 400 450 500 Charging power (Mvar) 195 292 389 487 584 681 779 876 974

Step 6. Determine the design of the neutral point reactance of the high-voltage shunt reactor.

my country's UHV transmission lines generally use single-phase reclosing to improve the stability of system operation. In addition, the overvoltage of single-phase reclosing is much lower than that of three-phase reclosing. UHV lines are also intended to use single-phase reclosing. In order to improve the success rate of single-phase reclosing, the problem of submerged supply current and recovery voltage in the process of line reclosing must be considered.

As shown in FIG. 3 , FIG. 3 is a schematic diagram of the submerged current supply of the present invention.

即为潜供电流，其电弧称之为潜供电弧。When a single-phase (A-phase) ground fault occurs in the line, after the circuit breaker at both ends of the faulted phase trips, the other two phases (B, C-phase) are still running and maintain the working voltage. Due to the action _of the phase-to-phase capacitance C12 and the phase-to-phase mutual inductance M, a certain current still flows through the fault point

That is the submerged supply current, and its arc is called submerged arc.

The submerged supply current is composed of two parts, namely, a capacitive component and an inductive component (also referred to as a transverse component and a longitudinal component).

Among them, the capacitance component refers to the current provided by the voltage _of the normal phase to the fault point through the phase-to-phase capacitance C12. At the same time, the load current on the normal phase induces an electromotive force on the faulty phase through the phase-to-phase mutual inductance. This electromotive force provides current to the fault point through the loop formed by the relative-to-ground capacitance and high reactance. In most cases without compensation, the capacitive component plays a major role. .

Among them, the inductive component means that the load current on the normal phase induces an electromotive force on the faulty phase through the mutual inductance between the phases. This electromotive force provides current to the fault point through the loop formed by the relative ground capacitance and high reactance.

In order to improve the success rate of single-phase automatic reclosing, both the submerged supply current and the recovery voltage should be limited to small values. The submerged supply current and recovery voltage of the line are related to the parameters of the transmission line, the compensation of the line, the operating voltage and transmission flow at both ends of the line, and the network structure on both sides of the line has little influence on it. When the submerged supply current is large and the recovery voltage is high, some measures must be taken to speed up the extinguishment of the submerged supply arc.

In order to limit the submerged supply current and its recovery voltage, the method of adding a neutral point reactance of a high-voltage shunt reactor is used to reduce the submerged supply current and recovery voltage. The neutral point reactance of high-voltage shunt reactor is also called small reactance.

Next, according to the two dimensions of accelerating submerged arc extinguishing and suppressing resonance overvoltage, the value of neutral point reactance of high-voltage shunt reactor is calculated through the determined values of capacitive reactance and high reactance between lines.

(1) Select small reactance according to the requirement of accelerating submerged arc extinguishing.

UHV lines often use single-phase reclosing as a measure to improve dynamic stability. However, when a single-phase grounding fault occurs, due to the capacitive coupling and mutual inductance coupling of the line, the submerged supply current at the grounding point is difficult to self-extinguish, which reduces the success rate of single-phase reclosing. After connecting the small reactance at the neutral point of the shunt reactor, the interphase capacitance can be compensated, and the mutual inductance component can be partially compensated to reduce the amplitude of the submerged supply current. When a small resistance is added to the small reactance, the phase can also be changed, thereby accelerating the extinguishing of the submerged arc. The optimal compensation of small reactance is related to system parameters, compensation degree of shunt reactor, installation position and failure mode. In engineering design, the system professional should calculate the submerged supply current and recovery voltage for various schemes, and select the best reactance value. The submerged supply current should be less than (15~20)A.

From the perspective of compensating the phase-to-phase capacitance alone, the small reactance value can be approximated according to equation (19):

In the formula: the reactance value of the neutral point small reactance of X ₀ , the positive sequence reactance value of the X _L shunt reactor, and the phase-to-phase capacitive reactance value of the X ₁₂ line.

(2) Select small reactance according to the requirement of suppressing resonance overvoltage.

In order to suppress the power frequency transfer resonance overvoltage, the small reactance of the neutral point can be calculated according to the formula (20):

In the formula: the zero-sequence reactance value of the _XL0 shunt reactor, for a single-phase reactor, _XL0 = _XL ; for a three-phase three-column reactor, _XL0 = _XL /2.

The high reactance compensation of UHV line generally adopts single-phase reactor, then formulas (19) and (20) are the same, _C0 takes the zero-sequence capacitance of the UHV line as 0.00852uF/km, and the positive sequence capacitor _C1 of the UHV line is 0.01378uF /km, then the interphase capacitive reactance C ₁₂ can be obtained by the following formula (21).

According to Table 4 and the capacitance parameters of the line, the value of the neutral point small reactor can be obtained as shown in the following table.

Table 5 Calculation results of compensation for high neutral point small reactance

Line distance (km) 100 150 200 250 300 350 400 450 500 Corresponding to small reactance value (Ω) 1261 841 630 504 420 360 315 280 252

It can be seen from the above calculation results that the high reactance compensation value at one end of the 300km line is 584Mvar, and the one-side high reactance small reactor value is 420Ω.

In the above steps, the parallel high reactance value is calculated by analyzing the long-line capacity lift effect, the line load shedding, and the single-phase grounding fault of the line, and considering the reactive power compensation of the line and other factors at the same time. Determine the final neutral point small reactance value according to the determined high reactance value and line parameters. Through a series of measures, it provides basic technical support for power frequency overvoltage in UHV power grid and its impact on power grid equipment.

The ultra-high voltage shunt reactor and the method for selecting the value of the high-resistance neutral point and small reactance provided by the embodiment of the present invention strictly follow the laws of circuits and magnetic circuits. In the calculation, it is considered that the excitation impedances of the three phases are the same, so all derivations are based on the lack of phase overvoltage Starting from the premise that the amplitude of the rated voltage is close to the premise, the calculation and selection of the reactor and the small reactance value of the neutral point in turn make this premise true. The calculation method is simple and practical, and can be easily used in engineering practice.

Example 2

Based on the same inventive concept, an embodiment of the present invention further provides a computer storage medium, where a computer program is stored on the computer storage medium, and when the computer program is executed by a processor, one of the features described in Embodiment 1 or 2 is implemented. Steps of high-resistance design method for high-voltage limiting power frequency overvoltage and latent supply current.

As will be appreciated by those skilled in the art, the embodiments of the present application may be provided as a method, a system, or a computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each process and/or block in the flowchart illustrations and/or block diagrams, and combinations of processes and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Modifications or equivalent replacements are made to the specific embodiments of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (10)

1. a high-resistance design method of ultra-high voltage limiting power frequency overvoltage and potential supply current, it is characterized in that: comprise the following steps: Step 1. Establish a system based on electromagnetic transient simulation model; Step 2. Determine the power frequency overvoltage at the end of the no-load long line of the UHV transmission line; Step 3. Find the increase in power frequency voltage caused by line load shedding; Step 4. Determine the power frequency overvoltage caused by the single-phase short circuit of the UHV line; Step 5. Determine the high reactance value of the UHV line; Step 6. Determine the neutral point reactance of the high-voltage shunt reactor. 2. the high-resistance design method of a kind of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: the electromagnetic transient simulation model based on the described establishment system of step 1 is based on collected System parameters, based on the electromagnetic transient modeling method, establish the distributed model of UHV transmission and transformation lines, the detailed model of main transformer and UHV interconnection engineering, and the equivalent model of regional power supply and load. 3. the high-resistance design method of a kind of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 2, it is characterized in that: the system parameter of described collection, comprises the main parameter of local synchronous motor, the main parameter of transmission line Parameters; the main parameters of the local synchronous motor include: synchronous motor, main transformer, series compensation, low-voltage reactor compensation, low-voltage capacitor compensation, section load system parameters; the main parameters of the transmission line include: transmission line-to-ground capacitance, phase-to-phase Capacitance, inductance per unit length, susceptance (capacitance) circuit parameters. 4. the high-resistance design method of a kind of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: the power frequency overvoltage at the end of the no-load long line of the UHV transmission line is determined according to step 2. The voltage is compared by simply considering the capacity rise effect of the line and taking into account the capacity rise effect of the no-load line after taking into account the power supply reactance. ; Let the length of the no-load lossless line be l, when the terminal current

Calculate the head-end voltage

terminal voltage

and the voltage at a point in the line

is formula (1):

where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, L ₀ is the reactance per unit length; C ₀ is the capacitance per unit length, and l is the line length; The voltage transfer coefficient from the end of the line to the head end is defined as formula (2):

In the formula: head-end voltage

terminal voltage

The voltage transfer coefficient from the end of the line to the head end is K ₁₂ ; From formula (2), it can be known that the voltage on the line is from the head end

It gradually rises from

When the maximum value is reached, for example, when βl=90°, when viewed from the head end of the line, it is equivalent to series resonance, K ₁₂ →∞,

At this time, the line length is 0.25 times the wavelength of the voltage distribution on the long power frequency no-load line; at the same time, the capacitive current of the no-load line will also form a voltage increase on the power supply reactance, so that the voltage at the head end of the line is higher than the power supply electromotive force, and further Increased power frequency overvoltage; After considering the reactance of the power supply, the relationship between the voltage at the end of the line and the electromotive force of the power supply can be obtained, as follows:

In the above formula,

is the generator electromotive force, j is the imaginary number symbol, Z _C is the wave impedance, X _S is the power supply reactance,

is the current at the head end of the line; make:

By modifying the formula (3), the transfer function K ₀₂ between the voltage at the end of the line and the electric power source can be obtained, as follows:

The influence of the mains reactance X _s through the angle

said that when

When K ₀₂ →∞,

at this time

It is equivalent to that the power supply reactance increases the line length, and the resonance point is advanced. It can be seen that the power supply reactance also increases the power frequency voltage multiple; The transfer function of the voltage at the end of the line to the electric power supply is expressed as follows:

In formula (5):

is the wave impedance;

is the phase constant. 5. the high-resistance design method of a kind of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: the power frequency voltage rise caused by the line load rejection described in step 3 is obtained, is When the system is in normal operation, the voltage at the head end of the line is

Line head current

The power factor is

then the transmitted active power

reactive power

If the power source reactance X _s , the generator electric formula E is:

Before load shedding, if a considerable amount of active and inductive reactive power is transmitted on the line, the power generation electric type E must be higher than the voltage value U ₁ at the head end of the line, E>U ₁ ; After load shedding, according to the principle of constant flux linkage, it is considered that the transient electromotive force of the power supply remains unchanged, and the transient electromotive force of the power supply E′ _d ≈ E, E is the electromotive force of the generator; because the circuit breaker at the end of the line is opened, the power supply with no-load long line is formed. Operation mode: After the end load sheds, the voltage at the head end of the line is higher than the electromotive force of the power supply, and the overvoltage at the end of the long line is more serious. 6. A kind of high-resistance design method of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: described in step 4, it is determined that the single-phase short circuit of the ultra-high voltage line causes power frequency overvoltage, including : Assuming that a single-phase ground fault occurs in the A-phase of the system, its boundary conditions

Then there are:

in the formula

are the positive sequence, negative sequence and zero sequence components of the voltage at the fault point;

are the positive sequence, negative sequence and zero sequence components of the current at the fault; According to the set boundary conditions, a composite sequence network is formed when the single phase is grounded, and the sequence current and the sound phase voltage can be obtained from the sequence network, as follows:

In the above formula, a=e ^j120° ; Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point,

is the phase B voltage of the grid,

is the phase C voltage of the grid,

is the A-phase electromotive force of the power supply; with K ⁽¹⁾ representing the rise of the sound phase voltage after a single-phase ground fault, equation (5) can be simplified as:

In the above formula,

Phase voltage for grid sound; in:

In the above formula, Z ₁ , Z ₂ , and Z ₀ are the positive-sequence, negative-sequence, and zero-sequence impedances of the network viewed from the fault point. For UHV transmission systems with large transmission capacity, Z ₁ ≈ Z ₂ , ignoring The resistance components of each sequence impedance are simplified as:

In the above formula: X ₀ is zero-sequence reactance, and X ₁ is positive-sequence reactance; It can be seen from the above formula that the power frequency overvoltage has a great relationship with X ₀ /X ₁ (the ratio of zero sequence and positive sequence reactance) seen from the fault point; the increase of X ₀ /X ₁ will make the single-phase ground fault load shed. Overvoltage tends to increase; Take X ₀ /X ₁ =2.6 for a typical UHV transmission line; then find K ⁽¹⁾ and U:

U=1.21E In the above formula: E is the power supply potential, and U is the voltage. 7. the high-resistance design method of a kind of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: determining the high-resistance value of the ultra-high voltage line described in step 5 is based on three conditions of work. Frequency overvoltage, combined with the reactive power compensation of typical projects, comprehensively determine the high reactance value of UHV lines; The lossless long-line equation of the voltage and current along the UHV transmission line is:

where:

is the wave impedance;

is the phase constant; x is the distance from the receiving end, x ₀ is the reactance per unit length; b ₀ is the susceptance per unit length, and the voltage at a certain point in the line is

current is

The receiving terminal voltage is

current is

The imaginary number symbol is j, sinβx is a sine function, and cosβx is a cosine function; at the receiving terminal voltage

As the benchmark, if the transmission power of the receiving end is: S _r =P _r +jQ _r (13) In the above formula: S _r is the transmission power of the receiving end, P _r is the active power, Q _r is the reactive power, and j is the imaginary number symbol; Then the expression form of formula (12) can be transformed into:

The charging reactive power generated by a line of length l is expressed in the integral form of the charging power of the susceptance b ₀ per unit length:

In the above formula: Q _C is the long-line charging power,

is the voltage conjugate at point x, b ₀ is the unit susceptance, Z _C is the wave impedance, x is the length of a certain point of the line,

is the voltage at a point in the line; Combined with the voltage equation in equation (13), the long-line charging power _QC is:

In the above formula, P _r is the active power, and Q _r is the reactive power; It can be seen from equation (16) that the line charging reactive power is related to the line transmission power, the line length and the unit reactance and susceptance; in the power transmission process, the high reactance design is based on the long-line charging power Q _c , and Q _c varies slightly with the active power. There is an increase, but the capacitance of the line plays a major role; at the same time, the high-resistance design satisfies the suppression of the highest voltage under light load conditions, so the light-load line parameters are used as the control conditions for the high-resistance value; Equation (16) is simplified to:

In the above formula: Q _c is the charging reactive power of the long line, U _e is the rated phase voltage of the system; The high resistance design is determined by the following formula:

In the above formula, Q _L is the high resistance compensation capacity, Q _c is the charging reactive power of the long line, and B is the compensation coefficient. 8. A kind of high-resistance design method for ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 1, it is characterized in that: determining the neutral point reactance of the high-voltage shunt reactor according to the step 6, when a single line occurs in the line. When a phase-to-earth fault occurs, after the circuit breakers at both ends of the faulted phase are tripped, the other two phases are still running and maintain the working voltage; due to the effect of the phase-to-phase capacitance C ₁₂ and the phase-to-phase mutual inductance M, a certain current still flows through the fault point

It is the submerged supply current, and its arc is called the submerged supply arc; The submerged supply current includes: capacitive component and inductive component; The capacitive component refers to the current provided by the voltage _of the normal phase to the fault point through the phase-to-phase capacitor C12; at the same time, the load current on the normal phase induces an electromotive force on the faulty phase through the phase-to-phase mutual inductance, and the electromotive force is formed by the phase-to-ground capacitance and high reactance. The loop provides current to the fault point, and the capacitive component plays a major role in most uncompensated situations; The inductance component means that the load current on the normal phase induces an electromotive force on the faulty phase through the mutual inductance between the phases, and this electromotive force provides current to the fault point through the loop formed by the relative ground capacitance and high reactance; Both the submersible supply current and the recovery voltage should be limited to a small value. When the submerged supply current is large and the recovery voltage is high, in order to limit the submerged supply current and its recovery voltage, the method of adding a neutral point reactance of a high-voltage shunt reactor is used. In order to reduce the submerged supply current and recovery voltage, including: accelerating the submerged arc extinguishing and suppressing the resonant overvoltage in two dimensions, the neutral point reactance of the high-voltage shunt reactor is calculated through the determined line-to-line capacitive reactance and high reactance values. numerical value. 9. A kind of high-resistance design method of ultra-high voltage limiting power frequency overvoltage and submerged supply current according to claim 8, it is characterized in that: select small reactance according to the requirement of described accelerating submerged supply arc extinguishing; The submerged supply current is less than (15～20)A; From the perspective of compensating the interphase capacitance, the small reactance value can be approximated according to equation (19):

In the formula: the reactance value of the neutral point small reactance of X ₀ , the positive sequence reactance value of the X _L shunt reactor, and the phase-to-phase capacitive reactance value of the X ₁₂ line; Select a small reactance according to the requirements for suppressing resonance overvoltage as described: In order to suppress the resonant overvoltage transmitted by the power frequency, the small reactance of the neutral point is calculated according to the formula (20):

In the formula: the zero-sequence reactance value of _XL0 shunt reactor, for single-phase reactor, _XL0 = _XL ; for three-phase three-column reactor, _XL0 = _XL /2; Single-phase reactor is used for high reactance compensation of UHV line, then formulas (19) and (20) are the same; By analyzing the long-line capacity rise effect, line load rejection, and line single-phase grounding fault, and considering the reactive power compensation of the line, the parallel high reactance value is calculated; according to the determined high reactance value and line parameters, the final intermediate Sexual point small reactance value. 10. A computer storage medium, characterized in that: a computer program is stored on the computer storage medium, and when the computer program is executed by a processor, an ultra-high voltage limiting power frequency overvoltage according to claims 1-9 is realized. and the steps of the high-impedance design method for the potential supply current.

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