A method and device for power grid distance protection based on online identification of power supply composition ratio

Abstract

The present invention discloses a method and device for distance protection of a power grid based on online identification of the proportion of power supply composition, and the method includes a "replacement" method. The method is effective in dealing with line short-circuit faults occurring in power grids containing a high proportion of inverter power supplies, so that after a fault occurs, the distance between the fault point and the protection installation location can be measured, thereby improving the existing distance protection, thereby selectively cutting off the faulty part and ensuring the normal operation of the non-faulty part. At the same time, the protection method does not require additional installation of equipment, can fully utilize traditional distance protection devices, and has a certain degree of adaptive capability, which can effectively reduce the construction and operation costs of the power system.

Description

[0001] This application is a divisional application with the application date of January 17, 2022, application number 202210047266.6, and the invention name is A power grid distance protection method and device based on online identification of power supply composition ratio. Technical Field

[0002] The present invention relates to a power grid distance protection method and device based on online identification of power supply composition ratio, belonging to the field of power system relay protection. Background Art

[0003] At present, human society is increasingly dependent on electricity, and the global demand for electricity is growing rapidly. At the same time, the pollution and damage to the ecological environment caused by the large-scale consumption of fossil energy are becoming increasingly serious. Against this background, the promotion and use of renewable energy power generation has received widespread attention, and clean energy power generation such as wind power, solar power and tidal power has ushered in new development opportunities.

[0004] With the development of new energy and the proposal of the "dual carbon" goal, the power sources in the existing power grid tend to be a mixture of traditional rotating motors and inverter power sources, and the proportion of inverter power sources continues to increase. Under extreme conditions, when all inverter power sources are disconnected from the grid due to weather and other reasons, and only traditional rotating motors are used as power sources, the power grid structure is like Figure 1 As shown in the figure; when all traditional rotating motors are disconnected from the grid due to mechanical failure and other reasons, and only the inverter power supply is used as the grid power supply, the grid structure is as follows Figure 2 shown.

[0005] Normally, the power supply in the power grid is a mixture of traditional rotating motors and inverter power supplies. However, after a fault occurs, the inverter power supply will automatically limit or lock the output, resulting in the fault output current of the inverter power supply being much smaller than the output current of a traditional rotating motor of the same capacity. When the proportion of inverter power supplies in the power grid is low, the actual fault current value flowing through the line after the fault is slightly different from the fault current value of a traditional rotating motor power supply of the same capacity. The currently feasible processing method is to regard the short-circuit current provided by the inverter as an error (auxiliary current), assume that the measured fault current only contains the fault current value provided by the traditional rotating motor, and exclude the influence of the error current in the action area of ​​the distance protection through appropriate constant setting.

[0006] With the development of new energy generation, when the capacity of the inverter power supply is equal to or even exceeds the capacity of the traditional rotating motor, the fault current output by the inverter power supply can no longer be regarded as an error. In addition, due to the nonlinear control of the controller, the sensitivity of the measured impedance (measured voltage / measured current at the protection installation) becomes smaller, so the traditional distance protection method and device cannot operate accurately. With the development of renewable energy, the proportion of inverter power supplies based on renewable energy in the power system power supply is also increasing. With the large-scale access of inverter power supplies in the power grid, the existing power grid power supply presents a hybrid form as a whole. Because the inverter power supply contains a large number of power electronic devices, usually after a fault occurs in the power system, the short-circuit characteristics of the power grid change significantly. For example, in order to ensure that the internal power electronic devices are not damaged, the inverter power supply will limit the output, which will greatly reduce the fault current in the line, and the fault information is not obvious. It is difficult for the existing protection device to directly obtain the fault distance information, so it cannot accurately operate to remove the fault. It can be seen that with the continuous increase in the proportion of inverter power supplies in the hybrid power supply, and its large volatility, the traditional distance protection can no longer be applied, which poses a great threat to the safe operation of the power grid. Summary of the invention

[0007] The purpose of the present invention is to provide a power grid distance protection method and device based on online identification of power supply composition ratio, which is conducive to calculating the distance from the fault point to the protection installation point, so that the improved distance protection can operate accurately.

[0008] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0009] In a first aspect, the present invention provides a power grid distance protection method based on online identification of power supply composition ratio, comprising the following steps:

[0010] Step A: Identify and obtain the power supply composition ratio, where the power supply composition ratio is the ratio of the respective capacities of the traditional rotating motor and the inverter power supply at the power supply end side of the power grid;

[0011] Step B: Real-time monitoring to obtain circuit information;

[0012] Step C: Determine whether there is a fault point based on the circuit information obtained by monitoring. If there is a fault point, start the protection and jump to step D. Otherwise, jump to step A.

[0013] Step D: Processing circuit information according to the power supply composition ratio to obtain the distance from the corresponding fault point to the protection installation location;

[0014] Step E: If the protection action conditions are met, jump to step F, otherwise, jump to step C;

[0015] Step F: Start the protection interruption service, that is, send an action command to the corresponding circuit breaker to cut off the fault, and jump to step A.

[0016] Furthermore, the method for identifying the proportion of power supply composition includes:

[0017] The components of the power supply side of the protection installation are identified through the distance protection measurement circuit and stored in the protection device.

[0018] Furthermore, the circuit information includes the fault current I flowing through the short-circuit point k , Rated output current I of the inverter power supply N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s ;

[0019] A method for processing circuit information according to the power supply composition ratio to obtain the distance from the corresponding fault point to the protection installation includes a "removal method", which removes the fault output current of the inverter power supply from the line current of the hybrid model, leaving only the traditional rotating motor output part, and then calculates the distance from the short-circuit point to the protection installation based on the traditional rotating motor output part.

[0020] Further, the "removal method" specifically includes the following steps:

[0021] Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0022] Calculate the fault current I of the inverter power supply after the fault. k1 , the calculation formula is as follows:

[0023] I k1 = k × I N

[0024] In the formula, I N is the rated output current of the inverter power supply; k is the proportionality coefficient;

[0025] Calculate the fault current I output by the traditional rotating motor after the fault k2 , the calculation formula is as follows: k2 =I k -I k1 ;

[0026] Calculate the distance l from the fault point to the protection installation location. The calculation formula is as follows:

[0027]

[0028] Where, E is the internal potential of the traditional rotating motor; X s is the internal impedance of the traditional rotating motor; Xl It is the impedance value per unit length of the power line.

[0029] The above calculation formula is generally linear, but there is still a certain nonlinear deviation. In engineering, it can be corrected according to the following engineering experience formula:

[0030] L = a1 3 +bl 2 +cl+d

[0031] Where l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation; a, b, c, and d are coefficients obtained from engineering experience.

[0032] Furthermore, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply is directly measured by the existing measuring device. N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s Obtained from the nameplate parameters of the rotating motor and inverter power equipment or existing measuring devices.

[0033] Furthermore, the circuit information includes the fault current I flowing through the short-circuit point k , Rated output current I of the inverter power supply N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s ;

[0034] Methods for processing circuit information according to the power composition ratio and obtaining the distance from the corresponding fault point to the protection installation include the "replacement method", which converts the inverter power supply in the hybrid model into a rotating motor power supply of the same capacity. After the conversion, the total power capacity remains unchanged, but the composition is completely composed of traditional rotating motors. Then, the distance from the short-circuit point to the protection installation is calculated according to the converted voltage / current values.

[0035] Further, the “replacement method” includes the following steps:

[0036] Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0037] Calculate the fault current I of the inverter power supply after the fault. k1 , the calculation formula is as follows:

[0038] I k1 = k × I N

[0039] In the formula, I N is the rated output current of the inverter power supply; k is the proportionality coefficient;

[0040] Theoretically, the inverter power supply in the power grid is replaced by traditional rotating machines with the same number and output power, and the fault current value I equivalent to that of the rotating machine is obtained. k1 * , the calculation formula is:

[0041]

[0042] In the formula, I k is the line fault current measured after the fault, I k1 is the rated output current of the inverter power supply, that is, I k -I k1 is the fault current output by the rotating motor after the fault, k is the proportional coefficient, the proportion of the inverter power supply is m%, and the proportion of the rotating motor is n%;

[0043] Calculate the equivalent line fault current value I after replacing the inverter power supply k * , the calculation formula is as follows: k * =(I k -I k1 )+I k1 * ;

[0044] Calculate the distance l from the fault point to the protection installation location. The calculation formula is as follows:

[0045]

[0046] Where, E is the internal potential of the traditional rotating motor; X s ' is the equivalent internal impedance of the power supply side after the inverter power supply is equivalently replaced by the traditional rotating motor; X l It is the impedance value per unit length of the power line.

[0047] The above calculation formula is generally linear, but there is still a certain nonlinear deviation. In engineering, it can be corrected according to the following engineering experience formula:

[0048] L = a1 3 +bl 2 +cl+d

[0049] Where l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation; a, b, c, and d are coefficients obtained from engineering experience.

[0050] Furthermore, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply is directly measured by the existing measuring device. N, the internal potential E of the traditional rotating motor and the internal impedance X of the equivalent power supply side s 'Obtained by direct measurement or conversion from the nameplate parameters of rotating electrical machines and inverter power equipment or existing measuring devices.

[0051] In a second aspect, the present invention further provides a power grid distance protection device based on online identification of power supply composition ratio, comprising:

[0052] Identification module: used to identify and obtain the power supply composition ratio, where the power supply composition ratio is the respective ratio of the traditional rotating motor and the inverter power supply at the power supply end side of the power grid;

[0053] Monitoring module: used to monitor and obtain circuit information in real time;

[0054] The first judgment module is used to judge whether there is a fault point according to the circuit information obtained by monitoring. If there is a fault point, the protection is started and the distance module is jumped. Otherwise, the identification module is jumped.

[0055] Distance module: used to process circuit information according to the power supply composition ratio and obtain the distance from the corresponding fault point to the protection installation location;

[0056] The second judgment module is used to jump to the protection action module if the protection action condition is met, otherwise, jump to the first judgment module;

[0057] Protection action module: used to start the protection interruption service, that is, to act on the corresponding circuit breaker to cut off the fault and jump to the identification module.

[0058] In a third aspect, the present invention provides a power grid distance protection device based on online identification of power supply composition ratio, including a processor and a storage medium;

[0059] The storage medium is used to store instructions;

[0060] The processor is used to operate according to the instructions to execute the steps of the method described in the first aspect.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] 1. The method of the present invention is aimed at a power system containing a hybrid power source (including an inverter power source and a traditional rotating motor). Before a fault occurs, the corresponding power source composition ratio information (i.e., the capacity ratio of the inverter power source and the traditional rotating motor) can be obtained. When a power line fault occurs, the ratio will not change. Therefore, the protection device can calculate the distance from the fault point to the protection installation location based on the ratio information and the measured current / voltage information, so that the improved distance protection can operate accurately.

[0063] 2. The present invention aims at a power system containing a hybrid power source (inverter power source and a traditional rotating motor), and introduces a power grid distance protection method based on online identification of the power source composition ratio. This method can effectively solve the distance protection problem caused by the large difference in fault characteristics between the inverter power source and the traditional power grid (mainly the current limiting effect of the inverter). The distance from the fault point to the protection installation can be calculated through the corresponding model, providing a basis for the action of the distance protection.

[0064] 3. The grid distance protection method based on online identification of power source composition ratio proposed in the present invention does not require additional installation of equipment (online monitoring and identification through the existing measurement circuit of traditional distance protection), and can fully utilize traditional distance protection devices. It is essentially a distance protection method with adaptive capability for power source composition ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a schematic diagram of the power grid structure that fully uses traditional rotating motors as power sources;

[0066] Figure 2 This is a schematic diagram of the power grid structure that fully uses inverter power as power supply;

[0067] Figure 3 A schematic diagram of a power grid structure containing a hybrid power source (inverter power source and a traditional rotating motor);

[0068] Figure 4 It is the schematic diagram for online identification of power supply composition ratio;

[0069] Figure 5 This is the distance protection action flow of the "replacement" method. DETAILED DESCRIPTION

[0070] The present invention is further explained in detail below in conjunction with the accompanying drawings and specific embodiments, but it should be understood that the protection scope of the present invention is not limited to the specific embodiments.

[0071] Embodiment 1:

[0072] This embodiment provides a power grid distance protection method based on online identification of the power source composition ratio. This method is aimed at power systems containing hybrid power sources (including inverter power sources and traditional rotating motors), and can obtain the corresponding power source composition ratio information (i.e., the capacity ratio of inverter power sources and traditional rotating motors) before a fault occurs. When a power line fails, the ratio will not change. Therefore, the protection device can calculate the distance from the fault point to the protection installation based on the ratio information and the measured current / voltage information, so that the improved distance protection can operate accurately. In essence, this method is also an adaptive protection method (tracking changes in the power source composition ratio).

[0073] This embodiment proposes a power grid distance protection method based on online pre-identification of power source proportion, including two specific schemes: a "removal" method and a "replacement" method.

[0074] The specific scheme of the "removal" method is essentially to remove the fault output current of the inverter power supply from the line fault current of the hybrid model, leaving only the traditional rotating motor output part, and then calculate the distance from the short-circuit point to the protection installation according to the measured data and the calculated data. The mathematical calculation steps of the specific scheme of the "removal" method are:

[0075] Step 1: Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0076] Step 2: Calculate the fault current I of the inverter power supply after the fault. k1 , and I k1 = k × I N (Wherein, I N is the rated output current of the inverter power supply; k is the proportionality coefficient, which can be 1.0-2.0);

[0077] Step 3: Calculate the fault current I output by the traditional rotating motor after the fault k2 , and I k2 =I k -I k1 ;

[0078] Step 4: Calculate the distance l from the fault point to the protection installation, and (Where E is the internal potential of the traditional rotating motor; X s is the internal impedance of the traditional rotating motor; X l is the impedance value per unit length of the power line);

[0079] Step 5. The above calculation formula is generally linear, but there is still a certain nonlinear deviation, which can be used in engineering. Therefore, it is corrected based on the given engineering experience:

[0080] L = a1 3 +bl 2 +cl+d

[0081] In the formula, l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation, and a, b, c, and d are coefficients obtained from engineering experience. The empirical correction formula here can be built on the simulation platform under the same line conditions, with a simulation comparison model containing a hybrid power supply and a simulation comparison model containing only a rotating motor on the power supply side. Faults are set at different points, data is obtained, and then fitted by software such as MATLAB. Under different power proportions, the coefficients may be different, but they can be corrected according to different situations in engineering, which will not affect engineering applications.

[0082] Afterwards, according to the distance L between the corresponding fault point and the protection installation location, the distance protection equipped on the corresponding circuit breaker will operate to clear the fault;

[0083] Among them, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply can be directly measured by the existing measuring device. N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s It can be directly obtained from the nameplate parameters of rotating motors and inverter power equipment or existing measuring devices.

[0084] The specific scheme of the "replacement" method is essentially to convert the inverter power supply in the hybrid model into a traditional rotating motor power supply of the same capacity. After the conversion, the total power supply capacity remains unchanged, but the components are completely composed of traditional rotating motors. Then, the distance from the short-circuit point to the protection installation is calculated according to the converted voltage / current value. The mathematical calculation steps of the specific scheme of the "replacement" method are:

[0085] Step 1: Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0086] Step 2: Calculate the fault current I of the inverter power supply after the fault. k1 , and I k1 = k × I N (Wherein, I N is the rated output current of the inverter power supply; k is the proportionality coefficient, which can be 1.0-2.0);

[0087] Step 3: Theoretically, replace the inverter power supply in the power grid with traditional rotating motors of the same number and output power to obtain the fault current value I equivalent to that of the rotating motor. k1 * ;

[0088] Step 4: Calculate the equivalent line fault current value I after replacing the inverter power supply k * , and I k *=(I k -I k1 )+I k1 * ;

[0089] Step 5: Calculate the distance l from the fault point to the protection installation location, and (Where E is the internal potential of the traditional rotating motor; X s ' is the equivalent internal impedance of the power supply side after the inverter power supply is equivalently replaced by a traditional rotating motor; X l is the impedance value per unit length of the power line);

[0090] Step 6. The above calculation formula is generally linear, but there is still a certain nonlinear deviation, which can be used in engineering. Therefore, it is corrected based on the given engineering experience:

[0091] L = a1 3 +bl 2 +cl+d

[0092] In the formula, l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation, and a, b, c, and d are coefficients obtained from engineering experience. The empirical correction formula here can be built on the simulation platform under the same line conditions, with a simulation comparison model containing a hybrid power supply and a simulation comparison model containing only a rotating motor on the power supply side. Faults are set at different points, data is obtained, and then fitted by software such as MATLAB. Under different power proportions, the coefficients may be different, but they can be corrected according to different situations in engineering, which will not affect engineering applications.

[0093] Afterwards, according to the distance L between the corresponding fault point and the protection installation location, the distance protection equipped on the corresponding circuit breaker will operate to clear the fault;

[0094] Among them, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply can be directly measured by the existing measuring device. N , the internal potential E of the traditional rotating motor and the internal impedance X of the equivalent power supply side s 'It can be directly measured or converted from the nameplate parameters of the rotating motor and inverter power supply equipment or existing measuring devices.

[0095] In both schemes, after calculating the distance L from the fault point to the protection installation, the relay protection device on the corresponding circuit breaker can be activated to eliminate the fault.

[0096] Specifically, the method of this embodiment includes the following steps:

[0097] Step 1: Identify and obtain the power supply composition ratio, where the power supply composition ratio is the ratio of the traditional rotating motor and the inverter power supply at the power supply end side of the power grid;

[0098] Step 2: Real-time monitoring to obtain circuit information;

[0099] Step 3: According to the circuit information obtained by monitoring, determine whether there is a fault point. If there is a fault point, start the protection and jump to step 4. Otherwise, jump to step 1.

[0100] Step 4: Process the circuit information according to the power supply composition ratio to obtain the distance from the corresponding fault point to the protection installation location;

[0101] Step 5: If the protection action conditions are met, jump to step 6, otherwise, jump to step 3;

[0102] Step 6: Start the protection interruption service, that is, send an action command to the corresponding circuit breaker to cut off the fault, and jump to step 1 to continue to identify the power supply composition ratio to prepare for the next fault.

[0103] Identify the proportion of each power source, that is, identify the total power of the rotating motor and the inverter power source. Since the rated power of each inverter power source is generally constant, that is, the rated output current under normal conditions is constant, in the removal method, the rated current of the equivalent inverter power source is the rated current of a single unit × the number of units. For example, in the replacement method, if the proportion of the traditional rotating motor is m%, and the proportion of the inverter power source is n%, the fault output current of the rotating motor with the same capacity when the inverter power source is replaced is

[0104] The method for identifying the proportion of power supply composition includes: identifying the composition of the power supply direction at the protection installation location through the measurement circuit of the distance protection, and storing it in the protection device.

[0105] Specifically, the circuit information includes the fault current I flowing through the short-circuit point k , Rated output current I of the inverter power supply N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s .

[0106] A method for processing circuit information according to the power supply composition ratio to obtain the distance from the corresponding fault point to the protection installation includes a "removal method", which removes the fault output current of the inverter power supply from the line current of the hybrid model, leaving only the traditional rotating motor output part, and then calculates the distance from the short-circuit point to the protection installation based on the traditional rotating motor output part.

[0107] Specifically, the "removal method" includes the following steps:

[0108] Step 1: Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0109] Step 2: Calculate the fault current I of the inverter power supply after the fault. k1 , the calculation formula is as follows:

[0110] I k1 = k × I N

[0111] In the formula, I N is the rated output current of the inverter power supply; k is the proportionality coefficient;

[0112] Step 3: Calculate the fault current I output by the traditional rotating motor after the fault k2 , the calculation formula is as follows: k2 =I k -I k1 ;

[0113] Step 4: Calculate the distance l from the fault point to the protection installation location. The calculation formula is as follows:

[0114]

[0115] Where, E is the internal potential of the traditional rotating motor; X s is the internal impedance of the traditional rotating motor; X l It is the impedance value per unit length of the power line.

[0116] Step 5. The above calculation formula is generally linear, but there is still a certain nonlinear deviation, which can be used in engineering. Therefore, it is corrected based on the given engineering experience:

[0117] L = a1 3 +bl 2 +cl+d

[0118] In the formula, l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation, and a, b, c, and d are coefficients obtained from engineering experience. The empirical correction formula here can be built on the simulation platform under the same line conditions, with a simulation comparison model containing a hybrid power supply and a simulation comparison model containing only a rotating motor on the power supply side. Faults are set at different points, data is obtained, and then fitted by software such as MATLAB. Under different power proportions, the coefficients may be different, but they can be corrected according to different situations in engineering, which will not affect engineering applications.

[0119] Specifically, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply can be directly measured by the existing measuring device. N, the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s It can be directly obtained from the nameplate parameters of rotating motors and inverter power equipment or existing measuring devices.

[0120] Specifically, the circuit information includes the fault current I flowing through the short-circuit point k , Rated output current I of the inverter power supply N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s ;

[0121] Methods for processing circuit information according to the power composition ratio and obtaining the distance from the corresponding fault point to the protection installation include the "replacement method", which converts the inverter power supply in the hybrid model into a rotating motor power supply of the same capacity. After the conversion, the total power capacity remains unchanged, but the composition is completely composed of traditional rotating motors. Then, the distance from the short-circuit point to the protection installation is calculated according to the converted voltage / current values.

[0122] Specifically, the "replacement method" includes the following steps:

[0123] Step 1: Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ;

[0124] Step 2: Calculate the fault current I of the inverter power supply after the fault. k1 , the calculation formula is as follows:

[0125] I k1 = k × I N

[0126] In the formula, I N is the rated output current of the inverter power supply; k is the proportionality coefficient;

[0127] Step 3: Theoretically, replace the inverter power supply in the power grid with traditional rotating motors of the same number and output power to obtain the fault current value I equivalent to that of the rotating motor. k1 * , the calculation formula is:

[0128]

[0129] In the formula, I k is the line fault current measured after the fault, I k1 is the rated output current of the inverter power supply, that is, I k -I k1 is the fault current output by the rotating motor after the fault, k is the proportional coefficient, the proportion of the inverter power supply is m%, and the proportion of the rotating motor is n%;

[0130] Step 4: Calculate the equivalent line fault current value I after replacing the inverter power supply k * , the calculation formula is as follows: k * =(I k -I k1 )+I k1 * ;

[0131] Step 5: Calculate the distance l from the fault point to the protection installation location. The calculation formula is as follows:

[0132] Where, E is the internal potential of the traditional rotating motor; X s ' is the equivalent internal impedance of the power supply side after the inverter power supply is equivalently replaced by a traditional rotating motor; X l It is the impedance value per unit length of the power line.

[0133] Step 6. The above calculation formula is generally linear, but there is still a certain nonlinear deviation, which can be used in engineering. Therefore, it is corrected based on the given engineering experience:

[0134] L = a1 3 +bl 2 +cl+d

[0135] In the formula, l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation, and a, b, c, and d are coefficients obtained from engineering experience. The empirical correction formula here can be built on the simulation platform under the same line conditions, with a simulation comparison model containing a hybrid power supply and a simulation comparison model containing only a rotating motor on the power supply side. Faults are set at different points, data is obtained, and then fitted by software such as MATLAB. Under different power proportions, the coefficients may be different, but they can be corrected according to different situations in engineering, which will not affect engineering applications.

[0136] Furthermore, the fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply can be directly measured by the existing measuring device. N , the internal potential E of the traditional rotating motor and the internal impedance X of the equivalent power supply side s 'It can be directly measured or converted from the nameplate parameters of the rotating motor and inverter power supply equipment or existing measuring devices.

[0137] It should be noted that the power system fault in this embodiment is a three-phase symmetrical short circuit fault, and the power transmission line model is regarded as a "straight line", that is, the distance L between the fault point and the protection installation and the unit length impedance X of the power line l The product of is the line impedance from the short-circuit point to the protection installation.

[0138] Implementation principle: Figure 1 The figure shows a schematic diagram of a power grid structure that fully uses traditional rotating motors as power sources. In a traditional power grid, only traditional rotating motors are used as power sources for the power grid. In this case, after a fault occurs in the power grid, the fault current flowing through the line is: (Where E is the potential inside the generator, X s is the internal impedance of the generator, X L To protect the line impedance between the installation location and the fault point). Under normal circumstances, the fault current value output by the traditional rotating motor is very high, which can reach 20 to 50 times the normal current. The existing distance protection method and device can be more mature and effective in dealing with various faults in the power grid containing only traditional rotating motors.

[0139] like Figure 2 As shown in the figure, the schematic diagram of the power grid structure that fully uses the inverter power supply as the power supply. After a fault occurs in the power grid, due to the limitation of the power electronic device inside the inverter power supply, the fault current flowing through the line is: I k = k × I N (Among them, I N is the rated current value of the inverter power supply output under normal circumstances, and k is the proportional coefficient between the inverter power supply output current value and the inverter power supply rated current after the fault. In general, k is determined by the design redundancy of the inverter power supply itself). Usually, k is 1.0~2.0. Therefore, compared with traditional rotating motors, the output current value of the inverter power supply after the fault is very small, and under the action of nonlinear control, the fault current size hardly changes with the change of the short-circuit point distance. Therefore, the existing distance protection method and device cannot directly obtain fault distance information, and cannot achieve accurate isolation of the fault.

[0140] This embodiment proposes a power grid distance protection method based on online identification of power supply composition ratio, and determines the power supply ratio of traditional rotating motors and inverters on the power supply side through an online identification method.

[0141] The principle of this identification method is to use the existing distance protection measurement circuit to identify the components of the power supply direction at the protection installation location and store them in the protection device. Figure 4 As shown, the disturbance source is a large load fluctuation or short circuit fault on the line side, so the identification method has a certain time-varying tracking performance.

[0142] Normally, the traditional rotating motor can be regarded as a voltage source, and the inverter power supply can be regarded as a controlled current source. Due to the different response characteristics of the voltage source and the current source, after a certain disturbance signal is given to the system, the voltage / current response information on the power supply side will also vary with the different proportions of the power supply composition, so that the respective proportions of the inverter power supply and the traditional rotating generator in the power grid can be obtained. There are many actual power supply devices on the power supply side, but the synchronous machine is basically a constant voltage source, and the inverter basically meets the characteristics of current control. Therefore, the model structure can be regarded as an equivalent power supply after the traditional rotating motor and the inverter power supply are equivalently merged (using the Thevenin theorem and Norton theorem, etc.).

[0143] Obviously, in the short period before and after the fault occurs, the composition ratio of the power supply side remains unchanged, that is, the respective capacity ratios of the traditional rotating motor and the inverter power supply will not change.

[0144] Embodiment 2:

[0145] This embodiment provides a power grid distance protection device based on online identification of power supply composition ratio, including:

[0146] Identification module: used to identify and obtain the power supply composition ratio, where the power supply composition ratio is the respective ratio of the traditional rotating motor and the inverter power supply at the power supply end side of the power grid;

[0147] Monitoring module: used to monitor and obtain circuit information in real time;

[0148] The first judgment module is used to judge whether there is a fault point according to the circuit information obtained by monitoring. If there is a fault point, the protection is started and the distance module is jumped. Otherwise, the identification module is jumped.

[0149] Distance module: used to process circuit information according to the power supply composition ratio and obtain the distance from the corresponding fault point to the protection installation location;

[0150] The second judgment module is used to jump to the protection action module if the protection action condition is met, otherwise, jump to the first judgment module;

[0151] Protection action module: used to start the protection interruption service, that is, to send an action instruction to the corresponding circuit breaker to cut off the fault and jump to the identification module.

[0152] The device of this embodiment can be applied to implement the method described in the first embodiment.

[0153] Embodiment three:

[0154] This embodiment provides a power grid distance protection device based on online identification of power supply composition ratio, including a processor and a storage medium;

[0155] The storage medium is used to store instructions;

[0156] The processor is used to operate according to the instructions to execute the steps of the method described in embodiment 1.

[0157] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the protection content of the present invention.

[0158] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0159] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0160] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A power grid distance protection method based on online identification of power supply composition ratio, characterized in that: The following steps are involved: Step A: Identify and obtain the power supply composition ratio, where the power supply composition ratio is the ratio of the respective capacities of the traditional rotating motor and the inverter power supply on the power supply side of the power grid; Step B: Real-time monitoring to obtain circuit information; Step C: Determine whether there is a fault point based on the circuit information obtained by monitoring. If there is a fault point, start the protection and jump to step D. Otherwise, jump to step A. Step D: Processing circuit information according to the power supply composition ratio to obtain the distance from the corresponding fault point to the protection installation location; Step E: If the protection action conditions are met, jump to step F, otherwise, jump to step C; Step F: Start the protection interruption service, that is, send an action command to the corresponding circuit breaker to cut off the fault, and jump to step A; The circuit information includes the fault current I flowing through the short-circuit point k , Rated output current I of the inverter power supply N , the internal potential E of the traditional rotating motor and the internal impedance X of the traditional rotating motor s ; The method of processing the circuit information according to the power composition ratio and obtaining the distance from the corresponding fault point to the protection installation also includes a "replacement method", which converts the inverter power supply in the hybrid model into a rotating motor power supply of the same capacity. After the conversion, the total capacity of the power supply remains unchanged, but the components are completely composed of traditional rotating motors. Then, the distance from the short-circuit point to the protection installation is calculated according to the converted voltage / current values; The "replacement method" includes the following steps: Measure the fault current I flowing through the short-circuit point after a short-circuit fault occurs in the power system k ; Calculate the fault current I of the inverter power supply after the fault. k1 , the calculation formula is as follows: I k1 =k×I N In the formula, I N is the rated output current of the inverter power supply; k is the proportionality coefficient; Theoretically, the inverter power supply in the power grid is replaced by traditional rotating machines with the same number and output power, and the fault current value I equivalent to that of the rotating machine is obtained. k1 * , the calculation formula is: In the formula, I k is the fault current flowing through the short-circuit point, I k1 is the fault current of the inverter power supply after the fault, that is, I k -I k1 is the fault current output by the rotating motor after the fault, k is the proportional coefficient, the proportion of the inverter power supply is m%, and the proportion of the rotating motor is n%; Calculate the equivalent line fault current value I after replacing the inverter power supply k * , the calculation formula is as follows: k * =(I k -I k1 )+I k1 * ; Calculate the distance l from the fault point to the protection installation location. The calculation formula is as follows: Where, E is the internal potential of the traditional rotating motor; X s ' is the equivalent internal impedance of the power supply side after the inverter power supply is equivalently replaced by the traditional rotating motor; X l is the impedance value per unit length of the power line; According to the following engineering experience formula, make corrections: <h2 style=";text-align:left;direction:ltr">L=al<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> +bl<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +cl+d Where l is the calculated distance from the fault point to the protection installation; L is the corrected distance from the fault point to the protection installation; a, b, c, and d are coefficients obtained from engineering experience.

2. The power grid distance protection method according to claim 1, characterized in that: Methods for identifying the proportion of power supply components include: The components of the power supply side of the protection installation are identified through the distance protection measurement circuit and stored in the protection device.

3. The power grid distance protection method according to claim 1, characterized in that: Fault current I flowing through the short-circuit point k The rated output current I of the inverter power supply is directly measured by the existing measuring device. N , the internal potential E of the traditional rotating motor and the internal impedance X of the equivalent power supply side s 'Obtained by direct measurement or conversion from the nameplate parameters of rotating electrical machines and inverter power equipment or existing measuring devices.

4. A power grid distance protection device based on online identification of power supply composition ratio for executing the method according to any one of claims 1 to 3, characterized in that: include: Identification module: used to identify and obtain the power supply composition ratio, where the power supply composition ratio is the ratio of the respective capacities of the traditional rotating motor and the inverter power supply on the power supply side of the power grid; Monitoring module: used to monitor and obtain circuit information in real time; The first judgment module is used to judge whether there is a fault point according to the circuit information obtained by monitoring. If there is a fault point, the protection is started and the distance module is jumped. Otherwise, the identification module is jumped. Distance module: used to process circuit information according to the power supply composition ratio and obtain the distance from the corresponding fault point to the protection installation location; The second judgment module is used to jump to the protection action module if the protection action condition is met, otherwise, jump to the first judgment module; Protection action module: used to start the protection interruption service, that is, to act on the corresponding circuit breaker to cut off the fault and jump to the identification module.

5. A power grid distance protection device based on online identification of power supply composition ratio, characterized in that: including processor and storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 3.

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