Virtual voltage differential protection method for power transmission line of new energy power grid

Abstract

The invention discloses a virtual voltage differential protection method for a new energy power grid power transmission line, and relates to the technical field of power system relay protection, and the method comprises the following steps: 1, building a two-end concentrated inductance-capacitance-resistance mixed segment lossless line parameter model of the new energy power grid power transmission line; 2, a high-precision voltage sensor and a current sensor are used for collecting three-phase voltage and current at the left end and the right end of the new energy power grid power transmission line respectively, and positive-sequence voltage and positive-sequence current at the left end and the right end of the power transmission line are calculated through Clark transformation; 3, according to the Kirchhoff's law of voltage, calculating the voltage of the lumped parameter points at the left and right ends; 4, calculating a virtual voltage at the midpoint of the power transmission line by adopting a weighted average method; 5, the two virtual voltages obtained through calculation are subtracted, and whether the power transmission line breaks down or not is judged; according to the method provided by the invention, the accuracy of fault detection can be improved, so that misjudgment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection for electric power systems, and in particular to a virtual voltage differential protection method for a new energy power grid transmission line. Background Art

[0002] With the growth of energy demand and the emphasis on environmental protection, the proportion of renewable energy in the power grid continues to rise. Compared with traditional power grids, renewable energy power grids have many unique properties. Renewable energy power generation comes from a variety of sources, including solar energy, wind energy, hydropower (small hydropower, etc. belong to the category of renewable energy), bioenergy, etc., and the power generation characteristics of these energy sources are different. For example, solar photovoltaic power generation is greatly affected by light intensity and temperature, while wind power generation depends on the randomness of wind speed and wind direction. This makes the output power of the renewable energy power grid highly intermittent and volatile.

[0003] In terms of new energy grid transmission lines, this volatility brings many challenges to the stable operation of transmission lines. Most of the transmission line protection methods of traditional power grids are designed based on stable power supply and relatively regular load conditions. However, in new energy grids, due to the access of a large number of distributed power sources, the power flow distribution of transmission lines has become complex and difficult to predict. The traditional protection method based on power frequency electrical quantities may no longer be applicable.

[0004] From the perspective of power system stability, the uncertainty of renewable energy generation may lead to an increase in the voltage fluctuation range of transmission lines. When the voltage fluctuation exceeds a certain range, it may affect the normal operation of power equipment and even cause chain failures. For example, low voltage may cause some voltage-sensitive equipment to stop working, while high voltage may damage the insulation of equipment.

[0005] In addition, new energy power generation equipment usually needs to be connected to the power grid through power electronic converters, and these power electronic devices will generate a large amount of harmonics. Harmonics will interfere with the voltage and current signals on the transmission line, making it easy for protection devices based on traditional signal analysis to misjudge. Moreover, as the scale of new energy power grids expands, the types of faults in transmission lines are more complex, including intermittent faults, high-resistance faults, etc. Traditional protection methods have limitations in detecting and distinguishing these types of faults.

[0006] Furthermore, the topology of new energy grids is becoming increasingly complex, with a large number of distributed power sources and microgrids connected. This makes the magnitude and direction of fault current no longer follow the rules of traditional grids, and traditional protection methods based on the current differential principle may fail because they cannot accurately determine the direction and magnitude of fault current.

[0007] To sum up, in order to ensure the safe, stable and efficient operation of the new energy power grid transmission lines, there is an urgent need for a transmission line protection method specifically tailored to the characteristics of the new energy power grid. The new energy power grid transmission line virtual voltage differential protection method of the present invention is proposed based on this demand. Summary of the invention

[0008] The purpose of the present invention is to provide a virtual voltage differential protection method for a new energy power grid transmission line, so as to solve the problems in the prior art that the traditional protection method has low accuracy in fault detection and effective signals are difficult to accurately extract.

[0009] To achieve the above object, the present invention provides a virtual voltage differential protection method for a new energy power grid transmission line, comprising the following steps:

[0010] Step 1: Establish a concentrated inductor-capacitor-resistor (LCR) hybrid segmented lossless line parameter model at both ends of the new energy power grid transmission line; compared with a single resistance model, this model can more comprehensively cover the inductance, capacitance and resistance characteristics of the transmission line, thereby accurately reflecting the electrical characteristics of the transmission line in actual operation;

[0011] Step 2: Use high-precision voltage sensors and current sensors to collect the three-phase voltage and current at the left and right ends of the new energy power grid transmission line, and calculate the positive sequence voltage and positive sequence current at the left and right ends of the transmission line through Clarke transformation;

[0012] Step 3: Calculate the voltage at the concentrated parameter points on the left and right ends according to Kirchhoff's voltage law;

[0013] Step 4: Use the weighted average method to calculate the virtual voltage at the midpoint of the transmission line; this method can comprehensively consider the voltage conditions at both ends and more reasonably reflect the voltage state at the midpoint.

[0014] Step 5: Difference the two calculated virtual voltages to determine whether a transmission line fault occurs. This fault determination method is based on the accurate calculation of the virtual voltage of the transmission line. By comparing the difference between the two virtual voltages and the set threshold value, it can quickly and accurately detect whether a transmission line fault occurs.

[0015] Preferably, the two-end concentrated inductor-capacitor-resistor hybrid segmented lossless line parameter model established in step 1 is specifically as follows:

[0016] For the lumped parameter on the left, the calculation expression is as follows:

[0017] inductance capacitance resistance

[0018] For the concentrated parameter on the right side, the calculation expression is as follows:

[0019] inductance capacitance resistance

[0020] In the formula, the length of the transmission line is L, n represents the number of sections, L0 represents the inductance of each section, R0 represents the resistance of each section, C0 represents the capacitance of each section, and the inductance L0, capacitance C0 and resistance R0 of each section are evenly distributed.

[0021] Preferably, in step 2, a high-precision voltage sensor and a current sensor are used to respectively collect the three-phase voltage and current at the left and right ends of the new energy power grid transmission line, and the process of calculating the positive sequence voltage and positive sequence current at the left and right ends of the transmission line by Clarke transformation is as follows:

[0022] S21, use high-precision voltage sensors and current sensors to collect the three-phase voltage U at the left and right ends of the new energy grid transmission line 1a , U 1b , U 1c and U 2a , U 2b , U 2c And the three-phase current I 1a ,I 1b ,I 1c and I 2a ,I 2b ,I 2c ;

[0023] S22. Based on the vector synthesis relationship of the three-phase system in the plane rectangular coordinate system, the Clarke transformation matrix T is constructed. Clark , specifically:

[0024]

[0025] S23. According to the Clarke transformation formula, the positive sequence voltage U″ at the left end is obtained. 11 and positive sequence current I″ 11 , the calculation expression is as follows:

[0026]

[0027] S24. According to the Clarke transformation formula, the positive sequence voltage U″ at the right end is obtained. 21 and positive sequence current I″ 21 , the calculation expression is as follows:

[0028]

[0029] Preferably, in step 3, according to Kirchhoff's voltage law, the calculation expression for calculating the voltage at the concentrated parameter points at the left and right ends is as follows:

[0030] Voltage U″ at the left concentrated parameter point L The calculation expression is as follows:

[0031]

[0032] Voltage U″ at the right concentrated parameter point R The calculation expression is as follows:

[0033]

[0034] Preferably, the expression for calculating the virtual voltage at the midpoint of the transmission line using the weighted average method in step 4 is as follows:

[0035] The relationship between the midpoint virtual voltage and the left end is:

[0036]

[0037] The relationship between the midpoint virtual voltage and the right end is:

[0038]

[0039] In the formula, U″ mid1 Indicates the relationship between the midpoint virtual voltage and the left end, U″ mid2 Represents the relationship between the midpoint virtual voltage and the right end.

[0040] Preferably, the specific content of step 5 is as follows:

[0041] S51, taking the difference of the two calculated virtual voltages, the calculation expression is as follows:

[0042] ΔU″=U″ mid1 -U″ mid2 ;

[0043] S52: Determine whether the difference ΔU″ is greater than a preset differential voltage threshold value U″ set , if ΔU″>U″ set , it is determined that the transmission line is faulty, otherwise it is determined that the transmission line is in normal working condition.

[0044] Therefore, the present invention adopts the above-mentioned virtual voltage differential protection method for a new energy power grid transmission line, which has the following beneficial effects:

[0045] (1) Improved model accuracy: The hybrid segmented lossless line parameter model with two-terminal concentrated inductance-capacitance-resistance (LCR) is adopted. Compared with the single resistance model, it more comprehensively considers the actual characteristics of the transmission line, including the combined effects of inductance, capacitance and resistance, and improves the modeling accuracy of the new energy power grid transmission line;

[0046] (2) Enhanced anti-interference capability: Clarke transform is used to calculate positive sequence voltage and current. Compared with the positive and negative zero sequence transformation matrix, it can better extract effective signals and reduce the interference of harmonics on protection judgment in the presence of a large amount of harmonic interference (generated by power electronic equipment in new energy grids);

[0047] (3) Improved fault detection accuracy: When calculating the voltage at the concentrated parameter points on the left and right ends, the effects of resistance, inductance and capacitance are comprehensively considered, making the voltage calculation more in line with the actual situation. The weighted average method is used to calculate the virtual voltage, which can more reasonably reflect the voltage state at the midpoint of the transmission line, thereby improving the accuracy of fault detection and reducing misjudgment.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The present invention is an overall flow chart of a virtual voltage differential protection method for a new energy power grid transmission line. DETAILED DESCRIPTION

[0050] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] See also Figure 1 , a virtual voltage differential protection method for a new energy power grid transmission line comprises the following steps:

[0052] Step 1: Establish a hybrid segmented lossless line parameter model of concentrated inductance-capacitance-resistance (LCR) at both ends of the new energy power grid transmission line; compared with a single resistance model, this model can more comprehensively cover the inductance, capacitance and resistance characteristics of the transmission line, thereby accurately reflecting the electrical characteristics of the transmission line in actual operation; wherein, the establishment of a hybrid segmented lossless line parameter model of concentrated inductance-capacitance-resistance at both ends of the new energy power grid transmission line is specifically as follows:

[0053] For the lumped parameter on the left, the calculation expression is as follows:

[0054] inductance capacitance resistance

[0055] For the concentrated parameter on the right side, the calculation expression is as follows:

[0056] inductance capacitance resistance

[0057] In the formula, the length of the transmission line is L, n represents the number of sections, L0 represents the inductance of each section, R0 represents the resistance of each section, C0 represents the capacitance of each section, and the inductance L0, capacitance C0 and resistance R0 of each section are evenly distributed.

[0058] Step 2: Use high-precision voltage sensors and current sensors to collect the three-phase voltage and current at the left and right ends of the new energy power grid transmission line, and calculate the positive sequence voltage and positive sequence current at the left and right ends of the transmission line through Clarke transformation; the specific process is as follows:

[0059] S21, use high-precision voltage sensors and current sensors to collect the three-phase voltage U at the left and right ends of the new energy grid transmission line 1a , U 1b , U 1c and U 2a , U 2b , U 2c And the three-phase current I 1a ,I 1b ,I 1c and I 2a ,I 2b ,I 2c ;

[0060] S22. Based on the vector synthesis relationship of the three-phase system in the plane rectangular coordinate system, the Clarke transformation matrix T is constructed. Clark , specifically:

[0061]

[0062] S23. According to the Clarke transformation formula, the positive sequence voltage U″ at the left end is obtained. 11 and positive sequence current I″ 11 , the calculation expression is as follows:

[0063]

[0064] S24. According to the Clarke transformation formula, the positive sequence voltage U″ at the right end is obtained. 21 and positive sequence current I″ 21 , the calculation expression is as follows:

[0065]

[0066] Step 3: According to Kirchhoff's voltage law, calculate the voltage at the concentrated parameter points on the left and right ends; the specific calculation expression is as follows:

[0067] Voltage U″ at the left concentrated parameter point L The calculation expression is as follows:

[0068]

[0069] Voltage U″ at the right concentrated parameter point R The calculation expression is as follows:

[0070]

[0071] Step 4: Calculate the virtual voltage at the midpoint of the transmission line using the weighted average method. This method can comprehensively consider the voltage conditions at both ends and more reasonably reflect the voltage state at the midpoint. The expression for calculating the virtual voltage at the midpoint of the transmission line using the weighted average method is as follows:

[0072] The relationship between the midpoint virtual voltage and the left end is:

[0073]

[0074] The relationship between the midpoint virtual voltage and the right end is:

[0075]

[0076] In the formula, U″ mid1 Indicates the relationship between the midpoint virtual voltage and the left end, U″ mid2 Represents the relationship between the midpoint virtual voltage and the right end.

[0077] Step 5: Difference is taken between the two calculated virtual voltages to determine whether a fault occurs in the transmission line. This fault determination method is based on the accurate calculation of the virtual voltage of the transmission line. By comparing the difference between the two virtual voltages and the set threshold value, it is possible to quickly and accurately detect whether a fault occurs in the transmission line. The specific contents are as follows:

[0078] S51, taking the difference of the two calculated virtual voltages, the calculation expression is as follows:

[0079] ΔU″=U″ mid1 -U″ mid2 ;

[0080] S52: Determine whether the difference ΔU″ is greater than a preset differential voltage threshold value U″ set , if ΔU″>U″ set , it is determined that the transmission line is faulty, otherwise it is determined that the transmission line is in normal working condition.

[0081] Therefore, the present invention adopts the above-mentioned virtual voltage differential protection method for the new energy power grid transmission line. First, a mixed segmented lossless line parameter model with concentrated inductance-capacitance-resistance at both ends is adopted to more comprehensively consider the actual characteristics of the transmission line; then, the positive sequence voltage and current are calculated by Clarke transform, which can better extract effective signals and reduce the interference of harmonics on protection judgment; finally, when calculating the voltage at the concentrated parameter points at the left and right ends, the effects of resistance, inductance and capacitance are comprehensively considered, so that the voltage calculation is more in line with the actual situation; at the same time, by adopting the weighted average method to calculate the virtual voltage, the voltage state of the midpoint of the transmission line can be more reasonably reflected, thereby improving the accuracy of fault detection and reducing misjudgment.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A virtual voltage differential protection method for a new energy power grid transmission line, characterized in that: The following steps are involved: Step 1: Establish a concentrated inductor-capacitor-resistor hybrid segmented lossless line parameter model at both ends of the new energy power grid transmission line; Step 2: Use high-precision voltage sensors and current sensors to collect the three-phase voltage and current at the left and right ends of the new energy power grid transmission line, and calculate the positive sequence voltage and positive sequence current at the left and right ends of the transmission line through Clarke transformation; Step 3: Calculate the voltage at the concentrated parameter points on the left and right ends according to Kirchhoff's voltage law; Step 4: Calculate the virtual voltage at the midpoint of the transmission line using a weighted average method; Step 5: Difference the two calculated virtual voltages to determine whether a fault occurs in the transmission line.

2. A virtual voltage differential protection method for a new energy power grid transmission line according to claim 1, characterized in that: The parameter model of the concentrated inductor-capacitor-resistor hybrid segmented lossless line at both ends of the new energy grid transmission line established in step 1 is as follows: For the lumped parameter on the left, the calculation expression is as follows: inductance capacitance resistance For the concentrated parameter on the right side, the calculation expression is as follows: inductance capacitance resistance In the formula, the length of the transmission line is L, n represents the number of sections, L0 represents the inductance of each section, R0 represents the resistance of each section, C0 represents the capacitance of each section, and the inductance L0, capacitance C0 and resistance R0 of each section are evenly distributed.

3. A virtual voltage differential protection method for a new energy power grid transmission line according to claim 2, characterized in that: In step 2, high-precision voltage sensors and current sensors are used to collect the three-phase voltage and current at the left and right ends of the new energy power grid transmission line, and the process of calculating the positive sequence voltage and positive sequence current at the left and right ends of the transmission line through Clarke transformation is as follows: S21, use high-precision voltage sensors and current sensors to collect the three-phase voltage U at the left and right ends of the new energy grid transmission line 1a , U 1b , U 1c and U 2a , U 2b , U 2c And the three-phase current I 1a ,I 1b ,I 1c and I 2a ,I 2b ,I 2c ; S22. Based on the vector synthesis relationship of the three-phase system in the plane rectangular coordinate system, the Clarke transformation matrix T is constructed. Clark , specifically: S23. According to the Clarke transformation formula, the positive sequence voltage U″ at the left end is obtained. 11 and positive sequence current I″ 11 , the calculation expression is as follows: S24. According to the Clarke transformation formula, the positive sequence voltage U″ at the right end is obtained. 21 and positive sequence current I″ 21 , the calculation expression is as follows:

4. A virtual voltage differential protection method for a new energy power grid transmission line according to claim 3, characterized in that: In step 3, according to Kirchhoff's voltage law, the calculation expression for the voltage at the concentrated parameter points on the left and right ends is as follows: Voltage U″ at the left concentrated parameter point L The calculation expression is as follows: Voltage U″ at the right concentrated parameter point R The calculation expression is as follows:

5. A virtual voltage differential protection method for a new energy power grid transmission line according to claim 4, characterized in that: The expression for calculating the virtual voltage at the midpoint of the transmission line using the weighted average method in step 4 is as follows: The relationship between the midpoint virtual voltage and the left end is: The relationship between the midpoint virtual voltage and the right end is: In the formula, U″ mid1 Indicates the relationship between the midpoint virtual voltage and the left end, U″ mid2 Indicates the relationship between the midpoint virtual voltage and the right end.

6. A virtual voltage differential protection method for a new energy power grid transmission line according to claim 5, characterized in that: The specific contents of step 5 are as follows: S51, taking the difference of the two calculated virtual voltages, the calculation expression is as follows: ΔU″=U″ mid1 -U″ mid2 ; S52: Determine whether the difference ΔU″ is greater than a preset differential voltage threshold value U″ set , if ΔU″>U″ set , it is determined that the transmission line is faulty, otherwise it is determined that the transmission line is in normal working condition.

Images