CN110470884B - Power frequency overvoltage calculation method applied to power restoration of high-voltage transmission line - Google Patents
Power frequency overvoltage calculation method applied to power restoration of high-voltage transmission line Download PDFInfo
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Abstract
The invention discloses a power frequency overvoltage calculation method applied to power restoration of a high-voltage power transmission line, and belongs to the field of power systems. The method calculates the fitting function of the power frequency overvoltage and the line length of each type of line, and uses the function to calculate the power frequency overvoltage of the high-voltage transmission line for power recovery. The method has good practicability and innovation, is applied to the overvoltage verification in the black start recovery process of a certain power grid, adopts the traditional modeling simulation to calculate the overvoltage in the past, and is not mentioned in the previous overvoltage verification; the method saves a large amount of calculation time for the decision process of the power restoration of the high-voltage transmission line, and has important guidance value.
Description
Technical Field
The invention relates to a power frequency overvoltage calculation method applied to power restoration of a high-voltage power transmission line, and belongs to the field of power systems.
Background
Because the dependence of the power grid on the power supply is higher and higher, the consequences caused by a major power failure accident become more serious, once an emergency power failure accident occurs, measures must be taken to recover the normal power supply of the system at the fastest speed, and the loss of the fault power failure is reduced to the lowest. Therefore, the research on prevention and recovery measures of the blackout accident is enhanced, a reasonable and feasible recovery plan is formulated, the training of operators and the overhaul of related equipment are enhanced, reasonable recovery operation can be carried out when the accident happens, and the loss is reduced to the maximum extent. Otherwise, the recovery process may be delayed, even the accident range is expanded, resulting in more serious consequences.
The system constructed in the initial stage of black start is a weak power grid structure, and if any out-of-limit fluctuation occurs, the whole black start can be unsuccessful, and larger loss is caused. Careful verification procedures are important for a safe, efficient black start scheme. At the tail end of the power transmission line, if the voltage amplitude is too large, equipment can be broken down to cause misoperation, so that the recovery of the black start of the system is unsuccessful, and great economic loss is caused. Therefore, the black start path recovery must pay attention to the verification of the power frequency overvoltage of the line, and the basis of the verification is to obtain the power frequency overvoltage.
Disclosure of Invention
The invention provides a power frequency overvoltage calculation method applied to power restoration of a high-voltage transmission line, which is used for obtaining power frequency overvoltage of the line.
The technical scheme of the invention is as follows: a power frequency overvoltage calculation method applied to power restoration of a high-voltage transmission line comprises the following steps:
step 1: extracting generator data, transformer data and line data information contained in a path according to a specified power recovery path of the high-voltage transmission line; the high-voltage transmission line refers to a main transmission line with 220kV and 110kV grades;
step 2: establishing an overvoltage simulation model of a series path consisting of a generator, a transformer and a circuit in a simulation environment;
step 3: fitting is carried out through power frequency overvoltage, and the fitting function of the power frequency overvoltage and the line length of each type of line is obtained as follows: u is al3+bl2+cl+d；
U is the power frequency overvoltage value of the corresponding circuit; l is the line length; a. b, c and d are constants of the fitting function, and the values of the constants are related to the model number and the voltage grade of the line;
step 4: and calculating power frequency overvoltage according to the number of the lines:
if only one line exists, the length of the line is substituted into a fitting function corresponding to the type of the line, and the power frequency overvoltage value of the line is calculated;
if the number of lines is multiple: firstly, calculating a voltage value at the tail end of a first line, and substituting the length of the line into a fitting function corresponding to the model of the line to calculate a power frequency overvoltage value of the line; the calculation process of the power frequency overvoltage value of the rest line is as follows: and (3) bringing the power frequency voltage value at the tail end of the (x-1) th line into a fitting function of the corresponding model of the (x) th line, solving a length value corresponding to the converted length value, bringing the calculated line length and the line length of the (x) th line into the fitting function of the corresponding model of the (x) th line again, finally solving a power frequency overvoltage value of the (x) th line, finishing the calculation of the power frequency overvoltage if the line is the last line, and otherwise, continuing to adopt the calculation process of the power frequency overvoltage values of the rest lines to calculate the power frequency overvoltage until the last line calculates the power frequency overvoltage.
Comparing the power frequency overvoltage value with an overvoltage standard, and verifying whether the overvoltage meets the requirement or not so as to judge to start a corresponding circuit; the overvoltage standard is as follows: in 220kV and 110kV systems, the line side power frequency overvoltage is not more than 1.3 times.
A synchronous generator model is simulated by a relatively simple three-phase voltage source module; the power transformer model is equivalent to the synthesis of an ideal transformer and an RT and LT impedance branch circuit because the excitation branch circuit is often ignored in an actual system; the power transmission line adopts a distributed parameter line model, and a small-loss Bergeron model of the power transmission line is established; the switch element module adopts a calculation switch model with a parallel leakage resistor and a parallel leakage capacitor and an oscilloscope module.
The invention has the beneficial effects that:
1. the method has good practicability and innovation, is applied to overvoltage verification in the black start recovery process of a certain power grid, adopts the traditional modeling simulation to calculate the overvoltage in the past, and is not mentioned in the previous overvoltage verification.
2. A large amount of calculation time is saved for the decision making process of the power restoration of the high-voltage transmission line, and the method has important guiding value.
Drawings
FIG. 1 is a flow chart of the present invention;
fig. 2 is a power transmission line restoration scheme according to embodiment 2 of the present invention.
Detailed Description
Example 1: as shown in fig. 1, a power frequency overvoltage calculation method applied to power recovery of a high-voltage transmission line, the invention firstly mainly aims at the power frequency overvoltage problem in the power recovery path recovery process, analyzes the influence of line parameters on the air charge overvoltage from the distribution parameter characteristics of the line, and analyzes the power frequency overvoltage characteristics when a plurality of branched lines recover power supply according to the capacity lift effect of the transmission line in the power recovery process; and then establishing a simulation model conforming to the reality by using simulation software MATLAB/Simulink, carrying out a simulation experiment aiming at the power frequency overvoltage of the power transmission line models of 220kV and 110kV grades, and obtaining the direct proportion relation between the amplitude of the power frequency overvoltage and the line length according to the simulation result. And finally, calculating a fitting function of the power frequency overvoltage and the line length of each type of line through MATLAB software, and using the function to calculate the power frequency overvoltage of the high-voltage transmission line for power recovery.
The method comprises the following specific steps:
step 1: extracting generator data, transformer data and line data information contained in a path according to a specified power recovery path of the high-voltage transmission line; the high-voltage transmission line refers to a main transmission line with 220kV and 110kV grades;
step 2: establishing an overvoltage simulation model of a series path consisting of a generator, a transformer and a line in an MATLAB simulation environment;
step 3: fitting the power frequency overvoltage through MATLAB to obtain a fitting function of the power frequency overvoltage and the line length of each type of line, wherein the fitting function is as follows:
U＝al3+bl2+cl+d(1)
u is the power frequency overvoltage value of the corresponding circuit; l is the line length; a. b, c and d are constants of the fitting function, and the values of the constants are related to the model number and the voltage grade of the line;
step 4: and calculating power frequency overvoltage according to the number of the lines:
if only one line exists, the length of the line is substituted into a fitting function corresponding to the type of the line, and the power frequency overvoltage value of the line is calculated;
if the number of lines is multiple: firstly, calculating a voltage value at the tail end of a first line, and substituting the length of the line into a fitting function corresponding to the model of the line to calculate a power frequency overvoltage value of the line; the calculation process of the power frequency overvoltage value of the rest line is as follows: and (3) bringing the power frequency voltage value at the tail end of the (x-1) th line into a fitting function of the corresponding model of the (x) th line, solving a length value corresponding to the converted length value, bringing the calculated line length and the line length of the (x) th line into the fitting function of the corresponding model of the (x) th line again, finally solving a power frequency overvoltage value of the (x) th line, finishing the calculation of the power frequency overvoltage if the line is the last line, and otherwise, continuing to adopt the calculation process of the power frequency overvoltage values of the rest lines to calculate the power frequency overvoltage until the last line calculates the power frequency overvoltage.
Step 5: the effectiveness of the method is verified for a specific example, and the result shows that the algorithm provided by the method has feasibility by comparing the overvoltage value calculated by a traditional method adopting MATLAB/Simulink model simulation with the overvoltage fitting method provided by the method. And comparing with an overvoltage standard to check whether the overvoltage meets the requirement.
Example 2: the power frequency overvoltage calculation method applied to power restoration of the high-voltage transmission line of 220kV and 110kV grades is described in detail by combining specific examples. And (3) establishing an overvoltage simulation calculation model aiming at the power transmission line recovery scheme shown in FIG. 2. Four lines are arranged, and the model, the voltage grade and the length of the lines are shown in the following table 1.
TABLE 1 line parameters
| Line name | Model number | Length of | Voltage class |
| Line 1 | LGJ-300 | 100km | 110kV |
| Line 2 | LGJ-185 | 60km | 110kV |
| Line 3 | LGJ-120 | 50km | 110kV |
| Line 4 | LGJ-150 | 200km | 110kV |
Step 1: and establishing an overvoltage simulation model in an MATLAB environment, wherein the simulation model is a series connection path consisting of a generator, a transformer and a line. The simulation model respectively refers to power frequency overvoltage values of the types of 110 kV-level power transmission lines, such as LGJ-300, LGJ-185, LGJ-120 and LGJ-150, under different lengths.
Step 2: fitting is carried out through MATLAB software power frequency overvoltage, and a fitting function of the line power frequency overvoltage and the line length is obtained.
The line model is LGJ-300:
U＝1.327×10-7×l3+4.446×10-6×l2+0.03494×l+109.8 (2)
the line model is LGJ-185:
U＝1.027×10-7×l3+2.183×10-5×l2+0.03005×l+109.9 (3)
the line model is LGJ-120:
U＝7.525×10-8×l3+3.215×10-5×l2+0.02776×l+109.9 (4)
the line model is LGJ-150:
U＝9.035×10-8×l3+2.678×10-5×l2+0.02935×l+109.9 (5)
wherein l is the line length (unit: km), and U is the power frequency overvoltage value (unit: kV).
Step 3: and calculating the overvoltage value of the high-voltage transmission line recovery scheme through the fitting function.
Step3.1: firstly, the voltage value of the tail end of the line 1(LGJ-300) is calculated, namely the length 100km of the line is substituted into a fitting function formula (2) of the model to obtain the overvoltage value of the line 1 to be 113.47kV,
step3.2: the corresponding length is obtained according to a fitting function formula (3) of the voltage value obtained by the line 1 and substituted into the line 2(LGJ-185), namely the corresponding length is obtained by substituting U-113.47 kV into the formula (3) and l-106.4795 km;
step3.3: adding the actual length of the 2 nd line to the calculated line length, the length of the 2 nd line finally becomes: 106.4795+60 is 166.4795km, the length value is substituted into the fitting function formula (3) again to obtain the corresponding overvoltage value, and the overvoltage value corresponding to the line 2 is obtained to be 115.98 kV.
Step3.4: the corresponding length is obtained according to a fitting function formula (4) of the voltage value obtained by the line 2 and substituted into the line 3(LGJ-120), namely, the corresponding length is obtained by substituting U-115.98 kV into the formula (4) and l-171.4027 km;
step3.5: adding the actual length of the 3 rd line to the calculated line length, the length of the 3 rd line finally becomes: 171.4027+50 is 221.4027km, the length value is substituted into the fitting function formula (4) again to obtain the corresponding overvoltage value, and the overvoltage value corresponding to the line 3 is 118.44 kV.
Step3.6: the corresponding length is obtained according to a fitting function formula (5) of the voltage value obtained by the line 3 and the line 4(LGJ-120), namely the corresponding length is obtained by substituting U (118.44 kV) into the formula (5) and l (216.7316 km);
step3.7: adding the actual length of the line 4 to the calculated line length, the length of the 4 th line finally becomes: 216.7316+200 is 416.7316km, the length value is substituted into the fitting function formula (5) again to obtain the corresponding overvoltage value, and the overvoltage value corresponding to the line 4 is 133.32 kV.
The power frequency overvoltage values of the four lines are calculated through functions and are shown in table 1.
TABLE 1 Power frequency overvoltage value calculated by fitting function
Step 4: to verify the effectiveness of the method, for a specific example, the effectiveness of the method is verified by comparing the overvoltage values calculated by the conventional method using MATLAB/Simulink model simulation with the method using overvoltage fitting proposed herein. And comparing with an overvoltage standard to check whether the overvoltage meets the requirement. The results are shown in Table 2.
TABLE 2 segmentation simulation results
As can be seen from table 2, the results show that a value calculated as a function of the line length and the line frequency overvoltage is possible as an overvoltage criterion. The power frequency overvoltage calculated through MATLAB model simulation is not much different from the voltage value calculated by the fitting function because a certain margin is reserved for the calculated value due to various factors such as asynchronous closing, different closing angles and the like in practical application. Four sections of overvoltage of the model are within an allowable range, and line side power frequency overvoltage does not exceed 1.3p.u.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (3)
1. A power frequency overvoltage calculation method applied to power restoration of a high-voltage transmission line is characterized by comprising the following steps: the method comprises the following steps:
step 1: extracting generator data, transformer data and line data information contained in a path according to a specified power recovery path of the high-voltage transmission line; the high-voltage transmission line refers to a main transmission line with 220kV and 110kV grades;
step 2: establishing an overvoltage simulation model of a series path consisting of a generator, a transformer and a circuit in a simulation environment;
step 3: fitting is carried out through power frequency overvoltage, and the fitting function of the power frequency overvoltage and the line length of each type of line is obtained as follows: u is al3+bl2+cl+d；
U is the power frequency overvoltage value of the corresponding circuit; l is the line length; a. b, c and d are constants of the fitting function, and the values of the constants are related to the model number and the voltage grade of the line;
step 4: and calculating power frequency overvoltage according to the number of the lines:
if only one line exists, the length of the line is substituted into a fitting function corresponding to the type of the line, and the power frequency overvoltage value of the line is calculated;
if the number of lines is multiple: firstly, calculating a voltage value at the tail end of a first line, and substituting the length of the line into a fitting function corresponding to the model of the line to calculate a power frequency overvoltage value of the line; the calculation process of the power frequency overvoltage value of the rest line is as follows: and (3) bringing the power frequency voltage value at the tail end of the (x-1) th line into a fitting function of the corresponding model of the (x) th line, solving a length value corresponding to the converted length value, bringing the calculated line length and the line length of the (x) th line into the fitting function of the corresponding model of the (x) th line again, finally solving a power frequency overvoltage value of the (x) th line, finishing the calculation of the power frequency overvoltage if the line is the last line, and otherwise, continuing to adopt the calculation process of the power frequency overvoltage values of the rest lines to calculate the power frequency overvoltage until the last line calculates the power frequency overvoltage.
2. The power frequency overvoltage calculation method applied to power restoration of the high-voltage transmission line according to claim 1, wherein the power frequency overvoltage calculation method comprises the following steps: comparing the power frequency overvoltage value with an overvoltage standard, and verifying whether the overvoltage meets the requirement or not so as to judge to start a corresponding circuit; the overvoltage standard is as follows: in 220kV and 110kV systems, the line side power frequency overvoltage is not suitable to exceed the overvoltage standard by 1.3 times.
3. The power frequency overvoltage calculation method applied to power restoration of the high-voltage transmission line according to claim 1, wherein the power frequency overvoltage calculation method comprises the following steps: a synchronous generator model is simulated by a relatively simple three-phase voltage source module; the power transformer model is equivalent to the synthesis of an ideal transformer and an RT and LT impedance branch circuit because the excitation branch circuit is often ignored in an actual system; the power transmission line adopts a distributed parameter line model, and a small-loss Bergeron model of the power transmission line is established; the switch element module adopts a calculation switch model with a parallel leakage resistor and a parallel leakage capacitor and an oscilloscope module.
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