CN110632374B - Load calculation method for suppressing no-load long line overvoltage - Google Patents

Load calculation method for suppressing no-load long line overvoltage Download PDF

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CN110632374B
CN110632374B CN201910884193.4A CN201910884193A CN110632374B CN 110632374 B CN110632374 B CN 110632374B CN 201910884193 A CN201910884193 A CN 201910884193A CN 110632374 B CN110632374 B CN 110632374B
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overvoltage
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刘志坚
王雁红
余进
徐慧
晏永飞
周于尧
王一妃
余莎
李鹏程
赵浩益
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Kunming University of Science and Technology
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    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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    • G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
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Abstract

The invention discloses a load quantity calculation method for restraining overvoltage of a no-load long line, and belongs to the technical field of high-voltage power grids. Firstly, building a simulation model, and carrying out a high-voltage transmission line empty charge experiment; and obtaining the active load and the reactive load to be solved according to the terminal voltage increase value caused by the capacitance effect of the power transmission line. The invention can enable a dispatcher to calculate the load according to the desired power frequency overvoltage of the power transmission line, and the tail end of the line is provided with a proper amount of load for switching on, so that the amplitude of the operation overvoltage and the power frequency overvoltage are in a reasonable range, the fluctuation is small, the burr phenomenon is reduced, and the invention has higher reference value for formulation and verification of a backbone network frame black start scheme, identification of voltage waveform and prediction of overvoltage in the black start process.

Description

Load calculation method for suppressing no-load long line overvoltage
Technical Field
The invention relates to a load quantity calculation method for restraining overvoltage of a no-load long line, and belongs to the technical field of high-voltage power grids.
Background
When a large-area power failure occurs in an electric power system, not only can great economic loss be brought to a power failure area, but also more importantly, the life order of people cannot be guaranteed after the accident. According to the national power system safety and stability control technical guide rules, each power company combines a self actual system to make a proper recovery scheme (including a black start scheme), so that an effective guide criterion is provided for a large area after a power failure accident, the loss of the area is reduced, and power is supplied to an important load in time. 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 operation overvoltage at the tail end of the line and the power frequency overvoltage. In order to limit the power frequency overvoltage of a long line, a shunt reactor is generally adopted to compensate the capacitance current of the line in an ultra-high voltage system and an extra-high voltage system at present, so that the capacitance effect of the line is weakened. Meanwhile, various methods in the current stage are not suitable for energy supply systems mainly comprising small-capacity hydropower stations, and the overvoltage phenomenon can be effectively inhibited only by considering the load.
Disclosure of Invention
The invention provides a load quantity calculation method for suppressing overvoltage of a no-load long line, which is used for obtaining the load quantity and effectively suppressing the overvoltage of the no-load long line.
The technical scheme of the invention is as follows: a load calculation method for suppressing no-load long line overvoltage comprises the following steps:
s1, building a simulation model, and performing a high-voltage transmission line empty charge experiment; the model comprises the following main modules: the device comprises a three-phase constant voltage source, a three-phase transformer, a three-phase distribution parameter circuit, a three-phase voltage and current measuring module, a three-phase circuit breaker and an oscilloscope;
s2, calculating delta U of the air charging line:
ΔU＝(P2′R+Q2′X)/U1
in the formula: delta U is a terminal voltage increase value caused by the capacitance effect of the power transmission line; p2′＝0.5×G×U2 2，Q2′＝-0.5×B×U2 2，U1For line head end voltage, U2The voltage at the tail end of the line, G is the conductance of the line, B is the susceptance of the line, R is the resistance of the line, and X is the reactance of the line;
step3, calculate PL、QL：
Figure BDA0002206787690000021
In the formula: u shapexFor a predetermined line end voltage, PLFor active load to be solved, QLFor reactive loads to be solved, PL＝aQLAnd a is a coefficient.
The high voltage refers to 220kV and 110kV voltage levels.
R ═ R1l、X＝x1l、G＝g1l、B＝b1l; wherein r is1Resistance per unit length of line, x1Reactance per unit length of line, g1Conductance per unit length of line, b1Is the susceptance per unit length of the line.
The invention has the beneficial effects that: the invention can enable a dispatcher to calculate the load according to the desired power frequency overvoltage of the power transmission line, and the tail end of the line is provided with a proper amount of load for switching on, so that the amplitude of the operation overvoltage and the power frequency overvoltage are in a reasonable range, the fluctuation is small, the burr phenomenon is reduced, and the invention has higher reference value for formulation and verification of a backbone network frame black start scheme, identification of voltage waveform and prediction of overvoltage in the black start process.
Drawings
FIG. 1 is a simulation diagram of the transmission line terminal voltage under no load condition;
FIG. 2 is a simulation diagram of line terminal voltage after switching on with load;
FIG. 3 is the effect of an on-load on the over-voltage after closing;
FIG. 4 is a comparison of 110kV operating overvoltage;
FIG. 5 is a comparison of 110kV power frequency overvoltage;
FIG. 6 is a comparison of 220kV operating overvoltage;
FIG. 7 is a comparison of 220kV power frequency overvoltage;
FIG. 8 is a flow chart of the present invention.
Detailed Description
Example 1: as shown in fig. 1 to 8, a load calculation method for suppressing an over-voltage of a dead-length line includes the following steps:
s1, building a simulation model, and performing a high-voltage transmission line empty charge experiment; the model comprises the following main modules: the device comprises a three-phase constant voltage source, a three-phase transformer, a three-phase distribution parameter circuit, a three-phase voltage and current measuring module, a three-phase circuit breaker and an oscilloscope;
s2, calculating delta U of the air charging line:
ΔU＝(P2′R+Q2′X)/U1
in the formula: delta U is a terminal voltage increase value caused by the capacitance effect of the power transmission line; p2′＝0.5×G×U2 2，Q2′＝-0.5×B×U2 2，U1For line head end voltage, U2The voltage at the tail end of the line, G is the conductance of the line, B is the susceptance of the line, R is the resistance of the line, and X is the reactance of the line;
step3, calculate PL、QL：
Figure BDA0002206787690000031
In the formula: u shapexFor a predetermined line end voltage, PLFor active load to be solved, QLFor reactive loads to be solved, PL＝aQLAnd a is a coefficient.
Further, the high voltage finger may be set to a voltage level of 220kV, 110 kV.
Further, R may be provided1l、X＝x1l、G＝g1l、B＝b1l; wherein r is1Resistance per unit length of line, x1Reactance per unit length of line, g1Conductance per unit length of line, b1Is the susceptance per unit length of the line.
The obtained active load and reactive load are brought into a model, and the load can be verified to well inhibit the overvoltage amplitude when the power transmission line is switched on in a no-load mode.
Example 2: the load calculation method for suppressing the no-load long line overvoltage of the invention is described in detail by combining the specific examples:
A. modeling and simulation of power systems
And researching influence factors of line tail end power frequency overvoltage and operation overvoltage amplitude when the backbone net rack restores a power supply path. Then, model construction is carried out under MATLAB/Simulink software, and the simulation structure mainly comprises the following main modules: the device comprises a three-phase constant voltage source, a three-phase transformer, a three-phase distribution parameter circuit, a three-phase voltage and current measuring module, a three-phase circuit breaker and an oscilloscope. According to a modeling principle, a 220kV and 110kV voltage class line idle charge experiment is established for power frequency overvoltage, operation overvoltage and a plurality of main factors (line length and power supply capacity, asynchronous closing overvoltage and phase angle of power supply voltage during closing) influencing the overvoltage.
B. Overvoltage characteristic of transmission line
The method and the device aim at carrying out the air charging experiment on the line of each voltage class, and study the influence of light load closing and proper load input after air charging on the voltage amplitude at the tail end of the line. In a qualified black start scheme, the condition that operation overvoltage or power frequency overvoltage and voltage mutation is not allowed to occur during line recovery; for example, the simulation waveforms of a power transmission line with model number and length of LGJQ-400 and 250km under the voltage class of 220kV when the power transmission line is closed without load are shown in figure 1 (the abscissa is time and the ordinate is three-phase voltage). Under the condition, the amplitude of the operation overvoltage measured at the tail end of the line is 532.91kV, and is smaller than a limit value of 660 kV; the power frequency overvoltage amplitude is 322.72kV, which is larger than the limit value 308kV, if the line is selected as a recovery line, compensation measures must be taken to limit the power frequency overvoltage.
Calculating the required load amount to be P when the line with the line model number of LGJQ-400 is 250kmL＝0.4046MW、QL0.1618Mvar (line r of type LGJQ-400 as used herein)1＝0.07875(Ω/km)，x1＝0.405(Ω/km)，b1＝2.815*10-6(Ω/km)，g10 (since leakage is usually small, when designing a line, it has been checked whether the radius of the selected wire meets the requirement of not generating corona in clear weather, and therefore g is set10), a 2.5). Bring in PL、QLThe simulation result is shown in fig. 2, and after a proper amount of load is loaded, the operating overvoltage amplitude is 286.45kV, which is lower than the operating overvoltage amplitude of the closing without load by 246.46 kV. The power frequency overvoltage amplitude is 226.40kV, 96.32kV is reduced compared with the power frequency overvoltage amplitude without load closing, and the power frequency overvoltage amplitude is close to the voltage value of the head end of the power transmission line. Comparing fig. 1 and fig. 2, it can be seen that the voltage is reduced after the load is switched on, the waveform becomes more stable, and the burrs are obviously reduced.
Fig. 3 is different from fig. 2 in that the load is added at the beginning, but after the line is empty charged for 0.0s, the power frequency overvoltage at the tail end of the transmission line is 279.72kV, and after the proper load is put into the transmission line for 0.3 s (P)L＝0.4046MW、QL0.1618Mvar), the voltage was restored to 226.54 kV. It can be seen that the calculated load capacity enables the transmission line voltage value to be close to the rated range.
Simulation analysis is carried out under the voltage grades of 220kV and 110kV, the load amount of the line under different lengths is calculated based on the method provided by the application, and fig. 4 and 5 are overvoltage comparison simulation graphs obtained by respectively carrying out simulation on the transmission line with the model number of LGJQ-400 under the voltage grade of 110kV and between 400km and 900km in length.
As can be seen from fig. 4 (the abscissa is the line length, the ordinate is: Operating overvoltage with out load represents the Operating overvoltage without load, Operating overvoltage with preprpritation load represents the Operating overvoltage with proper load, Limit value represents the Limit value, Power frequency overvoltage with out load represents the Power frequency overvoltage without load, Rated voltage value represents the Rated value), without compensation measures, the Operating overvoltage increases with the increase of the line length, and after the line reaches about 800km, the Operating overvoltage value is higher than the Limit value (330 kV). After the load is loaded in a proper amount, the operation overvoltage value is stabilized between 150kV and 200kV, and the change trend of the operation overvoltage tends to be stable along with the increase of a line. Therefore, the load quantity calculated by the method can effectively inhibit the operation overvoltage during the empty charge.
It can be seen from fig. 5 that, in the absence of compensation measures, the power frequency overvoltage also increases with the increase of the length of the line, and after the line reaches about 600km, the power frequency overvoltage exceeds the limit value (154 kV). After the load is loaded in a proper amount, the operation overvoltage value is stabilized between 95kV and 115kV, and the change trend of the operation overvoltage tends to be stable along with the increase of a line. Therefore, the load calculated by the method can effectively inhibit the power frequency overvoltage during the empty charge.
As can be seen from fig. 6 and 7, at 220kV level, the load amount calculated by the method of the present application can still effectively limit the operating overvoltage and the power frequency overvoltage generated during the empty charging of the power transmission line.
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 load calculation method for suppressing an over-voltage of a no-load long line is characterized in that: the method comprises the following steps:
s1, building a simulation model, and performing a high-voltage transmission line empty charge experiment; the model comprises the following main modules: the device comprises a three-phase constant voltage source, a three-phase transformer, a three-phase distribution parameter circuit, a three-phase voltage and current measuring module, a three-phase circuit breaker and an oscilloscope;
s2, calculating delta U of the air charging line:
ΔU＝(P′2R+Q′2X)/U1
in the formula: delta U is a terminal voltage increase value caused by the capacitance effect of the power transmission line; p'2＝0.5×G×U2 2，Q′2＝-0.5×B×U2 2，U1For line head end voltage, U2The voltage at the tail end of the line, G is the conductance of the line, B is the susceptance of the line, R is the resistance of the line, and X is the reactance of the line;
step3, calculate PL、QL：
Figure FDA0003011363350000011
In the formula: u shapexFor a predetermined line end voltage, PLFor active load to be solved, QLFor reactive loads to be solved, PL＝aQLAnd a is a coefficient.
2. The load amount calculation method for suppressing an unloaded long line overvoltage according to claim 1, characterized in that: the high voltage refers to 220kV and 110kV voltage levels.
3. The load amount calculation method for suppressing an unloaded long line overvoltage according to claim 1, characterized in that: r ═ R1l、X＝x1l、G＝g1l、B＝b1l; wherein r is1Resistance per unit length of line, x1Reactance per unit length of line, g1Conductance per unit length of line, b1Is the susceptance per unit length of the line and l is the length of the line.
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