A method for evaluating three-phase unbalance degree of power transmission line based on multi-source data

Abstract

The present application relates to the technical field of transmission line monitoring and evaluation, and particularly relates to a transmission line three-phase imbalance degree evaluation method based on multi-source data, which obtains three-phase electrical deviation amount by comparing baseline with operation baseline, maps the deviation amount to spatial deviation vector broken line according to the spatial arrangement position of the conductor, calculates the ruggedness of the form to distinguish static structure type and dynamic disturbance type imbalance; for dynamic disturbance type, the spatial smoothing gradient law of air pressure field is used to cross verify the monitoring points along the line to screen effective temperature data, calculate the thermal deviation component and deduct it from the total deviation, and the residual deviation amount is analyzed again in the form of spatial broken line, which further distinguishes the dynamic disturbance type into thermal effect sag type and mechanical implicit structure damage type, and finally outputs differentiated operation and maintenance strategy according to the cause type. The present application realizes the fine classification and accurate identification of three-phase imbalance causes, and provides a scientific basis for differentiated operation and maintenance decision.

Description

Technical Field

[0001] This invention relates to the field of transmission line monitoring and evaluation technology, and in particular to a method for evaluating the three-phase imbalance of transmission lines based on multi-source data. Background Technology

[0002] Three-phase imbalance can lead to increased zero-sequence current, increased transformer losses and equipment overheating risk, and also cause grid voltage fluctuations, affecting the safe and stable operation of electrical equipment; in severe cases, it can also cause motor torque fluctuations, increased vibration, or even equipment damage.

[0003] Currently, the calculation and analysis of three-phase unbalance in overhead transmission lines is mainly based on the geometric and electrical parameters established during the line design phase. Designers use static parameters such as tower head dimensions, conductor arrangement, conductor type, and sag to calculate the impedance and admittance matrices of the line using the Carson formula or the complex penetration depth method, thereby deducing the line's unbalance. In engineering practice, lines identified as having significant unbalance during the design phase are typically optimized through methods such as conductor transposition or phase sequence adjustment.

[0004] However, the above method has the following technical drawbacks:

[0005] Firstly, existing calculation methods use "design parameters" as the sole calculation benchmark, assuming that the actual operating state of the line is consistent with the design state. However, in actual operation, changes in ambient temperature can cause changes in conductor sag, wind speed and sunshine can cause conductor swing and fluctuations in distance to the ground, and load changes can cause dynamic adjustments in the current distribution of each phase. These dynamic deviations generated during operation are superimposed on the static structural deviations that already exist in the design stage, making the measured unbalance a mixed signal. Existing technology can only provide the numerical value of the unbalance, and cannot distinguish whether the unbalance is due to the inherent structural asymmetry during tower erection or the environmental coupling disturbance during operation. Since the solutions for the two types of causes are completely different: the former requires line modification or phase sequence adjustment, while the latter can be addressed through dynamic compensation or load adjustment, the inability to distinguish the causes will directly lead to inaccurate operation and maintenance decisions.

[0006] Secondly, existing technologies address the impact of environmental factors on imbalance by directly reading meteorological monitoring data. However, meteorological monitoring points along transmission lines are affected by local microclimates, equipment aging, or obstructions from installation locations, and the data from some monitoring points may deviate from the actual physical field distribution of the region. Directly substituting these unverified temperature data into the imbalance correction model will lead to significant errors in the calculation of the thermally induced deviation component, and may even misjudge normal sag fluctuations caused by thermal effects as abnormal damage to the line's mechanical structure, thereby causing unnecessary power outages for maintenance.

[0007] Third, existing technologies lack the means to correlate electrical quantity deviations with mechanical quantity conditions. When mechanical structural damage occurs in the line, such as broken strands, loose fittings, or uneven icing, the electrical manifestation is also an increase in three-phase imbalance, which is very similar to the electrical characteristics caused by thermal sag changes. Existing technologies cannot separate independent evidence of structural damage from the appearance of electrical deviations, making it difficult to detect latent mechanical faults in a timely manner. Summary of the Invention

[0008] To address this, the present invention provides a method for assessing the three-phase imbalance of transmission lines based on multi-source data, thereby overcoming the problems in the prior art where the assessment of three-phase imbalance cannot distinguish the cause type, cannot verify the validity of multi-source sensor data, and cannot associate electrical deviations with mechanical damage.

[0009] To achieve the above objectives, the present invention provides a method for evaluating the three-phase imbalance of transmission lines based on multi-source data, comprising:

[0010] The three-phase theoretical electrical parameters of the transmission line during the design phase and the three-phase actual electrical parameters calculated based on the measured synchronous phasor data during operation are obtained respectively to determine the design baseline and the operation baseline.

[0011] The deviation of the actual electrical parameters of each phase line from the theoretical electrical parameters is calculated to obtain the three-phase deviation.

[0012] The three-phase deviations are mapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, and the three mapping points are connected in sequence in the coordinate system to generate a spatial deviation vector polygonal line.

[0013] Wherein, the horizontal axis represents the spatial arrangement of the conductors, and the vertical axis represents the deviation amplitude;

[0014] The morphological ruggedness of the spatial deviation vector polygon is calculated to characterize the degree of curvature of the polygon in the spatial arrangement direction;

[0015] The cause of the three-phase imbalance is determined based on the morphological ruggedness.

[0016] In response to the dynamic disturbance type of the cause, a secondary causal analysis is triggered to determine the cause type.

[0017] The types of causes include static structural types and dynamic disturbance types, and the dynamic disturbance types include thermal effect sag types and mechanical implicit structural damage types.

[0018] Determine the adjustment strategy based on the aforementioned cause type;

[0019] The secondary cause analysis includes calculating the air pressure deviation of each monitoring point based on the air pressure and temperature values ​​collected synchronously at several monitoring points along the transmission line, classifying the corresponding monitoring points according to the air pressure deviation, calculating the theoretical thermally induced deviation component and residual deviation based on the effective temperature values ​​collected from the effective monitoring points, and determining the cause type of three-phase imbalance a second time based on the residual deviation.

[0020] As a preferred technical solution for the three-phase unbalance assessment method of transmission lines based on multi-source data, the three-phase deviation is mapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, including:

[0021] Determine the arrangement order of each phase conductor on the crossarm of the tower and use the position number of each phase in the arrangement order as the horizontal axis coordinate value. The arrangement order includes a horizontal arrangement order or a vertical arrangement order.

[0022] The deviation of each phase conductor under the stated arrangement is obtained as the vertical axis coordinate value, and the deviation includes impedance deviation and admittance deviation;

[0023] Determine the coordinates of phases A, B, and C in a two-dimensional coordinate system;

[0024] Connect the coordinates of adjacent positions with straight line segments to form a vector polyline that is connected end to end.

[0025] As a preferred technical solution for the three-phase unbalance assessment method of transmission lines based on multi-source data, the calculation of the morphological ruggedness of the spatial deviation vector piecewise linear curve includes:

[0026] Determine the turning angle between each adjacent straight line segment on the spatial deviation vector polygonal line;

[0027] The total turning angle is determined by the sum of the absolute values ​​of the turning angles between all adjacent line segments.

[0028] The ratio of the total turning angle to the total span of the broken line in the spatial arrangement direction is determined as the morphological ruggedness.

[0029] The total span is the horizontal distance between the first and last points of the broken line.

[0030] As a preferred technical solution for the three-phase imbalance assessment method of transmission lines based on multi-source data, the cause type of three-phase imbalance is determined according to the morphological ruggedness, including:

[0031] In response to the condition that the morphological roughness is not greater than a preset roughness, the cause type of the three-phase imbalance is determined to be static structural type;

[0032] In response to the morphological roughness being greater than a preset roughness, the cause of the three-phase imbalance is determined to be dynamic disturbance type.

[0033] As a preferred technical solution for evaluating the three-phase unbalance of transmission lines based on multi-source data, the monitoring points are classified, including:

[0034] Acquire air pressure and temperature values ​​simultaneously collected from multiple monitoring points along the transmission line;

[0035] By combining the spatial arrangement and spacing of each monitoring point with the central value of the air pressure field in the area, a theoretical gradient distribution curve of air pressure value as a function of spatial location is constructed.

[0036] The measured air pressure values ​​at each monitoring point are compared with the corresponding theoretical air pressure values ​​in the theoretical gradient distribution curve to calculate the air pressure deviation at each monitoring point.

[0037] The monitoring points are classified according to the air pressure deviation, wherein:

[0038] In response to the air pressure deviation being greater than a preset air pressure deviation, the corresponding monitoring point is determined to be an invalid monitoring point.

[0039] In response to the air pressure deviation not being greater than the preset air pressure deviation, the corresponding monitoring point is determined as a valid monitoring point.

[0040] The temperature values ​​collected from the invalid monitoring points are discarded, and the temperature values ​​collected from the valid monitoring points are recorded as valid temperature values.

[0041] As a preferred technical solution for evaluating the three-phase unbalance of transmission lines based on multi-source data, a theoretical gradient distribution curve of air pressure values ​​varying with spatial location is constructed, including:

[0042] Determine the spatial distance of each monitoring point relative to the center of the pressure field;

[0043] Obtain the center value of the pressure field and the edge value of the pressure field of the weather system;

[0044] Using spatial distance and air pressure values ​​as the horizontal and vertical axes respectively, and based on the center value of the air pressure field, the edge value of the air pressure field, and the spatial distance of each monitoring point, a theoretical gradient curve of air pressure changing with spatial distance is fitted.

[0045] The air pressure values ​​at each position on the theoretical gradient curve satisfy the spatial smooth distribution law of atmospheric physics, and the weather system includes a passing low-pressure trough or a high-pressure ridge.

[0046] As a preferred technical solution for evaluating the three-phase unbalance of transmission lines based on multi-source data, the theoretical thermally induced deviation component and residual deviation are calculated based on the effective temperature values ​​collected from effective monitoring points, including:

[0047] The effective average temperature is determined by calculating the average of the effective temperature values ​​collected at each effective monitoring point within the same time window.

[0048] The effective average temperature is substituted into the conductor sag-temperature physical model to calculate the theoretical sag change of each phase conductor.

[0049] The change in distance to ground of each phase conductor is calculated based on the theoretical sag change of each phase conductor.

[0050] The theoretical admittance change of each phase conductor is calculated based on the change in distance to ground of each phase conductor, and the theoretical admittance changes of phase A, phase B, and phase C are respectively determined as the theoretical thermally induced deviation component of phase A, the theoretical thermally induced deviation component of phase B, and the theoretical thermally induced deviation component of phase C.

[0051] The residual deviations of phase A, phase B, and phase C are determined based on the differences between the deviations of phase A, phase B, and phase C and the theoretical thermally induced deviation components of the corresponding phases.

[0052] As a preferred technical solution for the three-phase imbalance assessment method of transmission lines based on multi-source data, the cause type of three-phase imbalance is determined twice based on the residual deviation, including:

[0053] The residual deviations of phase A, phase B, and phase C are remapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the crossarm of the tower, and the three mapping points are connected in sequence to generate a residual space deviation polygonal line.

[0054] Calculate the residual shape ruggedness of the residual spatial deviation polygonal line;

[0055] The cause type of three-phase imbalance is determined twice based on the roughness of the residual shape.

[0056] As a preferred technical solution for the three-phase imbalance assessment method of transmission lines based on multi-source data, the cause type of three-phase imbalance is determined secondaryly based on the residual morphology ruggedness, including:

[0057] In response to the residual morphology roughness not being greater than the preset residual roughness, the cause type of the three-phase imbalance is determined to be thermal effect sag type.

[0058] In response to the residual morphology roughness being greater than a preset residual roughness, the maximum residual deviation among the residual deviations of phase A, phase B, and phase C is determined, the target phase corresponding to the maximum residual deviation is determined, and the cause type of the three-phase imbalance is determined for the second time to be the mechanical hidden structural damage type of the target phase.

[0059] As a preferred technical solution for the three-phase imbalance assessment method of transmission lines based on multi-source data, the adjustment strategy is determined according to the cause type, including:

[0060] In response to the fact that the cause type is static structural type, the subsequent analysis process is terminated, and the static structural type label is directly output as the evaluation conclusion.

[0061] In response to the cause type being thermal effect sag type, a reactive power compensation adjustment suggestion is output to the operation and maintenance end;

[0062] In response to the cause being classified as mechanical latent structural damage, an inspection alarm for the target phase is output to the maintenance department.

[0063] Compared with existing technologies, the beneficial effects of this invention are as follows: by constructing a comparison framework between design data and operational data, the deviation of three-phase electrical parameters is mapped into a spatial deviation vector broken line according to the actual physical arrangement of the conductors on the tower crossarm. Furthermore, the geometric characteristic parameter of morphological ruggedness is introduced to characterize the severity of the bending changes in the broken line, thus achieving a primary classification of the causes of three-phase imbalance. This distinguishes between static structural imbalance caused by inherent structural asymmetry during tower erection and dynamic disturbance imbalance caused by external factors during operation. Based on this, for dynamic disturbance imbalance, the residual deviation is obtained by subtracting the thermally induced deviation component. Then, using spatial broken line morphology analysis as the criterion, dynamic disturbance imbalance is further subdivided into thermal effect sag imbalance and mechanically implicit structural damage imbalance. Therefore, this invention refines the causes of three-phase imbalance from a vague category into three categories with clear physical orientations.

[0064] In particular, this invention introduces the inherent spatial smooth distribution law of atmospheric pressure field into the field of three-phase imbalance assessment of transmission lines. It uses the inviolable physical law that air pressure changes continuously and smoothly in space as an objective benchmark to construct a theoretical gradient distribution curve of air pressure changing with spatial location. The measured air pressure values ​​at each monitoring point are compared with the theoretical values, and invalid monitoring points and their temperature data that deviate from the physical law are eliminated, retaining only the valid temperature data that conforms to the spatial distribution of atmospheric physics for subsequent calculations. This cross-validation mechanism does not rely on artificially set sensor reliability models, but is directly rooted in the inherent laws of physics, ensuring the quality of multi-source data fusion and the objectivity of assessment conclusions from the source.

[0065] In particular, this invention outputs differentiated operation and maintenance strategies based on the finally determined cause type: for static structural types, the analysis is terminated directly and the conclusion is output, avoiding waste of computing power; for thermal effect sag types, since this type of imbalance is reversible with temperature changes, no power outage maintenance is required, and only reactive power compensation adjustment suggestions are output to achieve effective suppression; for mechanical hidden structural damage types, since this type involves potential safety hazards such as broken conductor strands and loose hardware, an immediate response is required, and residual analysis is used to identify abnormal target phases and output targeted inspection alarms to guide operation and maintenance personnel to accurately locate and investigate; these three types of strategies realize the process from discovering imbalance to locating the cause of imbalance and then taking targeted measures, avoiding blind maintenance and over-maintenance, and greatly improving the efficiency and pertinence of operation and maintenance decisions. Attached Figure Description

[0066] Figure 1 This is a flowchart of a method for evaluating the three-phase imbalance of transmission lines based on multi-source data, according to an embodiment of the present invention. Detailed Implementation

[0067] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0068] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0069] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0070] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0071] In actual transmission line operation monitoring, a long-distance overhead line with excessive three-phase imbalance as indicated by an online monitoring system may be affected by structural asymmetry pre-existing in the design phase, increased sag due to high temperatures, or hidden mechanical damage such as broken strands in a certain phase conductor. The three causes of imbalance are highly similar in electrical manifestation (i.e., all reflect an increase in negative or zero-sequence components). However, the solutions for the three are quite different: structural problems require line modification or phase sequence adjustment, thermal effect problems only require dynamic reactive power compensation, and mechanical damage requires immediate power outage inspection and troubleshooting.

[0072] To address this phenomenon, this invention provides a method for assessing the three-phase imbalance of transmission lines based on multi-source data. It establishes a deviation perception foundation through design and operation of dual-baseline comparison. Firstly, it classifies the three-phase deviation by mapping the actual physical arrangement of conductors on the tower crossarms into a spatial deviation vector broken line and calculating its morphological ruggedness, thus distinguishing between static structural imbalance and dynamic disturbance imbalance. For dynamic disturbance imbalance, it further utilizes the inherent spatial smoothing gradient law of the atmospheric pressure field to perform physical cross-validation of monitoring points along the line to filter effective temperature data. Based on the effective temperature values, it calculates the thermally induced deviation component and deducts it from the total deviation. Finally, it performs spatial broken line morphology analysis on the residual deviation again to differentiate between thermally induced sag imbalance and mechanically hidden structural damage imbalance, thus identifying imbalance, locating its causes, and outputting differentiated operation and maintenance suggestions.

[0073] Please see Figure 1 The diagram shows a flowchart of a method for evaluating the three-phase imbalance of transmission lines based on multi-source data, according to an embodiment of the present invention. This embodiment of the present invention provides a method for evaluating the three-phase imbalance of transmission lines based on multi-source data, comprising:

[0074] Step S1: Obtain the three-phase theoretical electrical parameters of the transmission line during the design phase and the three-phase actual electrical parameters calculated based on the measured synchronous phasor data during operation, in order to determine the design baseline and the operation baseline.

[0075] In implementation, the three-phase theoretical electrical parameters of the transmission line during the design phase are first obtained as the design baseline. The three-phase theoretical electrical parameters include the theoretical impedance and theoretical admittance values ​​of each phase of the line, which are calculated using the Carson formula method, the complex penetration depth method, or the manual formula method. In addition, PMU synchronous phasor measurement devices are installed along the transmission line to collect the amplitude and phase of each phase voltage and the amplitude and phase of each phase current under operating conditions.

[0076] Understandably, the PMU (Phase Measurement Unit) is installed in the substations at the beginning and end of the transmission line. It has a global positioning system synchronization function, a sampling frequency of not less than 100Hz, and an angle measurement accuracy of not less than 0.01 degrees, in order to capture the dynamic changes in the line's operating status. Under normal power system operation, the PMU continuously collects the amplitude and phase of each phase voltage and the amplitude and phase of each phase current.

[0077] In implementation, based on single-ended or double-ended electrical quantities, the series impedance matrix and parallel admittance matrix of the transmission line are calculated by inversion using a distributed parameter model or a lumped parameter model. For short lines with a length not exceeding 100 kilometers, a lumped parameter model can be used. Equivalent circuit model; for long lines exceeding 100 kilometers in length, a distributed parameter model should be used to account for the distribution characteristics of line parameters along the line;

[0078] The specific methods for inversion calculation include: obtaining the voltage phasor Us and current phasor Is at the beginning of the line, and the voltage phasor Ur and current phasor Ir at the end of the line (which can be obtained synchronously from PMU data at both ends of the line, or iteratively derived from single-end PMU data combined with line parameters); based on the transmission line equations:

[0079] ,

[0080] Where A, B, C, and D are the transmission parameter matrices of the line, for a π-type equivalent circuit, B=Z Where Z is the series impedance matrix and Y is the parallel admittance matrix; by substituting the measured Us, Is, Ur, and Ir of the PMU into the above equation, the Z and Y matrices can be solved inversely, and then the actual impedance and actual admittance values ​​of each phase of the line can be obtained; it can be understood that the actual electrical parameters obtained by inversion calculation reflect the true electrical characteristics of the line under the current operating state, including both the structural factors inherent in the design stage and the influence of environmental factors and mechanical state changes during operation;

[0081] In practice, based on the collected synchronous phasor data, the actual impedance and actual admittance values ​​of each phase line are calculated using the least squares method or Kalman filtering method, which serve as the operating baseline.

[0082] Step S2: Calculate the deviation of the actual electrical parameters of each phase line from the theoretical electrical parameters to obtain the three-phase deviation.

[0083] In implementation, the difference between the actual electrical parameters and the theoretical electrical parameters of each phase line is determined as the deviation of that phase. It should be understood that the deviation can be the impedance deviation or the admittance deviation. The impedance deviation reflects the difference in current transmission capacity of each phase of the line, while the admittance deviation reflects the difference in capacitance between each phase to ground and between phases. Preferably, the impedance deviation is used.

[0084] Step S3: Map the three-phase deviations to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, and connect the three mapping points in the coordinate system to generate a spatial deviation vector broken line.

[0085] In implementation, the arrangement order of each phase conductor on the crossarm of the tower is determined. This arrangement order can be horizontal, vertical, or triangular. The most common arrangement is horizontal, where the left, middle, and right positions of the conductors on the crossarm correspond to phases A, B, and C, respectively, and position numbers 1, 2, and 3 are used as the horizontal axis coordinates. Then, the impedance deviation of each phase conductor under this arrangement order is obtained as the vertical axis coordinate. Thus, the coordinate points corresponding to phases A, B, and C are determined in the two-dimensional coordinate system. Finally, straight line segments are used to connect the coordinate points of adjacent arrangement positions in sequence to form a vector broken line with the beginning and end connected.

[0086] It should be understood that the spatial deviation vector broken line is not a time series curve, but a spatial sequence broken line constructed based on the arrangement of the three-phase conductors in physical space. The horizontal axis represents the spatial positional relationship of the conductors on the tower rather than the time dimension, and the vertical axis represents the degree to which the electrical parameters of each phase deviate from the design value. Therefore, the geometric shape of the spatial deviation vector broken line directly reflects the distribution law of the three-phase deviation in the spatial physical arrangement.

[0087] Step S4: After generating the spatial deviation vector polygonal line, calculate the morphological ruggedness of the polygonal line. The morphological ruggedness characterizes the degree of curvature of the polygonal line in the spatial arrangement direction.

[0088] Specifically, calculating the morphological ruggedness of the spatial deviation vector polygon includes:

[0089] Step S41: Determine the turning angle between adjacent straight line segments on the spatial deviation vector polygonal line; in practice, for each intermediate coordinate point on the polygonal line excluding the first and last points, calculate the turning angle between the straight line segment preceding and following that point. (i is the i-th intermediate coordinate point, (where n is the number of intermediate coordinate points) The size of the included angle reflects the degree of curvature of the broken line at that point;

[0090] Step S42: The sum of the absolute values ​​of the turning angles between all adjacent line segments is determined as the total turning angle; it can be understood that the total turning angle... ;

[0091] Step S43: The ratio of the total turning angle to the total span of the broken line in the spatial arrangement direction is determined as the morphological ruggedness; wherein, the total span is the horizontal axis distance between the first and last points of the broken line;

[0092] Understandably, if the three-phase deviation changes linearly or nearly linearly along the spatial arrangement of the conductor (e.g., increasing or decreasing uniformly from left to right), the broken line tends to be straight or has a monotonous slope shape, with small turning angles between adjacent segments and low ruggedness. This indicates that the distribution of the three-phase deviation has an orderly spatial pattern, often caused by inherent structural asymmetry during line construction. Conversely, if the three-phase deviation fluctuates drastically and disorderly along the spatial arrangement of the conductor (e.g., the deviation of the middle phase is abnormally large, the deviations of the two side phases are abnormally small, or the three-phase deviation fluctuates alternately), the broken line exhibits a drastically distorted shape, with large turning angles between adjacent segments and high ruggedness. This disordered shape indicates that the three-phase deviation does not originate from fixed structural factors, but is affected by some dynamic disturbance that changes with external conditions.

[0093] Step S5, determining the cause type of three-phase imbalance based on the morphological ruggedness, including:

[0094] If the morphological roughness is not greater than the preset roughness, it indicates that the spatial deviation vector line is relatively smooth and the distribution of the three-phase deviation is spatially ordered. Therefore, the cause of the three-phase imbalance is determined to be static structural type. It should be understood that static structural imbalance originates from fixed structural factors that exist in the line design stage, including inconsistent electromagnetic environments of each phase due to incomplete or non-complete transposition of the line, asymmetry of three-phase ground parameters due to unequal heights of the three-phase crossarms of the towers, and differences in the three-phase coupling coefficients due to the mixed arrangement of triangular and horizontal arrangements. Therefore, static structural three-phase imbalance has long-term stability and does not change significantly with short-term changes in external environmental conditions. Therefore, when it is determined to be static structural type, no further analysis process is required. The static structural type label can be directly output as the evaluation conclusion, and the operation and maintenance personnel can arrange long-term management measures such as line modification or phase sequence optimization accordingly.

[0095] In response to the morphological ruggedness being greater than the preset ruggedness, it indicates that the spatial deviation vector broken line is significantly distorted and the distribution of the three-phase deviation lacks an orderly spatial pattern, which means that there is some dynamic factor disturbing the balance of the three-phase parameters. Therefore, the cause of the three-phase imbalance is determined to be dynamic disturbance type.

[0096] In practice, the preset ruggedness is determined based on the voltage level of the line, the tower type and the conductor arrangement. It is understood that the preset ruggedness is determined by statistically analyzing historical data of multiple lines with known causes or by simulation calculation. In one implementation, (1) for horizontally arranged double-circuit lines with voltage levels of 220kV and above, the preset ruggedness ranges from 0.3 to 0.6; (2) for single-circuit lines, the preset ruggedness ranges from 0.2 to 0.4.

[0097] Step S6: In response to the cause type being dynamic disturbance, a secondary cause analysis is triggered to determine the cause type. It should be understood that dynamic disturbance imbalance is a temporary or evolving imbalance caused by external environmental factors or changes in line status, and it is necessary to further locate the specific causes in order to formulate targeted operation and maintenance strategies.

[0098] The types of causes include static structural types and dynamic disturbance types, and the dynamic disturbance types include thermal effect sag types and mechanical latent structural damage types.

[0099] Specifically, the secondary causal analysis includes:

[0100] Step A1: Validate the air pressure data of each monitoring point along the transmission line by utilizing the inherent spatial smooth distribution law of the atmospheric pressure field, and classify the monitoring points accordingly.

[0101] Specifically, the following steps are included:

[0102] Step A11: Obtain air pressure and temperature values ​​synchronously collected from multiple monitoring points along the transmission line. In practice, the monitoring points are usually micro-meteorological monitoring devices deployed along the transmission line towers. The distance between each monitoring point is usually 3km to 10km. Each monitoring point synchronously collects meteorological parameters such as air pressure, temperature, and humidity within the same time window to ensure the spatiotemporal consistency of the data.

[0103] Step A12: Combining the spatial arrangement and spacing of each monitoring point with the center value of the air pressure field in the area, construct a theoretical gradient distribution curve of air pressure value as a function of spatial location;

[0104] Specifically, the spatial distribution sequence of each monitoring point is determined based on their spatial arrangement and spacing. At the same time, the center value and edge value of the pressure field of the weather system in the area where each monitoring point is located are determined. With spatial distance as the horizontal axis and pressure value as the vertical axis, a theoretical gradient curve of pressure variation with spatial distance is fitted based on the center value, edge value, and spatial distance of each monitoring point relative to the center of the pressure field. The pressure values ​​at each position on the theoretical gradient curve satisfy the spatial smooth distribution law of atmospheric physics, that is, the change of pressure in space is continuous and smooth, without abrupt changes or local drastic fluctuations.

[0105] During implementation, weather system information is obtained from the meteorological analysis reports of the regional meteorological bureau, or it can be automatically identified by the meteorological monitoring network deployed along the route. It should be understood that common related weather systems include passing low-pressure troughs and high-pressure ridges. In the scenario of a passing low-pressure trough, the air pressure gradually decreases from both sides of the trough line towards the center, while in the scenario of a high-pressure ridge, the air pressure gradually decreases from the ridge line towards both sides.

[0106] Step A13: Compare the measured air pressure values ​​at each monitoring point with the corresponding theoretical air pressure values ​​in the theoretical gradient distribution curve to calculate the air pressure deviation at each monitoring point.

[0107] Step A14: Classify the corresponding monitoring points according to the air pressure deviation, wherein:

[0108] If the pressure deviation is greater than the preset pressure deviation, it indicates that the measured pressure at the monitoring point deviates significantly from the theoretical gradient curve, which means that there is an anomaly in the pressure sensor data at the monitoring point. The causes of this anomaly may include sensor calibration failure, the installation location being affected by local microclimate (such as wind field distortion caused by proximity to buildings or mountains), and measurement drift caused by equipment aging. Therefore, the corresponding monitoring point is determined to be an invalid monitoring point, and the temperature value collected synchronously is judged to be an unreliable temperature value and is removed in subsequent calculations.

[0109] In response to the fact that the pressure deviation is not greater than the preset pressure deviation, that is, the measured pressure at the monitoring point basically matches the theoretical gradient curve, the corresponding monitoring point is determined as a valid monitoring point, and the temperature value collected synchronously is determined as a valid temperature value and retained for subsequent calculation of the thermal deviation component.

[0110] In practice, the preset air pressure deviation is based on the maximum permissible error of the air pressure sensor (not exceeding...). Furthermore, the normal fluctuation range of atmospheric pressure in diurnal variation (1hPa to 2.5hPa in mid-latitude regions) is comprehensively determined, usually 1.0hPa to 1.5hPa, to avoid misjudging normal weather system pressure fluctuations as sensor anomalies;

[0111] Step A15: Remove the temperature values ​​collected from the invalid monitoring points and record the temperature values ​​collected from the valid monitoring points as valid temperature values;

[0112] Understandably, by using the inherent physical laws of the atmospheric pressure field to measure and verify the reliability of data from various sensors, this cross-validation does not rely on artificially set sensor reliability models, but is directly based on inviolable physical laws. It has a high degree of objectivity and robustness. Even if multiple monitoring points show anomalies at the same time, as long as they deviate from the theoretical gradient curve, they can be accurately identified and isolated.

[0113] Step A2, based on the effective temperature values ​​collected from the effective monitoring points, calculate the theoretical thermally induced deviation component and the residual deviation, including:

[0114] Step A21: Calculate the average of the effective temperature values ​​collected by each effective monitoring point within the same time window to determine the effective average temperature Tavg;

[0115] Step A22: Substitute the effective average temperature into the conductor sag-temperature physical model to calculate the theoretical sag change of each phase conductor.

[0116] In practice, the mathematical expression of the conductor sag-temperature physical model is as follows: In the formula, Let fi be the change in sag of the i-th phase conductor, and f0 be the initial sag at the design reference temperature. Tref is the linear thermal expansion coefficient of the conductor, and Tref is the design reference temperature (usually taken as 20℃ or 25℃).

[0117] It should be understood that the actual sag changes of different phase conductors may differ due to their different arrangement positions on the crossarm and different conditions of sunlight exposure and heat dissipation. Therefore, it is necessary to calculate the theoretical sag changes of each phase separately.

[0118] Step A23: Calculate the change in distance to ground of each phase conductor based on the theoretical sag change of each phase conductor. It can be understood that an increase in sag leads to a decrease in distance to ground, and a decrease in sag leads to an increase in distance to ground. That is, the change in distance to ground is negatively correlated with the change in sag. Usually, the change in distance to ground is the opposite of the change in sag.

[0119] Step A24: Based on the change in the distance to ground of each phase conductor, calculate the change in the capacitance to ground of each phase conductor (it should be understood that the capacitance to ground of the conductor is inversely proportional to the distance to ground; when the distance to ground decreases, the capacitance to ground increases, and when the distance to ground increases, the capacitance to ground decreases), and convert the change in capacitance to ground into the change in admittance (i.e., the theoretical thermally induced deviation component of each phase conductor). The theoretical admittance changes corresponding to phases A, B, and C are respectively determined as the theoretical thermally induced deviation components of phase A, phase B, and phase C.

[0120] Step A25: Determine the residual deviation of phase A, phase B, and phase C respectively based on the difference between the deviation of phase A, phase B, and phase C and the theoretical thermally induced deviation component of the corresponding phase.

[0121] It should be understood that the residual deviation amount = deviation amount - theoretical calorific value deviation component. The residual deviation amount represents the remaining deviation component that cannot be explained after excluding the inherent structural deviation and thermal effect deviation of the design. This remaining component represents that there is some non-structural, non-thermal abnormal factor in the line, which is independently causing the electrical parameters of one or several phases to deviate.

[0122] Step A3, determining the cause type of three-phase imbalance a second time based on the residual deviation, includes:

[0123] Step A31: Remap the residual deviations of phase A, phase B, and phase C to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, and connect the three mapping points in sequence to generate a residual spatial deviation polygonal line. It can be understood that the construction method of the residual spatial deviation polygonal line is the same as that of the original spatial deviation vector polygonal line, with the horizontal axis representing the spatial arrangement of the conductor and the vertical axis representing the residual deviation amplitude.

[0124] Step A32: Calculate the residual shape ruggedness of the residual spatial deviation polygonal line; it is understood that the calculation method of residual shape ruggedness is the same as the calculation method of shape ruggedness, so it will not be described again.

[0125] Step A33: Determine the cause type of three-phase imbalance a second time based on the residual morphology roughness, wherein:

[0126] If the residual morphology roughness is no greater than the preset residual roughness, it indicates that after deducting the thermally induced deviation component, the residual line recovers its smoothness, and the three-phase residual deviation is spatially ordered. This means that the thermally induced deviation component can explain most of the dynamic distortion components in the original deviation line, and the disturbance in the original deviation is mainly caused by the sag change caused by temperature changes. At this point, the final cause of the three-phase imbalance is determined to be thermally induced sag imbalance. Thermally induced sag imbalance is a temporary parameter shift caused by changes in ambient temperature, which is reversible. When the ambient temperature returns to the normal range, the imbalance will automatically recover. Therefore, for this type of imbalance, the maintenance department does not need to arrange line outages for maintenance. It only needs to adjust the output strategy of the reactive power compensation device or adjust the series compensation degree of the line to suppress the increase of imbalance at the electrical level.

[0127] If the residual morphology roughness is greater than the preset residual roughness, it indicates that even after deducting the thermally induced deviation component, the residual line still shows significant distortion, and there is at least one phase of residual deviation that cannot be explained by thermal effects. At this time, it is necessary to further determine the maximum residual deviation among the residual deviation of phase A, phase B, and phase C, and determine the target phase corresponding to the maximum residual deviation, and determine that the final cause of the three-phase imbalance is the mechanical hidden structural damage type imbalance of the target phase.

[0128] Understandably, mechanical latent structural damage-type imbalance indicates that the target phase conductor or connecting hardware has undergone some non-thermal mechanical structural change, leading to a continuous shift in the electrical parameters (especially impedance) of that phase. Common mechanical latent structural damages include: conductor strand breakage (partial conductor strand breakage leads to a reduction in effective conductive cross-section and an increase in resistance), loose conductor joints (increased contact resistance), wear or corrosion of hardware leading to changes in connection impedance, insulator string tilting leading to conductor deviation from the design position, and uneven conductor icing leading to abnormal tension distribution. These damages often do not show obvious macroscopic signs in the early stages, but this method can reverse-locate the target phase with abnormalities from the residual electrical deviation, achieving early detection of latent damage.

[0129] In implementation, the preset residual roughness is determined by comprehensively considering the noise floor (0.05–0.10) generated by the propagation of PMU measurement error to impedance deviation inversion results, the residual roughness introduced by the calibration error of the physical model parameters of the thermally induced deviation component (0.05–0.08), and the additional roughness (0.15–0.25) generated by minor mechanical damage (such as 5%–10% conductor strand breakage). Typically, its value ranges from 0.15 to 0.35. In one implementation, the preset residual roughness is 0.15–0.20 for a 110kV single-circuit horizontally arranged line, the preset residual roughness is the middle value of 0.25–0.30 for a 220kV double-circuit line on the same tower, and the preset residual roughness is the upper limit of 0.30–0.35 for 500kV and above or multi-circuit lines on the same tower.

[0130] Step S7, determining the adjustment strategy based on the cause type, including:

[0131] In response to the fact that the cause type is static structural type, the subsequent analysis process is terminated, and the static structural type label is directly output as the evaluation conclusion.

[0132] In response to the cause being thermal sag, a reactive power compensation adjustment suggestion is output to the operation and maintenance end to adjust the output capacity of the static var compensator or parallel capacitor bank to compensate for the line parameter deviation caused by sag at the electrical level. At the same time, a temperature monitoring prompt is issued and it is suggested that operation and maintenance personnel continuously monitor the trend of ambient temperature change and start the compensation strategy in advance before the high temperature period.

[0133] In response to the cause being classified as mechanically latent structural damage, an inspection alarm for the target phase is output to the maintenance department. The inspection alarm includes the phase identifier and line location information of the target phase, guiding inspection personnel to conduct targeted and detailed inspections of the conductors, fittings, clamps, and insulator strings of the target phase. It also provides inspection priority suggestions, namely, to inspect items in the order of probability of strand breakage, probability of fitting looseness, and probability of icing, thereby improving inspection efficiency. In practice, the residual deviation value and the degree of deviation of this value from the normal fluctuation range serve as a quantitative reference for inspection personnel to judge the severity of the damage.

[0134] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the three-phase imbalance of transmission lines based on multi-source data, characterized in that, include: The three-phase theoretical electrical parameters of the transmission line during the design phase and the three-phase actual electrical parameters calculated based on the measured synchronous phasor data during operation are obtained respectively to determine the design baseline and the operation baseline. The deviation of the actual electrical parameters of each phase line from the theoretical electrical parameters is calculated to obtain the three-phase deviation. The three-phase deviations are mapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, and the three mapping points are connected in sequence in the coordinate system to generate a spatial deviation vector polygonal line. Wherein, the horizontal axis represents the spatial arrangement of the conductors, and the vertical axis represents the deviation amplitude; The morphological ruggedness of the spatial deviation vector polygon is calculated to characterize the degree of curvature of the polygon in the spatial arrangement direction; The cause of the three-phase imbalance is determined based on the morphological ruggedness. In response to the dynamic disturbance type of the cause, a secondary causal analysis is triggered to determine the cause type. The types of causes include static structural types and dynamic disturbance types, and the dynamic disturbance types include thermal effect sag types and mechanical implicit structural damage types. Determine the adjustment strategy based on the aforementioned cause type; The secondary cause analysis includes calculating the air pressure deviation of each monitoring point based on the air pressure and temperature values ​​collected synchronously at several monitoring points along the transmission line, classifying the corresponding monitoring points according to the air pressure deviation, calculating the theoretical thermally induced deviation component and residual deviation based on the effective temperature values ​​collected from the effective monitoring points, and determining the cause type of three-phase imbalance a second time based on the residual deviation.

2. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 1, characterized in that, The three-phase deviation is mapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the tower crossarm, including: Determine the arrangement order of each phase conductor on the crossarm of the tower and use the position number of each phase in the arrangement order as the horizontal axis coordinate value. The arrangement order includes a horizontal arrangement order or a vertical arrangement order. The deviation of each phase conductor under the stated arrangement is obtained as the vertical axis coordinate value, and the deviation includes impedance deviation and admittance deviation; Determine the coordinates of phases A, B, and C in a two-dimensional coordinate system; Connect the coordinates of adjacent positions with straight line segments to form a vector polyline that is connected end to end.

3. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 1, characterized in that, Calculating the morphological ruggedness of the spatial deviation vector polygon includes: Determine the turning angle between each adjacent straight line segment on the spatial deviation vector polygonal line; The total turning angle is determined by the sum of the absolute values ​​of the turning angles between all adjacent line segments. The ratio of the total turning angle to the total span of the broken line in the spatial arrangement direction is determined as the morphological ruggedness. The total span is the horizontal distance between the first and last points of the broken line.

4. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 3, characterized in that, The cause of the three-phase imbalance is determined based on the morphological ruggedness, including: In response to the condition that the morphological roughness is not greater than a preset roughness, the cause type of the three-phase imbalance is determined to be static structural type; In response to the morphological roughness being greater than a preset roughness, the cause of the three-phase imbalance is determined to be dynamic disturbance type.

5. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 1, characterized in that, The monitoring points are categorized as follows: Acquire air pressure and temperature values ​​simultaneously collected from multiple monitoring points along the transmission line; By combining the spatial arrangement and spacing of each monitoring point with the central value of the air pressure field in the area, a theoretical gradient distribution curve of air pressure value as a function of spatial location is constructed. The measured air pressure values ​​at each monitoring point are compared with the corresponding theoretical air pressure values ​​in the theoretical gradient distribution curve to calculate the air pressure deviation at each monitoring point. The monitoring points are classified according to the air pressure deviation, wherein: In response to the air pressure deviation being greater than a preset air pressure deviation, the corresponding monitoring point is determined to be an invalid monitoring point. In response to the air pressure deviation not being greater than the preset air pressure deviation, the corresponding monitoring point is determined as a valid monitoring point. The temperature values ​​collected from the invalid monitoring points are discarded, and the temperature values ​​collected from the valid monitoring points are recorded as valid temperature values.

6. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 5, characterized in that, Construct a theoretical gradient distribution curve of air pressure values ​​as a function of spatial location, including: Determine the spatial distance of each monitoring point relative to the center of the pressure field; Obtain the center value of the pressure field and the edge value of the pressure field of the weather system; Using spatial distance and air pressure values ​​as the horizontal and vertical axes respectively, and based on the center value of the air pressure field, the edge value of the air pressure field, and the spatial distance of each monitoring point, a theoretical gradient curve of air pressure changing with spatial distance is fitted. The air pressure values ​​at each position on the theoretical gradient curve satisfy the spatial smooth distribution law of atmospheric physics, and the weather system includes a passing low-pressure trough or a high-pressure ridge.

7. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 1, characterized in that, The theoretical thermally induced deviation component and residual deviation are calculated based on the effective temperature values ​​collected from effective monitoring points, including: The effective average temperature is determined by calculating the average of the effective temperature values ​​collected at each effective monitoring point within the same time window. The effective average temperature is substituted into the conductor sag-temperature physical model to calculate the theoretical sag change of each phase conductor. The change in distance to ground of each phase conductor is calculated based on the theoretical sag change of each phase conductor. The theoretical admittance change of each phase conductor is calculated based on the change in distance to ground of each phase conductor, and the theoretical admittance changes of phase A, phase B, and phase C are respectively determined as the theoretical thermally induced deviation component of phase A, the theoretical thermally induced deviation component of phase B, and the theoretical thermally induced deviation component of phase C. The residual deviations of phase A, phase B, and phase C are determined based on the differences between the deviations of phase A, phase B, and phase C and the theoretical thermally induced deviation components of the corresponding phases.

8. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 1, characterized in that, The causes of three-phase imbalance are determined a second time based on the residual deviation, including: The residual deviations of phase A, phase B, and phase C are remapped to a two-dimensional coordinate system according to the actual physical arrangement of each phase conductor on the crossarm of the tower, and the three mapping points are connected in sequence to generate a residual space deviation polygonal line. Calculate the residual shape ruggedness of the residual spatial deviation polygonal line; The cause type of three-phase imbalance is determined twice based on the roughness of the residual shape.

9. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 8, characterized in that, The causes of three-phase imbalance are determined secondaryly based on the residual morphology ruggedness, including: In response to the residual morphology roughness not being greater than the preset residual roughness, the cause type of the three-phase imbalance is determined to be thermal effect sag type. In response to the residual morphology roughness being greater than a preset residual roughness, the maximum residual deviation among the residual deviations of phase A, phase B, and phase C is determined, the target phase corresponding to the maximum residual deviation is determined, and the cause type of the three-phase imbalance is determined for the second time to be the mechanical hidden structural damage type of the target phase.

10. The method for evaluating the three-phase imbalance of transmission lines based on multi-source data according to claim 9, characterized in that, Based on the aforementioned cause type, an adjustment strategy is determined, including: In response to the fact that the cause type is static structural type, the subsequent analysis process is terminated, and the static structural type label is directly output as the evaluation conclusion. In response to the cause type being thermal effect sag type, a reactive power compensation adjustment suggestion is output to the operation and maintenance end; In response to the cause being classified as mechanical latent structural damage, an inspection alarm for the target phase is output to the maintenance department.

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