Research On Orthogonal Coupled Vector Electric Field Sensor And Non-Intrusive Voltage Measurement Technology Of Transmission Line

As the composition of the supply and demand side of the new power system becomes more and more diversified,the voltage components of the transmission lines,such as power frequency steady-state,high-order harmonics,and high-frequency transient components have gradually increased.The existing voltage measurement methods are mainly limited by the size of the device,response capability,and application scenarios,and it is gradually difficult to meet the large-scale data requirements in wide-area panoramic perception and evaluation of the operation status.The non-intrusive voltage measurement method using electric field(E-field)as an indirect parameter has the advantages of wide response frequency,simple installation,and convenient layout.It is of great importance in real-time diagnosis,intelligent control,and operation protection of transmission lines.However,the current E-field sensor is mainly oriented to scalar measurement,and its amplitude and direction characteristics are easily affected by angular deviation.In terms of the voltage inversion method,some of the integral node parameters of the E-field integration method cannot meet the actual application conditions of the sensor,while the three-phase voltage decoupling method requires installing multiple sensors with a complex coefficient matrix and low inversion accuracy.Therefore,given the above measurement problems,a vector E-field sensor and system with the broadband response and anti-angular deviation measurement capability are designed,and two types of node-parameter-corrected E-field integration methods are proposed to optimize the position of sensors.The E-field self-decoupling method is proposed to realize the voltage inversion of the three-phase transmission line by a single sensor.The detailed work and results are summarized as follows:(1)Aiming at the non-intrusive voltage measurement,the forward and inverse problem analysis of the "source-field-inductance" relationship of the transmission line is completed.Firstly,the spatial E-field distribution of the typical charge system,the calculation method of the E-field for the forward problem,the field-source boundary problem,and the time-harmonic field analysis of the transmission line are introduced from the source to the field.Secondly,the dispersion and polarization effects of the sensor’s sensitive electrode under the field-effect are discussed.Finally,the calculation method of the field-to-source inverse problem and the ill-conditioned discussion is introduced.The research provides a theoretical basis for the spatial E-field effect of transmission lines,field-circuit coupling design of vector E-field sensors,and the nonintrusive voltage inversion and its optimization algorithm.(2)A three-dimensional orthogonal coupling arc-surfaced six-electrode vector Efield sensor and its measurement system with broadband and anti-angular deviation measurement characteristics are researched and designed.Firstly,based on the principle of multi-dimensional E-field coupling,the sensitive electrode division,and vector synthesis method are studied.By which,a curved six-electrode E-field sensor is proposed,and two types of equivalent circuit analysis are completed.Secondly,the sensor’s designing parameters are determined according to the finite element capacitance simulation and the results from circuit analysis,and the anti-angular deviation measurement mechanism is also discussed.Finally,the preparation of multi-type probes of the sensor and the design of the measurement system is completed,and the transient,steady-state,and anti-angular deviation tests are carried out respectively.The results show that the sensor can measure the wideband three-dimensional vector E-field signal with anti-angular deviation capability,and the relative error is less than 2%.(3)The E-field integration voltage inversion method based on node parameter correction is studied to solve the problem that some nodes are difficult to meet the onsite application conditions.The reconstructed-node Chebyshev integration(RNCI)method and the fixed-node Legendre integration(FNLI)method are respectively proposed.Through the near-earth/near-source area division and the fixed-node interpolation,the position parameters and weight parameters are corrected,which realize the highest node is far away from the wire by more than 10%,and the lowest node is raised from the ground by more than 10%.These methods improve the accuracy of voltage measurement and ensure the adaptability of the sensor in on-site installation.The results show that the measurement errors of the two integration methods are both less than 0.5%,and the RNCI method has higher voltage measurement accuracy than the FNLI method.(4)The vector E-field self-decoupling method of the transmission line is studied to realize the inversion calculation of three-phase voltage by a single sensor.Firstly,the selfdecoupling forward problem matrix between the vector E-field and the three-phase voltage is derived to reduce the dimension of the sensing signal and integrate the parameters adaptively.Secondly,according to the structure of horizontal,equilateral triangles,inverted triangle transmission lines,and orthogonal coupling sensors,the maximum equivalent of matrix coefficients is carried out,the scale of the decoupling matrix is simplified,and three-phase voltage inversion is realized.Thirdly,the measurement point optimization flow based on the gradient descent method is introduced to ensure the position of the overvoltage measuring point that meets the target requirements.Finally,the transient overvoltage measurement performance of the sensor is tested under both the single-phase and three-phase overvoltage experimental platforms.The results show that the amplitude measurement error of the E-field sensor under singlephase overvoltage excitation is less than 3%,the standard error is less than 0.088%,and the three-phase voltage amplitude error of the vector E-field integration method is less than 3.5%,which has good measurement accuracy.(5)For the E-field integration and self-decoupling methods,the specific uncertainty assessment models are established based on the node parameters or the decoupling coefficient matrix to evaluate the stability of each non-invasive voltage inversion method.According to the results of repeated experiments and uncertainty evaluation,the uncertainty of the FNLI method is smaller than that of the RNCI method,and it has better voltage measurement stability.The relative expansion uncertainty of the three-phase voltage inversion results at the optimal measurement point of the E-field self-decoupling method is 8.74%,6.44%,and 7.95%,which is much smaller than the corresponding uncertainty of the other non-optimal measurement points.It demonstrated the effectiveness of the E-field self-decoupling and measuring point optimization method for non-intrusive voltage measurement.