Study On Recognition Method Of Over-voltage Of Ehv Power Grid Basing On Transient Electric Field Characteristics

The over-voltage with different waveforms, amplitudes and lasting time is a major research direction in the development of HV transmission lines. It is not only of great concern to the insulation design, but also to the system security. From the analysis of the black out faults both at home and abroad, there are frequent accidents resulting from the system over-voltage, and the insulation faults often occurs. Therefore, it is meaningful to monitoring, identify and suppress the over-voltage with relevant approach.In the suppression of the over-voltage, the accuracy data about the over-voltage acquired from the on-line monitoring equipment is of vital importance concerning the subsequent identification and suppression, and also where the difficulty lies. Currently, the over-voltage data is acquired by the on-line monitoring equipment which is directly connected with the primary apparatus in the 110 kV (and below) systems. Although this approach is characterized with data accuracy, it may leads to the apparatus heating and subsequent safety hazard threatening the entire power grid. Thus the traditional'contacting'monitoring approach can not meet the safety concerned demands in the 500 kV (and above) transmission systems. Whereas as the main grid for the power transmission and connecting belt for the local grid, the safety operation of EHV grid is of great concern. Their on-line monitoring should not only maintain the data accuracy but also decrease its threatening to the system security. So the on-line monitoring of the EHV transmission lines should be brought out in a non-contacting way. Thus the data acquirement and identification of the 500 kV transmission lines is the key point to the over-voltage suppression.Based on large number of corresponding literature, this thesis constructs the calculating program of the temporary electrical field by using the FDTD. It calculates the lightning over-voltage, grounding faults, and breaking operating dependant temporary electrical field in the substation. The characteristic factors are extracted by the joint application of wavelet analysis and Fourier transform. c The main conclusion is as follows:(1) Based on the MATLAB, the FDTD dependant temporary electrical field calculation model is constructed. Taking the electrical field resulting from different conductors into consideration makes this model more similar to the real condition. The calculation results of lightning over-voltage, single phase grounding fault, over-voltage caused by switching capacitors,switching unloaded lines and switching no-load transformer are demonstrated, and the results show that each over-voltage leading electrical field has its own characteristic.(2) The transient electric fields'characteristic parameters were extracted with Fourier transform and wavelet analysis, the results show that the characteristic parameters can describe the characteristics of transient electric field.(3) The RBF dependant over-voltage identification system is constructed based on the temporary electrical field. Through the validation tests, it is proved to be capable of the over-voltage identification and classification.