Research On Parameter Identification Scheme Of Three-winding Transformer Based On PMU Data

As the main equipment in power system,the accuracy of transformer parameters plays an important role in the safety and stability analysis of power system.Traditional methods for obtaining transformer parameters,such as theoretical calculation and offline measurement,cannot take into account the actual operating state of the transformer,while the parameter identification method based on PMU data can realize online identification.However,there are errors or deviations in the measured PMU data,which will affect the identification results of transformer parameters,and then affect the advanced application of power system.In response to the above problems,this paper has carried out the following work:(1)A set of credibility indicators of PMU data based on single-point and multi-point measurements is constructed for the three-winding transformer.Firstly,the relationship between the three-winding voltage and current phasors during transformer operation is considered to form a credibility index based on single-point measurement.Secondly,combined with statistical knowledge,the credibility index based on multi-point measurement is formed.Finally,the correctness and effectiveness of the credibility index are verified by the measured data.(2)Combined with the estimation of active and reactive power loss of transformer,an abnormal detection method of transformer power measurement is proposed.Firstly,the PMU measurement voltage,current and power of the three windings of the transformer should meet certain electrical constraints,so as to detect the unilateral power measurement of the transformer.Secondly,the threshold of power deviation is set under the condition of considering the parameter error of transformer and transformer,and the measured value and estimated value of active and reactive power are compared within the range of threshold,so as to judge whether the active and reactive power measurement of three windings of transformer is abnormal,and the effectiveness of the detection method is verified by simulation and actual calculation examples.(3)Combined with sensitivity,the influence characteristics of voltage and current amplitude and phase angle measurement error and variable ratio error on the parameter identification of three-winding transformer are revealed,and the dominant factors are determined.Through sensitivity analysis,the influence characteristics of amplitude measurement error,phase angle measurement error and ratio error of voltage and current of three-winding transformer on identification parameters are obtained.The correctness of sensitivity calculation is verified by simulation results.Combined with sensitivity analysis,the dominant factors affecting transformer parameter identification are determined.(4)Combined with the error influence characteristics,a step-by-step robust parameter identification scheme is proposed for the three-winding transformer.Firstly,based on the positive sequence equivalent model of the three-winding transformer,the parameter identification equation at a single time is established.Secondly,considering the problem that the position of the transformer tap is unknown in actual operation,the actual ratio is calculated by the phasor relationship between the voltage and current of the transformer and the tap is selected.Finally,the data of multiple time periods are substituted into the parameter identification equation and solved by the least square method.In order to make the identification results have better robust performance,the median robust algorithm is used to process the parameter identification results of the least square method.The simulation and experimental results show that the parameter identification scheme is effective and has good robustness.