Ueseerch On Transformer Operation And Maintenance Strategy And Economic Life Based On Health Status

The current condition evaluation of transformers relies heavily on the subjective experience of experts.The evaluation results are not totally accurate and objective.The maintenance plan of the power company’s existing operation and maintenance mode are need to be improved.When making the decision of repairing or decommissioning,more attention to reliability and less attetion to economic are taken into consideration.It is often the case that some transformers actually need to be decommissioned while continues to operate and some transformers should not be decommissioned was decommissioned in advance,which causing huge economic losses.As the scale of China’s power grid further increased,this problem became more and more prominent.Therefore,it is necessary to further study the transformer state evaluation method and consider the reliability and economics of the transformer together.On the basis of satisfying the reliability of the transformer,the maintenance plan is arranged reasonably from the perspective of the whole life cycle,so as to achieve the maximum value of use and the best economy when the transformer is retired,thereby improving the management level of the transformer and the economy of the power company.This thesis makes full use of the large amount of data accumulated in the development of online monitoring technology in recent years.Data-driven methods and physical models are combined to carry out three major research work:transformer condition evaluation,fault probability calculation and economic life prediction.The first part:the indices from the multi-source panoramic state information are selected to establish the comprehensive health evaluation index system of the transformer;the model of the weight gaming and modified evidence theory applied on the condition assessment of transformers based on the evaluation index is established to evaluate the insulation state of transformer;finally the transformer comprehensive health index calculation model is set up.The second part:transformer fault probability prediction model based on comprehensive health index is modelled.The third part:on the basis of fault probability prediction model,a transformer full life cycle cost model that comprehensively considers reliability and economy is established.Taking the lowest annual average cost of the whole life cycle as the objective function,the maintenance time and maintenance degree are optimized,finally the economic life expectancy corresponding to the lowest annual average cost is obtained.The main conclusions of the thesis are:(1)The transformer condition evaluation index system is determined.Then the comprehensive weight calculation method based on expert subjective weight and data information entropy weight is constructed,which considering the expert experience and the data itself change law fully.What’s more,the improved evidence fusion theory is applied to the transformer condition evaluation,which solves the problem that the traditional evidence theory may obtain a wrong result when the conflicts between different factors.Case studies show that the results of the proposed model are closer to the actual condition of the transformer.(2)The transformer failure probability is divided into accidental failure period and aging failure period according to the operation period.In the accidental failure period,the failure probability index function model based on the comprehensive health index is established.In the aging failure period,a transformer failure probability prediction model based on vector autoregression is established.In this model,the impact of comprehensive health index,equivalent operating period and historical failure rate on failure probability are comprehensively considerred.Finally,the example shows that the proposed model has higher accuracy than the existing models.(3)The life efficiency index model is set up to measure the maintence effect evaluation model;the operation and maintenance cost,maintenance cost,interruption cost and generalized depreciation cost are considerred to establish the annual life cost model of the transformer life cycle;the lowest annual average cost is adopted as the criterion,while the cuckoo optimization algorithm is used to optimize the maintence time,maintenance degree and service life to obtain the best economic life of the transformer.Finally,the proposed model is used to evaluate the economic life of ideal new transformers and in-service transformer.