Research On Key Technologies For On-site Maintenance Of High-voltage Converter Transformers

China Southern Power Grid operates and maintains 11 of DC transmission systems,including a large number of core equipment converter transformers.The failure rate of the converter transformer is about twice that of the AC transformer.If a major repair is required after a failure,it must be transported back to the transformer factory for repair.Due to the large volume and heavy weight of the converter transformer,and the operating locations of the converter stations at the sending end are mostly located in mountainous areas,it has a long transportation cycle,high cost,and difficult coordination.In the past,transformer maintenance work was carried out on site,and the work site was relatively simple,and the drying method of the body was mostly carried out by the hot oil spray method,which was far inferior to the kerosene gas phase method used in the return to the factory.In addition,due to the influence of the operating equipment,there is a lot of interference during the factory test on site,and the test effect is not ideal.The maintenance hall of the converter station of UHVDC project is located in the converter station.Therefore,through the study of the grounding and electromagnetic shielding of the hall,it is concluded that the ground network of the hall should be connected with the ground network of the converter station,so as to ensure that the stepping voltage and contact potential in the hall and converter station are less than the allowable value.In order to meet the requirements of the discharge test in the converter station,the results of radiation resistance and electromagnetic interference resistance of the hall are calculated.The method of hot oil spray drying is adopted to dry the change of rheology after site maintenance,and the technical measures of installing heating plate at the bottom of the fuel tank,covering the surface of the heat preservation cover and aligning the spray nozzle with the iron core can make the site drying effect meet the operation requirements.In addition,the evaluation index of hot oil spray and the parameter configuration method of solvent gas phase drying device based on 800 kV rheological exchange structure were put forward,the drying process control requirements were studied.The field test items and standards for converter transformer after field overhaul are studied and formulated.Taking the field overhaul of 800 kV converter transformer in Pu ’er station as an example,the field test items and standards are determined in combination with the field overhaul hall test conditions.The main parameters of the key equipment required by the field overhaul after rheology change were calculated,and the dimensions of the equal-pressure ring and anti-halo conductor for the test were designed and calculated according to the characteristics of the high voltage in the field test,so as to ensure the smooth development of the field test.On-site rheological change maintenance can greatly reduce the rheological change maintenance cost and shorten the construction period,which is of great significance to the operation and maintenance of UHVDC transmission project.