Development Of A Comprehensive System Analyzer For Dry Transformer Materials

In the production process of the conventional distribution network dry type transformer,since the aluminum line is lower in price than the copper line,and the coil is hard-packed by the resin,the user cannot discriminate the material.Therefore,in order to increase the profit margin,some manufacturers use aluminum instead of copper as the winding material of the dry-type transformer in the production process,thereby greatly reducing the cost.However,the conductivity is reduced,which affects the current quality and poses a safety hazard.Such situations occur frequently during the sampling process of the State Grid Corporation.The current common method for this situation is to check through the transformer hoist,but this method is not only complicated to operate but also causes damage to the insulation of the transformer.Therefore,it is necessary to use a non-destructive testing equipment.The winding material discrimination method was studied.A set of dry network transformer integrated system analysis equipment(referred to as “analyzer”)was designed and developed.It is a dry-type transformer material testing and capacity test,characteristic test and direct resistance test.Instrument with variable ratio test.Firstly,based on the function of the analyzer,the requirements of the analyzer are analyzed,and then according to the characteristics of the conductivity(current density value)of the copper-aluminum material,the material identification method of the "current density method" is finally selected,and the current density is based on the measurement of parameters such as cross-sectional area,DC resistance and transformer capacity.Secondly,based on the characteristics of the above three parameters,the test plan is designed.For the cross-sectional area of the transformer winding conductor,a special measuring winding is used,which is placed on the iron core concentric with the transformer,and an excitation signal is applied.Based on the voltage method,the windings are based on the known voltage and the number of turns.The ratio of the voltages is the ratio of the number of turns of the coil,thereby measuring the number of turns of the other coils.For the DC resistance of the transformer,since the measured resistance value is small,there are errors in the balanced bridge method and the voltage drop method,so the DC resistance of the transformer is tested by the "four-wire method".For the capacity of the transformer,first calculate the capacity of the transformer according to the impedance voltage method,and then carry out measurement according to the no-load loss,short-circuit loss and transformer technical parameters under this capacity,according to whether the loss can be judged within the error range,the true capacity of the transformer can be achieved by the national standard.Finally,the software test platform of the analyzer was established by using LabVIEW software,and the design function and feasibility of the software were introduced.For theanalyzer,the materials and parameters of the four transformers were tested in the field.The measurement results showed that there was a 4.53% error in the transformer capacity test,which did not affect the judgment of the capacity,and the material judgment result was accurate.The integrated network analyzer model of the dry-type transformer material developed by the paper realizes the discrimination of the material of the dry-type transformer,and can measure the parameters such as the dry load loss,DC resistance and transformer capacity of the dry-type transformer.Prove the effectiveness and feasibility of the device.