Calculation Of Electric Field And Wave Process In Ultra Over Voltage Power Transformer

Practice shows that the transformer fault lies mainly in the insulation.Therefore. improving insulation capacity of transformer and carrying on the reasonable design of insulation become the primary tasks of the transformer designs.In order to design insulation structure,we must know the internal electric field distribution as well as over voltage distribution when the transformer receives exterior disturbance.According to the electric field distribution,we can determine electric field intensity in windings,and discover the location of maximum electric field intensity,which is also the position of problems arising from the transformer insulation.With the increase of transformer capacity and voltage level,the transformer insulation have many problems to be solved.Such as the design margin indicates serious imbalance in various partsin the insulation design,and in some parts the electric field intensity is too high,even insulation hidden dangers exist;some parts electric field intensity is too low, insulating material can be further reduced in size,etc.Therefore,the paper calculated and analyzed main insulation and longitudinal insulation of the transformer.The internal insulation of transformer can be divided into main insulation and longitudinal insulation.As for the calculation of the main insulation electric field,it mainly examined the voltage under industry frequency,and carried on a reasonable simplification of the electric field between high-low voltage windings and between low voltage windings and the iron core,divided the electric field into three regions,established a two-dimensional finite element model,carried on the calculation using ANSOFT software,obtained the electrio potential distribution and the electric field intensity distribution as well as the electric field intensity vector distribution map of each part,calculated the electric field insulation margin of all parts,identifiedthe maximum field strength of the insulation and the minimum margin.All these are of certain guiding significance for the insulation design. In connecting wire casing insulation of the electric field,the paper established the two-dimensional model,calculated it using the finite element method,and obtained the maximum electric field strength and the location which the maximum value appeared, calculated the minimum insulation margin.For the longitudinal insulation,it mainly conducted the calculation of over-voltage under the action of thunder and lightning.During the calculations,we established the simplified winding model and the equivalent circuit,reasonably determined the inductance, capacitance,and other parameters,and carried on the computation of wave process.Thus we respectively obtained the electric potential distribution and the electric potential gradient distribution of high and low voltage windings under the action of full wave and the truncation wave,discovered the oil road of the largest electric potential gradient, calculated the insulation margin of corresponding oil road under the action of full wave and truncation wave,and provided the reference basis for the engineering design.