Structure Design Of Gradient Electric Field Enamel Wire Based On Dielectric Constant Control

With the increase of the operating voltage and frequency of the drive motor of new energy vehicles,the enamelled wire carrying high voltage is more prone to partial discharge,corona and other phenomena,thus causing great damage to the motor insulation system.Therefore,improving the performance of the enamelled wire from the perspective of corona resistance or corona prevention can greatly improve the service life of the drive motor.The dielectric gradient material is used to construct the non-linear enamelled wire insulation structure.By adjusting the distribution of dielectric or conductivity parameters,the electric field distribution can be adjusted to alleviate the local electric field concentration.The construction of dielectric gradient insulating materials can be adjusted from two directions:low dielectric materials and high dielectric materials.Hyperbranched polyester is a kind of polyfunctional monomer as the central core,which is further grafted with all levels of branched monomers to synthesize a polymer.It has a unique spherical structure under the three-dimensional structure.Therefore,it can be used as a low dielectric modifier.It can be added to the matrix resin to greatly increase the content of free volume in the system,thereby reducing the content of polar functional groups in unit volume,Macroscopically,the dielectric constant of the matrix resin decreases.The experimental results show that when the content of hyperbranched polyester is 0,2.5 wt.%,5 wt.%,7.5 wt.%,and 10 wt.%,the dielectric constant of insulating paint is 5.3,4.7,4.3,4.1,and 5.7 at 100 Hz,respectively.At the same time,the addition of hyperbranched polyester can significantly improve the insulating property of insulating paint by 6.1%～37.8%.This shows that by adjusting the amount of hyperbranched polyester,the dielectric constant of insulating paint presents gradient distribution,Thus,a series of low dielectric insulating paints meeting the requirements are obtained.Graphene is a common conductive filler.When the amount of graphene added reaches a certain threshold,a small amount of filler can be used to prepare composites with high dielectric constant.Research shows that when the content of modified GO is 0.3 wt.%,the dielectric constant at 100 Hz reach 24.6,which is 364%higher than that of pure insulating paint,while the dielectric loss is only 0.26.At the same time,the characteristic breakdown field strength of the insulating paint added with modified GO remained above 26.9 kV·mm-1.These indicate that using modified graphene as high dielectric modified filler can obtain high dielectric insulating paint that meets the requirements.By using the insulating paint with gradient dielectric constant,an insulation structure with nonlinear dielectric distribution is constructed in a laminated manner,so that the dielectric constant is gradually increased from the inside to the outside.At the same time,a layer of nonlinear shielding paint is coated on the outer layer,and the enamelled wire insulation layer with high electrical resistance is designed.The simulation results show that the use of nonlinear shielding paint on the outer surface of the insulation layer can significantly reduce the electric field of the outer layer,which is affected by the nonlinear conductivity and dielectric constant When 0.4 wt.%KGO paint is used as the shielding paint,the electric field strength of the surface of the insulation layer near the air side is 80.6%lower than that of the outermost surface when pure epoxy resin is used,which is less than the air breakdown electric field strength.At the same time,the difference in the dielectric constant of adjacent interfaces is reduced,The dielectric constant is gradually increased from the inside to the outside,so that the electric field in the high electric field area is effectively reduced and the electric field in the weak electric field area is increased.The maximum field strength is reduced from 17.26 kV·mm-1 in the case of a single dielectric constant to 16.7 kV·mm-1 and the field strength difference in the inner layer is reduced from 1.56 kV·mm-1 in the case of a single medium to 0.3 kV·mm-1 further reducing the electric field distortion of adjacent interfaces.These prove that the construction of nonlinear dielectric structure is a feasible means to suppress corona.