Research And Application Of Saturation Model Of Single-phase Four-column Converter Transformer Based On UMEC

With the development of UHV power transmission,the capacity of UHV converter transformers is gradually increasing.UHV converter transformers generally adopt a single-phase structure(three-phase transformer group),and with the increase of the capacity of single-phase transformers,the limitation of transportation width and the need to reduce magnetic density,single-phase converter transformers adopt multi-column parallel structure,Such as single-phase four-column type.However,the current model library built in electromagnetic transient software such as PSCAD/EMTDC does not contain a single-phase four-leg structure,so it is very necessary to construct a single-phase four-leg converter transformer saturation model suitable for engineering applications.In order to accurately and quickly perform electromagnetic transient simulation of single-phase four-leg converter transformers,this paper first proposes a single-phase four-leg converter transformer saturation model based on no-load test data and UMEC(Unified Magnetic Equivalent Circuit).Based on the UMEC magnetic circuit model,the method for solving the incidence matrix,inductance matrix and core permeance of the single-phase four-leg converter transformer is deduced.When considering the saturation situation,the excitation branch is equivalent to the parallel connection of the nonlinear resistance and the nonlinear inductance,and the piecewise linearization curve of the instantaneous value of u-i R and u-i L of the excitation branch is obtained through the no-load test data.In this way,the core loss and the non-linearity of the magnetic permeability are simulated.This method is used to simulate and calculate the scaled down model of the actual converter transformer under normal operating conditions and DC bias conditions,and to compare with experimental measurements.Finally,the algorithm of this paper is used to simulate the no-load test of the product-level converter transformer of a converter station to verify the effectiveness of the method on the product-level converter transformer.And through the simulation of the inrush current of the converter transformer under no-load closing conditions,the no-load closing phase angle,time constant(closing resistance)and the exit time of the closing resistance are analyzed in detail.The influence of magnetizing inrush current,and proposed to control the closing phase angle(to avoid closing at the voltage zero crossing point),install circuit breaker closing resistance and control the exit time of the closing resistance,etc.,to avoid no-load closing Magnetizing inrush current causes harm to power systems and converter transformers.