Research On Residual Flux Evaluation Technology Of The Transformer

One of the most important electrical equipment in the power system of a transformer,its safety and stable operation plays a vital role in the power system.When the transformer is turned on and off,due to the existence of residual magnetism of the transformer,the core is saturated for half a week,and the magnetizing inrush current is also generated.It has an impact on the transformer and can cause malfunction of the relay protection device.At present,the phase selection closing is a very effective means of suppressing the magnetizing inrush current.The principle is that the energization angle is calculated under the condition that the residual magnetization is known,and the biasing and remanence at the time of closing can cancel each other.This topic is mainly for the study of residual magnetization estimation under the interception and overvoltage of transformers.The research contents are as follows:Firstly,when the transformer is unloaded,due to the self-characteristics of the vacuum circuit breaker,the current will suddenly cross the zero point.At this time,the energy of the transformer is converted,resulting in the generation of the cut-off overvoltage.Due to the overvoltage,the hysteresis loop will change accordingly,and the remanence will change.Using the ATP-EMTP software,the equivalent model of the transformer is established.The actual transformer parameter setting is used to simulate the over-voltage of the no-load transformer.The theoretical calculation results are compared to verify the correctness.Secondly,based on the original static hysteresis model,the original model is changed so that the magnetic flux density is the static hysteresis model of the input.The experimentally measured hysteresis loop uses the particle swarm optimization(PSO)algorithm for different magnetic flux densities.The five parameters in the model are identified,and the calculated results are compared with the measured data to prove the correctness of the identification results.And the hysteresis model under the local hysteresis loop is considered.According to the core loss separation theory,the dynamic hysteresis model of the core is established and its parameters are identified.Then the calculation results are compared with the measured data to prove the correctness of the parameter identification.Thirdly,an experimental platform based on the measured magnetic properties of the Epstein square was built to measure the hysteresis loop.Considering the existence of DC flux density,a hysteresis model is established for this,and the model parameters are identified,and the parameters are fitted to the parameters to correct the dynamic hysteresis model parameters of the core.Finally,the magnetic flux density after the over-voltage integration is taken as the input of the dynamic hysteresis model of the core,and the calculated current is obtained by the Ampere loop law,which is compared with the measured data.When the error is not satisfied,the magnetic flux density is adjusted.When the error range is satisfied,the iteration is stopped.The actual hysteresis loop is thus obtained,and the last point of the hysteresis loop is the remanence value.