Study On The Inrush Currents Suppression And Sympathetic Inrush Currents For Power Transformer

During no-load closing of a power transformer,due to the influence of the non-periodic component of the magnetic flux,the transformer core will enter a saturated state,resulting in inrush current which is several times the rated current.Inrush current will cause the malfunction of the protection device.And a large number of harmonics in the inrush will have a certain impact on the power system.In this paper,the inrush current of transformer is studied in depth,the principle of its generation is analyzed,and the method of suppressing it is put forward.For the inrush current generated by no-load closing of a single three-phase transformer,this paper separately discusses whether there is remanence in the transformer or not.Considering that there is remanence before closing and the opening angle is known,starting from the introduction of the generating principle of the inrush current,this paper studies the method of suppressing inrush current by analyzing the phase selection closing technology of the circuit breaker and the change of remanence of the core after the opening of the transformer,and determines the method of suppressing inrush current under the condition of the known opening angle by combining with the dynamic simulation experiment.In the view of the operation conditions of unknown opening angle such as the maintenance of the transformer,considering the method to make the remanence of transformer zero,this paper studies and analyzes the closing strategy of suppressing inrush current under the condition of no remanence,and determines the closing strategy by the means of dynamic simulation experiment and digital simulation experiment.The strategy that closing in a specific angle range at the same time is put forward.In order to solve the problem of differential protection maloperation caused by sympathetic inrush,the mechanism of sympathetic inrush is analyzed by mathematical analysis,and the criterion of recognition of sympathetic inrush based on the peak change of differential current is proposed,and the feasibility of the criterion is verified by digital simulation.At the end of the paper,the research of the whole paper is summarized,and the future work is put forward.