A novel soft start method based on auto-transformer and magnetic control

In order to deal with the current secondary impact problem that produced by traditional auto-transformer starter and further reduce the start current, a new autotransformer and magnetic control (ATMC) soft start method is proposed. The work principle of ATMC is analyzed and a simplified equivalent circuit model of the main circuit is established. Using the circuit model, the relationship between the motor current and the grid current in auto-transformer start stage and the principle of avoiding the current secondary impact in magnetron regulator stage are analyzed in detail. Four different cases (direct start, auto-transformer start, magnetic control reactor start and ATMC soft start) are simulated and a start experiment of 19000kW super large capacity and high voltage induction motor is carried out with the proposed ATMC method. Simulation and experiment results show that the ATMC soft starter can avoid the current secondary impact effectively, and the motor start current is constrained to be less than three times of the rated current.