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1·Increasing core length properly can raise motor efficiency and power factor, but it will reduce locked-rotor torque ratio and breakdown torque ratio.

适当增加铁心长度可以有效提高电机效率和功率因数，但会导致启动转矩倍数和最大转矩倍数减小。

2·The breakdown of transmission shaft in the main drive system is due to too high roll torque. Overpower protection mode of motor current does not reflect the true dynamic character of roll torque.

轧制力矩过大是轧机主传动系统传动轴断裂的主要原因，传统的电机电流过载保护方式不能真实反映轧机主传动系统扭矩的动力学特性。