一臺三相繞線式異步電動機(jī),PN =75kW,UN =380V,IN =148A,nN =720r/min,ηN=90.5%,cosφN=0.85,λm =2.4,E2N=213V,I2N=220A。求: (1)額定轉(zhuǎn)矩; (2)最大轉(zhuǎn)矩; (3)臨界轉(zhuǎn)差率; (4)求出固有機(jī)械特性曲線上的四個(gè)特殊點(diǎn)。