一臺(tái)三相異步電動(dòng)機(jī),定子繞組接到頻率為f1=50Hz的三相對(duì)稱電源上,已知它運(yùn)行在額定轉(zhuǎn)速nN=960r/min。問(wèn): (1)該電動(dòng)機(jī)的極對(duì)數(shù)p是多少? (2)額定轉(zhuǎn)差率SN是多少? (3)額定轉(zhuǎn)速運(yùn)行時(shí),轉(zhuǎn)子電動(dòng)勢(shì)的頻率f2是多少?