As we know that the formula of motor speed ” r.p.m. ” ( without sleeping ) is :
r.p.m. = 60 x f / n
– f : the frequency
– n : the nomber of each 2 poles
so, as in the most of case ” n ” for a motor is not changeable, that means to change the speed for a motor we can change the frequency, that we can do by using the ” Variable Speed Drive “. Noting that the frequency can be changed by the Variable Speed Drive from ” 0 ” to ” 100 Hz ” and in some V.S.D. we can achieve ” 500 Hz “. But we should be careful, because :
– It's possible that we have some Mechanical problems in the motor ( specially with the bearings ) if it runs on high speed for a long time ( more than his nominal speed ).