One of the biggest problems in Power Quality is the disconnection of electric motors due to the presence of sags. In order to study this phenomenon it became necessary to build a sag generator to, for example, develop immunity curves for induction motors as well as for synchronous motors. In this way it is possible to evaluate the quantitative impact of sags in these machines. This paper also analyzes the effects in current, torque and speed caused by sags, in particular A, B and C types.