## 1 Introduction  
The aspects regarding the effects of the power quality (PQ) disturbances on the electromechanical receivers are justified, due to the first rank of the electricity consumed by these types of receivers, in general consumption. Electric motors and the systems they drive are the single largest electrical end-use, consuming more than twice as much as lighting, the next largest end-use. It is estimated that electric motor-driven systems (EMDS) account for between 43% and 46% of all global electricity consumption, giving rise to about 6040 Mt of CO2 emissions. By 2030, without comprehensive and effective energy-efficiency policy measures, energy consumption from electric motors is expected to rise to 13,360 TWh per year and CO2 emissions to 8570 Mt per year. End-users now spend USD 565 billion per year on electricity used in EDMS; by 2030, that could rise to almost USD 900 billion [1]. Induction motors (IMs) account for some 68% of the energy consumption of industry worldwide; thus, to reduce the global consumption of electricity, it is essential to improve their efficiency. Furthermore, improving the efficiency of IM and drive mechanical systems might reduce around 20%-30% of the energy consumption, also reducing some 10% of the overall electricity demand [2]. IM has one disadvantage, the fact that the mechanical speed of the machine is directly coupled to the frequency of the supply voltage, which limits its flexibility when supplied directly from the grid. Although the usage of AC power converters can adjust the supply frequency, only 25% of the newly installed machines are supplied from an AC power converter [3; 4]. For IM supplied directly from the AC network, it is essential to determine the tolerability limits of the different types of disturbances affecting the PQ, as well as to identify those disturbances leading to power losses, both in the machine itself and in the power grid. The harmonics consequences are very topical, due to the increasing use of different types of static converters as well as receivers supplied by electronic power equipment [5; 6; 7]. The operating of motors on a polluted harmonic system results in reduced machine efficiency and service life due to the increase in iron and copper losses at the harmonic frequencies. In addition, voltage and current harmonics can affect the torque developed. More, harmonics in rotating machinery can cause vibrations and noises. Negative sequence harmonics cause negative torque which opposes the fundamental motor torque, thus causing a decrease of the global motor efficiency. In the literature, there are numerous studies to reduce losses in the IM and, consequently, increase the efficiency of this type of motor. If the efficiency of IM is to be increased, this can be achieved at every design parameter of the machine, and the PQ of the power supply should be considered. In [8; 9; 10], the authors propose estimation methods for some characteristic parameters of the IM, such as currents, losses, or efficiency, but the harmonics, unbalanced regime, or other PQ disturbances in the supply voltages are not considered. Although the detrimental effects of a low PQ on electric motors are known, they are mostly neglected or ignored. However, some works cover both the analysis of the additional losses that are caused by supply voltage distortion and other papers address temperature rise and derating of motors under distortion [11; 12; 13; 14]. Other works that are based on experiments usually have the harmonic content injected by programmable power supply [15; 16; 17]. In [18], the authors evaluate the effect of voltage distortion on the operation of IM, with a focus on a practical setup that is often encountered in industry. In [19], motor efficiency is analyzed in the presence of voltage harmonics; however, the use of a single equivalent circuit is proposed, instead of applying the principle of superposition of the equivalent circuits corresponding to each harmonic level.