**1. Introduction**

Today, about 50% of electrical energy produced is used in electric drives. Electrical motors consume around 40% of total consumed electrical energy (Almeida et al., 2007) and of that thereof, induction motors account for 96% of energy consumption. Around 67% of this energy is used in induction motors with a rating below 75 kW and it can be shown that 85% of the energy losses are dissipated in these rating motors. Efficiency improvements of constant-speed drives, both constant-torque and variable-torque drives, is very important. It is usual that techniques for efficiency improvements of variable-torque drives are different from those of constant-speed and constant-torque applications. The latter is dealt with through optimization; it is very difficult to design and build a motor with high rating efficiency and rating power factor - it has been shown (Fei et al., 1989) that higher efficiencies are associated with lower power factor. It is especially difficult to design and build a drive operating at high efficiency and power factor over an entire range of loads, say from 25 - 100% of rated load (*PN*), i.e. at partial load.

Electrical energy savings in the drive could be realized by improvements of power quality in the consumer network. Term power quality (Linders, 1972; Bonnett, 2000) mostly means quality of supply voltage that should meet the following requirements:


Power losses and reactive loads depend from on voltage magnitude and they are further increased due to unbalanced voltage and (or) the presence of harmonics in supply voltage.

Unbalance voltage can occur due to the presence of larger single-phase consumers or asymmetrical capacitor banks with damage or capacitors that are switched off due to the fuse burning only in one phase. Nowadays, the presence of higher harmonics in the supply voltage is ever more frequent due to the growth of consumers who are supplied through the rectifiers and inverters: regulated actuators, electrothermical consumers and consumers alike.

Effects of Voltage Quality on Induction Motors' Efficient Energy Usage 129

and reactive loads on voltage value will be presented, as well as proceedings for calculation

**Figure 1.** Efficiency versus load for various applied voltages in percent of its 460 V rating for a standard

In order to determine total dependence of power losses on voltage, for the load range from no-load to full load, it is necessary to determine no-load power - voltage dependency, *P0(u)* :

Load losses component (PLL) depend on relative load (*pL=PL/PN*) and relative voltage values

, / *P LL N P P pu*

2 2

0 0 () () () *Cu Fe fw Pu P u P u P* (1)

(2)

**2.1. Dependency of power losses and reactive loads on voltage value** 

efficiency motor (10 HP and 50 HP)

*PCu0* copper losses in no-load, *PFe* core losses in no-load,

*PfW* friction and windage losses in no-load.

Where are

(*u=U/UN*):

and analysis of power losses and reactive loads on voltage value.

The effect of a variation in supply voltage, wave-form or frequency on the motor's efficiency and power factor characteristics depends on the individual motor design. Typical variations of current, speed, power factor and efficiency with voltage for constant output power are given in Fink (1983). The usual characteristics of induction motors within the ±10% voltage band (*Un*±10%) are well known. These are included in corresponding table for typical 30- 100 kW, 1500 or 1800 1/min motors (Linders, 1972; Fink, 1983), but the effect of saturation has been largely neglected in these tables. However, it is the author's intent to show a correlation between motor characteristics and voltage level.

This proposed has three parts:

