# Power Quality Impact and Its Assessment: A Review and a Survey of Lithuanian Industrial Companies
## 2 Literature Review
### Social Impact
Figure 7: (**a**) Phase-to-phase and (**b**) phase-to-ground voltages at the end of the 330 kV 100 km line when a two-phase fault occurs at the generator’s terminals in the beginning of this 100 km line obtained by [2] during the simulation (Scenario No. 1, two-phase fault, voltage at the monitor M2). Currently, it is not clear which array—one phase-to-phase supply interruption with two 10% depth voltage sags or one healthy phase-to-ground voltage with two 50% depth voltage sag—is more favorable to the operator from the juridical point of view. Next example to discuss is the calculation of voltage unbalance. In a three-phase system, negative and zero sequence unbalances are defined as follows:  
\[u^{-}[\%]=\frac{|U^{-}|}{|U^{+}|}.100, \tag{7}\]  
\[u^{0}[\%]=\frac{|U^{0}|}{|U^{+}|}.100, \tag{8}\]  
where \(|U^{+}|\), \(|U^{-}|\) and \(|U^{0}|\) are magnitudes of the positive, negative and zero sequence phasors, respectively. These magnitudes must be calculated by taking into account the phase angles (i.e., by performing operations with complex numbers). IEC 61000-4-30:2015 notes that algorithms that use RMS values fail to evaluate contributions of angular displacement to these magnitudes, and requires that the voltage unbalance measurement uncertainty of both class A and class B shall not exceed \(\pm 0.15\%\). On the other hand, since symmetrical components are an intermediate result and do not necessarily have to be presented, IEEE Std 1159-2019 (pp. 25-27) provides alternative methods that can be applied by using only RMS measurements without the angle when symmetrical component calculation functionality is unavailable. These alternatives are valid only if phase-to-phase measurements are used, harmonic content is low (in this case, there is no difference between the standard RMS and true-RMS methods--see [8] for more details), and the zero sequence component is zero (as it is in practice when the unbalance is caused by loads, not by earthed faults). The first method is based on ANSI C84.1-2016 [93], which defines voltage unbalance as the ratio of the maximum deviation of a phase-to-phase voltage from the average phase-to-phase voltage to the average phase-to-phase voltage. Mathematically, this can be written as follows:  
\[u^{-}[\%]=\frac{\max\{\big{|}|U_{\max}|-\big{|}U_{\mathrm{avg}}|\big{|};\ \big{|}|U_{\mathrm{min}}|-\big{|}U_{\mathrm{avg}}|\big{|}\big{|}\}}{|U_{ \mathrm{avg}}|}.100, \tag{9}\]  
where \(|U_{\mathrm{max}}|\)--the highest RMS voltage of the array with three phase-to-phase RMS voltages; \(|U_{\mathrm{min}}|\)--the lowest RMS voltage of the array with three phase-to-phase RMS voltages; \(|U_{\mathrm{avg}}|\)--the average of the array phase-to-phase RMS voltages. The second method uses the following equation:  
\[u^{-}[\%]=\sqrt{\frac{1-\sqrt{3-6\beta}}{1+\sqrt{3-6\beta}}}.100, \tag{10}\]  
Figure 8: **(a)** Phase-to-phase and **(b)** phase-to-ground voltages in the 10 kV line where a single-phase fault occurs obtained by [2] during the simulation (Scenario No. 3, single-phase fault, voltage at the monitor M2a). It is clear that this fault will not be noticed if only phase-to-phase voltage is taken into consideration, as is required by EN 50160-2010.  
where parameter \(\beta\) is calculated as follows:  
\[\beta=\frac{\left|U_{\text{AB}}\right|^{4}+\left|U_{\text{BC}}\right|^{4}+\left| U_{\text{CA}}\right|^{4}}{\left(\left|U_{\text{AB}}\right|^{2}+\left|U_{\text{BC}} \right|^{2}+\left|U_{\text{CA}}\right|^{2}\right)^{2}}, \tag{11}\]  
where \(U_{\text{AB}}\), \(U_{\text{BC}}\) and \(U_{\text{CA}}\) are phase-to-phase RMS voltages. The calculation examples provided in the standard show that the results obtained by applying Equations (7), (9) and (10) differ by no more than 0.1%. The limit established by EN 50160:2010 for negative sequence unbalance is 2% (during 95% of the time in one week). Further, let us continue with voltage flicker and harmonic assessment. Flickering lights can cause fatigue, lack of concentration, migraine or epileptic seizure [94].