# Power Quality Impact and Its Assessment: A Review and a Survey of Lithuanian Industrial Companies
## 2 Literature Review
### Social Impact
275-282): the situation in the networks of Austria, Belgium, Hungary, Ireland, Kosovo, Portugal, and Slovenia has been assessed by expressing the data as the number of voltage sags per number of monitored points in the voltage sag table of EN 50160:2010 (which will be used in this paper as well); however, for example, the strategies of for selecting monitoring sites are not described, thus it is unclear when a voltage sag caused by the same event was recorder multiple times (i.e., by multiple monitors), and when only once, as well as it is unclear whether PQ mitigation devices was used and what is their impact on the statistics. Next, by comparing Tables 2 and 3, it can be noticed that the absence or presence of responsibility (including its severity) is dependent not only on voltage sag parameters but also on their treatment and the structure of the table. Generally speaking, this is dependent on PQ assessment methodology--different methods, formulas, definitions, various uncertainties and gaps can lead to different outcome, data errors and misinterpretation,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{Voltage, p.u.} & \multicolumn{6}{c}{**Duration, s**} \\  & **0 \(\leq\) t \(\leq\) 0.1** & **0.1 \(<\) t \(\leq\) 0.15** & **0.15 \(<\) t \(\leq\) 0.2** & **0.2 \(<\) t \(\leq\) 0.5** & **0.5 \(<\) t \(\leq\) 0.6** & **0.6 \(<\) t \(\leq\) 1** & **1 \(<\) t \(\leq\) 5** & **5 \(<\) t \(\leq\) 60** \\ \hline \multicolumn{8}{c}{**Networks above 45 kV**} \\ \hline
0.9 \(>\) U \(\geq\) 0.8 & A & A & B & B & B & B & B \\
0.8 \(>\) U \(\geq\) 0.7 & A & A & B & B & C & C \\
0.7 \(>\) U \(\geq\) 0.4 & A & B & B & B & C & C \\
0.4 \(>\) U \(\geq\) 0.05 & A & B & B & B & C & C \\ U \(<\) 0.05 & A & B & B & B & C & C \\ \hline \multicolumn{8}{c}{**Networks up to and including 45 kV**} \\ \hline
0.9 \(>\) U \(\geq\) 0.8 & A & A & A & B & B & B & B \\
0.8 \(>\) U \(\geq\) 0.7 & A & A & A & B & B & B & B \\
0.7 \(>\) U \(\geq\) 0.4 & A & A & B & B & B & C \\
0.4 \(>\) U \(\geq\) 0.05 & B & B & B & B & B & C \\ U \(<\) 0.05 & B & B & B as well as are an obstacle in the algorithm development process. Let us continue with RMS voltage variations based on the information given by [2] that performs short circuit simulation on the created BRELL-based test grid. EN 50160:2010 requires to take into consideration only one--phase-to-phase for three-wire systems and phase-to-ground for four-wire systems--voltage. Obviously, this is not relevant for three-phase faults since, according to the axiom established by [2], both depths of a symmetrical voltage sag are equal and independent of neutral mode. A few examples are given in Figures 6-8: currently, it is not clear (agreed) which assessment method of both two-phase-to-ground and two-phase faults incurs lighter/heavier liability, but it is clear that if only phase-to-phase voltage of the Lithuanian MV and LV grids is considered, in most cases single-phase faults will remain unnoticed (this does not apply to the HV grid). It is noteworthy that, in 2025, after the disconnection of the Baltic power grids from the BRELL system on 8 February and synchronization with the Continental European system on 9 February after the isolated operation test, the obtained results remain completely realistic and valid for Lithuania as well as Latvia, Estonia, Russia and Belarus. The results are valid for other countries' systems as well, but not necessarily completely due to different features of their networks. Figure 6: (**a**) Phase-to-phase and (**b**) phase-to-ground voltages in the 330 kV 100 km line at the generator’s terminals where a two-phase-to-ground fault occurs obtained by [2] during the simulation (Scenario No. 1, two-phase-to-ground fault, voltage at the monitor M1). Currently, it is not clear which array—one phase-to-phase supply interruption with two 50% depth voltage sags or two phase-to-ground supply interruptions with a 10% depth voltage sag—is more favorable to the operator from the juridical point of view.