# Grid Nodes Selection Strategies for Power Quality Monitoring
## 4 Problems and Future Prospects
### Case Study: PQ Monitoring System Development in Lithuania  
This subchapter presents the stages of PQ monitoring system development by Lithuanian DSO (\"Energijios skirstymo operatorius\", AB) including monitors' allocation criteria, campaign size, duration, economics, communications, and integration with other systems. The concept is presented in Figure 11. Stage I encompasses smart meters with PQ functionality linking to MDM with 3G GPRS communication, PQ analyzers (IEC 61000-4-30 class A) installation, and connection to the PQ data system with fiber optics (according to the agreed allocation plan). Stage II encompasses both relay protection and fault management systems integration to SCADA/DMS, and MDM system interconnection with PQ data system. SCADA/DMS integration to PQ data system is going to be implemented in Stage III. Lithuanian monitors' allocation strategy is presented in Figure 12. PQ analyzers (550 units) are going to be installed in all HV/MV substations during Stage I (maximum term is 2-3 years, including procedures of public tenders), CAPEX--2.8M EUR (budget year: 2021). In addition, the stage involves PQ-measuring energy meters' installation for households. Stage II is parallel with Stage I; the duration is 3-5 years: monitors are installed in MV substations (preferentially in 35/10 kV) where optical fiber is available. If optical fiber is unavailable, smart meters with PQ functionality and GPRS will be installed in addition to fixed non-remote monitors (250 units). Both devices will be installed on  
Figure 11: Development stages of remote PQ monitoring system in Lithuanian DSO grid. Figure 10: Phase-to-ground voltage array loss in 35 kV node during PQ measurements campaign in Lithuanian power system. Weak array (necessary for EN 50160 assessment) had been corrupted. secondary winding, CAPEX--1.3M EUR. In Stage III, remote PQ monitoring must be ensured in every MV substation: PQ analyzers will be integrated to PQ system along with optical fiber advance. In addition, the stage encompasses MV switching stations if optical fiber is available, else--PQ smart meter installation. Work priority is determined by substation ranking, a newly mentioned concept in this paper. Ranking can be reviewed as a new intermediate allocation category which stands between AI algorithms and abstract non-quantitative criteria. The advantage of ranking  
Figure 12: PQ monitors allocation strategy and other details about the development of remote PQ monitoring system in Lithuanian DSO grid. is simplicity (i.e., ratio determination without complex mathematics, algorithms). In the general case, a ranking approach does not require scientific software such as MATLAB, or Microsoft Excel can be a sufficient tool for task implementation. The disadvantages are as follows: ranking is not a multidimensional approach, only the main parameters can be considered, and adequacy depends on researcher competence. The proposed substations ranking has been based on transformer load and nominal power as follows:  
\[P_{1}=\frac{P^{1}_{i}}{\max\{P^{1}_{i}\}}, \tag{7}\]  
\[P_{2}=\frac{P^{2}_{i}}{\max\{P^{2}_{i}\}}, \tag{8}\]  
\[P_{3}=\frac{P^{3}_{i}}{\max\{P^{3}_{i}\}}, \tag{9}\]  
\[\text{Score}=\left\{ \begin{array}{l}w_{1}P_{1}+w_{2}P_{2}+w_{3}P_{3}\\ \sum\limits_{i=1}^{3}w_{i}=1\end{array} \right. \tag{10}\]  
where \(P^{1}_{i}\)--average yearly apparent load of a transformer; \(\max\{P^{1}_{i}\}\)--apparent load of the largest DSO transformer; \(P^{2}_{i}\)--relative apparent load of a transformer; \(\max\{P^{2}_{i}\}\)--relative apparent load of the largest DSO transformer; \(P^{3}_{i}\)--nominal power of a transformer; \(\max\{P^{3}_{i}\}\)--nominal power of the largest DSO transformer; \(w_{i}\)--weights. In addition, remote PQ energy meters are installed in all type B and type C power plants with a non-remote PQ analyzer (see Figure 12). In the case of fiber optics' availability, a remote PQ analyzer is installed with a non-remote PQ energy meter. Guidelines for portable monitors are also included into the strategy.