# Grid Nodes Selection Strategies for Power Quality Monitoring
## 3 Discussion
### Criteria
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Monitors Allocation Criteria** & **Application in Practice** & **Theoretical Validation** \\ \hline \multirow{3}{*}{[6] (2005)} & Fixed monitors—in critical HV/MV substations, & \multirow{3}{*}{Monitoring campaign in} & \multirow{3}{*}{No} \\  & on MV side; portable monitors—regarding & & \\  & customer’s complaints and consultation, and for & & \\  & specific load investigation & & \\ \hline \multirow{3}{*}{[7] (2008)} & \multirow{3}{*}{All TSO grid (voltage and current) observability} & \multirow{3}{*}{No} & IEEE 14, IEEE 30, IEEE 57, \\  & & & IEEE 118; Brazilian 48-busbar \\  & & & \\  & & test system \\ \hline \multirow{3}{*}{[8] (2009)} & Only MV: line length and type, customers’ & \multirow{3}{*}{Monitoring campaign in} & \multirow{3}{*}{No} \\  & density (and quantity), neutral mode, random & & \\  & selection & & \\ \hline \multirow{3}{*}{[9] (2013)} & Power stations, all EHV/HV, EHV/MV, HV/MV, & \multirow{3}{*}{State-of-the-art review} \\  & and selected MV/LV substations, all HV and MV & & \\  & PCC, random LV PCC & & \\ \hline \multirow{3}{*}{[10] (2012)} & Most severe short-circuit observability (coverage) & \multirow{3}{*}{No} & IEEE 30, IEEE 34 \\  & defined by residual voltage threshold & & \\ \hline \multirow{3}{*}{[11] (2015)} & Total observability of grid, i.e., voltage and & \multirow{3}{*}{No} & IEEE 14, IEEE 30, \\  & current measurements of all nodes without & & IEEE 57 \\ \cline{1-1}  & prioritization. Costs are taken into consideration & & \\ \hline \multirow{3}{*}{[12] (2016)} & Value of nontechnical losses caused by & \multirow{3}{*}{No} & IEEE 14, IEEE 30, IEEE 118; \\  & additional loading & & Brazilian DSO 40-busbar test \\  & & & system \\ \hline \multirow{3}{*}{[13] (2016)} & All TSO grid (voltage and current) observability & No & Brazilian TSO 65-busbar test \\  & & system \\ \hline \multirow{3}{*}{[14] (2018)} & Only symmetrical short-circuit observability at & \multirow{3}{*}{No} & IEEE 13, IEEE 34, \\  & minimal costs & & IEEE 37 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Reviewed papers summary regarding PQ monitors allocation strategy. Table 3 summarizes the criteria selection frequency in the reviewed papers. There is no most common criterion in the practical papers. The most common criterion in the theoretical papers--focus on PQ issues and related parameters observability: the most common case is residual voltage and short-circuits calculation. Table 4 presents the cross-section product of Tables 2 and 3. It is important to distinguish exact criterion from abstract. In this paper, the proposed criteria groups are as follows:  
1. Random selection (abstract criterion). Used only in the practical papers. Those papers do not specify selection principle; nodes are identified as \"freely chosen\". In case of theoretical papers (hypothetically), the random number generator should be specified; however, this approach is not used, and perhaps is senseless. 2. Critical substation (abstract criterion). Used only once in the practical papers. The authors do not specify exactly which substation is considered to be critical, for example, it could be in a poor technical condition or important transmission grid node. 3. Specific load investigation (abstract criterion). Used only once in the practical papers. Research can be focused either on an emission source, or on PQ immunity. In this case, the authors do not provide any exact information about load features. 4. Customers' complaints usually are an important factor for an operator to begin at least temporary measurements at PCC with a portable monitor. In addition, attention to the client is important from a successful business perspective. 5. All selected-type substations, busbars. Includes maximal coverage tasks, and encompasses such concepts as \"all HV or MV busbars in most HV/MV substations\" and \"whole grid observability\". In general, the criterion reflects a massive campaign.