# Grid Nodes Selection Strategies for Power Quality Monitoring
## 2 Literature Review
### Scientific Papers and Practical Reports
\right.\] (4) where \(f_{i}\)--target functions of four scenarios; \(X\)--independent variable; \(\mathbf{U}\)--universal set; \(\mathbf{R}\)--subset of \(\mathbf{U}\). Figure 4: Voltage sag matrix: 6-node grid example. Solving the optimal allocation problem for different scenarios. Optimization targets weights and the final decision must be agreed by experts, considering different scenarios and objectives (such as planning, marketing, operation, and maintenance). The proposed method was applied to 110-750 kV regional grid in eastern provinces of China. Total bus number is 205; other features of the grid: 135 critical substations, 2 HVDC converters, 2 electrified railways, 4 sensitive customers, 5 wind farms. Case results: 15 PQ monitors are required for the grid planning stage, 19 for the operation and maintenance stage, 37 for the grid market scenario. In [20] (2018), an example of a practical measurement campaign in Italy is given. The authors affirm that they present the data which are \"obtained by the most extensive program in the world for monitoring PQ.\" The program was established by the largest DSO in Italy--\"Enel Distribuzione\". About 3500 analyzers (IEC 61000-4-30 class A) were installed in 2014 on MV busbars in chosen HV/MV substations, i.e., at PCC between TSO and DSO property zones; thus, the research can be considered as an example of a massive monitoring campaign. The main focus was on voltage sags monitoring and their assessment methodology research, regarding voltage sag propagation and events counting (if voltage sag is registered with few neighboring PQ monitors). Therefore, detailed PQ monitors displacement strategies were not applied. The Turkish monitoring experience is presented in [21] (2009). A PQ measurement campaign was carried out in Turkish TSO grid (63, 154, 220, and 400 kV) with mobile analyzers for July 2006-February 2007. Weekly measurements were taken in 205 nodes with approximately 20 portable monitors (IEC 61000-4-30 class B). The criteria for nodes selection are as follows: frequency of faults, consumption density, and amount of modern industrial loads. In addition, an Estonian PQ measurement campaign (2004-2017) with portable analyzers is described in [22] (2018). The total number of sites was 73 and measurement weeks were 160. In contrast to the previous papers, measurements were taken in the LV network and initiated after customers' complaints. In [23] (2017), an Australian \"large and long-running\" PQ monitoring campaign is presented, which was initiated by the University of Wollongong and was executed since 2002. The main target of the campaign was an assessment of network compliance. Since the beginning, data were gathered from over 12,000 sites provided by 12 of the 16 Australian DSOs. In 2017, the project database contained approximately 500 GB of data (900 million records) which were measured in the LV grid along with the MV and HV grid (6.6-132 kV). The participants supply electricity to at least 90% of the Australian population. Measured parameters: steady state voltage magnitude, voltage unbalance, voltage harmonics (up to 25 th and THD), flickers, and voltage sags. In the paper, it is concluded that \"installation of PQ instrumentation remains costly\". Moreover, many devices (e.g., smart meters, protection relays) monitor only a subset of parameters required for compliance verification. Many questions were raised for further research, including the required (optimal) number of sites for both PQ surveys (focus on compliance of LV and MV grid) and transmission systems (focus on HV grid). Two general case recommendations are given for the search of optimal number of required LV and MV sites, and it is affirmed that the literature available on this topic is very limited (until 2016, i.e., until date of publication):  
1.