# Grid Nodes Selection Strategies for Power Quality Monitoring
## 2 Literature Review  
### Legislation and Policy  
Legislation is perhaps the most important factor promoting PQ monitoring and compliance verification. In the PQ field, legislation mainly consists of standards. In general, standards are not mandatory unless they are mentioned in national or international (e.g.,  
Figure 1: Structure of a remote PQ monitoring process: extended IEC 61000-4-30 block diagram of a non-remote PQ monitoring process. European Union) legal documents. There are some additional nuances regarding European harmonized standards and national legislation (e.g., in Lithuania, along with the main PQ standard LST EN 50160:2010, time limit values for supply interruptions are added) but any detailed analysis of these cases is not relevant to the scope of this paper. Two main PQ standard groups defining different PQ concepts can be highlighted--European and North American (IEEE standards). In Europe, voltage phenomena are regarded as PQ events (in most cases, requirements are determined for grid, system), and electric current phenomena are regarded as EMC events (in most cases, requirements are determined for end-user equipment; but there are some exceptions, for example, IEC 61800-3). On the contrary, different PQ concepts and definitions are given in the IEEE standards, a more extended classification of PQ events is presented, and both current and voltage phenomena are regarded as PQ events (or at least closely related). Moreover, IEEE standards often highlight a good practice from the EMC standards (which are European harmonized standards, which are (can be) used to verify compliance with relevant European or EU legislation). Therefore, the analysis of world standards completeness, adequacy and comprehensiveness is perhaps the most important factor for world experience evaluation. The main PQ standards are listed below:  
* EN 50160:2010 \"Voltage characteristics of electricity supplied by public electricity networks\" [1]. This European standard focuses on the PQ phenomena definition, normalization, and is imperative in most European countries. * IEC 61000-4-30 \"Electromagnetic compatibility (EMC)--Part 4-30: Testing and measurement techniques--Power Quality measurement methods\" [2]. This harmonized standard defines the methods for measurement and interpretation of results for PQ parameters in an AC power system with a declared fundamental frequency of 50 Hz or 60 Hz. Measurement parameters (covered by this standard) are limited to conducted phenomena in power systems. Requirements for some parameters such as accuracy and dynamic range are given for part PQ events. However, the standard does not provide any information about appropriate measurement instruments' displacement and its importance. * IEC 61000-4-7 is a harmonized standard which defines methods for voltage harmonics and inter-harmonics measurement, thus is outside the scope of this paper. * IEC 61000-4-15 is a harmonized standard which defines methods for flicker measurement, thus, is outside the scope of this paper. * IEEE Std 1159-2019 \"Recommended Practice for Monitoring Electric Power Quality\" [3]. This North American standard focuses on PQ phenomena definitions and provides more detailed and unique approaches than those of EN 50160. In contrast to EN 50160, current (including EMC) phenomena along with voltage are treated as either closely related or PQ events. Moreover, IEC EMC standards are often mentioned as a good practice. Despite being more informative, IEEE Std 1159 does not include any normalization (limits), but gives some important practical ideas about monitors' displacement:  
* PQ situation of monitored node depends on the monitor's proximity to the source, system impedances, and dynamics of the load;
* Initial locations of PQ meters depend on the objective;
* If the objective is to investigate the overall PQ of a facility supply, a monitor should be placed on the secondary winding of the main entrance transformer.