# Grid Nodes Selection Strategies for Power Quality Monitoring
###### Abstract  
In the past few years, technical progress has determined traditional electric power system conversion to Smart Grids, and consequently empowered a worldwide renaissance in the forgotten PQ field. Since the installation of PQ monitors is currently associated with high investments and operational costs, it is inappropriate to install a monitor on each grid busbar. Hence, grid operators must establish the best cost-benefit scenario for monitors installation and achieve maximal observability with a limited number of analyzers. Firstly, this paper presents a review of the state-of-the-art of displacement strategies, and discusses them regarding the tendencies of node selection criteria, the test schemes used, and the grid size. Secondly, the relevant fundamental issues which must be solved in the future in order to eliminate restrictions in PQ monitors' allocation planning are presented and discussed. These issues concern the treatment, interpretation, and assessment of PQ events, measurement chain technical features, PQ's role in the grid planning stage, communication technologies, and other remote monitoring aspects, and integration with other Smart Grid applications. The provided insights are based on experience which has been obtained during the PQ measurement campaign in the Lithuanian DSO grid. Finally, a PQ system development strategy--both short-term and long-term perspectives--in the Lithuanian distribution grid is presented, including monitors allocation criteria.  
Smart Grid; power quality; monitoring; nodes prioritization; allocation strategy +
Footnote †: journal: _Sci._  
In general, the prioritization strategies for nodes depend on the desired aim. Based on the authors' knowledge, the aim can be classified into two main groups regarding the main focus, focusing on either the customer or the electrical grid. Some examples are provided below:  
1. Focus on customers--mainly low-voltage (LV) grid monitoring: * Industrial customers' complaints: point of common coupling (PCC) monitoring or any in-plant grid point monitoring. * Industrial, commercial, and residential customers' installed power ratio. * Load types: for example, priority to large electric motors or critical loads (i.e., sensitive to voltage sags, harmonics). * Random selection of PCC or other nodes for short-duration measurements with portable PQ monitors. * Yearly energy consumption. * Critical and problematic nodes which are known a priori by DSO.
2. Focus on the electric power grid--mainly high-voltage (HV) and medium-voltage (MV) grid monitoring: * Most critical substations and their technical conditions (for example, the availability of communications for remote monitoring). * Connection points of power plants or other PQ-mitigating devices, such as capacitor banks, synchronous compensators, surge arresters, etc. * Penetration of distributed generation and renewable energy sources. * Line length and presence of HVDC lines.  
In addition, the type of monitoring must be considered. Firstly, measurements can be performed with either a fixed or a portable PQ monitor, a smart meter, or another device. Each option has its own features, such as measured PQ events, sampling frequency, accuracy, and cost. Secondly, monitoring can be either remote or non-remote. In the case of remote monitoring, additional communication issues must be addressed, but many advantages are offered, such as: diminished resources (time, human, transport) for data gathering, easier to process data, fast data loss, and error detection, etc.  
The main aim of this paper is to examine the current state-of-the-art methods of PQ nodes selection and discuss and expand them with our own insights, experience, and proposals (including future prospects).