This part of IEC TS 63222 defines technical requirements for designing a power quality monitoring system for public power supply networks. It is applicable for LV, MV, and HV public power supply networks. The design procedure of a power quality monitoring system (PQMS) generally includes the following four steps: • Step 1: purpose and application analysis Analyse power quality monitoring (PQM) demand and define the purpose of power quality monitoring. • Step 2: preliminary study Collect background information such as network configuration, the parameter of instrument transformers, e.g. the output levels and performance capabilities , attributes of loads or Distributed Generations (DG), communication conditions, budgets, and other restrictive conditions, and select the parameters to be monitored and monitoring sites according to corresponding principles. • Step 3: system structure design Design the overall structure of the monitoring system according to the monitoring purpose based on the analysis of the advantages and disadvantages of various system structures . • Step 4: detailed design of functional modules Design the function modules of data collection, communication, data storage, data processing and analysis in detail according to the functional requirements. This Technical Specification defines the main purposes of power quality monitoring and gives recommendations for preliminary study, such as how to select monitoring sites and monitoring parameters, whether the instrument transformer is suitable for monitoring. This Technical Specification also classifies the PQMS structure and specifies the functional requirements of the modules such as data collection, communication, data storage, data processing and analysis.