Study On The Power Quality Assessment System Of Modern Power Systems

According to the power quality (PQ) characteristics of modern power system, a novel classifying method was presented, succession type and event type of PQ. The succession type includes harmonics, voltage unbalance, voltage deviation, power frequency deviation and flicker. The event type includes voltage sags, swells, short duration interruption, sustained interruption and transient over-voltage.The definition of custom assessment and public assessment of PQ were presented for the need of electric customers. The relationship of single assessment, comprehensive assessment, sites assessment, system assessment, planning assessment, compatibility assessment, quantifying assessment, qualitative assessment, custom assessment and public assessment of power quality were analyzed. Based on it, an infrastructure of power quality assessment system (PQESI) was built from different views. It has two layers. On the technology layer PQ assessment can be made according to quality contents, net circumstances, the forms of outcomes. The results of assessments on the technology layer can be mirrored to the application layer, which faces the entities of electricity market, utilities and power customers. Under the PQESI, from the assessment process, time aggregation, phase aggregation and indices definition, five assessment models of succession type PQ were built, including the assessment models of voltage harmonics, current distortion, voltage unbalance, voltage deviation, and power frequency deviation. Based on the analysis of event-type PQ common characteristics and the influence on end-users caused by them, the assessment model of event-type PQ was proposed. Under the model four-type indices of voltage sags were proposed, 1) event times, 2) economic equivalent interruption hours of events, 3) sag energy, 4) cost of event, and then the comprehensive index of event-type PQ, the corrected reliability index RS*, was represented.Finally, the comprehensive assessment model of PQ was proposed, including quantifying comprehensive index (QCI) and comprehensive hierarchy evaluation (CHE). All of them are based on the cask effect theory and the limited level of the PQ standards. The value of the QCI is a measure of how much a disturbance type exceeds a maximum acceptable value. The expression of QCI conveniently gives some intuitive judgment and control-decision assistance to the operators. The PQ grade of CHE with limited number of grades is more adaptable to market operation.An assessment system of PQ (PQAS) was made up of One PQESI and seven assessment models of PQ (PQAMs). Many cases studies based on actual monitored data of PQ showed that the PQAS could effectively test the actual levels of modern PQ.