Study On The Current Quality Assessment System Based On Current Physical Components

With the development of modern power system, power quality has become an important part in the research of intelligent electric grid. Recently, the study on power quality has been very abundant and mature. The relevant assessment system and assessment limits have also been complete. However, except the research on harmonic current and fundamental negative sequence current, the research on the current quality is relatively absent. The existing assessment method of current quality is based on the assessment about voltage quality, ignoring the characteristic of current.The paper researched the assessment of current quality, which is based on current physical components. With the generation and transmission of disturbance signals, there must exist disturbance power and current. So the relationship between current and power are very close. The current decomposition in power theories has been taken into consideration. IEEE Standard 1459-2010 and Current Physical Component (CPC) theory are compared deeply and the advantages and disadvantages of those power theories are shown completely. Because that the current components decomposed in CPC theory have clear physical meanings, the CPC theory is selected as the theoretical basis for the assessment.After a thorough analysis of CPC theory, a perfect assessment system of current quality was proposed, which contains constraint indexes and economic indexes. Economic indexes include the utilization of equipment, the operation efficiency of system, reactive current, while constraint indexes include unbalanced current, generated current, scattered current, inter-harmonics current, the fluctuation of current and frequency. What’s more, the assessment model and method are provided and the constraint limits are discussed.Based on the assessment system of current quality, the current components and powers were acquired with the help of MATLAB. Then, the assessed values were got, too Finally, the measurement data of a 35kV bus were assessed, which has a load of EAF. The results reflected the disturbance characteristics of EAF and can be used to measure its influence on power system. Besides, compared with the assessment limits, we can know whether the parameters were out of limits or not. And the results can be the theory basis and data basis of the subsequent governance. The implementation of this assessment proved the feasibility and practicability of the method discussed in this paper.